Control circuit, control method of power adapter and power adapter

Abstract

The application discloses a power adapter control method, a control circuit and a power adapter. The output control module is connected with the power end of the freewheeling switch tube to detect the drain-source voltage of the freewheeling switch tube and obtain a voltage detection signal. During the conduction of the main power switch tube, the voltage detection signal is located at a first voltage value. During the conduction of the freewheeling switch tube, the voltage detection signal is located at a second voltage value, which is smaller than the first voltage value. The output control module compares the voltage detection signal with a reference signal to control the output power of the power adapter according to the comparison result. According to the voltage of the power end of the freewheeling switch tube, the output current information is obtained, and the output current is controlled within a proper range to meet the power requirement of the power adapter.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to a control circuit, control method, and power adapter for a power adapter. Background Technology

[0002] Existing power adapters, used to convert AC input signals to DC output signals, typically employ isolated flyback converters, such as... Figure 1 As shown, the flyback converter includes isolated primary and secondary sides. The primary side controls the primary power switch S1 to turn on and off through a primary side control chip, while the secondary side controls the secondary freewheeling switch S2 to turn on and off through a secondary side control chip. By controlling the switching states of the primary power switch S1 and the freewheeling switch S2, the input signal is converted into the desired output signal.

[0003] Power adapters typically need to meet the power requirements of the load, i.e., the rated output power, to satisfy safety requirements. For example... Figure 1 As shown, the existing technology obtains the output current information of the output terminal by sampling the sampling resistor R1, and judges whether the output power meets the requirements based on the obtained output current information. However, if the output sampling resistor is abnormal, such as short circuit, the output current cannot be reliably detected, and the power output cannot be reliably achieved. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a control circuit, control method and power adapter for a power adapter, so as to solve the technical problem of the inability to reliably detect the output current in the prior art.

[0005] The technical solution of this invention is to provide a control circuit for a power adapter. The power adapter includes an isolated primary-side main power switch and a secondary-side freewheeling switch. The control circuit includes an output control module connected to the power terminal of the freewheeling switch to detect the drain-source voltage of the freewheeling switch and obtain a voltage detection signal. During the conduction of the main power switch, the voltage detection signal is at a first voltage value. During the conduction of the freewheeling switch, the voltage detection signal is at a second voltage value, where the second voltage value is less than the first voltage value. The output control module compares the voltage detection signal with a reference signal to control the output power of the power adapter based on the comparison result.

[0006] Preferably, the reference signal includes a first reference signal. The output control module compares the voltage detection signal with the first reference signal to obtain a first comparison result. The value of the first reference signal is greater than the second voltage value and less than the first voltage value. The output control module obtains a current feedback signal based on the first comparison result. The current feedback signal is transmitted to the primary-side control chip that controls the primary-side main power switch or to the secondary-side control chip that controls the freewheeling switch, thereby controlling the output power of the power adapter.

[0007] Preferably, during the period when both the main power switch and the freewheeling switch are off, the power adapter operates in a resonant state, the voltage detection signal includes a resonant peak value, and the value of the first reference signal is less than the resonant peak value.

[0008] Preferably, the output control module includes an output current acquisition circuit and a current feedback circuit. The output current acquisition circuit receives the first comparison result to obtain an output current characterization signal based on the first comparison result. The current feedback circuit receives the output current characterization signal and performs error calculation between the output current characterization signal and the output current reference signal to obtain the current feedback signal.

[0009] Preferably, the output current acquisition circuit includes a time detection circuit and an estimation circuit. The time detection circuit obtains the switching cycle time of the power adapter and the freewheeling time of the freewheeling switch based on the first comparison result. The estimation circuit calculates the output current of the power adapter based on the switching cycle time, the freewheeling time, the output voltage of the power adapter, and the inductance value of the power adapter, so as to obtain the output current characterization signal.

[0010] Preferably, the time detection circuit includes a single-pulse circuit and a timing circuit. The single-pulse circuit receives the first comparison result and generates a single-pulse signal after masking the first comparison result for a predetermined time. The timing circuit times the information of the single-pulse signal to obtain the switching cycle time based on the information of the single-pulse signal. The timing circuit also times the information of the single-pulse signal to obtain the freewheeling time based on the information of the single-pulse signal and the first comparison result.

