KR102335419B1 - Power circuit - Google Patents

Abstract

The present invention discloses a power supply circuit that digitally controls power conversion. The power circuit includes a control unit, wherein the control unit determines the on time of the switching element to correspond to the base point of the resonance period of the voltage between the drain and the source of the switching element resonant after the zero current point of the primary side of the power conversion circuit, and , configured to provide a driving signal obtained by changing the on-time of the switching element in units of resonance periods in response to a change in load to the switching element.

Description

power circuit {POWER CIRCUIT}

The present invention relates to a power supply circuit, and more particularly, to a power supply circuit for digitally controlling power conversion.

A power circuit is provided in various devices such as an audio device, a display device, a notebook computer, and a white home appliance, and the power circuit may be implemented in a flyback converting method to convert DC power or AC power.

The power supply circuit of the flyback conversion method may include a power conversion circuit including a transformer and a switching element for driving the primary side of the transformer. The switching element performs a switching operation of driving the primary side of the transformer using a driving pulse, and the transformer is configured to convert power from the primary side to the secondary side in response to the switching operation of the switching element.

Power conversion in the power circuit is accompanied by power loss. Therefore, the power circuit should be designed to minimize power loss occurring in power conversion.

Power loss in power circuits can occur for a variety of reasons.

First, when the switching element operates to have a fixed on-time regardless of load variation, excessive power may be supplied in response to a small load. Accordingly, power loss may occur unnecessarily. In order to solve this problem, the on-time of the switching element may be controlled in response to a change in the load. However, when the on-time of the switching element is reduced in response to a decrease in the load, the operating frequency of the switching element is increased. As a result, there is a problem in that the switching element acts as a noise source.

In addition, a switching loss occurs in the switching element during power conversion. The above-described switching loss is generated by a difference in voltage applied between the drain and the source of the switching element in the turned-on state and the turned-off state.

As described above, power loss may occur in the power circuit from various viewpoints, and there is a need to design the power circuit to minimize the power loss.

It is an object of the present invention to use a digital signal processing block to control the driving of a switching element in response to the feedback of an output voltage, and to a power circuit that can be applied to various devices such as an audio device, a display device, a notebook computer, and a white home appliance is intended to provide.

Another object of the present invention is to determine the on-time of the switching element in correspondence to the base point of the resonance period of the resonance generated by the difference between the input voltage and the voltage between the drain and the source of the switching element, and determine the on-time in response to a change in the load. An object of the present invention is to provide a power supply circuit capable of reducing power loss by gradually changing within a resonance period while controlling in units of a resonance period.

In the power circuit for performing power conversion in the power conversion circuit by driving the switching element of the present invention, the on-time corresponding to the base point of the resonance period of the voltage between the drain and the source of the switching element is gradually changed in response to a change in load. and a control unit configured to provide, to the switching element, a driving signal to which the on-time, which is changed gradually, is applied to the switching element.

The power supply circuit of the present invention comprises: a power conversion circuit for performing power conversion by driving a switching element; a feedback circuit for providing a feedback signal corresponding to a load state of the power conversion circuit; Detects a zero current time point of the primary side current of the power conversion circuit, and provides a delayed detection signal from the zero current time point to a time point corresponding to the base point of the resonance period of the voltage between the drain and the source of the switching element sensing circuit; and by performing counting after the zero current time point, a time point at which a predetermined value and a count value coincide with the on time point of the switching element is determined, and the on time point of the switching element is gradually changed in response to a change in the load. and a control unit that changes in units of resonance periods and provides a driving signal to which the gradually changed ON time is applied to the switching element.

According to the present invention, it is possible to provide a power supply circuit applicable to various devices such as an audio device, a display device, a notebook computer, and a white home appliance.

In addition, according to the present invention, the driving of the switching element can be controlled by feeding back the state of the load using the digital signal processing block.

In addition, according to the present invention, the on-time of the switching element is controlled in units of the resonance period of the voltage between the drain and the source of the switching element, the voltage between the drain and the source of the switching element is increased and decreased within the resonance period, and the drain and the source Power loss can be reduced by turning on the switching element in a state where the voltage difference between them is small.

