TWI723421B - Power supply device - Google Patents

Abstract

A power supply device includes a switch circuit, a resonant circuit, a transformer, an output rectifier, and a controller. The switch circuit includes a plurality of low-pass filters. The switch circuit generates a switch voltage according to an input voltage, a first clock voltage, a second clock voltage, a first control voltage, and a second control voltage. The resonant circuit generates a resonant voltage according to the switch voltage. The transformer generates a transformation voltage according to the resonant voltage. The output rectifier generates an output voltage according to the transformation voltage. The controller detects a sensing voltage relative to the output rectifier. The controller determines the first control voltage and the second control voltage according to the sensing voltage, so as to enable a portion of the low-pass filters and disable the other portion of the low-pass filters.

Description

Power Supplier

The present invention relates to a power supply, and more particularly to a power supply capable of suppressing noise.

The switching clock frequency of the switching circuit of a conventional power supply is usually between 80kHz and 140kHz. When performing electromagnetic interference tests, traditional power supplies are prone to generate double-frequency switching noise, which may fall within the target test frequency range of 150kHz to 30MHz and cause poor test results. In view of this, it is necessary to propose a new solution to overcome the problems faced by the prior art.

In a preferred embodiment, the present invention provides a power supply including: a switching circuit including a plurality of low-pass filters, wherein the switching circuit is based on an input potential, a first clock potential, and a second time. Pulse potential, a first control potential, and a second control potential to generate a switching potential; a resonant circuit generates a resonance potential based on the switching potential; a transformer generates a variable potential based on the resonance potential; An output rectifier generates an output potential according to the variable voltage potential; and a controller detects a sensed potential of the output rectifier, wherein the controller determines the first control potential and the first control potential according to the sensed potential The second control potential enables a part of the low-pass filters and disables the rest of the low-pass filters.

In order to make the purpose, features and advantages of the present invention more comprehensible, specific embodiments of the present invention are listed below, with the accompanying drawings, and detailed descriptions are as follows.

In the specification and the scope of patent application, certain words are used to refer to specific elements. Those skilled in the art should understand that hardware manufacturers may use different terms to refer to the same component. This specification and the scope of patent application do not use differences in names as a way to distinguish elements, but use differences in functions of elements as a criterion for distinguishing. The terms "include" and "include" mentioned in the entire specification and the scope of the patent application are open-ended terms and should be interpreted as "including but not limited to". The term "approximately" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range and achieve the basic technical effect. In addition, the term "coupling" includes any direct and indirect electrical connection means in this specification. Therefore, if it is described in the text that a first device is coupled to a second device, it means that the first device can be directly electrically connected to the second device, or indirectly electrically connected to the second device through other devices or connection means. Two devices.

FIG. 1 is a schematic diagram of a power supply 100 according to an embodiment of the invention. For example, the power supply 100 can be applied to a desktop computer, a notebook computer, or an integrated computer. As shown in Figure 1, the power supply 100 includes: a switching circuit 110, a resonance circuit 130, a transformer 140, an output rectifier 150, and a controller 160, wherein the switching circuit 110 includes a plurality of low-pass The filters 120-1, 120-2, ..., 120-N, and N can be any positive integer greater than 1. It should be noted that although not shown in Figure 1, the power supply 100 may further include other components, such as a voltage regulator or (and) a negative feedback circuit.

