TWI384740B - Extensible switching power circuit - Google Patents

Description

Expandable switching power supply circuit

The invention relates to a switched power supply circuit, in particular to an expandable switching power supply circuit capable of providing matching current according to different power loads.

At present, the switching power supply circuit is widely used in electronic products to convert AC power into a DC working power supply for electronic circuits in electronic products, and the high-power type switching power supply circuit includes a flyback type and a forward type. Isolated power supply circuits such as full-bridge, half-bridge and push-pull.

Referring to FIG. 1 , there is a first switching power supply circuit 40 , that is, a flyback power supply circuit, which includes: a rectifying and filtering circuit 41 for connecting an AC voltage, and rectifying and filtering the AC voltage into a DC voltage. The output of the transformer 42 has one end of the primary winding L1 connected to the output end of the rectifying and filtering circuit 41, and one end of the secondary winding L2 is connected with a half-wave rectifier D1 and an output capacitor Cout, which are connected in sequence. The voltage waveform of the secondary winding L2 is further filtered into a DC voltage level, and the output capacitor Cout is an output terminal Vo of the flyback power supply circuit; wherein the output capacitor is a capacitance value of 100 uF or more; and an active switch 43 is connected in series The other end of the primary winding L1 of the transformer 42, that is, the other end of the primary winding L1 of the transformer 42 is sequentially grounded via the active switch 43 and a resistor; a pulse width modulation controller 44 is connected to the control end of the active switch 43. The active switch 43 outputs a pulse width modulation signal; a feedback circuit 45 is connected between the output terminal Vo of the secondary winding L2 of the transformer 42 and the pulse width modulation controller 44 to The reaction output voltage changes to the pulse width modulation controller 44.

The pulse width modulation controller 44 adjusts the pulse width time of the pulse width modulation signal according to the change of the voltage of the output terminal Vo according to the feedback circuit 45, that is, when the current state is the heavy load state, the pulse width modulation controller 44 The adjustment pulse width time is increased to control the conduction time of the active switch 43 to become longer, so that the secondary winding L2 of the transformer 42 obtains a larger current to supply the power required for the heavy load. On the other hand, when the current mode is reduced to medium heavy load or light load, the pulse width modulation controller 44 reduces the pulse width time of the pulse width modulation signal outputted to the active switch 43 to reduce the secondary winding L2 of the transformer 42. The current; thus, the flyback power supply circuit can provide a regulated DC power supply according to the load state.

However, the above-mentioned flyback power supply circuit 40 provides a DC power supply because the output voltage Cout filters the induced voltage of the secondary winding L2 into a DC level Vo. However, as shown in FIG. 2, the DC level Vout is unstable. A chopping waveform, and the chopping current amplitude is related to the on-time of the active switch 43. If the on-time is shorter, the charging time of the output capacitor Cout is shortened and the discharging time is increased, and the chopping current amplitude is increased; The current amplitude is low, and long-term use may damage the load.

Referring to FIG. 3, there is a second switching power supply circuit 50 for improving the output current waveform of the single-stage flyback power supply circuit. The method includes: a rectifying and filtering circuit 51 connected to an alternating current voltage to convert the alternating current voltage. After DC high voltage output, four sets of transformers TA~TD, one end of four sets of primary windings L11~L41 are connected to the rectifying and filtering circuit 51 and the other end is grounded through an active switch Q1, Q2, Q3, Q4, respectively. The secondary windings L12~L42 of the group transformer TA~TD are respectively output through a diode TD1, TD2, TD3, TD4, and are commonly connected to an output terminal Vo; a pulse width modulation controller 52 includes four The group pulse width modulation signal output terminals T1~T4 are respectively connected to the control terminals of the active switches Q1, Q2, Q3 and Q4 of the corresponding transformer TA~TD to control the opening and closing of the four groups of active switches Q1, Q2, Q3 and Q4; A feedback circuit 53 is connected between the four sets of parallel output terminals Vo and the pulse width modulation controller 52, and reacts the voltage change of the output terminal Vo to the pulse width modulation controller 52, so that the pulse width adjustment The variable controller 52 adjusts the pulse width of the pulse width modulation signal according to the output voltage change.

