CN212785179U - Synchronous rectification control chip, switching power supply and electrical equipment - Google Patents
Synchronous rectification control chip, switching power supply and electrical equipment Download PDFInfo
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- CN212785179U CN212785179U CN202021510352.9U CN202021510352U CN212785179U CN 212785179 U CN212785179 U CN 212785179U CN 202021510352 U CN202021510352 U CN 202021510352U CN 212785179 U CN212785179 U CN 212785179U
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- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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Abstract
The utility model provides a synchronous rectification control chip, a switching power supply and electrical equipment, wherein the synchronous rectification control chip comprises a first comparison circuit and a second comparison circuit; the positive input end of the first comparison circuit is used for being connected with the secondary side of the first transformer so as to receive a signal with the frequency consistent with the clock signal of the primary side frequency control circuit, the negative input end of the first comparison circuit is connected with a first reference voltage, and the output signal of the first comparison circuit is used for realizing the control of the second rectifier switch; and the positive input end of the second comparison circuit is used for being connected with the secondary side of the second transformer so as to receive a signal with the frequency consistent with the clock signal of the primary side frequency control circuit, the negative input end of the second comparison circuit is connected with a second reference voltage, and the output signal of the second comparison circuit is used for realizing the control of the first rectifier switch. The utility model discloses not only can retrench synchronous rectification control circuit structure, can also accurate, reliable realization synchronous rectification control.
Description
Technical Field
The utility model relates to an electronic circuit technical field especially relates to a synchronous rectification control chip, switching power supply and electrical equipment.
Background
At present, the switching power supply is developing towards high power density and high efficiency, and the LLC resonant converter is increasingly widely used due to its excellent soft switching characteristics and boosting capability.
In order to reduce the switching loss, a resonant converter with a multi-transformer structure is also provided at present, for example, in the technical scheme disclosed in patent publication No. CN109995242A, a resonant inductor Lr in a conventional LLC resonant converter is replaced by a transformer, and the transformer is used as a resonant inductor, that is, the resonant converter includes two transformers with primary sides connected in series, so that energy in a resonant cavity can be output to a secondary side in dead time, which is further beneficial to reducing the switching loss of the primary sides, and the resonant converter can work at a high frequency.
The increase of the switching frequency of the LLC resonant converter is beneficial to improving the power density of the whole circuit, but the increase of the switching frequency also easily brings the increase of the conduction loss of the rectifier switch, and the conduction loss of the rectifier switch can be reduced by adopting the synchronous rectification technique, but for the resonant converter of the above-mentioned multi-transformer structure, the circuit adopted for implementing the synchronous rectification control is somewhat complicated.
SUMMERY OF THE UTILITY MODEL
Based on above-mentioned current situation, the utility model discloses a main aim at provides a synchronous rectification control chip, switching power supply and electrical equipment, can simplify the synchronous rectification control circuit who utilizes the transformer as resonant inductance's LLC resonant transformation circuit.
In order to achieve the above object, the present invention provides a synchronous rectification control chip for synchronous rectification control in an LLC resonant converting circuit, wherein the LLC resonant converting circuit includes a frequency control circuit, a first bridge arm switch, a second bridge arm switch, a first rectification switch, a second rectification switch, a resonant capacitor, a first transformer and a second transformer connected in series with the resonant capacitor, the first transformer and the second transformer are the same transformer, excitation inductances of the first transformer and the second transformer are alternately used as resonant inductances, and the synchronous rectification control chip includes a first comparison circuit and a second comparison circuit;
the positive input end of the first comparison circuit is used for being connected with the secondary side of the first transformer so as to receive a signal with the frequency consistent with the clock signal of the frequency control circuit on the primary side, the negative input end of the first comparison circuit is connected with a first reference voltage, and the output signal of the first comparison circuit is used for realizing the control of the second rectifier switch;
and the positive input end of the second comparison circuit is used for being connected with the secondary side of the second transformer so as to receive a signal with the frequency consistent with the clock signal of the primary side frequency control circuit, the negative input end of the second comparison circuit is connected with a second reference voltage, and the output signal of the second comparison circuit is used for realizing the control of the first rectifier switch.
Furthermore, the synchronous rectification control chip further comprises a transconductance circuit, a third comparison circuit, a first and gate and a second and gate;
the positive input end of the transconductance circuit is connected with a reference voltage, the negative input end of the transconductance circuit is connected with an output feedback voltage of the LLC resonant conversion circuit, and the output of the transconductance circuit is an error voltage between the output feedback voltage and the reference voltage;
the positive input end of the third comparison circuit is connected with the output end of the transconductance circuit, and the negative input end of the third comparison circuit is connected with a third reference voltage;
a first input end of the first AND gate is connected with an output end of the first comparison circuit, a second input end of the first AND gate is connected with an output end of the third comparison circuit, and an output of the first AND gate is a control signal for controlling the second rectifier switch;
the first input end of the second AND gate is connected with the output end of the second comparison circuit, the second input end of the second AND gate is connected with the output end of the third comparison circuit, and the output of the second AND gate is a control signal for controlling the first rectifier switch.
Further, the synchronous rectification control chip further comprises: the voltage sampling circuit comprises an output feedback voltage pin, an error voltage pin, a voltage sampling pin of a first transformer secondary side, a voltage sampling pin of a second transformer secondary side, a first rectifier switch control signal output pin and a second rectifier switch control signal output pin;
the positive input end of the first comparison circuit is connected with a voltage sampling pin of the secondary side of the first transformer; the output end of the first AND gate is connected with the second rectifier switch control signal output pin;
the positive input end of the second comparison circuit is connected with the voltage sampling pin of the secondary side of the second transformer; the output end of the second AND gate is connected with the first rectifying switch control signal output pin;
and the negative input end of the transconductance circuit is connected with the output feedback voltage pin, and the output end of the transconductance circuit is connected with the error voltage pin.