[0011] Preferably, the output control module includes a current limiting circuit, which receives the output current characterization signal and compares the output current characterization signal with a preset reference current limiting value or with a preset overcurrent threshold to limit the output current value of the power adapter.

[0012] Preferably, the current feedback circuit includes an error amplifier, a first switching transistor, and a filter circuit. The input terminal of the error amplifier receives the output current characterization signal and the output current reference signal to output an error signal. The first terminal of the filter circuit receives the output current characterization signal through a resistor, and the second terminal is connected to the drain power terminal of the first switching transistor. The control terminal of the first switching transistor receives the error signal, and the source power terminal is connected to a reference ground. The signal at the common connection point of the filter circuit and the drain power terminal of the first switching transistor serves as the current feedback signal.

[0013] Preferably, the reference signal includes a second reference signal; the output control module compares the voltage detection signal with the second reference signal to obtain a second comparison result, wherein the value of the second reference signal is greater than the second voltage value and less than the first voltage value; the output control module obtains a judgment signal for judging the input voltage level of the power adapter based on the second comparison result, and generates an output current reference signal corresponding to the input voltage level of the power adapter based on the judgment signal.

[0014] Preferably, the output control module includes a current feedback circuit. The current feedback circuit receives an output current characterization signal representing the power adapter and performs error calculation between the output current characterization signal and the output current reference signal to obtain a current feedback signal. The current feedback signal is transmitted to the primary-side control chip that controls the primary-side main power switch or to the secondary-side control chip that controls the freewheeling switch, thereby controlling the output power of the power adapter.

[0015] Preferably, during the period when both the main power switch and the freewheeling switch are off, the power adapter operates in a resonant state, the voltage detection signal includes a resonant peak value, and the value of the second reference signal is greater than the resonant peak value.

[0016] Preferably, the output control module includes a reference signal generation circuit, which includes a delay circuit, a trigger, and a reference signal adjustment circuit. The delay circuit receives the NOT signal of the second comparison result and generates a delayed signal after delaying it. The trigger receives the second comparison result as a set signal, receives the delayed signal as a reset signal, and outputs the judgment signal. The reference signal adjustment circuit receives the judgment signal to generate an output current reference signal corresponding to the high or low input voltage of the power adapter.

[0017] Preferably, the output control module includes an input voltage power-down detection circuit, the reference signal includes a third reference signal, the output control module compares the voltage detection signal with the third reference signal to obtain a third comparison result, the value of the third reference signal is greater than the second voltage value and less than the first voltage value; the input voltage power-down detection circuit receives the third comparison result and counts the high and low level states of the third comparison result within a preset time to obtain a first voltage signal, the first voltage signal is compared with a power-down reference signal to obtain a power-down discrimination signal for whether the input voltage has been powered down.

[0018] Preferably, the control circuit includes a second switching transistor connected between the power adapter and the load, and the power failure detection signal is used to control the switching state of the second switching transistor.

[0019] Preferably, the output control module is integrated into an integrated chip, or the output control module and the secondary control chip of the power adapter are in the same integrated chip. The integrated chip includes a drain pin, which is connected to the power terminal of the freewheeling switch to detect the drain-source voltage of the freewheeling switch.

[0020] This invention provides a control method for a power adapter, the power adapter including an isolated primary-side main power switch and a secondary-side freewheeling switch. The method detects the drain-source voltage information of the freewheeling switch to obtain a voltage detection signal. During the conduction period of the main power switch, the voltage detection signal is at a first voltage value; during the conduction period of the freewheeling switch, the voltage detection signal is at a second voltage value, the second voltage value being less than the first voltage value. The voltage detection signal is compared with a reference signal to control the output power of the power adapter based on the comparison result.

[0021] Preferably, the reference signal includes a first reference signal. The voltage detection signal is compared with the first reference signal to obtain a first comparison result. The value of the first reference signal is greater than the second voltage value and less than the first voltage value. The current feedback signal is obtained based on the first comparison result. The current feedback signal is used to control the output power of the power adapter, or to count the high and low level states of the first comparison result within a preset time to obtain a first voltage signal. The first voltage signal is compared with a power-down reference signal to obtain a power-down discrimination signal indicating whether the input voltage has been de-energized.

