CN113252974A - Load current detection circuit - Google Patents
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- CN113252974A CN113252974A CN202110743463.7A CN202110743463A CN113252974A CN 113252974 A CN113252974 A CN 113252974A CN 202110743463 A CN202110743463 A CN 202110743463A CN 113252974 A CN113252974 A CN 113252974A
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- G01R19/255—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques using analogue/digital converters of the type with counting of pulses during a period of time proportional to voltage or current, delivered by a pulse generator with fixed frequency
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Abstract
The present disclosure provides a load current detection circuit, which generates a first voltage signal according to a first time period in which a first switching tube and a second switching tube are alternately turned on in a switching period through a first detection unit; generating a second voltage signal by using a second detection unit according to a second time period in the switching period when the first switching tube and the second switching tube are both cut off; the pulse signal is output by comparing the first voltage signal and the second voltage signal which are accessed by the input end of the comparator; and then, counting the number of pulses of the pulse signal in a single switching period by using a control unit, and outputting the average load current according to a counting result. Therefore, the complexity of the load current detection circuit can be effectively reduced, and the precision and accuracy of load current detection are improved.
Description
Technical Field
The present disclosure relates to the field of integrated circuit technologies, and in particular, to a load current detection circuit for a DC/DC switching power supply, and more particularly, to a load current detection circuit for a DC/DC switching power supply operating in a Discontinuous Current (DCM) mode in a very light load state.
Background
The circuit form of the DC/DC switching power converter comprises a charge pump circuit realized by a capacitor, and also comprises a Buck type Buck switching circuit, a Boost type Boost circuit and a negative voltage Buck-Boost circuit realized by an inductor. In order to accurately control the current in the switching power converter circuit, for example, when the load current becomes small enough, the system automatically enters a sleep state, which requires accurate detection of the load current, and thus a load current detection circuit capable of detecting a light load current is required.
In the prior art, one of the common load current detection methods is the technical solution as shown in fig. 1, in the Buck-type switching power converter 100, the connection node SW between the switch Q1 and the inductor L is used as the sampling node of the inductor current, and is connected to the negative input terminal of the operational amplifier 102 in the load current detection circuit 120, the positive input terminal of the operational amplifier 102 and the first terminal of the switch Q1 are commonly connected to the input terminal of the switching power converter 100 for receiving the input signal Vin, the freewheeling tube Q2 is connected between the node SW and ground, the switch Q1 and the control terminal of the follow current tube Q2 are commonly connected to a logic control circuit 110 to obtain a gate signal GP and a gate signal GN respectively, the current signal I11 output by the operational amplifier 102 generates a voltage drop across the current sensing resistor Rsense, the capacitor C0 connected to the series resistor R0 is charged and discharged to output the average voltage Vave. Since the current flowing through the load sensing resistor Rsen also flows through the inductor, the operational amplifier 102 can indirectly sense the current flowing through the sensing resistor Rsen and the inductor through the voltage of the sensing resistor Rsense, so that the average voltage Vave is used to characterize the load current. In the external current detection resistor scheme, the operational amplifier 102 needs to detect the voltage across the switching tube Q1 at any time, so that the speed and accuracy requirements of the operational amplifier are extremely high, and the efficiency of the switching power converter is lost.
The buck DC/DC (buck) switching power converter 100 operates in Discontinuous Current Mode (DCM) under the ultra-light load mode, and the DCM has the advantages of improving the conversion efficiency and reducing the switching loss under the light load. However, the switching period of the power transistor operating in DCM is very long, which results in the failure of the conventional method of detecting the load current by sampling and averaging the inductor current. Because the voltage value corresponding to the sampled current is very low, even only a few mV, and the switching period is very long, the load current when not switching can not be obtained by sampling.
Disclosure of Invention
In order to solve the technical problem, the present disclosure provides a load current detection circuit, which can effectively reduce the complexity of the load current detection circuit and improve the accuracy and precision of load current detection.