Further, a first driving circuit is arranged between the output end of the first and gate and the second rectification switch control signal output pin;
and a second driving circuit is also arranged between the output end of the second AND gate and the first rectifying switch control signal output pin.
Furthermore, the synchronous rectification control chip also comprises a protection circuit which is used for outputting a protection signal when detecting that the output voltage is overvoltage, undervoltage, overcurrent, overtemperature, overpower or short circuit;
the first and second and gates each include a third input terminal and both receive the protection signal.
In order to achieve the above object, the technical solution of the present invention provides a switching power supply, including frequency control circuit, first bridge arm switch, second bridge arm switch, resonant capacitor, first rectifier switch, second rectifier switch, with first transformer and the second transformer that resonant capacitor establishes ties, first transformer with the second transformer is the same transformer, its characterized in that, switching power supply still includes: a synchronous rectification control chip as described above;
the synchronous rectification control chip is characterized in that a voltage sampling pin of a first transformer secondary side serving as an input pin is connected with the first transformer secondary side, and a voltage sampling pin of a second transformer secondary side serving as an input pin is connected with the second transformer secondary side; the first rectifier switch control signal output pin as an output pin is connected with the control end of the first rectifier switch, and the second rectifier switch control signal output pin as an output pin is connected with the control end of the second rectifier switch.
Further, the switching power supply further comprises a feedback voltage sampling circuit;
the input end of the feedback voltage sampling circuit is connected with the output voltage of the switching power supply, the output end of the feedback voltage sampling circuit is connected with the output feedback voltage pin of the synchronous rectification control chip, the feedback voltage sampling circuit is used for outputting the output feedback voltage, and the error voltage pin of the synchronous rectification control chip is used for outputting the error voltage between the output feedback voltage and the reference voltage.
Further, the feedback voltage sampling circuit includes: two divider resistors connected in series;
and an output feedback voltage pin of the synchronous rectification control chip is connected with a common end between the two divider resistors.
Furthermore, the switch power supply further comprises an optical coupler, wherein the emitting end of the optical coupler is connected with an error voltage pin of the synchronous rectification control chip, the receiving end of the optical coupler is connected with a frequency setting pin of the frequency control circuit, and the error voltage is fed back to the primary side from the secondary side through the optical coupler so as to generate a first current;
the frequency control circuit comprises a voltage control type oscillator and a bridge arm switch control signal generating circuit;
the voltage control type oscillator is used for generating a third current according to the first current and a second current generated by an internal current source, and generating a clock signal with adjustable frequency and invariable pulse width according to the third current;
the bridge arm switch control signal generating circuit is used for outputting a first control signal for controlling the first bridge arm switch and outputting a second control signal for controlling the second bridge arm switch according to the clock signal, and the first control signal and the second control signal form a fixed dead zone.
Further, the switching power supply further comprises a frequency compensation circuit and a voltage feedback compensation circuit;
the frequency compensation circuit is arranged between the receiving end of the optocoupler and a frequency setting pin of the frequency control circuit;
one end of the voltage feedback compensation circuit is connected with an output feedback voltage pin of the synchronous rectification control chip, and the other end of the voltage feedback compensation circuit is connected with an error voltage pin of the synchronous rectification control chip.
In order to achieve the above object, the present invention further provides an electrical apparatus, including the above switching power supply.
The embodiment of the utility model provides a synchronous rectification control chip adopts the secondary limit of transformer among the LLC resonance converting circuit of comparison circuit connection double-transformer structure (the transformer replaces resonance inductance), receives the signal unanimous with frequency control circuit's clock signal, and comparison circuit realizes synchronous rectification control according to the signal of this receipt, not only can retrench synchronous rectification control circuit structure, can also accurate, reliable realization synchronous rectification control.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:
fig. 1 is a schematic diagram of a synchronous rectification control chip according to an embodiment of the present invention;
fig. 2 is a schematic diagram of another synchronous rectification control chip provided in an embodiment of the present invention;
fig. 3 is a schematic diagram of another synchronous rectification control chip provided in an embodiment of the present invention;
fig. 4 is a schematic diagram of a switching power supply according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a frequency compensation circuit according to an embodiment of the present invention;
fig. 6 is a schematic diagram of a voltage feedback compensation circuit according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a partial structure of a frequency control circuit according to an embodiment of the present invention;
fig. 8 is a schematic diagram of a partial structure of another frequency control circuit according to an embodiment of the present invention;
fig. 9 is a schematic waveform diagram of a switching power supply according to an embodiment of the present invention.
Detailed Description
The present invention will be described below based on examples, but the present invention is not limited to only these examples. In the following detailed description of the present invention, certain specific details are set forth in order to avoid obscuring the spirit of the present invention, well-known methods, procedures, flows, and components have not been described in detail.
Further, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.
Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, what is meant is "including, but not limited to".
In the description of the present invention, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.
