JP2017163773A - Switching power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a rise of a smooth output voltage waveform by performing smooth starting even when a large capacity load with a large capacity capacitor is connected.SOLUTION: A switching power supply unit includes an output voltage control part 10 on-off controlling a switching element. An output voltage control part 10 has a precharge period H12 comprised of a first fixed period H1 and a second fixed period H2 before a soft-start period H3 at starting, thereby performing smooth starting even when a large capacity load with a large capacity capacitor is connected with the output side.SELECTED DRAWING: Figure 1

Description

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

  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 an input voltage of DC (direct current) into AC (alternating current) by means of, a series resonance circuit that receives an AC voltage output from the switching circuit and resonates at a predetermined resonance frequency, and the resonance circuit A transformer (transformer) having a primary winding and a secondary winding for inputting a resonance signal output from the secondary winding, a rectifier circuit for rectifying an AC voltage output from the secondary winding, and the rectified And an output capacitor for smoothing the voltage and outputting a DC output voltage.

  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. Therefore, when starting from a state where the output voltage is 0 V, the switching frequency is gradually decreased from a high frequency (that is, soft start (walk-in)) to prevent overcurrent due to the charge current of the output capacitor. doing. 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 a switching element is generated by pulse width modulation (hereinafter referred to as “PWM”) control so as to reduce an error between an output voltage and a target value. It has a soft start function that gradually increases the duty of the switching signal until the output voltage reaches the target value after the regulator starts, and reduces the duty of the switching signal until the output voltage reaches the target value. Overshoot is suppressed.

  However, in the control circuit for generating the switching signal based on the output voltage, a delay of signal processing occurs, and even if the output voltage reaches the target value, 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 the output voltage is reached until the output voltage reaches the target value.

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 the output voltage Vout is 0 V when the operation starts (start-up), the soft start period H elapses, and the soft start is completed at the soft start completion time Tend. The output 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 is not performed using the current for charging the output capacitor, so that the switching element is stressed and the switching element is deteriorated.

In addition, if a large-capacity load having a large-capacitance capacitor is connected to the output side of the current resonance type converter, the primary overcurrent operation for protecting the switching element on the primary side may not be started. Occurs.
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, it is considerably difficult to apply the technique of Patent Document 1 to a current resonance converter as it is to solve the above problem.

  The switching power supply device of the present invention includes a switching circuit having a switching element that is turned on / off by a switching signal, a rectifying / smoothing circuit that rectifies and smoothes an output signal of the switching circuit and outputs an output voltage, and the switching element. And a control unit that generates the switching signal for on / off operation and controls a soft switching operation and a normal operation for the switching element.

  The control unit sets a first fixed control amount and outputs a first fixed control amount setting signal during a first fixed period from the start of activation of the switching circuit before the control of the soft switching operation. Whether the output voltage reaches a specified value and pull-charging is completed at the end of the first fixed period and at the end of the first fixed period and the second fixed period after the end of the first fixed period. Precharge determination means for performing a precharge determination on whether or not to output a precharge determination result; and when the precharge determination result has not reached the specified value at the end of the first fixed period, A second fixed control amount setting means for setting a second fixed control amount that raises the output voltage to the specified value during a fixed period, and outputting a second fixed control amount setting signal; And when the precharge is completed at the end of the first fixed period or when the precharge is completed during the second fixed period, and at the end of the second fixed period. When the precharge is not completed without reaching the specified value, the soft start transition means for ending the control of the precharge operation and shifting to the control of the soft switching operation, the first fixed control amount setting signal, and the Switching signal generating means for generating the switching signal based on a second fixed control amount setting signal.

For example, when the precharge is completed, the soft start transition means shifts to the control of the soft switching operation using the voltage and current at the completion of the precharge as a starting point, and the precharge Is not completed, the process proceeds to the control of the soft switching operation using the voltage and current when the precharge is not completed as the starting point.
The second fixed control amount is the same as or different from the first fixed control amount.