The present disclosure provides a load current detection circuit for a switching power converter, the switching power converter including a first switching tube and a second switching tube operating according to a switching control signal, wherein the load current detection circuit includes:
the first detection unit generates a first voltage signal according to a first time period in which the first switching tube and the second switching tube are alternately conducted in a switching period;
the second detection unit generates a second voltage signal according to a second time period in which the first switching tube and the second switching tube are both cut off in the switching period;
the input end of the comparator is respectively connected with the output ends of the first detection unit and the second detection unit and provides a pulse signal according to the first voltage signal and the second voltage signal;
and the control unit is connected with the output end of the comparator and used for counting the number of pulses of the pulse signal in a single switching period and outputting the average load current according to the counting result.
Preferably, in a single switching cycle, the switching period includes a time period in which the first switching tube and the second switching tube are alternately switched on and a time period in which the first switching tube and the second switching tube are both switched off,
the first time period is a sum of the superposition of the conduction time of the alternating conduction of the first switch tube and the second switch tube, and the second time period is a time period of the cutoff of the first switch tube and the second switch tube.
Preferably, the first detecting unit connects a connection node between the first switching tube and the second switching tube, and includes:
a first branch including a first switching element, a first current source and a first capacitor connected in series between a power supply terminal and ground, the first switching element communicating with the first branch for the first period of time in a single switching cycle and outputting the first voltage signal through a connection node of the first current source and the first capacitor;
and the first transistor is connected in parallel with two ends of the first capacitor, and the control end of the first transistor is connected with the output end of the control unit.
Preferably, the second detecting unit connects a connection node of the first switching tube and the second switching tube, and includes:
a second branch circuit including a second switching element, a second current source, and a second capacitor connected in series between the power supply terminal and the ground, the second switching element communicating the second branch circuit for the second period in a single switching cycle, and outputting the second voltage signal through a connection node of the second current source and the second capacitor;
and the second transistor is connected in parallel with two ends of the second capacitor, and the control end of the second transistor is connected with the output end of the comparator.
Preferably, the inverting input terminal of the comparator is connected to the output terminal of the first detecting unit, the non-inverting input terminal of the comparator is connected to the output terminal of the second detecting unit, the output terminal provides the pulse signal,
and the output end of the comparator is connected with the control end of the second transistor, and the pulse signal is also used for controlling the on-off of the second transistor so as to regulate and control the charging and discharging process of the second capacitor.
Preferably, the aforementioned control unit comprises:
the counting module is connected with the output end of the comparator and used for counting the number of the pulses of the pulse signal in a single switching period and outputting a counting result;
the detection module is connected with a connection node of the first switch tube and the second switch tube to obtain a peak value of an inductive current signal;
and the calculating module is respectively connected with the counting module and the detecting module, and calculates and outputs the average load current according to the counting result and the peak value of the inductive current signal.
Preferably, the reference current provided by the first current source in the first branch and the reference current provided by the second current source in the second branch are equal, and the first capacitor and the second capacitor have the same specification.
Preferably, the topology type of the aforementioned switching power converter may be any one of a boost type topology, a buck type topology and a boost/buck type topology.
The beneficial effects of this disclosure are: the load current detection circuit is used for connecting a connecting node of a first switching tube and a second switching tube in the switching power converter to obtain a node signal (inductance current signal) representing a switching control signal of the switching power converter working in a DCM mode, so that the response speed of a system is improved, not only is the complex circuit design avoided, but also the detection precision of the load current is improved, and the complexity and the design difficulty of the circuit are reduced.
The load current detection circuit generates a first voltage signal through a first detection unit according to a first time period in which the first switch tube and the second switch tube are alternately conducted in a switch period; generating a second voltage signal by using a second detection unit according to a second time period in the switching period when the first switching tube and the second switching tube are both cut off; the pulse signal is output by comparing the first voltage signal and the second voltage signal which are accessed by the input end of the comparator; and then, counting the number of pulses of the pulse signal in a single switching period by using a control unit, and outputting the average load current according to a counting result. The complexity of the load current detection circuit can be effectively reduced, the unstable influence of failure caused by overlong switching period (namely overlong time for switching off the first switching tube and the second switching tube) in a method for detecting the load current by sampling and averaging the inductive current by using a traditional detection circuit is avoided, and the extremely small load current is detected, so that the accuracy of load state detection is greatly improved, the dead zone range of the current detection of the low load is reduced, the probability of false detection of the low load current is reduced, and the accuracy and the precision of the load current detection are improved.
Drawings
The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of the embodiments of the present disclosure with reference to the accompanying drawings.
