JP2017229140A - Power supply controller, semiconductor integrated circuit, and resonance type converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly protect an overcurrent without monitoring an input voltage.SOLUTION: A power supply controller 1 of an embodiment, is the power supply controller 1 that is used for a resonance type converter 100 and turns on/off semiconductor switches Q1 and Q2 controlling a current flowing in a primary winding T1 of a transformer T, and comprises: an overcurrent determination part 10 that determines whether the current flowing in the primary winding T1 is an overcurrent by using an overcurrent protection threshold value which is reduced in accordance with a lapse time after the semiconductor switch Q1 or Q2 turned on; and an output voltage suppressing part 20 that increases a switching frequency of the semiconductor switch Q1 or Q2 in the case where it is determined that the current flowing in the primary winding T1 is the overcurrent by the overcurrent determination part 10.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a power supply control device, a semiconductor integrated circuit, and a resonant converter.

  Conventionally, an LLC current resonance power supply is known as one of resonance type converters. In this LLC current resonance power supply, the current (resonance current) flowing in the primary winding is made close to a sine wave by utilizing the resonance between the leakage inductance of the transformer and the resonance capacitor connected to the primary winding of the transformer. , Reducing noise and improving conversion efficiency.

  As an overcurrent protection measure, the LLC current resonance power supply performs an operation of suppressing the output voltage when it is detected that the resonance current exceeds an overcurrent protection threshold (hereinafter also referred to as “OCP threshold”, OCP: Over Current Protection). . A PFC circuit (power factor correction circuit) is often provided in the previous stage (input stage) of the LLC current resonance power supply. When the PFC circuit is provided, the fluctuation of the input voltage of the LLC current resonance power supply is small. For this reason, no particular problem has occurred even if the OCP threshold is kept constant.

  However, in recent years, there are an increasing number of cases in which a PFC circuit is not provided in front of the LLC current resonance power supply. When the input voltage of the LLC current resonance power supply fluctuates, the peak value of the resonance current fluctuates greatly. For this reason, when the OCP threshold value is made constant, the point (output current value) at which overcurrent protection is applied varies greatly (see FIG. 5A). As a result, a large stress may be applied to the components of the LLC current resonance power supply. For example, an overcurrent may flow through a semiconductor switch (such as a MOSFET) for controlling the current flowing through the primary winding, leading to destruction.

  Patent Document 1 describes a switching power supply device in which an OCP threshold is generated using a voltage obtained by dividing an input voltage with a resistor so that the OCP threshold is changed according to the input voltage. .

JP 2012-170218 A

  However, in the case of Patent Document 1, since a resistor for dividing a high input voltage is required, there are problems that the number of components of the resonant converter is increased, the manufacturing cost and the mounting area are increased. Furthermore, there is a problem that a loss increases due to a current flowing through a voltage dividing resistor. In addition, there is a problem that the possibility of malfunction increases due to a change in resistance value caused by electrolytic corrosion or the like when used for a long time.

  Accordingly, an object of the present invention is to provide a power supply control device, a semiconductor integrated circuit, and a resonant converter that can appropriately perform overcurrent protection without monitoring an input voltage.

The power supply control device according to the present invention includes:
A power supply control device for turning on / off a semiconductor switch used for a resonant converter and controlling a current flowing in a primary winding of a transformer,
An overcurrent determination unit that determines whether or not the current flowing through the primary winding is an overcurrent using an overcurrent protection threshold that decreases according to an elapsed time after the semiconductor switch is turned on; ,
An output voltage suppression unit that increases the switching frequency of the semiconductor switch when the overcurrent determination unit determines that the current flowing through the primary winding is an overcurrent;
It is characterized by providing.

In the power supply control device,
A monitor terminal for inputting a voltage corresponding to the current flowing through the primary winding;
A feedback terminal for inputting a voltage based on the output voltage of the resonant converter;
May be further provided.

In the power supply control device,
The overcurrent determination unit
A first input terminal for inputting the voltage of the monitor terminal; and a second input terminal for inputting a voltage based on the voltage of the feedback terminal. The voltage of the first input terminal is the second input. You may have the 1st comparator which outputs an overcurrent detection signal, when higher than the voltage of a terminal.

In the power supply control device,
The overcurrent determination unit
A third input terminal for inputting the voltage of the monitor terminal; and a fourth input terminal for inputting a voltage based on the voltage of the feedback terminal. The voltage of the third input terminal is the fourth input. You may have the 2nd comparator which outputs an overcurrent detection signal, when lower than the voltage based on the voltage of a terminal.

In the power supply control device,
The output voltage suppression unit includes a discharge acceleration semiconductor switch that is turned on when a first main electrode is electrically connected to the feedback terminal, a second main electrode is grounded, and the overcurrent detection signal is received. You may have.

In the power supply control device,
A gradient setting terminal for inputting a preset voltage;
A multiplier that outputs a voltage based on a voltage obtained by multiplying the voltage of the feedback terminal by the voltage of the gradient setting terminal; and
The overcurrent determination unit
A first input terminal electrically connected to the monitor terminal; and a second input terminal electrically connected to the output terminal of the multiplier, wherein the voltage at the first input terminal is You may have a 1st comparator which outputs an overcurrent detection signal, when higher than the voltage of a 2nd input terminal.

In the power supply control device,
A monitor terminal for inputting a voltage corresponding to the current flowing through the primary winding;
A feedback terminal for inputting a voltage based on the output voltage of the resonant converter;
A slope setting terminal for setting a slope of the overcurrent protection threshold,
The overcurrent determination unit may include a multiplier that outputs a voltage based on a voltage obtained by multiplying the voltage of the feedback terminal by the voltage of the gradient setting terminal.

