JP2017077076A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid stress on a switching element at activation by achieving smooth rising of an output voltage waveform.SOLUTION: A switching power supply device comprises a controller 20, 30 for controlling a converter main circuit 10 having a switching element. The controller 20, 30 has: first switching frequency setting means 21 that sets a switching frequency f1 in a soft start time period H1; second switching frequency setting means 22 that sets a switching frequency f2 at switching to a soft start time period H2; and frequency control means 23, 30 that generates a switching signal having the switching frequencies f1 and f2, and performs switching control from the soft start time period H1 to the soft start time period H2 to perform on/off-operation of the switching element.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a switching power supply device such as a current resonance type converter (which is also referred to as “LLC converter”) that performs a soft switching operation using a resonance circuit, and more particularly to control of the soft start.

  2. Description of the Related Art Conventionally, a current resonance type converter which is one of switching power supply devices has a switching element that is turned on / off by a switching signal having a switching frequency, as described in Patent Document 2, for example. A switching circuit that converts a direct current (hereinafter referred to as “DC”) input voltage into alternating current (hereinafter referred to as “AC”), and an AC voltage output from the switching circuit is input to resonate at a predetermined resonance frequency. A series resonance circuit, a primary winding for inputting a resonance signal output from the resonance circuit, and a transformer having a secondary winding (hereinafter referred to as “transformer”), and an output from the secondary winding. A rectifying circuit for rectifying the AC voltage to be output; and an output capacitor for smoothing the rectified voltage and outputting a DC output voltage. That.

  In the control of such a current resonance type converter, the output voltage of the output capacitor is controlled by controlling the switching frequency of a switching signal for turning on / off the switching element. The switching frequency is designed to operate at a frequency lower than the resonance frequency of the resonance circuit, for example. When the switching frequency is increased (that is, closer to the resonance frequency), the output voltage is decreased, and when the switching frequency is decreased. (I.e., away from the resonant frequency), the output voltage increases. In this type of current resonance type converter, the switching loss is reduced by the soft switching technology that uses the resonance phenomenon by the resonance circuit at the time of switching of the switching element and performs switching in a state where the voltage or current becomes zero. It is possible to increase the efficiency of the power supply and reduce noise. In soft switching, switching performed in a state where the voltage is zero is generally referred to as zero voltage switching (hereinafter referred to as “ZVS”), and switching performed in a state where the current is zero is referred to as zero current switching (hereinafter referred to as “ZCS”). ing.

  The current resonance type converter performs frequency control of a switching signal for controlling on / off operation of the switching element, and the switching frequency is uniquely determined by the output voltage and the output current. For this reason, when the output voltage starts from 0 V, the switching frequency is gradually decreased from a high frequency (that is, soft start) to prevent overcurrent due to the charge current of the output capacitor. At this time, since a current for charging the output capacitor flows through the switching element that performs switching, ZVS can be performed using this current.

  As a technique related to the current resonance converter as described above, Patent Document 1 describes a switching regulator that boosts an input voltage by ON / OFF operation of a switching element. In this switching regulator, a switching signal for turning on / off the switching element is generated by pulse width modulation (hereinafter referred to as “PWM”) control so as to reduce an error between the output voltage and the target voltage. It has a soft start function that gradually increases the duty of the switching signal until the output voltage reaches the target voltage after the regulator starts up, and reduces the duty of the switching signal until the output voltage reaches the target voltage. Overshoot is suppressed.

  However, in the control circuit for generating the switching signal based on the output voltage, a delay in signal processing occurs, and even if the output voltage reaches the target voltage, the duty of the switching signal does not become zero, but exceeds the output voltage. Shooting may occur. Therefore, in the switching regulator of Patent Document 1, overshooting is suppressed by increasing the output voltage in two stages from when it is activated until the output voltage reaches the target voltage.

JP 2008-131848 A JP 2012-29436 A

  FIG. 2 is a schematic diagram showing a startup waveform in a conventional general current resonance converter including Patent Document 2, in which the horizontal axis represents time T and the vertical axis represents the output voltage Vout (V). The start-up waveform shown in FIG. 2 indicates that when the output voltage Vout is 0V at the start of operation (at start-up), the soft start period H elapses, and the soft start is completed at the soft start completion time Tend, the output voltage Vout becomes the target rated output. The voltage VoT has been reached.

  The conventional current resonance type converter controls the output voltage Vout by changing the switching frequency. However, even when the switching frequency is constant, the input / output conditions (particularly load conditions) of the current resonance type converter are different. Changes the output voltage Vout. Therefore, since the necessary switching frequency is unknown in advance, it is difficult to produce a smooth rising waveform of the output voltage Vout in the soft start period H of the current resonance type converter as shown in FIG. When the rising waveform of the output voltage Vout is not smooth, ZVS using the current for charging the output capacitor is not performed, which causes problems such as stress on the switching element and deterioration of the switching element.

  In order to solve such a problem, it is conceivable to apply the technique of Patent Document 1.

  However, the switching regulator of Patent Document 1 controls the output voltage Vout by PWM control, whereas the current resonance type converter in particular by pulse frequency modulation (hereinafter referred to as “PFM”) control different from PWM control. The output voltage Vout is controlled, and in the current resonance type converter, the output voltage Vout varies depending on the load condition. Therefore, there is a problem that it is considerably difficult to apply the technique of Patent Document 1 as it is to a current resonance converter to solve the above-described problem.

  The switching power supply device according to the present invention includes a switching circuit having a switching element that is turned on / off by a switching signal, a rectifier circuit that rectifies an output voltage of the switching circuit, and the switching signal that turns the switching element on / off. A control unit that generates and controls a soft switching operation with respect to the switching element.

