CN220043226U - APFC and PWM composite control combined type switching power supply - Google Patents

Abstract

The utility model provides an APFC and PWM composite control combined type switching power supply which comprises a first controller and a second controller, wherein the first controller is electrically connected with the second controller, the first controller is used for controlling a continuous conduction mode boost converter at the front end through an average current mode, and the second controller is used for a current mode or a voltage mode and is used as a switching converter. The combined controller FAN4800PFC+PWM combined controller is selected to be applied, the PFC controller adopts average current mode control and is used for a Continuous Conduction Mode (CCM) boost converter of the front end, the PWM controller can be used for a current mode or a voltage mode for a switching converter, so that the current waveform of a power grid becomes sinusoidal, harmonic and harmonic components of a switching power supply are restrained, the distortion degree is improved, and the correction of an active power factor is carried out.

Description

APFC and PWM composite control combined type switching power supply

Technical Field

The utility model relates to the technical field of switching power supplies, in particular to an APFC and PWM composite control combined switching power supply.

Background

With the rapid development of power electronic devices, various converters such as frequency converters, inverter power supplies, high-frequency switch power supplies and the like are widely applied to various fields of life and production, and as the converter devices basically obtain a direct current power supply through a rectifying link, the rectifying link is widely provided with a diode uncontrolled rectifying or thyristor phase-controlled rectifying circuit, a large amount of harmonic waves and reactive power are injected into a power grid, and serious power grid pollution is caused.

Disclosure of Invention

Aiming at the defects of the prior art, the utility model provides an APFC and PWM composite control combined type switching power supply.

The utility model solves the technical problems by the following technical means: an APFC and PWM composite control combined type switching power supply comprises a first controller and a second controller, wherein the first controller is electrically connected with the second controller, the first controller is used for controlling a front-end continuous conduction mode boost converter through an average current mode, and the second controller is used for a current mode or a voltage mode and is used as a switching converter.

Preferably, the first controller is a PFC controller, the second controller is a PWM controller, the PFC controller includes a multiplier, a corrector, and a current regulator, an input end of the current regulator is electrically connected to an output end of the multiplier, and an output end of the current regulator is electrically connected to an input end of the corrector.

Preferably, the first control includes an L1 boost inductor, a VTI power switch MOS, a VDS high frequency rectifier diode, a CO output capacitor, and an APFC boost converter, and the L1 boost inductor, the VTI power switch MOS, the VDS high frequency rectifier diode, the CO output capacitor, and the APFC boost converter are connected in series.

Preferably, the first controller includes a rectifying and boosting circuit, the rectifying and boosting circuit includes a rectifying bridge BD1, the positive pole of the rectifying bridge BD1 is connected to the positive pole of the filter electrolytic capacitor C5 through an RTH1 thermistor, the negative pole of the C5 is connected to one end of an over-current resistor R5, R2 of the APFC circuit, the other end of the over-current resistor R5, R2 is connected to the negative pole of the rectifying bridge, the positive pole of the diode D5 is connected to one end of the L1 boosting inductor, the negative pole of the diode D5 is connected to the positive pole of the C5 of the filter electrolytic capacitor, the drains of the switching power mosfets Q1, Q2 are connected together and then connected to the negative pole of the filter electrolytic capacitor C5, a resistor R8 is connected between the gate and the source of the Q1, a driving resistor R6 is connected in series with the base of the PNP transistor Q5, the emitter of the Q5 is connected to the gate of the APFC circuit, the negative pole of the filter electrolytic capacitor Q5 is connected to the negative pole of the Q7, the base of the PNP transistor Q5 is connected to the base of the p 4, the base of the PNP transistor Q5 is connected to the p 2 is connected to the drain of the p 4, the base of the p 4 is connected to the p 4, and the drain of the p 4 is connected to the base of the Q4 is connected to the Q4 of the Q4.

Preferably, the second controller includes an overheat protection circuit, the overheat protection circuit includes a transformer T1, one winding of the secondary of the transformer T1 is rectified and then connected to a collector of an NPN triode Q300, a resistor R305 is connected between a base and a collector of the Q300, a base of the Q300 is connected to a cathode of a voltage regulator ZD300, an anode of an electrolytic capacitor C301 is connected to an emitter of the Q300, a cathode of the C301 is connected to an emitter of a PNP triode Q322, a collector of the Q322 is connected to an anode of the electrolytic capacitor C321, an anode of the C321 is connected to an anode of a fan, a cathode of the C321 is connected to a cathode of the fan, a base of the Q322 and an emitter of the triode Q323 are connected to one end of a thermistor RTH3, the other end of the resistor R319 is connected to one pin of an AZ431 precision voltage regulator programmer, two pins of the one pin pair of the resistor R320.AZ431 are connected to a secondary ground, three pins of AZ431 are connected to the base of the triode Q322 through a resistor R323 and a base of the AZ431 are connected between the anode of the resistor C321 and the resistor R321 through a resistor 324 and the anode of the resistor C321.