In the power supply control device,
The overcurrent determination unit
A first input terminal electrically connected to the monitor terminal; and a second input terminal electrically connected to the output terminal of the multiplier, wherein the voltage at the first input terminal is You may further have the 1st comparator which outputs an overcurrent detection signal, when higher than the voltage of a 2nd input terminal.

In the power supply control device,
The overcurrent determination unit
A third input terminal electrically connected to the monitor terminal; and a fourth input terminal electrically connected to the output terminal of the multiplier. The voltage of the third input terminal is You may further have the 2nd comparator which outputs an overcurrent detection signal, when lower than the voltage of a 4th input terminal.

  A semiconductor integrated circuit according to the present invention is characterized in that the power supply control device is formed on a semiconductor substrate.

The resonant converter according to the present invention is
A transformer having a primary winding and a secondary winding;
A resonant capacitor connected in series with the primary winding;
A rectifying / smoothing unit that rectifies and smoothes the voltage generated in the secondary winding of the transformer;
A power supply control device having a monitor terminal, a feedback terminal, a first gate signal output terminal, and a second gate signal output terminal for inputting a voltage corresponding to a resonance current flowing in the primary winding;
A light emitting diode that emits light with a light amount corresponding to the output voltage of the rectifying and smoothing unit;
A capacitor having one end electrically connected to the feedback terminal and the other end grounded;
A phototransistor whose collector terminal is electrically connected to the feedback terminal, whose emitter terminal is grounded, and whose current transfer ratio changes according to the amount of light of the light emitting diode;
A first semiconductor switch having a drain terminal electrically connected to a positive electrode of a DC power source and a gate terminal connected to the first gate signal output terminal;
A second semiconductor switch having a drain terminal electrically connected to a source terminal of the first semiconductor switch, a source terminal grounded, and a gate terminal connected to the second gate signal output terminal;
The power supply control device
Whether or not the current flowing through the primary winding is an overcurrent by using an overcurrent protection threshold that decreases according to an elapsed time after the first semiconductor switch or the second semiconductor switch is turned on. An overcurrent determination unit for determining whether or not
An output voltage suppression unit that increases the switching frequency of the first and second semiconductor switches when the overcurrent determination unit determines that the current flowing through the primary winding is an overcurrent;
It is characterized by having.

In the resonant converter,
The overcurrent determination unit may use a voltage based on the voltage of the feedback terminal as the overcurrent protection threshold.

In the resonant converter,
The power supply control device further includes a gradient setting terminal for setting a gradient of the overcurrent protection threshold value,
The overcurrent determination unit may use a voltage based on a voltage obtained by multiplying the voltage of the feedback terminal by the voltage of the gradient setting terminal as the overcurrent protection threshold.

  In the present invention, the current flowing in the primary winding is excessively exceeded by using an overcurrent protection threshold that decreases with the elapsed time from when the semiconductor switch that controls the current flowing in the primary winding of the transformer is turned on. It is determined whether or not the current is a current, and if it is determined that the current flowing through the primary winding is an overcurrent, the switching frequency of the semiconductor switch is increased to suppress the output voltage of the resonant converter. Thereby, according to this invention, overcurrent protection can be performed appropriately, without monitoring input voltage.

1 is a diagram showing a schematic configuration of a resonant converter 100 according to the present embodiment. 4 is a graph showing switching frequency characteristics of output voltage of a resonant converter 100. It is a figure showing a schematic structure of power supply control device 1 concerning an embodiment. It is a figure which shows the time waveform of the voltage of a feedback terminal, and a resonant current. (A) is a graph showing the characteristics of the output current and output voltage of the resonant converter when the OCP threshold is fixed, and (b) is a resonant type when the OCP threshold is changed as in the embodiment. It is a graph which shows the characteristic of the output current and output voltage of a converter. It is a figure which shows schematic structure of 1 A of power supply control apparatuses which concern on another embodiment. It is a figure which shows an example of the time waveform of various signals at the time of using the power supply control device 1A.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

<Resonant converter 100>
First, with reference to FIG. 1, a resonant converter 100 according to an embodiment of the present invention will be described.

  Resonant converter 100 supplies DC power obtained by converting power input from DC power supply Vin to load 200. Regarding the input / output characteristics of the resonant converter 100, as shown in FIG. 2, the output voltage becomes higher over the entire switching frequency as the input voltage is higher. The switching frequency f is selected to be higher than the resonance frequency f0.

  As shown in FIG. 1, the resonant converter 100 includes a power supply control device 1, a semiconductor switch Q1, a semiconductor switch Q2, a transformer T, a resonant capacitor C1, a rectifying / smoothing unit 110, an output voltage detecting unit 120, and the like. The current-voltage conversion unit 130, the light emitting diode PC1, and the phototransistor PC2. The resonant converter 100 is not provided with a circuit for monitoring the input voltage (the voltage of the DC power supply Vin).

  Hereinafter, each component of the resonant converter 100 will be described.

  The power supply control device 1 is used for the resonant converter 100. The power supply control device 1 will be described in detail later, but is configured to turn on / off the semiconductor switches Q1 and Q2. The power supply control device 1 is configured as an IC chip, for example. That is, the power supply control device 1 can be configured as a semiconductor integrated circuit formed on a semiconductor substrate.

  A current flowing through the semiconductor switches Q1, Q2 flows through the primary winding T1 of the transformer T. The semiconductor switches Q1 and Q2 control the current flowing through the primary winding T1 of the transformer T. The semiconductor switch Q1 (first semiconductor switch) is a high-side switch, and the semiconductor switch Q2 (second semiconductor switch) is a low-side switch. The semiconductor switches Q1 and Q2 are configured by, for example, an N-type MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). In addition, the semiconductor switches Q1 and Q2 may be a SiC power device, a GaN power device, a silicon power device, an IGBT, or the like.

