JP4830467B2 - Resonant type converter - Google Patents

Description

  The present invention relates to a resonant converter in which a resonant circuit is coupled to a switching element, and more specifically to a switching control technique for the resonant converter.

  2. Description of the Related Art Conventionally, in a switching power supply device, there is a resonance type converter in which a resonance circuit including a resonance inductor and a resonance capacitor is coupled to a switching element (for example, Patent Document 1). According to such a resonant converter, the current or voltage flowing through the switching element is fluctuated in a sinusoidal waveform, and when the switching element is turned on, the current or voltage flowing through the switching element can be made zero. An effect that switching loss and switching noise can be reduced is obtained.

  The resonance type converter includes a current resonance type that resonates the current flowing through the switching element, and a voltage resonance type that resonates the voltage applied to the switching element, and prevents a reverse current from flowing through the switching element. There are a half waveform type in which a resonance waveform appears only half of one cycle by connecting a diode in series with the switching element, and a full waveform type in which a resonance waveform appears for one cycle without providing such a diode.

  FIG. 6 shows a configuration example of a conventional general full waveform type current resonance converter. FIG. 7 is an operation waveform diagram of the current resonance type converter. In FIG. 6, SW1 is a switching element, Lr is a resonance inductor, Cr is a resonance capacitor, L is a reactor that intermittently inputs the input voltage Vin by switching and accumulates electric energy, D1 is a rectifier diode, and C is smooth. It is a capacitor. The output voltage Vout of the converter is output to the load 31, and the switching element SW1 is controlled by, for example, frequency modulation control so that the output voltage Vout becomes constant by a control circuit (not shown).

Conventionally, in such a current resonance type converter, the period during which the switching element SW1 is turned on is generally set to a certain time in accordance with the resonance frequency determined by the resonance inductor Lr and the resonance capacitor Cr. That is, after the switching element SW1 is turned on by frequency modulation control, the switching element SW1 is turned off at a timing when a certain time set in accordance with the resonance frequency has elapsed. The timing of turning off is most preferably a timing T _[pi and T _{2 [pi} resonance current ILr is zero, typically, these timing T _[pi including margin, opposite between T _{2 [pi} i.e. switching element SW1 It is set to the timing when the directional current is flowing.
JP-A-9-103070

  However, there is some variation in the inductance value of the resonance inductor and the capacitance value of the resonance capacitor. These values also change depending on the operating temperature. Therefore, if the period during which the switching element is turned on is set to a certain period in accordance with the resonance frequency determined by the resonance inductor and the resonance capacitor, the actual timing at which the switching element is turned off is set to a predetermined desired value. There was a problem that it deviated from the timing.

The timing of turning off the switching element, the reverse if during (T _[pi through T _{2 [pi} in FIG. 7) direction current is flowing, therefore the current after turning off flows in the internal diode of switch losses in the switching element Minutes only matter. However, or a timing before the timing T _[pi 7 prematurely timing of turning off, when or become timing later than the timing T _{2 [pi} and timing slow to OFF, the switching element is a forward current flows In this state, the switching element is turned off, so that the effects of reducing the switching loss and the switching noise, which are the advantages of the resonant converter, cannot be obtained. Furthermore, since the current flowing through the resonance inductor Lr changes abruptly, a very large electromotive force is generated in the resonance inductor Lr, which may destroy the switching element SW1.

Such a problem is not limited to the full-waveform resonance type converter as described above, and similarly occurs even in a half-waveform type resonance type converter. That is, when the switching element is turned off during the period (T _{0 to} T _π ) during which the resonance current flows, the same problem as described above occurs.

  Further, in the resonant converter, since it is difficult to control the timing for turning off the switching element as described above, this synchronous rectification method is applied when the synchronous rectification method using the switching element instead of the rectifier diode D1 is applied. There is also a problem that the same difficulty occurs in the switching control of the switching element. The synchronous rectification method has an effect of improving the power conversion efficiency of the converter by reducing the loss in the rectifier diode.

  An object of the present invention is to provide a resonance type that can perform switching control at an appropriate timing even when the inductance value of the resonance inductor and the capacitance value of the resonance capacitor vary or the value changes due to temperature characteristics. To provide a converter.

