KR100547290B1 - Method for series resonant converter control with synchronous rectifier - Google Patents

Abstract

The present invention relates to a series resonant converter for synchronous rectification.

According to the present invention, an input side switching unit converts a DC input voltage into an AC voltage using an input side switching element, and an LC resonant circuit unit connected to the input side switching unit to store energy in L and C using an LC resonance phenomenon and then transfer the output to an output. The primary winding is connected to the LC resonant circuit and the full-bridge circuit is composed of an insulated transformer and a switch of Q11, Q12, Q13 and Q14 that convert the resonant current into secondary current according to the turns ratio and transmit it through the secondary winding. In a series resonant converter having a synchronous rectification including an output side switching part in which a positive terminal is connected between a switch Q11 and a Q12 and a negative terminal is connected between a switch Q13 and a Q14, the output DC voltage has a predetermined level. A method of controlling such that (a) resonating the input voltage input through the input side switching section in the LC resonant circuit section During the process, when the resonant current is maintained at the positive stage, the synchronous rectification series resonant converter short-circuits the output circuit by using the output side switching unit to charge the positive resonant current of the LC resonant circuit unit to the resonant inductor of the LC resonant circuit unit. ; (b) controlling the output side switching unit to release the short circuit of the output side circuit, inputting the positive resonant current charged in the LC resonant circuit unit to the isolation transformer unit, performing synchronous rectification through the output side switching unit, and outputting the output voltage. ; (c) The synchronous rectification series resonant converter short-circuits the output circuit using the output-side switching circuit to short-circuit the LC resonance when the resonant current remains negative during the process of resonating the input voltage input through the input-side switching section in the LC resonant circuit section. Charging the negative resonant current of the circuit portion to the resonant inductor of the LC resonant circuit portion; And (d) controlling the output side switching unit to release a short circuit of the output side circuit, input a negative resonant current charged in the LC resonant circuit unit to the isolation transformer, perform synchronous rectification through the output side switching unit, and output the output voltage. It provides a step-up control method of a series resonant converter having a synchronous rectification, characterized in that it comprises a step.

According to the present invention, by using a synchronous rectifier of a series resonant converter for synchronous rectification as a boost converter, it is possible to operate as a series resonant boost converter, thereby reducing the manufacturing cost of an insulated power supply device for improving power factor. In addition, since all the switching elements perform zero voltage switching, there is an effect of increasing the efficiency of the power supply device.

Synchronous Rectification, Series Resonant Converter, Step-Up, Power Factor Correction

Description

Step-up control method of series resonant converter with synchronous rectification {Method for Series Resonant Converter Control with Synchronous Rectifier}

1 is a view showing an insulated power supply of a two-stage (Stage) method widely applied to mass production products,

2 is a circuit diagram of a series resonant converter power supply device performing synchronous rectification;

FIG. 3 is a circuit diagram of a series resonant converter power supply operating in a step-down type by connecting a boost converter to a circuit of a series resonant converter power supply for synchronous rectification. drawing,

4 is a circuit diagram of a high efficiency series resonance boost converter having synchronous rectification according to a preferred embodiment of the present invention;

5 is an equivalent circuit diagram of a high-efficiency series resonant boost type converter for synchronous rectification according to a preferred embodiment of the present invention.

6 is a view showing a simple operation waveform to understand the control of the high efficiency series resonant boost type converter for synchronous rectification according to a preferred embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

400: input power supply unit 410: rectifier

412: input side capacitor 420: input side switching unit

430: LC resonant circuit portion 440: insulated transformer

450: output side switching unit

The present invention relates to a series resonant converter. More particularly, the present invention relates to a method of operating a series resonant converter in a step-up mode while enabling zero voltage switching of the entire switching element, and a series resonant converter.

With the rapid development of electronic, computer and semiconductor technologies, our lives are changing rapidly. For example, in the past, you had to look at a map to find your way, but now the navigation system not only makes it easy to find your way to your desired destination, but also provides directions to your destination, depending on your transportation choices. In addition, due to the development of the Internet, you can enjoy shopping without going outside, meet and talk in cyberspace without being restricted by distance from people in distant places. It has also been developed to add convenience to life.