Fig. 1 shows a circuit configuration diagram of a Buck-type switching power converter in the prior art;
FIG. 2 is a timing diagram of the node SW voltage and inductor current for the switching power converter of FIG. 1 operating in a (DCM) discontinuous current mode;
fig. 3 shows a circuit configuration diagram of a switching power converter provided in an embodiment of the present disclosure;
fig. 4 is a block diagram illustrating a load current detection circuit in the switching power converter shown in fig. 3;
fig. 5 is a circuit configuration diagram showing a control unit in the load current detection circuit shown in fig. 4;
fig. 6 shows an operation timing diagram of signals of the switching power converter shown in fig. 3 operating in a (DCM) discontinuous current mode.
Detailed Description
The Buck type switching power supply converter is a Buck DC/DC conversion system adopting a Buck Regulator mode in the meaning of the application; the input voltage is greater than the output voltage;
the meaning of a Boost type switching power supply converter in the application is a Boost DC/DC conversion system adopting a Boost Regulator mode; the output voltage is greater than the input voltage;
the Buck-Boost type switching power converter is a negative voltage DC/DC conversion system adopting a Buck-Boost Regulator mode in the application;
PWM is the abbreviation of English Pulse Width Modulation, and Chinese means Pulse Width Modulation; the Pulse Width Modulation (PWM) switch power converter achieves the purpose of stabilizing output voltage by adjusting the duty ratio under the condition that the output frequency of a control circuit is not changed;
PFM is the abbreviation of English Pulse Frequency Modulation, and Chinese means Pulse Frequency Modulation; a Pulse Frequency Modulated (PFM) switching type voltage regulator circuit is an "equal-width frequency modulation" method, i.e., the chopping frequency of the circuit is adjusted to achieve the purpose of stabilizing the output voltage.
CCM is an abbreviation of english Continuous Conduction Mode, which means a Continuous Conduction Mode, and means a working Mode in which a power tube in a switching power converter is alternately and continuously conducted so that current in an inductor is continuously changed;
DCM: the switching Mode is an abbreviation of english Discontinuous Conduction Mode, and the chinese meaning is Discontinuous Conduction Mode, which refers to a working Mode in which the current in the inductor is changed discontinuously when the power tube is turned off in the switching power converter.
Detailed Description
To facilitate an understanding of the present disclosure, the present disclosure will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present disclosure are set forth in the accompanying drawings. However, the present disclosure may be embodied in different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used in the description of the disclosure herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure.
The basic principle of the inductance type switching power converter is that the energy storage characteristics of an inductor and a capacitor are utilized to realize voltage change, and the change rate of the inductor current is equal to the voltage at two ends of the inductor divided by the inductor Henry value; the change of the inductive current is a linear process, the change speed of the inductive current is related to the slope of the linear change of the inductive current and the voltage and the inductance value at two ends of the inductor, and when the external voltage at two ends of the inductor is constant and the inductive value is also determined, the rising slope and the falling slope of the inductive current are also fixed.
The present disclosure is described in detail below with reference to the accompanying drawings.
Fig. 2 is a timing diagram illustrating a node SW voltage and an inductor current of the switching power converter shown in fig. 1 in a (DCM) discontinuous current mode, and fig. 3 is a circuit structure diagram of the switching power converter provided by the embodiment of the disclosure.
Referring to fig. 3, the switching power converter 200 described in the embodiment of the present disclosure is substantially the same as the basic features of the switching power converter 100 in the prior art shown in fig. 1, and also includes: in the CCM operation mode, the switching power converter 200 controls the two power switching tubes (the first switching tube Q1 and the second switching tube Q2) to be alternately turned on through the logic control circuit 210, wherein one switching cycle of the switching power converter includes an inductor current rising time period (Ton) and an inductor current falling time period (Toff); in the DCM operation mode, the switching power converter 200 controls the two power switch transistors (the first switch transistor Q1 and the second switch transistor Q2) to be turned on alternately and turned off at intervals through the logic control circuit 210, that is, in one switching cycle, including an inductor current rising period (Ton), an inductor current falling period (Toff), and a period (Tsep) during which the inductor current is zero.