The utility model has the beneficial effects that:

the utility model adopts a PFC and PWM composite control combination mode, adopts an active power factor correction and fixed frequency average current mode control mode, selects a combination controller FAN4800PFC+PWM combination controller to apply, combines the PFC controller and the PWM controller, adopts an average current mode to control the PFC controller, is used for a Continuous Conduction Mode (CCM) boost converter of the front end, and can be used for a current mode or a voltage mode for a switch converter, so that the current waveform of a power grid becomes sinusoidal, harmonic and harmonic components of a switch power supply are restrained, the distortion degree is improved, and the correction of the active power factor is carried out.

Drawings

Fig. 1 is a circuit diagram of a PFC and PFC composite control combined switching power supply of the present utility model;

FIG. 2 is a graph of boost inductor current variation according to the present utility model;

FIG. 3 is a schematic diagram of AN AN4800 fixed frequency average current mode control circuit according to the present utility model;

fig. 4 is a diagram of an active power factor correction boost circuit of the present utility model.

Fig. 5 is a circuit diagram of the intelligent temperature control fan and the power overheat protection circuit of the utility model.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present utility model more apparent, the technical solutions of the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model, and it is apparent that the described embodiments are some embodiments of the present utility model, but not all embodiments of the present utility model. All other embodiments, which can be made by those skilled in the art based on the embodiments of the utility model without making any inventive effort, are intended to be within the scope of the utility model.

It will be understood that when an element is referred to as being "fixed to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present.

Example 1

Referring to fig. 1, the APFC and PWM combined control combined switch power supply according to the present embodiment adopts a PFC and PWM combined control mode, and uses an active power factor correction and fixed frequency average current mode control mode, and selects a combination controller FAN4800pfc+pwm combined controller for application. FAN4800 combines a PFC controller that employs average current mode control for a front-end Continuous Conduction Mode (CCM) boost converter with a PWM controller. The PWM controller may be used in either current mode or voltage mode for a switching converter, input grid voltage 85VAC-264VAC, output 24V13.4A (320W output power).

Referring to fig. 2, the PFC control mode of FAN4800 is a fixed frequency average current mode control mode, in which the average current control is developed based on the peak current control, and a current regulator is added between the output of the multiplier and the corrector of the PFC control chip. The average value of the input current is regulated and controlled to make the waveform of the current programming signal identical, and the current loop has high gain, small broadband tracking error and good transient characteristic, so that the current loop is insensitive to noise and is suitable for high power.

Referring to fig. 3, the FAN4800 controller includes an L1 boost inductor, a VTI power switch MOS, a VDS high-frequency rectifier diode, a CO output capacitor, and a fixed-frequency average current mode APFC boost converter, which has a DC output voltage and AC input voltage closed-loop control circuit, and also has a current sensing loop.

The controller IC contains a DC output voltage sense error amplifier, analog multiplier, current amplifier, current sense logic and MOSFET gate driver, typically with a fixed high frequency oscillator.

The duty cycle of the controller output PWM drive pulses depends on the ratio between the APFC boost converter DC output voltage and the AC input voltage and follows so-called sinusoidal pulse width modulation.

When the power switch is on, the current IL flowing through the boost choke increases and flows back to the low value current sense resistor RS.

During this time, since the high frequency rectifier diode VD5 is reverse biased, the input storage capacitor CO provides current to the LOAD, and when the current command and current feedback signals reach equilibrium, the power switch MOSFET turns off, and the inductor current decays due to flowing into the storage capacitor CO.

The actual current IL through the inductor has ripple wave identical to the switching frequency, and its average current tracks the full-bridge rectified sine half-wave direct current in sine wave according to sine rule and is in phase with the AC input voltage, so that the system power factor almost reaches the level of 1.

The output direct current voltage of the APFC boost converter is controlled by closed loop feedback, and is not changed along with the change of the input voltage and the load, and is always kept at a stable value.