The electronic products that have been established as a part of our lives are mostly in the form of several devices combined in one main body, and each device in the electronic products is operated by supplying power supplied from the outside to perform the original operation of the electronic products. Make it.

However, since the power supplied to the main body is not the same as the operating power of the level required by each device in the electronic product, a DC / DC converter is placed in front of each device so that the power input from outside Convert to operating power. Since DC / DC converters are needed for each device, the better conversion efficiency, the more power-saving power supplies can be made.

Figure 1 is a two-stage (instage) insulated power supply that is widely applied to mass production products. The power supplied to the two-stage isolated type power supply is AC power, and the AC power is rectified through rectifiers D1 to D4 composed of bridge diodes, and then Vdc is formed by a general boost converter.

There are two types of converters: boost and step down. The boost converter is a converter whose input voltage is smaller than the output voltage, and the step-down converter is a converter whose input voltage is larger than the output voltage. In FIG. 1, the AC power passes through the boost converter through the rectifier, and the output voltage increases, and the increased output voltage Vdc passes through the isolated DC / DC converter to generate the output voltage Vo.

DC / DC isolated converters include flyback converters, forward converters, push-pull converters, half bridge converters, and series resonant converters. And a variety of circuit methods such as a parallel resonant converter (Parellel Resonant Converter).

2 is a circuit diagram of a series resonant converter power supply device for synchronous rectification. In a power conversion system, the control supply must have an output voltage that is constant with respect to variations in input voltage and load, and the output must be electrically isolated from the input. In FIG. 2, a switching device used a commonly used MOSFET (Metal-Oxide Semiconductor Field Effect Transistor). By turning on / off the output MOSFET of the transformer according to the polarity of the output current, the conduction loss caused by the forward voltage drop of the diode can be greatly reduced, which is a great advantage in a low voltage high current power supply.

3 is a circuit diagram in which a series resonant converter power supply operating in a step-down manner by connecting a boost converter to a circuit of a series resonant converter power supply for synchronous rectification is replaced with a series resonant step-up converter power supply. Since a general series resonant converter power supply operates in a step-down type, a boost converter must be connected to the series resonant converter power supply in order to convert to a boost type.

However, when the boost converter and the DC / DC converter is connected in series, it is difficult and costly to make the power conversion efficiency better than a single converter.

SUMMARY OF THE INVENTION In order to solve this problem, an object of the present invention is to provide a method and a series resonant converter for operating zero voltage switching of all switching elements while operating a series resonant converter in a boost type.

In order to achieve this object, according to the first object of the present invention, the input side switching unit for converting a DC input voltage into an alternating voltage using an input side switching element, connected to the input side switching unit L and C using the LC resonance phenomenon LC resonant circuit unit for storing energy and transmitting it to the output, the primary winding is connected to the LC resonant circuit unit, and the insulation transformer for converting the resonant current to the secondary current according to the ratio of the winding and transmitted through the secondary winding, and Q11, Q12, A full bridge circuit is formed by the switches of Q13 and Q14, and a series resonance is performed for synchronous rectification including an output side switching part having a positive terminal connected between switches Q11 and Q12 and a negative terminal connected between switches Q13 and Q14. A method of controlling an output DC voltage to a predetermined level in a type converter, the method comprising: (a) passing through an input switching unit; The synchronous rectification series resonant converter short-circuits the output side circuit by using the output side switching part while the resonant current maintains (+) while resonating the input input voltage by the LC resonant circuit part. Charging the resonant inductor in the LC resonant circuit portion; (b) controlling the output side switching unit to release the short circuit of the output side circuit, inputting the positive resonant current charged in the LC resonant circuit unit to the isolation transformer unit, performing synchronous rectification through the output side switching unit, and outputting the output voltage. ; (c) When the resonant current remains negative during the process of resonating the input voltage input through the input side switching part in the LC resonant circuit part, the synchronous rectification series resonant converter short-circuits the output side circuit using the output side switching part to perform LC resonance. Charging the negative resonant current of the circuit portion to the resonant inductor of the LC resonant circuit portion; And (d) controlling the output side switching unit to release the short circuit of the output side circuit, input the negative resonant current charged in the LC resonant circuit unit to the isolation transformer unit, perform synchronous rectification through the output side switching unit, and output the output voltage. It provides a step-up control method of the series resonant converter for synchronous rectification, characterized in that it comprises a step of.

