TWI466428B - Switching power supply and its control method - Google Patents

Description

Switching power supply and control method thereof

The invention relates to an exchange type power supply and a control method thereof, in particular to a related technology for adjusting the switching frequency of an AC-to-DC converter to control a switching frequency of a resonance type converter to obtain an optimum efficiency frequency and improving work efficiency. .

Generally, the switching power supply system is shown in FIG. 8 and includes an AC-to-DC converter 70 and a DC-DC converter 80. The AC-DC converter 70 is used to convert AC power into a high-voltage DC power supply. (Example 380 volts), and then the DC-to-DC converter 80 converts the high-voltage DC power to a DC power supply of the required voltage. When the DC-to-DC converter 80 is constructed of a resonant converter (such as an LLC converter), zero voltage or zero current switching can be achieved.

As shown in FIG. 9, a circuit configuration of an LLC converter 90 is disclosed, which includes a half bridge circuit 91, a resonant circuit 92, a transformer 93, and an output circuit 94. The half bridge circuit 91 is transmitted through the resonant circuit 92. The primary side of the transformer 93 is connected; the secondary side of the transformer 93 is connected to the output circuit 94; the resonant circuit 92 includes a resonant capacitor Cr, a magnetizing inductance Lm, and a leakage inductance Lr of the transformer 93; and the resonant circuit 92 has two resonant frequencies. The first resonant frequency (Fr1) is determined by the resonant capacitor Cr, the magnetizing inductance Lm, and the leakage inductance Lr of the transformer 93. The second resonant frequency (Fr2) is determined by the resonant capacitor Cr and the leakage inductance Lr of the transformer 93. .

Therefore, the switching frequency (Fs) of the LLC converter 90, the relationship between the two resonant frequencies (Fr1, Fr2) and the gain are as shown in FIG. 10, and the horizontal axis of the characteristic graph is the switching frequency (Fs), and the above is displayed. The two resonant frequencies (Fr1, Fr2), when the load is lightly loaded or the input voltage of the LLC converter 90 is too high, its switching frequency (Fs) will be greater than the resonant frequency (Fr2), and its output will be the gain of the input (G It will be lowered, when the load is heavy or the input voltage of the LLC converter 90 is too low, the switching frequency (Fs) of the resonant converter 90 is lowered to relatively increase its gain (G) to meet the load demand. At this time, the switching frequency (Fs) is smaller than the resonance frequency (Fr2). As can be seen from the above, the LLC converter 90 adjusts the switching frequency according to the change of the load or the input voltage. When the input voltage is fixed, when the load is light load, the switching frequency increases, and if the rising range is too large, the switching loss increases. Causes light load efficiency to be poor. If the load is heavy, the switching frequency is reduced. If the falling amplitude is too large, a large conduction loss will occur and the current passing through the power switch will have a large glitch and easy to enter the zero current switching region, causing system control failure. problem. Therefore, how to adjust the switching frequency and improve the working efficiency according to different load conditions, that is, it is necessary to seek a positive and feasible solution.

Therefore, the main object of the present invention is to provide a control method for a switching power supply, which mainly adjusts the switching frequency and the input voltage of the resonant converter according to the load condition, thereby obtaining an optimum efficiency frequency, so as to improve the working efficiency.

The main technical means for achieving the above purpose is that an exchange power supply includes an AC to DC converter and a resonance type converter, and the AC to DC converter outputs a DC power to the resonance type converter. The converter has a switching frequency and a resonant frequency; and performs the following steps: determining whether the resonant converter enters a steady state; when the resonant converter enters a steady state, it enters a voltage adjusting mode; the voltage adjusting mode is a resonant type conversion The switching frequency of the device is compared with a preset frequency, and a difference is generated to send a control command to the AC-to-DC converter to adjust the DC voltage outputted by the AC-to-DC converter, thereby changing the switching frequency of the resonant converter. Approaching the preset frequency; in the foregoing method, the output voltage of the AC-DC converter is dynamically adjusted according to the difference between the switching frequency and the preset frequency, that is, the input of the resonant converter is adjusted. Voltage, when the input voltage of the resonant converter is large, the switching frequency will increase, and conversely, when the resonant converter is lost Voltage decreases, the switching frequency will reduce, thereby dynamically adjusting the switching frequency of the resonator can be of a transducer, it approaches the predetermined frequency, thereby improving work efficiency.

