CN208226866U - Advanced limiting power constant value circuit and switching power supply using same - Google Patents

Abstract

The utility model relates to an advanced limit power constant value circuit and use its switching power supply. The limiting power constant circuit is formed by electrically connecting transistors Q1-Q7, amplifiers A1-A2, a comparator C1, a low-voltage power supply module, a logic conversion module, an oscillator OSC and resistors R1-R3. The utility model discloses can pass through in the circuit to former limit peak current's control, let the output limit power of system undulant minimizing in the high-low line input voltage scope effectively, ensure user's consumer's security, have better use value. Additionally, the utility model discloses owing to adopted the sample hold method to avoid under the low pressure heavy load condition switching signal big wavelet and the limit power value problem that leads to on the low side.

Description

An Advanced Limit Power Constant Value Circuit and Its Switching Power Supply

technical field

The utility model belongs to the field of electric power electronics, in particular to an advanced limit power constant value circuit and a switching power supply using the same.

Background technique

As the power supply equipment of all electronic products, the power supply needs to be able to be used normally in all countries in the world. Since the standards of the global line voltage power supply system are not uniform, the line voltage input range is 85~264VAC, and the switching power supply system is suitable for such a wide input range. It is necessary to satisfy the requirement that the output maximum limit power is a fixed value with less fluctuation, so that the safety of downstream electrical equipment can be well protected.

A conventional switching power converter is described in FIG. 1 , and FIG. 1 depicts a power converter 100 based on a conventional pulse width modulation technique. The voltage in the auxiliary coil of the transformer TR1 is divided and sampled to the FB port of the power converter 100 to generate a square wave signal (Vsw) with a variable pulse width to control the power transistor (M1) to be turned on and off. Through the overcurrent comparison The device generates an over-current signal to turn off M1, but due to the delay of the output signal of the over-current protection comparator, M1 generates a peak current greater than the set value when it is turned off, causing the output power to exceed the set value. Since the slope of the peak current in M1 is positively correlated with the input voltage, the greater the input voltage, the greater the slope of the peak current flowing through M1, and the higher the peak current increment during the delay time of the output signal of the overcurrent protection comparator, It will lead to the output limit power of the switching power supply system under high input line voltage is far greater than the output limit power under low input line voltage, which greatly affects the safety of electrical equipment.

Therefore, it is necessary to adopt special technology to control the consistency of the limit output power of the switching power supply system under high and low line voltage input conditions, so that the safety of the power supply equipment can be effectively guaranteed.

Contents of the invention

The purpose of this utility model is to provide an advanced limit power constant value circuit and a switching power supply using it, which can effectively minimize the fluctuation of the output limit power of the system in the range of high and low line input voltages, and ensure the safety of the user's electrical equipment In addition, the utility model avoids the problem of low limit power value caused by the large and small waves of the switching signal under the condition of low voltage and heavy load due to the adoption of the sample and hold method.