According to a second object of the present invention, there is provided a method for switching and controlling a series resonant converter which performs synchronous rectification to receive a DC input voltage in a series resonant converter performing synchronous rectification and to output an output DC voltage higher than the DC input voltage. The step-up control method of a series resonant converter having synchronous rectification is characterized by applying the control method of claim 1 in a specific control section by dividing the control section.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are used as much as possible even if displayed on different drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

4 is a circuit diagram of a series resonant boost type converter for synchronous rectification according to a preferred embodiment of the present invention.

The series resonant voltage step-up converter according to the present invention uses a switching element on the input side and output side of a transformer for supplying power through a rectifying diode from an AC power source and electrically insulating between the input side circuit and the output side circuit. It is made up.

The input power supply unit 400 serves to supply power to the entire circuit, and may supply both AC power and DC power.

The rectifier 410 is used when the power of the input power source 400 is AC power, and converts AC power into DC power using bridge diodes D1, D2, D3, and D4.

Input side switching units (Q1, Q2, Q3, Q4) 420 perform zero voltage switching (ZVS) to reduce power loss in output side switching units (Q11, Q12, Q13, Q14) 450. The switching is performed according to the polarity of the resonant current input to the LC resonant circuit 430 through the input side switching unit 420.

The input capacitor 412 located between the rectifier 410 and the input side switching unit 420 serves as a filter to smooth and reduce the high frequency current of the input voltage input to the input side switching unit 420 via the rectifying unit 410.

The LC resonant circuit 430 stores electric energy coming from the input side switching unit 420 as magnetic energy of the resonant inductor and electrostatic energy of the resonant capacitor.

The isolation transformer 440 is positioned between the input side switching unit 420 and the output side switching unit 450 to electrically insulate the input side switching unit 420 and the output side switching unit 450, and the input side switching unit 420 Convert the input voltage and current.

The output side switching unit 450 is configured to perform zero voltage switching to prevent loss of power consumed during switching. In addition, in the present invention, the resonance is supplied from the input side switching unit 420 while the output side circuit is shorted by shorting the output side circuit by operating the switch of the output side switching unit 450 from the control method operating in the step-down type. The resonant current charged in the LC resonant circuit unit 430 is supplied to the insulation transformer 440 during the short circuited time when the current is charged into the resonant inductor and the output circuit recovers the short circuit by the switch operation of the output side switching unit 450. ) And an output voltage through the output side switching unit 450.

5 is an equivalent circuit diagram of a series resonant boost type converter for synchronous rectification according to a preferred embodiment of the present invention.

In the circuit diagram of FIG. 4, the switch of the input side switching unit and the output side switching unit is replaced with a MOSFET which can be used as a synchronous rectifier because of low switching loss and resistance in conduction. MOSFETs have a body diode and a body capacitor, and the body capacitor controls the slope of the voltage rise.

6 is a view showing a simple operation waveform to understand the control of the series resonant boost type converter for synchronous rectification according to a preferred embodiment of the present invention. The operation waveform of FIG. 6 performs different operations in 18 sections from t0 to t18. The operation of each section is as follows.

1.Interval 1 (t0-t1)

The resonant current Ir was held positive before t0, and t0 is the time point at which Q12 is turned off. When Q12 is off, the drain-source voltage Vds12 of Q12 increases, and the drain-source voltage Vds14 of Q14 starts to decrease. In section 1, the input side switch has Q1 and Q4 turned on so that the input side current flows through Q1 and Q4.

2. Section 2 (t1-t2)

t1 is the time when Vds12 becomes Vo and Vds14 becomes zero. When Vds14 goes to zero, then current begins to flow through DQ14. At this time, Vds14 becomes the forward voltage drop of the diode, which can be assumed to be 0V, which is sufficiently small compared to the output voltage. Therefore, turning on Q14 in section 2 results in zero voltage switching (ZVS) with zero turn-on switching loss. The operation waveform of FIG. 6 is a case where Q14 is turned on at t2. In section 2, the input side switch has Q1 and Q4 on, so the input side current flows through Q1 and Q4.