  The control unit further sets a soft start control amount such that the output voltage rises to a target value during a soft start period after the control of the precharge operation, and a soft start control amount setting signal A soft start control amount setting means for outputting a normal operation control amount setting signal so that the output voltage follows the target value after the end of the soft start period, and a normal operation control amount setting signal is output. Normal operation control amount setting means, and the switching signal generation means includes the first fixed control amount setting signal, the second fixed control amount setting signal, the soft start control amount setting signal, and the normal operation control. The switching signal is generated based on a quantity setting signal.

  The control amount is a frequency.

  The control amount is a pulse width.

  Further, the switching power supply device is, for example, a current resonance type converter, and a resonance circuit that resonates at a predetermined resonance frequency with an output signal of the switching circuit with respect to the switching power supply device, and an output signal of the resonance circuit. A transformer that converts the voltage into a predetermined voltage level and supplies the voltage to the rectifying and smoothing circuit is added.

  According to the switching power supply device of the present invention, the following effects (1) to (3) are obtained.

  (1) Since a precharge period consisting of a first fixed period and a second fixed period is provided at the time of start-up, even when a large-capacity load having a large-capacitance capacitor is connected to the output side, it is smoothly (smooth) It can be started. Further, when the control unit is constituted by a processor such as a digital signal processor (hereinafter referred to as “DSP”), for example, a precharge period can be easily provided without adding a hardware circuit.

  (2) Since the control amount of the soft start is set based on the detection signal of the output voltage detected at the end of the precharge period, it is possible to smoothly shift to the soft start period and realize a smooth rise of the output voltage. Therefore, the stress of the switching power supply device at startup can be avoided.

  (3) Based on the output voltage detection signal detected at the end of the precharge period, the rising time or rising slope of the output voltage can be adjusted (set) in the subsequent soft start period. Therefore, by preventing a sudden change in the output voltage or output current, it is possible to reduce or avoid load stress at startup.

FIG. 1 is a schematic functional block diagram showing an output voltage control unit in the switching power supply device of FIG. 3 in 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 switching power supply device according to the first embodiment of the present invention. FIG. 4 is a startup waveform diagram of the switching power supply device of FIG. FIG. 5 is a flowchart showing a control process at the start-up in the output voltage control unit of FIG.

  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. 3 is a schematic circuit diagram illustrating a configuration example of the switching power supply device according to the first embodiment of the present invention.

  This switching power supply device is, for example, a current resonance type converter, and includes a positive input terminal 1a for inputting a DC input voltage Vin supplied from a DC power supply such as a solar battery and a negative input terminal 1b on the ground side. Yes. A half-bridge type switching circuit 3 is connected between the input terminals 1a and 1b via a smoothing input capacitor 2. The half-bridge type switching circuit 3 includes two switching elements (for example, field effect transistors, hereinafter referred to as “FETs”) 3 a and 3 b, and these FETs 3 a and 3 b are connected to the positive electrode of the input capacitor 2 and the negative electrode. It is connected in series between the side electrodes.

  The two FETs 3a and 3b are complementarily turned on / off by two switching signals S1 and S2. A parasitic diode 3a1 and 3b1 for commutation is provided between the drain electrode and the source electrode of the FETs 3a and 3b. Each is connected in antiparallel. A transformer 5 is connected to the connection point N1 between the source electrode of the FET 3a and the drain electrode of the FET 3b and the source electrode of the FET 3b through the resonance circuit 4.

  The resonance circuit 4 has two resonance capacitors 4a and 4b and a resonance inductor 4c. The two resonance capacitors 4a and 4b are connected in series between the drain electrode of the FET 3a and the source electrode of the FET 3b. The resonance inductor 4c and the primary winding 5a of the transformer 5 are connected in series between the connection point N1 and the connection point N2 between the two resonance capacitors 4a and 4b. The resonance circuit 4 has a specific resonance frequency fr determined by the capacitances of the resonance capacitors 4a and 4b and the inductance of the resonance inductor 4c.

