CN112217398B

CN112217398B - Power conversion device with damping control, module and operation method thereof

Info

Publication number: CN112217398B
Application number: CN202011150406.XA
Authority: CN
Inventors: 姚宇桐; 洪宗良
Original assignee: Shenzhen Shengnengjie Technology Co ltd; Yarongyuan Technology Shenzhen Co ltd; Yaruiyuan Technology Shenzhen Co ltd
Current assignee: Shenzhen Shengnengjie Technology Co ltd; Yarongyuan Technology Shenzhen Co ltd; Yaruiyuan Technology Shenzhen Co ltd
Priority date: 2020-10-23
Filing date: 2020-10-23
Publication date: 2023-01-20
Anticipated expiration: 2040-10-23
Also published as: CN112217398A

Abstract

A power conversion device with damping control, a module and an operation method thereof, in particular to a power conversion device capable of reducing electromagnetic interference, a damping control module and an operation method thereof. A power conversion device: when the damping control module detects the resonance voltage from the secondary side, the damping control module performs damping operation on the resonance voltage to reduce the amplitude of the resonance voltage by providing damping; the damping control module: when the level of the winding voltage is in an enabled interval set by the reference voltage, the logic control unit enables the damping unit to provide the damping for the secondary side winding so as to reduce the amplitude of the winding voltage; the invention can reduce the electromagnetic interference of the power conversion device, thereby enabling the power conversion device to conform to the safety standard in the full frequency band.

Description

Power conversion device with damping control, module and operation method thereof

Technical Field

The invention relates to a power conversion device with damping control, a module and an operation method thereof, in particular to a power conversion device with damping control, a module with damping control and an operation method thereof, which can reduce electromagnetic interference.

Background

Conventionally, the requirement of the flyback converter has been increased because the input terminal and the output terminal can be isolated by a transformer and can be applied to the control of power supply (PD). In particular, the flyback converter can be used for voltage-up conversion or voltage-down conversion of power, so that the flyback converter becomes a mainstream converter in the industry under the condition that the power can be flexibly configured.

However, when the conventional flyback converter is usually operated in Discontinuous Conduction Mode (DCM), the current of the secondary winding of the transformer is reduced to 0, and then the parasitic capacitance of the primary-side power switch resonates with the exciting inductance. The resonance generates a resonance voltage with a frequency of about several hundred kHz to 10MHz, which may cause the electromagnetic interference (EMI) middle frequency band to exceed the safety specification. However, in the conventional solution, an RC damping shock absorber is additionally installed on the primary side of the transformer to absorb the amplitude of the resonant voltage, but the effect of this method is not accurate enough and the suppression effect is limited, and the flyback converter may continuously consume power during operation, resulting in poor efficiency of the flyback converter.

Therefore, how to design a power conversion device with damping control, a damping control module and an operation method thereof to actively reduce the amplitude of the resonant voltage is a subject to be studied by the present inventors.

Disclosure of Invention

To solve the above problems, the present invention provides a power conversion apparatus with damping control, comprising: the transformer comprises a primary side and a secondary side, wherein the primary side receives an input voltage, and the secondary side is coupled with the output end. And the power switch is coupled with the primary side. The control module is coupled with the power switch and controls the power switch to be continuously switched on and off so as to convert the input voltage into the output voltage through the transformer and provide the output voltage through the output end. And the damping control module is coupled with the secondary side. When the damping control module detects the resonance voltage from the secondary side, the damping control module performs damping operation on the resonance voltage to reduce the amplitude of the resonance voltage by providing damping.

Further, the damping control module obtains winding voltage by detecting a secondary side winding of the secondary side, and the winding voltage generates resonance voltage when the power switch is turned off; and the damping control module judges whether the winding voltage is the resonance voltage according to the winding voltage and the output voltage.

Further, the secondary side includes a rectification module, the rectification module including: and the rectifier switch is coupled with the secondary side winding. The output capacitor is coupled with the rectifier switch and the output end and provides output voltage to the output end. And the rectification controller is coupled with the rectification switch and controls the rectification switch to be continuously switched on and off synchronously with the power switch. The damping control module is integrated with the rectification controller to provide damping operation according to the resonant voltage when the rectification controller controls the rectification switch to be switched off.

Further, the damping control module includes: the resonance detection unit receives the output voltage and the winding voltage, compares the winding voltage with a threshold voltage corresponding to the output voltage, and provides an enabling signal representing that the winding voltage starts to generate oscillation according to a comparison result. The quasi-position trigger unit receives the winding voltage, compares the winding voltage with the reference voltage and provides a trigger signal representing the damping providing time according to the comparison result. The logic control unit receives the enable signal and the trigger signal. And the damping unit is coupled with the logic control unit and the secondary side winding. When the level of the winding voltage is in an enabling interval set by the reference voltage, the logic control unit enables the damping unit to provide damping for the secondary side winding.

Furthermore, the logic control unit enables the damping unit only when the level of the winding voltage reaches the enabling interval for the first time.

Further, the damping control module further comprises: and the counting unit is coupled with the resonance detection unit and the logic control unit. The counting unit sets the expected times, and counts the oscillation times after the winding voltage begins to oscillate; when the number of times reaches the expected number of times, the counting unit provides an enabling signal representing that the number of times of oscillation reaches the expected number of times.

Further, the damping control module further comprises: the open circuit detection unit is coupled with the logic control unit and the secondary side. Wherein, the open circuit detecting unit detects whether the path between the output end and the secondary side winding is open circuit or not, and provides an open circuit signal to the logic control unit; when the path is broken and the level of the winding voltage is in the enabling interval, the logic control unit enables the damping unit.

Further, the damping control module further comprises: and the disabling unit receives the winding voltage and the output voltage and is coupled with the logic control unit. When the disabling unit knows a path channel between the output end and the secondary side winding through the winding voltage and the output voltage or the power switch is switched on, the disabling unit informs the logic control unit to disable the damping unit through a disabling signal.

Furthermore, the disabling unit informs the logic control unit to disable the damping unit through a disabling signal when the level of the winding voltage is not in the enabling interval according to the winding voltage and the reference voltage.