Referring to FIG. 4A to FIG. 4E, the pulse width modulation controller 52 outputs waveforms of two sets of pulse width modulation signals V _G1 /V _G2 , because of the pulse width time of each pulse width modulation signal V _G1 /V _G2 . It is equal to the corresponding transformer TA/TB primary winding L11/L21 voltage signal existence time. When the voltage signal of the primary winding L11 of the first transformer TA disappears, the secondary winding L12 of the first transformer TA outputs the induced voltage V _L12 and continues until the voltage signal of the primary winding L1 is generated, but only the voltage signal of the primary winding L11 During the existence, the secondary winding L12 is caused to generate a counter electromotive force, so that the output voltage V _L12 of the secondary winding L12 of the first transformer TA has an energy gap V _inv1 phenomenon; similarly, the second transformer TB primary winding During the presence of the L21 voltage signal, the secondary winding L22 output voltage V _L22 also produces an energy gap V _inv2 .

Since the switching power supply circuit adopts a single pulse width modulation controller 52, different phases of the complex pulse width modulation signal V _G1 /V _G2 are controlled, as shown in FIG. 4A and FIG. 4C , wherein two pulse width modulation signals are provided. The partial pulse width of V _G1 /V _G2 overlaps between t2-t3, t6-t7, t10-t11, and t14-t15, so the output ends of the two first and second transformers TA and TB secondary windings L12 and L22 The energy gap V _inv1 V _inv2 can be complemented and filled, and a DC voltage Vout of a near DC level is outputted at the parallel output terminal, and a large output capacitor of _{100 uF} or more is not used at each output end, but as shown in FIG. 4E, The output of the DC voltage Vout is still relatively unstable, and the number of terminals of the pulse width modulation output of the single pulse width modulation controller 52 is fixed, and the maximum number of active switches Q1 to Q4 is limited by the above, for example, There are still limits on the scope of application, and further improvements must be made.

In view of the above disadvantages of the existing switched power supply circuit, the main object of the present invention is to provide an expandable switching power supply circuit capable of providing matching current according to different power loads, and without using a large capacitance value output capacitor, which is helpful. Reduce production costs.

The main technical means used to achieve the above purpose is that the expandable switching power supply circuit system comprises: a rectifying and filtering circuit for supplying an alternating voltage connection, and rectifying and filtering the alternating current voltage into a high-current high-voltage output; the complex power supply mode The plurality of input ends are connected to the output end of the rectifying and filtering circuit, and the plurality of voltage output ends are connected in parallel to an output end, and each power module comprises at least one transformer and a pulse width modulation controller, wherein the transformer comprises a primary winding and a secondary winding; at least one synchronization signal generating unit, each of the at least one synchronization generating unit is connected in series between the two power modules, wherein the at least one synchronous signal generating unit reflects the two power modules a transformer voltage signal of a power module, and generates a synchronization signal and outputs the pulse width modulation controller to another power module as a basis for determining the phase of the driving signal for driving the active switch, wherein the two power modules The pulse widths of the pulse width modulation signals do not overlap each other.

The synchronous signal generating unit generates a synchronization signal according to a voltage change of a transformer of one power module, and outputs the synchronization signal to a pulse width modulation controller of another power module, so that the pulse width modulation controller outputs the signal to the active switch. The driving signal does not overlap with another set of power modules; thus, the time of presence/absence of the output voltage waveforms of the two sets of power modules overlaps, and the overlapping area is greater than 101%, meaning that one of them The energy present time of the group power module must exceed at least 1~10% overlap ratio of the no-energy time of the other power module. Therefore, the two power modules connected by the synchronous signal generating unit of the present invention can not only fully complement the energy gap of the output end, but also increase the overall output current without using a large output capacitor; Adjust the number of power modules and synchronous signal generation units for different rated power loads, and the application flexibility is large.

Referring to FIG. 5 and FIG. 6 , a first preferred embodiment of the scalable switchable power supply circuit 10 of the present invention includes: a rectifying and filtering circuit 11 for supplying an alternating voltage connection, and rectifying and filtering the alternating current voltage into a After DC high voltage output, the plurality of power modules 20 are connected in parallel, and the plurality of input ends are connected to the output end of the rectifying and filtering circuit 11, and the plurality of voltage output terminals V1, V2, ..., Vn are commonly connected to one In the present embodiment, each power module 20 is a flyback power supply circuit, and each power module 20 includes a transformer T1 including a primary winding L11 and a primary winding L12; The secondary winding L12 is connected to the at least one diode TD1 as an output terminal; in the embodiment, the two-pole connector TD1 is further connected with a small filter capacitor C _F (about 104 pF) for electromagnetic interference; at least one active The switch Q1 is connected to the rectifying and filtering circuit 11 in series with the primary winding L11 of the transformer T1; and a pulse width modulation controller 23 whose output end is connected to the control terminal G1 of the corresponding active switch Q1 for controlling Opening and closing of the corresponding active switch Q1 Further, an input terminal of the pulse width modulation controller 23 is connected to the voltage output terminal V1 by a feedback circuit 24 to obtain a voltage change of the voltage output terminal V1, so the pulse width modulation controller 23 changes according to the voltage. The pulse width modulation signal is output to the corresponding active switch Q1 to control its on-time.