The logic control circuit 210 in the switching power converter 200 not only generates the basic switching signal of the switching power converter 200, such as the PWM switching signal, but also generates the gate signal GP and the gate signal GN for controlling the two power switching transistors; when the gate signal GP is at a low level, one of the power switches (e.g., the first switch Q1) is turned on; when the grid signal GN is at a high level, the other power switch tube (the second switch tube Q2) is turned on; the gate signal GP controlling the first switch Q1 and the gate signal GN controlling the second switch Q2 are both generated based on the PWM switch signal, so the gate signal GP and the gate signal GN are converted from the PWM signal, and are synchronized with each other. The inductor current rising period (Ton) and the inductor current falling period (Toff) are synchronized with the gate signal GP and the gate signal GN; the gate signal GP, the gate signal GN, and the PWM switching signal are synchronized, so that the inductor current rising period (Ton) and the inductor current falling period (Toff) can be obtained by using the high-low level period of the PWM switching signal.
As shown in fig. 2, the inductor current I of the inductor-type switching power converter 100LIs a triangular wave, and as can be seen from the figure, the inductor current climbs upwards from the time t0 to the time t 1; the inductor current drops downward from time t1 to time t 2. The inductor current I is in each switching cycle when the load current is constantLThe starting point of the rise is equal to the end point of the fall, if not, the inductor current I if the end point of each fall is higher than the starting point of the riseLIt will always become larger and vice versa it will always become smaller. If the inductive current I is measuredLThe middle point of the rising edge and the middle point of the falling edge being connected, the segment of the line being parallel to the X-axis, i.e. the inductor current ILIs equal to the inductor current ILThe midpoint of the fall, so the midpoint of the sampled inductor current rise period and the midpoint of the sampled inductor current fall period, are equivalent variations.
For any type of inductive switching power converter using an inductor, according to the characteristic that the inductor current linearly changes in this interval, as long as the magnitude of the inductor current at the rising midpoint time or the falling midpoint time is found, and the current at the sampling time is sampled and held, the magnitude of the load current can be converted through simple operation. If the middle point moment of the rising edge of the inductive current or the middle point moment of the falling of the inductive current, namely the inductive current at the middle point moment of the triangular wave of the inductive current, is obtained, the load current of the whole switching period can be obtained through calculation, and therefore the two moments are key points of sampling current. To obtain the middle point of the rising period or the falling period of the inductor current in the current switching cycle, the real-time characteristic of the circuit is often highly required.
For the Buck-type switching power converter 100 in the prior art, it is assumed that the Buck-type switching power converter 100 operates in CCM mode, i.e., continuous operation mode, and the output load current is equal to the average value of the inductor current. Under the condition that no load current sampling resistor exists, the current on the inductor is difficult to sample directly, but the inductor current is divided into two parts, wherein one part is that when the first switch tube Q1 is opened, the current flowing through the first switch tube Q1 is equal to the current of the inductor, the current flowing through the second switch tube Q2 is 0 at the moment, the other part of the inductor current is that when the second switch tube Q2 is opened, the current flowing through the second switch tube Q2 is equal to the current of the inductor, and the current flowing through the first switch tube Q1 is 0, so that the load current is the average value of the sum of the currents flowing through the first switch tube Q1 and the second switch tube Q2. When the load current is constant, the current flowing through the first switch tube Q1 in each switching period is a linearly increasing current; firstly, the opening time Ton of the first switch tube in one period is obtained, in the opening time Ton of the first switch tube in the current period, the inductor current, namely the load current is sampled, and the load current sampling value at the moment is kept until the first switch tube conduction time in the next period. Supposing that the Buck type switching power supply converter works in a DCM mode, namely a discontinuous working mode, the output current is very small, when the first switching tube Q1 and the second switching tube Q2 are not conducted, no current flows out to the load, and the output voltage Vout is maintained only by the output capacitor Cout; when neither the first switching transistor Q1 nor the second switching transistor Q2 is turned on, the load current cannot be output externally by sampling.
In order to solve the problem, the present disclosure provides a new load current detection method for a switching power converter and a circuit thereof, which can effectively reduce the complexity of the load current detection circuit, and can detect an extremely small load current when neither the first switching tube Q1 nor the second switching tube Q2 is turned on, thereby improving the accuracy and precision of load current detection.