In order to solve the above problems, the present invention provides a damping control module, and therefore, the damping control module of the present invention is coupled to a power conversion device, the power conversion device includes a primary side and a secondary side, and the primary side is coupled to a power switch, and the damping control module includes: and the resonance detection unit receives the output voltage output by the power conversion device and the winding voltage of the secondary side and the side winding of the secondary side, compares the winding voltage with the threshold voltage corresponding to the output voltage, and provides an enabling signal representing that the winding voltage starts to generate oscillation according to the comparison result. The quasi-position trigger unit receives the winding voltage, compares the winding voltage with the reference voltage and provides a trigger signal representing the damping providing time according to the comparison result. The logic control unit receives the enable signal and the trigger signal. And the damping unit is coupled with the logic control unit and the secondary side winding. When the level of the winding voltage is in an enabling interval set by the reference voltage, the logic control unit enables the damping unit to provide damping for the secondary side winding so as to reduce the amplitude of the winding voltage.

Further, the method also comprises the following steps: the counting unit is coupled to the level triggering unit and the logic control unit. The counting unit sets the expected times, and counts the oscillation times after the winding voltage begins to oscillate; when the number of times reaches the expected number of times, the counting unit provides an enabling signal representing that the number of times of oscillation reaches the expected number of times.

Further, the method also comprises the following steps: the open circuit detection unit is coupled with the logic control unit and the secondary side. Wherein, the open circuit detecting unit detects whether a path between an output end for providing the output voltage and the secondary side winding is open circuit or not, and provides an open circuit signal to the logic control unit; when the path is broken and the level of the winding voltage is in the enabling interval, the logic control unit enables the damping unit.

Further, the method also comprises the following steps: and the disabling unit receives the winding voltage and the output voltage and is coupled with the logic control unit. When the disabling unit knows a path channel between the output end and the secondary side winding through the winding voltage and the output voltage or the power switch is conducted, the disabling unit informs the logic control unit to disable the damping unit through a disabling signal.

To solve the above problems, the present invention provides an operation method of a damping control module. Therefore, the operation method of the damping control module of the present invention is applied to a power conversion device including a primary side and a secondary side, wherein the primary side is coupled to a power switch; the power conversion device converts an input voltage into an output voltage through a primary side and a secondary side by controlling a power switch to be continuously turned on and off, and the operation method comprises the following steps: the output voltage is received with a winding voltage on a secondary side winding of the secondary side. The winding voltage is compared with a threshold voltage corresponding to the output voltage to provide an enable signal representing the start of oscillation of the winding voltage according to the comparison result. The winding voltage is compared with a reference voltage to provide a trigger signal representative of the timing of providing damping based on the comparison. And judging whether the level of the winding voltage is in an enabling interval set by the reference voltage or not according to the enabling signal and the triggering signal. And when the level of the winding voltage is in the enabling interval, enabling the damping unit to provide damping for the secondary side winding so as to reduce the amplitude of the winding voltage.

Further, the operation method further comprises the following steps: the damping unit is enabled only when the level of the winding voltage reaches an enabling interval for the first time.

Further, the method of operation further comprises the steps of: the expected number of times is set. After the winding voltage begins to oscillate, the number of oscillations is counted. And providing an enabling signal representing the number of the oscillations reaches the expected number when the number reaches the expected number.

Further, the method of operation further comprises the steps of: it is detected whether a path between an output terminal supplying an output voltage and the secondary side winding is open. When the path is broken and the level of the winding voltage is in the enabling interval, the damping unit is enabled.

Further, the method of operation further comprises the steps of: and when the path channel between the output end and the secondary side winding is known according to the winding voltage and the output voltage or the power switch is conducted, the damping unit is forbidden to be energized. And disabling the damping unit when the level of the winding voltage is not in the enabling interval according to the winding voltage and the reference voltage.

Has the advantages that:

the main objective and effect of the present invention is to detect whether the winding voltage generates the resonant voltage by using the damping control module coupled to the secondary side, and provide damping when the winding voltage generates the resonant voltage, so that the resonant voltage is not gradually damped in an underdamped manner, but is rapidly damped within a resonant period to greatly reduce the amplitude of the resonant voltage. By reducing the amplitude of the resonant voltage, the electromagnetic interference (EMI) of the power conversion device is reduced, so that the power conversion device can meet the safety standard in the full frequency band.

The damping control module of the present invention has a programmable design, can precisely control damping parameters and delay time, even has the functions of light-load frequency hopping and turning off, and does not need to use an external resistor or a capacitor passive component. And because the pin position is similar to that of the secondary side controller of the transformer, the method can be integrated into the secondary side controller, parameters are set and recorded by the digital controller, and the method has high security and circuit design sharing property, so that different damping parameters can be applied under different load conditions, and the advantage of taking efficiency and electromagnetic interference (EMI) into consideration is achieved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a diagram of a power conversion device with shock absorption control according to the present invention;

FIG. 2 is a schematic diagram of a voltage across a power switch with a single switching cycle according to the present invention;

FIG. 3 is a block diagram of the circuit of the damping control module of the present invention;

FIG. 4A is a schematic circuit diagram of a damping unit according to a first embodiment of the present invention;

FIG. 4B is a schematic circuit diagram of a damping unit according to a second embodiment of the present invention;

FIG. 5 is a schematic diagram of a logic circuit of the damping control module according to the present invention;

FIG. 6A is a schematic waveform diagram of a power conversion apparatus according to a first embodiment of the present invention;

FIG. 6B is a schematic waveform diagram illustrating a power conversion apparatus according to a second embodiment of the present invention;

FIG. 6C is a waveform diagram illustrating a power conversion apparatus according to a third embodiment of the present invention.

Wherein, 100 power conversion devices, 100-1 input terminals, 100-2 output terminals, 10 transformers, 10-1 primary sides, 102 primary side windings, 10-2 secondary sides, 104 secondary side windings, 20 power switches, coss parasitic capacitors, 30 control modules, 40 rectifier modules, 402 rectifier switches, 404 output capacitors, 406 rectifier controllers, 50 damping control modules, 502 resonance detection units, OP1 comparators, 504 level trigger units, OP2 comparators, tn negative edge triggers, 504-1 counting units, 506 logic control units, F1, F2 triggers, AND gates, 508 damping units, 508-1 damping units, 508-2 damping units, 602 counting units, cr counters, tp positive edge triggers, 604 open-circuit detection units, NOT reverse gates, 606 disabling units, OP3, OP4 comparators, OR OR gates, 702 on-off units, 704 functional on-off units, Q switches, R resistors, GND switches

200 loads, vin input voltage, vo output voltage, vds voltage, vr resonance voltage, vw winding voltage, vaux auxiliary voltage, vt threshold voltage, vref reference voltage, PWM pulse width modulation signal, sc control signal, ss enable signal, st trigger signal, se enable signal, so open circuit signal, sd disable signal, sd1 first disable signal, sd2 second disable signal, S signal, sl load signal, sf output signal, sa output signal, sp output signal, il path current, da damping, t 1-t 4, t 01-t 02 and t11 time.