In order to achieve the above object, the technical solution of the utility model is: an advanced limit power constant value circuit, which includes transistors Q1~Q7, resistors R1~R3, capacitor Csh, amplifiers A1~A2, comparator C1, low voltage power supply module, a logic conversion module, an oscillator OSC and five ports; the five ports include a first terminal VCC, a second terminal GATE, a third terminal OCP, a fourth terminal SENSE and a fifth terminal CLK; the first terminal of the transistor Q1 One end is respectively connected to the third end of the transistor Q2, the third end of the transistor Q3, and the second end of Q3, the second end of the transistor Q1 is respectively connected to the negative input end of the amplifier A1, the first end of the resistor R1, and the second end of the transistor Q1 The three terminals are connected to the output terminal of the amplifier A1; the first terminal of the transistor Q2 is connected to the second terminal of the low-voltage power supply module, and the second terminal of the transistor Q2 is respectively connected to the first terminal of the resistor R3, the second terminal of the transistor Q7, and the transistor Q4 the second terminal of the transistor Q3; the first terminal of the transistor Q3 is connected to the second terminal of the low-voltage power supply module; the first terminal of the transistor Q4 is respectively connected to the first terminal of the transistor Q5 and the second terminal of the low-voltage power supply module, and the transistor The third end of Q4 is respectively connected to the second end of the transistor Q5, the third end of the transistor Q5, and the first end of the transistor Q6; the second end of the transistor Q6 is respectively connected to the first end of the resistor R2 and the negative electrode of the amplifier A2. Input terminal, the third terminal of transistor Q6 is connected to the output terminal of amplifier A2; The first terminal of described transistor Q7 is respectively connected to the first terminal of capacitor Csh, the first terminal of comparator C1, and the third terminal of transistor Q7 is connected to logic The second end of the conversion module; the second end of the resistor R1, the second end of R2, the second end of R3 and the second end of the capacitor Csh are respectively grounded; the positive input terminal of the amplifier A1 is connected to the oscillator The second terminal of the OSC; the positive input terminal of the amplifier A2 is connected to the third terminal of the low-voltage power supply module; the first terminal of the oscillator OSC is connected to the second terminal of the low-voltage power supply module; the third terminal of the oscillator OSC Connect to the fifth terminal CLK; the first terminal of the low-voltage power supply module is connected to the first terminal VCC; the first terminal of the logic change module is connected to the first terminal VCC, and the third terminal of the logic change module is connected to the second terminal GATE ; The positive input terminal of the comparator C1 is connected to the fourth terminal SENSE, and the output terminal of the comparator C1 is connected to the third terminal OCP.

In one embodiment of the present utility model, the transistors Q1, Q6, and Q7 are all NPN transistors or NMOS transistors, the first end of the NPN transistor is the collector, the second end is the emitter, the third end is the base, and the NMOS transistor The first end is the drain, the second end is the source, and the third end is the gate; the transistors Q2~Q5 are all PNP transistors or PMOS transistors, the first end of the PNP transistor is the emitter, the second end is the collector, and the third end is the gate. The three terminals are the base, the first terminal of the PMOS transistor is the source, the second terminal is the drain, and the third terminal is the gate.

The utility model also provides a switching power supply using the above-mentioned advanced limiting power constant value circuit, which includes a transformer, a switching power supply controller for generating a switching signal for adjusting the pulse width of the transformer, and a power switching tube M1 The switching power supply controller is coupled to a feedback unit located at the output end of the transformer; the first end of the power switching tube is connected to the input end of the transformer, and the second end of the power switching tube is respectively connected to the switching power supply controller and the limiter. The first end of the current resistance Rs, the third end of the power switch tube is connected to the switching power supply controller; the switching power supply controller includes an undervoltage lockout circuit, an advanced limiting power constant value circuit, a pulse width modulator and A driving circuit; the driving circuit is respectively connected with the undervoltage lockout circuit, the advanced limiting power constant value circuit and the pulse width modulator; the advanced limiting power constant value circuit is connected with the pulse width modulator.

In an embodiment of the present invention, the first terminal of the driving circuit is connected to the fourth terminal PWM of the pulse width modulator, the second terminal of the driving circuit is connected to the power supply VCC, and the third terminal of the driving circuit is connected to the power supply The third end of the tube M1; the first end SENSE of the pulse width modulator is respectively connected to the first end of a sampling resistor Rs and the second end of the power tube M1, and the second end FB of the pulse width modulator is connected to the return The feedback end of the granting unit, the third end of the pulse width modulator is connected to the third end OCP of the advanced limit power constant value circuit, and the fifth end of the pulse width modulator is connected to the advanced limit power constant value circuit. The fifth end CLK; the first end VCC of the advanced limit power constant value circuit is connected to the power supply VCC, and the second end GATE of the advanced limit power constant value circuit is connected to the third end of the power switch tube M1; the advanced limit The fourth end SENSE of the power constant value circuit is respectively connected to the first end of the external sampling resistor Rs and the second end of the power tube M1; the first end of the undervoltage lockout circuit is connected to the first end of the limiting power constant value circuit. terminal VCC; the second terminal of the sampling resistor Rs is grounded.

In an embodiment of the present invention, the power switch M1 is a power transistor, the first end of the power switch M1 is a drain, the second end is a source, and the third end is a gate.

In an embodiment of the present invention, the under-voltage lockout circuit, the advanced limiting power constant value circuit, the pulse width modulator, and the driving circuit are embedded in an integrated circuit.