Fig. 4 is a block diagram illustrating a load current detection circuit in the switching power converter shown in fig. 3, fig. 5 is a circuit diagram illustrating a control unit in the load current detection circuit shown in fig. 4, and fig. 6 is a timing diagram illustrating operation of signals of the switching power converter shown in fig. 3 in a (DCM) discontinuous current mode.
Referring to fig. 4 to 6, an embodiment of the present disclosure provides a load current detection circuit 220 for a switching power converter 200, the load current detection circuit 220 obtains a node signal representing a switching control signal of the switching power converter 200 operating in an interrupted current mode by connecting a connection node SW of a first switching tube Q1 and a second switching tube Q2 of the switching power converter 200, and the load current detection circuit 220 includes: a first detection unit 221, a second detection unit 222, a comparator 223 and a control unit 224,
the first detecting unit 221 connects the connection node SW of the first switch Q1 and the second switch Q2, and generates a first voltage signal vc1 according to a first time period T1, in which the first switch Q1 and the second switch Q2 are alternately turned on (sum of time) in a single switching period T of the DCM mode of the switching power converter 200; the second detecting unit 222 connects the connection node SW of the first switch Q1 and the second switch Q2, and generates a second voltage signal Vc2 according to a second time period T2 during which the first switch Q1 and the second switch Q2 are both turned off in a single switching period T of the DCM mode of the switching power converter 200; the inverting input terminal of the comparator 223 is connected to the first detecting unit 221 to receive the first voltage signal Vc1, the non-inverting input terminal is connected to the second detecting unit 222 to receive the second voltage signal Vc2, and the output terminal provides the pulse signal V3; the control unit 224 is connected to the output end of the comparator 223, and is configured to count the number of pulses of the pulse signal V3 in a single switching period T, and output an average load current Iload according to the aforementioned count result, so as to greatly improve the accuracy of load state detection, reduce the dead zone range of current detection of a low load, and reduce the probability of false detection of a low load current.
It should be noted that, in the present embodiment, the schematic diagrams of fig. 3 to fig. 6 and the following description are illustrated by taking a Buck (Buck) type switching power converter as an example, but the present invention is not limited thereto, and in alternative embodiments, the load current detection circuit 220 may also be applied to a Boost (Boost) type or Buck-Boost (Buck-Boost) type switching power converter, which is not limited herein.
Referring to fig. 6, in the present embodiment, when the switching power converter 200 operates in the DCM mode, in a single switching period T, a period T1 (T1 = Ton + Toff) in which the first switching tube Q1 and the second switching tube Q2 are alternately turned on and a period T2 in which both the first switching tube Q1 and the second switching tube Q2 are turned off are included,
the first time period T1 is a sum of conducting times of the first switch Q1 and the second switch Q2 alternately conducting, and the second time period T2 is a time period when both the first switch Q1 and the second switch Q2 are off.
Referring to fig. 4, the aforementioned first detecting unit 221 includes a first branch and a first transistor M1, wherein the first branch includes a first switching element Sa connected in series between a power supply terminal (connected to a power supply voltage VDD, which is not described below) and ground, a first current source I21 and a first capacitor C21, a control terminal of the first switching element Sa is connected to a first control signal S1, the first control signal S1 is a switching control signal in a single switching period T when the switching power converter 200 operates in the DCM mode, and in the switching period T, as shown in fig. 6, a first time period T1 and a second time period T2 are included, the first switching element Sa is turned on in the first time period T1, and is turned off in the second time period T2. The first switching element Sa connects the first branch in a first time period T1 in a single switching period T, and outputs the aforementioned first voltage signal Vc1 through a connection node of a first current source I21 and a first capacitor C21; the first transistor M1 is connected in parallel to two ends of the first capacitor C21, and the control terminal is connected to the output terminal of the control unit 224.
In this embodiment, the second detecting unit 222 includes a second branch and a second transistor M2, wherein the second branch includes a second switch element Sb connected in series between the power supply terminal and the ground, a second current source I22 and a second capacitor C22, and a control terminal of the second switch element Sb is connected to a second control signal
The second switching element Sb is turned off during the first period T1 and turned on during the second period T2. The second switching element Sb connects the second branch in the second period T2 of the single switching period T and outputs the aforementioned second voltage signal Vc2 through the connection node of the second current source I22 and the second capacitor C22; the second transistor M2 is connected in parallel to both ends of the second capacitor C22, and has a control terminal connected to the output terminal of the comparator 223.