  As shown in FIG. 1, a semiconductor switch Q1 and a semiconductor switch Q2 connected in series are connected between a positive electrode and a negative electrode of a DC power supply Vin. More specifically, the semiconductor switch Q1 has a drain terminal electrically connected to the positive electrode of the DC power supply Vin, and a gate terminal electrically connected to the gate signal output terminal G1 (first gate signal output terminal) of the power supply control device 1. It is connected. The semiconductor switch Q2 has a drain terminal electrically connected to the source terminal of the semiconductor switch Q1, a source terminal grounded, and a gate terminal connected to the gate signal output terminal G2 (second gate signal output terminal) of the power supply control device 1. Electrically connected.

  The transformer T has a primary winding T1 and secondary windings T2 and T3. The primary winding T1 is insulated from the secondary windings T2 and T3. The primary winding T1 is connected in parallel with the semiconductor switch Q2. The secondary windings T2 and T3 are connected to the rectifying and smoothing unit 110.

  The resonant capacitor C1 is connected in series with the primary winding T1. The arrangement of the resonance capacitor C1 is not limited to this, and for example, the resonance capacitor C1 may be provided between the connection point N of the semiconductor switch Q1 and the semiconductor switch Q2 and the primary winding T1.

  The rectifying / smoothing unit 110 includes diodes D1 and D2 and a smoothing capacitor C5, and rectifies and smoothes the voltage generated in the secondary windings T2 and T3 of the transformer T. A load 200 is connected to the output side of the rectifying and smoothing unit 110. The light emitting diode PC1 and the output voltage detection unit 120 are electrically connected to the output of the rectifying / smoothing unit 110, respectively.

  The light emitting diode PC1 has an anode terminal connected to the output of the rectifying / smoothing unit 110 via a resistor R8 and a cathode terminal connected to the output voltage detecting unit 120. The light emitting diode PC1 emits light with a light amount corresponding to the output voltage of the rectifying and smoothing unit 110.

  The light emitted from the light emitting diode PC1 is received by the phototransistor PC2. The phototransistor PC2 is provided corresponding to the light emitting diode PC1, and is disposed at a position where it can receive light emitted from the light emitting diode PC1. The phototransistor PC2 has a collector terminal electrically connected to the feedback terminal FB of the power supply control device 1, and an emitter terminal grounded. The current transfer ratio of the phototransistor PC2 varies depending on the light amount of the light emitting diode PC1. As a result, the current flowing through the phototransistor PC2 increases as the amount of received light increases.

  The collector terminal of the phototransistor PC2 is connected to the feedback terminal FB of the power supply control device 1 through the resistor R4. A resistor R3 and a capacitor C3 are connected in parallel to the phototransistor PC2 and the resistor R4.

  The output voltage detection unit 120 monitors the DC voltage supplied to the load 200, and increases the amount of light emitted from the light emitting diode PC1 by increasing the current flowing through the light emitting diode PC1 as the DC voltage increases. Let

  The current-voltage converter 130 converts a current (resonant current) flowing through the primary winding T1 of the transformer T into a voltage and outputs the voltage to the monitor terminal MON of the power supply control device 1. As the resonance current increases, the voltage output from the current-voltage converter 130 increases. In the present embodiment, the current-voltage conversion unit 130 includes resistors R5, R6, and R7 and a capacitor C4 as shown in FIG.

<Power supply control device 1>
Next, the power supply control device 1 will be described in detail mainly with reference to FIG.

  The power supply control device 1 is configured to generate a gate signal (switching signal) for switching the semiconductor switches Q1 and Q2 in accordance with the voltage at the feedback terminal FB and the voltage at the monitor terminal MON.

  First, various terminals included in the power supply control device 1 will be described. The power supply control device 1 includes a monitor terminal MON, a feedback terminal FB, a gate signal output terminal G1, a gate signal output terminal G2, and a ground terminal GND.

  The monitor terminal MON inputs a voltage corresponding to the current (resonant current) flowing through the primary winding T1 of the transformer T. More specifically, the monitor terminal MON inputs a voltage obtained by converting the current flowing through the primary winding T1 of the transformer T by the current-voltage conversion unit 130.

  Feedback terminal FB inputs a voltage based on the output voltage of resonant converter 100. The power supply control device 1 turns on and off the semiconductor switches Q1 and Q2 at a frequency according to the voltage of the feedback terminal FB. The feedback terminal FB is grounded via a capacitor C3, grounded via a resistor R3, and grounded via a resistor R4 and a phototransistor PC2 connected in series. Therefore, the current flowing through the feedback terminal FB includes a current flowing through the resistor R3 and a current flowing through the resistor R4 and the phototransistor PC2. During the discharge period of the capacitor C3 (a period in which a semiconductor switch Q4 described later is in an off state), the voltage at the feedback terminal FB drops as time passes. As will be described below, the voltage at the feedback terminal FB varies depending on the storage state of the capacitor C3 and the amount of light received by the phototransistor PC2.

  As shown in FIG. 1, the voltage of the feedback terminal FB is equal to the voltage between the electrodes of the capacitor C3. The capacitor C3 has one end electrically connected to the feedback terminal FB and the other end grounded, and is charged by a current source CS (described later) of the power supply control device 1. The electric charge charged in the capacitor C3 is discharged through the resistor R3, the resistor R4 and the phototransistor PC2 connected in series. More specifically, the electric charge charged in the capacitor C3 is always discharged by the resistor R3 and discharged by the resistor R4 and the phototransistor PC2 in accordance with the amount of light received by the phototransistor PC2. As will be described in detail later, the discharge time of the capacitor C3 is shortened when the semiconductor switch (discharge acceleration semiconductor switch) Q3 in the power supply control device 1 is turned on.