The aforementioned preset frequency refers to the resonant frequency of the resonant type converter, and the voltage adjusting mode causes the switching frequency to approach the resonant frequency.

The aforementioned preset frequency refers to an optimum efficiency frequency measured according to different load conditions, and the voltage adjustment mode is such that the switching frequency approaches the optimal efficiency frequency.

It is still another object of the present invention to provide an exchange power supply that dynamically adjusts the switching frequency of its resonant converter to approach the resonant frequency to improve the operating efficiency of the resonant converter.

The main technical means adopted to achieve the foregoing objectives The power supply device comprises: an AC-to-DC converter having a power factor correction circuit and a PFC controller, wherein the input of the power factor correction circuit is connected to an AC power source, and the output end thereof provides a DC power supply; the PFC control The device has a feedback terminal and a control terminal, and the control terminal is connected with the power factor correction circuit to control the DC voltage outputted by the power factor correction circuit; the DC-to-DC converter has a resonance type converter and a resonance controller The input end of the resonant type converter is connected to the output end of the power factor correction circuit; the resonant controller has a feedback end and a control end, and the feedback end is connected to the output end of the resonant type converter, and the control thereof is controlled The terminal is connected to the resonance type converter to control the switching frequency thereof; a feedback compensation controller is respectively connected with the PFC controller, the resonance type converter and the resonance controller thereof for comparing the switching frequency of the resonance type converter Adjusting the feedback signal of the PFC controller according to the difference frequency and adjusting the output voltage of the power factor correction circuit.

The switching power supply can be used to dynamically adjust the output voltage of the power factor correction circuit according to the difference between the switching frequency and the resonant frequency, that is, adjust the input voltage of the resonant converter, thereby dynamically adjusting The switching frequency of the resonant converter is brought closer to the preset frequency, thereby improving the working efficiency.