The switching circuit 110 generates a switching potential VW according to an input potential VIN, a first clock potential VK1, a second clock potential VK2, a first control potential VC1, and a second control potential VC2. The input potential VIN can come from an external power source, where the input potential VIN can be an AC potential with any frequency and any amplitude. For example, the frequency of the AC potential can be about 50Hz or 60Hz, and the root mean square value of the AC potential can be about 110V or 220V, but it is not limited to this. The operating frequency of each of the first clock potential VK1 and the second clock potential VK2 may be between 80 kHz and 140 kHz. The first clock potential VK1 and the second clock potential VK2 may have complementary logic levels. That is, if the first clock potential VK1 is a low logic level (logic "0"), the second clock potential VK2 must be a high logic level (logic "1"), and if the first clock potential VK1 If it is a high logic level, the second clock potential VK2 must be a low logic level. The resonance circuit 130 generates a resonance potential VR according to the switching potential VW. The transformer 140 generates a variable voltage VT according to the resonance potential VR. The output rectifier 150 generates an output potential VOUT according to the variable voltage VT. The output potential VOUT can be a DC potential having any level. For example, the level of the output potential VOUT can be approximately a constant 19V, but it is not limited to this. The controller 160 may be a pulse width modulation integrated circuit. In some embodiments, the controller 160 includes a detection circuit, a comparison circuit, and a processing circuit (not shown). The controller 160 can detect a sensed potential VE related to the output rectifier 150. The controller 160 determines the first control potential VC1 and the second control potential VC2 according to the sensed potential VE to enable the low-pass filters 120 -1, 120-2, ..., a part of 120-N and disable the rest of the low-pass filters 120-1, 120-2, ..., 120-N. In response to different output currents, the power supply 100 can be operated in a light load mode or a heavy load mode, wherein the first clock potential VK1 and the second clock potential VK2 can each have a light load operating frequency or a heavy load operation Frequency, and the light load operating frequency can be higher than the heavy load operating frequency. For example, the light load operating frequency may be approximately equal to 133 kHz, and the heavy load operating frequency may be equal to 90 kHz, but it is not limited to this. By appropriately controlling the low-pass filters 120-1, 120-2, ..., 120-N, the switching circuit 110 can automatically filter out unnecessary noise frequencies and suppress the doubling frequency switching noise, thereby improving The electromagnetic interference test result of the power supply 100.

The following embodiments will introduce the detailed structure and operation of the power supply 100. It must be understood that these drawings and descriptions are only examples, and are not used to limit the scope of the present invention.

FIG. 2 is a schematic diagram of the power supply 200 according to an embodiment of the invention. In the embodiment of Figure 2, the power supply 200 has an input node NIN and an output node NOUT, and includes a switching circuit 210, a resonance circuit 230, a transformer 240, an output rectifier 250, and a controller 260 , Wherein the switching circuit 210 includes a first low-pass filter, a second low-pass filter, a third low-pass filter, and a fourth low-pass filter (that is, the aforementioned positive integer N may be exactly 4 ). The input node NIN of the power supply 200 can receive an input potential VIN from an external power source, and the output node NOUT of the power supply 200 can be used to output an output potential VOUT to an electronic device (such as a laptop).

The switching circuit 210 includes a first transistor M1, a second transistor M2, a third transistor M3, a fourth transistor M4, a first resistor R1, a second resistor R2, a first capacitor C1, a second capacitor C2, a third capacitor C3, and a fourth capacitor C4. For example, each of the first transistor M1, the second transistor M2, the third transistor M3, and the fourth transistor M4 can each be an N-type MOSFET. The control terminal of the first transistor M1 is coupled to a first node N1, the first terminal of the first transistor M1 is coupled to a second node N2 to output a switching potential VW, and the first transistor M1 The second terminal is coupled to the input node NIN. The control terminal of the second transistor M2 is coupled to a third node N3, the first terminal of the second transistor M2 is coupled to a ground potential VSS (for example: 0V), and the second terminal of the second transistor M2 The terminal system is coupled to the second node N2. The first resistor R1 has a first end and a second end. The first end of the first resistor R1 is coupled to the controller 260 to receive a first clock potential VK1, and the first resistor R1 has a The second terminal is coupled to the first node N1. The first end of the second resistor R2 is coupled to the controller 260 to receive a second clock potential VK2, and the second end of the second resistor R2 is coupled to the third node N3. Because the first clock potential VK1 and the second clock potential VK2 have complementary logic levels, the first transistor M1 and the second transistor M2 also have complementary operation modes. For example, if the first transistor M1 is enabled, the second transistor M2 can be disabled, and if the first transistor M1 is disabled, the second transistor M2 can be enabled.