The at least one synchronization signal generating unit 30 is connected in series between the two power modules 20; in this embodiment, each of the at least one synchronization generating unit 30 is connected in series with each other. Between the parallel power modules 20, the two adjacent power modules 20 are a first and second power module 20, and the at least one synchronization signal generating unit 30 is a transformer that reacts to the first power module 20. The voltage signal generates a synchronization signal and outputs the signal to the pulse width modulation controller 23 of the second power module 20 as a basis for determining the phase of the driving signal of the active switch Q2 of the second power module 20. In this embodiment, the at least one synchronization signal generating unit 30 is configured to reflect the transformer TA voltage signal of the first power module 20 of each adjacent power module 20, that is, the voltage signal of the primary winding L11 of the transformer TA can be reacted. The voltage signal of the winding of the stage winding L12.

Referring to FIG. 7, a second preferred embodiment of the scalable switching power supply circuit 10a of the present invention is substantially the same as the first preferred embodiment, but each power module 20a is a push-pull power supply circuit. The utility model comprises: a middle tap transformer T1′, comprising a second end of the primary winding L11, the two ends of the primary winding L11 are respectively connected with the two active switches Q11/Q12, and the tap end of the primary winding L11 is connected with the rectifying and filtering circuit 11 output connection, and the second winding L12 of the intermediate tap transformer T1' is connected with two sets of diodes TD11/TD12, the tap end of the secondary winding L12 is grounded; and a pulse width modulation controller 23a, is connected to the control end of two corresponding active switches Q11/Q12, and outputs two sets of pulse width modulation signals to the corresponding active switches Q11/Q12 to control the on-time of the two active switches Q11/Q12. In this embodiment, each of the synchronization signal generating units 30 is also connected between the pulse width modulation controllers 23a of the two adjacent parallel power modules 20a, and the first power source of each of the two adjacent parallel power modules 20a is sensed. The primary winding L11 voltage signal of the middle tapping transformer T1' of the module is further reacted to the pulse width modulation controller 23a of the second power module 20a for adjusting the pulse width modulation controller 23a of the second power module 20a. Wide adjustment signal phase and pulse width.

In addition, the power modules 20, 20a of the present invention may be full-bridge and half-bridge isolated switching power supply circuits.

Please refer to FIG. 6, FIG. 11 and FIG. 12 simultaneously to further explain the detailed circuit and circuit operation of the synchronous signal generating unit 30. 6 is a detailed circuit diagram of a first preferred embodiment of the present invention, FIG. 11 is a detailed circuit diagram of the synchronous signal generating unit 30 of the first preferred embodiment, and FIG. 12 is a waveform diagram of FIG.

The synchronization signal generating unit 30 includes a phase detecting circuit 321, a synchronous phase delay reference unit 32, a phase delay correction control circuit 34, a synchronous delay phase pulse extracting unit 33, and a synchronous signal capturing circuit 35.

The phase detecting circuit 321 obtains the voltage signal V _A of the primary winding L11 of the first power module 20 through a current comparator 25, and detects the energy gap of the power source.

The input end of the synchronous phase delay reference unit 32 is connected to the phase detecting circuit 321 to obtain a power supply energy gap, and then generates an AND winding with the primary winding L11 according to the upper edge or lower edge signal V _B outputted by the phase detecting circuit 321 . The sub-voltage waveform periodically synchronizes the phase delay reference signal V _D ; the phase delay reference signal V _D can be an analog sawtooth wave or a digital pulse wave. In this embodiment, the synchronous phase delay reference unit 32 is an RC integration circuit, but may also be a digital delay chopping counter or an analog sawtooth signal generating circuit.

The phase delay correction control circuit 34 is connected to the primary winding L11 of the first-stage power module 20 through a phase delay correction circuit 31, wherein the phase delay correction circuit 31 is an RC integration circuit R10/C3, so The voltage signal V _{A of the} primary winding L11 is integrated, and the DC voltage V _{E is} taken out.