The switching and duty cycle of this type of APFC converter is varied, once each switching cycle is the same, so the switching frequencies are fixed and highly integrated FAN4800A/C and FAN4801/02/02L are specifically designed for power supplies that include boost PFC and PWM, requiring few external components to achieve multiple protection/compensation, with 16-pin DIP and SOP packages, which can be used in either current mode or voltage mode.

In voltage mode, feed forward from the PFC output bus may reduce auxiliary output ripple, and FAN4800A/C and FAN4801/02/02L may operate at lower current than previous products ML4800 and FAN4800, which may save power consumption in external devices.

FAN4800A/C and FAN4801/02/2L had accurate 49.9% maximum PWM duty cycle so that the run time was kept longer without under-voltage protection and PFC soft start functions in ML4800 and FAN4800, and it was evaluated whether FAN4800A/C, FAN4801/02/02L was suitable for replacing existing FAN4800 and ML4800 boards.

Five tasks must be completed before the trimming process:

1. changing the RAC resistance from the old value to a higher resistance: between 6mΩ and 8mΩ;

2. changing the RT/CT pin from the existing value to rt=6.8 kΩ and ct=1000 pF, so that fpfc=64 KHz, fpwm=64 KHz;

vrms requires 1.224V at vin=85 VAC to apply universal input in line input of 85VAC to 270VAC, two poles of Vrms of FAN4801/02/02L need not be much slower than FAN4800, about 5 to 10 times;

4. at full load, the average VEA needs to be-4.5 v, and the ripple on VEA needs to be less than 400mV;

5. soft start pin, soft start current has been reduced by half compared to FAN4800 capacitor.

FAN4800 is a controller applied to power factor correction equipment, and PFC circuits allow the use of smaller, low-cost, high-capacity capacitors, thereby reducing line power loads and stress on switching power tubes, and finally fully meeting IEC-1000-3-2 specifications.

FAN4800 includes an execution leading edge circuit, an average current circuit, a boost type power factor correction circuit, and a PWM circuit.

The need for external drive circuitry for the 1A gate drive capability is reduced as much as possible, and the need for low power increases efficiency and reduces component cost.

The over-voltage comparator may shut down the PFC section when the load suddenly decreases, the PFC section further including a peaking circuit and an input voltage power down.

In the current power factor correction circuit, the main circuit formed by the BOOST converter is most commonly used, and is divided into DCM, CRM, CCM modes according to the continuity of the input current.

DCM mode is commonly used in low power applications because of its simple control, but discontinuous input current, and its high peak value.

In contrast to the CCM mode, the input current is continuous, the current ripple is small, the CCM mode is suitable for high-power occasions, CRM between DCM and CCM is called a current critical continuous mode, the mode generally adopts a variable-frequency control mode, current zero crossing signals of a boost inductor are collected, when the current is zero crossing, a MOS tube is turned on, and the control mode is very common in a low-power PFC circuit.

Active power factor correction and fixed frequency average current mode control boost circuit based on FAN4800 chip, known parameters:

the frequency fac of the alternating current power supply is 50Hz;

the lowest alternating voltage effective value Umin-85 Vac;

the highest ac voltage effective value Umax-265 Vac;

outputting a direct-current voltage Udc-400 VDC;

output power Pout-400W (320W power supply, PFC section set to 400W);

the full load efficiency eta-92% under the worst condition;

switching frequency fs-65 KHz;

outputting voltage peak value Voutp-p-10V;

we can do the following calculation:

1. output current iout=pout/udc=400/400=1a;

2. maximum input power pin=pout/η=400/0.92=652W;

3. input current maximum effective value iinrmsmax=pin/umin=652/85=7.67A;

4. then the peak value of the input current effective value is Iinrmsmax 1.414=10.85a;

5. the high frequency ripple current takes 20% of the input current peak, then ihf=0.2×iinrmsmax=0.2×10.85=2.17A;

6. the input current peak value ilpk=iinrmsmax+0.5×ihf=10.85+0.5×2.17=11.94A;

7. minimum inductance of boost inductor;

Lmin＝(0.25*Uout)/(Ihf*fs)＝(0.25*400)/(2.17*65KHz)＝709uH

8. the output capacitance minimum value is:

cmin=iout/(3.14×2×fac×voutpp) =1.5/(3.14×2×50×10) =477.7 uF, and the hold time is also considered in the actual circuit, so the capacitance may need to be recalculated according to the hold time requirement. In an actual circuit, 1320uF and 4 330uF are used in parallel.