Detailed Description

The technical content and the detailed description of the present invention are described below with reference to the drawings:

fig. 1 shows a power conversion device with shock absorption control according to the present invention. The power conversion device 100 receives an input voltage Vin from an input terminal 100-1 and provides an output voltage Vo to power a load 200 from an output terminal 100-2. The power conversion apparatus 100 includes a transformer 10, a power switch 20, a control module 30, a rectification module 40, and a damping control module 50, and the transformer 10 includes a primary side 10-1 and a secondary side 10-2. The primary side 10-1 includes a primary side winding 102, and one end of the primary side winding 102 receives an input voltage Vin through an input terminal 100-1, and the other end is coupled to the power switch 20. The secondary side 10-2 includes a secondary side winding 104, and the secondary side winding 104 couples the rectifying module 40 and the output terminal 100-2.

The control module 30 is coupled to the power switch 20, and controls the power switch 20 to be continuously turned on and off by the PWM signal PWM to convert the input voltage Vin into the output voltage Vo through the primary side 10-1 and the secondary side 10-2 of the transformer 10, so as to provide the output voltage Vo through the output terminal 100-2 to power the load 200. The rectifying module 40 includes a rectifying switch 402, an output capacitor 404 and a rectifying controller 406, wherein one end of the rectifying switch 402 is coupled to the secondary winding 104, and the other end of the rectifying switch 402 is coupled to the output capacitor 404 and the output terminal 100-2. The output capacitor 404 stores the output voltage Vo and provides the output voltage Vo to the load 200 through the output terminal 100-2. The rectifier controller 406 is coupled to the rectifier switch 402, and controls the rectifier switch 402 to be continuously turned on and off in synchronization with the power switch 20 through the control signal Sc. The advantage of the rectifier switch 402 being turned on and off continuously in synchronization with the power switch 20 is that the power loss of the rectifier module 40 can be reduced, thereby increasing the operation efficiency of the power conversion apparatus 100. The present invention can utilize the on/off of the rectifier switch 402 to determine the damping control, as will be described in further detail below.

The damping control module 50 is coupled to the secondary side 10-2, and when the damping control module 50 detects a resonance voltage from the secondary side 10-2, the damping control module 50 damps the resonance voltage to reduce the amplitude of the resonance voltage by providing damping. Specifically, please refer to fig. 2, which is a waveform diagram of the cross voltage across the power switch with a single switching period according to the present invention, and refer to fig. 1. The single switching period is a voltage-crossing diagram of the two terminals of the power switch 20 when the control module 30 controls the power conversion apparatus 100 to operate in the Discontinuous Conduction Mode (DCM). When control module 30 controls power switch 20 to be on (Ton), the voltage across Vds of power switch 20 is approximately 0V. When the control module 50 controls the power switch Q to turn off (time t 1), the voltage across the drain-source (D-S) is substantially maintained at the input voltage Vin plus n times the output voltage Vo (n is the turns ratio of the primary winding 102 to the secondary winding 104). At time t2 when the control module 30 controls the power switch 20 to turn off (Toff), the energy stored in the exciting inductor of the primary winding 102 is completely released, so that the current of the secondary side 10-2 is completely zero, and an open circuit state is presented, and at this time, the primary side 10-1 has a set of RLC resonance tanks (i.e., a line resistance, the exciting inductor of the primary winding 102, and a parasitic capacitance Coss across the power switch 20), so that resonance occurs (time t 2-t 3). The resonance oscillates back and forth with the input voltage Vin as the center point, and the amplitude gradually attenuates in an underdamped manner. The oscillating voltage is called the resonance voltage Vr. Therefore, in summary, when the power switch 20 is turned off (time t 1) and the energy stored in the exciting inductor is completely released, the primary side 10-1 of the transformer 10 generates the resonant voltage Vr. The resonant voltage Vr can be obtained by detecting the voltage Vds across the power switch 20, the winding voltage Vw of the secondary winding 104, and even the auxiliary voltage Vaux of the auxiliary winding 106. Therefore, the amplitude of the resonance voltage Vr can be reduced by performing the damping operation for the 3 points.

The damping control module 50 detects whether the winding voltage Vw oscillates (i.e., the resonant voltage Vr) by coupling to the secondary side 10-2, and provides damping to make the resonant voltage Vr not gradually attenuate in an underdamped manner when the winding voltage Vw oscillates, but rapidly attenuate in a resonant period to greatly reduce the amplitude of the resonant voltage Vr (i.e., provide damping operation). By reducing the amplitude of the resonance voltage Vr, the electromagnetic interference (EMI) of the power conversion apparatus 100 is reduced, so that the power conversion apparatus 100 meets the safety standard in the full frequency band. It should be noted that in an embodiment of the present invention, the purpose of the damping control module 50 detecting the winding voltage Vw and damping the winding voltage Vw is only to obtain a voltage waveform of the winding voltage Vw (which corresponds to the voltage waveform of the primary side 10-1 when the power switch 20 is turned off) with a better quality through the electrical isolation of the transformer 10, but not limited thereto. In other words, the damping control module 50 can also perform a damping operation on the cross voltage Vds or the auxiliary voltage Vaux, and the corresponding coupling and detecting positions thereof are changed accordingly. In addition, in an embodiment of the invention, the power conversion apparatus 100 is a flyback converter, but not limited thereto, as long as the converter generates the resonant voltage Vr as shown in fig. 2 when the power switch 20 is turned on or off, the damping control module 50 of the invention can be applied to perform the damping operation.

Further, as shown in fig. 1, since the coupling position of the damping control module 50 is preferably the secondary side 10-2 of the power conversion apparatus 100, the coupling position and the detection point of the damping control module 50 are similar to those of the rectification controller 406. In this case, the damping control module 50 may be integrated with the rectification controller 406 to provide a damping operation according to the resonance voltage Vr when the rectification controller 406 controls the rectification switch 402 to be turned off. By integrating the damping control module 50 and the rectification controller 406, the overall circuit size of the power conversion apparatus 100 can be reduced, and the rectification controller 406 and the damping control module 50 can perform synchronous operation by using the same signal source, thereby improving the system stability of the power conversion apparatus 100.