  The transformer 5 has a primary winding 5a connected between an electrode at one end of the inductor 4c and the connection point N2, and a secondary winding 5b electromagnetically coupled to the primary winding 5a. doing. In the primary winding 5a, the exciting inductance of the transformer 5 exists in parallel therewith. A rectifying and smoothing circuit 6 is connected to both end electrodes of the secondary winding 5b.

  The rectifying / smoothing circuit 6 includes a diode bridge circuit including four diodes 6a to 6d for full-wave rectification of the induced voltage induced in the secondary winding 5b, and a smoothing output capacitor 6e. A positive output terminal 7a and a ground negative output terminal 7b are connected to both end electrodes of the output capacitor 6e. A DC output voltage Vout is output from between the output terminals 7a and 7b. An output voltage control unit 10 as a control unit is connected to the output terminals 7a and 7b.

  The output voltage control unit 10 detects the DC output voltage Vout, generates switching signals S1 and S2 for turning on / off the FETs 3a and 3b by PFM control based on the detection signal, and precharges the FETs 3a and 3b. This circuit controls the operation, soft switching operation and normal operation. The output voltage control unit 10 includes, for example, a processor such as a DSP that is a microprocessor specialized in digital signal processing, a real circuit of a digital circuit, or a real circuit of an analog circuit such as a frequency control integrated circuit. Yes.

  FIG. 1 is a schematic functional block diagram showing an output voltage control unit 10 in the switching power supply device of FIG. 3 according to Embodiment 1 of the present invention.

  The output voltage control unit 10 is configured by a processor such as a DSP, and includes an output voltage detection unit 11, a first fixed frequency setting unit 12 as a first fixed control amount setting unit, a first fixed period measurement unit 13, and a precharge determination. Means 14, second fixed frequency setting means 15 as second fixed control amount setting means, second fixed period measuring means 16, soft start transition means 17, soft start frequency setting means 18 as soft start control amount setting means, normal A normal operation frequency setting means 19 as an operation control amount setting means and a switching signal generation means 20 are provided.

  The output voltage detection means 11 detects the DC output voltage Vout and outputs this detection signal S11 to the precharge determination means 14, the soft start transition means 17, the soft start frequency setting means 18, and the normal operation frequency setting means 19. And is constituted by a resistance voltage dividing circuit or the like.

  The first fixed frequency setting means 12 has a first fixed control amount (for example, the first fixed amount) according to a preset switching frequency value during the first fixed period H1 from the start of the switching circuit 3 before the soft switching operation is controlled. 1 fixed frequency) f1 is set, and the first fixed frequency setting signal S12 as the first fixed control amount setting signal is output to the first fixed period measuring means 13 and the switching signal generating means 20.

  The first fixed period measuring means 13 measures the first fixed period H1 and outputs the measurement result to the precharge determining means 14, and is constituted by a timer or the like.

  The precharge determination unit 14 is based on the detection signal S11 of the output voltage detection unit 11, the measurement result of the first fixed period measurement unit 13, and the measurement result of the second fixed period measurement unit 16, at the end of the first fixed period H1. And in the second fixed period H2 after the end of the first fixed period H1, whether or not the output voltage Vout has reached a predetermined precharge completion voltage Vp (that is, whether or not Vout ≧ Vp). And the precharge determination result is output to the second fixed frequency setting means 15 and the soft start transition means 17.

  The second fixed frequency setting means 15 outputs the output during the second fixed period H2 when the precharge determination result of the precharge determination means 14 has not reached the precharge completion voltage Vp at the end of the first fixed period H1. A second fixed control amount (for example, a second fixed frequency) f2 that raises the voltage Vout to the precharge completion voltage Vp is set, and a second fixed frequency setting signal S15 as a second fixed control amount setting signal is set. The second fixed period measuring means 16 and the switching signal generating means 20 are outputted. The second fixed frequency f2 is the same frequency as the first fixed frequency f1 or a frequency lower than the first fixed frequency f1.