  The gate signal output terminal G1 is a terminal for outputting a gate signal for turning on / off the semiconductor switch Q1. The gate signal output terminal G2 is a terminal for outputting a gate signal for turning on / off the semiconductor switch Q2.

  The ground terminal GND is grounded. In the present embodiment, the ground terminal GND is connected to the negative electrode of the DC power supply.

  Next, the internal configuration of the power supply control device 1 will be described with reference to FIG.

  As shown in FIG. 3, the power supply control device 1 includes an overcurrent determination unit 10, an output voltage suppression unit 20, a control unit 30, a drive unit 40, a reference voltage generation unit 50, semiconductor switches Q1H, Q1L, Q2H and Q2L. Note that the power supply control device 1 may be provided with a soft start control unit (not shown) for causing the semiconductor switches Q1 and Q2 to perform a soft start operation at a given soft start frequency.

  The overcurrent determination unit 10 uses the OCP threshold that decreases according to the elapsed time from when the semiconductor switch (semiconductor switch Q1 or Q2) is turned on to generate a current (resonant current) flowing through the primary winding T1. It is comprised so that it may be determined whether it is an overcurrent. As will be described later, the overcurrent determination unit 10 uses a voltage based on the voltage of the feedback terminal FB as the OCP threshold.

  The overcurrent determination unit 10 includes comparators CMP 1 and 2, rising detection units 11 and 12, an OR gate 13, a voltage level adjustment unit 14, and a NOT gate 15.

  The voltage level adjustment unit 14 adjusts the level of the voltage of the feedback terminal FB to a voltage suitable for the input voltage of the comparators CMP1 and CMP2, and outputs the voltage. The number of voltage input lines of the voltage level adjusting unit 14 is two in FIG. 3, but may be one. The NOT gate 15 is connected between the voltage level adjustment unit 14 and the comparator CMP2, inverts the output voltage of the voltage level adjustment unit 14, and outputs the inverted voltage to the non-inverting input terminal (+) of the comparator CMP2. The NOT gate 15 may be included in the voltage level adjustment unit 14.

  The comparator CMP1 (first comparator) detects whether or not the current flowing through the primary winding T1 when the semiconductor switch Q1 is on is an overcurrent. The comparator CMP1 is electrically connected to the first input terminal (+) (non-inverting input terminal) electrically connected to the monitor terminal MON and the feedback terminal FB via the voltage level adjustment unit 14. And a second input terminal (−) (inverted input terminal). The first input terminal inputs the voltage of the monitor terminal MON, and the second input terminal inputs a voltage based on the voltage of the feedback terminal FB (in this embodiment, the voltage after the level adjustment by the voltage level adjustment unit 14). To do.

  The comparator CMP2 (second comparator) detects whether or not the current flowing through the primary winding T1 when the semiconductor switch Q2 is on is an overcurrent. The comparator CMP2 includes a third input terminal (−) electrically connected to the monitor terminal MON, and a fourth input terminal electrically connected to the feedback terminal FB via the voltage level adjustment unit 14 and the NOT gate 15. Input terminal (+). The third input terminal inputs the voltage of the monitor terminal MON, and the fourth input terminal is a voltage based on the voltage of the feedback terminal FB (in this embodiment, the level is adjusted by the voltage level adjustment unit 14 and inverted by the NOT gate 15) Enter the voltage after).

  The comparator CMP1 outputs an overcurrent detection signal when the voltage at the first input terminal is higher than the voltage at the second input terminal. The comparator CMP2 outputs an overcurrent detection signal when the voltage at the third input terminal is lower than the voltage at the fourth input terminal. In the present embodiment, the overcurrent detection signal is an H level signal, but is not limited thereto.

  The rising edge detection unit 11 detects that the voltage input from the comparator CMP1 has changed from the L level to the H level. Similarly, the rising edge detection unit 12 detects that the voltage input from the comparator CMP2 has changed from the L level to the H level. Output signals from the rise detection units 11 and 12 are input to the OR gate 13. The OR gate 13 takes the logical sum of the rise detection units 11 and 12 and outputs the logical sum to the output voltage suppression unit 20 (gate terminal of the semiconductor switch Q3).

  As described above, the comparators CMP1 and CMP2 perform overcurrent determination based on the voltage of the feedback terminal FB. In other words, in the present embodiment, the OCP threshold is determined based on the voltage of the feedback terminal FB.

  When the overcurrent determination unit 10 determines that the current flowing through the primary winding T1 is an overcurrent, the output voltage suppression unit 20 increases the switching frequency of the semiconductor switch Q1 and the semiconductor switch Q2 (ie, the on-state is turned on). / Off period is shortened). In the present embodiment, the output voltage suppression unit 20 includes a semiconductor switch (discharge acceleration semiconductor switch) Q3 as shown in FIG. The semiconductor switch Q3 is turned on when an overcurrent detection signal is output from the comparator CMP1 or the comparator CMP2. The semiconductor switch Q3 is, for example, an N-type MOSFET. In this case, the semiconductor switch Q3 is turned on when the drain terminal (first main electrode) is electrically connected to the feedback terminal FB, the source terminal (second main electrode) is grounded, and an overcurrent detection signal is received. become. When the overcurrent determination unit 10 is configured so that the overcurrent detection signal becomes an L level signal, a P-type MOSFET is used for the semiconductor switch Q3.