A preferred embodiment of the switching power supply of the present invention, as shown in FIG. 1, includes an AC to DC converter 10, a DC to DC converter 20, and a feedback compensation controller 30; The AC to DC converter 10 has a power factor correction circuit 11 and a PFC controller 12, the input of the power factor correction circuit 11 and an AC power source ACin, the output of which provides a rectified and boosted DC voltage VBulk; The PFC controller 12 has a feedback terminal FB and a control terminal Duty, and the control terminal Duty is connected to the power factor correction circuit 11 to control the power factor correction circuit 11 to output a DC voltage VBulk according to the feedback signal; the DC to DC The converter 20 has a resonant converter 21 and a resonant controller 22. The resonant converter 21 can be in the form of LLC, series resonant (SRC), parallel resonant (PRC), etc., in this embodiment, LLC Form, and the input end of the resonant converter 21 is connected to the output of the power factor correction circuit 11, that is, the DC voltage VBulk outputted by the power factor correction circuit 11 is sent to the resonant converter 2 1. The DC voltage VBulk is an input voltage of the resonant converter 21; the resonant controller 22 has a feedback terminal FB and a control terminal Duty, and the feedback terminal FB is connected to the output end of the resonant converter 21, The control terminal Duty is connected to the resonance type converter 21 to control the switching frequency thereof so that the switching frequency approaches a predetermined frequency. In the embodiment, the predetermined frequency refers to the resonance of the resonance type converter 21. The feedback compensation controller 30 is connected to the PFC controller 12, the resonance converter 20 and its resonance controller 22, respectively, for comparing the switching frequency and the resonance frequency of the resonance converter 20, and according to the switching frequency and The difference between the resonant frequencies is used to adjust the feedback signal of the PFC controller 12, thereby adjusting the DC voltage VBulk output by the power factor correction circuit 11. The specific configuration of a feasible embodiment of the feedback compensation controller 30 is shown in FIG. The control unit 31 has two or more input terminals and one or more output terminals, and the two input terminals are respectively connected to obtain the switching frequency Fs of the resonance type converter 21 and the resonance frequency Fr, and according to the switching frequency. The difference between Fs and the resonant frequency Fr generates a control command, which is sent by the output of the control unit 31. A switching unit 32 determines whether the control command of the control unit 31 is sent according to whether the resonant converter 21 enters a steady state. Whether the resonant converter 21 enters the steady state can be judged by the state of the feedback current or the switching frequency, wherein the feedback current can be the current Itr of the transformer, and when the variation of the transformer current Itr or the switching frequency Fs is within a certain range, It can be determined that the steady state has been entered. In this embodiment, the switching unit 32 has a switch 321 and a filter 322. The switch 321 is disposed at the output end of the control unit 31, and the switch 321 is outputted by the filter 322. Control, the input end of the filter 322 is used to receive the transformer current I _tr , that is, the transformer current I _tr determines whether the switch 321 is turned on and the control unit 32 sends a control command; the specific control is based on the resonant converter When the state 21 enters the steady state, the feedback controller 30 sends a control command to adjust the output voltage VBulk of the power factor correction circuit 10, thereby controlling the resonance type conversion. The input voltage of 21 and its switching frequency; if the resonant converter 21 does not enter the steady state, the switch 321 will switch to a null segment 321a; a feedback signal generator 34 is provided at the feedback end of the PFC controller 12 On the FB, a feedback signal is generated and transmitted back to the PFC controller 12, and the feedback signal is calculated according to the DC voltage Vbulk outputted by the power factor correction circuit 11 and a fixed normal voltage control command BVC (Bulk Voltage Command). The normal voltage control command BVC is sent to the feedback signal generator 34 after being sent to the feedback signal generator 34 through a communication interface and sent to the feedback signal generator 34. In other words, before the control unit 31 sends the control command, for example, in the transient state, The feedback signal generator 34 generates a feedback signal based on the DC voltage Vbulk output from the power factor correction circuit 11 and the normal voltage control command BVC, and sends it to the PFC controller 12 to control the DC voltage Vbulk output by the power factor correction circuit 11, Mainly based on voltage regulation; once the resonant converter 21 enters a steady state, the feedback compensation controller 30 then enters a voltage adjustment mode, which is controlled by the control unit 31 according to the resonance The difference between the switching frequency of the converter 21 and the resonant frequency generates a control command, which is sent to the feedback signal generator 34 via the communication interface, and the DC voltage VBulk output by the feedback signal generator 34 according to the control command and the power factor correction circuit 11 is outputted by the feedback signal generator 34. The feedback signal FB is generated after the operation with the normal voltage control command BVC.

The feedback compensation controller 30 constructed by the above configuration can compare the switching frequency Fs and the resonance frequency Fr of the resonance type converter 21 after the resonance type converter 21 enters the steady state, and generate a control command according to the difference thereof to join The normal voltage control command BVC, which in turn is operated with the output voltage Vbulk of the power factor correction circuit 11, changes the feedback signal of the power factor correction circuit 11 to change its output voltage Vbulk, since the output voltage Vbulk of the power factor correction circuit 11 changes, the resonance The input voltage of the type converter 21 is thus changed, and the switching frequency Fs is adjusted to be close to the resonant frequency Fr, so that the ratio of the switching frequency Fs to the resonant frequency Fr approaches or equals 1, thereby increasing the resonance type. The operating efficiency of the converter 21.