  The control unit includes a first switching frequency setting means for setting a first switching frequency in a first soft start period for starting the switching circuit, and after the first soft start period has elapsed, When switching to the second soft start period in which the output voltage of the rectifier circuit is increased, a reference voltage is obtained based on the output voltage of the rectifier circuit at the end of the first soft start period, and the output voltage of the rectifier circuit A second switching frequency setting means for setting a second switching frequency by comparing and calculating the reference voltage; generating the switching signal having the first switching frequency and the second switching frequency; Switch control from the first soft start period to the second soft start period , And having a frequency control means for turning on / off operation of the switching element.

  The switching power supply device is, for example, a current resonance type converter. A resonance circuit that resonates at a predetermined resonance frequency with an output voltage of the switching circuit with respect to the switching power supply device, and outputs an output voltage of the resonance circuit to a predetermined value. A transformer for converting to a voltage level and supplying it to the rectifier circuit is added.

  According to the switching power supply device of the present invention, it is possible to avoid stress of the switching element at the start-up by realizing a smooth rise of the output voltage waveform in the rectifier circuit. Furthermore, since the rising waveform in the output voltage of the rectifier circuit can be adjusted, it is possible to avoid load stress by preventing a sudden voltage change.

FIG. 1 is a schematic functional block diagram showing a switching power supply apparatus according to Embodiment 1 of the present invention. FIG. 2 is a startup waveform diagram of a conventional current resonance type converter. FIG. 3 is a schematic circuit diagram showing a configuration example of the converter main circuit of FIG. FIG. 4 is a startup waveform diagram of the switching power supply device of FIG. FIG. 5 is a flowchart showing processing at the start-up in the control circuit in FIG. FIG. 6 is a startup waveform diagram showing the effect of the first embodiment. FIG. 7 is a startup waveform diagram showing the effect of the first embodiment. FIG. 8 is a schematic circuit diagram showing a switching power supply apparatus according to Embodiment 2 of the present invention. FIG. 9 is a schematic functional block diagram showing a switching power supply apparatus according to Embodiment 3 of the present invention. FIG. 10 is a flowchart showing processing at the time of startup in the control circuit in FIG. FIG. 11 is a schematic circuit diagram showing a switching power supply apparatus according to Embodiment 4 of the present invention.

  Modes for carrying out the present invention will become apparent from the following description of the preferred embodiments when read in light of the accompanying drawings. However, the drawings are only for explanation and do not limit the scope of the present invention.

(Configuration of Example 1)
FIG. 1 is a schematic functional block diagram showing a switching power supply apparatus according to Embodiment 1 of the present invention.

  This switching power supply device is, for example, a current resonance type converter, and has an input terminal 1 for inputting a DC input voltage Vin supplied from a DC power source such as a solar battery. An output terminal 17 that outputs a DC output voltage Vout is connected to the input terminal 1 via the converter main circuit 10.

  The converter main circuit 10 includes a plurality of (for example, four) switching elements (for example, field effect transistors, hereinafter referred to as “FETs”) that are turned on / off by a plurality of (for example, four) switching signals S31 to S34 having a switching frequency fs. A switching circuit having a resonance frequency fr composed of an inductor and a capacitor, a transformer that insulates between the input and output terminals, a rectifier circuit that rectifies the output voltage of the transformer to a DC voltage, and the like And is constituted by.

  In this converter main circuit 10, a DC input voltage Vin is input from the input terminal 1, and a soft switching operation is performed on the FET that is turned on / off by the switching signals S31 to S34 using the resonance operation of the resonance circuit. The DC input voltage Vin is converted to AC, the AC voltage is transmitted through a transformer, and the AC voltage is converted to a DC output voltage Vout by a rectifier circuit or the like and output from the output terminal 17. Yes.

  A controller for PFM controlling the converter main circuit 10 is connected to the output terminal 17 side. The control unit includes a control circuit 20 and a driver 30. The control circuit 20 and the driver 30 are circuits that generate switching signals S31 to S34 based on the DC output voltage Vout to turn on / off the FET in the converter main circuit 10.

  The control circuit 20 includes a first switching frequency setting means 21 that operates when the output voltage rises (that is, at the time of startup), a second switching frequency setting means 22 that operates at the time of startup and thereafter, and a first switching frequency setting means 22 thereof. And a frequency switching control unit 23 connected to the output side of the second switching frequency setting means 21 and 22.

  The first switching frequency setting means 21 includes a switching frequency setting unit 21a that sets the first switching frequency f1 in the first soft start period H1 at the time of startup, and a timer 21b that measures the first soft start period H1. ,have. The switching frequency setting unit 21a sets the first switching frequency f1 by a preset switching frequency value (for example, 300 kHz), and controls the frequency switching of the passage of the first soft start period H1 measured by the timer 21b. The function of notifying the unit 23 is provided.

  The second switching frequency setting means 22 sets the second soft start period H2 following the first soft start period H1 and the second switching frequency f2 at the subsequent steady state, and sets the first reference voltage. Unit 22a, second reference voltage generation unit 22b, and frequency calculation unit 22c. The first reference voltage setting unit 22a sets the first reference voltage Vr1 based on the output voltage Vout at the end of the first soft start period H1, and the second reference voltage generation unit 22b is connected to the output side. Is connected. The second reference voltage generator 22b generates a second reference voltage Vr2 that is gradually increased from the first reference voltage Vr1 to a preset final target value. A calculation unit 22c is connected. The frequency calculation unit 22c sets the second switching frequency f2 by comparing the output voltage Vout and the second reference voltage Vr2, and the frequency switching control unit 23 is connected to the output side. .