The utility model provides a synchronous rectification control chip for carry out synchronous rectification control in LLC resonance converting circuit, LLC resonance converting circuit include frequency control circuit, first bridge arm switch, second bridge arm switch, first rectifier switch, second rectifier switch, resonance capacitance, with first transformer and the second transformer that resonance capacitance establishes ties, first transformer with the second transformer is the same transformer, the excitation inductance of first transformer and second transformer is as resonance inductance in turn, refer to fig. 1, synchronous rectification control chip includes first comparison circuit U11, second comparison circuit U12;
the positive input end of the first comparison circuit U11 is connected with a voltage sampling pin TXH on the secondary side of the first transformer and is used for being connected with the secondary side of the first transformer so as to receive a signal with the frequency consistent with the clock signal of the frequency control circuit on the primary side, the negative input end of the first comparison circuit U11 is connected with a first reference voltage V6, the output end of the first comparison circuit U11 is connected with a second rectifier switch control signal output pin SRLVG, and the output signal of the first comparison circuit U11 is used for realizing the control of the second rectifier switch;
the positive input end of the second comparison circuit U12 is connected to the voltage sampling pin TXL on the secondary side of the second transformer, and is used for connecting the secondary side of the second transformer so as to receive a signal with a frequency consistent with the clock signal of the frequency control circuit on the primary side, the negative input end of the second comparison circuit U12 is connected to the second reference voltage V7, the output end of the second comparison circuit U12 is connected to the first rectifier switch control signal output pin SRHVG, and the output signal of the second comparison circuit U12 is used for controlling the first rectifier switch.
The first comparison circuit and the second comparison circuit can be realized by adopting comparators.
The embodiment of the utility model provides a synchronous rectification control chip adopts the secondary limit of transformer among the LLC resonance converting circuit of comparison circuit connection double-transformer structure (the transformer replaces resonance inductance), receives the signal unanimous with frequency control circuit's clock signal, and comparison circuit realizes synchronous rectification control according to the signal of this receipt, not only can retrench synchronous rectification control circuit structure, can also accurate, reliable realization synchronous rectification control.
For example, in the embodiment of the present invention, when the voltage of the positive input end of the first comparison circuit is greater than the first reference circuit, the first comparison circuit outputs a high level, so as to control the second rectification switch to be turned on, and when the voltage of the positive input end of the second comparison circuit is greater than the second reference circuit, the second comparison circuit outputs a high level, so as to control the first rectification switch to be turned on.
Preferably, in an embodiment, referring to fig. 2, the synchronous rectification control chip further includes a transconductance circuit U9, a third comparison circuit U13, a first and gate U21, and a second and gate U22;
the positive input end of the transconductance circuit U9 is connected with a reference voltage V2, the negative input end of the transconductance circuit U9 is connected with an output feedback voltage of the LLC resonant conversion circuit, the output of the transconductance circuit U9 is an error voltage between the output feedback voltage and the reference voltage, and the error voltage can reflect the current frequency of the LLC resonant conversion circuit and is smaller as the working frequency of the LLC resonant conversion circuit is higher;
the positive input end of the third comparing circuit U13 is connected to the output end of the transconductance circuit U9, the negative input end of the third comparing circuit U13 is connected to a third reference voltage V8, and when the error voltage of the transconductance circuit U9 is smaller than the third reference voltage V8, the output of the third comparing circuit U13 is at a low level;
a first input end of the first and gate U21 is connected to an output end of the first comparison circuit U11, a second input end of the first and gate U21 is connected to an output end of the third comparison circuit U13, an output of the first and gate is a control signal for controlling the second rectification switch, and the first and gate U21 is configured to and process an output signal of the first comparison circuit U11 and an output signal of the third comparison circuit U13, so that a purpose of rectification protection is achieved;
a first input end of the second and gate U22 is connected to an output end of the second comparison circuit U12, a second input end of the second and gate U22 is connected to an output end of the third comparison circuit U13, an output of the second and gate U22 is a control signal for controlling the first rectification switch, and the second and gate U22 is configured to and process an output signal of the second comparison circuit U12 and an output signal of the third comparison circuit U13, so that a purpose of rectification protection is achieved.
In addition, in this embodiment, the synchronous rectification control chip includes: the transformer secondary side voltage sampling circuit comprises an output feedback voltage pin FB, an error voltage pin COM, a voltage sampling pin TXH of a first transformer secondary side, a voltage sampling pin TXL of a second transformer secondary side, a first rectifier switch control signal output pin SRHVG and a second rectifier switch control signal output pin SRLVG;
the positive input end of the first comparison circuit U11 is connected with a voltage sampling pin TXH of the secondary side of the first transformer; the output end of the first AND gate U21 is connected with a second rectifier switch control signal output pin SRLVG;
the positive input end of the second comparison circuit U12 is connected with a voltage sampling pin TXL of the secondary side of the second transformer; the output end of the second AND gate U22 is connected with a first rectifier switch control signal output pin SRHVG;
the negative input end of the transconductance circuit U9 is connected to the output feedback voltage pin FB, and the output end is connected to the error voltage pin COM.
Preferably, in this embodiment, a first driving circuit 11 is further disposed between the output end of the first and gate U21 and the second rectifier switch control signal output pin SRLVG, and the first driving circuit 11 may amplify an output signal of the first and gate U21;
a second driving circuit 12 is further disposed between the output terminal of the second and gate U22 and the first rectifying switch control signal output pin SRHVG, and the second driving circuit 12 may amplify an output signal of the second and gate U22.
Preferably, in an embodiment, referring to fig. 3, the synchronous rectification control chip further includes a protection circuit 13, configured to output a protection signal when detecting that the output is over-voltage, under-voltage, over-current, over-temperature, over-power, or short-circuit, so as to further improve the reliability and safety of the LLC resonant conversion circuit, for example, the protection signal may be a low-level signal;
the first and gate U21 and the second and gate U22 each include a third input end and receive the protection signal, the first and gate U21 is configured to and process the protection signal output by the protection circuit 13, the output signal of the first comparison circuit U11, and the output signal of the third comparison circuit U13 to obtain a control signal for controlling the second rectifier switch, and the second and gate U22 is configured to and process the protection signal output by the protection circuit 13, the output signal of the second comparison circuit U12, and the output signal of the third comparison circuit U13 to obtain a control signal for controlling the first rectifier switch.