Fig. 3 is a block diagram of the damping control module according to the present invention, which is combined with fig. 1-2. The damping control module 50 includes a resonance detecting unit 502, a level triggering unit 504, a logic control unit 506 and a damping unit 508, and the logic control unit 506 is coupled to the resonance detecting unit 502, the level triggering unit 504 and the damping unit 508. The resonance detecting unit 502 receives the output voltage Vo and the winding voltage Vw, and compares the winding voltage Vw with a threshold voltage Vt corresponding to the output voltage Vo to determine whether the winding voltage Vw oscillates (i.e., generates the resonance voltage Vr). The corresponding threshold voltage Vt may be set to be proportional times of the output voltage Vo (for example, but not limited to, 0.8 times of the output voltage Vo). When the winding voltage Vw is greater than the threshold voltage Vt, it represents that the energy stored in the magnetizing inductor of the primary winding 102 has not been released, and when the winding voltage Vw is less than the threshold voltage Vt, it represents that the energy stored in the magnetizing inductor of the primary winding 102 has been released, so that the voltage of the primary side 10-1 starts to oscillate.

The resonance detection unit 502 provides the enable signal Ss to the logic control unit 506 according to the comparison result, and the level change of the enable signal Ss represents whether the winding voltage Vw starts to oscillate. It should be noted that in an embodiment of the present invention, since the voltage level (usually within ten volts) that the controller (referred to as the control module 30, the rectifier controller 406 and the damping control module 50 in the present invention) can accept is usually much lower than the voltage level (possibly to several hundred volts) on the main path of the power conversion apparatus 100, in an embodiment of the present invention, if the controller receives or detects the voltage on the main path of the power conversion apparatus 100 (such as, but not limited to, the winding voltage Vw, the output voltage Vo, etc.), it may need to be stepped down (i.e., stepped down proportionally to the voltage level that the controller can tolerate). The step-down process can be usually achieved by a conventional step-down technique (such as a voltage divider resistor), and for convenience of description, additional details regarding the conventional step-down technique are not described herein.

The level triggering unit 504 receives the winding voltage Vw, and compares the winding voltage Vw with the reference voltage Vref to determine whether the voltage level of the resonant voltage Vr reaches the enabling interval, so as to enable the damping unit 508 to provide the damping Da. The reference voltage Vref is used to set an enable interval. For example, but not limited to, when the reference voltage Vref is set to 0V, it represents that the damping unit 508 is enabled when the voltage level of the resonant voltage Vr is a positive value, and the damping unit 508 is disabled when the voltage level is a negative value (or a negative value is enabled and a positive value is disabled). The level trigger unit 504 provides the trigger signal St to the logic control unit 506 according to the comparison result, and the level variation of the trigger signal St represents the timing of providing the damping Da. However, the logic control unit 506 still includes other logic determination mechanisms, so even if the level triggering unit 504 determines that the damping Da is available, the logic control unit 506 still needs to further determine whether to control the damping unit 508 to provide the damping Da. It should be noted that the level trigger unit 504 can set the control manner of the enabling interval, such as but not limited to the positive half cycle and the negative half cycle of the resonant voltage Vr, or the whole interval (i.e. the positive half cycle and the negative half cycle) of the resonant voltage Vr is the enabling interval. After the winding voltage Vw reaches the enabling interval preset by the reference voltage Vref, single, multiple or continuous triggering can be set, and various combinations such as positive half-cycle triggering or negative half-cycle triggering are set, and the size of the enabling interval is determined by the reference voltage Vref.

The logic control unit 506 receives the enable signal Ss and the trigger signal St, and determines whether to enable the damping unit 508 according to the enable signal Ss and the trigger signal St. The damping unit 508 is coupled between the logic control unit 506, the secondary winding 104 and the ground GND, and receives the enable signal Se provided by the logic control unit 506. When logic control unit 506 enables damping unit 508 via enable signal Se, damping unit 508 provides damping Da to reduce the amplitude of resonant voltage Vr, and thus the amplitude of primary side 10-1 voltage (coupled via transformer 10).

Further, the logic control unit 506 includes 2 ways to enable the damping unit 508. One of them is to enable the damping unit 508 every time the voltage level of the resonance voltage Vr reaches the enabling interval. Therefore, the logic control unit 506 enables the damping unit 508 when the voltage level of the resonant voltage Vr is in one half of the cycle (positive half cycle or negative half cycle), and disables the damping unit 508 in the other half cycle. The advantage of this control method is that the amplitude of the resonant voltage Vr can be rapidly reduced to a very low level, which is beneficial to the effect of electromagnetic interference (EMI) suppression. Alternatively, the logic control unit 506 enables the damping unit 508 only when the voltage level of the resonant voltage Vr reaches the enabling interval for the first time, and after the single enabling, the damping unit 508 is not enabled again. After the damping unit 508 is enabled for the first time, the amplitude of the resonance voltage Vr can be reduced to be below a certain amplitude, and the subsequent amplitude of the resonance voltage Vr will not exceed the certain amplitude. The advantage of this control method is that the disposable enabling damping unit 508 can save the power consumption of the damping control module 50, thereby improving the operation efficiency of the entire power conversion device 100, and the resonance voltage Vr with lower amplitude can still make the electromagnetic interference (EMI) of the power conversion device 100 meet the safety standard. However, the operator can adjust the enabling times according to the actual requirement.

The damping unit 508 has various embodiments, such as, but not limited to: like the embodiment of the switch Q with the resistor R shown in fig. 4A, the switch Q of the damping unit 508-1 is enabled by the enabling signal Se to provide the damping Da to the resistor R. Alternatively, as in the embodiment of fig. 4B, the active damper (i.e. the damping unit 508-2) is enabled by the enable signal Se to provide the damping Da in the form of a current source. Specifically, the higher the level of the winding voltage Vw, the higher the current, the higher the ratio of current to voltage can be designed based on a current mirror set by digital parameters, and the higher the gain ratio is set, the stronger the damping Da suppression effect is. Or the damping unit 508 may be a device capable of providing damping Da, such as a circuit analog equivalent resistor, an electric energy-heat energy converter, a constant current source, etc., and may be driven by receiving the enable signal Se. Therefore, the type of the damping unit 508 is not limited herein, and any device capable of providing the damping Da should be included in the scope of the present embodiment.