The synchronous delay phase pulse extracting unit 33 includes a forward input terminal +, an inverting input terminal - and an output terminal F; wherein the forward input terminal + is connected to the output terminal D of the synchronous phase delay reference unit 32. a phase delay reference signal V _{D is obtained} , and the inverting input terminal is connected to the output terminal E of the phase delay correction control circuit 34 via a resistor R9 to obtain a DC signal V _E ; The output of the phase pulse extraction unit 33 compares the levels of the phase delay reference signal V _D and the DC signal V _E to determine the pulse width time of a pulse width signal V _F and outputs the pulse width signal V _F .

Finally, the synchronous signal acquisition circuit 35 connected to the output end of the synchronous phase pulse extraction unit 33 captures the upper edge signal V _{G of} the pulse width signal V _F and shapes the waveform through a synchronous signal shaping output circuit 351. The pulse signal V _{H is} synchronized and output to the pulse width modulation controller 23 of the second power module 20 . In this embodiment, the synchronous signal acquisition circuit 35 is composed of a first differential phase delay circuit.

Since the phase delay reference signal V _D outputted by the synchronous phase delay reference unit 32 is the same and in phase with the primary winding L11 voltage signal V _{A of the} transformer TA, the DC voltage V _E output by the phase delay correction control circuit 34 is lower than the phase delay reference. The signal V _D corresponds to the DC signal of the signal amplitude at the lower edge, so the synchronous delay phase pulse extraction unit 33 outputs the pulse width signal V _{F. The} upper edge signal time falls on the upper edge and the lower edge of the primary winding L11 voltage signal V _A . In the meantime, the synchronous signal generating unit 30 of the present invention generates a pulse signal V _H and outputs to the second power module during the upper edge and the lower edge of the primary winding voltage signal V _A of the first power module 20 . The pulse width modulation controller 23 of 20 is used as a basis for outputting the pulse width modulation signal to the active switch Q2 by the second power module 20.

Referring to FIG. 8, a third preferred embodiment of the scalable switching power supply circuit 10b of the present invention is substantially the same as the first preferred embodiment of FIG. 6. However, the phase detecting circuit 321 can also be directly connected to the first A control terminal of the active switch Q1 of the power module 20.

Referring to FIG. 9, a fourth preferred embodiment of the scalable switchable power supply circuit 10c of the present invention is substantially the same as the first preferred embodiment of FIG. 6. The phase detecting circuit 321 can be directly connected to the pulse width. An output of the modulation controller 23 is modulated.

Referring to FIG. 10A to FIG. 10D, the circuit actions and functions of the present invention will be further described in detail with the main node waveform of the secondary power module 20 of the first preferred embodiment.

First, referring to FIG. 10A and FIG. 10C, the first switching power supply module 20 transformer T1 primary winding L11 voltage signal V _L1 can be the pulse width modulation signal V _G1 output to the control terminal of the active switch Q1 as the primary winding. When the L11 voltage signal disappears, the secondary winding L12 of the transformer TA outputs the induced voltage V _L12 and continues until the next primary winding L12 voltage signal is generated, but during the existence of the primary winding L11 voltage signal V _L11 , the secondary winding L12 is caused. The output voltage V _{L12 is} formed with an energy gap V _inv1 . Similarly, as shown in FIG. 10B and FIG. 10D , the second-stage power module 20 outputs a voltage of the secondary winding L22 during the presence of the voltage signal of the primary winding L21 of the transformer T _B . V _L22 will cause an energy gap V _inv2 .

Since the synchronous signal generating circuit 30 is connected in series between the two parallel power modules 20, the first power module 20 primary winding L11 voltage signal V _{L11 can} be time-reactive to the pulse width of the second power module 20 The modulation controller 20 is such that the pulse width modulation controller 23 of the second power module 20 can accurately know the existence time of the primary winding L11 voltage signal V _L11 , thereby controlling the active switching Q2 pulse width modulation signal. Phase. Referring to FIG. 10A and FIG. 10B , after receiving the pulse signal, the pulse width modulation controller 23 of the second power module 20 outputs the pulse width modulation signal after determining that the voltage of the primary winding L11 of the first power module 20 does not exist. V _L21; is, the second power module PWM signal V _L21 20 does not overlap with the first power supply module 20 the PWM signal V _L22.