The first terminal of the first capacitor C1 is coupled to the first node N1, and the second terminal of the first capacitor C1 is coupled to a fourth node N4. The first end of the second capacitor C2 is coupled to the third node N3, and the second end of the second capacitor C2 is coupled to the fourth node N4. The control terminal of the third transistor M3 is coupled to the controller 260 to receive a first control potential VC1, the first terminal of the third transistor M3 is coupled to the ground potential VSS, and the second terminal of the third transistor M3 It is coupled to the fourth node N4. The first end of the third capacitor C3 is coupled to the first node N1, and the second end of the third capacitor C3 is coupled to a fifth node N5. The first end of the fourth capacitor C4 is coupled to the third node N3, and the second end of the fourth capacitor C4 is coupled to the fifth node N5. The control terminal of the fourth transistor M4 is coupled to the controller 260 to receive a second control potential VC2, the first terminal of the fourth transistor M4 is coupled to the ground potential VSS, and the second terminal of the fourth transistor M4 It is coupled to the fifth node N5.

The resonant circuit 230 includes a fifth capacitor C5, a first inductor (Inductor) L1, and a second inductor L2. The second inductor L2 can be contributed by a magnetizing inductance of the transformer 240, which It may not be an independent circuit element. The first terminal of the fifth capacitor C5 is coupled to the second node N2 to receive the switching potential VW, and the second terminal of the fifth capacitor C5 is coupled to a sixth node N6. The first end of the first inductor L1 is coupled to the sixth node N6, and the second end of the first inductor L1 is coupled to a seventh node N7 to output a resonance potential VR. The first end of the second inductor L2 is coupled to the seventh node N7, and the second end of the second inductor L2 is coupled to the ground potential VSS.

The transformer 240 includes a main coil 241 and a secondary coil 242. The primary coil 241 can be located on one side of the transformer 240 and the secondary coil 242 can be located on the opposite side of the transformer 240. The first end of the main coil 241 is coupled to the seventh node N7 to receive the resonance potential VR, and the second end of the main coil 241 is coupled to the ground potential VSS. The first end of the auxiliary coil 242 is coupled to an eighth node N8 to output a variable voltage VT, and the second end of the auxiliary coil 242 is coupled to a ninth node N9.

The output rectifier 250 includes a first diode (Diode) D1, a second diode D2, a third diode D3, a fourth diode D4, a third resistor R3, and a sixth diode. Capacitor C6. The anode of the first diode D1 is coupled to the eighth node N8 to receive the variable voltage VT, and the cathode of the first diode D1 is coupled to the output node NOUT. The anode of the second diode D2 is coupled to the ninth node N9, and the cathode of the second diode D2 is coupled to the output node NOUT. The anode of the third diode D3 is coupled to a tenth node N10, and the cathode of the third diode D3 is coupled to the eighth node N8. The anode of the fourth diode D4 is coupled to the tenth node N10, and the cathode of the fourth diode D4 is coupled to the ninth node N9. The first end of the third resistor R3 is coupled to the tenth node N10 to output a sensing potential VE to the controller 260, and the second end of the third resistor R3 is coupled to the ground potential VSS. The first end of the sixth capacitor C6 is coupled to the output node NOUT, and the second end of the sixth capacitor C6 is coupled to the ground potential VSS.

The operating principle of the power supply 200 can be as follows. The power supply 200 can operate in a light load mode or a heavy load mode. In the light load mode, the first clock potential VK1 and the second clock potential VK2 can each have a light load operating frequency FL, while in the heavy load mode, the first clock potential VK1 and the second clock potential VK2 can be Each has a heavy-duty operating frequency FH, where the light-duty operating frequency FL can be higher than the heavy-duty operating frequency FH. For example, the light load operating frequency FL may be approximately equal to 133 kHz, and the heavy load operating frequency FH may be approximately equal to 90 kHz, but it is not limited to this. The first resistor R1 and the first capacitor C1 form a first low-pass filter of the switching circuit 210. The second resistor R2 and the second capacitor C2 form a second low-pass filter of the switching circuit 210. The first resistor R1 and the third capacitor C3 form the third low-pass filter of the switching circuit 210. The second resistor R2 and the fourth capacitor C4 form a fourth low-pass filter of the switching circuit 210. For example, the aforementioned filter can be set according to the following equations (1) and (2).