Referring to fig. 3, the damping control module 50 further includes a counting unit 602, a disconnection detecting unit 604 and a disabling unit 606. The counting unit 602 is coupled to the resonance detecting unit 502 and the logic control unit 506, and the counting unit 602 sets the expected times. When the winding voltage Vw is smaller than the threshold voltage Vt, the resonance voltage Vr starts to be generated to oscillate on behalf of the winding voltage Vw, so that the counting unit 602 starts to count the oscillations. Each time the counting unit 602 counts once, i.e. representing that the resonance voltage Vr generates an oscillatory wave. When the number of times counted by the counting unit 602 reaches the expected number of times preset by the counting unit 602, the counting unit provides the enable signal Ss representing that the number of times the resonant voltage Vr oscillates reaches the expected number of times. That is, when the number of times the resonance voltage Vr oscillates reaches the expected number of times, the counting unit 602 changes the level of the enable signal Ss to inform the logic control unit 506 that the number of times the resonance voltage Vr oscillates has reached the expected number of times. Therefore, the damping control module 50 can flexibly set the resonant voltage Vr to enable the damping operation only when a specific oscillating wave is reached.

The open circuit detecting unit 604 is coupled to the logic control unit 506 and the secondary side 10-2, and detects whether the path between the output terminal 100-2 and the secondary side winding 104 is open to provide an open circuit signal So to the logic control unit 506. This path has only 2 open circuits possible under normal operation of the power conversion apparatus 100. When one of the two switches is turned on and the rectifier switch 402 is turned off synchronously, the exciting inductor of the primary winding 102 stores energy and the voltage Vds across the power switch 20 is 0. Another situation is that after the rectifier switch 402 is turned on synchronously (the power switch 20 is turned off at this time), the energy stored in the exciting inductor of the primary winding 102 is completely released, so that the current of the secondary side 10-2 is completely zero, and the rectifier switch 402 is turned off, which results in an open circuit in the path between the output terminal 100-2 and the secondary winding 104. The disconnection detecting unit 604 is designed to prevent the damping control module 50 from starting a damping operation when the rectifier switch 402 is turned on (which may cause malfunction of the power conversion apparatus 100 and thus disable the power conversion apparatus 100).

Specifically, the simplest detection method for determining whether the path between the output terminal 100-2 and the secondary winding 104 is open can be determined by the control signal Sc provided by the rectifier controller 406 to the rectifier switch 402, so that it can be determined whether the path between the output terminal 100-2 and the secondary winding 104 is open (as shown in fig. 3) as the damping control module 50 shown in fig. 1 receives the control signal Sc. When the path between the output terminal 100-2 and the secondary winding 104 is broken and the level of the winding voltage Vw is in the enabling interval, the logic control unit 506 enables the damping unit 508 to perform a damping operation on the oscillation of the winding voltage Vw. It should be noted that, in an embodiment of the present invention, whether the path between the output terminal 100-2 and the secondary winding 104 is open or not is determined only according to the control signal Sc (which is only a manner easy to implement), and the circuit design can also be determined by the voltage variation of each point of the power conversion apparatus 100, which is not described herein again.

The disable unit 606 receives the winding voltage Vw and the output voltage Vo, and is coupled to the logic control unit 506 to provide a disable signal Sd to the logic control unit 506. The disabling unit 606 mainly provides a function of preventing the shock absorption control module 50 from malfunctioning, and it mainly uses the voltage difference between the winding voltage Vw and the output voltage Vo to perform the determination. When the path between the output terminal 100-2 and the secondary winding 104 is the channel, the winding voltage Vw is greater than the output voltage Vo. Therefore, the path between the output terminal 100-2 and the secondary winding 104 can be determined as a channel by using the characteristic, and in this state, the logic control unit 506 should be prevented from enabling the damping unit 508. In addition, when the winding voltage Vw is smaller than the proportional multiple of the output voltage Vo (for example, but not limited to-1.2 times the output voltage Vo), it represents that the power switch 20 is turned on, and therefore it is also necessary to avoid that the logic control unit 506 enables the damping unit 508 in this state. When the above two conditions occur, the disabling unit 606 changes the level of the disabling signal Sd to notify the logic control unit 506, so that the logic control unit 506 disables the damping unit 508.

In addition, the disabling unit 606 may also be coupled to the level triggering unit 504, and performs the disabling control of the damping control module 50 during the activation. Specifically, after the resonance detecting unit 502 notifies the logic control unit 506 to enable the damping control module 50, and when the disabling unit 606 knows that the level of the winding voltage Vw is not within the enabling interval according to the winding voltage Vw and the reference voltage Vref (the level triggering unit 504 notifies the disabling unit 606 through another signal S), the logic control unit 506 is notified through the disabling signal Sd (i.e., the operation logic of the level triggering unit 504 is opposite). In addition, the disabling unit 606 may also disable the damping unit 508 to limit the number of times that it is enabled. For example, but not limited to, when the logic control unit 506 only enables the damping unit 508 after the level of the winding voltage Vw (corresponding to the resonance voltage Vr) reaches the enabling interval for the first time, and after the single enabling, the disabling unit 606 notifies the logic control unit 506 through the disabling signal Sd, so that the logic control unit 506 does not enable the damping unit 508 for the second time.

In addition, referring back to fig. 3, the damping control module 50 further includes an on/off unit 702 and a functional on/off unit 704. The on-off unit 702 receives the open-circuit signal So and the disable signal Sd, and turns on the damping control module 50 when the open-circuit signal So indicates that the path between the output terminal 100-2 and the secondary winding 104 is open-circuit, and turns off the damping control module 50 when the disable signal Sd disables the damping unit 508. Therefore, the damping control module 50 can be started when the damping operation is required to be performed on the resonance voltage Vr, and the damping control module 50 can be closed when the damping control module 50 is not required to be used, so as to reduce the overall power consumption of the power conversion device 100, and further improve the operation efficiency of the power conversion device 100.