  When the semiconductor switch Q3 is turned on, the charge stored in the capacitor C3 is discharged through the semiconductor switch Q3, so that the discharge time of the capacitor C3 is shortened. As a result, the switching frequency of the semiconductor switches Q1, Q2 is increased. As a result, as can be seen from the characteristics of the resonant converter 100 described with reference to FIG. 2, the output voltage of the resonant converter 100 decreases.

  The control unit 30 controls the switching frequency based on the voltage of the feedback terminal FB. The control unit 30 includes a current source CS, a semiconductor switch Q4, and a comparator (drive pulse generating comparator) CMP. The current source CS is a current source that outputs a constant current, and is connected to the feedback terminal FB via the semiconductor switch Q4. The current source CS is a current source for charging the capacitor C3 connected to the feedback terminal FB. More specifically, the current source CS charges the capacitor C3 when the semiconductor switch Q4 is on.

  The semiconductor switch Q4 is a switch for controlling whether or not the capacitor C3 is charged, and operates based on the output signal of the comparator (drive pulse generating comparator) CMP. In this embodiment, the semiconductor switch Q4 is configured by a P-type MOSFET. The source terminal of the semiconductor switch Q4 is connected to the output of the current source CS, and the drain terminal is electrically connected to the feedback terminal FB. When an L level signal is input to the gate terminal, the semiconductor switch Q4 is turned on, and the capacitor C3 is charged by the current source CS.

  The comparator CMP outputs a drive pulse signal based on the voltage at the feedback terminal FB. More specifically, the comparator CMP outputs an H level signal (first signal) when the voltage at the feedback terminal FB is higher than the reference voltage Vref, and when the voltage at the feedback terminal FB is lower than the reference voltage Vref. An L level signal (second signal) is output to. The comparator CMP is preferably a hysteresis comparator, but may be a normal comparator.

  The control unit 30 charges the capacitor C3 with the current source CS until the voltage at the feedback terminal FB reaches the reference voltage Vref. Thereafter, when the reference voltage Vref is reached, the semiconductor switch Q4 is turned off, and the control unit 30 stops charging the capacitor C3. Thereafter, when the voltage at the feedback terminal FB drops to the reference voltage Vref, the semiconductor switch Q4 is turned on, and the capacitor C3 is charged again by the current source CS. The length of the discharge period of the capacitor C3 can be adjusted by, for example, the capacitance of the capacitor C3 and the resistance values of the resistors R3 and R4.

  As shown in FIG. 3, the drive unit 40 includes a T-type flip-flop 41, AND gates 42 and 43, and a dead time generation unit 44.

  The drive unit 40 generates a gate signal supplied to the gate terminals of the semiconductor switches Q1H, Q1L, Q2H, and Q2L based on the drive pulse signal supplied from the control unit 30 (comparator CMP). The drive unit 40 generates a gate signal having an oscillation frequency corresponding to the frequency of the drive pulse signal at an amplitude level corresponding to the semiconductor switches Q1H, Q1L, Q2H, and Q2L. As a result, gate signals for controlling the semiconductor switches Q1 and Q2 are output from the gate signal output terminals G1 and G2 so that the semiconductor switches Q1 and Q2 are alternately turned on with a dead time interposed therebetween. Here, the dead time is a period during which both the semiconductor switches Q1 and Q2 are off.

  In this embodiment, the semiconductor switches Q1H and Q2H are P-type MOSFETs, and the semiconductor switches Q1L and Q2L are N-type MOSFETs. As shown in FIG. 3, the gate signal output terminal G1 is connected to the drain terminal of the semiconductor switch Q1H and the drain terminal of the semiconductor switch Q1L. A reference voltage generation unit 50 that generates a reference voltage is connected to the source terminal of the semiconductor switch Q1H. The source terminal of the semiconductor switch Q1L is connected to a reference potential source (such as ground). The drive unit 40 is connected to the gate terminals of the semiconductor switches Q1H and Q1L.

  The reference voltage generation unit 50 generates a reference voltage and supplies the reference voltage to the drive unit 40 and the source terminals of the semiconductor switch Q1H and the semiconductor switch Q2H.

<Operation of Resonant Type Converter 100>
Next, the operation of the resonant converter 100 configured as described above will be described.

  The resonant converter 100 controls the current flowing through the primary winding T1 by alternately turning on the semiconductor switches Q1 and Q2 with a dead time between the gate signals generated by the power supply control device 1. Then, the DC voltage output from the rectifying / smoothing unit 110 is supplied to the load 200.

  In a period in which the semiconductor switch Q1 is on and the semiconductor switch Q2 is off, the current output from the positive electrode of the DC power source Vin is supplied to the primary winding T1 of the transformer T via the semiconductor switch Q1. . Therefore, a current flows in the positive direction of the primary winding T1 of the transformer T (that is, from the connection point N toward the resonance capacitor C1). Then, an electromotive force is generated in the secondary windings T2 and T3 of the transformer T to cause a current to flow in the negative direction opposite to the positive direction. In the diode D1, the anode voltage becomes higher than the cathode voltage. Diode D1 conducts. As a result, the electromotive force generated in the secondary windings T2 and T3 is rectified, smoothed by the smoothing capacitor C5, and supplied to the load 200.

