JP2017108592A - Switching electric power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the reduction of an EMI noise occurred by an intermittent action.SOLUTION: A switching electric power supply comprises a surge current suppression circuit which switches a driving current value of a main switching element or a driving resistance value by using: an output of a comparator which fetches a drain-source voltage signal of the main switching element or a corrector-emitter voltage signal, and compares the fetched voltage signal and a preset threshold value; and a switching period signal that switches a switching period for switching at a predetermined switching frequency and a stopping period in which the switching is not performed. After the shifting to the switching period from the stopping period, the surge current suppression circuit detects that the voltage signal is reduced in the preset threshold value or less, and the driving current value of the main switching element is increased, or the driving resistance value is reduced. After that, the circuit detects that switching period is shifted to the stopping period, and reduces the driving current value of the main switching element, or increases the driving resistance value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a switching power supply device having a simple configuration capable of reducing noise particularly in intermittent operation applied in a light load state for high efficiency.

  The switching power supply generally includes a main switching element that controls a current flowing in a primary winding of a transformer to which a DC input voltage is applied, and a rectifying / smoothing voltage induced in the secondary winding of the transformer. A voltage output circuit for generating a predetermined DC output voltage is provided. The switching power supply device further includes a switching control circuit that inputs a feedback signal corresponding to a DC output voltage to control on / off of the main switching element, thereby making the DC output voltage constant.

  Here, the circuit system of the switching power supply device includes a forward system, a flyback system, a current resonance system, or a voltage resonance system. As an example, a current resonance type switching power supply device is configured as shown in FIG. This switching power supply device includes two switching elements 13 and 14 connected in series as a main switching element. The switching element 13 is connected in parallel to the primary winding of the transformer 16 via the resonance capacitor 15, and the switching element 14 is connected in series to the primary winding of the transformer 16. These switching elements 13 and 14 are made of, for example, MOS-FETs, and are generally turned on and off in response to a gate signal from the switching control circuit 2 integrated into an integrated circuit.

  A DC input voltage Vin is applied to the primary winding of the transformer 16 from a DC power source via the resonance capacitor 15 and the switching element 14. For example, the DC power supply rectifies a commercial AC power supply to generate a DC input voltage Vin, and the DC input voltage Vin is smoothed through an input capacitor 1 and supplied to a switching power supply device.

  Here, when the switching element 14 is turned on, the current Icr flows through the primary winding of the transformer 16 via the resonance capacitor 15 and also stores energy in a resonance circuit including the resonance capacitor 15 and the resonance inductance of the transformer 16. Take on. Further, the switching element 13 plays a role of discharging the energy stored in the resonance circuit through the primary winding of the transformer 16 when it is turned on, and causing a reverse current Icr to flow through the primary winding. As a result, the current Icr flowing through the primary winding of the transformer 16 has a sinusoidal waveform describing a resonance arc.

  In this way, a predetermined voltage is induced in the secondary winding of the transformer by the current Icr flowing through the primary winding of the transformer 16. The voltages induced in the secondary winding of the transformer 16 are rectified by both waves via the diodes 17 and 18 and then smoothed by the output capacitor 27. That is, the diodes 17 and 18 and the output capacitor 27 constitute a voltage output circuit that generates a DC output voltage Vout supplied to the load RL from the voltage induced in the secondary winding of the transformer 16.

  The switching power supply configured in this way is as described in detail in, for example, Patent Document 1 and the like.

  By the way, in the above-described switching power supply device, when the rated load is 100%, the current Icr flowing through the primary winding of the transformer 16 with a complementary ON / OFF of the switching elements 13 and 14 becomes a substantially sine wave. Designed to maximize efficiency η. On the other hand, when the load is light, the peak value of the current Icr is greatly reduced compared to when the load is 100%, and the waveform of the current Icr flowing through the primary winding of the transformer 16 is a sawtooth shape in which a part of sine waves are alternately combined. It will be a wave. The exciting current itself of the transformer at this time hardly changes regardless of the load. This exciting current is a so-called reactive current in the switching power supply, and causes a loss due to the impedance of the circuit constituting the switching power supply. Therefore, even if the switching power supply device is designed so that the efficiency η is maximized at the rated load, there is a problem that the efficiency η at the light load is lowered.