The utility model also provides a switching power supply using the above-mentioned advanced limiting power constant value circuit, and the switching power supply is a secondary side feedback switching power supply or a primary side feedback switching power supply.

Compared with the prior art, the utility model has the following beneficial effects: the circuit of the utility model can effectively minimize the fluctuation of the output limit power of the system in the range of high and low line input voltages through the control of the peak current of the primary side in the circuit , which guarantees the safety of the user's electrical equipment and has good use value; in addition, the utility model avoids the problem of low limit power value caused by the large and small waves of the switching signal under the condition of low voltage and heavy load due to the adoption of the sample and hold method.

Description of drawings

Figure 1 is a schematic diagram of a conventional switching power supply conversion system.

Fig. 2 is a schematic diagram of the circuit connection of the advanced limiting power constant value circuit of the present invention.

Fig. 3 is a schematic diagram of a switching power supply conversion system of the present invention.

Fig. 4 is a timing diagram of Vcsth, V1, Vsh, and Vsw of the advanced limiting power constant value circuit of the present invention.

Fig. 5 is a curve diagram of the limit output power of the switching power supply system of the present invention in the range of 85~264VAC line voltage.

Description of main component symbols:

100: Traditional switching power supply controller

100A: using the switching power supply controller of the utility model

2000: Undervoltage lockout circuit

3000: Pulse Width Modulator

4000: drive circuit

5000: Advanced limit power constant value circuit

5000A: Vcsth, V1, Vsh, Vsw timing diagram of the advanced limit power constant value circuit of the utility model

5000B: The limit output power curve of the switching power supply system of this utility model in the range of 120~374V line voltage

OSC: Oscillator

Q1~Q7: switching transistors

M1: external power switch tube

TR1: Transformer

D1, D2: Diodes

R1, R2, R3, Ron, Rs: Resistors

Cvcc, C1, Csh: Capacitors

V _IN : Input line voltage

Vsw: switch signal

V _FB : Feedback voltage

PWM: pulse width comparator output signal

Is: primary coil inductance peak current

Vcc: power supply voltage

Vth: the critical conduction threshold of the power transistor M1.

Detailed ways

Below in conjunction with accompanying drawing, the technical solution of the utility model is described in detail.

The utility model provides an advanced limit power constant value circuit, which includes transistors Q1~Q7, resistors R1~R3, capacitor Csh, amplifiers A1~A2, comparator C1, low voltage power supply module, logic conversion module, oscillator OSC And five ports; the five ports include a first terminal VCC, a second terminal GATE, a third terminal OCP, a fourth terminal SENSE and a fifth terminal CLK; the first terminal of the transistor Q1 is respectively connected to the third terminal of the transistor Q2 end, the third end of the transistor Q3, the second end of Q3, the second end of the transistor Q1 is respectively connected to the negative input end of the amplifier A1, the first end of the resistor R1, and the third end of the transistor Q1 is connected to the output end of the amplifier A1; The first end of the transistor Q2 is connected to the second end of the low-voltage power supply module, and the second end of the transistor Q2 is respectively connected to the first end of the resistor R3, the second end of the transistor Q7, and the second end of the transistor Q4; The first terminal of Q3 is connected to the second terminal of the low-voltage power supply module; the first terminal of the transistor Q4 is respectively connected to the first terminal of the transistor Q5 and the second terminal of the low-voltage power supply module, and the third terminal of the transistor Q4 is respectively connected to the transistor Q5 The second terminal of the transistor Q5, the first terminal of the transistor Q6; the second terminal of the transistor Q6 is respectively connected to the first terminal of the resistor R2, the negative input terminal of the amplifier A2, and the third terminal of the transistor Q6 Connect the output terminal of the amplifier A2; the first end of the transistor Q7 is respectively connected to the first end of the capacitor Csh, the first end of the comparator C1, and the third end of the transistor Q7 is connected to the second end of the logic transformation module; The second end of the resistor R1, the second end of R2, the second end of R3 and the second end of the capacitor Csh are respectively grounded; the positive input terminal of the amplifier A1 is connected to the second end of the oscillator OSC; the The positive input terminal of the amplifier A2 is connected to the third terminal of the low-voltage power supply module; the first terminal of the oscillator OSC is connected to the second terminal of the low-voltage power supply module; the third terminal of the oscillator OSC is connected to the fifth terminal CLK; the The first end of the low-voltage power supply module is connected to the first end VCC; the first end of the logic change module is connected to the first end VCC, and the third end of the logic change module is connected to the second end GATE; the positive of the comparator C1 The input terminal is connected to the fourth terminal SENSE, and the output terminal of the comparator C1 is connected to the third terminal OCP.