Specific configuration of a further feasible embodiment of the aforementioned feedback compensation controller 30 Referring to FIG. 3, the control unit 31 includes a control unit 31, a switching unit 32, and a feedback signal generator 34, which are substantially the same as the foregoing embodiment, except that the embodiment further includes a digital analog converter 33. The digital analog converter 33 has an input end and an output end, and its input end is connected to the output end of the control unit 31 through the aforementioned switch 321.

The feedback signal generator 34 is connected to the output of the digital analog converter 33 through a filter 35. The feedback signal generator 34 is based on the DC voltage Vbulk output from the power factor correction circuit 11, and a normal voltage control command. The BVC is generated after the operation of the control command sent from the control unit 31. When the resonant type converter 21 enters the steady state, the feedback compensation controller 30 then enters a voltage adjustment mode, and the control unit 31 generates a control command according to the difference between the switching frequency of the resonant type converter 21 and the resonant frequency, and then converts to analogy. After being processed and sent to the feedback signal generator 34, the feedback signal generator 34 calculates the DC voltage Vbulk output from the power factor correction circuit 11 and the normal voltage control command BVC and the control command sent from the control unit 31. A feedback signal FB is generated.

A general resonant converter (such as an LLC converter) increases the switching frequency Fs at a light load to reduce the gain, resulting in increased switching loss and poor efficiency at light loads; if the load is heavy, the switching frequency is reduced. Fs increases the gain, but may cause the switching frequency Fs to be smaller than the resonance frequency Fr, resulting in a large conduction loss and a large surge. However, the present invention utilizes the foregoing techniques to adjust the switching frequency Fs of the resonant type converter at a steady state depending on different load conditions to bring it closer to the resonant frequency Fr to improve efficiency and solve the aforementioned problems. One of the ways to adjust the switching frequency Fs is achieved by changing the input voltage of the resonant converter.

As shown in FIG. 4, a comparison graph of an input voltage of a conventional resonant type converter and an input voltage of the resonant type converter of the present invention is disclosed, and the vertical axis of the graph is the output voltage Vbulk of the power factor correcting circuit 11 (ie, The input voltage of the resonant converter), the horizontal axis changes from left to right for the load (from light to heavy); the fixed horizontal line shown in the figure refers to the feedback on the traditional PFC controller. The normal voltage control command BVC, that is, the PFC controller of the conventional switched power supply, keeps the output voltage of the power factor correction circuit constant; and the physical curve shown in the figure as the load changes is the present invention in the PFC controller. The dynamic voltage control command bvc generated on the grant end can be seen from the figure. The dynamic voltage control command bvc is incremented with the weight of the load, that is, when the load is light, the dynamic voltage control command bvc will make the resonant type converter The input voltage is lowered. Under this condition, since the input voltage of the resonant converter is lowered, the switching frequency Fs will be lowered to approach the resonant frequency, thereby solving the conventional resonant converter at light load. The switching frequency Fs is greater than the resonant frequency Fr, resulting in poor efficiency; conversely, when the load is increased, the switching frequency Fs of the resonant converter is originally reduced, and may even be less than the resonant frequency Fr, causing excessive conduction loss, so the present invention improves dynamics. The voltage control command bvc, in turn, increases the input voltage of the resonant converter. Under this condition, the switching frequency Fs will be increased and approach the resonant frequency, so that the switching frequency Fs can be effectively prevented from switching due to the resonant frequency Fr. The problem of excessive loss is greatly increased, and the overall efficiency is greatly improved.

As shown in FIG. 5, a comparison graph of the switching frequency Fs and the load variation of the conventional resonant converter and the present invention is disclosed. The vertical axis of the graph is the switching frequency Fs of the resonant converter, and the horizontal axis is the load variation. Condition Left to right represents the load from light to heavy); the dotted line shown in the figure decrements with load emphasis refers to the switching frequency Fs of the conventional resonant converter, while the horizontal line that remains constant is the switching frequency Fs controlled by the present invention. ', the switching frequency Fs' and approaches the resonant frequency.