  As a technique for improving the efficiency reduction at such a light load, the switching elements 13 and 14 are intermittently turned on and off with a predetermined stop period at a light load, thereby reducing the switching loss and the conduction loss. To be done.

  The intermittent operation of the switching elements 13 and 14 can be realized by the following configuration, for example. First, in the switching control circuit 2, the load power is calculated from the voltage signal DET acquired via the load detection resistor Rs provided on the secondary side of the transformer 16. In the switching control circuit 2, as shown in FIG. 9, an intermittent operation control circuit 31 for generating a switching period signal VTsw having a predetermined duty ratio between a switching period and a stop period according to the load power and a drive circuit 32 are provided. . Then, the drive circuit 32 receives the switching period signal VTsw, which is the output of the intermittent operation control circuit 31, and generates gate signals HO and LO for turning on / off the switching elements 13 and 14 only during the switching period.

  As a result, there is no switching loss or the like of the switching elements 13 and 14 during the period when the on / off operation of the switching elements 13 and 14 is stopped, thereby preventing a decrease in the overall efficiency η at light load. The intermittent operation control circuit is introduced in detail in Patent Documents 2 to 5, for example.

Japanese Patent No. 4423458 JP 2013-42628 A JP 2010-288334 A US Patent Application Publication No. 2013/0229829 US Pat. No. 8,314,489

  However, the conventional intermittent operation typified by the above-described patent document, for example, at the timing when the drain-source voltage VS of the switching element is high as seen in the waveform of the drain current IDL of the low-side switching element 14 in FIG. Since the suspension period shifts to the switching period, hard switching is performed. Therefore, there is a problem that a surge current is generated at this timing and EMI noise is generated.

  On the other hand, the noise of switching power supplies is required to meet the requirements of EMC standards represented by CISPR and the like. To realize low noise, it is conceivable to use passive components such as choke coils and capacitors. However, there is a problem that the size of the device is increased, the number of components is increased, and the cost is increased. is there.

  The present invention has been made in response to such a conventional situation, and an object of the present invention is to provide a switching power supply apparatus that can reduce EMI noise caused by intermittent operation at low cost.

In order to achieve the above object, the switching power supply device of the present invention is configured such that the gate resistance value (drive resistance value) of the main switching element is changed to the normal gate during the switching operation at the timing when the switching period is shifted to the stop period during the intermittent operation. A circuit that increases the gate current (driving current) by setting the resistance value higher than the resistance value and returning to the normal resistance value during the first switching operation after the transition to the switching period is provided. Thereby, in the first switching operation after the start of the switching period, the gate voltage gradually rises, so that the surge of the drain current or the collector current can be suppressed. The switching of the gate resistance is realized by detecting the drain voltage or the collector voltage, reducing the gate resistance value when the value becomes sufficiently low, and realizing the soft switching by fully turning on the main switching element.
Specifically, the switching power supply according to the present invention includes a main switching element that controls a current flowing in a primary winding of a transformer to which a DC input voltage is applied, and a voltage induced in the secondary winding of the transformer. A switching power supply body including a voltage output circuit that rectifies and generates a predetermined DC output voltage;
A switching power supply device comprising: a switching control circuit that inputs a feedback signal corresponding to the DC output voltage and controls the frequency of a switching signal for turning on and off the main switching element to make the DC output voltage constant. And
The drain-source voltage signal or the collector-emitter voltage signal of the main switching element is taken in, the output of the comparator that compares the voltage value of the fetched voltage signal with a preset threshold value, and switching is performed by the switching signal. Using a switching period signal that switches between a switching period to perform and a stop period in which switching is not performed, and a surge current suppression circuit that switches a driving current value or a driving resistance value of the main switching element,
The surge current suppression circuit detects that the voltage value of the voltage signal has dropped below the threshold after the transition from the stop period to the switching period, or increases the drive current value of the main switching element, or The drive resistance value is decreased, and then the transition from the switching period to the stop period is detected, and the drive current value of the main switching element is decreased or the drive resistance value is increased.

  The main switching element and a part of the element that rectifies the induced voltage of the secondary winding of the transformer may be formed of a wide band gap semiconductor.