For example, referring to fig. 4, in this embodiment, the LLC resonant conversion circuit includes an input end M1, an output end M2, a first leg switch Q1, a second leg switch Q2, a resonant capacitor C1, a first rectifier switch Q3, a second rectifier switch Q4, a first transformer TX1 and a second transformer TX2 connected in series with the resonant capacitor C1, the input end M1 is connected with an external power supply V1, the output end M2 is connected with an external load R1, a first bridge arm switch Q1 and a second bridge arm switch Q2 are connected between the input end M1 and the ground in series, a common end (node A) connected with the first bridge arm switch Q1 and the second bridge arm switch Q2 is connected with one end of a resonant capacitor C1, the primary side of a first transformer TX1 is connected with the primary side of a second transformer TX2 in series, the first end of the primary side of the first transformer TX1 is connected with the other end of the resonant capacitor C1, and the second end of the primary side of the second transformer TX2 is connected with the ground; a secondary side of the first transformer TX1 and a secondary side of the second transformer TX2 are connected in series, and a first end of the secondary side of the first transformer TX1 is connected to the ground through a first rectifying switch Q3; a second end of the secondary side of the second transformer TX2 is connected to ground through a second rectifier switch Q4; the common end of the secondary side of the first transformer TX1 and the secondary side of the second transformer TX2 is connected with an output end M2;
the first transformer TX1 and the second transformer TX2 are the same transformer, the excitation inductances of the first transformer TX1 and the second transformer TX2 are the same and are both Lm, the turn ratios of the primary side and the secondary side are the same, a symmetrical double-transformer structure is formed, in the operation period of the resonant converter, a resonant capacitor C1 can form an LLC resonant circuit with the primary side of the first transformer TX1 and the primary side of the second transformer TX2 respectively, and the excitation inductances of the first transformer TX1 and the second transformer TX2 are alternately used as resonant inductances;
the LLC resonant conversion circuit further comprises an output filter capacitor C2 connected in parallel with the load R1;
the first bridge arm switch Q1, the second bridge arm switch Q2, the first rectifier switch Q3, and the second rectifier switch Q4 may be MOS transistors, and in other embodiments, may also be electronic switching devices, for example, the first rectifier switch Q3 and the second rectifier switch Q4 may also be wide bandgap semiconductor power field effect transistors, such as gallium nitride field effect transistors;
the LLC resonant conversion circuit in this embodiment can adopt the above-mentioned synchronous rectification control chip to implement synchronous rectification control, the frequency control circuit of the LLC resonant conversion circuit is located on the primary side of the LLC resonant conversion circuit, control the first bridge arm switch Q1, second bridge arm switch Q2 through the frequency control circuit, the frequency control circuit includes the voltage control type oscillator, bridge arm switch control signal generating circuit 200, frequency setting pin RFmin, oscillator capacitance pin CF, dead zone setting pin DeadT, first bridge arm switch control signal output pin HVG, second bridge arm switch control signal output pin LVG and optocoupler U13, wherein the voltage control type oscillator includes the voltage control type current source 110, the current control type current source 120, the current control type oscillation circuit 130;
in this embodiment, the output feedback voltage of the LLC resonant conversion circuit can be obtained by a feedback voltage sampling circuit, which includes a first voltage-dividing resistor R2 and a second voltage-dividing resistor R3, the first voltage-dividing resistor R2 and the second voltage-dividing resistor R3 are connected in series and then connected between the output end M2 of the LLC resonant conversion circuit and ground, and the common end of the first voltage-dividing resistor R2 and the second voltage-dividing resistor R3 is connected to the output feedback voltage pin FB of the synchronous rectification control chip;
a voltage sampling pin TXH of a first transformer secondary side of the rectification control chip is connected with a first end of the first transformer secondary side, a voltage sampling pin TXL of a second transformer secondary side is connected with a second end of the second transformer secondary side, a first rectification switch control signal output pin SRHVG is connected with a control end of a first rectification switch, and a second rectification switch control signal output pin SRLVG is connected with a control end of a second rectification switch;
the emitting end of the optical coupler U13 is connected with an error voltage pin COM of the synchronous rectification control chip, the receiving end of the optical coupler U13 is connected with a frequency setting pin RFmin of the frequency control circuit through a frequency compensation circuit Z1, and the error voltage on the error voltage pin COM is fed back to the primary side from the secondary side through the optical coupler U13 so as to generate a first current I1In addition, the frequency setting pin RFmin is also grounded through a first resistor R5, and the first current I1The frequency compensation circuit Z1 can be changed with the change of the output feedback voltage, for example, referring to fig. 5, the frequency compensation circuit Z1 can include a resistor R7, a resistor R8 and a capacitor C4, a first end of the resistor R7 and a first end of the resistor R8 are connected to the frequency setting pin RFmin of the frequency control circuit, a second end of the resistor R7 is grounded through the capacitor C4, and a second end of the resistor R8 is connected to the lightA receiving end of coupler U13;
in addition, a voltage feedback compensation circuit Z2 is disposed between the output feedback voltage pin FB and the error voltage pin COM, for example, referring to fig. 6, the voltage feedback compensation circuit Z2 may include a capacitor C5, a capacitor C6, and a resistor R9, wherein a first end of the capacitor C5 and a first end of the capacitor C6 are connected to the error voltage pin COM, a second end of the capacitor C5 is connected to a first end of the resistor R9, and a second end of the resistor R9 and a first end of the capacitor C6 are connected to the output feedback voltage pin FB;
wherein the voltage-controlled current source 110 is configured to generate a second current I on the first resistor R5 according to a first reference voltage2One end of the voltage control type current source 110 is connected to the frequency setting pin RFmin, and the other end is connected to the current control type current source 120;
the current control type current source 120 is used for generating the first current I1And the second current I2Generating a third current I3；
The current-controlled oscillation circuit 130 is used for generating the third current I3The clock signal is generated, a first end of the current-controlled oscillation circuit 130 is connected to the current-controlled current source 120, a second end of the current-controlled oscillation circuit 130 is connected to the oscillator capacitor pin CF, a third end of the current-controlled oscillation circuit 130 is connected to the dead zone setting pin DeadT, a fourth end of the current-controlled oscillation circuit 130 is connected to the bridge arm switch control signal generating circuit 200, the oscillator capacitor pin CF is connected to an oscillation capacitor C3, the dead zone setting pin DeadT is connected to one end of the second resistor R6, and the other end of the second resistor R6 is grounded.