  The second fixed period measuring means 16 measures the second fixed period H2 and outputs the measurement result to the precharge determining means 14 and the soft start transition means 17, and is composed of a timer or the like.

  Based on the detection signal S11 of the output voltage detection unit 11, the precharge determination result of the precharge determination unit 14, and the measurement result of the second fixed period measurement unit 16, the soft start transition unit 17 determines that the precharge determination result is the first. When the precharge completion voltage Vp is reached at the end of the fixed period H1 or during the second fixed period H2, and when the precharge completion voltage Vp is not reached at the end of the second fixed period H2, This control is terminated and the process proceeds to the control of the next soft switching operation, and the transition result is output to the soft start frequency setting means 18 as the soft start control amount setting means.

  The soft start frequency setting means 18 controls the soft start control amount (for example, the soft start frequency so that the output voltage Vout gradually rises to the target value during the next soft start period H3 after the control of the precharge operation. ) F3 is set, and the soft start frequency setting signal S18 as the soft start control amount setting signal is output to the normal operation frequency setting means 19 and the switching signal generation means 20 as the normal operation control amount setting means. .

  The soft start frequency setting unit 18 includes, for example, a reference voltage setting unit and a frequency calculation unit. The reference voltage setting unit is configured to set the reference voltage gradually increased to a preset target value based on the detection signal S11 of the output voltage detection unit 11 after the control of the precharge operation. Further, the frequency calculation unit has a function of comparing and calculating the detection signal S11 of the output voltage detection means 11 and its reference voltage to generate the soft start frequency setting signal S18.

  Based on the detection signal S11 of the output voltage detection means 11 and the soft start frequency setting signal S18, the normal operation frequency setting means 19 follows the target value in the normal operation period H4 after the end of the soft start period H3. The normal operation frequency f4 is set, and the normal operation frequency setting signal S19 is output to the switching signal generating means 20.

  The normal operation frequency setting means 19 is composed of a reference voltage setting section and a frequency calculation section, for example, in substantially the same manner as the soft start frequency setting means 18. The reference voltage setting unit sets a constant reference voltage that is a target value in the normal operation period H4 after the end of the soft start period H3. The frequency calculation unit has a function of comparing and calculating the detection signal S11 of the output voltage detection means 11 and a constant reference voltage to generate a normal operation frequency setting signal S19.

  The switching signal generation means 20 has a function as a frequency control means, and is based on the first fixed frequency setting signal S12, the second fixed frequency setting signal S15, the soft start frequency setting signal S18, and the normal operation frequency setting signal S19. A control pulse is generated by PFM control, and the control pulse is driven to generate complementary switching signals S1 and S2, thereby turning on / off the FETs 3a and 3b.

(Operation of Example 1)
FIG. 4 is a waveform diagram at the time of startup showing the output voltage Vout of the switching power supply device of FIG.

  In FIG. 4, the horizontal axis represents time T, and the vertical axis represents the output voltage Vout. On the horizontal axis, H12 is a precharge period including a first fixed period H1 and a second fixed period H2 which is the maximum period, H3 is a soft start period, and H4 is a normal operation period. The solid line waveform Vout1 is an output voltage in the case of a large capacity load having a large capacity capacitor, and the broken line waveform Vout2 is an output voltage in the case of a normal load without a large capacity capacitor.

  FIG. 5 is a flowchart showing a control process at the time of start-up in the output voltage control unit 10 of FIG.