[0022] Preferably, during the period when both the main power switch and the freewheeling switch are off, the power adapter operates in a resonant state, the voltage detection signal includes a resonant peak value, and the value of the first reference signal is less than the resonant peak value.

[0023] Preferably, obtaining the current feedback signal based on the first comparison result, wherein the current feedback signal is used to control the output power of the power adapter, specifically includes the following steps: receiving the first comparison result to obtain an output current characterization signal based on the first comparison result; receiving the output current characterization signal and performing an error calculation between the output current characterization signal and an output current reference signal to obtain the current feedback signal.

[0024] Preferably, the switching cycle time of the power adapter and the freewheeling time of the freewheeling switch are obtained based on the first comparison result; the output current of the power adapter is calculated based on the switching cycle time, the freewheeling time, the output voltage of the power adapter, and the inductance value of the power adapter to obtain the output current characterization signal.

[0025] Preferably, the reference signal includes a second reference signal, and the voltage detection signal is compared with the second reference signal to obtain a second comparison result, wherein the value of the second reference signal is greater than the second voltage value and less than the first voltage value; a current feedback signal is obtained based on the second comparison result, and the current feedback signal is used to control the output power of the power adapter.

[0026] Preferably, during the period when both the main power switch and the freewheeling switch are off, the power adapter operates in a resonant state, the voltage detection signal includes a resonant peak value, and the value of the second reference signal is greater than the resonant peak value.

[0027] Preferably, the output current characterization signal of the power adapter is received, and the output current characterization signal is compared with the output current reference signal to obtain the current feedback signal.

[0028] Specifically, a judgment signal for determining the input voltage level of the power adapter is obtained based on the second comparison result, thereby generating an output current reference signal corresponding to the input voltage level of the power adapter.

[0029] The present invention provides a power adapter for providing output energy to a load, wherein the control circuit is used to control the output power of the power adapter to meet the load requirements.

[0030] The control circuit scheme of this invention involves an output control module that samples the drain-source terminal of a freewheeling switch to obtain its drain-source voltage information. A comparison circuit then compares the detected drain-source voltage signal with a first reference signal to obtain a first comparison result. Based on the comparison result, the output voltage information of the power adapter, and the inductance value of the power adapter, the output control module obtains the output current characterization information of the power adapter. Feedback current processing is performed based on this output current characterization information to control the output current at a suitable value to meet the load's output power requirements. This application's scheme can also detect whether the power adapter's input terminal is powered down based on the first comparison result, allowing for timely control of the downstream load. By comparing the detected drain-source voltage signal with a second reference signal to obtain a second comparison result, the magnitude of the input voltage is determined based on the second comparison result, thereby adjusting the magnitude of the output reference signal and controlling the output power of the power adapter. Attached Figure Description

[0031] Figure 1 A circuit block diagram of a power adapter with output adjustment circuitry in the prior art;

[0032] Figure 2 A circuit block diagram of a power adapter with an output control module according to the present invention;

[0033] Figure 3 Here is a circuit block diagram of the output control module according to the present invention;

[0034] Figure 4 Based on Figure 3 Circuit diagram of the first embodiment of the output control module;

[0035] Figure 5 Based on Figure 4 The specific circuit diagram of the time detection circuit;

[0036] Figure 6 Based on Figure 5 The working waveform diagram in the image;

[0037] Figure 7 Based on Figure 3 Circuit diagram of the reference signal generation circuit;

[0038] Figure 8 Based on Figure 7 Working waveform diagram;

[0039] Figure 9 The circuit diagram for the power failure detection circuit. Detailed Implementation

[0040] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the present invention.

[0041] To provide the public with a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the invention, but those skilled in the art can fully understand the invention without these details.