  In order to achieve the above object, according to the present invention, in a current resonance type converter, a resonance current flowing through a switching element is indirectly detected to control an off timing of the switching element. For the detection of the resonance current, the resonance current is not directly detected by using a detection resistor or the like, but the resonance current and the voltage between the electrodes of the resonance capacitor are changed synchronously to take advantage of the resonance capacitor. The resonance current is detected indirectly from the voltage.

  That is, power is intermittently taken from the input voltage (Vin) by turning on / off the first switching element (SW1), and an output voltage (Vout) is generated based on this power, and resonance with the resonance inductor (Lr) is achieved. In the resonant converter (10) in which a resonance circuit having a capacitor (Cr) is coupled to the first switching element (SW1) so that a current flowing through the first switching element resonates, the resonance capacitor And a detection circuit (2) for detecting a first timing when the current flowing through the first switching element (SW1) becomes a zero current or a reverse current based on the voltage (VCr) of the first switching element (SWr), and based on the detection output of the detection circuit Thus, the first switching element is turned off.

  Specifically, the detection circuit (2) compares the first voltage (Vin), which is the center potential of the resonance voltage of the resonance capacitor (Cr), with the voltage (VCr) of the resonance capacitor. A predetermined multiple from the second timing when the comparator (Comp1) and the first switching element (SW1) are turned on to the third timing when the comparison result of the first comparator (Comp1) changes (specifically, Is preferably configured to detect the first timing based on the time measurement result of the time measuring means.

  According to such a configuration, even if the resonance frequency changes due to variations in the values of the resonance inductor or the resonance capacitor or changes in the value due to the operating temperature, at a desired timing corresponding to the actual frequency of the resonance current. The first switching element can be turned off.

  Here, the first voltage to be compared by the first comparator depends on the type of the resonant converter (step-down type, step-up type, step-up / step-down type, etc.), and the input voltage, output voltage, input voltage and output voltage, respectively. The voltage is different from the voltage obtained by adding.

  Further, as the above-mentioned time measuring means, a capacitor (C11), one or a plurality of constant current sources (16, 17) for charging and discharging the capacitor, and a comparing means for comparing the voltage of the capacitor with a reference voltage (Comp3), the charging of the capacitor is started by the constant current source based on the first switching element being turned on, and the comparison result of the first comparing means is changed It is preferable that the discharge is started and the timing is completed based on a change in the result of comparison between the voltage of the capacitor and the reference voltage by the comparison means.

  In addition, in this item, although the code | symbol showing the corresponding relationship with embodiment was described in the parenthesis, this invention is not restrict | limited to this.

  According to the present invention, in the resonance type converter, the first switching element can be turned off at a desired timing corresponding to the actual frequency of the resonance current, whereby the tolerance of the characteristics of the elements constituting the resonance circuit can be increased. In addition, there is an effect that a stable operation can always be obtained even when the operating temperature changes relatively large.

  Also, when comparing full-wave type and half-wave type resonant converters, the full-wave type has the advantage that the change in switching frequency can be reduced with respect to load fluctuations. However, in such a full-waveform type resonant converter, it is possible to eliminate the difficulty of switching control without reducing the above-mentioned advantages. is there.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing a basic configuration of a current resonance type converter according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an entire configuration including a control circuit of the current resonance type converter.
In the current resonance type converter 10 of this embodiment, the input voltage Vin is intermittently input by the switching operation of the first switching element SW1 to accumulate energy in the reactor L, and the voltage based on the accumulated energy is smoothed. Thus, the switching power supply device supplies the output voltage Vout to the load 31. Further, a resonance circuit composed of a resonance inductor Lr and a resonance capacitor Cr is coupled to the first switching element SW1, thereby resonating the current flowing through the first switching element SW1 to realize soft switching. This resonant converter 10 is a full-wave-type current resonant converter in which the resonant current changes in a sine wave shape and a sinusoidal current waveform for one cycle appears in one resonance period.

  As shown in FIG. 1, the current resonance type converter 10 includes a first switching element SW1 composed of a P-channel MOSFET having a source terminal connected to an input terminal of the input voltage Vin, and a drain terminal of the first switching element SW1. A resonance inductor Lr and a resonance capacitor Cr connected in series between the ground (frame ground) and a connection point between the resonance inductor Lr and the resonance capacitor Cr and an output terminal of the output voltage Vout. The reactor L for energy storage, the smoothing capacitor C for smoothing the output voltage of the reactor L, and the current connected to the reactor L during the off period of the first switching element SW1 connected in parallel with the resonance capacitor Cr. Second switching element (for example, N-channel MOSFET) SW for synchronous rectification When, and a driving circuit 20, 23 for driving the first and second switching elements SW1, SW2, respectively.