………………………..(1)

………………………..(1)

………………………..(2) 其中「F1」代表第一低通濾波器和第二低通濾波器之每一者之低通截止頻率F1，「F2」代表第三低通濾波器和第四低通濾波器之每一者之低通截止頻率F2，「R1」代表第一電阻器R1之電阻值，「R2」代表第二電阻器R2之電阻值，「C1」代表第一電容器C1之電容值，「C2」代表第二電容器C2之電容值，「C3」代表第三電容器C3之電容值，「C4」代表第四電容器C4之電容值，「FH」代表電源供應器200之重載操作頻率FH，而「FL」代表電源供應器200之輕載操作頻率FL。

……………………….. (2) where "F1" represents the low-pass cutoff frequency F1 of each of the first low-pass filter and the second low-pass filter, and "F2" represents the third lowest The low-pass cutoff frequency F2 of each of the pass filter and the fourth low-pass filter, "R1" represents the resistance value of the first resistor R1, "R2" represents the resistance value of the second resistor R2, "C1" Represents the capacitance value of the first capacitor C1, "C2" represents the capacitance value of the second capacitor C2, "C3" represents the capacitance value of the third capacitor C3, "C4" represents the capacitance value of the fourth capacitor C4, and "FH" represents the power supply The high-load operating frequency FH of the power supply 200, and "FL" represents the light-load operating frequency FL of the power supply 200.

It can be seen from the above that the low-pass cut-off frequency F1 of each of the first low-pass filter and the second low-pass filter can be approximately equal to the heavy-duty operating frequency FH of the power supply 200, and the third low-pass filter and the first low-pass filter The low-pass cutoff frequency F2 of each of the four low-pass filters may be approximately equal to the light-load operating frequency FL of the power supply 200.

The controller 260 is used to detect the sensed potential VE of the output rectifier 250, wherein the controller 260 determines the first control potential VC1 and the second control potential VC2 according to the sensed potential VE, so as to enable the aforementioned low-pass filter Part and disable the rest of the aforementioned low-pass filter. The controller 260 can compare the sensing potential VE with a threshold potential. For example, when the power supply 200 is operating in the light load mode, the sensed potential VE of the output rectifier 250 may be equal to a lower potential (because the output current of the output rectifier 250 is relatively small), and when the power supply 200 is operated in a heavy load In the mode, the sensed potential VE of the output rectifier 250 can be equal to a higher potential (because the output current of the output rectifier 250 is larger). At this time, the aforementioned critical potential may be approximately equal to the average value of both the lower potential and the higher potential. In some embodiments, if it is determined that the sensing potential VE is lower than the critical potential, the controller 260 outputs the first control potential VC1 at a low logic level and the second control potential VC2 at a high logic level to disable the third power. Crystal M3 and the fourth transistor M4 are enabled. At this time, only the third low-pass filter and the fourth low-pass filter are enabled, while the first low-pass filter and the second low-pass filter are disabled. Yes, so the low-pass cutoff frequency F2 of the third low-pass filter and the fourth low-pass filter can be applied to the power supply 200; conversely, if it is determined that the sensed potential VE is higher than or equal to the critical potential, the controller 260 is Output the first control potential VC1 of the high logic level and the second control potential VC2 of the low logic level to enable the third transistor M3 and disable the fourth transistor M4. At this time, only the first low-pass filter and The second low-pass filter is enabled, and the third low-pass filter and the fourth low-pass filter are disabled. Therefore, the low-pass cutoff frequency F1 of the first low-pass filter and the second low-pass filter can be Apply to the power supply 200.