The function on/off unit 704 is coupled to the power conversion apparatus 100 and receives a load signal Sl associated with a load amount. When the function starting and stopping unit 704 knows that the load amount is within the specific range (for example, but not limited to no load), the function of the damping control module 50 for damping operation is started. The load signal Sl can be obtained from feedback of the output voltage Vo, a switching frequency of the power switch 20, or signals provided by the control module 30 and the load 200, and the load amount can be calculated by the functional start/stop unit 704 or reported by an external device (such as, but not limited to, the control module 30 and the load 200). Specifically, when the load is heavy, the control module 30 generally operates the power conversion apparatus 100 in a Continuous Conduction Mode (CCM) or a critical conduction mode (CRM). Therefore, the resonance voltage Vr is not generated at the primary side 10-1 without performing the damping operation using the damping control module 50. Although the control module 30 usually operates the power conversion apparatus 100 in the Discontinuous Conduction Mode (DCM) when the load amount is light load, the quasi-resonant control mode (QRmode) is more efficient than the damping control module 50 in reducing the amplitude of the resonant voltage Vr when the load amount is light load, and therefore the quasi-resonant control mode (QR mode) is preferably selected when the load amount is light load.

However, when the load is not loaded (or is close to being unloaded), the quasi-resonant control mode (QR mode) is not significant to improve the efficiency, but if the quasi-resonant control mode (QRmode) is not used and the resonant voltage Vr is continuously oscillated, the electromagnetic interference is improved, so that it is better to reduce the amplitude of the resonant voltage Vr by using the damping control module 50 when the load is not loaded to suppress the electromagnetic interference. Therefore, when the function start/stop unit 704 knows that the load amount is within a specific range (for example, but not limited to no load), the function of the damping control module 50 for damping operation can be started, and it is a better option to suppress the electromagnetic interference. It should be noted that in an embodiment of the present invention, since the efficiency of selecting to let the resonant voltage Vr oscillate continuously may be better than the efficiency of using the damping control module 50 to reduce the amplitude of the resonant voltage Vr, in an embodiment, the damping control module 50 may be turned off by using the function turning-on/off unit 704 according to actual requirements, so as not to provide the damping operation function.

Fig. 5 is a schematic diagram of a logic circuit of the damping control module according to the present invention, and is combined with fig. 1 to 4B. The logic circuit of fig. 5 is based on the control and detection scheme of fig. 3, and utilizes the simplest and most relevant logic circuit built by the actual components (e.g., comparing two voltages can be basically achieved by a comparator, etc.). However, the actual circuit may actually be formed by a plurality of circuits with the same function, and therefore the damping control module 50 should not be limited to the circuit shown in fig. 5. In fig. 5, the resonance detecting unit 502 may be formed by a comparator OP 1. The comparator OP1 compares the winding voltage Vw with the 0.8 times of the output voltage Vo (i.e., the threshold voltage Vt), and generates a high level signal when the winding voltage Vw is smaller than the 0.8 times of the output voltage Vo. The counting unit 602 may be composed of a counter Cr and a positive edge flip-flop Tp, wherein the counter Cr sets the expected number of times, and informs the positive edge flip-flop Tp when the number of times that the comparator OP1 generates the high level signal reaches the expected number of times, so that the positive edge flip-flop Tp generates the enable signal Ss of the positive edge flip-flop to the logic control unit 506.

The level trigger unit 504 can be composed of a comparator OP2, a negative edge trigger Tn and a counting unit 504-1, and the comparator OP2 compares the winding voltage Vw with a reference voltage Vref of 0V. The reference voltage Vref is set to 0V or more as an enable interval. When the winding voltage Vw is greater than the reference voltage Vref of 0V, a low-level signal is generated, and the negative edge trigger Tn generates the negative edge triggered trigger signal St according to the state transition of the level of the comparator OP 2. The counting unit 504-1 receives the trigger signal St, and stops providing the trigger signal St with the high level to the logic control unit 506 when the counting unit 504-1 counts the number of times that the trigger signal St is transited to the high level. Thus, the number of times damping unit 508 provides damping Da may be set. The damping unit 508 may be configured to provide the damping Da only once when power saving is required. In addition, the counting unit 504-1 can set the control manner of the enabling interval, such as but not limited to the positive half cycle and the negative half cycle of the resonant voltage Vr, or the whole interval (i.e. the positive half cycle and the negative half cycle) of the resonant voltage Vr as the enabling interval. After the state of the trigger signal St is known to be at the high level, the trigger signal St may be set to be a signal triggered once, multiple times or continuously.

The open-circuit detecting unit 604 can be a back gate NOT, when the control signal Sc is at a low level, the output of the open-circuit detecting unit 604 is a high-level open-circuit signal So, and the high-level open-circuit signal So represents that the rectifier switch 402 is turned off. The disable signal Sd provided by the disable unit 606 includes a first disable signal Sd1 and a second disable signal Sd2, and the disable unit 606 includes comparators OP3 and OP4 and an OR gate OR. The comparator OP3 compares the winding voltage Vw with the-1.2 times output voltage Vo, and provides a first disable signal Sd1 to the logic control unit 506. When the winding voltage Vw is smaller than-1.2 times the output voltage Vo, which represents that the power switch 20 is turned on, the comparator OP3 provides the first disable signal Sd1 with a high level to the logic control unit 506.

The logic control unit 506 includes flip-flops F1 AND F2 AND an AND gate, AND the flip-flop F1 receives the enable signal Ss AND the first disable signal Sd1. When the enabling signal Ss is at the high level (i.e., the winding voltage Vw generates the resonant voltage Vr to start oscillating), and the first disabling signal Sd1 is at the low level (the power switch 20 is turned off), the output signal Sf of the flip-flop F1 is at the high level "1". The AND gate AND in the logic control unit 506 receives the output signal Sf of the flip-flop F1, the shutdown signal So, AND the trigger signal St, AND provides the output signal Sa with high level to the flip-flop F2 when all three signals are at high level "1".

The comparator OP4 receives the winding voltage Vw and the output voltage Vo, and compares the winding voltage Vw with the output voltage Vo to provide an output signal Sp to the OR gate OR. When the path between the output terminal 100-2 and the secondary winding 104 is the channel, the winding voltage Vw is greater than the output voltage Vo, and therefore the high level output signal Sp is generated. On the other hand, the output terminal of the comparator OP2 is also coupled to the OR gate OR. When the level of the comparison result between the winding voltage Vw and the reference voltage Vref of 0V is not in the enabled interval, the output of the comparator OP2 is the signal S with high level. When the level of the comparison result between the winding voltage Vw and the reference voltage Vref of 0V is not in the enable interval OR the winding voltage Vw is greater than the output voltage Vo, the second disable signal Sd2 output by the OR gate OR is all at the high level. The flip-flop F2 receives the output signal Sa of the AND gate AND the second disable signal Sd2 of the OR gate OR, AND when the output signal Sa is at the high level "1", the flip-flop F2 provides the high-level enable signal Se to enable the switch Q in the damping unit 508, so that the resistor R of the damping unit 508 provides the damping Da, AND the path current Il from the secondary winding 104 to the ground GND through the damping unit 508 is generated. When the second disable signal Sd2 is at the high level "1", the flip-flop F2 provides the low-level enable signal Se to disable the switch Q in the damping unit 508.