1 is a block diagram showing an embodiment of a power supply circuit of the present invention;
Figure 2 is a detailed block diagram of the control unit of Figure 1;
3 is a circuit diagram illustrating an operation corresponding to turn-on of a switching element;
Fig. 4 is a waveform diagram corresponding to the operation of the switching element of Fig. 3;
5 is a circuit diagram for explaining an operation corresponding to turn-off of a switching element;
Fig. 6 is a waveform diagram corresponding to the operation of the switching element of Fig. 5;
7 is a timing diagram for explaining a change in an ON time of a switching element;

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The terms used in the present specification and claims are not limited to a conventional or dictionary meaning, and should be interpreted in a meaning and concept consistent with the technical matters of the present invention.

The embodiments described in this specification and the configurations shown in the drawings are preferred embodiments of the present invention, and do not represent all of the technical spirit of the present invention, so various equivalents and modifications that can replace them at the time of the present application there may be

Referring to FIG. 1 , the power circuit includes a power supply unit 10 , a start-up circuit 12 , a power conversion circuit 14 , a switching element Q, an output circuit 16 , a feedback circuit 18 , and a control unit 20 . ) and a zero current sensing circuit 22 . In FIG. 1 , RL is a load, D is a diode for blocking the flow of counter electromotive current, C is a capacitor for charging the operating voltage applied to the control unit 20 , and R is a resistance.

The power circuit of the present invention implemented as shown in FIG. 1 may be implemented to be applied to various devices such as an audio device, a display device, a notebook computer, and a white home appliance. For example, when applied to an audio device, the controller 20 may be configured as one package. And, when applied to a display device, the control unit 20 and the start-up circuit 12 may be included in one package. And, when applied to a notebook computer and white goods, the control unit 20, the start-up circuit 12, and the switching element Q may be included in one package.

A configuration and operation of each component configured in the embodiment of FIG. 1 will be described.

The power supply unit 10 may provide AC power or DC power, and for the purposes of the present invention, the power supply unit 10 may provide an input voltage VIN and an input current i _VIN.

The start-up circuit 12 provides an operating voltage Vcc for the operation of the control unit 20 by using the input voltage VIN of the power supply unit 10 in response to a section in which the power conversion circuit 14 does not provide the operating voltage Vcc. it is to do

The power conversion circuit 14 converts the input voltage VIN and may include a transformer for this purpose. The input voltage VIN may be an AC voltage or a DC voltage, but for the description of the embodiment, it is exemplified as an AC voltage.

The transformer includes a plurality of coils for inducing a current corresponding to the voltage change, a number of coils may be divided into a primary side _(P N) and the outlet _(S N) and secondary coil (N _A). The LM shown in the electric power conversion circuit 14 is a representation of the inductance component of the primary winding (N _P) equivalently, hereinafter referred to as the inductor (LM). An inductor voltage V _LM and an inductor current i _M may be applied to the inductor LM. In order to distinguish it from _{the input-side current i VIN} corresponding to the input voltage VIN of the power conversion circuit 14, the _{inductor current i M} of the inductor LM is described as the _{primary-side (NP} ) current of the transformer, that is, the power conversion circuit 14 can be Transformer performs power conversion in accordance with the turns ratio of the primary winding (N _P) and the secondary side (N _S). Then, the secondary coil (N _A) of the transformer is sensed according to a change in the current primary _(P N) to the turns ratio.

The switching element Q _{has a drain connected to the primary side N P} of the transformer and may be formed of a high voltage NMOS transistor using a field effect transistor (FET). The source of the switching element Q is connected to the ground through the resistor R, and the driving signal GD is provided to the gate of the switching element Q.

A switching element (Q) and the switching operation by a drive signal (GD), it can be driving the primary winding (N _P) of the transformer in conjunction with the turn-on and turn-off of the switching device (Q). The driving signal GD may be provided as a pulse waveform in which a high level and a low level are periodically repeated. The switching element Q is turned on by the high-level driving signal GD, and at this time, the voltage Vds between the drain and the source of the switching element Q may be “0V” in the embodiment. And, the low-level driving The switching element Q is turned off by the signal GD, and at this time, the voltage Vds between the drain and the source of the switching element Q is the input voltage VIN and the voltage of the secondary side N _{S due} to the turn ratio of the primary side N _P ) can be the sum of the voltage delivered to it.