Figure 3 shows a frequency response diagram of the output gain of the power supply 200 according to an embodiment of the present invention, where the horizontal axis represents the operating frequency (MHz), and the vertical axis represents the output gain (dB). If the operating frequency approaches 0, the power supply 200 can have a low frequency maximum gain GL. According to the measurement results in Figure 3, when the power supply 200 is operating in the heavy load mode (as shown by a first curve CC1), only the first low-pass filter and the second low-pass filter are enabled to filter out Input noise higher than the heavy-load operating frequency FH (ie, low-pass cut-off frequency F1), and when the power supply 200 is operating in light-load mode (as shown by a second curve CC2), only the third low-pass filter The filter and the fourth low-pass filter are enabled to filter out input noise higher than the light-load operating frequency FL (ie, the low-pass cut-off frequency F2). Under this design, no matter in the light load mode or the heavy load mode, the double-frequency switching noise of the first clock potential VK1 and the second clock potential VK2 cannot pass through the switching circuit 210, so the electromagnetic interference of the power supply 200 The test results can be greatly improved.

In some embodiments, the component parameters of the power supply 200 may be as described below. The resistance value of the first resistor R1 may be between 0.9kΩ and 1.1kΩ, preferably 1kΩ. The resistance value of the second resistor R2 may be between 0.9kΩ and 1.1kΩ, preferably 1kΩ. The resistance value of the third resistor R3 can be between 0.18Ω and 0.22Ω, preferably 0.2Ω. The capacitance value of the first capacitor C1 can be between 1.42nF and 2.12nF, preferably 1.77nF. The capacitance value of the second capacitor C2 can be between 1.42nF and 2.12nF, preferably 1.77nF. The capacitance value of the third capacitor C3 can be between 0.96 nF and 1.44 nF, preferably 1.2 nF. The capacitance value of the fourth capacitor C4 can be between 0.96 nF and 1.44 nF, preferably 1.2 nF. The capacitance value of the fifth capacitor C5 may be between 176 pF and 264 pF, preferably 220 pF. The capacitance value of the sixth capacitor C6 can be between 1200 μF and 1800 μF, preferably 1500 μF. The inductance value of the first inductor L1 can be between 34.47 μH and 42.13 μH, preferably 38.3 μH. The inductance value of the second inductor L2 can be between 5.88 mH and 7.18 mH, preferably 6.53 mH. The ratio of the number of turns of the primary coil 241 to the secondary coil 242 can be between 10 and 30, preferably 20. When the power supply 200 is operating in the light-load mode, the sensed potential VE of the output rectifier 250 may be approximately equal to 0.04V, and the light-load operating frequency FL of the power supply 200 may be approximately equal to 133kHz. When the power supply 200 is operating in the heavy load mode, the sensed potential VE of the output rectifier 250 may be approximately equal to 3.4V, and the heavy load operating frequency FH of the power supply 200 may be approximately equal to 90 kHz. The critical potential compared with the sensing potential VE may be approximately equal to 1.7V. The above parameter range is obtained based on the results of many experiments, which helps to optimize the conversion efficiency and noise suppression effect of the power supply 200.

The present invention proposes a novel power supply, which includes a switching circuit using a plurality of low-pass filters. According to the actual measurement results, the aforementioned low-pass filter can effectively eliminate the frequency multiplication switching noise of the power supply, so as to comply with the specifications of the International Electrotechnical Commission. Generally speaking, the power supply of the present invention can significantly improve the test results of electromagnetic interference, so it is very suitable for application in various types of electronic devices.

It is worth noting that the above-mentioned potential, current, resistance value, inductance value, capacitance value, and other component parameters are not the limiting conditions of the present invention. The designer can adjust these settings according to different needs. The power supply of the present invention is not limited to the state shown in Figures 1-3. The present invention may only include any one or more of the features of any one or more of the embodiments shown in FIGS. 1-3. In other words, not all the features shown in the figures need to be implemented in the power supply of the present invention at the same time. Although the embodiment of the present invention uses Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) as an example, the present invention is not limited to this, and those skilled in the art can use other types of transistors instead. For example: Junction Gate Field Effect Transistor (JFET), or Fin Field Effect Transistor (Fin Field Effect Transistor, FinFET), etc., without affecting the effect of the present invention.

The ordinal numbers in this specification and the scope of the patent application, such as "first", "second", "third", etc., do not have a sequential relationship with each other, and they are only used to distinguish two having the same Different components of the name.