The boost inductor can be designed by inductance and input current, and the magnetic core of the boost inductor of the PFC circuit can be selected from the following modes: magnetic powder core, ferrite core, amorphous/microcrystalline alloy core with air gap.

Wherein,

the magnetic powder core has the advantages that the mu value is low, so that an air gap is not required to be opened additionally, the air gap is average, the magnetic leakage is small, the electromagnetic interference is low, and the saturation is not easy; the disadvantage is that the coil is basically annular, the coil winding is difficult, but EE type exists in the market at present, in addition, the mu value is reduced along with the increase of the magnetic field intensity, and repeated iterative calculation is needed in the design.

The ferrite core has the advantages of small loss, multiple specifications, low price and stable magnetic permeability after an air gap is formed; the disadvantage is that an air gap is required, in addition, the saturation point is relatively low, and the DC bias magnetic resistance is relatively poor.

The amorphous/microcrystalline alloy has the advantages of high saturation point and stable magnetic permeability after air gap is opened; the same disadvantage is the need to open an air gap and, in addition, is mostly annular.

Although the winding of the annular iron core is difficult, the E-shaped iron core is not easy to wind, but the inductance of the annular iron core is small in distribution capacitance, so that convenience is brought to future electromagnetic compatibility treatment, the E-shaped iron core is wound in a plurality of layers, and then the interlayer capacitance is relatively large, so that the EMC is adversely affected.

In addition, the iron core with the air gap is opened, and copper loss becomes large at the air gap because leakage flux at the air gap generates eddy current loss on the copper wire.

The following selects the annular magnetic powder core as the core of the PFC inductor, and I calculate several parameters:

input current maximum effective value iinrmsmax=pin/umin=652/85=7.67A;

the input current peak value ilpk=iinrmsmax+0.5×ihf=10.85+0.5×2.17=11.94A;

minimum inductance of boost inductor;

Lmin＝(0.25*Uout)/(Ihf*fs)＝(0.25*400)/(2.17*65KHz)＝709uH；

the calculation is continued as follows:

the coil selection current density is 5A/square millimeter, and the wire diameter of the enameled wire required to be used is calculated as follows: 2×sqrt (7.67/(5×3.14))=1.4 mm;

since the maximum input voltage, that is to say the maximum input current, is calculated, the current density can be obtained with a relatively large margin, and can be increased practically according to different cost requirements, for example, if the current density is 8A/mm square, the wire diameter can be obtained as: 2×sqrt (7.67/(8×3.14))=1.1 mm.

Because the CCM mode is adopted, the fundamental wave is a low-frequency half sine wave, and a single enameled wire can be selected.

Several formulas are commonly used: l: inductance, I: current, N: turns, Δb: magnetic induction intensity variation, ae: magnetic core cross-sectional area m=n×n×al: inductance h=0.4×3.14×n×i/le: magnetic path length.

There are several methods for calculating the size of the magnetic core, the AP method is most commonly used, but in practice, since the permeability of the magnetic powder core varies greatly with the magnetic field strength, the calculation often needs iterative repetition.

The needed magnetic core can be obtained through calculation of the magnetic core parameters, and the more the experience is, the faster the calculation is.

The magnetic powder cores suitable for PFC inductance mainly have three types: iron nickel Molybdenum (MPP), iron nickel 50 (high flux), iron silicon aluminum (fesai).

Wherein,

the saturation point of the iron-nickel-molybdenum powder core is approximately near B=0.6, and the two powder cores can reach more than 1, and the FeNi50 powder core with initial magnetic permeability of mu 0=60 is selected, when the magnetic field strength is 100Oe, the magnetic permeability is 65%, and when the magnetic field strength is 100Oe, the magnetic induction strength is 0.65T and is far less than the saturation point.

The maximum magnetic field strength was designed to be 100Oe, and the constraints obtained from l=n×n×al, h=0.4×3.14×n×i/Le were: since 0.4X3.14XSQRT (L/Al). Times.I/Le <100, the permeability is only 65% of the initial value at 100Oe, al in the above formula is multiplied by this coefficient. Then the relevant parameters l=709uh, i=11.94A are taken in:

0.4X3.14XSQRT (709E-6/(0.65XAl)). Times.11.94/Le <100, obtained after simplification:

0.495/(Le×SQRT(Al))<100

note that: in the above formula, the units of Le are: cm, al units are: H/(N)

The core parameters are taken into calculation.

Selecting one of: h60-572a, le=14.3cm, al=140 nH/(n×n), ae=2.889 square cm, obtained after the introduction: 92.5<100, it is clear that this core is possible.