It should be noted that, in an embodiment of the present invention, the damping control module 50 may be formed by the above-mentioned physical elements, and a programmable controller may be further used to design the damping control module 50. The design of the damping control module 50 using a programmable controller is advantageous in that all parameters inside the damping control module 50 are adjustable (including damping Da, reference voltage Vref, etc.)

Fig. 6A is a schematic waveform diagram of a power conversion device according to a first embodiment of the present invention, fig. 6B is a schematic waveform diagram of a power conversion device according to a second embodiment of the present invention, and fig. 6C is a schematic waveform diagram of a power conversion device according to a third embodiment of the present invention, which are combined with fig. 1 to 5. In the embodiment of fig. 6A, the damping unit 508 is enabled at the first wave of the resonance voltage Vr, the enabling interval is set at the positive half cycle of the resonance voltage Vr, and the number of times the damping unit 508 provides the damping Da is not limited. In the embodiment of fig. 6B, the damping unit 508 is enabled after the first oscillation of the resonant voltage Vr, the enabling interval is set at the positive half cycle of the resonant voltage Vr, and the damping unit 508 is limited to provide the damping Da only once. In the embodiment of fig. 6C, the damping unit 508 is enabled at the first wave of the resonant voltage Vr, the enabling interval is set at the positive half cycle of the resonant voltage Vr, and the whole interval (i.e. the positive half cycle and the negative half cycle) is set as the enabling interval.

As shown in fig. 6A, when the PWM signal PWM controls the power switch 20 to turn off (time t 1), the control signal Sc controls the rectifier switch 402 to turn on, the current of the resonant inductor of the primary side 10-1 starts to decrease, so that the secondary side current Is sensed by the secondary side winding 104 starts to decrease, and the winding voltage Vw corresponds to the voltage across Vds of the power switch 20. At this time, the enable signal Ss and the trigger signal St are both low, so that the enable signal Se is also low. When the energy stored in the exciting inductor of the primary winding 102 Is completely released, and the secondary side current Is completely zero (time t 2), the control signal Sc controls the rectifier switch 402 to turn off. At this time, the winding voltage Vw starts to generate the resonance voltage Vr and starts to decrease, and the enabling signal Ss and the trigger signal St are still at the low level, so that the enabling signal Se is also at the low level.

When the winding voltage Vw falls below the threshold voltage Vt (time t 3), the enable signal Ss is high. Since the winding voltage Vw does not trigger the reference voltage Vref of 0V preset in the level trigger unit 504 (i.e., using the negative edge trigger of fig. 5), the trigger signal St is still at the low level, so that the enable signal Se is also still at the low level. When the resonance voltage Vr rises from the negative half cycle to the reference voltage Vref of 0V or higher (time t 4), the enabling signal Ss and the triggering signal St are both at the high level, so that the enabling signal Se is turned to the high level to trigger the damping unit 508. At this time, the damping unit 508 provides damping Da to reduce the amplitude of the resonance voltage Vr, and generates a path current Il from the secondary winding 104 to the ground GND through the damping unit 508. After time t4, the trigger signal St is toggled from the low level to the high level every time the resonance voltage Vr rises from the negative half cycle to the reference voltage Vref of 0V, so that the logic control unit 506 controls the damping unit 508 to provide the damping Da (i.e. the trigger signal St is all at the high level at the positive half cycle of the resonance voltage Vr) during the predetermined interval.

Fig. 6B is different from fig. 6A in that the damping control module 50 uses the counting unit 602 to count the number of times of oscillation of the resonance voltage Vr, and after the first oscillation of the resonance voltage Vr, the winding voltage Vw is decreased to be lower than the threshold voltage Vt, and then the high-level enable signal Ss is provided (time t 01). Since the winding voltage Vw does not trigger the reference voltage Vref of 0V preset in the level trigger unit 504 (i.e., using the negative edge trigger of fig. 5), the trigger signal St is still at the low level, so that the enable signal Se is also still at the low level. When the resonant voltage Vr rises from the negative half cycle to the reference voltage Vref of 0V or higher (time t 02), the enable signal Ss and the trigger signal St are both at the high level, so that the enable signal Se is converted to the high level to trigger the damping unit 508. At this time, the damping unit 508 provides damping Da to reduce the amplitude of the resonance voltage Vr, and generates a path current Il from the secondary winding 104 to the ground GND through the damping unit 508. Since the damping unit 508 is limited to provide the damping Da only once, the trigger signal St is no longer transited from the low level to the high level after the time t02, so that the damping unit 508 no longer provides the damping Da.

The difference between FIG. 6C and FIG. 6A is that the level trigger unit 504 sets the full interval (i.e., the positive half cycle and the negative half cycle) as the enabled interval. When the resonant voltage Vr rises from the negative half cycle to the reference voltage Vref of 0V or higher (time t 11), the enabling signal Ss and the triggering signal St are both at the high level, so that the enabling signal Se is converted to the high level to trigger the damping unit 508. At this time, the damping unit 508 provides damping Da to reduce the amplitude of the resonance voltage Vr, and generates a path current Il from the secondary winding 104 to the ground GND through the damping unit 508. Since the level trigger unit 504 sets the full interval (i.e. the positive half cycle and the negative half cycle) as the enabled interval, the trigger signal St remains at the high level after the time t11, so that the damping unit 508 continuously provides the damping Da.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A power conversion device with shock absorption control, which supplies power to a load from an output end, is characterized by comprising:

a transformer including a primary side and a secondary side, the primary side receiving an input voltage, and the secondary side being coupled to the output terminal;

a power switch coupled to the primary side;

the control module is coupled with the power switch and controls the power switch to be continuously switched on and off so as to convert the input voltage into output voltage through the transformer and provide the output voltage through the output end; and

a damping control module coupled to the secondary side;

when the damping control module detects the resonance voltage from the secondary side, the damping control module performs damping operation on the resonance voltage to reduce the amplitude of the resonance voltage by providing damping;

the damping control module obtains winding voltage by detecting a secondary side winding of the secondary side, and the winding voltage generates the resonance voltage when the power switch is turned off; the damping control module judges whether the winding voltage is the resonance voltage according to the winding voltage and the output voltage;

this shock attenuation control module includes:

the resonance detection unit receives the output voltage and the winding voltage, compares the winding voltage with a threshold voltage corresponding to the output voltage, and provides an enabling signal representing that the winding voltage starts to generate oscillation according to a comparison result;

a quasi-position trigger unit for receiving the winding voltage and comparing the winding voltage with a reference voltage to provide a trigger signal representing the time for providing the damping according to the comparison result;

a logic control unit for receiving the enable signal and the trigger signal; and

the damping unit is coupled with the logic control unit and the secondary side winding;

when the level of the winding voltage is within an enabled interval set by the reference voltage, the logic control unit enables the damping unit to provide the damping for the secondary side winding.