  The frequency switching control unit 23 generates a control pulse S23 of the switching signals S31 to S34 having the first and second switching frequencies f1 and f2, and changes from the first soft start period H1 to the second soft start period H2. Switching is controlled, and a driver 30 is connected to the output side. The driver 30 drives the control pulse S23 given from the frequency switching control unit 23, and outputs switching signals S31 to S34 for turning on / off the switching elements in the converter main circuit 10. The frequency switching control unit 23 and the driver 30 constitute frequency control means.

  The control circuit 20 is a processor such as a digital signal processor (DSP) which is a microprocessor specialized in digital signal processing, an actual circuit of a digital circuit, or a frequency control integrated circuit (hereinafter referred to as “frequency control IC”). The actual circuit of the analog circuit.

  When the control circuit 20 is configured by a processor, for example, the following may be performed.

  The processor is controlled by, for example, a program memory storing a control program at startup and steady state, a central processing unit (hereinafter referred to as “CPU”) that performs calculation and control processing according to the control program, and program processing of the CPU. An input unit, an output unit, and the like. Therefore, the functions of the first and second switching frequency setting means 21 and 22 can be executed by the program processing of the input unit and the CPU, and the function of the frequency switching control unit 23 can be executed by the program processing and the output unit of the CPU. That's fine.

FIG. 3 is a schematic circuit diagram showing a configuration example of the converter main circuit 10 of FIG.
The converter main circuit 10 includes a smoothing input capacitor 11 and a full bridge type switching circuit 12 connected to a positive input terminal 1a constituting the input terminal 1 and a negative input terminal 1b on the ground GND side. Yes. The full bridge type switching circuit 12 has four FETs 12-1 to 12-4 as switching elements, and an FET 12-1, a node N1, and an FET 12-2 are connected in series between the input terminal 1a and the input terminal 1b. The FET 12-3, the node N2, and the FET 12-4 are connected in series. A series resonant circuit 13 and a transformer 14 are connected to the nodes N1 and N2.

  The FETs 12-1 and 12-2 are complementarily turned on / off by the switching signals S31 and S32. Further, the FETs 12-3 and 12-4 are complementarily turned on / off by the switching signals S33 and S34. Parasitic capacitances 12-1a, 12-2a, 12-3a, 12-4a, etc. exist between the drains and sources of the FETs 12-1, 12-2, 12-3, 12-4, respectively.

  For example, when the FETs 12-1 and 12-4 are turned off and the FETs 12-2 and 12-3 are turned on by the switching signals S 31 to S 34, the DC input current input from the input terminal 1 a is the on-state FET 12. −3 → node N2 → the primary side of the resonance circuit 13 and the transformer 14 → the node N1 → the FET 12-2 in the on state → the input terminal 1b.

  The resonance circuit 13 connected to the node N2 includes a resonance capacitor 13a having a capacitance Cr and a resonance inductor 13b having an inductance Lr, which are connected in series. The resonance circuit 13 has a specific resonance frequency fr determined by the capacitance Cr of the resonance capacitor 13a and the inductance Lr of the resonance inductor 13b. For example, when the resonance current Ir flows through the capacitor 13a and the inductor 13b, the capacitor 13a. And a resonance voltage is generated between the both end electrodes of the inductor 13b. A transformer 14 is connected to the electrode side of one end of the inductor 13b.

  The transformer 14 includes a primary winding 14a connected between an electrode at one end of the inductor 13b and the node N1, and a secondary winding 14b insulated from the primary winding 14a. Yes. The turn ratio N between the primary winding 14a and the secondary winding 14b is N1: N2. In the primary winding 14a, an inductor 14c, which is an exciting inductance Lm of the transformer 14, exists in parallel with the primary winding 14a. For example, when the resonance current Ir flows through the capacitor 13a and the inductor 13b, the resonance current Ir is divided into an excitation current Im flowing through the inductor 14c and a primary current It flowing through the primary winding 14a (that is, Ir = Im + It). At this time, the exciting voltage generated between the both end electrodes of the inductor 14c is equal to the primary voltage generated between the both end electrodes of the primary winding 14a. When the primary current It flows through the primary winding 14a, a secondary voltage is generated between both end electrodes of the secondary winding 14b. A rectifier circuit 15 is connected to both end electrodes of the secondary winding 14b.

  The rectifier circuit 15 is a circuit for full-wave rectification of the secondary voltage generated in the secondary winding 14b, and is constituted by, for example, a diode bridge circuit including four diodes 15-1 to 15-4. The output side of the rectifier circuit 15 is connected via a smoothing output capacitor 16 to a positive output terminal 17a constituting the output terminal 17 and a negative output terminal 17b on the ground GND side. The output capacitor 16 has a capacitance Co. When a DC output current is output from the output terminal 17a, a DC output voltage Vout appears between the output terminals 17a and 17b.

(Operation of Example 1)
The startup operation (I) and the steady operation (II) of the switching power supply according to the first embodiment will be described.

(I) Operation at Startup FIG. 4 is a waveform diagram at startup showing the output voltage Vout of the switching power supply device of FIG. In FIG. 4, the horizontal axis represents time T, the vertical axis represents the output voltage Vout, H1 represents the first soft start period, H2 represents the second soft start period, and Tend represents the soft start completion time. At the soft start completion time Tend, after the output voltage Vout reaches the target rated output voltage VoT, the operation shifts to a constant voltage control operation in a steady state.

  FIG. 5 is a flowchart showing processing at the time of startup in the control circuit 20 in FIG.

  In FIG. 5, when the control circuit 20 in FIG. 1 starts processing at startup, in step ST1, the control circuit 20 determines whether or not the converter main circuit 10 is started, and determines that it is not started. When it is determined (No), the process is terminated, and when it is determined that the process is activated (Yes), the process proceeds to step ST2 of the first soft start process. The switching power supply device according to the first embodiment is a current resonance type converter, and the current resonance type converter has a strong dependency on the output voltage Vout depending on the load condition. Start fs at a fixed frequency.