[0042] The invention is described in more detail below by way of example with reference to the accompanying drawings. It should be noted that the drawings are in a simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0043] refer to Figure 2 A circuit block diagram and reference diagram of a power adapter with an output control module according to the present invention. Figure 3 This is a circuit block diagram of an embodiment of the output control module according to the present invention; the power adapter is used to provide output energy, such as output power to the load. The power adapter includes an isolated primary-side main power switch S1, a secondary-side freewheeling switch S2, a primary-side control chip controlling the primary-side main power switch, and a secondary-side control chip controlling the freewheeling switch. The control circuit includes an output control module, which detects the drain-source voltage of the freewheeling switch S2 to obtain a voltage detection signal Vdrain. During the conduction period of the main power switch, the voltage detection signal is at a first voltage value; during the conduction period of the freewheeling switch, the voltage detection signal is at a second voltage value, the second voltage value being less than the first voltage value. The output control module compares the voltage detection signal with a reference signal to control the output power of the power adapter according to the comparison result. Here, the power terminal of the freewheeling switch S2 refers to either the drain power terminal or the source power terminal. In this embodiment, the source power terminal of the freewheeling switch is grounded. The output control module is connected to the drain power terminal of the freewheeling switch S2 to detect the drain-source voltage of the freewheeling switch. In other embodiments, the output control module is connected to both the drain and source power terminals of the freewheeling switch S2 to detect the drain-source voltage of the freewheeling switch.

[0044] refer to Figure 2 The output control module includes a comparison circuit. The input terminal of the comparison circuit receives the voltage detection signal and the reference signal to obtain a comparison result, denoted as V. DCEThe comparison result is transmitted to the first control circuit of the output control module. The first control circuit obtains a current feedback signal based on the first comparison result. The current feedback signal is transmitted to the primary-side control chip that controls the primary-side main power switch or to the secondary-side control chip that controls the freewheeling switch, thereby controlling the output power of the power adapter.

[0045] In a first embodiment, the reference signal includes a first reference signal, such as Vref1, and the comparison circuit compares the voltage detection signal with the first reference signal to obtain a first comparison result V. DCE1 The value of the first reference signal is greater than the second voltage value and less than the first voltage value. During the period when both the main power switch S1 and the freewheeling switch S2 are off, the power adapter operates in a resonant state, and the voltage detection signal includes a resonant peak value. The value of the first reference signal is less than the resonant peak value. In this example, the value of the first reference signal is slightly greater than the second voltage value.

[0046] refer to Figure 3 The circuit block diagram of the output control module according to the present invention, and reference Figure 4 Based on Figure 3 A circuit diagram of the first embodiment of the output control module, and reference. Figure 5 Based on Figure 4 A detailed circuit diagram of the time detection circuit is provided. In this embodiment, the output control module includes an output current acquisition circuit and a current feedback circuit. Here, the first control circuit specifically includes the output current acquisition circuit and the current feedback circuit.

[0047] The output current obtaining circuit receives the first comparison result V. DCE1 To obtain the output current characterization signal I based on the first comparison result. out_EST Specifically, refer to Figure 4 The output current acquisition circuit includes a time detection circuit and an estimation circuit. The time detection circuit obtains the switching cycle time of the power adapter and the freewheeling time of the freewheeling switch based on the first comparison result. The estimation circuit calculates the output current of the power adapter based on the switching cycle time T, the freewheeling time Toff, the output voltage Vo of the power adapter, and the inductance Ls of the power adapter, to obtain the output current characterization signal I. out_EST .

[0048] Specifically, refer to Figure 5 and Figure 6 The corresponding waveform diagram shows that the time detection circuit includes a single-pulse circuit and a timing circuit, and the single-pulse circuit receives the first comparison result V. DCE1After the first comparison result is masked for a predetermined time, a single pulse signal V is generated. RE The timing circuit times the information V of the single-pulse signal. RE The switching cycle time T is obtained based on the information of the single pulse signal, and the timing circuit times the information V of the single pulse signal. RE The follow-through time Toff is obtained based on the information of the single pulse signal and the first comparison result.