For example, in one embodiment, the third current I3First current I1+ a second current I2；
For example, in one embodiment, referring to fig. 7, the voltage-controlled current source 110 includes: a second operational amplifier U2, a positive input terminal of the second operational amplifier U2 is connected with a first reference voltage V3, a negative input terminal is connected with the frequency setting pin RFmin, and an output terminal of the second operational amplifier U2 is connected with a base electrode of a first triode Q5; an emitter of the first triode Q5 is connected with a frequency setting pin RFmin;
the current control type current source 120 includes: a second triode Q6 connected with the first triode Q5 in series, and a third triode Q7 forming a mirror current source with the second triode Q6;
the current-controlled oscillation circuit 130 includes: a first control switch and a second control switch, a first comparator U3, a second comparator U4, an RS trigger U5;
one end of the first control switch is connected to the collector of the third transistor, and the other end is connected to the oscillator capacitor pin CF, wherein in this embodiment, the first control switch includes: the anode of the second diode D2 and the fourth triode Q8 are connected with the collector of the third triode Q7, the cathode of the second diode D2 is connected with the oscillator capacitor pin CF, the collector of the fourth triode Q8 is connected with the anode of the second diode D2, the emitter of the fourth triode Q8 is grounded, and the base of the fourth triode Q8 is connected with the NQ end of the RS trigger U5;
one end of the second control switch is connected to the oscillator capacitor pin CF, and the other end of the second control switch is connected to the dead zone setting pin DeadT, wherein in this embodiment, the second control switch is an NPN triode Q9, and a base of the second control switch Q9 is connected to an NQ end of the RS flip-flop U5;
the positive input end of the first comparator U3 is connected with a second reference voltage V4, and the negative input end of the first comparator U3 is connected with an oscillator capacitor pin CF;
the negative input end of the second comparator U4 is connected with a third reference voltage V5, and the positive input end of the second comparator U4 is connected with an oscillator capacitor pin CF;
the input of the RS end of the RS trigger U5 is connected with the output of the first comparator U3, and the input of the R end is connected with the output of the second comparator U4; the output signal of the NQ end of the RS flip-flop is the clock signal and is used as the control signal of the second control switch, and the output signal of the NQ end of the RS flip-flop U5 is also used as the control signal of the first control switch.
In this embodiment, the third current I generated by the current-controlled current source 1203For charging a capacitor C3 and by varying a third current I3Can adjust the charging speed of C3, and further realize the current control type oscillation electricityThe clock signal generated by the circuit is subjected to frequency adjustment to realize the adjustment of the working frequency of the LLC resonant conversion circuit;
in addition, the first control switch and the second control switch are controlled by clock signals, so that the capacitor C3 stops discharging when being charged and stops charging when being discharged, thereby being convenient for accurately setting dead time, being beneficial to further ensuring that upper and lower switches of a half bridge cannot be directly connected and short-circuited when working at high frequency, simultaneously setting the maximum duty ratio of a clock signal at full load low frequency and the minimum duty ratio of the clock signal at light load high frequency during the dead time, and reducing the duty ratio D of the clock signal along with the increase of the working frequency fw of the LLC resonant conversion circuit, namely, the duty ratio D is in inverse linear proportion to the fw;
specifically, when Q8 is turned off and Q9 is turned off, the current control type current source 130 charges the first end of the oscillating capacitor C3, and when Q8 is closed and Q9 is closed, the current control type current source 130 stops charging the first end of the oscillating capacitor C3 and the first end of the oscillating capacitor C3 is discharged through the second resistor R6, so that the dead time can be accurately set.
In another embodiment, referring to fig. 8, the control signal of the first control switch K1 is the Q output signal of the RS flip-flop U5, and the control signal of the second control switch K2 is the NQ output signal of the RS flip-flop U5, for example, the first control switch K1 may adopt a transistor, an emitter of the transistor is connected to a current-controlled current source, a collector of the transistor is connected to the first end of the capacitor C3, when the first control switch K1 is turned on, the second control switch K2 is turned off, and when the first control switch K1 is turned off, the second control switch K2 is turned on.
For example, in one embodiment, the second reference voltage V4 is 0.9V, the third reference voltage V5 is 3.9V, when the first terminal (pin CF) of the capacitor C3 is greater than 3.9V, the R terminal of the RS flip-flop U5 is high, the U4 resets the U5, and the capacitor C3 is discharged; when the first end (pin CF) of the capacitor C3 is less than 0.9V, the S end of the RS trigger U5 is at a high level, the U3 triggers the U5, and the capacitor C3 is charged; when the first end (pin CF) of the capacitor C3 is greater than 0.9 volt and less than 3.9 volts, the R end and the S end of the RS trigger are both low level;
the charging process of the capacitor C3 is controlled by the current-controlled current source 120, and the discharging process is controlled by the discharging time (dead time) set by the capacitor C3 and the second resistor R6 of the pin CF, so that an oscillating triangular wave is formed at the pin CF, a clock signal CLK is generated at the QN end of the RS flip-flop U5, and a Delay signal Delay is generated at the Q end of the RS flip-flop U5;
in this embodiment, the upper and lower limits of the oscillation frequency can be set by the resistor R5 and the resistor R8, respectively, and the dead time can be set by the resistor R6.