  As described above, the switching power supply device according to the present invention detects that the drain-source voltage or the collector-emitter voltage of the main switching element has dropped below the threshold value after the transition from the stop period in the intermittent operation to the switching period. The drive current value of the switching element is increased or the drive resistance value is decreased. Therefore, the switching power supply device of the present invention can suppress a steep surge current generated at the start of the switching period, and can reduce conduction noise and radiation noise caused by the surge current.

It is a circuit diagram which shows the structure of the switching power supply device by the 1st Embodiment of this invention. It is explanatory drawing of the input / output signal of the surge current suppression circuit which the switching control circuit of FIG. 1 has. It is a block diagram of the surge current suppression circuit of FIG. FIG. 3 is a logic circuit diagram of the surge current suppression circuit of FIG. 2. 5 is a timing chart showing the operation of the main circuit and each part during intermittent operation according to the embodiment of the present invention. It is a circuit diagram which shows the structure of the switching power supply device by the 2nd Embodiment of this invention. FIG. 7 is a logic circuit diagram of a surge current suppression circuit provided in the switching control circuit of FIG. 6. It is a circuit diagram which shows the structure of the conventional switching power supply apparatus. It is explanatory drawing of the input-output signal of the intermittent operation control circuit with which the switching control circuit of FIG. 8 is provided. It is a timing chart which showed the operation of the main circuit at the time of intermittent operation of the conventional switching power supply device, and each part.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a half-bridge current resonance circuit will be described as an example. However, the present invention can be similarly applied to other types of switching power supply devices such as flyback, forward, full-bridge current resonance circuit, and voltage resonance circuit.

  FIG. 1 is a circuit diagram showing a configuration of a switching power supply device according to a first embodiment of the present invention. The difference from the conventional circuit shown in FIG. 8 is that a surge current suppressing circuit 40a in which a resistor 8 and a switch 7 are connected in parallel is connected from the low-side gate signal output terminal LO of the switching control circuit 2 to the gate of the low-side switching element 14. It is inserted in the signal path. Further, a surge current suppression circuit (control side) 40b is added to the switching control circuit 2 as shown in FIG. The continuity / open state of the switch 7 is switched by the output signal Rg of the surge current suppression circuit (control side) 40b. The surge current suppressing circuit 40a that switches the drive current of the switching element 14 having the switch 7 and the surge current suppressing circuit (control side) 40b that generates a switching signal (Rg) to the switch 7 includes the surge current suppressing circuit 40. Configure. Since others are the same as those in FIGS. 8 and 9, the same elements are denoted by the same reference numerals and description thereof is omitted. In the present embodiment, the surge current suppression circuit (control side) 40b is built in the switching control circuit 2, but may be provided outside the switching control circuit 2.

  In the present embodiment, since it is assumed that the low-side switching element 14 is always turned on during intermittent operation, the surge current suppression circuit 40a is applied only to the low-side. Therefore, for example, when the circuit is configured to be always turned on from the high side switching element 13, the surge current suppression circuit 40a may be inserted only on the high side. On the other hand, if the start of turn-on is not defined as either high side or low side, that is, if it is uncertain from which switching element the high side or low side starts when switching to the switching period, It is necessary to insert a surge current suppression circuit 40a for both the side and the low side.

  As shown in FIG. 3, the surge current suppression circuit (control side) 40b built in the switching control circuit 2 compares the low-side drain-source voltage VS with a preset threshold voltage VSth and outputs the comparison result. A driving current value / resistance value switching circuit 50 for inputting the output signal VTsw from the comparator 60, the intermittent operation control circuit 31 and the output signal from the comparator 60, and outputting the switching signal Rg to the surge current suppression circuit 40a. It is composed of

  An example of a logic circuit diagram of the surge current suppression circuit (control side) 40b is shown in FIG. In this figure, the comparator 60 outputs a logic “1” when the low-side drain-source voltage VS falls below the threshold voltage VSth. The output of the comparator 60 and the switching period signal VTsw are connected to the input terminal of the first AND circuit 55 that calculates the logical product. In addition, a monostable multi-circuit 51 that outputs a pulse that is logic “1” only during the time T at the fall of the switching period signal VTsw is provided. The output terminal Q of the monostable multi-circuit 51 is connected to the input terminal of the second AND circuit 54, and the output terminal Q is connected to the other input terminal of the second AND circuit 54 via the resistor 52. Has been. The input terminal on the resistor 52 side of the second AND circuit 54 is connected to the reference potential via the capacitor 53. The resistor 52 and the capacitor 53 constitute an RC filter having a time constant τ. The one-shot pulse width T of the monostable multi-circuit 51 is set slightly larger than the delay time set by the time constant τ.