Please refer to FIG. 10C and FIG. 10D simultaneously, the energy gap V _inv1 generated at the output end of the first power module 20 is generated corresponding to the induced voltage time V _{L22 of the} secondary winding L22 of the second power module 20, and the two-stage power mode is added. The output of the group 20 is commonly connected to the output terminal Vo. Therefore, the secondary winding L22 of the second power module 20 induces the voltage V _L22 to compensate the energy gap V _{inv1 of the} first power module 20; similarly, the second power mode The energy gap v _inv2 at the output of the group 20 corresponds to the induced voltage V _{L12 of the} secondary winding L12 of the first power module 20, and the energy gap complementary function is achieved; therefore, each power module 20 does not need to be connected with the output capacitance of the large capacitor, that is, The power supply circuit of the present invention outputs a stable voltage waveform as shown in Fig. 10E. As described above, the time when the energy of the output voltage waveform of the second power module 20 is present is overlapped with the output voltage waveform of the first power module 20, and the overlapping area is greater than 101%, that is, the The energy present time of the second power module 20 is at least more than 1~10% overlap ratio of the first power module 20.

Furthermore, since the pulse width modulation signal outputted by the first power module 20 pulse width modulation controller 23 does not overlap with the output pulse width modulation signal of the second power module 20 pulse width modulation controller 23, FIG. 10C As shown in FIG. 10D, the induced currents of the first and second stage power modules 20 may overlap, so that if the pulse width time of the pulse width modulation signal of the second power module 20 is controlled, the time width can be increased. The power supply circuit of the present invention outputs a current.

As can be seen from the above description, since the present invention includes a plurality of power modules, and the phase width modulation signals of all the power modules are not overlapped, the complementary energy gap can be avoided to avoid the use of large output capacitors, and the overall Output current. When the present invention parallels two or more sets of power modules, the output current is relatively increased; therefore, the present invention can expand the switching power supply circuit according to the required power of the load, and adjust the number of parallel connection of the power modules.

10. . . Power circuit

10a-10c. . . Power circuit

11. . . Rectifier filter circuit

20. . . Power module

20a. . . Power module

twenty one. . . transformer

twenty two. . . Active switch

twenty three. . . Pulse width modulation controller

twenty four. . . Feedback circuit

25. . . Current comparator

30. . . Synchronous signal generating unit

31. . . Phase delay correction circuit

321. . . Phase detection circuit

32. . . Synchronous phase delay reference unit

33. . . Synchronous delay phase pulse extraction unit

34. . . Phase delay correction control circuit

35‧‧‧Synchronous signal acquisition circuit

40‧‧‧First switched power supply circuit

41‧‧‧Rectifier filter circuit

42‧‧‧Transformers

43‧‧‧active switch

44‧‧‧ Pulse width modulation controller

45‧‧‧Return circuit

50‧‧‧First switched power supply circuit

51‧‧‧Rectifier filter circuit

52‧‧‧ Pulse width modulation controller

53‧‧‧Return circuit

Figure 1: A circuit diagram of an existing switched power supply.

Figure 2: is a waveform diagram of Figure 1.

Figure 3: Another circuit diagram of an existing switched power supply.

4A to E: are waveform diagrams of FIG. 3.

Figure 5 is a block diagram of the present invention.

Figure 6 is a detailed circuit diagram of a first preferred embodiment of the present invention.

Figure 7 is a detailed circuit diagram of a second preferred embodiment of the present invention.

Figure 8 is a detailed circuit diagram of a third preferred embodiment of the present invention.

Figure 9 is a detailed circuit diagram of a fourth preferred embodiment of the present invention.

10A to E: are waveform diagrams of Fig. 6.

Figure 11 is a detailed circuit diagram of the synchronous signal generating circuit of the present invention.

12A to 12F: Fig. 11 is a waveform diagram.

10. . . Power circuit

11. . . Rectifier filter circuit

20. . . Power module

30. . . Synchronous signal generating unit

Claims (13)