In this embodiment, the inverting input terminal of the comparator 223 is connected to the output terminal of the first detecting unit 221, the non-inverting input terminal is connected to the output terminal of the second detecting unit 222, the output terminal provides the pulse signal V3, the output terminal of the comparator 223 is connected to the control terminal of the second transistor M2, and the pulse signal V3 is further used for controlling the on/off of the second transistor M2 to regulate the charging and discharging processes of the second capacitor C22.
Referring to fig. 6, in the present embodiment, the node signal connected to the connection node SW of the first switch Q1 and the second switch Q2 may be an inductive current signal ILThe inductor current signal ILThe positive slope duration of (1) is the on-time Ton of the first switch Q1, the negative slope duration of the inductor current signal is the on-time Toff of the second switch Q2, the inductor current signal ILThe slope peak value Ipeak is a preset parameter with adjustable amplitude, and the inductive current signal ILThe time period maintained at 0A is the second time period T2 in which both the first switching tube Q1 and the second switching tube Q2 are turned off.
Referring to fig. 5, in the present embodiment, the aforementioned control unit 224 includes: a counting module 2241, a detecting module 2242 and a calculating module 2243, wherein the counting module 2241 is connected to the output end of the comparator 223, and is configured to count the number of pulses of the pulse signal V3 in a single switching period T and output a counting result; the detecting module 2242 is connected to a connection node SW of the first switch transistor Q1 and the second switch transistor Q2 to obtain an inductor current signal ILPeak value Ipeak of; the calculating module 2243 is connected to the counting module 2241 and the detecting module 2242, respectively, and is configured to calculate the counting result and the inductive current signal I according to the counting result and the inductive current signal ILCalculates and outputs the aforementioned average load current Iload.
In this embodiment, the reference currents provided by the first current source I21 in the first branch and the second current source I22 in the second branch when they are turned on are equal, and the specifications of the first capacitor C21 and the second capacitor C22 are the same.
When the switching power converter 200 operates in the DCM mode, the output capacitor Cout is chargedDuring the power-on period, the first switch tube Q1 is conducted, and the inductive current ILRise once the inductor current ILWhen the set Ipeak value (adjustable) is touched, the first switch tube Q1 is closed, and the second switch tube Q2 is opened, so that the inductive current I is inLWhen the current of the second switch tube Q2 drops to 0mA, the second switch tube Q2 is closed. Then the total charge delivered to the output during charging is:
Qc=1/2*Ipeak*(Ton+Toff) （1）
when the Buck-type switching power converter 200 operates in the DCM mode, neither the first switching transistor Q1 nor the second switching transistor Q2 can conduct for a long time, so that the load can only be discharged through the charge on the output capacitor Cout. During the discharging phase, the voltage on the output capacitor Cout will slowly decrease. Then the total charge consumed by the load during a single switching period T is:
Qdis=Qc=Iload*T （2）
where Iload is the average load current of the output, T is the single switching cycle time, and T = T1+ T2.
From the total charge transferred to the output capacitor Cout being equal to the total charge consumed by the output load current, in combination with equation (1) and equation (2), one can obtain
In the present embodiment, two identical charging currents I21= I22 and two identical capacitors C21= C22 are used. A control terminal of the first switching element Sa receives a first control signal S1, and a control terminal of the second switching element Sb receives a second control signal
And the high time T1 of the first control signal S1 is (Ton + Toff), the second control signal
The high level time T2 is (T-Ton + Toff), i.e. in the first switch tube Q1 or the second switch tubeDuring the on-time of Q2, the first switch element Sa is turned on, and the first branch is connected to charge the first capacitor C21 through the first current source I21, so as to generate the first voltage signal Vc1 at the connection node between the first current source I21 and the first capacitor C21. The charging time of the first capacitor C21 is Ton + Toff, then:
I21*(Ton+Toff)=C21*Vc1 （5）
namely, Vc1= I21 (Ton + Toff)/C21 (6)
In the above equations (5) and (6), I21 represents the magnitude of the reference current provided by the first current source I21, and C21 is the capacitance value of the first capacitor C21.
During the time T1, the first transistor M1 is kept off, the first capacitor C21 is charged, the first voltage signal Vc1 rises, and the second switching element Sb is turned off, and the second voltage signal Vc2 is kept at a low level.