The voltage between the drain and the source of the switching element Q resonates after the point in time when the _{primary side (NP) current of the transformer of the power conversion circuit 14 becomes 0 (Zero).} At this time, the resonance occurs due to the difference between the input voltage VIN and the voltage Vds between the drain and the source applied to the switching element Q, and corresponds to the LC resonance caused by the parasitic capacitor between the inductor LM and the drain-source of the switching element. The resonator is an input voltage VIN and the secondary side (N _S) voltage is a first value obtained by adding the voltage delivered to the primary winding (N _P) by the turns ratio (VIN + (Np / Ns) Vo) and the input voltage VIN and the secondary side of a a second value (VIN- (Np / Ns) Vo ) of the convergence caused by the car and having a resonant period the input voltage VIN of the voltage (N _S), minus the voltage that is delivered to the primary winding (N _P) by the turns ratio do.

In addition, the sensing signal CS may be output from a node between the source of the switching element Q and the resistor R, and it may be understood that the sensing signal CS has a value corresponding to a voltage applied to the resistor R. .

On the other hand, the power conversion and a secondary side (N _S), the output circuit 16 to the transformer of the circuit 14 is configured, the output circuit 16 forwards the voltage of the secondary side of the transformer (N _S) to the load (RL) do. To this end, the output circuit 16 includes a diode Do and a capacitor Co, and the current passing through the diode Do _{can be expressed as a diode current i D} , and the load by charging and discharging the capacitor Co. The current provided by (RL) can be expressed as the output current (io). The diode current i _D corresponds to the secondary-side current of the power conversion circuit 14 , that is, the transformer.

The feedback circuit 18 generates a feedback signal FB corresponding to the state of the load RL and transmits the feedback signal FB to the control unit 20 . The feedback circuit 18 may generate the feedback signal FB by detecting the output voltage Vo or the output current io provided to the load. The feedback circuit 18 may be variously configured according to the intention of the manufacturer, and may be typically configured using a photo coupler.

On the other hand, a zero current detection circuit 22 is configured to sense the sensed voltage V _A that is output from the secondary coil (N _A) of the transformer of the power conversion circuit 14.

Sensing the voltage V _A is the primary side of the point that is the transformer kept at the high level, while the secondary side (N _S) current of a transformer flows and the secondary side of the transformer (N _S) current of the diode current i _D is to be zero (Zero) ( When _{the current of N P} ) becomes zero, the level starts to drop, and theoretically, the level may drop along the resonance of the voltage between the drain and the source of the switching element Q. Sensing the voltage V _A has to detect the zero current point, the current of the secondary side (N _S) to the diode current i _D is zero (Zero) is the time that is the primary side (N _P) of the transformer is a transformer that is zero (Zero) It can be used as a zero current sensing signal for

A zero current detection circuit 22 is configured to provide a sense signal V _BD delayed by a predetermined time from the zero-current point in time for sensing the voltage V _A will start to fall from the high level to the control unit 20. The zero current sensing circuit 22 may include elements having capacitance and resistance for delay.

The resonance period of the voltage between the drain and the source of the switching element Q may be known in advance by a test. Therefore, the zero current sensing circuit 22 _{is configured to have a preset delay time for matching the point at which the sensing signal V BD} reaches the low level with the base point of the resonance period of the voltage between the drain and the source of the switching element Q. can be

Meanwhile, the controller 20 may include a digital signal processing block 210 and a gate driver 220 as shown in FIG. 2 . The gate driver 220 generates and outputs a driving signal GD corresponding to the control of the digital signal processing block 210 . In addition, the digital signal processing block 210 receives the sensing signal CS, the sensing signal V _BD, and the feedback signal FB, and controls generation and output of the driving signal GD of the gate driver 220 .

The control unit 20 is operated by the operating voltage VCC provided from the start-up circuit 12 at the initial stage when the input voltage VIN is applied, that is, before the power conversion circuit 14 is driven, and the power conversion circuit 14 is driven. after it is operated by using a sensing voltage V _a supplied from the secondary coil (N _a) as an operating voltage VCC.

The operation of controlling the driving signal GD in response to the sensing signal CS, the sensing signal V _BD, and the feedback signal FB is performed by the digital signal processing block 210 . However, for convenience of description, the present invention describes that the control operation of the digital signal processing block 210 is performed by the controller 20 .

When the load RL is kept constant, the controller 20 may perform an operation of controlling the generation and output of the driving signal GD so that the output current io may be kept constant in response to the sensing signal CS.