  Further, as shown in FIG. 2, the current resonance type converter 10 is a control circuit that performs switching control of the first and second switching elements SW1 and SW2, and a detection resistor R11 that detects the output voltage Vout by resistance division. , R12, a constant current source 13 and a Zener diode Z1 for generating a reference voltage, an error amplifying circuit 11 for amplifying a difference voltage between the reference voltage and a detection voltage of the output voltage Vout, and an output of the error amplifying circuit 11 A VCO (voltage controlled oscillator) 12 that changes the oscillation frequency, a first control circuit 2 that determines a timing for turning off the first switching element SW1 based on a voltage between electrodes of the resonance capacitor Cr, and an electrode of the resonance capacitor Cr A second control circuit 3 for determining the timing for turning on the second switching element SW2 based on the inter-voltage; It is provided.

  The error amplifier circuit 11, the VCO 12, and the detection resistors R11 and R12 control the switching period of the first and second switching elements SW1 and SW2 by a frequency modulation method so that the output voltage Vout is maintained at a predetermined value. Is.

  The first control circuit 2 includes a first comparator Comp1 such as a hysteresis comparator that compares the input voltage Vin and the voltage of the resonance capacitor Cr, a first constant current source 15 and a Zener diode Z11 connected in series. A reference voltage generating circuit, a second constant current source 16 and a Zener diode Z12 formed in the same structure and size as each element of the reference voltage generating circuit, and a switch S11 connected in series to the Zener diode Z12. A capacitor C11 connected between the second constant current source 16 and the ground, and a third constant current source 17 connected in parallel with the capacitor C11 and in series between the second constant current source 16 and the ground. And the switch S12, the voltage at the cathode terminal of the Zener diode Z11 (reference voltage Vref), and the Zener diode Z12 voltage. A third comparator Comp3 such as a hysteresis comparator for comparing the voltage at the node terminal, an asynchronous flip-flop 19 for generating a timing signal for driving the first switching element SW1, and drive signals for the switches S11 and S12. A NAND circuit 14 to be generated, an inverter 18 and the like are provided.

  Among these, the constant voltage sources 15 to 17, the capacitor C11, the Zener diodes Z11 and Z12, the first and third comparators Comp1 and Comp3, the NAND circuit 14, and the inverter 18 cause the capacitor voltage VCr to become the central potential from the start of resonance. A time measuring circuit for measuring a period of about twice as long as the reaching period is configured.

  The flip-flop 19 is set so that “1” is set when the output of the VCO 12 changes to a low level and reset to “0” when the output of the third comparator Comp3 changes to a high level. A signal of the VCO 12 is input to the terminal S, and a signal based on the output of the third comparator Comp3 is input to the reset terminal R. Then, the signal at the output terminal Q is output to one input terminal of the NAND circuit 14, and the signal at the inverting output terminal NQ is output to the drive circuit 20.

  The first comparator Comp1 receives the input voltage Vin at the non-inverting input terminal and the voltage VCr of the resonance capacitor Cr at the inverting input terminal, and sends the comparison result signal to the other input terminal of the NAND circuit 14 and the inverter 18. Output.

  The second control circuit 3 that performs switching control of the second switching element SW2 drives the second comparator Comp2 such as a hysteresis comparator that compares the voltage VCr of the resonance capacitor Cr and the ground potential, and the second switching element SW2. And a flip-flop 22 for generating a signal.

  The flip-flop 22 is reset to “0” when the output of the VCO 12 changes to low level, and is reset to “1” when the output of the second comparator Comp2 changes to high level. A signal of the VCO 12 is input to the terminal R, and a signal based on the output of the second comparator Comp2 is input to the set terminal S. Then, the signal at the output terminal Q is output to the drive circuit 23.

FIG. 3 shows a time chart for explaining the switching operation of the current resonance type converter 10.
In the current resonance type converter 10 of this embodiment, as shown in FIG. 3, when the output of the VCO 12 becomes low level, "1" is set in the flip-flop 19 of the first control circuit 2, and the first switching element SW1 is turned on, and "0" is reset in the flip-flop 22 of the second control circuit 3, so that the second switching element SW2 is turned off. As a result, a current (= inductor current ILr) flows through the first switching element SW1, and resonance of this current is started. The voltage VCr of the resonance capacitor Cr also starts to resonate.