3. Section 3 (t2-t3)

t2 is a time point when Q14 is turned on, and when Q14 is turned on, energy stored in the resonant circuit is transferred to the output. Since the resonant current is positive in section 3, it becomes the positive direction of D11 and D14, but the current also flows through Q11 and Q14 because Q11 and Q14 are on. At this time, if the voltage drop of Q11 and Q14 is sufficiently smaller than the forward voltage drop of the diode, most of the current is synchronous rectification flowing through Q11 and Q14. Synchronous rectification continues until Q1 and Q4 are turned off at t3 just before the resonance current becomes zero.

4. Section 4 (t3-t4)

t3 is the time to turn off Q1 and Q4. When Q3 and Q4 are turned off, Vds3 begins to descend and Vds4 begins to rise. At t4, Vds3 becomes 0 and Vds4 becomes | Vac |.

5. Section 5 (t4 ~ t5)

t4 is the point when Vds3 becomes 0 and Vds4 becomes | Vac |. From t4, the resonant current flows through DQ2 and DQ3 on the primary side. Therefore, if Q2 and Q3 are turned on in the interval 5, zero voltage switching becomes zero. Since the resonant current is positive, the output current flows through Q11 and Q14 in the direction of DQ11 and DQ14. In the waveform, Q2 and Q3 are turned on at t5.

6. Section 6 (t5 ~ t6)

t5 is the time when Q2 and Q3 are turned on. At this time, the resonant current is larger than zero, but becomes shorter than zero past the zero point. If the resonant current is less than 0, the current flows in the positive direction of DQ2 and DQ3 at the input side in the positive direction of Q2 and Q3, and the current flows in the positive direction of Q11 and Q14 in the positive direction of DQ11 and DQ14 at the output side. When the resonant current is less than zero, the energy starts flowing back into the resonant circuit at the output, and after that, it turns off Q11 within the shortest time (at t6).

7. Section 7 (t6 ~ t7)

t6 is the time to turn off Q11. When Q11 is off, Vds11 rises and Vds13 begins to fall, and at t7, Vds11 becomes Vo and Vds13 becomes zero.

8. Section 8 (t7-t8)

t7 is the point when Vds11 becomes Vo and Vds13 becomes zero. From t7, the resonant current begins to flow through DQ13 and Q14 on the output side. Turning on Q13 in interval 8 results in zero voltage switching with zero switching loss. In the operating waveform, Q13 was turned on at t8.

9. Section 9 (t8-t9)

At t8, when Q13 is on and the voltage across Q13 is sufficiently smaller than the diode's forward voltage drop, most resonant currents begin to flow through Q13 and Q14 in the direction of DQ13. In the period between t8 and t9, energy flows into the resonant circuit from the input side and the resonant current starts to increase. The flow of energy is simultaneously transferred from the resonant capacitor to the resonant inductor at the input side power source. Interval 9 continues until Q14 is turned off at t9. t0 to t9 correspond to half of the entire switching period. The interval between t9 and t18 is opposite to the interval between t0 and t9, and the voltage and current polarities are reversed. The switching element replaces the switching element as an element facing up and down in one pole.

10. Section 10 (t9 to t10)

Before t9, the resonant current remained negative. t9 is the point at which Q14 is turned off. When Q14 is off, Vds14 of Q14 increases and Vds12 of Q12 begins to decrease. In section 10, the input side switch has Q2 and Q3 turned on so that the input current flows through Q2 and Q3.

11.Section 11 (t10 to t11)

At t10 Vds14 becomes Vo and Vds12 becomes zero. When Vds12 goes to zero, current begins to flow through DQ12. Turning on Q12 in section 11 results in zero voltage switching with zero turn-on switching loss. The operating waveform is when Q12 is turned on at t11. In section 11, input switch Q2 and Q3 are on, so input current flows through Q2 and Q3.

12.Section 12 (t11 to t12)

t11 is a time point when Q12 is turned on, and when Q12 is turned on, energy stored in the resonant circuit is transferred to the output. In the section 12, the current flows in the positive direction of DQ12 and DQ13 because the resonance current is negative, but the current also flows through Q12 and Q13 because Q12 and Q13 are on. At this time, if the voltage drop of Q12 and Q13 is sufficiently smaller than the forward voltage drop of the diode, most of the current is synchronous rectification flowing through Q12 and Q13. Synchronous rectification continues until Q2 and Q3 are turned off at t12 just before the resonance current becomes zero.