_{Then, the control unit 20 performs counting after the zero current time of the primary side (NP} ) current of the power conversion circuit 14, and the time when the predetermined value and the count value coincide with the ON time of the switching element (Q) decide Here, the predetermined value may be set to correspond to a base point of a desired resonance period among resonance periods of the voltage between the drain and the source of the switching element Q. In this way, the on-time of the switching element Q may be determined, and the control unit 20 changes the on-time of the switching element Q in units of resonance periods in response to a change in the load RL, and within one resonance period. The driving signal GD, which can be changed gradually and to which the changed ON time is applied, is provided to the switching element Q).

The control unit 20 determines the on time point corresponding to the base point of the resonance period of the voltage between the drain and the source of the switching element Q after the zero current point of the _{primary side (NP) current of the power conversion circuit 14} For this, the sensing signal V _BD of the zero current sensing circuit 22 is used.

In addition, the control unit 20 uses the feedback signal FB to increase or decrease the on time of the switching element Q according to a change in the load RL.

An operation of the power circuit configured as in FIGS. 1 and 2 will be described. First, the operation of the power circuit in a state in which the switching element Q is turned on will be described with reference to FIGS. 3 and 4 , and the power circuit in a state in which the switching element Q is turned off with reference to FIGS. 5 and 6 is described. Describe the action.

3 and 4 , when the driving signal GD is provided at a high level, the switching element Q is turned on. The switching element Q may have a diode function to block the flow of counter electromotive force equivalently, and the voltage Vds between the drain and the source may be formed to be low.

After the switching element Q is turned on, the input current i _VIN gradually increases. The input current i _VIN flows through the inductor LM and the switching element Q of the power conversion circuit 14, and after the switching element Q is turned on, the inductor voltage V _LM is maintained at the input voltage VIN level, and the inductor The current i _M follows the increase of the input current i _{VIN .}

In this case, the output circuit 16 may discharge the energy accumulated in the capacitor Co to the load RL in response to the switching element Q being turned off in the period before the driving signal GD. Therefore, the output voltage Vo decreases.

Further, the secondary side from the primary side of the power conversion circuit _{(14) (N P) (} N S) to the energy transfer is not performed. Therefore, the diode current i _D does not flow, and the sensing voltage V _A and the sensing signal V _BD are not formed.

Thereafter, when the driving signal GD is provided at a low level, the switching element Q is turned off. The operation of the power circuit will be described with reference to FIGS. 5 and 6 .

When the switching element Q is turned off, it _{does not provide a path for the flow of the input current i VIN} and the drain-source voltage Vds is formed high. At this time, the drain and the source between the switching element (Q) may be a "winding ratio of the input voltage (VIN) +1 winding (N _P) and the secondary side _{(N S) (N P /} N S) * Output voltage Vo" have. That is, the input current i _VIN does not flow, and the inductor voltage V _LM may be low. In one example, the inductor voltage V _LM may be a "primary winding (N _P) turns ratio (N _P / N _S) of the secondary _(S N) * Output voltage Vo". In addition, the voltage between the drain and the source of the switching element Q at the turn-on time may have a transient characteristic.

When the switching device (Q) is turned off by the energy stored in the inductor (LM), generated in the closed loop for the inductor current i _M including the inductor primary winding (N _P) of the (LM) and the power conversion circuit 14 do. The flow of the diode current i _{D in the secondary side N S} of the current conversion circuit 14 is initiated by induced in the primary side (N _{P ) current flow.} The amount of diode current i _{D follows} the amount by which the inductor current i _M is reduced.

At this time, the output circuit 16 transfers _{the energy by the diode current i D} to the load RL while charging the capacitor Co. Therefore, the output voltage Vo increases.

The flow of the diode current i _D of the power conversion circuit 14 may be sensed in the _{auxiliary coil N A .} A secondary coil (N _A) is a sensing voltage V _A for outputting a high level, a zero current detection circuit 22 is also detected in a high level corresponding to the sensing voltage V _A signal V _BD corresponding to the flow of diode current i _D Output at high level. In one example, a high level sensing voltage V _A and the high level of the sense signal V _BD may be in the "turns ratio of the secondary winding (N _A) and the secondary side _{(N S) (N A /} N S) * Output voltage Vo" have. And, to be the "winding ratio (N _A / N _P) * input voltage VIN of the secondary winding (N _A) and the primary winding (N _P)" of the low level sensing voltage V _A and the low level of the sense signal V _BD is theoretically and may have negative values. However, in practice, the sensing voltage V _A and the low-level sensing signal V _BD may be theoretically set to maintain a substantially “0” level with respect to a case having a negative value.