[0049] exist Figure 6 Taking the power adapter operating in an intermittent state as an example, the value of the first reference signal is greater than the second voltage value, less than the first voltage value, and less than the resonant peak value of the drain-source voltage. The first comparison result between the voltage detection signal characterizing the drain-source voltage information of the freewheeling switch and the first reference signal is V. DCE1 ,like Figure 6 As shown, the first comparison result V DCE1 After delay and single-pulse processing, a single-pulse signal V is obtained. RE The delay is to mask the first comparison result V. DCE1 The high level is generated due to resonance. From Figure 6 As can be seen from this, the switching cycle from the turn-on of the freewheeling switch at time t1 to the turn-on of the freewheeling switch at time t5 is one switching cycle, corresponding to the single-pulse signal V. RE The switching cycle begins at time t2 and ends at time t6, the start time of the next single-pulse signal. Therefore, the switching cycle time T can be obtained by timing the rising edge of the single-pulse signal. Similarly, from... Figure 6 As can be seen, the freewheeling switch turns on at time t1 and turns off at time t4, which is a freewheeling time Toff (corresponding to the main power transistor turning off). Therefore, by analyzing the rising edge of the single pulse signal and the first comparison result V... DCE1 The freewheeling time Toff can be obtained by timing detection at the falling edge of the current. To eliminate errors, the calculated freewheeling time Toff generally needs to be compensated for a fixed time to approximate the true value.

[0050] In a flyback power adapter, the flyback converter output current in discontinuous mode can be calculated using the following formula:

[0051] I out_EST =(Vo*Toff*Toff) / (2*Ls*T)

[0052] Substituting the calculated freewheeling time Toff, switching cycle time T, output voltage Vo, and inductance value into the formula, the output current characterization signal I can be obtained. out_EST The value of .

[0053] Continue to refer to Figure 3 The current feedback circuit receives the output current characterization signal and converts the output current characterization signal I... out_EST With output current reference signal V ref_cc Error calculation is performed to obtain the current feedback signal OPTO. Specifically, the current feedback circuit includes an error amplifier, a first switching transistor, and a filter circuit. The input terminal of the error amplifier receives the output current characterization signal I. out_EST and the output current reference signal V ref_cc The filter circuit outputs an error signal. Its first terminal receives the output current characterization signal via a resistor, and its second terminal is connected to the drain power terminal of the first switching transistor. The control terminal of the first switching transistor receives the error signal, and its source power terminal is connected to reference ground. The signal at the common connection point of the filter circuit and the drain power terminal of the first switching transistor serves as the current feedback signal OPTO. This current feedback signal is transmitted to either the primary-side control chip controlling the primary-side main power switching transistor or the secondary-side control chip controlling the freewheeling switching transistor, thereby controlling the output power of the power adapter. For example, the output power can be adjusted based on the current feedback signal to meet the load power requirements.

[0054] In one example, the output control module includes a current limiting circuit that receives the output current characterization signal and compares it with a preset reference current limit value or a preset overcurrent threshold to limit the output current value of the power adapter. Based on the above calculations, the output current characterization signal can be obtained by detecting the drain-source voltage of the freewheeling switch. Therefore, the calculated output current characterization signal can be directly compared with the current limiting threshold or reference value to control the output current of the power adapter, avoiding the unreliability issues that occur when sampling through a sampling resistor. The output signal of the current limiting circuit can control the switch connecting the power adapter to the load to limit the current or transmit it to the primary or secondary control chip for current limiting.

[0055] In the second embodiment, the output control module includes an input voltage power-down detection circuit, and the reference signal includes a third reference signal. The output control module compares the voltage detection signal with the third reference signal to obtain a third comparison result. The value of the third reference signal is greater than the second voltage value and less than the first voltage value. Here, the third reference signal may be equal to or unequal to the first reference signal. Taking them as equal as an example, the third comparison result is the same as the first comparison result. Figure 9 The circuit diagram is for the input power failure detection circuit. The input voltage power failure detection circuit receives the first comparison result V. DCE1The system counts the high and low levels of the third comparison result within a preset time to obtain a first voltage signal V1. This first voltage signal is compared with a power-down reference signal VP_ref to obtain a power-down discrimination signal indicating whether the input voltage has been powered down. For example, a clock signal can be used for timing. If the first voltage signal V1 is greater than the power-down reference signal VP_ref within the valid time of the clock signal, it indicates that there is no power failure; if the first voltage signal V1 is less than the power-down reference signal VP_ref, it indicates that there is a power failure. The control circuit includes a second switching transistor connected between the power adapter and the load. The power-down discrimination signal is used to control the switching state of the second switching transistor.