  Therefore, in step ST <b> 2, the switching frequency setting unit 21 a in the first switching frequency setting unit 21 sets the first switching frequency f <b> 1 (for example, 300 kHz), which is a fixed frequency, and supplies it to the frequency switching control unit 23. The frequency switching control unit 23 generates the control pulse S23 by PFM control based on the first switching frequency f1. The generated control pulse S23 is driven by the driver 30 to generate switching signals S31 to S34, and the FETs 12-1 to 12-4 in the switching circuit 12 shown in FIG. 3 are turned on / off.

  For example, when the FETs 12-1 and 12-4 are turned off and the FETs 12-2 and 12-3 are turned on by the switching signals S31 to S34, they are turned on by the DC input current input to the input terminal 1a in FIG. A current flows between the drain and source of the FET 12-3 in the state. When this current flows to the node N2, the resonance current Ir flows in the resonance circuit 13. The resonance current Ir is shunted to the inductor 14c as an exciting current Im and is shunted to the primary winding 14a of the transformer 14 as a primary current It. The divided excitation current Im and the primary current It merge and flow to the node N1 in the switching circuit 12. The current flowing to the node N1 flows out to the input terminal 1b through the drain and source of the FET 12-2 in the on state.

  When a primary current flows through the primary winding 14a of the transformer 14, a primary voltage is generated between both end electrodes of the primary winding 14a. Then, a secondary current (= It * N = It * (N1 / N2)) is induced in the secondary winding 14b of the transformer 14, and a secondary voltage (= primary) is generated between the electrodes at both ends of the secondary winding 14b. Voltage * (1 / N) = primary voltage * (N2 / N1)). The secondary current flowing through the secondary winding 14b is full-wave rectified by the rectifier circuit 15, the full-wave rectified current is smoothed by the output capacitor 16, and the smoothed DC output voltage Vout is output to the output terminals 17a and 17b. Is output from. As shown in the first soft start period H1 in FIG. 4, the output voltage Vout rises from time 0 at the time of activation. From time 0, the timer 21b measures the elapsed time.

  When the timer 21b measures the end time of the first soft start period H1 in FIG. 4, the timer 21b notifies the frequency switching control unit 23 through the switching frequency setting unit 21a, and proceeds to step ST3 in FIG. The feature of the first embodiment is that, in the switching to the second soft start period H2 in which the output voltage Vout is increased after the end of the first soft start period H1, smooth switching of the state is performed by measuring the output voltage value in advance. It can be realized.

  Therefore, in step ST3 in FIG. 5, the second switching frequency setting means 22 in FIG. 1 operates as follows in order to appropriately set the reference voltage at the start of the second soft start period H2. . That is, in the second switching frequency setting means 22, the first reference voltage setting unit 22a detects the output voltage Vout at the end of the first soft start period H1, and the first reference voltage Vr1 is detected from the output voltage detection value. Is calculated and set, and is supplied to the second reference voltage generator 22b. The second reference voltage generation unit 22b generates a second reference voltage Vr2 that is gradually increased to a preset final target value, supplies the second reference voltage Vr2 to the frequency calculation unit 22c, and performs the second soft start process in FIG. It progresses to step ST4 to perform.

  In step ST4, the frequency calculation unit 22c compares the output voltage Vout and the second reference voltage Vr2 to determine the second switching frequency f2 (= f (Vout, Vr2)), and determines the determined second The switching frequency f2 is given to the frequency switching control unit 23. The frequency switching control unit 23 generates the control pulse S23 by PFM control based on the second switching frequency f2. The generated control pulse S23 is driven by the driver 30 to generate switching signals S31 to S34, and the FETs 12-1 to 12-4 in the switching circuit 12 shown in FIG. 3 are turned on / off. Thereby, the first soft start period H1 smoothly transitions to the second soft start period H2, the output voltage Vout gradually increases, and at the soft start completion time Tend at the end of the second soft start period H2, The target rated output voltage VoT is reached. Thereby, the second soft start process ends. Thereafter, the following steady state operation is performed.

(II) Regular operation When the output voltage Vout fluctuates with respect to the rated output voltage VoT due to load fluctuation or the like, the second switching frequency f2 is controlled by the second switching frequency setting means 22 so as to suppress the fluctuation. Is set and given to the frequency switching control unit 23.

  The frequency switching control unit 23 generates the control pulse S23 by PFM control based on the second switching frequency f2. The generated control pulse S23 is driven by the driver 30 to generate switching signals S31 to S34, and the FETs 12-1 to 12-4 in the switching circuit 12 shown in FIG. 3 are turned on / off. Thereby, fluctuations in the output voltage Vout are suppressed, and constant voltage control is performed so that the rated output voltage VoT is obtained.

(Effect of Example 1)
The switching power supply device according to the first embodiment has the following effects (1) to (3).

  (1) Since the second switching frequency f2 is set based on the output voltage Vout at the end of the first soft start period H1, the transition to the second soft start period H2 can be made smoothly, and the smooth output voltage Vout Can be realized. Therefore, the stress of the switching power supply device at startup can be avoided.

  (2) FIG. 6 is a startup waveform diagram of the output voltage Vout showing the effect of the first embodiment. In FIG. 6, the horizontal axis represents time T, the vertical axis represents the output voltage Vout (V), Tend represents the soft start completion time, the solid line waveform Vout1 represents the output voltage at light load (small output current), and the solid line waveform Vout2. Is the output voltage under heavy load (large output current).

  As shown in FIG. 6, since the difference in load conditions is adjusted by the second switching frequency f2 that is the operation amount, all load conditions can be handled.