When the turn-off state of the switching device (Q) maintained as described above, the diode current i _D of the secondary winding _(S N) of the power conversion circuit 14 is a 0 (Zero). At this time, the _{inductor current i M that is the primary side (NP} ) current of the power conversion circuit 14 also becomes 0 (Zero).

The voltage Vds between the drain and the source of the switching element Q in the turned-off state is formed to be high. When the switching element Q is turned on in this state, a large difference in the voltage Vds between the drain and the source may result in a large switching loss in the switching element Q, and as a result, a large amount of power loss may occur.

In order to reduce the above-described power loss, in the present invention, the on-time of the switching element Q can be adjusted by the digital control of the digital signal processing block 210 . The switching element Q may be controlled to be turned on at a point in time when the voltage difference between the drain and the source is the lowest.

As described above, the zero current sensing circuit 22 is the drain of the switching element Q after the zero current time point when the _{inductor current i M, which is the primary side (NP} ) current of the power conversion circuit 14, becomes 0 (Zero). _A delay operation corresponding to the sensing voltage V _{A is performed so that the sensing signal V BD} reaches a low level when the voltage between the source and the source coincides with the base point Pb of the resonance period. Voltage of the resonance cycle base point (Pb) of may be a "winding ratio of the input voltage VIN-1 side _(P N) and the secondary side _{(N S) (N P /} N S) * Output voltage Vo".

That is, the switching element Q may be turned on at the base point Pb of the resonance period with the lowest voltage difference between the drain and the source. As a result, the switching loss of the switching element Q may be minimized, and power loss by the switching element Q may be reduced.

4 and 6, the inductor current i _{M, which is the primary side (NP} ) current of the power conversion circuit 14, becomes 0 (Zero), that is, the zero current time point is described as T1, and the zero current sensing circuit 22 ) at which the sensing signal V _BD outputted from the low level reaches the low level is referred to as T2. In contrast to these, when the sensing voltage V _A reaches the low level, the time when the sensing signal V _BD reaches the low level is delayed, and the time when the sensing signal V _BD reaches the low level is the time of the switching element Q. It can be understood that the voltage between the drain and the source coincides with the base point (Pb) of the resonance period.

As described above, the control unit 20 uses the sensing signal V _BD output from the zero current sensing circuit 22 to resonate the switching element Q after the zero current time point T1 of the output side of the power conversion circuit 14 . The on time of the switching element Q may be determined to correspond to the base point Pb of the resonance period of the voltage between the drain and the source of , and the driving signal GD applied with the on time may be provided to the switching element Q .

In addition, the control unit 20 performs counting, and the count value coincides with a predetermined value so as to be set to correspond to the base point Pb of the desired resonance period among the resonance periods of the voltage between the drain and the source of the switching element Q determining the on-time of the switching element Q as the on-time of the switching element Q, and changing the on-time of the switching element Q in units of resonance periods in response to a change in the load RL, and gradually changing within one resonance period, The driving signal GD may be provided to the switching element Q.

In more detail, the operation of the control unit 20 will be described with reference to FIG. 7 .

The control unit 20 performs counting and can know how many times the resonance has been performed using the counting result. The control unit 20 may count using the resonance period pulse generated at the base point of the resonance period, and determines whether the count value matches a predetermined value.

The controller 20 generates a resonance cycle pulse BD synchronized with a timing corresponding to the base point of each resonance cycle with reference to a time point T2 when the _{detection signal V BD reaches the low level.} When the count value and the predetermined value match, the control unit 20 determines the on-time by determining that it corresponds to the base point of the desired resonance period among the resonance periods of the voltage between the drain and the source of the switching element Q.

The control unit 20 may receive the feedback signal FB corresponding to the load state of the output side of the power conversion circuit 14 and detect a change in the load by using the feedback signal FB.

When a change in load is sensed using the feedback signal FB, the controller 20 may change the on-time so that the on-time of the switching element Q can be increased or decreased in response to an increase or a decrease in the load.

The control unit 20 may change the on time point in units of the resonance period in response to a change in load, for example, switching between the base point Pb3 of the third resonance period and the base point Pb4 of the fourth resonance period as shown in FIG. 7 . The on-time of the device Q may be configured to gradually decrease.