[0056] In the third example, refer to Figure 7 The circuit diagram for the reference signal generation circuit, and the reference. Figure 3 The reference signal includes a second reference signal. The output control module compares the voltage detection signal Vdrain with the second reference signal Vref2 to obtain a second comparison result V. DCE2 The value of the second reference signal is greater than the second voltage value but less than the first voltage value. During the period when both the main power switch and the freewheeling switch are off, the power adapter operates in a resonant state. The voltage detection signal includes a resonant peak value, and the value of the second reference signal is greater than the resonant peak value. This embodiment uses the power adapter operating in intermittent mode as an example. In one example, the value of the second reference signal is slightly less than the first voltage value.

[0057] refer to Figure 3 The output control module includes a current feedback circuit. This circuit receives an output current characterization signal representing the power adapter and performs an error calculation between the output current characterization signal and an output current reference signal to obtain a current feedback signal. This current feedback signal is transmitted to either the primary-side control chip controlling the primary-side main power switch or the secondary-side control chip controlling the freewheeling switch, thereby controlling the output power of the power adapter. Here, the output control module obtains a judgment signal based on the second comparison result to determine the input voltage level of the power adapter, and generates an output current reference signal corresponding to the input voltage level of the power adapter based on the judgment signal. This embodiment can be combined with the first or second embodiment. For example, in this embodiment, the output current reference signal is adjustable according to the input voltage level, and the output current characterization signal can be obtained through direct sampling or by the calculation method described above. In the first embodiment, the output current reference signal can be a fixed value or an adjustable value corresponding to the input voltage level.

[0058] Specifically, refer to Figure 7 as well as Figure 8 Based on Figure 7 The waveform diagram shows that the output control module includes a reference signal generation circuit, which comprises a delay circuit, a trigger, and a reference signal adjustment circuit. The delay circuit receives the second comparison result V. DCE2 The non-signal is used to delay the signal to generate a delayed signal V. RESET The trigger receives the second comparison result as a set signal, receives the delay signal as a reset signal, and outputs the judgment signal V. H_L The reference signal adjustment circuit receives the judgment signal to generate an output current reference signal V corresponding to the input voltage level of the power adapter. ref_cc . refer to Figure 8 At time t4, the input voltage decreases, therefore, the first voltage value of the voltage detection signal Vdrain decreases accordingly. During the delay period, the second comparison result V... DCE2 If the non-signal is always high, then the delayed signal V RESET If the jump is high, then the judgment signal V H_L A jump to a high level indicates a decrease in input voltage, and the reference signal adjustment circuit adjusts the signal based on the judgment signal V. H_L Adjust the output current reference signal V ref_cc The size, such as reducing the output current reference signal V ref_cc The magnitude of the input voltage is determined, thereby outputting power that matches the input voltage. Similarly, when the judgment signal V... H_L Increasing the input voltage can increase the output current reference signal V. ref_cc Size.

[0059] Finally, in one embodiment, the output control module and the secondary control chip are integrated in the same integrated chip, or the output control module is integrated in the same integrated chip, the integrated chip including a drain pin, the drain pin being connected to the power terminal of the freewheeling switch to detect the drain-source voltage of the freewheeling switch.

[0060] The present invention obtains the drain-source voltage information of the freewheeling switch by sampling the drain-source terminal of the freewheeling switch. The detection signal of the drain-source voltage is compared with a first reference signal by a comparison circuit or with a second reference signal. Based on the comparison result, the output power of the power adapter can be adjusted, and power-down protection or current limiting protection can also be performed. The present invention only requires one drain pin to realize multiple control functions.

[0061] The embodiments described above do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the above embodiments should be included within the scope of protection of this technical solution.