Then, n=88 turns (the number of turns of the boost inductance is 88T) is calculated from 92.5=0.4×3.14×n×i/Le.

Example 2

Referring to fig. 4, the positive electrode of the rectifier bridge BD1 is connected to the positive electrode of the rectifier diode D1 through an RTH1 thermistor, and the negative electrode of the rectifier diode is connected to the positive electrode of the filter electrolytic capacitor C5.

The cathode of the C5 is connected with one ends of overcurrent resistors R5 and R2 of the APFC circuit, the other ends of the overcurrent resistors R5 and R2 are connected with the cathode of the rectifier bridge stack, the anode of the diode D5 is connected with one end of the L1 boost inductor, and the cathode of the diode D5 is connected with the anode of the C5 of the filter electrolytic capacitor;

the drains of the switching power MOSFETs Q1 and Q2 are firstly connected together and then connected to the cathode of the filter electrolytic capacitor C5, a resistor R8 is connected in parallel between the grid electrode and the source electrode of the filtering electrolytic capacitor C1, a driving resistor R6 is connected in series with a diode D6 and connected to the base electrode of the PNP triode Q5, the emitter electrode of the Q5 is connected with the grid electrodes of the resistors R7 and Q1, the collector electrode of the triode Q5 is connected with the cathode of the filtering electrolytic capacitor, and the base electrode of the PNP triode Q5 is connected to a 12-pin PFCOUT (PFC output driving signal end) of FAN4800 through a connecting resistor R15;

a resistor R23 is connected between the grid electrode and the source electrode of the Q2 in parallel, a diode D11 connected in series with a driving resistor R11 is connected to the base electrode of a PNP triode Q4, the emitter electrode of the Q4 is connected to the grid electrodes of the resistors R10 to Q2, the collector electrode of the triode Q4 is connected to the negative electrode of the filter electrolytic capacitor, and the base electrode of the PNP triode Q4 is connected with the base electrode of the PNP triode Q5.

Referring to fig. 5, in the case of using an active heat dissipation switching power supply, the fan is used to dissipate heat to reduce the temperature of the power cavity, and the rotation speed of the fan is adjusted according to the temperature in the power cavity, so as to achieve the best heat dissipation effect.

When the cavity is overheated or the fan stops running, the power supply is automatically protected, the output is cut off, the power supply cannot be damaged, the intelligent and protective functions are achieved through a circuit, one winding of the secondary side of the transformer T1 is connected to the collector of the NPN triode Q300 after rectification, a resistor R305 is connected between the base and the collector of the NPN triode Q300, the base of the Q300 is connected with the negative electrode (secondary ground) of the voltage stabilizing tube ZD300, the positive electrode of the electrolytic capacitor C301 is connected to the emitter of the Q300, and the negative electrode of the electrolytic capacitor C301 is connected to the (secondary ground);

the emitter of the Q300 is connected to the emitter of the PNP triode Q322, the collector of the Q322 is connected to the positive electrode of the electrolytic capacitor C321, the positive electrode of the C321 is connected to the red line+ of the fan, and the negative electrode (secondary ground) is connected to the black line of the fan;

the base electrode and emitter electrode of Q322 are connected with resistor R322. The emitter electrode of triode Q323 is connected with one end of thermistor RTH3, another end is connected with resistor R319, another end of R319 is connected with one pin of AZ431 (SHR 3) precision voltage-stabilizing programmer, and one pin is connected with secondary ground, and two pins of resistor R320.AZ431 (SHR 3) are connected with secondary ground;

three feet of AZ431 are connected with the base electrode of the triode Q322 through a resistor R323, a diode D323 is connected between the positive electrode of a capacitor C321 and one foot of the AZ431 in series with the resistor R324, after the thermistor with a negative temperature coefficient is heated, the voltage of a power supply fan is accurately regulated by the AZ431 after the resistance value is reduced, the conduction of the triode Q323 is regulated, so that when the temperature of a power supply cavity is low, the fan does not rotate, the voltage of the fan is intelligently regulated according to the load and heating conditions of the power supply, the loss of the fan is reduced, and the service life of the fan is prolonged.

When the FAN fails or the device of the power supply in the cavity is overheated, the resistance value of the thermistor RTH3 is suddenly reduced, so that the voltage stabilizing tube ZD302 is conducted, current is generated by connecting to the secondary of the optocoupler and is transmitted to the primary of the optocoupler, the SCR is triggered, the anode and the cathode of the SCR are conducted to the ground (primary ground), the anode of the SCR is connected with the 13-pin (VCC) and the 5-pin SS soft start pin of the FAN4800, the voltage of the ports is pulled to the ground (primary ground), the FAN4800 stops working, and the power supply has no output and plays a role in protection.