  On the other hand, during the period in which the semiconductor switch Q1 is in the off state and the semiconductor switch Q2 is in the on state, the energy stored in the transformer T during the period in which current flows in the positive direction of the primary winding T1 is used. That is, during this period, current is supplied from the primary winding T1 of the transformer T to the negative electrode of the DC power supply Vin via the semiconductor switch Q2 by the energy stored in the transformer T. That is, a current flows in the negative direction of the primary winding T1. Then, an electromotive force is generated in the secondary windings T2 and T3 of the transformer T so as to cause a current to flow in the positive direction of the primary winding T1, and in the diode D2, the anode voltage becomes higher than the cathode voltage. The diode D2 becomes conductive. As a result, the electromotive force generated in the secondary windings T2 and T3 of the transformer T is rectified, smoothed by the smoothing capacitor C5, and supplied to the load 200.

  The DC voltage supplied to the load 200 is supplied to the light emitting diode PC1 through the resistor R8 and also supplied to the output voltage detection unit 120. The current flowing through the phototransistor PC2 increases as the amount of received light increases. For this reason, as the output voltage of the resonant converter 100 increases, the discharge rate of the capacitor C3 increases, and as a result, the switching frequency of the semiconductor switches Q1, Q2 increases.

FIG. 4 shows the time waveform of the voltage V _{FB at} the feedback terminal FB and the time waveform of the current _ID flowing through the primary winding T 1 for each input voltage of the resonant converter 100. In FIG. 4, the time waveform of the current _ID shows a waveform when the semiconductor switch Q1 is in an on state, and a waveform when the semiconductor switch Q2 is in an on state is not shown.

As shown in FIG. 4, when the input voltage is low, the switching frequency of the semiconductor switch Q1 is relatively low, and the ON period of the semiconductor switch Q1 is relatively long. As the input voltage increases, the switching frequency of the semiconductor switch Q1 increases, and the ON period of the semiconductor switch Q1 decreases. Further, regarding the current _ID flowing through the primary winding T1, when the input voltage is low, the peak value of the current _ID is relatively high, and the timing of reaching the peak value (phase in the on period) is early. As the input voltage increases, the peak value of the current _ID decreases, and the timing (phase during the ON period) when the peak value is reached is delayed. Thus, the current peak value and the timing of reaching the peak value vary depending on the input voltage.

Conventionally, as described above, the input voltage is monitored, and the OCP threshold is set according to the input voltage. On the other hand, in this embodiment, the OCP threshold is set using the voltage of the feedback terminal FB. As shown in FIG. 4, the voltage of the feedback terminal FB gently decreases during the ON period due to the discharge of the capacitor C3. As the input voltage increases, the timing at which the current _ID flowing through the primary winding T1 reaches a peak is delayed and the peak is decreased. By utilizing this fact, the OCP threshold value can be set according to the input voltage by setting the OCP threshold value according to the voltage of the feedback terminal FB.

As described above, since the OCP threshold is set using the voltage V _FB of the feedback terminal FB, the OCP threshold decreases according to the elapsed time since the semiconductor switch Q1 (or Q2) is turned on. When the input voltage is low, the peak of the resonance current is high and the phase is fast, and the OCP threshold is also high, so that overcurrent detection according to the low input voltage is possible. On the other hand, when the input voltage is high, the peak of the resonance current is low and the phase is slow, and the OCP threshold is also low, so that overcurrent detection according to the high input voltage is possible. In this way, according to the present embodiment, it is possible to set an appropriate OCP threshold corresponding to the fluctuation of the input voltage. As a result, as shown in FIG. 5B, even when the input voltage fluctuates as DC360V, 390V, and 420V, the fluctuation of the point (output current value) at which the overcurrent protection function operates can be suppressed. it can.

  As described above, according to this embodiment, even when the input voltage varies, overcurrent protection can be appropriately performed without monitoring the input voltage.

  Furthermore, according to the present embodiment, since a resistor for monitoring the input voltage is not required, the number of components of the resonant converter is reduced, and the manufacturing cost and the mounting area can be reduced. In addition, in the case of a conventional resonant converter, there is a risk of malfunction due to a change in resistance value caused by electric corrosion or the like when used for a long period of time. However, in this embodiment, there is no resistance for monitoring the input voltage. There is no fear.

  In the present embodiment, the comparators CMP1 and CMP2 are used to monitor the overcurrent during the ON period for both the high-side switch (semiconductor switch Q1) and the low-side switch (semiconductor switch Q2). For this reason, even when an instantaneous overcurrent flows only during the ON period of the semiconductor switch Q1 (or the semiconductor switch Q2), the overcurrent protection operation can be performed.

  Furthermore, in this embodiment, since the OCP threshold value is set based on the voltage of the feedback terminal FB, the overcurrent protection operation can be performed by accurately grasping the state of the load from the phase of the resonance current. Therefore, the reliability of the overcurrent protection can be improved compared to the case where the overcurrent protection operation is performed using the input voltage.

  In the above embodiment, the currents flowing through the semiconductor switches Q1 and Q2 are monitored by the comparators CMP1 and CMP2, respectively, but only the current flowing through one of the semiconductor switches may be monitored. In this case, the OR gate 13 can be deleted in addition to any one of the comparators CMP1 and CMP2 and the rising edge detection unit associated with the comparator to be deleted. As a result, the number of parts can be reduced and the cost can be reduced. In the above embodiment, the semiconductor switch Q1 is turned on during the discharging period of the capacitor C3 as described in FIG. 4, but it may be turned on during the charging period of the capacitor C3.

<Power control device 1A>
Next, a power supply control device 1A according to another embodiment will be described with reference to FIG. One of the differences from the power supply control device 1 described above is that a gradient setting terminal SSD for setting the gradient of the OCP threshold is provided. In FIG. 6, the same components as those of the power supply control device 1 are denoted by the same reference numerals.