  When the start control of the output voltage control unit 10 is started in step ST1 of FIG. 5, the first fixed frequency setting means 12 in the output voltage control unit 10 of FIG. 1 operates during the first fixed period H1 of FIG. The first fixed frequency f1 is set, and the first fixed frequency setting signal S12 is output to the switching signal generating means 20. Then, the switching signal generation means 20 generates a control pulse by PFM control based on the first fixed frequency setting signal S12, and drives the control pulse to generate complementary switching signals S1 and S2. The FETs 3a and 3b in the circuit 3 are turned on / off.

  For example, when the FET 3a in the switching circuit 3 is turned on by the switching signal S1 and the FET 3b is turned off by the switching signal S2, the accumulated charge of the positive electrode of the input capacitor 2 to which the DC input voltage Vin is applied is To the negative electrode of the input capacitor 2 via the FET 3a in the ON state, the connection point N1, the resonance inductor 4c in the resonance circuit 4, the primary winding 5a of the transformer 5, the connection point N2, and the resonance capacitor 4b. Current flows.

  Next, when the FET 3a is turned off by the switching signal S1 and the FET 3b is turned on by the switching signal S2, the primary winding of the junction N2 and the transformer 5 is generated by the accumulated charge of the positive electrode of the resonance capacitor 4b. A current flows to the negative electrode of the resonance capacitor 4b via 5a, the resonance inductor 4c, the connection point N1, and the on-state FET 3b.

  As a result, the current flowing through the resonance inductor 4c, the primary winding 5a of the transformer 5 and the resonance capacitor 4b resonates, and an induced voltage is generated in the secondary winding 5b of the transformer 5. The generated induced voltage is full-wave rectified by the rectifying and smoothing circuit 6 and then smoothed, and the DC output voltage Vout is output from the output terminals 7a and 7b.

  When a normal load without a large-capacitance capacitor is connected to the output terminals 7a and 7b, the output voltage Vout2 increases as shown by the broken line waveform in FIG. However, when a large-capacity load having a large-capacitance capacitor is connected, it may not be possible to start up, as shown by the solid line waveform in FIG. 4, and thus the output voltage Vout1 does not rise. Therefore, the process proceeds to the next steps ST2 and ST3.

  In step ST2, the first fixed period measuring means 13 in FIG. 1 measures the preset first fixed period H1 in FIG. 4, and when this first fixed period H1 ends (YES), this end time is pre-set. The charge determination unit 14 is notified and the process proceeds to step ST3. In step ST3, the precharge determination unit 14 determines the precharge completion voltage at which the output voltage Vout (= Vout1, Vout2) is a specified value based on the detection signal S11 of the output voltage detection unit 11 at the end of the first fixed period H1. It is determined whether or not Vp has been reached (that is, whether or not Vout1, Vout2 ≧ Vp), and the determination result is notified to the second fixed frequency setting means 15. In the case of a normal load, since the output voltage Vout2 has reached the precharge completion voltage Vp (YES), the process proceeds to step ST5. In the case of a large capacity load, since the output voltage Vout1 has not increased (NO), the process proceeds to step ST4.

  In step ST4, the second fixed frequency setting means 15 sets the second fixed frequency f2 such that the output voltage Vout1 rises to the precharge completion voltage Vp during the second fixed period H2 in FIG. The fixed frequency setting signal S15 is output to the switching signal generating means 20. Based on the second fixed frequency setting signal S15, the switching signal generation means 20 generates the switching signals S1 and S2 by PFM control, turns on / off the FETs 3a and 3b, and proceeds to step ST5.

  In step ST5, the precharge determination unit 14 determines whether or not the output voltage Vout1 has reached the precharge completion voltage Vp based on the detection signal S11 of the output voltage detection unit 11 in the second fixed period H2 (that is, Vout1 ≧ Vp is determined) and the determination result is notified to the soft start transition means 17. In the case of a normal load, since the output voltage Vout2 has reached the precharge completion voltage Vp (YES), the process proceeds to step ST7. In the case of a large capacity load, since the output voltage Vout1 has not increased (NO), the process proceeds to step ST6.