It is noted that relational terms such as first and second, and the like, if any, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.

The above embodiments are only for illustrating the technical solution of the present utility model, and are not limiting; although the utility model has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present utility model.

Claims (5)

1. An APFC and PWM composite control combined type switching power supply is characterized in that: the switching converter comprises a first controller and a second controller, wherein the first controller is electrically connected with the second controller, the first controller is controlled by an average current mode, the front end of the switching converter is subjected to continuous conduction mode boost converter, and the second controller is used for a current mode or a voltage mode and is used as the switching converter.

2. The APFC and PWM composite control combined switching power supply of claim 1, wherein: the first controller is a PFC controller, the second controller is a PWM controller, the PFC controller comprises a multiplier, a corrector and a current regulator, the input end of the current regulator is electrically connected with the output end of the multiplier, and the output end of the current regulator is electrically connected with the input end of the corrector.

3. The APFC and PWM composite control combined switching power supply of claim 2, wherein: the first control comprises an L1 boost inductor, a VTI power switch MOS, a VDS high-frequency rectifying diode, a CO output capacitor and an APFC boost converter, and the L1 boost inductor, the VTI power switch MOS, the VDS high-frequency rectifying diode, the CO output capacitor and the APFC boost converter are connected in series.

4. An APFC and PWM composite control combined switching power supply according to claim 3, wherein: the first controller comprises a correction boost circuit, the correction boost circuit comprises a rectifier bridge BD1, the positive electrode of the rectifier bridge BD1 is connected to the positive electrode of a filter electrolytic capacitor C5 through an RTH1 thermistor, the negative electrode of the rectifier diode is connected to the positive electrode of the rectifier diode D1, the negative electrode of the C5 is connected to one ends of over-current resistors R5 and R2 of an APFC circuit, the other end of the over-current resistor R5 is connected to the negative electrode of the rectifier bridge, the positive electrode of the diode D5 is connected to one end of an L1 boost inductor, the negative electrode of the diode D5 is connected to the positive electrode of the filter electrolytic capacitor C5, the drains of switching power MOSFETQ1 and Q2 are connected together, then connected to the negative electrode of the filter electrolytic capacitor C5, a resistor R8 is connected between the grid electrode and the source electrode of the Q1, a driving resistor R6 is connected to the base electrode of the PNP transistor Q5 in series, an emitter electrode of the Q5 is connected to the grid electrode of the APFC circuit, the collector electrode of the triode Q5 is connected to the negative electrode of the filter electrolytic capacitor, the base electrode of the PNP 5 is connected to the drain electrode of the PNP 4 through a connecting resistor R4810, the drain electrode of the PNP 4 is connected to the drain electrode of the PNP 4, and the drain electrode of the power MOSFETQ1 is connected to the drain electrode of the PNP 4, and the drain electrode of the drain power MOSFET Q4 is connected to the drain electrode of the drain electrode.

5. The APFC and PWM composite control combined switching power supply of claim 4, wherein: the second controller comprises an overheat protection circuit, the overheat protection circuit comprises a transformer T1, one winding of a secondary of the transformer T1 is connected to a collector of an NPN triode Q300 after rectification, a resistor R305 is connected between a base and a collector of the Q300, the base of the Q300 is connected with a cathode of a voltage stabilizing tube ZD300, an anode of an electrolytic capacitor C301 is connected to an emitter of the Q300, a cathode of the C301 is connected to an emitter of a PNP triode Q322, the collector of the Q322 is connected with an anode of an electrolytic capacitor C321, an anode of the C321 is connected with an anode of a fan, a cathode of the C321 is connected with a cathode of the fan, a base and an emitter of the Q322 are connected with a resistor R322, an emitter of a triode Q323 is connected to one end of a thermistor RTH3, the other end of the triode Q319 is connected with a resistor R319, the other end of the resistor R431 is connected with one pin of an AZ431 precision voltage stabilizing programmer, two pins of the AZ431 are connected with a secondary ground, three pins of the AZ431 are connected with the base of the triode Q322 through a resistor R323 and the base of the AZ 322, and the diode D323 is connected between the anode of the capacitor C321 and one pin of the triode Q321 in series through the resistor R324 and the resistor.