  The inductor current ILr changes in a sine wave shape with a period corresponding to the resonance frequency determined by the inductance value and the capacitance value of the resonance circuit, and the voltage VCr of the resonance capacitor Cr is a phase of π / 2 with the inductor current ILr. It changes with a sinusoidal waveform synchronized with a minute delay. The capacitor voltage VCr resonates with the input voltage Vin as the center potential.

When "1" is set in the flip-flop 19 and the output is sent to the NAND circuit 14, the switch S11 is turned on, and charging of the capacitor C11 is started by the second constant current source 16 of the timing circuit (timing T ₀ ). Before the output of the VCO 12 is high, the switch S11 is turned on and the switch S12 is turned off, and the potential of the inverting input terminal (point a) of the third comparator Comp3 is The voltage is almost the same as the reference voltage Vref. Therefore, the potential at the point a rises from the reference voltage Vref in proportion to the time when the charging is started.

Next, when the capacitor voltage VCr exceeds the input voltage Vin (timing Tπ _{/ 2} ), this is detected by the first comparator Comp1, and the switch S11 is turned on and the switch S12 is turned off based on the output. The Then, the difference current between the current (2I) of the third constant current source 17 and the current (I) of the second constant current source 16 is extracted from the capacitor C11 of the timing circuit. Decreases in proportion. Here, since the current drawn from the capacitor C11 is the same as the current at the time of charging, the change in the potential at the point a has the same magnitude in the opposite direction between charging and discharging.

Third comparator Comp3, by comparing the potential with a reference voltage Vref of a point, the timing of the potential of the point a becomes again the reference voltage Vref (T _[pi), i.e., the capacitor voltage VCr the input voltage from the resonance start The output is changed in a period twice as long as the period until it becomes Vin. The output of the third comparator Comp3 resets the flip-flop 19 and turns off the first switching element SW1.

  After the first switching element SW1 is turned off, a current flows only in the reverse direction through the built-in diode Di1 of the first switching element SW1, whereby the inductor current ILr resonates for one cycle and stops at zero current.

  The first comparator Comp1 turns the output high when the capacitor voltage VCr falls below the input voltage Vin again to turn off the switch S12, whereby the potential at the point a is returned to the reference voltage Vref.

Further, when the capacitor voltage VCr rises and falls from the start of resonance and becomes the ground potential again (timing T _2π ), the output of the second comparator Comp2 changes and “1” is set in the flip-flop 22. Then, the output of the flip-flop 22 turns on the second switching element SW2.

FIG. 4 shows a time chart for explaining the switching operation when a load current flows in the current resonance type converter 10.
As shown in FIG. 4, when the load current becomes relatively large, the resonance capacitor Cr is immediately affected by the electromotive force of the reactor L when the first switching element SW1 is turned on and the current resonance is started. The capacitor voltage VCr resonates with a slight delay in phase.

  Further, the inductor current ILr flowing through the first switching element SW1 is slightly shifted in the same manner as the phase of the resonance waveform is delayed due to the delay of the phase of the capacitor voltage VCr. Further, the center current of the resonance waveform has a value (Io) larger than zero.

In current resonant converter 10 of this embodiment, in this manner when the load current is relatively large, the first control circuit 2, the first switching element SW1 at the timing T ₀ is the resonance operation is turned on After the start, the timing (T ₁ ) at which the capacitor voltage VCr exceeds the input voltage Vin is detected, and the first switching element SW1 is turned off in a period twice that (timing T ₂ ).
Therefore, the first switching element SW1 is turned off at the timing when the current flowing through the element SW1 is zero or reverse.

  As described above, according to the current resonance type converter 10 of this embodiment, the inductance value of the resonance inductor Lr and the capacitance value of the resonance capacitor Cr vary, or these values change due to temperature characteristics. However, the switching control of the first switching element SW1 and the second switching element SW2 can be performed at a desired timing according to the actual resonance frequency. Therefore, a switching power supply device that does not have a particularly small tolerance of the constituent elements and that can always obtain stable operation even when the operating temperature changes relatively large, and that reduces switching loss and switching noise by so-called soft switching. Can be realized.