The bridge arm switch control signal generation circuit 200 comprises a frequency divider U6, an and gate U7 and an and gate U8;
the frequency divider U6 is configured to divide the frequency of the clock signal by 1/2 to obtain a first frequency-divided signal and a second frequency-divided signal, where the frequencies of the first frequency-divided signal and the second frequency-divided signal are both 1/2 of the frequency of the clock signal, and the first frequency-divided signal and the second frequency-divided signal are opposite signals, for example, the frequency divider U6 may be implemented by using a JK flip-flop, a Q terminal of the JK flip-flop outputs the first frequency-divided signal, and a QN terminal of the JK flip-flop outputs the second frequency-divided signal;
the input of the and gate U7 is a first frequency division signal and a Q-end output signal of the RS flip-flop U5, and the output is used as the first control signal, and the output end of the and gate U7 is connected to a first bridge arm switch control signal output pin HVG;
and the input of the and gate U8 is a second frequency division signal and a Q-end output signal of the RS flip-flop U5, and the output is used as the second control signal, and the output end of the and gate U8 is connected to a second bridge arm switch control signal output pin LVG.
The embodiment of the utility model provides an in, multiplexing a transformer that is in inductance mode of operation, the transformer passes to synchronous rectification control chip with the signal, synchronous rectification control chip accepts the unanimous signal of frequency and former side frequency control circuit's clock signal, not only can realize the synchronous control of four switches on former vice both sides, can also simplify the circuit device, furthermore, when underloading and start moment, pin COM is in the low level, operating frequency risees when setting for the frequency or output current is interrupted, utilize the third comparison circuit can turn-off synchronous rectification, when the output is excessive pressure, under-voltage, overcurrent, the excess temperature, overpower, or during the short circuit, utilize protection circuit can turn-off synchronous rectification, thereby can improve the safety and the reliability of synchronous rectification greatly.
The embodiment of the utility model provides a switching power supply is still provided, including frequency control circuit, first bridge arm switch, second bridge arm switch, resonant capacitor, first rectifier switch, second rectifier switch, with resonant capacitor establishes ties first transformer and second transformer, first transformer with the second transformer is the same transformer, switching power supply still includes: a synchronous rectification control chip as described above;
the synchronous rectification control chip is characterized in that a voltage sampling pin TXH of a first transformer secondary side serving as an input pin is connected with the first transformer secondary side, and a voltage sampling pin TXL of a second transformer secondary side serving as an input pin is connected with the second transformer secondary side; the first rectifier switch control signal output pin SRHVG as an output pin is connected with the control end of the first rectifier switch, and the second rectifier switch control signal output pin SRLVG as an output pin is connected with the control end of the second rectifier switch.
For example, in one embodiment, the switching power supply further comprises a feedback voltage sampling circuit;
the input end of the feedback voltage sampling circuit is connected with the output voltage of the switching power supply, the output end of the feedback voltage sampling circuit is connected with an output feedback voltage pin FB of the synchronous rectification control chip, the feedback voltage sampling circuit is used for outputting the output feedback voltage, and an error voltage pin COM of the synchronous rectification control chip is used for outputting an error voltage between the output feedback voltage and a reference voltage.
For example, in one embodiment, the feedback voltage sampling circuit includes: two divider resistors connected in series;
and an output feedback voltage pin FB of the synchronous rectification control chip is connected with a common end between the two divider resistors.
For example, in an embodiment, the switching power supply further includes an optical coupler, a transmitting terminal of the optical coupler is connected to an error voltage pin COM of the synchronous rectification control chip, a receiving terminal of the optical coupler is connected to the frequency control circuit, and the error voltage is fed back from a secondary side to a primary side through the optical coupler, so as to generate a first current;
the frequency control circuit comprises a voltage control type oscillator and a bridge arm switch control signal generating circuit;
the voltage control type oscillator is used for generating a third current according to the first current and a second current generated by an internal current source, and generating a clock signal with adjustable frequency and invariable pulse width according to the third current;
the bridge arm switch control signal generating circuit is used for outputting a first control signal for controlling the first bridge arm switch and outputting a second control signal for controlling the second bridge arm switch according to the clock signal, and the first control signal and the second control signal form a fixed dead zone.
For example, in one embodiment, the switching power supply further comprises a frequency compensation circuit and a voltage feedback compensation circuit;
the frequency compensation circuit is arranged between the receiving end of the optocoupler and a frequency setting pin of the frequency control circuit;
one end of the voltage feedback compensation circuit is connected with an output feedback voltage pin of the synchronous rectification control chip, and the other end of the voltage feedback compensation circuit is connected with an error voltage pin of the synchronous rectification control chip.