  In step ST6, the second fixed period measuring means 16 measures the second fixed period H2, and determines whether or not the second fixed period H2 has ended. When the second fixed period H2 has not ended, the process returns to step ST5, and when the second fixed period H2 has ended, the process proceeds to step ST7.

  In step ST7, the soft start frequency setting unit 18 detects the output voltage Vout (=) based on the detection signal S11 of the output voltage detection unit 11 (that is, detects the output voltage) during the soft start period H3 after the precharge ends. A soft start frequency f3 is set such that Vout1, Vout2) gradually increases to the target value, and a soft start frequency setting signal S18 is output to the normal operation frequency setting means 19 and the switching signal generation means 20. The switching signal generation means 20 generates switching signals S1 and S2 by PFM control based on the soft start frequency setting signal S18, turns on / off the FETs 3a and 3b, and targets the output voltage Vout (= Vout1 and Vout2). Gradually increase to value. When the output voltage Vout (= Vout1, Vout2) rises to the target value, the process proceeds to step ST8.

  In step ST8, the start-up control is terminated, and the process proceeds to the normal operation control. In this normal operation control, the normal operation frequency setting means 19 is based on the detection signal S11 of the output voltage detection means 11 and the soft start frequency setting signal S18 in the normal operation period H4 after the end of the soft start period H3. A normal operation frequency f4 is set such that the output voltage Vout follows the target value, and a normal operation frequency setting signal S19 is output to the switching signal generating means 20. The switching signal generation means 20 generates switching signals S1 and S2 by PFM control based on the normal operation frequency setting signal S19, and turns on / off the FETs 3a and 3b. Thus, constant voltage control is performed such that fluctuations in the output voltage Vout are suppressed and the rated output voltage is reached.

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

  (1) Since the precharge period H12 including the first fixed period H1 and the second fixed period H2 is provided at the time of start-up, even when a large-capacity load having a large-capacitance capacitor is connected to the output side, smooth It can be started. Further, when the output voltage control unit 10 is configured by a processor such as a DSP, for example, the precharge period H12 can be easily provided without adding a hardware circuit.

  (2) Since the soft start frequency f3 is set based on the output voltage Vout at the end of the precharge period H12 (that is, the output voltage is detected), the transition to the soft start period H3 can be made smoothly, and the smooth output The rise of the voltage Vout can be realized. Therefore, the stress of the switching power supply device at startup can be avoided.

  (3) Based on the detection signal S11 of the output voltage Vout detected at the end of the precharge period H12, the rising time or rising slope of the output voltage Vout can be adjusted (set) in the subsequent soft start period H3. Therefore, by preventing a sudden change in the output voltage Vout and the output current, load stress at startup can be reduced or avoided.

(Modification of Example 1)
The present invention is not limited to the first embodiment, and various usage forms and modifications are possible. For example, the following forms (a) to (e) are available as usage forms and modifications.

  (A) The converter main circuit including the switching circuit 3, the resonance circuit 4, the transformer 5, and the rectifying / smoothing circuit 6 in FIG. 3 may be changed to a configuration other than that illustrated. For example, the FETs 3a and 3b constituting the switching circuit 3 may be constituted by switching elements such as other transistors. The switching circuit 3 may be changed to a full bridge configuration using four switching elements.

  (B) The output voltage control unit 10 in FIG. 1 may be changed to a configuration other than that illustrated. For example, since the soft start frequency setting unit 18 and the normal operation frequency setting unit 19 have substantially the same configuration, the soft start frequency setting unit 18 and the normal operation frequency setting unit 19 are configured by a common frequency setting unit. It may be configured.

  (C) In the first embodiment, the configuration example for performing the constant voltage control has been described. However, by changing the circuit configuration, the configuration is changed to the configuration for performing the constant current control, or the constant voltage control and the constant current control are performed. It is also possible to change the configuration.

  (D) In the first embodiment, the frequency is used as the control amount, but it is also possible to use a pulse width instead of the frequency.