  In addition, when comparing a full-wave type and a half-wave type resonant converter, the full-wave type generally has the advantage that the change in switching frequency can be reduced with respect to load fluctuations, while the resonant switch However, according to the current resonance type converter 10 of the above-described embodiment, switching control is difficult without reducing the above-described advantages in the full-waveform type resonance converter. There is an effect that can be eliminated.

  The present invention is not limited to the above embodiment, and various modifications can be made. FIG. 5 shows a variation of the basic configuration of the current resonance type converter according to the present invention. In the figure, (a) is a step-down DC-DC converter, (b) is a step-up DC-DC converter, and (c) a step-up / step-down DC-DC converter. Components corresponding to those in FIG. ing.

  That is, Vin is an input voltage, Vout is an output voltage, L is a reactor that accumulates electric energy, SW1 is a switching element that intermittently supplies the input voltage Vin to the reactor L, SW2 is a switching element for synchronous rectification, and Lr is a resonance. Inductor, Cr is a resonance capacitor, C is a smoothing capacitor, and 31 is a load.

  The current resonance type converter of the present invention is not limited to the step-down DC-DC converter as shown in FIG. 1 and FIG. 5A, but is a step-up DC-DC converter as shown in FIG. The same can be applied to a step-up / step-down DC-DC converter as shown in FIG.

  In other words, a control circuit similar to that shown in FIG. 2 may be added to the basic configuration shown in FIGS. 5B and 5C so as to control the switching elements SW1 and SW2. However, since the center potential of the interelectrode voltage of the resonance capacitor Cr that resonates is different in each configuration of FIGS. 5A to 5C, the comparison reference voltage input to the first comparator Comp1 depends on each configuration. Need to change.

  Specifically, in the step-down DC-DC converter of FIG. 1 or FIG. 5A, the center potential is the input voltage Vin, so the input voltage Vin is input to the first comparator Comp1 as a comparison reference voltage. . On the other hand, in the step-up DC-DC converter of FIG. 5B, since the center potential is the output voltage Vout, the output voltage Vout is input as a comparison reference voltage. Further, in the step-up / step-down DC-DC converter of FIG. 5C, the center potential is a voltage obtained by adding the input voltage Vin and the negative output voltage Vout. Therefore, the added voltage is calculated from the input voltage Vin and the output voltage Vout. Generate and input as a comparison reference voltage.

  In the above embodiment, a non-insulated converter is illustrated, but the present invention can be similarly applied to an isolated converter that supplies power to the output side via a transformer. . The present invention can be similarly applied to a half-wave type current resonance type converter in which a diode is connected in series with the first switching element so that a reverse current does not flow through the first switching element.

  In addition, the detailed configuration specifically shown in the embodiment can be appropriately changed without departing from the gist of the invention.

It is a circuit diagram which shows the basic composition of the current resonance type | mold converter of embodiment of this invention. It is a circuit diagram which shows the control circuit of the current resonance type | mold converter of embodiment. It is a time chart which shows the switching operation of the current resonance type | mold converter of embodiment. It is a time chart which shows switching operation in case load current is flowing. The variation of the basic composition of the current resonance type converter concerning the present invention is shown, (a) is a step-down type converter, (b) is a step-up type converter, and (c) A buck-boost type converter. It is a circuit diagram which shows the conventional current resonance type | mold converter. It is a time chart which shows the switching operation of the conventional current resonance type | mold converter.

Explanation of symbols

10 Current Resonant Type Converter 11 Error Amplifier 12 VCO
19, 22 Flip-flop SW1 1st switching element SW2 2nd switching element L reactor C Smoothing capacitor Lr Resonance inductor Cr Resonance capacitor Comp1 1st comparator Comp2 2nd comparator Comp3 3rd comparator 15-17 Constant current source C11 Time circuit capacitor Z11, Z12 Zener diode S11, S12 Switch Vin Input voltage Vout Output voltage

Claims (11)