13. Section 13 (t12 to t13)

t12 is a time point at which Q2 and Q3 are turned off. When Q2 and Q3 are off, Vds4 starts to fall and Vds3 starts to rise. At t13, Vds4 becomes 0 and Vds3 becomes | Vac |.

14. Section 14 (t13-t14)

t13 is the time when Vds4 becomes 0 and Vds3 becomes | Vac |. From the point when Vds4 becomes 0 and Vds3 becomes | Vac |, the resonant current flows through DQ1 and DQ4 on the input side. Therefore, if Q1 and Q4 are turned on in the interval 14, zero voltage switching becomes zero. Since the resonant current is negative, the output current flows through Q12 and Q13 in the direction of DQ12 and DQ13. In the waveform, Q1 and Q4 are turned on at t14.

15.Section 15 (t14 to t15)

t14 is a time point when Q1 and Q4 are turned on. When Q1 and Q4 are on, the resonant current is less than zero, but soon beyond zero it becomes greater than zero. If the resonant current is greater than zero, it means that the current flows in the positive direction of DQ1 and DQ4 in the positive direction of DQ1 and DQ4 on the input side and in the positive direction of Q12 and Q13 in the positive direction of DQ12 and DQ13 on the secondary side. . When the resonant current is greater than zero, energy begins to flow back into the resonant circuit at the output. Therefore, Q13 is turned off within the shortest time (at t15) after it is greater than zero.

16.Section 16 (t15 to t16)

t15 is the time when Q13 is turned off. When Q13 is off, Vds13 rises and Vds11 begins to fall, and at t16, Vds13 becomes Vo and Vds11 becomes zero.

17.Section 17 (t16 to t17)

t16 is the time when Vds13 becomes Vo and Vds11 becomes 0. From t16, the resonant current begins to flow through DQ11 and Q12 on the output side. Turning on Q11 in interval 17 results in zero voltage switching with zero switching loss. In the operating waveform, Q11 was turned on at t17.

18.Section 18 (t17 to t18)

At t17, if Q11 is on and the voltage across Q11 is sufficiently less than the diode's forward voltage drop, most resonant currents begin to flow through Q11 and Q12 in the direction of DQ11. In section 18, energy flows into the resonant circuit from the input side and the resonant current starts to increase. The flow of energy is simultaneously transferred from the resonant capacitor to the resonant inductor at the input side power source. Interval 18 continues until Q12 is turned off at t18. Turning off Q12 at t18 is exactly the same as turning off Q12 at t0, completing the switching cycle.

In the operating waveform of the present invention, every switching period is repeated in the operating period of t0 to t18 described above. Section 9 (t8 ~ t9) and section 18 (t17 ~ t18) of the operating waveforms have the same function as switching on of boost converter, so switching on switching period (t0 ~ t9, or t9 ~ t18) The larger the ratio of, the larger the ratio of the output voltage to the input voltage. That is, the larger the switching on, the larger the output voltage at the same input voltage.

In the present invention, the gate driving circuit for driving the input side switching unit 420 and the output side switching unit 450 is easily known to those skilled in the art and will be omitted.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

As described above, according to the present invention, by using a synchronous rectifier of a series resonant converter for synchronous rectification as a step-up converter, it is possible to operate as a series resonant step-up converter, and thus to improve the power factor. The manufacturing cost can be reduced, and the efficiency of the power supply device can be increased by performing zero voltage switching of the entire switching element.