The controller 20 may set an enable section including one or more resonance periods in response to a change in load, and in the embodiment of FIG. 7 , the enable section is defined as the base point Pb3 of the third resonance period and the fourth resonance It is illustrated between the base points (Pb4) of the period.

The control unit 20 may sequentially generate transition control signals BDS1 to BDSn that are sequentially shifted at every cycle of the driving signal GD during the enable section based on the resonance cycle pulse BD of the base point PB3 of the third cycle, The control unit 20 sequentially turns on from the base point Pb3 of the third resonance period to the base point Pb4 of the fourth resonance period in response to each transition control signal BDS1 to BDSn at every cycle of the driving signal GD (P1 to Pn). ) may provide a variable driving signal GD.

The switching element Q receives a driving signal GD whose on time is changed every cycle from P1 to Pn in response to a change in load from the control unit 20, and a driving signal GD whose ON time gradually decreases in response to a decrease in load can be driven by

As described above, the controller 20 may change the on-time so that the on-time of the driving signal GD is increased or decreased. If the controller 20 is implemented as an analog circuit, it may not be easy to design to increase or decrease the on time. However, the controller 20 implemented in the present invention uses a digital signal processing block. Therefore, the controller 20 implemented in the present invention can easily implement increasing or decreasing the on-time of the driving signal GD by using a digital operation.

As described above, the present invention can provide a power circuit for various devices such as an audio device, a display device, a notebook computer, and a white home appliance, and uses a digital operation to feed back the state of the load to easily control the driving of the switching element. There are advantages to being able to

In addition, the present invention controls the on-time of the switching element for driving the power change in units of the resonance period of the voltage between the drain and the source of the switching element and gradually increases and decreases within the resonance period so that the voltage between the drain and the source is controlled. Power loss can be reduced by turning on the switching element in

Claims (10)

In the power supply circuit for performing power conversion in the power conversion circuit by driving a switching element,
By performing counting after the zero current time point of the primary side of the power conversion circuit, an ON time point corresponding to a base point of a resonance period of a voltage between a drain and a source of the switching element is determined, and the ON time point corresponds to a change in load and a control unit that gradually changes in units of the resonance period and provides a driving signal to which the gradually changed ON time is applied to the switching element. According to claim 1,
The control unit includes a digital signal processing block,
The digital signal processing block determines a time point at which a predetermined value and a count value coincide with the on time point by performing counting after the zero current point of the primary side of the power conversion circuit, and the drive according to the change in the load A power circuit for gradually changing the on-time so that the on-time of the switching element can be increased or decreased for every cycle of the signal. 3. The method of claim 2,
The control unit calculates the count value by counting using a resonance period pulse generated at a base point of the resonance period. 3. The method of claim 2,
Detects the zero current time point at which the primary-side current of the power conversion circuit reaches zero, and provides a delayed detection signal from the zero current time point to a time point corresponding to the base point of the resonance period to the control unit A power supply circuit further comprising a zero current sensing circuit to: 5. The method of claim 4,
The zero current sensing circuit detects the zero current time point by using a sensing voltage sensing the current of the primary side of the power conversion circuit, and delays the sensing voltage to output the sensing signal. According to claim 1,
The control unit generates a transition control signal that is sequentially shifted during an enable period including at least one resonance period in response to a change in the load, and changes the ON time in synchronization with the sequential shift of the transition control signal power circuit. According to claim 1,
The control unit receives a feedback signal corresponding to the state of the load, and the power circuit for detecting a change in the load by using the feedback signal. According to claim 1,
and a start-up circuit for providing an operating voltage to the control unit in response to an initial input of power, wherein the start-up circuit and the control unit are included in one package. 9. The method of claim 8,
A power supply circuit in which the switching element is further included in the package. a power conversion circuit for performing power conversion by driving a switching element;
a feedback circuit for providing a feedback signal corresponding to a load state of the power conversion circuit;
Zero current for detecting a zero current point of the primary side current of the power conversion circuit and providing a delayed detection signal from the zero current point to a point corresponding to the base point of the resonance period of the voltage between the drain and the source of the switching element sensing circuit; and
By performing counting after the zero current time point, a time point at which a predetermined value and a count value coincide is determined as the ON time point of the switching element, and the ON time point of the switching element is gradually changed in response to a change in the load to generate resonance The power circuit comprising: a control unit that changes in units of a cycle and provides a driving signal to which the gradually changed ON time is applied to the switching element.

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