Claims

1. A control circuit of a power adapter, the power adapter comprising an isolated primary main power switch and a secondary freewheeling switch, characterized in that, The control circuit comprises an output control module, The output control module is connected with the power terminal of the freewheeling switch tube to detect the drain-source voltage of the freewheeling switch tube and obtain a voltage detection signal, wherein the voltage detection signal is at a first voltage value during the conduction of the main power switch tube and is at a second voltage value during the conduction of the freewheeling switch tube, and the second voltage value is smaller than the first voltage value, The output control module compares the voltage detection signal with a reference signal to control the output power of the power adapter according to the comparison result. The reference signal comprises a first reference signal, the output control module compares the voltage detection signal with the first reference signal to obtain a first comparison result, the value of the first reference signal is greater than the second voltage value and smaller than the first voltage value, the output control module comprises an output current obtaining circuit, the output current obtaining circuit receives the first comparison result to obtain an output current characteristic signal according to the first comparison result, thereby controlling the output power of the power adapter, the output current obtaining circuit comprises a time detection circuit and an estimation circuit, the time detection circuit obtains the switching cycle time of the power adapter and the freewheeling time of the freewheeling switch tube according to the first comparison result, and the estimation circuit calculates the output current of the power adapter according to the switching cycle time, the freewheeling time, the output voltage of the power adapter and the inductance value of the power adapter to obtain the output current characteristic signal.

2. The control circuit of the power adapter according to claim 1, wherein The output control module obtains a current feedback signal according to the output current characteristic signal, the current feedback signal is transmitted to a primary side control chip for controlling the primary side main power switch tube or a secondary side control chip for controlling the freewheeling switch tube, thereby controlling the output power of the power adapter.

3. The control circuit of a power adapter according to claim 2, wherein, During the off of the main power switch tube and the freewheeling switch tube, the power adapter works in a resonance state, the voltage detection signal comprises a resonance peak value, and the value of the first reference signal is smaller than the resonance peak value.

4. The control circuit of a power adapter according to claim 2, wherein, The output control module comprises a current feedback circuit, The current feedback circuit receives the output current characteristic signal and performs error operation on the output current characteristic signal and an output current reference signal to obtain the current feedback signal.

5. The control circuit of a power adapter according to claim 1, wherein, The time detection circuit comprises a single pulse circuit and a timing circuit, The single pulse circuit receives the first comparison result, generates a single pulse signal after shielding the first comparison result for a predetermined time, and The timing circuit times the information of the single pulse signal to obtain the switching cycle time according to the information of the single pulse signal, The timing circuit times the information of the single pulse signal to obtain the freewheeling time according to the information of the single pulse signal and the first comparison result.

6. The control circuit of a power adapter according to claim 1, wherein, The output control module comprises a current limiting circuit, The current limiting circuit receives the output current characteristic signal, compares the output current characteristic signal with a preset reference current limiting value or compares the output current characteristic signal with a preset overcurrent threshold value, to limit the output current value of the power adapter.

7. The control circuit of a power adapter according to claim 4, wherein, The current feedback circuit comprises an error amplifier, a first switch tube and a filter circuit, The input end of the error amplifier receives the output current characteristic signal and the output current reference signal to output an error signal; The first end of the filter circuit receives the output current characteristic signal through a resistor, and the second end is connected to the drain power end of the first switch tube, The control end of the first switch tube receives the error signal, and the source power end is connected to a reference ground, The signal at the common connection point of the filter circuit and the drain power end of the first switch tube is the current feedback signal.

8. The control circuit of the power adapter according to claim 4, wherein, The reference signal further comprises a second reference signal; The output control module compares the voltage detection signal with the second reference signal to obtain a second comparison result, the value of the second reference signal being greater than the second voltage value and less than the first voltage value; The output control module obtains a judgment signal judging the high or low of the input voltage of the power adapter according to the second comparison result, and generates the output current reference signal corresponding to the high or low of the input voltage of the power adapter according to the judgment signal.

9. The control circuit of a power adapter according to claim 8, characterized in that, During the off period of the main power switch tube and the freewheeling switch tube, the power adapter works in a resonant state, the voltage detection signal comprises a resonant peak value, and the value of the second reference signal is greater than the resonant peak value.