Preferably, in this embodiment, the frequency control circuit is configured to make the full load operating frequency of the LLC resonant conversion circuit greater than (2 x 1), where f1 is the resonant frequency,
in the formula, Cr is a capacitance value of a resonance capacitor of the LLC resonance conversion circuit, and Lm is excitation inductance of a first transformer and a second transformer of the LLC resonance conversion circuit;
in the switching power supply of the present embodiment, when the operating frequency fw is greater than (2 × 1), a waveform diagram of the switching power supply is shown in fig. 9;
wherein, from T0 to T4, there is one control cycle, "U-CF" is a voltage waveform (triangular waveform) of the pin CF whose rising edge corresponds to the on time of Q1 or Q2 and whose falling edge corresponds to the dead time, "U-Q1" is a voltage waveform of the first control signal, "U-Q2" is a voltage waveform of the second control signal, "CLK" is a waveform (high level corresponds to the dead time) of the clock signal generated by the current-controlled oscillation circuit, "IP" is a current waveform at IP in fig. 2, "IQ 3" is a current waveform at the first rectifier switch Q3, "IQ 4" is a current waveform at the second rectifier switch Q4, "U-SRHVG/U-SRLVG" is a voltage waveform of the pin SRHVG (i.e., a control signal for controlling the first rectifier switch Q3) and the pin SRLVG (i.e., a control signal for controlling the second rectifier switch Q4), "U-TXH/U-TXL" is the voltage waveform of pin TXH (i.e. the first end of the secondary side of the first transformer TX 1) and pin TXL (i.e. the second end of the secondary side of the second transformer TX 2);
from T0 to T1, there is a dead zone (Td), before time T0, TX2 operates in an inductive mode, i.e., a flyback transformer, whose stored energy is output to a load through Q4, the voltage of node a rises from zero and rises to a voltage of V1 before time T1, Q1 is in a Zero Voltage State (ZVS), and is turned on at time T1, the primary current IP of the transformer changes from negative to positive and passes through zero before time T1;
the time from T1 to T2 is Q1 on time, TX2 works in a forward transformer mode, energy is output to a load through Q4, a clock triangular wave U-CF rises from zero to a top point, the primary side current IP of the transformer rises from zero to a maximum value, Q1 is turned off at the time of T2, the primary side current IP of the transformer starts to fall from the peak value, falls to zero in the dead time (Td) from T2 to T3, and passes through the zero point at the time of T3;
the time from T2 to T4 is the next half period, the time from T2 to T3 is a dead zone Td, before the time of T2, TX1 works in an inductance mode, namely a flyback transformer, stored energy of the flyback transformer is output to a load through Q3, the voltage of a node A starts to drop from the voltage of V1 and drops to zero before the time of T3, Q2 is in a Zero Voltage State (ZVS), the flyback transformer is turned on at the time of T3, the current IP of the primary side of the transformer is turned on from positive to negative, and passes through a zero point before the time of T3;
the time from T3 to T4 is Q2 on time, TX1 works in a forward transformer mode, energy is output to a load through Q3, a clock triangle wave U-CF rises from zero to a top point, the primary side current IP of the transformer is reduced from zero to a minimum value, Q2 is turned off at the time of T4, the primary side current IP of the transformer is zeroed from a peak value, returns to zero in the dead time Td from T4 to T5, and crosses the zero point at the time of T5.
The embodiment can simultaneously and accurately control all the switches on the two sides of the original pair, and the control logic of the switching power supply adopts the same clock to synchronously control the frequency and the time sequence of the four switches on the two sides of the original pair.
In this embodiment, the switching power supply may implement step-by-step voltage reduction from the input end to the output end, for example, a half-bridge converter may reduce the input voltage by half, and the winding turn ratio of the series-connected transformers TX1 and TX2 may be reduced again, so that the turn ratio of the transformer may be reduced, and the design of the transformer is simplified.
In addition, the existing body diode-based detection type synchronous rectification technology can only be used for a low-frequency resonant converter, and has low efficiency and poor reliability. The control type synchronous rectification technology of the resonant converter based on the double-transformer structure can reliably and accurately control each switching device of the primary side and the secondary side synchronously, the working time sequence of each switching device is controlled by the same clock, the technical requirements of high frequency, high efficiency and reliability are met, and the circuit can be simplified; by adopting the working mode based on the alternation of flyback (dead time working) and forward (non-dead time working), continuous output current is realized, output ripple waves can be greatly reduced, output filter capacitance can be greatly reduced, the size of the power supply can be greatly reduced, and the power density can be improved.
The embodiment of the utility model provides an electrical equipment is still provided, including foretell switching power supply, for example, this electrical equipment can be equipment such as PC, server or display.
It will be appreciated by those skilled in the art that the above-described preferred embodiments may be freely combined, superimposed, without conflict.
It will be understood that the above-described embodiments are illustrative only and not restrictive, and that various obvious and equivalent modifications and substitutions may be made in the details described herein by those skilled in the art without departing from the basic principles of the invention.
Claims (11)
1. A synchronous rectification control chip is used for synchronous rectification control in an LLC resonant conversion circuit, the LLC resonant conversion circuit comprises a frequency control circuit, a first bridge arm switch, a second bridge arm switch, a first rectification switch, a second rectification switch, a resonant capacitor, a first transformer and a second transformer which are connected in series with the resonant capacitor, the first transformer and the second transformer are the same transformer, and excitation inductors of the first transformer and the second transformer are alternately used as resonant inductors, and the synchronous rectification control chip is characterized by comprising a first comparison circuit and a second comparison circuit;
the positive input end of the first comparison circuit is used for being connected with the secondary side of the first transformer so as to receive a signal with the frequency consistent with the clock signal of the frequency control circuit on the primary side, the negative input end of the first comparison circuit is connected with a first reference voltage, and the output signal of the first comparison circuit is used for realizing the control of the second rectifier switch;
and the positive input end of the second comparison circuit is used for being connected with the secondary side of the second transformer so as to receive a signal with the frequency consistent with the clock signal of the primary side frequency control circuit, the negative input end of the second comparison circuit is connected with a second reference voltage, and the output signal of the second comparison circuit is used for realizing the control of the first rectifier switch.