When the time T1 reaches the time T2, the charging of the first capacitor C21 is finished, the first control signal S1 goes low, the first switching element Sa is turned off, the first voltage signal Vc1 is in the voltage holding state, and at this time, the second switching element Sb is turned on, the second transistor M2 is turned off, the second branch is connected and charges the second capacitor C22 through the second current source I22, the second voltage signal Vc2 rises, during this time, when the level of the second voltage signal Vc2 rises to be the same as that of the first voltage signal Vc1, the comparator 223 outputs a high-level pulse, and the high-level pulse instantaneously turns on the second transistor M2 to rapidly discharge the second capacitor C22, and after the second transistor M2 is turned off, the second capacitor C22 starts to be charged again, and so on, the comparator 223 outputs the pulse signal V3 of a plurality of continuous pulses in a single switching period T.
Since I21= I22, C21= C22, and Vc1= Vc2, the method is applicable to a large-scale industrial production
I21= C21= Vc1, I22 × T3= C22 × Vc2, then
T3=(Ton+Toff)=T1 （7）
That is, the interval of one pulse per output of the comparator 223 is T1.
From the foregoing, T = T1+ T2, T1= Ton + Toff, T2= n × T3, and equation (7) we can derive:
T2=n*(Ton+Toff) （8）
wherein, T2 is a time period during which both the first switching tube Q1 and the second switching tube Q2 are turned off in a single switching period T, and n is the number of counting pulses, i.e., how many T1 time periods exist in the T2 time.
Combining equation (4) and equation (8) yields:
in general, in practical applications, the number n of counting pulses is usually large, so the denominator in equation (9) can also be reduced to 2 × n.
Therefore, with the load current detection circuit 220 for the switching power converter 200 provided in the embodiment of the present disclosure, the magnitude of the average load current Iload can be obtained only by counting the output pulses of the comparator 223, so as to realize the detection of the extremely small load current, thereby improving the accuracy and precision of the load current detection.
In summary, the load current detection circuit 220 for the switching power converter 200 according to the embodiment of the present disclosure can obtain a node signal (inductor current signal) representing a switching control signal of the switching power converter 200 operating in the DCM mode by connecting the connection node SW of the switching transistor Q1 and the freewheeling transistor Q2 in the switching power converter 200, so that the node signal rising period and the node signal falling period are synchronized with the gate signal GP and the gate signal GN; therefore, the rising time period and the falling time period of the node signal (inductive current signal) are synchronous with the basic switch signal, so that the response speed of the system is improved, the complicated circuit design is avoided, the detection precision of the load current is improved, and the complexity and the design difficulty of the circuit are reduced.
Moreover, the load current detection circuit 220 generates a first voltage signal Vc1 by the first detection unit 221 according to a first time period T1 in which the first switch Q1 and the second switch Q2 are alternately turned on (sum of the turn-on time sums) in the switching period T; generating a second voltage signal Vc2 by the second detecting unit 222 according to a second time period T2 during which the first switching tube Q1 and the second switching tube Q2 are both turned off in the switching period T; and the pulse signal V3 is output by comparing the first voltage signal Vc1 and the second voltage signal Vc2, which are accessed by the input terminal of the comparator 223; the control unit 224 then counts the number of pulses of the aforementioned pulse signal V3 in a single switching period T and outputs an average load current Iload according to the counting result. Therefore, the complexity of the load current detection circuit can be effectively reduced, the unstable influence of failure of a traditional method for detecting the load current by sampling and averaging the inductive current by the detection circuit due to overlong switching period (namely overlong time for switching off the first switching tube Q1 and the second switching tube Q2) is avoided, and the extremely small load current is detected, so that the accuracy of load state detection is greatly improved, the dead zone range of low-load current detection is reduced, the probability of low-load current false detection is reduced, and the accuracy and precision of load current detection are improved.
Meanwhile, the light load detection current point of the load current detection circuit 220 in the embodiment of the present disclosure has better discreteness, and is only related to the peak value of the inductor current and the number of pulses of the pulse signal V3 during the turn-off period of the two transistors (the first switching transistor Q1 and the second switching transistor Q2) in the DC/DC switching power converter in a single switching period T, and the on-resistance change or the temperature change of the internal power transistor has little influence on the peak value.