Although the present invention is disclosed as above in the preferred embodiment, it is not intended to limit the scope of the present invention. Anyone who is familiar with the art can make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, The scope of protection of the present invention shall be subject to those defined by the attached patent scope.

100,200～power supply; 110,210～switching circuit; 120-1,120-2,...,120-N～low pass filter; 130,230～resonant circuit; 140,240～transformer; 150,250 ～Output rectifier; 160,260～controller; 241～main coil; 242～secondary coil; C1～first capacitor; C2～second capacitor; C3～third capacitor; C4～fourth capacitor; C5～fifth capacitor ; C6 ~ sixth capacitor; CC1 ~ first curve; CC2 ~ second curve; D1 ~ first diode; D2 ~ second diode; D3 ~ third diode; D4 ~ fourth diode ; F1, F2～low-pass cutoff frequency; FH～heavy load operating frequency; FL～light load operating frequency; GL～low frequency maximum gain; L1～first inductor; L2～second inductor; M1～first transistor ; M2 ~ second transistor; M3 ~ third transistor; M4 ~ fourth transistor; N1 ~ first node; N2 ~ second node; N3 ~ third node; N4 ~ fourth node; N5 ~ fifth Node; N6～6th node; N7～7th node; N8～8th node; N9～9th node; N10～10th node; NIN～input node; NOUT～output node; R1～first resistor; R2 ~ Second resistor; R3 ~ third resistor; VC1 ~ first control potential; VC2 ~ second control potential; VE ~ sensing potential; VIN ~ input potential; VK1 ~ first clock potential; VK2 ~ second Clock potential; VOUT～output potential; VR～resonant potential; VSS～ground potential; VT～variable electric potential; VW～switching potential.

Fig. 1 is a schematic diagram of a power supply according to an embodiment of the invention. FIG. 2 is a schematic diagram of the power supply according to an embodiment of the invention. Figure 3 is a diagram showing the frequency response of the output gain of the power supply according to an embodiment of the present invention.

100～power supply; 110～switching circuit; 120-1, 120-2,...,120-N～low pass filter; 130～resonant circuit; 140～transformer; 150～output rectifier; 160～controller; VC1 ～first control potential; VC2～second control potential; VE～sensing potential; VIN～input potential; VK1～first clock potential; VK2～second clock potential; VOUT～output potential; VR～resonance potential; VT～Variable electric potential; VW～Switching potential.

Claims (8)