  (E) In the first embodiment, a current resonance type converter has been described as an example of a switching power supply device. However, the present invention can be applied to a switching power supply device that does not have the resonance circuit 4, a PWM control switching power supply device, and the like. Is possible. In the case of PWM control, not the switching frequency but the duty-controlled PWM signal becomes the switching signals S1 and S2.

3 Switching circuit 3a, 3b FET
DESCRIPTION OF SYMBOLS 4 Resonant circuit 5 Transformer 6 Rectification smoothing circuit 10 Output voltage control part 11 Output voltage detection means 12 1st fixed frequency setting means 13 1st fixed period measurement means 14 Precharge determination means 15 2nd fixed frequency setting means 16 2nd fixed period Measuring means 17 Soft start transition means 18 Soft start frequency setting means 19 Normal operation frequency setting means 20 Switching signal generating means

Claims (7)

A switching circuit having a switching element that is turned on / off by a switching signal;
A rectifying / smoothing circuit that rectifies and smoothes the output signal of the switching circuit and outputs an output voltage;
A controller that generates the switching signal for turning on / off the switching element, and controls a soft switching operation and a normal operation for the switching element;
A switching power supply device comprising:
The controller is
A first fixed control amount setting for setting a first fixed control amount and outputting a first fixed control amount setting signal during a first fixed period from the start of activation of the switching circuit before the control of the soft switching operation Means,
At the end of the first fixed period and in the second fixed period after the end of the first fixed period, a precharge determination is made as to whether or not the output voltage reaches a specified value and the pull charge is completed. Precharge determining means for outputting a precharge determination result;
If the precharge determination result does not reach the specified value at the end of the first fixed period, a second fixed value that increases the output voltage to the specified value during the second fixed period. Second fixed control amount setting means for setting a control amount and outputting a second fixed control amount setting signal;
When the precharge determination result reaches the specified value at the end of the first fixed period or during the second fixed period and the precharge is completed, and at the end of the second fixed period Soft start transition means for ending the control of the precharge operation and shifting to the control of the soft switching operation when the precharge is not completed without reaching the specified value in
Switching signal generating means for generating the switching signal based on the first fixed control amount setting signal and the second fixed control amount setting signal;
A switching power supply device comprising: The soft start transition means includes
When the precharge is completed, the voltage and current at the completion of the precharge are used as starting points, and the process proceeds to the control of the soft switching operation.
When the precharge is incomplete, the voltage and current when the precharge is incomplete is used as a starting point, and the control proceeds to the soft switching operation.
The switching power supply device according to claim 1. The second fixed control amount is
3. The switching power supply device according to claim 1, wherein the switching power supply device has a value that is the same as or different from the first fixed control amount. The control unit further includes:
A soft start control amount that outputs a soft start control amount setting signal by setting a soft start control amount such that the output voltage rises to a target value during a soft start period after the completion of the precharge operation control. Setting means;
A normal operation control amount setting means for setting a control amount for normal operation such that the output voltage follows the target value after the end of the soft start period, and outputting a normal operation control amount setting signal;
Have
The switching signal generating means includes
Based on the first fixed control amount setting signal, the second fixed control amount setting signal, the soft start control amount setting signal, and the normal operation control amount setting signal, the switching signal is generated.
The switching power supply device according to any one of claims 1 to 3.   The switching power supply according to claim 1, wherein the control amount is a frequency.   The switching power supply according to claim 1, wherein the control amount is a pulse width. The switching circuit;
A resonance circuit that resonates at a predetermined resonance frequency by the output signal of the switching circuit;
A transformer for converting the output signal of the resonance circuit to a predetermined voltage level;
The rectifying / smoothing circuit for rectifying and smoothing the output signal of the transformer and outputting the output voltage;
The control unit;
A switching power supply device according to any one of claims 1 to 6, wherein a current resonance converter is provided.

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