  (3) FIG. 7 is a startup waveform diagram of the output voltage Vout showing the effect of the first embodiment. In FIG. 7, the horizontal axis represents time T, the vertical axis represents the output voltage Vout (V), Tend1 represents the soft start completion time of the output voltage Vout3 whose solid line waveform rises quickly, and Tend2 represents the output voltage Vout4 whose solid line waveform rises slowly. This is the soft start completion time.

  As shown in FIG. 7, based on the output voltages Vout, Vout3, Vout4 detected at the end of the first soft start period H1, the rising times of the output voltages Vout, Vout3, Vout4 in the subsequent second soft start period H2, Alternatively, the rising slope can be adjusted (set). Therefore, by preventing a sudden change in the output voltage Vout and the output current, load stress at startup can be reduced or avoided.

(Configuration of Example 2)
FIG. 8 is a schematic circuit diagram illustrating a configuration example of the switching power supply device according to the second embodiment of the present invention. Elements common to those in FIG. 1 illustrating the first embodiment are denoted by common reference numerals. .

  The switching power supply apparatus according to the second embodiment is, for example, a current resonance type converter, and the control circuit 20 in FIG. 1 is configured by an analog circuit using a frequency control IC or the like.

  In the control circuit 20 of the second embodiment, the first reference voltage setting unit 22a in FIG. 1 uses the voltage dividing resistors 41 and 42 for detecting the output voltage Vout and the detected voltage of the voltage dividing resistors 41 and 42. And a buffer 43 for waveform shaping. A changeover switch 44 is connected to the output side of the buffer 43.

  The second reference voltage generator 22b includes a voltage source 45 for setting the second reference voltage Vr2, a variable current source 46 connected to the output side of the voltage source 45, and a buffer 43 according to an output signal of the timer 21b. Alternatively, the changeover switch 44 for switching the output voltage of the variable current source 46, the capacitor 47 for storing the output charge of the changeover switch 44, and the charge stored in the capacitor 47 or the zero potential of the ground GND are switched by the output signal of the timer 21b. And a changeover switch 48.

  The frequency calculation unit 22 c and the frequency switching control unit 23 perform voltage division resistors 51 and 52 for detecting the output voltage Vout, and a comparison calculation between the detection voltage of the voltage division resistors 51 and 52 and the output voltage of the changeover switch 48. An operational amplifier (hereinafter referred to as “op-amp”) 53 to be performed, a diode 54 for rectifying the output voltage of the operational amplifier 53, a voltage source 55 for setting the first switching frequency f1 constituting the switching frequency setting unit 21a, A diode 56 that rectifies the output voltage of the voltage source 55, a sawtooth generator 57, a comparator 58 that compares the output voltages of the diodes 54 and 56 with the output voltage of the sawtooth generator 57 and outputs a control pulse S23; , Is configured. The voltage dividing resistors 41 and 42 and the voltage dividing resistors 51 and 52 have the same resistance value.

(Operation of Example 2)
In the first soft start period H1 in FIG. 4, the changeover switch 44 is switched to the buffer 43 side and the changeover switch 48 is switched to the ground GND side by the output signal of the timer 21b. The output voltage of the voltage source 55 is rectified by the diode 56, and the output voltage of the diode 56 and the output voltage of the sawtooth generator 57 are compared by the comparator 58. Therefore, the control pulse S23 having the first switching frequency f1 is output from the comparator 58, and this control pulse S23 is driven by the driver 30 to generate the switching signals S31 to S34. By the switching signals S31 to S34, the FETs 12-1 to 12-4 in the converter main circuit 10 are turned on / off, and the output voltage Vout of the output terminals 17a and 17b rises from 0V.

  When the first soft start period H1 ends, the changeover switch 44 is switched to the variable current source 46 side and the changeover switch 48 is switched to the capacitor 47 side by the output signal of the timer 21b, and the second soft start period H2 Migrate to

  In the second soft start period H <b> 2 in FIG. 4, the first reference voltage Vr <b> 1 accumulated in the capacitor 47 is supplied to the operational amplifier 53 via the changeover switch 48. Next, the output voltage of the voltage source 45 is added to the first reference voltage Vr1 stored in the capacitor 47 via the variable current source 46 and the changeover switch 44, thereby generating a second reference voltage Vr2. In the operational amplifier 53, the second reference voltage Vr 2 and the detection voltages of the voltage dividing resistors 51 and 52 are compared and the calculation result is supplied to the comparator 58 via the diode 54. Therefore, the control pulse S23 having the second switching frequency f2 is output from the comparator 58, and this control pulse S23 is driven by the driver 30 to generate the switching signals S31 to S34. By the switching signals S31 to S34, the FETs 12-1 to 12-4 in the converter main circuit 10 are turned on / off, and the output voltage Vout of the output terminals 17a and 17b rises smoothly toward the rated output voltage VoT. To go.

  After the soft start completion time Tend when the second soft start period H2 in FIG. 4 ends, the following constant voltage control is performed.

  That is, when the output voltage Vout varies due to a load variation or the like, the output voltage Vout is detected by the voltage dividing resistors 51 and 52, and this detected voltage is supplied to the operational amplifier 53. Further, the rated output voltage VoT is supplied to the operational amplifier 53 via the voltage source 45, the variable current source 46, the changeover switch 44, the capacitor 47, and the changeover switch 48. In the operational amplifier 53, an error voltage is calculated such that an error between the rated output voltage VoT and the detection voltage is reduced, and this error voltage is supplied to the comparator 58 via the diode 54. For this reason, the control pulse S23 having the second switching frequency f2 that reduces the error is output from the comparator 58, and the control pulse S23 is driven by the driver 30 to generate the switching signals S31 to S34. By the switching signals S31 to S34, the FETs 12-1 to 12-4 in the converter main circuit 10 are turned on / off, and the varying output voltage Vout is maintained at the rated output voltage VoT.