2. The power conversion device of claim 1, wherein the secondary side comprises a rectification module comprising:

a rectifier switch coupled to the secondary winding;

an output capacitor coupled to the rectifier switch and the output terminal and providing the output voltage to the output terminal; and

the rectification controller is coupled with the rectification switch and controls the rectification switch to be continuously switched on and off synchronously with the power switch; the damping control module is integrated with the rectification controller to provide the damping operation according to the resonant voltage when the rectification controller controls the rectification switch to be switched off.

3. The power conversion device of claim 1, wherein the logic control unit enables the damping unit only when the level of the winding voltage first reaches the enabling interval.

4. The power conversion device of claim 1, wherein the damping control module further comprises:

a counting unit coupled to the resonance detection unit and the logic control unit;

the counting unit sets the expected times, and counts the times of the oscillation after the winding voltage starts to generate the oscillation; when the number reaches the expected number, the counting unit provides the enabling signal representing that the number of the oscillation reaches the expected number.

5. The power conversion device of claim 1, wherein the damping control module further comprises:

a disconnection detecting unit coupled to the logic control unit and the secondary side;

wherein the open circuit detecting unit detects whether a path between the output terminal and the secondary side winding is open circuit or not, and provides an open circuit signal to the logic control unit; the logic control unit enables the damping unit when the path is broken and the level of the winding voltage is in the enabling interval.

6. The power conversion device of claim 1, wherein the damping control module further comprises:

a disabling unit for receiving the winding voltage and the output voltage and coupled to the logic control unit;

when the disabling unit knows the path channel between the output end and the secondary side winding through the winding voltage and the output voltage or the power switch is conducted, the disabling unit informs the logic control unit to disable the damping unit through a disabling signal.

7. The power conversion device of claim 6, wherein the disabling unit further notifies the logic control unit to disable the damping unit through the disabling signal when the level of the winding voltage is not within the enabled interval according to the winding voltage and the reference voltage.

8. A damping control module coupled to the power conversion device of claim 1, comprising:

a resonance detection unit for receiving the output voltage output by the power conversion device and the winding voltage of the primary and side windings of the secondary side, and comparing the winding voltage with a threshold voltage corresponding to the output voltage to provide an enable signal representing that the winding voltage starts to generate oscillation according to a comparison result;

a quasi-position trigger unit for receiving the winding voltage and comparing the winding voltage with a reference voltage to provide a trigger signal representing the damping time according to the comparison result;

when the level of the winding voltage is in an enabled interval set by the reference voltage, the logic control unit enables the damping unit to provide the damping for the secondary side winding so as to reduce the amplitude of the winding voltage.

9. The damping control module according to claim 8, wherein the logic control unit enables the damping unit only when the level of the winding voltage reaches the enabling interval for the first time.

10. The damping control module according to claim 9, further comprising:

a counting unit coupled to the level triggering unit and the logic control unit;

11. The damping control module according to claim 8, characterized in that it further comprises:

wherein the open circuit detecting unit detects whether a path between an output terminal providing the output voltage and the secondary side winding is open circuit, and provides an open circuit signal to the logic control unit; when the path is broken and the level of the winding voltage is in the enabling interval, the logic control unit enables the damping unit.

12. The damping control module according to claim 11, characterized in that it further comprises:

when the disabling unit knows a path channel between the output end and the secondary side winding through the winding voltage and the output voltage or the power switch is switched on, the disabling unit informs the logic control unit to disable the damping unit through a disabling signal.

13. The damping control module according to claim 12, wherein the disabling unit notifies the logic control unit to disable the damping unit through the disabling signal when the level of the winding voltage is not within the enabled interval according to the winding voltage and the reference voltage.

14. The method of claim 8, wherein the method is applied to a power conversion device comprising a primary side and a secondary side, and the primary side is coupled to the power switch; the power conversion device converts an input voltage into an output voltage through the primary side and the secondary side by controlling the power switch to be continuously turned on and off, and the operation method comprises the following steps:

receiving the output voltage and a winding voltage on a secondary side winding of the secondary side;

comparing the winding voltage with a threshold voltage corresponding to the output voltage to provide an enable signal representing that the winding voltage starts to generate oscillation according to a comparison result;

comparing the winding voltage with a reference voltage to provide a trigger signal representing a timing of providing damping according to a comparison result;

judging whether the level of the winding voltage is in an energy-consistent interval set by the reference voltage according to the enabling signal and the triggering signal; and

when the level of the winding voltage is in the enabling interval, the damping unit is enabled, so that the damping unit provides damping for the secondary side winding to reduce the amplitude of the winding voltage.

15. The method of operation of claim 14, wherein the method of operation further comprises the steps of: enabling the damping unit only when the level of the winding voltage reaches the enabling interval for the first time.

16. The method of operation of claim 14, wherein the method of operation further comprises the steps of:

setting the expected times;

counting the number of times of the oscillation after the winding voltage starts to generate the oscillation; and

when the number reaches the expected number, the enable signal representing the number of the oscillations reaches the expected number is provided.

17. The method of operation of claim 14, wherein the method of operation further comprises the steps of:

detecting whether a path between an output terminal providing the output voltage and the secondary side winding is open;

when the path is broken and the level of the winding voltage is in the enabling interval, the damping unit is enabled.

18. The method of operation of claim 17, wherein the method of operation further comprises the steps of:

the path channel between the output end and the secondary side winding is known according to the winding voltage and the output voltage, or the damping unit is forbidden when the power switch is conducted; and

and disabling the damping unit when the level of the winding voltage is not in the enabling interval according to the winding voltage and the reference voltage.