2. The synchronous rectification control chip according to claim 1, further comprising a transconductance circuit, a third comparison circuit, a first and gate, and a second and gate;
the positive input end of the transconductance circuit is connected with a reference voltage, the negative input end of the transconductance circuit is connected with an output feedback voltage of the LLC resonant conversion circuit, and the output of the transconductance circuit is an error voltage between the output feedback voltage and the reference voltage;
the positive input end of the third comparison circuit is connected with the output end of the transconductance circuit, and the negative input end of the third comparison circuit is connected with a third reference voltage;
a first input end of the first AND gate is connected with an output end of the first comparison circuit, a second input end of the first AND gate is connected with an output end of the third comparison circuit, and an output of the first AND gate is a control signal for controlling the second rectifier switch;
the first input end of the second AND gate is connected with the output end of the second comparison circuit, the second input end of the second AND gate is connected with the output end of the third comparison circuit, and the output of the second AND gate is a control signal for controlling the first rectifier switch.
3. The synchronous rectification control chip according to claim 2, further comprising: the voltage sampling circuit comprises an output feedback voltage pin, an error voltage pin, a voltage sampling pin of a first transformer secondary side, a voltage sampling pin of a second transformer secondary side, a first rectifier switch control signal output pin and a second rectifier switch control signal output pin;
the positive input end of the first comparison circuit is connected with a voltage sampling pin of the secondary side of the first transformer; the output end of the first AND gate is connected with the second rectifier switch control signal output pin;
the positive input end of the second comparison circuit is connected with the voltage sampling pin of the secondary side of the second transformer; the output end of the second AND gate is connected with the first rectifying switch control signal output pin;
and the negative input end of the transconductance circuit is connected with the output feedback voltage pin, and the output end of the transconductance circuit is connected with the error voltage pin.
4. The synchronous rectification control chip according to claim 3, wherein a first driving circuit is further arranged between the output end of the first AND gate and the second rectification switch control signal output pin;
and a second driving circuit is also arranged between the output end of the second AND gate and the first rectifying switch control signal output pin.
5. The synchronous rectification control chip according to claim 2, further comprising a protection circuit for outputting a protection signal when detecting an output overvoltage, undervoltage, overcurrent, overtemperature, overpower or short circuit;
the first and second and gates each include a third input terminal and both receive the protection signal.
6. A switching power supply comprises a frequency control circuit, a first bridge arm switch, a second bridge arm switch, a resonant capacitor, a first rectifier switch, a second rectifier switch, a first transformer and a second transformer, wherein the first transformer and the second transformer are the same transformer, and the switching power supply is characterized by further comprising: the synchronous rectification control chip according to any one of claims 1 to 5;
the synchronous rectification control chip is characterized in that a voltage sampling pin of a first transformer secondary side serving as an input pin is connected with the first transformer secondary side, and a voltage sampling pin of a second transformer secondary side serving as an input pin is connected with the second transformer secondary side; the first rectifier switch control signal output pin as an output pin is connected with the control end of the first rectifier switch, and the second rectifier switch control signal output pin as an output pin is connected with the control end of the second rectifier switch.
7. The switching power supply according to claim 6, further comprising a feedback voltage sampling circuit;
the input end of the feedback voltage sampling circuit is connected with the output voltage of the switching power supply, the output end of the feedback voltage sampling circuit is connected with the output feedback voltage pin of the synchronous rectification control chip, the feedback voltage sampling circuit is used for outputting the output feedback voltage, and the error voltage pin of the synchronous rectification control chip is used for outputting the error voltage between the output feedback voltage and the reference voltage.
8. The switching power supply according to claim 7, wherein the feedback voltage sampling circuit comprises: two divider resistors connected in series;
and an output feedback voltage pin of the synchronous rectification control chip is connected with a common end between the two divider resistors.
9. The switching power supply according to claim 7, further comprising an optocoupler, wherein a transmitting terminal of the optocoupler is connected to an error voltage pin of the synchronous rectification control chip, a receiving terminal of the optocoupler is connected to a frequency setting pin of the frequency control circuit, and the error voltage is fed back from a secondary side to a primary side through the optocoupler, thereby generating a first current;
the frequency control circuit comprises a voltage control type oscillator and a bridge arm switch control signal generating circuit;
the voltage control type oscillator is used for generating a third current according to the first current and a second current generated by an internal current source, and generating a clock signal with adjustable frequency and invariable pulse width according to the third current;
the bridge arm switch control signal generating circuit is used for outputting a first control signal for controlling the first bridge arm switch and outputting a second control signal for controlling the second bridge arm switch according to the clock signal, and the first control signal and the second control signal form a fixed dead zone.
10. The switching power supply according to claim 9, further comprising a frequency compensation circuit and a voltage feedback compensation circuit;
the frequency compensation circuit is arranged between the receiving end of the optocoupler and a frequency setting pin of the frequency control circuit;
one end of the voltage feedback compensation circuit is connected with an output feedback voltage pin of the synchronous rectification control chip, and the other end of the voltage feedback compensation circuit is connected with an error voltage pin of the synchronous rectification control chip.
11. An electrical apparatus, characterized in that it comprises a switching power supply according to any one of claims 6-10.
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| CN202021510352.9U CN212785179U (en) | 2020-07-27 | 2020-07-27 | Synchronous rectification control chip, switching power supply and electrical equipment |
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| CN202021510352.9U CN212785179U (en) | 2020-07-27 | 2020-07-27 | Synchronous rectification control chip, switching power supply and electrical equipment |
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