Claims (10)

Input side switching part for converting DC input voltage into AC voltage using input switching element, LC resonant circuit part which is connected to input switching part and stores energy in L and C using LC resonance phenomenon and transfers it to output, primary side The winding is connected to the LC resonant circuit part, and a full bridge circuit is composed of an insulated transformer part which converts the resonant current into a secondary current according to the turns ratio and transmits it through the secondary winding, and a switch of Q11, Q12, Q13, and Q14. A positive resonant series resonant converter including an output terminal having a positive terminal connected between Q12 and Q12 and a negative terminal connected between switches Q13 and Q14 has the output DC voltage of a predetermined level. In the control method so that, (a) The synchronous rectified series resonant converter short-circuits the output circuit by using the output side switch when the resonant current is maintained in the process of resonating the input voltage input through the input side switch in the LC resonant circuit. Charging the resonant inductor in the LC resonant circuit part to form a positive resonant current; (b) controlling the output side switching unit to release the short circuit of the output side circuit, inputting the (+) resonant current charged in the LC resonant circuit unit to the insulating transformer, and performing synchronous rectification through the output side switching unit, Outputting at the output voltage; (c) The synchronous rectification series resonant converter uses the output side switching unit to output the circuit on the output side when the resonant current is maintained while the input voltage input through the input side switching unit is resonating in the LC resonant circuit unit. Charging a resonant inductor in the LC resonant circuit part by shorting the negative resonant current of the LC resonant circuit part; And (d) controlling the output side switching unit to release the short circuit of the output side circuit, input the negative resonant current charged in the LC resonant circuit unit to the insulation transformer unit, and perform synchronous rectification through the output side switching unit, Outputting at the output voltage Step-up control method of the series resonant converter for synchronous rectification, characterized in that it comprises a. The method of claim 1, In the step (a), in inputting the input voltage to the input side switching part, the input voltage includes an alternating voltage and a direct current voltage, and the voltage drop of the switches Q11 and Q14 of the output side switching part is small enough to be large. And a current flows through the switches Q11 and Q14 of the output side switching unit to be synchronous rectification. The method of claim 1, In the step (a), when the resonance current is less than zero, the switch Q11 of the output side switching unit is turned off to prevent inflow of energy from the output voltage from the output side circuit to the LC resonant circuit portion, and the output side switching unit After the drain-source voltage of the switch Q11 becomes Vo and the drain-source voltage of the switch Q13 becomes 0, the switch Q13 is turned on to perform the zero voltage switching and short-circuit the output side circuit. Step-up control method of series resonant converter with synchronous rectification. The method of claim 1, In the step (a), the output circuit is short-circuited and at the same time, the LC resonant circuit unit charges the positive resonant current to the resonant inductor by resonating the input voltage coming through the input side switching unit. Step-up control method of a series resonant converter. The method of claim 1, In the step (b), the switch Q12 is turned on after the output of the switch Q14 is turned off so that the drain-source voltage of the switch Q14 increases and the drain-source voltage of the switch Q12 decreases to 0. By switching the zero voltage switch and releasing the short circuit of the output side circuit to input the positive resonant current charged in the LC resonant circuit part to the insulation transformer part and output the output voltage through the output side switching part as an output voltage. Step-up control method of a series resonant converter for synchronous rectification. The method of claim 1, In the step (c), the voltage drop of the switches Q12 and Q13 of the output side switching part is sufficiently small that most current flows through the switches Q12 and Q13 of the output side switching part to perform synchronous rectification. Step-up control method of series resonant converter. The method of claim 1, In the step (c), when the resonance current is greater than 0, the switch Q13 of the output side switching unit is turned off to prevent inflow of the output voltage from the output side circuit to the LC resonance circuit unit, and the switch Q13 of the output side switching unit After the drain-source voltage of Vo becomes Vo and the drain-source voltage of the switch Q11 becomes 0, the synchronous rectification is characterized in that the switch Q11 is turned on to switch the zero voltage and short the output circuit. Step-up control method of a series resonant converter. The method of claim 1, In the step (c), the output circuit is short-circuited and at the same time the input voltage switching through the input side switching unit resonates with the LC resonant circuit unit to charge the resonant current to the resonant inductor. Step-up control method of a series resonant converter. The method of claim 1, In the step (d), the switch Q13 of the output side switching unit is turned off so that the drain-source voltage of the switch Q13 increases to become Vo, and the drain-source voltage of the switch Q11 decreases to 0 so that the switch Q11 is turned on to perform the zero voltage switching and release the short circuit of the output side circuit to input the negative resonant current charged in the LC resonant circuit part to the insulation transformer part, and output the output voltage through the output side switching part. A step-up control method of a series resonant converter, characterized in that the synchronous rectification. delete

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