A power supply includes: a switching circuit including a plurality of low-pass filters, wherein the switching circuit is based on an input potential, a first clock potential, a second clock potential, a first control potential, and A second control potential generates a switching potential; a resonant circuit generates a resonant potential based on the switching potential; a transformer generates a variable voltage potential based on the resonant potential; an output rectifier generates a variable voltage based on the variable potential An output potential; and a controller for detecting a sensing potential of the output rectifier, wherein the controller determines the first control potential and the second control potential according to the sensing potential so as to enable the low Part of the pass filter and disable the rest of the low-pass filters; wherein the switching circuit includes: a first transistor having a control terminal, a first terminal, and a second terminal, wherein The control terminal of the first transistor is coupled to a first node, the first terminal of the first transistor is coupled to a second node to output the switching potential, and the first transistor of the The second terminal is coupled to an input node to receive the input potential; a second transistor has a control terminal, a first terminal, and a second terminal, wherein the control terminal of the second transistor is coupled Connected to a third node, the first end of the second transistor is coupled to a ground potential, and the second end of the second transistor is coupled to the second node; a first resistor , Having a first terminal and a second terminal, wherein the first terminal of the first resistor is coupled to the controller to receive the first clock potential, and the first electrical The second end of the resistor is coupled to the first node; and a second resistor having a first end and a second end, wherein the first end of the second resistor is coupled to the The controller receives the second clock potential, and the second terminal of the second resistor is coupled to the third node. The power supply described in claim 1, wherein the switching circuit further includes: a first capacitor having a first terminal and a second terminal, wherein the first terminal of the first capacitor is coupled To the first node, and the second terminal of the first capacitor is coupled to a fourth node; a second capacitor having a first terminal and a second terminal, wherein the first terminal of the second capacitor Terminal is coupled to the third node, and the second terminal of the second capacitor is coupled to the fourth node; and a third transistor having a control terminal, a first terminal, and a second Terminal, wherein the control terminal of the third transistor is coupled to the controller to receive the first control potential, the first terminal of the third transistor is coupled to the ground potential, and the third transistor The second end is coupled to the fourth node. The power supply described in claim 2 wherein the switching circuit further includes: a third capacitor having a first terminal and a second terminal, wherein the first terminal of the third capacitor is coupled To the first node, and the second end of the third capacitor is coupled to a fifth node; a fourth capacitor having a first end and a second end, wherein the fourth capacitor The first terminal is coupled to the third node, and the second terminal of the fourth capacitor is coupled to the fifth node; and a fourth transistor has a control terminal and a first terminal, And a second terminal, wherein the control terminal of the fourth transistor is coupled to the controller to receive the second control potential, the first terminal of the fourth transistor is coupled to the ground potential, and the The second terminal of the fourth transistor is coupled to the fifth node. For example, in the power supply described in item 3 of the scope of patent application, if the sensing potential is lower than a critical potential, the controller disables the third transistor and enables the fourth transistor, and if the sensing potential is lower than a threshold potential, the controller disables the third transistor and enables the fourth transistor. If the sensing potential is higher than or equal to the threshold potential, the controller enables the third transistor and disables the fourth transistor. The power supply according to item 3 of the scope of patent application, wherein the power supply has a light-load operating frequency and a heavy-load operating frequency, the first resistor and the first capacitor form a first low-pass filter, The second resistor and the second capacitor form a second low-pass filter, the first resistor and the third capacitor form a third low-pass filter, and the second resistor and the fourth capacitor form a The fourth low-pass filter, the low-pass cutoff frequency of each of the first low-pass filter and the second low-pass filter is approximately equal to the heavy-duty operating frequency, and the third low-pass filter and the The low-pass cutoff frequency of each of the fourth low-pass filters is approximately equal to the light-load operating frequency. The power supply of claim 3, wherein the resonance circuit includes: a fifth capacitor having a first end and a second end, wherein the first end of the fifth capacitor is coupled to The second node receives the switching potential, and the fifth capacitor The second end of the inductor is coupled to a sixth node; a first inductor has a first end and a second end, wherein the first end of the first inductor is coupled to the sixth node Node, and the second terminal of the first inductor is coupled to a seventh node to output the resonance potential; and a second inductor having a first terminal and a second terminal, wherein the second inductor The first terminal of the device is coupled to the seventh node, and the second terminal of the second inductor is coupled to the ground potential. The power supply according to claim 6, wherein the transformer includes: a main coil having a first end and a second end, wherein the first end of the main coil is coupled to the seventh Node to receive the resonance potential, and the second end of the main coil is coupled to the ground potential; and a secondary coil having a first end and a second end, wherein the first end of the secondary coil is It is coupled to an eighth node to output the variable voltage potential, and the second end of the auxiliary coil is coupled to a ninth node. The power supply according to claim 7, wherein the output rectifier includes: a first diode having an anode and a cathode, wherein the anode of the first diode is coupled to the first diode Eight nodes are used to receive the variable voltage potential, and the cathode of the first diode is coupled to an output node to output the output potential; a second diode has an anode and a cathode, wherein the second diode The anode of the diode is coupled to the ninth node, and the cathode of the second diode is coupled to the output Out node; a third diode having an anode and a cathode, wherein the anode of the third diode is coupled to a tenth node, and the cathode of the third diode is coupled to The eighth node; a fourth diode having an anode and a cathode, wherein the anode of the fourth diode is coupled to the tenth node, and the cathode of the fourth diode is coupled Connected to the ninth node; a third resistor having a first end and a second end, wherein the first end of the third resistor is coupled to the tenth node to output the sensing potential to The controller, and the second terminal of the third resistor is coupled to the ground potential; and a sixth capacitor having a first terminal and a second terminal, wherein the first terminal of the sixth capacitor Is coupled to the output node, and the second end of the sixth capacitor is coupled to the ground potential.

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