An electric power is intermittently taken from an input voltage by turning on and off the first switching element, an output voltage is generated based on the electric power, and a resonance circuit having a resonance inductor and a resonance capacitor is provided in the first switching element. In a resonant converter coupled to resonate a current flowing through the first switching element,
A detection circuit for detecting a first timing at which a current flowing through the first switching element becomes a zero current or a reverse current based on a voltage of the resonance capacitor;
A resonance type converter configured to turn off the first switching element based on a detection output of the detection circuit. The detection circuit includes:
A first comparator that compares a first voltage that is a central potential of a resonance voltage of the resonance capacitor with a voltage of the resonance capacitor;
Timing means for timing a predetermined multiple period from the second timing when the first switching element is turned on to the third timing when the comparison result by the first comparator is changed,
2. The resonant converter according to claim 1, wherein the first timing is detected based on a time measurement result of the time measuring means. A step-down resonance type in which the first switching element, the resonance inductor, and the resonance capacitor are connected in series between an input terminal of the input voltage and a terminal to which a reference potential of the input voltage is applied. A converter,
3. The resonant converter according to claim 2, wherein the first voltage compared by the first comparator is the input voltage. A step-up resonance converter in which the first switching element, the resonance inductor, and the resonance capacitor are connected in series between an output terminal of an output voltage and a terminal to which a reference potential of the output voltage is applied. Because
3. The resonant converter according to claim 2, wherein the first voltage compared by the first comparator is the output voltage. The first switching element, the resonant inductor, and the resonant capacitor are step-up / step-down resonant converters connected in series between the input terminal of the input voltage and the output terminal of the output voltage,
The resonant converter according to claim 2, wherein the first voltage compared by the first comparator is a voltage obtained by adding the input voltage and the output voltage. The timing means is
A capacitor,
One or more constant current sources for charging and discharging the capacitor;
Comparing means for comparing the voltage of the capacitor with a predetermined reference voltage,
When the first switching element is turned on, charging of the capacitor is started by the constant current source, and discharging of the capacitor is started when a comparison result by the first comparing means is changed. 6. The resonant converter according to claim 2 , wherein the time measurement is completed based on a change in a result of comparison between the voltage of the capacitor and the reference voltage. A second switching element for synchronous rectification that is turned on during a period in which the first switching element is off and supplies a current to the output side;
The resonant converter according to any one of claims 1 to 6 , wherein the second switching element is turned on based on a voltage of the resonance capacitor. The resonance according to any one of claims 1 to 7 , wherein the resonance type is a full waveform type in which a diode for preventing a reverse current from flowing through the first switching element is not connected in series with the first switching element. Shape converter. A reactor that stores electrical energy;
A first field effect transistor for storing electric energy by supplying an input voltage to the reactor by a switching operation;
A smoothing circuit that smoothes and outputs a voltage based on the electrical energy accumulated in the reactor;
A resonance circuit comprising a resonance inductor and a resonance capacitor connected to the first field effect transistor so that a current flowing through the first field effect transistor resonates;
A frequency modulation circuit that outputs a timing signal for starting switching of the first field effect transistor and changes a frequency of the timing signal based on a detected value of an output voltage or an output current;
A first comparator for comparing the voltage of the resonance capacitor and the input voltage;
A timing circuit that counts a predetermined period from the output timing of the timing signal to the timing at which the output of the first comparator changes;
A first logic circuit that turns on the first field effect transistor based on the output of the timing signal and turns off the first field effect transistor based on completion of timing of the timing circuit;
A resonance type converter characterized by comprising: A second field effect transistor for synchronous rectification that supplies current to the reactor during a period when the first field effect transistor is off;
A second comparator for comparing the voltage of the resonance capacitor and the ground potential;
A second logic circuit that turns off the second field effect transistor based on the output of the timing signal and turns on the second field effect transistor based on a change in the output of the second comparator;
10. The resonant converter according to claim 9, further comprising: The timing circuit is
A first constant current source and a second constant current source for flowing the same first current;
A first Zener diode connected in series to the first constant voltage source;
A second Zener diode and a first switch connected in series to the second constant current source;
A capacitor connected in parallel with the second Zener diode and the first switch;
A third constant current source that draws twice the first current from the capacitor;
A second switch for disconnecting / conducting a current path of the third constant current source;
A third comparator for comparing the cathode voltage of the first Zener diode and the voltage of the capacitor;
The first switch is turned off from the output timing of the timing signal to the timing when the output of the first comparator changes, and the capacitor is charged by the current of the second constant current source, and the output of the first comparator is The second switch is turned on from the changed timing, and the difference current between the third constant current source and the second constant current source is drawn from the capacitor, and the time measurement is completed due to the change in the comparison result of the third comparator. 11. The resonant converter according to claim 9 , wherein a signal is output.

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