  The output terminal of the first AND circuit 55 is connected to the set input terminal S of the RS flip-flop 56, and the output terminal of the second AND circuit 54 is connected to the reset input terminal R of the RS flip-flop 56, respectively. The negative output Q * of the RS flip-flop 56 (here, “*” represents negative) is output as a switching signal Rg for controlling the switch 7.

  In the surge current suppression circuit 40a, when the switching signal Rg is logic “1”, the switch 7 is opened, and the LO output of the switching control circuit 2 is supplied to the gate of the low-side switching element 14 via the resistors 8 and 11. Supplied to the terminal. When the switching signal Rg is logic “0”, the switch 7 becomes conductive, and the LO output of the switching control circuit 2 is supplied to the gate terminal of the low-side switching element 14 without going through the resistor 8.

  FIG. 5 is a timing chart showing the operation of the main circuit and each part during intermittent operation. VTsw is a switching period signal, HO and LO are driving signals for the high-side / low-side switching elements 13 and 14 during intermittent operation, VgH and VgL are gate voltage signals for the high-side / low-side switching elements 13 and 14, and IDL is a low-side switching element. 14 is a drain current, VS is a drain-source voltage signal of the low-side switching element 14, and Rg is a switch switching signal output from the surge current suppression circuit (control side) 40b.

  Hereinafter, the operation of the switching power supply according to the present embodiment will be described with reference to the timing chart of FIG. In FIG. 5, t1 is the restart timing of the switching period during intermittent operation. At the same timing, the gate resistance of the low-side switching element 14 becomes a series resistance of the resistor 8 and the resistor 11. For this reason, for example, if the resistance value of the resistor 8 is set to about 10 times the resistance value of the resistor 11, the switching response of the low-side switching element 14 can be reduced by about 10 times. Therefore, the rising speed of VgL becomes dull compared to the case where the resistor 8 is not passed.

  Thereafter, VgL reaches the mirror region at the timing of t2, and IDL begins to flow gradually. As a result, VS continues to decrease gradually and crosses a preset threshold voltage VSth. At this timing t3, the output of the comparator 60 becomes logic “1”. At this time, the switching period signal VTsw is also logic “1” (switching period). Therefore, the output of the first AND circuit 55 becomes logic “1”. Therefore, the set input of the RS flip-flop 56 becomes logic “1”, and the switching signal Rg which is a negative output of the RS flip-flop 56 becomes logic “0”. As a result, the switch 7 becomes conductive, and the gate resistance value of the low-side switching element 14 becomes the resistance value of the resistor 11 (approximately 1/10 of the resistance value of the resistor 8). As a result, VgL rises sharply. At this time, since VS = VSth, practical switching can be avoided if VSth is set to several volts to several tens of volts.

  Thereafter, when the surge current suppression circuit (control side) 40b detects that the switching period signal VTsw is logic “0” at timing t4, that is, the switching period has ended, the monostable multi-circuit 51 performs one shot of the pulse width T. Output a pulse. Then, the second AND circuit 54 outputs a reset pulse to the RS flip-flop 56 after a delay time set by the time constant τ. As a result, the switching signal Rg becomes logic “1” after the delay time set by the time constant τ (timing t5), and the switch 7 is opened. Then, the gate resistance value is switched from a small value (resistance value of only the resistor 11) to a large value (total resistance value of the resistors 8 and 11). The delay time is set so that the switching signal Rg rises after the switching element is reliably turned off.

  As described above, according to the switching power supply according to the present embodiment, the conventional circuit can perform the intermittent operation while suppressing the surge current (see FIG. 10) generated at the start timing t1 of the switching period in the intermittent operation. Both efficiency improvements can be achieved.