Further, the transistors Q1, Q6, and Q7 are all NPN transistors or NMOS transistors, the first terminal of the NPN transistor is the collector, the second terminal is the emitter, the third terminal is the base, and the first terminal of the NMOS transistor is the drain. The second end is the source, and the third end is the gate; the transistors Q2~Q5 are all PNP transistors or PMOS transistors, the first end of the PNP transistor is the emitter, the second end is the collector, the third end is the base, and the PMOS The first end of the transistor is the source, the second end is the drain, and the third end is the gate.

Refer to Fig. 2 for the main circuit schematic diagram of a specific embodiment of the utility model. An advanced limiting power constant value circuit of the utility model is electrically connected together by transistors Q1~Q7, amplifiers A1~A2, comparator C1, low-voltage power supply, logic conversion, oscillator OSC, and resistors R1~R3. Specifically, refer to Figure 2. Figure 2 is a schematic diagram of the circuit connection of the advanced limiting power constant value circuit 5000 of this example. In the figure, transistors Q1~Q7, amplifiers A1~A2, comparator C1, low-voltage power supply, logic conversion, and oscillation The device OSC and the resistors R1~R3 are connected together according to the electrical coupling; it converts the periodic triangular wave voltage Vtri of the OSC and the reference voltage Vref1 into a voltage signal V1, and samples the voltage signal V1 to the capacitor Csh through the switch tube Q7 for current limiting The threshold voltage signal Vcsth and the signal Vsense of the port SENSE output an OCP signal at the OCP port after being compared with Vcsth. The OCP signal can control whether the external power switch tube is turned off through the pulse width modulator 3000 and the driving circuit 4000 to realize maximum power control. Vsh is a low-voltage synchronous level conversion of the Vsw signal, that is, the phases of Vsh and Vsw are the same, and the high-level potentials are different. When the line voltage input Vin potential rises, the slope of the current signal Is in the primary coil of the transformer rises (the slope is Vin/L, and L is the primary inductance of the transformer), which causes the peak voltage drop on the sampling resistor Rs to touch in advance When Vcsth is reached, the power switch tube is turned off, so the conduction time of the switching signal Vsw becomes shorter, that is, the conduction time of the Vsh signal becomes shorter. When the turn-on time of the Vsh signal becomes smaller, the V1 sampled at the end of the turn-on time of this cycle becomes lower, which in turn causes the OCP comparator threshold Vcsth of the next cycle to become smaller, thus suppressing the limit power of the switching power supply system from changing with the line voltage Vin potential rises and tends to increase, so that the maximum output power fluctuation in the full voltage range is minimal. In addition, because the utility model adopts the sampling and holding method to generate Vcsth, in view of the conduction time of each single switching cycle, the current limiting threshold Vcsth is a constant value, which can effectively avoid the slight magnetic saturation of the transformer under the condition of low voltage and heavy load The limit output power drop caused by large and small waves makes the limit power in the full voltage range more constant and the fluctuation is extremely small.

In addition, the advanced limit power constant value circuit provided by the utility model can be applied to both the secondary side feedback switching power supply and the primary measurement feedback switching power supply.