(Effect of Example 2)
The switching power supply device according to the second embodiment has the same effects as the first embodiment.

(Configuration of Example 3)
FIG. 9 is a schematic functional block diagram showing a switching power supply apparatus according to Embodiment 3 of the present invention. Elements common to those in FIG. 1 showing Embodiment 1 are denoted by common reference numerals.

  The switching power supply apparatus according to the third embodiment is, for example, a current resonance type converter, and includes a control circuit 20A having a configuration different from that of the control circuit 20 according to the first embodiment. The control circuit 20A includes a first switching frequency setting unit 21A having a configuration different from that of the first switching frequency setting unit 21 of the first embodiment, a second switching frequency setting unit 22 and a frequency switching control similar to those of the first embodiment. Part 23. The first switching frequency setting means 21A includes a switching frequency setting unit 21a similar to that of the first embodiment, a voltage gradient detection unit 21c newly added to the first embodiment, and a timer 21b of the first embodiment. 1 soft start completion detection unit 21d.

The voltage gradient detector 21c detects a voltage change rate (dv / dt) per unit time in the output voltage Vout, that is, a rising gradient (dv / dt) of the output voltage Vout. 1 soft start completion detection unit 21d is connected. The first soft start completion detection unit 21d includes the timer 21b of the first embodiment, and the first soft start period H1 ends when the rising slope (dv / dt) of the output voltage Vout falls below a predetermined value. The first soft start completion is detected, and the detection result is notified to the frequency switching control unit 23 via the switching frequency setting unit 21a.
Other configurations of the third embodiment are the same as those of the first embodiment.

(Operation of Example 3)
FIG. 10 is a flowchart showing processing at the time of activation in the control circuit 20A in FIG. 9. Elements common to the elements in FIG. 5 showing the first embodiment are denoted by common reference numerals.

  In the process at the time of startup of the third embodiment, instead of step ST2 indicating the first soft start process of the first embodiment, step ST2A indicating the first soft start process having a different process content is provided. Yes. The contents of steps ST1, ST3, ST4 showing other processes are the same as those in the first embodiment.

  In FIG. 10, when the control circuit 20A in FIG. 9 starts processing at startup, in step ST1, the control circuit 20A determines whether or not the converter main circuit 10 is started, as in the first embodiment. If it is determined that it is not activated (No), the process is terminated. If it is determined that it is activated (Yes), the process proceeds to step ST2A of the first soft start process.

  In step ST <b> 2 </ b> A, the switching frequency setting unit 21 a in the first switching frequency setting unit 21 </ b> A sets a first switching frequency f <b> 1 (for example, 300 kHz), which is a fixed frequency, and supplies it to the frequency switching control unit 23. The frequency switching control unit 23 generates the control pulse S23 by PFM control based on the first switching frequency f1. The generated control pulse S23 is driven by the driver 30 to generate switching signals S31 to S34, the FETs 12-1 to 12-4 in the switching circuit 12 shown in FIG. 3 are turned on / off, and the output voltage Vout is Output from the output terminal 17. As shown in the first soft start period H1 in FIG. 4, the output voltage Vout rises from time 0 at the time of activation.

  The output slope detection unit 21c detects the rising slope (dv / dt) of the output voltage Vout from time 0, and gives the detection result to the first soft start completion detection unit 21d. The first soft start completion detection unit 21d detects the first soft start completion when the first soft start period H1 ends when the rising slope (dv / dt) is equal to or less than a predetermined value. Then, the frequency switching control unit 23 is notified via the switching frequency setting unit 21a, and the process proceeds to step ST3.

  In step ST3, as in the first embodiment, the first reference voltage setting unit 22a in the second switching frequency setting means 22 detects the output voltage Vout at the end of the first soft start period H1, and this detected value. Is used to calculate and set the first reference voltage Vr1 and supply it to the second reference voltage generator 22b. The second reference voltage generation unit 22b generates a second reference voltage Vr2 that is gradually increased to a preset final target value, supplies the second reference voltage Vr2 to the frequency calculation unit 22c, and goes to step ST4 where a second soft start process is performed. move on.

  In step ST4, as in the first embodiment, the frequency calculation unit 22c compares and calculates the output voltage Vout and the second reference voltage Vr2, and determines the second switching frequency f2 (= f (Vout, Vr2)). Then, the determined second switching frequency f <b> 2 is given to the frequency switching control unit 23. The frequency switching control unit 23 generates the control pulse S23 by PFM control based on the second switching frequency f2. The generated control pulse S23 is driven by the driver 30 to generate switching signals S31 to S34, and the FETs 12-1 to 12-4 in the switching circuit 12 shown in FIG. 3 are turned on / off. Thereby, the first soft start period H1 smoothly transitions to the second soft start period H2, the output voltage Vout gradually increases, and at the soft start completion time Tend at the end of the second soft start period H2, The target rated output voltage VoT is reached. Thereby, the second soft start process ends.

  Thereafter, as in the first embodiment, the second switching frequency setting means 22 and the frequency switching control unit 23 perform constant voltage control during steady state.

(Effect of Example 3)
According to the switching power supply device of the third embodiment, there are substantially the same effects as the first embodiment. In particular, in the third embodiment, when the rising slope (dv / dt) of the output voltage Vout becomes equal to or lower than a predetermined value in the first soft start period H1, the transition to the second soft start period H2 is performed, so that smoother In the second soft start period H2, the output voltage Vout rises more smoothly.

(Configuration of Example 4)
FIG. 11 is a schematic circuit diagram showing a configuration example of the switching power supply device according to the fourth embodiment of the present invention, and is common to the elements common to those in FIG. 8 of the second embodiment and FIG. 9 of the third embodiment. The code | symbol is attached | subjected.