10. The control circuit of a power adapter according to claim 8, wherein, The output control module comprises a reference signal generation circuit, and the reference signal generation circuit comprises a delay circuit, a flip-flop and a reference signal adjustment circuit, The delay circuit receives the non-signal of the second comparison result to generate a delay signal after time delay, The flip-flop receives the second comparison result as a set signal and receives the delay signal as a reset signal to output the judgment signal; The reference signal adjustment circuit receives the judgment signal to generate the output current reference signal corresponding to the high or low of the input voltage of the power adapter.

11. The control circuit of a power adapter according to claim 1, characterized in that, The output control module comprises an input voltage power-down detection circuit, The reference signal further comprises a third reference signal, The output control module compares the voltage detection signal with the third reference signal to obtain a third comparison result, the value of the third reference signal being greater than the second voltage value and less than the first voltage value; The input voltage power-down detection circuit receives the third comparison result, counts the high or low level state of the third comparison result within a preset time, to obtain a first voltage signal, and compares the first voltage signal with a power-down reference signal to obtain a power-down judgment signal judging whether the input voltage is powered down.

12. The control circuit of a power adapter according to claim 11, characterized in that, The control circuit comprises a second switch tube connected between the power adapter and a load, The power-down judgment signal is used to control the switching state of the second switch tube.

13. The control circuit of a power adapter according to claim 1, wherein, The output control module is integrated in an integrated chip or the output control module and a secondary side control chip of the power adapter are in the same integrated chip, The integrated chip comprises a drain pin connected to a power terminal of the freewheeling switch tube to detect a drain-source voltage of the freewheeling switch tube.

14. A control method of a power adapter, the power adapter comprising an isolated primary side main power switch tube and a secondary side freewheeling switch tube, characterized in that, a drain-source voltage of the freewheeling switch tube is detected to obtain a voltage detection signal, during a conduction period of the main power switch tube, the voltage detection signal is at a first voltage value, during a conduction period of the freewheeling switch tube, the voltage detection signal is at a second voltage value, the second voltage value is less than the first voltage value; the voltage detection signal is compared with a reference signal to control an output power of the power adapter according to a comparison result; wherein the reference signal comprises a first reference signal, the voltage detection signal is compared with the first reference signal to obtain a first comparison result, a value of the first reference signal is greater than the second voltage value and less than the first voltage value, a switching period time of the power adapter and a freewheeling time of the freewheeling switch tube are obtained according to the first comparison result, an output current of the power adapter is calculated according to the switching period time, the freewheeling time, an output voltage of the power adapter and an inductance value of an inductor of the power adapter to obtain an output current representation signal, a current feedback signal is obtained according to the output current representation signal, the current feedback signal is used to control the output power of the power adapter.

15. The control method of the power adapter according to claim 14, characterized in that, a high-low level state of the first comparison result is counted in a preset time to obtain a first voltage signal, the first voltage signal is compared with a power-down reference signal to obtain a power-down judgment signal of an input voltage.

16. The control method of the power adapter according to claim 14 or 15, characterized in that, during a turn-off period of the main power switch tube and the freewheeling switch tube, the power adapter works in a resonance state, the voltage detection signal comprises a resonance peak value, a value of the first reference signal is less than the resonance peak value.

17. The control method of the power adapter according to claim 16, characterized in that, the output current representation signal is error operated with an output current reference signal to obtain the current feedback signal.

18. The control method of the power adapter according to claim 17, characterized in that, the reference signal further comprises a second reference signal, the voltage detection signal is compared with the second reference signal to obtain a second comparison result, a value of the second reference signal is greater than the second voltage value and less than the first voltage value; a judgment signal of a high-low input voltage of the power adapter is obtained according to the second comparison result, the output current reference signal corresponding to the high-low input voltage of the power adapter is generated according to the judgment signal.

19. The control method of the power adapter according to claim 18, wherein, during the period when both the main power switch and the freewheeling switch are off, the power adapter operates in a resonant state, the voltage detection signal comprises a resonant peak value, and the second reference signal has a value greater than the resonant peak value.

20. A power adapter for providing output power to a load, characterized in that, a control circuit according to any one of claims 1 to 13, the control circuit being configured to control the output power of the power adapter to meet a load requirement.

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