An expandable switching power supply circuit includes: a rectifying and filtering circuit for supplying an alternating voltage connection, rectifying and filtering the alternating current voltage into a high-current high-voltage output; and a plurality of power supply modules, wherein the plurality of input terminals are connected to the rectifying An output end of the filter circuit and a plurality of voltage output ends are connected to an output end, each power module includes at least one transformer and a pulse width modulation controller, wherein the transformer includes a primary winding and a secondary winding; at least one synchronization signal The generating unit's at least one synchronous signal generating unit is connected in series between the two power modules, and the at least one synchronous signal generating unit reflects the transformer voltage signal of one of the power modules of the two power modules, and generates a Synchronizing the signal and outputting it to the pulse width modulation controller of another power module as a basis for determining the phase of the driving signal for driving the active switch, wherein the pulse width modulation signals of the two power modules do not overlap each other The synchronization signal generating unit includes: a phase detecting circuit for detecting two adjacent parallel power modules. a transformer voltage signal of a power module for detecting an energy gap of the power source; a synchronous phase delay reference unit, wherein the input end detects the energy gap of the power source through the phase detecting circuit, and according to the phase detecting circuit The upper edge or the lower edge signal generates a phase delay reference signal synchronized with the transformer voltage waveform period; a phase delay correction control circuit is connected to the transformer of the first stage power module through a phase delay correction circuit, and takes out an integral method DC voltage; a synchronous delay phase pulse extraction unit that includes a positive direction An input end, an inverting input end, and an output end; wherein the forward input end is connected to the output end of the synchronous phase delay reference unit to obtain a phase delay reference signal, and the reverse input end is connected through a resistor Up to the output of the phase delay correction control circuit to obtain a DC signal; that is, the output of the synchronous delay phase pulse extraction unit compares the phase delay reference signal and the level of the DC signal to determine the pulse of a pulse width signal Wide time, and output the pulse width signal; and a synchronous signal acquisition circuit is connected to the output end of the synchronous phase pulse extraction unit, captures the upper edge signal of the pulse width signal, and shapes the output circuit via a synchronous signal The waveform is formed into a sync pulse signal and output to the pulse width modulation controller of the second power module. For example, the expandable switching power supply circuit of claim 1 includes a plurality of synchronous signal generating units, and each of the synchronous signal generating units is connected in series between two adjacent power modules, wherein each of the two adjacent parallel power supplies The module is a first and second power module, and the at least one synchronous signal generating unit reacts the transformer voltage signals of the two adjacent power modules connected in parallel, and generates a synchronization signal and outputs the signal to the second power source. The pulse width modulation controller of the module is used as a basis for determining the phase of the driving signal of the active switch of the second power module, that is, the pulse width of the pulse width modulation signal of the second switching power module is not switched with the first The pulse width modulation signal of the power module overlaps. For example, the expandable switching power supply circuit of claim 2 includes a plurality of synchronous signal generating units, and each of the synchronous signal generating units is configured to reflect a primary winding voltage signal of a transformer of each of the two adjacent power modules connected in parallel or Secondary winding voltage signal. For example, the scalable switching power supply circuit of claim 1 can be an analog sawtooth wave or a digital pulse wave. Such as the expandable switching power supply circuit of claim 4, the synchronous phase delay reference unit is an RC integration circuit, a digital delay A chirped wave counter or a analog sawtooth signal generating circuit. For example, the scalable switching power supply circuit of claim 5, the phase delay correction circuit is an RC integrator. For example, in the expandable switching power supply circuit of claim 1, the power supply module further includes: a transformer including a primary winding and a primary winding; wherein the secondary winding is connected to at least one diode as An output end; at least one active switch is connected to the rectifying and filtering circuit after being connected in series with the primary winding of the transformer; and a pulse width modulation controller, wherein the output end is connected to the control end of the corresponding active switch to control the corresponding The active switch is opened and closed; and an input end of the pulse width modulation controller is connected to the voltage output terminal by a feedback circuit to obtain a voltage change at the voltage output end, so the pulse width modulation controller changes according to the voltage The pulse width modulation signal is output to the corresponding active switch to control its conduction time. For example, in the expandable switching power supply circuit of claim 7, the diode connected to the secondary winding of the transformer is further connected with a filter capacitor. For example, the expandable switching power supply circuit of claim 8 of the patent scope has a filter capacitor of about 104 PF. For example, in the expandable switching power supply circuit of claim 1, the power supply module further includes: a middle tap transformer, wherein the two ends of the primary winding are respectively connected with the two active switches, and the tap end thereof is coupled with the rectifying filter. The output end of the circuit is connected, and the second end of the secondary winding of the transformer is respectively connected with a diode, and the tap end thereof is grounded; and a pulse width modulation controller is connected to the control end of the second active switch. The two sets of pulse width modulation signals are output to the corresponding active switches to control the on-time of the two active switches. For example, in the expandable switching power supply circuit of claim 1, the phase detecting circuit is connected to a current comparator to detect the primary winding voltage signal. The scalable switching power supply circuit of claim 1 is connected to the control terminal of the active switch. The scalable switching power supply circuit of claim 1 is connected to the output of the pulse width modulation controller.