Next, a second embodiment of the present invention will be described.
The switch power supply according to the present embodiment is configured such that the surge current suppression circuit 40a is integrated with a conventional gate resistor. That is, the surge current suppression circuit 40a according to the present embodiment is inserted in series with the resistor 11 and in parallel with the series circuit of the resistor 9 and the diode 10, as shown in FIG. With this circuit configuration, when the LO output becomes a logic “1”, the drive current is suppressed, and when the LO output becomes a logic “0”, the resistor 9 connected in parallel has a sufficient ability to draw a gate current. Can be secured. For this reason, the second embodiment does not need to adjust the return time of the switching signal Rg by the time constant τ in the first embodiment. That is, by applying the surge current suppression circuit 40a of the present embodiment, the RC circuit of the drive current value / resistance value switching circuit 50 can be omitted as shown in FIG. Thereby, a switching control circuit can be realized with a simpler configuration.

  The present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the scope of the invention. For example, in order to reduce switching loss and improve efficiency by high-speed switching, instead of a silicon semiconductor that has been widely used in the past, a part of the main switching element or an element that rectifies the induced voltage of the secondary winding, or Of course, it is possible to make all of these elements composed of wide band gap semiconductors such as silicon carbide, gallium nitride, gallium oxide, and diamond.

1 Smoothing capacitor (input capacitor)
2 switching control circuit 3 high-side switching element turn-off resistor 4 high-side switching element turn-off diode 5 high-side switching element turn-on resistance 6 high-side switching element gate-source resistance 7 switch (part of surge current suppression circuit 40)
8 Resistance (part of surge current suppression circuit 40)
9 Low-side switching element turn-off resistance 10 Low-side switching element turn-off diode 11 Low-side switching element turn-on resistance 12 High-side switching element gate-source resistance 13 High-side switching element 14 Low-side switching element 15 Resonant capacitor 16 Transformers 17 and 18 Rectifier diodes 19 and 21 , 22, 24, 26, 52 Resistors 20a, 20b Photocoupler 23 Shunt regulator 25, 53 Capacitor 27 Secondary smoothing capacitor (output capacitor)
31 intermittent operation control circuit 32 drive circuit 40 surge current suppression circuit 50 drive current value / resistance value switching circuit 51 monostable multicircuit (monostable multivibrator)
56 RS flip-flops 54 and 55 AND circuit 60 Comparator Rs Load detection resistor RL Load

Claims (5)

A main switching element that controls a current flowing in a primary winding of a transformer to which a DC input voltage is applied, and a voltage output circuit that rectifies a voltage induced in the secondary winding of the transformer and generates a predetermined DC output voltage A switching power supply body with
A switching power supply device comprising: a switching control circuit that inputs a feedback signal corresponding to the DC output voltage and controls the frequency of a switching signal for turning on and off the main switching element to make the DC output voltage constant. And
The drain-source voltage signal or the collector-emitter voltage signal of the main switching element is taken in, the output of the comparator that compares the voltage value of the fetched voltage signal with a preset threshold value, and switching is performed by the switching signal. Using a switching period signal that switches between a switching period to perform and a stop period in which switching is not performed, and a surge current suppression circuit that switches a driving current value or a driving resistance value of the main switching element,
The surge current suppression circuit detects that the voltage value of the voltage signal has dropped below the threshold after the transition from the stop period to the switching period, or increases the drive current value of the main switching element, or A switching power supply characterized in that the drive resistance value is decreased, and then the transition from the switching period to the stop period is detected, and the drive current value of the main switching element is decreased or the drive resistance value is increased. apparatus.   The drive current value of the main switching element is decreased or the drive resistance value is increased with a delay time longer than the turn-off time of the main switching element from the time when it is detected that the transition to the stop period is detected. The switching power supply device according to claim 1, wherein   2. The switching power supply main body and the switching control circuit are applied to a forward type switching power supply, a flyback type switching power supply, a current resonance type switching power supply, or a voltage resonance type switching power supply. Or the switching power supply device according to 2;   2. The element according to claim 1, wherein at least one of the main switching element and a part of the element that rectifies the induced voltage of the secondary winding of the transformer is an element composed of a wide band gap semiconductor. 3. The switching power supply device according to 2.   5. The switching power supply device according to claim 4, wherein the wide band gap semiconductor is formed of silicon carbide, a gallium nitride-based material, a gallium oxide-based material, or diamond.

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