Since the hardware circuit has a withstand voltage and a maximum or minimum output limit, the output voltage Vbulk of the power factor correction circuit 11 has a maximum voltage and a minimum voltage limit, so the dynamic voltage control command bvc must have a maximum limit value and a minimum limit value. For increasing the load so that the dynamic voltage control command bvc is higher than the maximum limit value (as shown by the b-axis of the horizontal axis in FIG. 5), maintaining the output voltage Vbulk of the power factor correction circuit 11 at the highest voltage limit, and letting the switching The frequency Fs' falls to continue maintaining the output voltage of the resonant type converter 21. That is, the dynamic voltage control command bvc is higher than its maximum limit value, that is, the voltage adjustment mode is ended.

Please refer to FIG. 6 , which is a specific configuration of a further feasible embodiment of the feedback compensation controller 30 . The basic structure of the feedback compensation controller 30 is substantially the same as that of the previous embodiment. The difference is that the digital pulse width modulator 36 is used in the embodiment. In place of the digital analog converter 33 in the previous embodiment, the control command sent by the control unit 31 is sent to the digital pulse width modulator 36 to generate a variable pulse width control command, which is sent to the feedback signal through the filter 35. The number generator 34 performs an adjustment operation of the feedback signal.

Referring to FIG. 7 again, the specific configuration of another feasible embodiment of the feedback compensation controller 30 is mainly implemented by an analog circuit structure, which includes: a voltage dividing circuit 37, which is mainly composed of a voltage dividing resistor. R1, R2, the series connection node of the two voltage dividing resistors R1, R2 and the PFC controller 12 (in this figure The feedback terminal of the power supply correction circuit 11 is connected to the output terminal Vbulk and the ground terminal of the power factor correction circuit 11 respectively. The current controller 38 is mainly composed of one. The transistor Q1 is composed of an adjustment resistor Rx, and the transistor Q1 is mainly composed of a double junction transistor (BJT), and the collector is connected to the serial connection node of the voltage dividing circuit 37 through the adjustment resistor Rx; the transistor The base current Ib of Q1 will affect its collector current Ic; a proportional integral controller 39 has a positive input, a negative input and an output, and the negative input takes the value of the switching frequency Fs, which is positive The terminal input takes the value of the resonant frequency Fr as a reference value, and its output terminal is connected to the base of the transistor Q1 of the current controller 38.

With the feedback compensation controller 30 described above, a proportional control controller 39 can generate a control signal according to the ratio of the switching frequency Fs of the resonance type converter 21 to the resonance frequency Fr to control the conduction degree of the transistor Q1 of the current controller 38. Therefore, the adjustment resistor Rx changes the voltage division ratio of the two voltage dividing resistors R1 and R2 on the voltage dividing circuit 37 to adjust the feedback signal of the PFC controller 12 and the output voltage of the power factor correction circuit 11, and change the input of the resonance type conversion device 21. The voltage and its switching frequency Fs cause the switching frequency Fs to approach the resonant frequency Fr at steady state.

As described above, one aspect of the present invention for improving the operational efficiency of the resonant converter 21 is to adjust its input voltage such that its switching frequency Fs approaches a predetermined frequency. In the foregoing embodiment, the preset frequency is The resonance frequency Fr of the resonance type converter 21. In addition, the present invention can build a lookup table in the control unit 31, and the most obtained in the comparison table according to different load conditions (such as heavy load, medium load and light load). Preferably, the voltage adjustment mode generates a control command according to the difference between the switching frequency Fs and the optimal efficiency frequency to adjust the DC voltage Vbulk output by the power factor correction circuit 11, thereby bringing the switching frequency Fs closer to the optimum. Efficiency frequency, thereby increasing work efficiency.