It should be noted that in the description of the present disclosure, it is to be understood that the terms "upper", "lower", "inner", and the like, indicate orientation or positional relationship, are only for convenience in describing the present disclosure and simplifying the description, but do not indicate or imply that the referenced components or elements must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the present disclosure.
Further, in this document, the contained terms "include", "contain" or any other variation thereof are intended to cover a non-exclusive inclusion, so that a process, a method, an article or an apparatus including a series of elements includes not only those elements but also other elements not explicitly listed or inherent to such process, method, article or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
Finally, it should be noted that: it should be understood that the above examples are only for clearly illustrating the present disclosure, and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention as herein taught are within the scope of the present disclosure.
Claims (8)
1. A load current detection circuit for a switching power converter, the switching power converter including a first switching tube and a second switching tube operating according to a switching control signal, wherein the load current detection circuit comprises:
the first detection unit generates a first voltage signal according to a first time period when the first switch tube and the second switch tube are alternately conducted;
the second detection unit generates a second voltage signal according to a second time period when the first switching tube and the second switching tube are both cut off;
the input end of the comparator is respectively connected with the output ends of the first detection unit and the second detection unit, and provides a pulse signal according to the first voltage signal and the second voltage signal;
and the control unit is connected with the output end of the comparator and used for counting the number of pulses of the pulse signal in a single switching period and outputting the average load current according to the counting result.
2. The load current detection circuit of claim 1, wherein a single switching cycle includes a time period during which the first and second switching tubes are alternately turned on and a time period during which the first and second switching tubes are turned off,
the first time period is the sum of the superposition of the conduction time of the alternate conduction of the first switch tube and the second switch tube, and the second time period is the time period of the cut-off of the first switch tube and the second switch tube.
3. The load current detection circuit according to claim 2, wherein the first detection unit connects a connection node of the first switching tube and the second switching tube, and comprises:
a first branch including a first switching element, a first current source, and a first capacitor connected in series between a power supply terminal and ground, the first switching element communicating with the first branch for the first period in the single switching cycle and outputting the first voltage signal through a connection node of the first current source and the first capacitor;
and the first transistor is connected to two ends of the first capacitor in parallel, and the control end of the first transistor is connected with the output end of the control unit.
4. The load current detection circuit according to claim 3, wherein the second detection unit connects a connection node of the first switching tube and the second switching tube, and comprises:
a second branch including a second switching element, a second current source, and a second capacitor connected in series between a power supply terminal and ground, the second switching element communicating the second branch for the second period in the single switching cycle and outputting the second voltage signal through a connection node of the second current source and the second capacitor;
and the second transistor is connected in parallel with two ends of the second capacitor, and the control end of the second transistor is connected with the output end of the comparator.
5. The load current detection circuit according to claim 4, wherein an inverting input terminal of the comparator is connected to the output terminal of the first detection unit, a non-inverting input terminal is connected to the output terminal of the second detection unit, and an output terminal provides the pulse signal,
and the output end of the comparator is connected with the control end of the second transistor, and the pulse signal is also used for controlling the on-off of the second transistor so as to regulate and control the charging and discharging process of the second capacitor.
6. The load current detection circuit according to claim 5, wherein the control unit comprises:
the counting module is connected with the output end of the comparator and used for counting the number of pulses of the pulse signal in a single switching period and outputting a counting result;
the detection module is connected with a connection node of the first switch tube and the second switch tube to obtain a peak value of an inductive current signal;
and the calculation module is respectively connected with the counting module and the detection module, and calculates and outputs the average load current according to the counting result and the peak value of the inductive current signal.
7. The load current detection circuit according to claim 6, wherein a first current source in the first branch and a second current source in the second branch provide a reference current with equal magnitude when turned on, and the first capacitor and the second capacitor have the same size.
8. The load current detection circuit of claim 1, wherein the switching power converter has any one of a boost topology, a buck topology, and a buck/boost topology.
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| CN114935681A (en) * | 2022-05-17 | 2022-08-23 | 上海数明半导体有限公司 | Load current detection circuit, step-down converter, and load current detection method |
| CN118174554A (en) * | 2024-05-09 | 2024-06-11 | 江苏芯潭微电子有限公司 | Device for controlling DC-DC converter |
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