  As illustrated in FIG. 6, the power supply control device 1 </ b> A further includes a gradient setting terminal SSD that inputs a preset voltage. This gradient setting terminal SSD is a terminal for setting the gradient of the OCP threshold.

  The voltage input to the gradient setting terminal SSD is preset by an element (capacitor C6 and resistor R9) externally connected to the gradient setting terminal SSD. The capacitor C6 and the resistor R9 are connected between the gradient setting terminal SSD and the ground. A current source (not shown) for charging the capacitor C6 is provided in the power supply control device 1A.

  As shown in FIG. 6, the power supply control device 1A includes an overcurrent determination unit 10A, an output voltage suppression unit 20, a control unit 30, a drive unit 40, a reference voltage generation unit 50, semiconductor switches Q1H, Q1L, Q2H and Q2L. Since the configuration other than the overcurrent determination unit 10A is the same as that of the power supply control device 1, description thereof is omitted.

  The overcurrent determination unit 10 </ b> A includes comparators CMP <b> 1 and 2, rising detection units 11 and 12, an OR gate 13, and multipliers 16 and 17. As will be described below, the overcurrent determination unit 10A is configured to set an overvoltage protection threshold based on the voltage of the feedback terminal FB and the voltage of the gradient setting terminal SSD.

  The multipliers 16 and 17 output a voltage based on a voltage obtained by multiplying the voltage of the feedback terminal FB by the voltage of the gradient setting terminal SSD. The multipliers 16 and 17 adjust the level of the voltage obtained by multiplication to a voltage suitable for the input voltage of the comparators CMP1 and CMP2, and output the voltage. Note that the multiplier 17 inverts the voltage of the multiplication result and outputs it to the non-inverting input terminal (+) of the comparator CMP2. The output terminal of the multiplier 16 is connected to the inverting input terminal of the comparator CMP1, and the output terminal of the multiplier 17 is connected to the non-inverting input terminal of the comparator CMP2.

  The comparator CMP1 (first comparator) includes a first input terminal (+) electrically connected to the monitor terminal MON and a second input terminal electrically connected to the output terminal of the multiplier 16. (-). The comparator CMP1 outputs an overcurrent detection signal (in this embodiment, an H level signal) when the voltage at the first input terminal is higher than the voltage at the second input terminal.

  The comparator CMP2 (second comparator) includes a third input terminal (−) electrically connected to the monitor terminal MON and a fourth input terminal electrically connected to the output terminal of the multiplier 17. (+). The comparator CMP2 outputs an overcurrent detection signal (in this embodiment, an H level signal) when the voltage at the third input terminal is lower than the voltage at the fourth input terminal.

  With the above configuration, the overcurrent determination unit 10A determines whether the current flowing through the primary winding T1 is an overcurrent using the output voltages of the multipliers 16 and 17 as the OCP threshold. Since the slope of the OCP threshold can be adjusted, a more appropriate OCP threshold can be set.

  In the above embodiment, the OCP threshold that decreases according to the elapsed time is generated based on the voltage of the feedback terminal FB by the overcurrent determination units 10 and 10A, but the present invention is not limited to this. For example, using a device capable of generating an arbitrary voltage waveform such as a microcomputer, a voltage that decreases according to the elapsed time after the semiconductor switch is turned on may be generated as an OCP threshold value and used for overcurrent determination. . A device such as a microcomputer may be provided in the power supply control device 1 or 1A, or may be externally attached to the power supply control device 1 or 1A.

FIG. 7 shows an example of time waveforms of various signals when the power supply control device 1A is used. In FIG. 7, V _GH is a gate signal output to the semiconductor switch Q1, and V _GL is a gate signal output to the semiconductor switch Q2. V _SSD is the voltage of the gradient setting terminal SSD. FIG. 7 is a diagram in which three patterns are combined into one when the voltage of the gradient setting terminal SSD is 2V, 3.5V, and 5V.

As can be seen from FIG. 7, as the voltage at the gradient setting terminal SSD increases, the initial value V ₁ of the OCP threshold does not change, whereas the convergence value V ₂ increases. Therefore, the gradient of the OCP threshold becomes gentle as the voltage of the gradient setting terminal SSD increases. In the example of FIG. 7, the convergence value V ₂ is equal to the initial value V ₁ when the voltage of the gradient setting terminal SSD is 5V. In this way, the slope of the OCP threshold can be adjusted by changing the voltage of the slope setting terminal SSD. As a result, a more appropriate OCP threshold can be set.

  Note that the overcurrent determination unit 10A may monitor only the current flowing through one of the semiconductor switches Q1 and Q2 as in the case of the overcurrent determination unit 10. In this case, since either one of the comparators CMP1 and CMP2, the OR gate 13 can be deleted in addition to the rise detection unit and multiplier associated with the comparator to be deleted, the number of parts is reduced and the cost is reduced. be able to.

  Based on the above description, those skilled in the art may be able to conceive additional effects and various modifications of the present invention, but the aspects of the present invention are not limited to the individual embodiments described above. . You may combine suitably the component covering different embodiment. Various additions, modifications, and partial deletions can be made without departing from the concept and spirit of the present invention derived from the contents defined in the claims and equivalents thereof.