10‧‧‧AC to DC converter

11‧‧‧Power Factor Correction Circuit

12‧‧‧PFC controller

20‧‧‧DC to DC converter

21‧‧‧Resonance converter

22‧‧‧Resonance controller

30‧‧‧Reward compensation controller

31‧‧‧Control unit

32‧‧‧Switch unit

321‧‧‧ switch

321a‧‧‧empty section

322‧‧‧ filter

33‧‧‧Digital Analog Converter

34‧‧‧Responsive signal generator

35‧‧‧ filter

36‧‧‧Digital Pulse Width Modulator

37‧‧‧ Voltage dividing circuit

38‧‧‧ Current controller

39‧‧‧Proportional Integral Controller

70‧‧‧AC to DC converter

80‧‧‧DC to DC converter

90‧‧‧LLC Converter

91‧‧‧Half-bridge circuit

92‧‧‧Resonance circuit

93‧‧‧Transformers

94‧‧‧Output circuit

1 is a schematic diagram of a circuit structure of the present invention.

2 is a block diagram of one possible embodiment of a controller of the present invention.

Figure 3 is a block diagram of yet another possible embodiment of the controller of the present invention.

Fig. 4 is a graph showing the relationship between the input voltage of the resonant type converter of the present invention and the light weight of the load.

Fig. 5 is a graph showing the relationship between the switching frequency of the resonant converter of the present invention and the light weight of the load.

Figure 6 is a block diagram of yet another possible embodiment of the controller of the present invention.

Figure 7 is a block diagram of another possible embodiment of the controller of the present invention.

Figure 8 is a block diagram of a known switched power supply.

Figure 9 is a block diagram of a known resonant type converter.

Figure 10 is a graph showing the switching frequency, resonant frequency and gain of a known resonant converter.

10. . . AC to DC converter

11. . . Power factor correction circuit

12. . . PFC controller

20. . . DC to DC converter

twenty one. . . Resonant converter

twenty two. . . Resonant controller

30. . . Feedback compensation controller

Claims (16)