  The switching power supply device according to the fourth embodiment is, for example, a current resonance type converter, and the control circuit 20A in FIG. 9 is configured by an analog circuit using a frequency control IC or the like.

In the control circuit 20A of the fourth embodiment, the voltage gradient detecting unit 21c in FIG. 9 includes a differentiation circuit including an input capacitor 61 and an inverting amplifier 62 connected to the output side of the charge storage capacitor 47, and a threshold setting. And a Schmitt trigger circuit 64 for noise removal connected to the differentiating circuit and the voltage source 63. Further, the first soft start completion detection unit 21d in FIG. 9 includes a timer 21b that measures the output pulse of the Schmitt trigger circuit 64 and detects the first soft start completion.
The other configuration of the fourth embodiment is the same as that of the switching power supply device of FIG.

(Operation of Example 4)
In the first soft start period H1 in FIG. 4, the changeover switch 44 is switched to the buffer 43 side and the changeover switch 48 is switched to the ground GND side by the output signal of the timer 21b. The output voltage of the voltage source 55 is rectified by the diode 56, and the output voltage of the diode 56 and the output voltage of the sawtooth generator 57 are compared by the comparator 58. Therefore, the control pulse S23 having the first switching frequency f1 is output from the comparator 58, and this control pulse S23 is driven by the driver 30 to generate the switching signals S31 to S34. By the switching signals S31 to S34, the FETs 12-1 to 12-4 in the converter main circuit 10 are turned on / off, and the output voltage Vout of the output terminals 17a and 17b rises from 0V.

  The differentiation circuit including the input capacitor 61 and the inverting amplifier 62 detects the rising slope (dv / dt) of the output voltage Vout from time 0. This detection result is converted into a pulse by the Schmitt trigger circuit 64 and given to the timer 21b. The timer 21b measures the output pulse of the Schmitt trigger circuit 64, and detects the completion of the first soft start when the first soft start period H1 ends when the rising slope (dv / dt) falls below a predetermined value. As a result, the first soft start period H1 is ended, and the changeover switch 44 is switched to the variable current source 46 side and the changeover switch 48 is switched to the capacitor 47 side by the output signal of the timer 21b. Transition to the start period H2.

  As in the second embodiment, in the second soft start period H2 in FIG. 4, the first reference voltage Vr1 stored in the capacitor 47 is supplied to the operational amplifier 53 via the changeover switch 48. Next, the output voltage of the voltage source 45 is added to the first reference voltage Vr1 stored in the capacitor 47 via the variable current source 46 and the changeover switch 44, thereby generating a second reference voltage Vr2. In the operational amplifier 53, the second reference voltage Vr 2 and the detection voltages of the voltage dividing resistors 51 and 52 are compared and the calculation result is supplied to the comparator 58 via the diode 54. Therefore, the control pulse S23 having the second switching frequency f2 is output from the comparator 58, and this control pulse S23 is driven by the driver 30 to generate the switching signals S31 to S34. By the switching signals S31 to S34, the FETs 12-1 to 12-4 in the converter main circuit 10 are turned on / off, and the output voltage Vout of the output terminals 17a and 17b rises smoothly toward the rated output voltage VoT. To go.

  After the soft start completion time Tend when the second soft start period H2 ends, as in the second embodiment, constant voltage control is performed, and the output voltage Vout is maintained at the rated output voltage VoT.

(Effect of Example 4)
According to the switching power supply device of the fourth embodiment, there are the same effects as the third embodiment.

(Modification of Examples 1-4)
This invention is not limited to the said Examples 1-4, A various utilization form and deformation | transformation are possible. For example, the following forms (a) to (h) are used as the usage forms and modifications.

  (A) The switching frequency setting unit 21a in FIGS. 1 and 9 may be changed to a configuration in which the first switching frequency f1 is set based on the switching frequency value determined from the output voltage Vout before activation.

  (B) Similar to the switching frequency setting unit 21a, the second reference voltage generation unit 22b in FIG. 1 and FIG. 9 determines the second reference voltage Vr2 from the output voltage Vout at the end of the first soft start period H1. You may change into the structure which changes a raise time or a raise characteristic.

  (C) In the first embodiment of FIG. 1, the start is started, and after the predetermined time measured by the timer 21b, the first soft start period H1 is switched to the second soft start period H2. It is not limited to this. For example, the frequency switching control unit 23 starts to start and changes to a configuration that performs switching control from the first soft start period H1 to the second soft start period H2 when the output voltage Vout reaches a predetermined voltage value. May be. Thereby, substantially the same effect as Example 1 is acquired.

  (D) In the first to fourth embodiments, the configuration example for performing the constant voltage control has been described. However, by changing the circuit configuration, the configuration can be changed to the configuration for performing the constant current control, or the constant voltage control and the constant current control It is also possible to change to a configuration in which

  (E) The converter main circuit 10 may be changed to a configuration other than that shown in FIG. For example, the FETs 12-1 to 12-4 constituting the switching circuit 12 may be composed of switching elements such as other transistors.

  (F) In the first to fourth embodiments, the current resonance type converter has been described as an example of the switching power supply device. However, the present invention can be applied to a switching power supply device that does not have the resonance circuit 13, a PWM control switching power supply device, and the like. Applicable. In the case of PWM control, not the switching frequency fs but the duty-controlled PWM signal becomes the switching signals S31 to S34. A switching power supply device other than such a current resonance type converter is configured, for example, as shown in (g) below.