1, 1A Power supply control device 10, 10A Overcurrent determination unit 11, 12 Rising detection unit 13 OR gate 14 Voltage level adjustment unit 15 NOT gate 16, 17 Multiplier 20 Output voltage suppression unit 30 Control unit 40 Drive unit 41 T-type flip-flop AND gate 44 Dead time generator 50 Reference voltage generator 100 Resonant converter 110 Rectifier smoother 120 Output voltage detector 130 Current voltage converter 200 Load C1 Resonant capacitors C3, C4 Capacitor C5 Smoother capacitor C6 Capacitor CMP, CMP1, CMP2 Comparator CS Current sources D1, D2 Diodes G1, G2 Gate signal output terminal FB Feedback terminal MON Monitor terminal PC1 Light emitting diode PC2 Phototransistors Q1, Q2, Q3, Q4, Q5 Semiconductor switches R3, R4 5, R6, R7, R8, R9 resistor SSD gradient setting terminal T transformer T1 1 winding T2 2 winding Vin DC power supply

Claims (13)

A power supply control device for turning on / off a semiconductor switch used for a resonant converter and controlling a current flowing in a primary winding of a transformer,
An overcurrent determination unit that determines whether or not the current flowing through the primary winding is an overcurrent using an overcurrent protection threshold that decreases according to an elapsed time after the semiconductor switch is turned on; ,
An output voltage suppression unit that increases the switching frequency of the semiconductor switch when the overcurrent determination unit determines that the current flowing through the primary winding is an overcurrent;
A power supply control device comprising: A monitor terminal for inputting a voltage corresponding to the current flowing through the primary winding;
A feedback terminal for inputting a voltage based on the output voltage of the resonant converter;
The power supply control device according to claim 1, further comprising: The overcurrent determination unit
A first input terminal for inputting the voltage of the monitor terminal; and a second input terminal for inputting a voltage based on the voltage of the feedback terminal. The voltage of the first input terminal is the second input. The power supply control device according to claim 2, further comprising a first comparator that outputs an overcurrent detection signal when the voltage is higher than a terminal voltage. The overcurrent determination unit
A third input terminal for inputting the voltage of the monitor terminal; and a fourth input terminal for inputting a voltage based on the voltage of the feedback terminal. The voltage of the third input terminal is the fourth input. 4. The power supply control device according to claim 2, further comprising a second comparator that outputs an overcurrent detection signal when the voltage is lower than a voltage based on a terminal voltage. 5.   The output voltage suppression unit includes a discharge acceleration semiconductor switch that is turned on when a first main electrode is electrically connected to the feedback terminal, a second main electrode is grounded, and the overcurrent detection signal is received. The power supply control device according to claim 3, wherein the power supply control device is provided. A monitor terminal for inputting a voltage corresponding to the current flowing through the primary winding;
A feedback terminal for inputting a voltage based on the output voltage of the resonant converter;
A slope setting terminal for setting a slope of the overcurrent protection threshold,
The power supply control device according to claim 1, wherein the overcurrent determination unit includes a multiplier that outputs a voltage based on a voltage obtained by multiplying the voltage of the feedback terminal by the voltage of the gradient setting terminal. . The overcurrent determination unit
A first input terminal electrically connected to the monitor terminal; and a second input terminal electrically connected to the output terminal of the multiplier, wherein the voltage at the first input terminal is The power supply control device according to claim 6, further comprising a first comparator that outputs an overcurrent detection signal when the voltage is higher than a voltage of the second input terminal. The overcurrent determination unit
A third input terminal electrically connected to the monitor terminal; and a fourth input terminal electrically connected to the output terminal of the multiplier. The voltage of the third input terminal is The power supply control device according to claim 6, further comprising a second comparator that outputs an overcurrent detection signal when the voltage is lower than a voltage of the fourth input terminal.   The output voltage suppression unit includes a discharge acceleration semiconductor switch that is turned on when a first main electrode is electrically connected to the feedback terminal, a second main electrode is grounded, and the overcurrent detection signal is received. The power supply control device according to claim 7, wherein the power supply control device is provided.   10. A semiconductor integrated circuit, wherein the power supply control device according to claim 1 is formed on a semiconductor substrate. A transformer having a primary winding and a secondary winding;
A resonant capacitor connected in series with the primary winding;
A rectifying / smoothing unit that rectifies and smoothes the voltage generated in the secondary winding of the transformer;
A power supply control device having a monitor terminal, a feedback terminal, a first gate signal output terminal, and a second gate signal output terminal for inputting a voltage corresponding to a resonance current flowing in the primary winding;
A light emitting diode that emits light with a light amount corresponding to the output voltage of the rectifying and smoothing unit;
A capacitor having one end electrically connected to the feedback terminal and the other end grounded;
A phototransistor whose collector terminal is electrically connected to the feedback terminal, whose emitter terminal is grounded, and whose current transfer ratio changes according to the amount of light of the light emitting diode;
A first semiconductor switch having a drain terminal electrically connected to a positive electrode of a DC power source and a gate terminal connected to the first gate signal output terminal;
A second semiconductor switch having a drain terminal electrically connected to a source terminal of the first semiconductor switch, a source terminal grounded, and a gate terminal connected to the second gate signal output terminal;
The power supply control device
Whether or not the current flowing through the primary winding is an overcurrent by using an overcurrent protection threshold that decreases according to an elapsed time after the first semiconductor switch or the second semiconductor switch is turned on. An overcurrent determination unit for determining whether or not
An output voltage suppression unit that increases the switching frequency of the first and second semiconductor switches when the overcurrent determination unit determines that the current flowing through the primary winding is an overcurrent;
A resonant converter comprising:   The resonant converter according to claim 11, wherein the overcurrent determination unit uses a voltage based on a voltage of the feedback terminal as the overcurrent protection threshold. The power supply control device further includes a gradient setting terminal for setting a gradient of the overcurrent protection threshold value,
The resonance type according to claim 11, wherein the overcurrent determination unit uses a voltage based on a voltage obtained by multiplying a voltage of the feedback terminal by a voltage of the gradient setting terminal as the overcurrent protection threshold. converter.

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