An exchange power supply comprises: an AC-to-DC converter having a power factor correction circuit and a PFC controller, wherein the input of the power factor correction circuit is connected to an AC power source, and the output end thereof provides a DC power supply; The PFC controller has a feedback terminal and a control terminal, and the control terminal is connected with the power factor correction circuit to control the DC voltage outputted by the power factor correction circuit; the DC-to-DC converter has a resonance type converter and a a resonant controller, wherein the input end of the resonant type converter is connected to an output end of the power factor correction circuit; the resonant controller has a feedback end and a control end, and the feedback end is connected to the output end of the resonant type converter The control end is connected with the resonance type converter to control the switching frequency thereof; a feedback compensation controller is respectively connected with the PFC controller, the resonance type converter and the resonance controller thereof for comparing the resonance type converter Switching frequency and a preset frequency, and adjusting the feedback signal of the PFC controller according to the difference, thereby adjusting the power factor correction circuit Voltage. The switching power supply device of claim 1, wherein the feedback compensation controller comprises: a control unit that generates a control command according to a difference between the switching frequency and the preset frequency, and sends the control command from the output of the control unit. a switching unit determines whether the control unit's control command is sent according to whether the resonant type converter enters a steady state; a feedback signal generator is disposed on the feedback end of the PFC controller to generate a return The signal is transmitted back to the PFC controller, and the feedback signal is based on the DC power output of the power factor correction circuit and a normal voltage control command. After the operation, the normal voltage control command is sent to the feedback signal generator after being added to the control command sent by the control unit through a communication interface. The switching power supply device of claim 1, wherein the feedback compensation controller comprises: a control unit that generates a control command according to a difference between the switching frequency and the preset frequency, and sends the control command from the output of the control unit. a switching unit determines whether the control unit's control command is sent according to whether the resonant type converter enters a steady state; a digital analog converter has an input end and an output end, and the input end is transmitted through the foregoing switch and control The output of the unit is connected; a feedback signal generator is disposed on the feedback end of the PFC controller, and is connected to the output of the digital analog converter through a filter. The switching power supply device of claim 1, wherein the feedback compensation controller comprises: a control unit that generates a control command according to a difference between the switching frequency and the preset frequency, and sends the control command from the output of the control unit. a switching unit determines whether the control unit's control command is sent according to whether the resonant type converter enters a steady state; a digital pulse width modulator has an input end and an output end, and the input end is transmitted through the switch Connected to the output of the control unit; a feedback signal generator is disposed on the feedback end of the PFC controller, and is coupled to the output of the digital pulse width modulator through a filter. The switching power supply of any one of claims 2 to 4, wherein the predetermined frequency is a resonant frequency of the resonant type converter. The switching power supply as claimed in claim 1, the preset frequency Rate refers to the optimal efficiency frequency set according to different load conditions. The switching power supply according to any one of claims 2 to 4, wherein the preset frequency is an optimal efficiency frequency set according to different load conditions, and the optimal efficiency frequency is built in a control form in a control table. In the unit. The switching power supply according to claim 5, wherein the switching unit has a switch and a filter, the switch is disposed at an output end of the control unit, and the switch is controlled by an output signal of the filter, and the input of the filter The terminal is used to receive the feedback current of the resonant converter. The switching power supply according to claim 6, wherein the switching unit has a switch and a filter, the switch is disposed at an output end of the control unit, and the switch is controlled by an output signal of the filter, and the input of the filter The terminal is used to receive the feedback current of the resonant converter. The switching power supply according to claim 7, wherein the switching unit has a switch and a filter, the switch is disposed at an output end of the control unit, and the switch is controlled by an output signal of the filter, and the input of the filter The terminal is used to receive the feedback current of the resonant converter. The switching power supply device according to claim 1, wherein the feedback compensation controller comprises: a voltage dividing circuit, which is mainly composed of a voltage dividing resistor, and the series connection node of the two voltage dividing resistors is back with the PFC controller. The terminal is connected, and the other end of the two-divided resistor is connected to the output end of the power factor correction circuit and the ground end respectively; a current controller is mainly composed of a transistor and an adjusting resistor, the transistor The collector is connected to the serial connection node of the voltage dividing circuit by adjusting the resistor; A proportional integral controller has a positive input, a negative input and an output, and the negative input takes the value of the switching frequency, and the positive input takes the value of the resonant frequency as a reference value, and the output end thereof Connected to the base of the transistor of the current controller. The switching power supply of claim 11, wherein the transistor is mainly composed of a double junction transistor (BJT). A switching power supply control method mainly comprises: an exchange power supply device comprising an AC to DC converter and a resonance type converter, wherein the AC to DC converter outputs a DC voltage to the resonance type converter, The resonant converter has a switching frequency and a resonant frequency; and performs the following steps: determining whether the resonant converter enters a steady state; when the resonant converter enters a steady state, it enters a voltage adjusting mode; the voltage adjusting mode is relatively resonant The switching frequency of the converter and a predetermined frequency, and a difference is generated to send a control command to the AC-to-DC converter to adjust the voltage value of the DC-to-DC converter output DC power, thereby changing the resonant converter. Switch the frequency so that it approaches the preset frequency. The control method of the switching power supply according to claim 13, wherein the predetermined frequency refers to a resonant frequency of the resonant type converter, and the voltage adjusting mode causes the switching frequency to approach the resonant frequency. The control method of the switching power supply according to claim 13, wherein the preset frequency refers to an optimal efficiency frequency measured according to different load conditions, and the voltage adjustment mode is such that the switching frequency approaches the optimal efficiency frequency. The switched power supply as claimed in any one of claims 13 to 15 The control method of the AC to DC converter has a power factor correction circuit, the output voltage of the power factor correction circuit has a maximum voltage limit, and the control command has a maximum limit value corresponding to the aforementioned maximum voltage limit, when the control command is greater than The maximum limit value ends the voltage adjustment mode and maintains the output voltage of the power factor correction circuit at the highest voltage limit.