  (G) For example, as shown in FIGS. 1, 3 and 9, the switching power supply device other than the current resonance type converter is a switching element (FET12-1 to 12-4) which is turned on / off by switching signals S31 to S34. And the switching signal S31 to S34 for turning on / off the switching element, and soft switching for the switching element is generated. And a control unit (corresponding to the control circuits 20, 20A and the driver 30) for controlling the operation. And the said control part has the 1st switching frequency setting means 21 and 21A, the 2nd switching frequency setting means 22, and a frequency control means (equivalent to the frequency switching control part 23 and the driver 30). Yes.

  Here, the first switching frequency setting means 21, 21 A sets the first switching frequency f 1 in the first soft start period H 1 in which the switching circuit 12 starts to be activated. When the second switching frequency setting means 22 switches to the second soft start period H2 in which the output voltage Vout of the rectifier circuit 15 is increased after the first soft start period H1 has elapsed, Reference voltages Vr1 and Vr2 are obtained based on the output voltage Vout of the rectifier circuit 15 at the end of the start period H1, and the output voltage Vout of the rectifier circuit 15 and the reference voltage Vr2 are compared and calculated to obtain a second switching frequency f2. Is set. Further, the frequency control means generates the switching signals S31 to S34 having the first switching frequency f1 and the second switching frequency f2, and the second soft start from the first soft start period H1. Switching to the period H2 is performed to turn on / off the switching element.

  By adopting such a configuration, it is possible to achieve substantially the same operational effects as in the first and third embodiments.

  (H) In the first to fourth embodiments, the second soft start period H2 is composed of one section, but is not limited thereto. For example, the second soft start period H2 is divided into a plurality of periods, and the second switching frequency setting unit 22 sets a plurality of second switching frequencies f2 corresponding to the divided plurality of periods. You may deform | transform into a structure. In the plurality of periods, processing in the subsequent period is performed based on the processing result in the previous period. Thereby, the rise of the output voltage Vout can be realized more smoothly.

10 Converter main circuit 12 Switching circuit 12-1 to 12-4 FET
DESCRIPTION OF SYMBOLS 13 Resonant circuit 14 Transformer 15 Rectifier circuit 20, 20A Control circuit 21, 21A 1st switching frequency setting means 21a Switching frequency setting part 21b Timer 21c Voltage inclination detection part 21d 1st soft start completion detection part 22 2nd switching frequency Setting means 22a First reference voltage setting unit 22b Second reference voltage generation unit 22c Frequency calculation unit 23 Frequency switching control unit 30 Driver

Claims (10)

A switching circuit having a switching element that is turned on / off by a switching signal;
A rectifying circuit for rectifying the output voltage of the switching circuit;
A controller that generates the switching signal for turning on / off the switching element and controls a soft switching operation for the switching element;
In a switching power supply device comprising:
The controller is
First switching frequency setting means for setting a first switching frequency in a first soft start period 1 for starting activation of the switching circuit;
When switching to the second soft start period for raising the output voltage of the rectifier circuit after the first soft start period has elapsed, a reference is made based on the output voltage of the rectifier circuit at the end of the first soft start period. A second switching frequency setting means for obtaining a voltage and setting a second switching frequency by comparing the output voltage of the rectifier circuit and the reference voltage;
The switching signal having the first switching frequency and the second switching frequency is generated, switching control from the first soft start period to the second soft start period is performed, and the switching element is turned on. / Frequency control means for operating off,
A switching power supply device comprising: The frequency control means includes
The switching circuit is started, and when the output voltage of the rectifier circuit reaches a predetermined voltage value, switching control from the first soft start period to the second soft start period is performed. The switching power supply device according to claim 1. The frequency control means includes
2. The switching power supply device according to claim 1, wherein the switching power supply device performs switching control from the first soft start period to the second soft start period when a predetermined time elapses after starting the switching circuit. . The frequency control means includes
When the switching circuit starts to be activated and the voltage change rate per unit time in the output voltage of the rectifier circuit becomes a predetermined value or less, switching from the first soft start period to the second soft start period 2. The switching power supply device according to claim 1, wherein control is performed. The first switching frequency setting means includes
The first switching frequency is set according to a switching frequency value set in advance or a switching frequency value determined from an output voltage of the rectifier circuit before the switching circuit is started. The switching power supply device according to any one of claims. The first switching frequency setting means includes
According to a switching frequency value set in advance or a switching frequency value determined from an output voltage of the rectifier circuit before the switching circuit is started, the first switching frequency is set.
4. The switching power supply device according to claim 3, wherein the elapse of the predetermined time is measured by a timer and notified to the frequency control means. The first switching frequency setting means includes
According to a switching frequency value set in advance or a switching frequency value determined from an output voltage of the rectifier circuit before the switching circuit is started, the first switching frequency is set.
5. The switching power supply device according to claim 4, wherein when the voltage change rate is detected and the voltage change rate becomes equal to or less than the predetermined value, the end of the first soft start period is notified to the frequency control means. . The second switching frequency setting means includes
A first reference voltage setting unit that sets a first reference voltage based on an output voltage of the rectifier circuit at the end of the first soft start period;
A second reference voltage generator that generates a second reference voltage that is gradually increased from the first reference voltage to the target reference voltage;
A frequency calculation unit that compares the output voltage of the rectifier circuit and the second reference voltage to set the second switching frequency;
The switching power supply device according to claim 1, comprising: The second soft start period is
Divided into multiple periods,
The second switching frequency setting means includes
The switching power supply according to claim 1, wherein a plurality of the second switching frequencies corresponding to the plurality of divided periods are set. The switching circuit;
A resonance circuit that resonates at a predetermined resonance frequency by an output voltage of the switching circuit;
A transformer for converting the output voltage of the resonant circuit to a predetermined voltage level;
A rectifier circuit for rectifying the output voltage of the transformer;
The control unit;
A switching power supply device according to any one of claims 1 to 9, wherein a current resonance converter is provided.

Images