In order to allow those skilled in the art to better understand the utility model, we will further describe the working principle of the utility model in conjunction with specific circuits below:

Please continue to refer to Figure 2, the advanced limiting power constant value circuit 5000, including transistors Q1~Q7, amplifiers A1~A2, comparator C1, low-voltage power supply module, oscillator OSC, resistors R1~R3; the first terminal of transistor Q1 is connected The third end of transistor Q2, Q3 and the second end of Q3, the second end of which is connected to the second end of amplifier A1 and the first end of resistor R1, the third end of which is connected to the third end of amplifier A1; the first end of transistor Q2 One end is connected to the second end of the low-voltage power supply module, and its second end is connected to the first end of the resistor R3, the second end of the transistor Q7, and the second end of the transistor Q4; the first end of the transistor Q3 is connected to the second end of the low-voltage power supply module. terminal; the first terminal of the transistor Q4 is connected to the second terminal of the low-voltage power supply module, and its third terminal is connected to the second and third terminals of the transistor Q5 and the first terminal of the transistor Q6; the first terminal of the transistor Q5 is connected to the low-voltage power supply module The second terminal; the second terminal of the transistor Q6 is connected to the first terminal of the resistor R2 and the second terminal of the amplifier A2, and its third terminal is connected to the third terminal of the amplifier A2; the first terminal of the transistor Q7 is connected to the first terminal of the capacitor Csh And the first end of the comparator C1, the third end of which is connected to the second end of the logic transformation module; the first end of the amplifier A1 is connected to the second end of the oscillator OSC; the first end of the amplifier A2 is connected to the third end of the low-voltage power supply module end; the second end of resistors R1, R2, R3, and capacitor Csh is grounded; the first end of the oscillator OSC is connected to the second end of the low-voltage power supply module, and the third end is connected to the fifth end of the advanced limiting power constant value circuit. terminal CLK; the first terminal of the low-voltage power supply module is connected to the first terminal VCC of the advanced limit power constant value circuit; the first terminal of the logic change module is connected to the first terminal VCC of the advanced limit power constant value circuit, and the third terminal is connected to The second terminal GATE of the advanced limiting power constant value circuit; the second terminal of the comparator C1 is connected to the fourth terminal SENSE of the advanced limiting power constant value circuit, and its third terminal is connected to the third terminal of the advanced limiting power constant value circuit OCP.

The working principle of the advanced limit power constant value circuit 5000 is as follows:

When the VCC signal is powered on, the low-voltage power supply generates an internal power supply VDD and an internal reference voltage Vref1. The oscillator OSC generates a periodic triangular wave voltage Vtri, which is converted into a periodic triangular wave current I1 by the amplifier A1. The internal reference voltage Vref1 is converted into a current I3 by the amplifier A2.

I1 = Vtri/R1 (1)

The reference current I1 generated by amplifier A1 passes through the current mirror (composed of Q2 and Q3) to generate reference currents I2,

I2=α*I1=αVtri/R1 (2)

Among them, α is the mirror image ratio coefficient of current mirror Q3, Q2,

I3 = Vref1/R2 (3)

The reference current I3 generated by amplifier A2 passes through the current mirror (composed of Q4 and Q5) to generate reference currents I4,

I4=β*I3=βVref1/R2 (4)

Among them, β is the mirror image ratio coefficient of current mirror Q5, Q4,

V1=(I2+I4)*R3=αVtri*R3/R1+βVref1*R3/R2 (5)

V1 is sampled by the sampling switch transistor Q7 to the capacitor Csh to generate the current limiting threshold Vcsth in the next cycle, and the sampling control signal is Vsh, as shown in Figure 4, Vcsth, V1, Vsh, Vsw timing, so there are expressions:

Vcsth=V1=V0*Tsw*D*α*R3/R1+βVref1*R3/R2 (6)

Among them, V0 is the constant reference voltage value, Tsw is the switching period, D is the duty cycle of the previous cycle, and the maximum duty cycle Dmax≦55%,

Vsense=Is*Rs=Rs*Tsw*D1*Vin/L (7)

Among them, D1 is the duty cycle of this cycle, Vin is the line voltage input potential, Vsense is the voltage on Rs,

Therefore, when Vsense touches the current-limiting threshold Vcsth, the signal OCP that turns off the external power switch M1 is generated, and the expression is:

Vcsth =Vsense=Rs*Tsw*D1*Vin/L (8)

It can be seen from the expression (8) that if the Vin voltage increases, D1 will decrease, resulting in a decrease in the sampled Vcsth in this period, and the current-limiting threshold in the next period will decrease accordingly. Therefore, when the input line voltage rises, the switching power supply system containing the utility model automatically suppresses the rise of the maximum limit power, suppresses the fluctuation of the limit power in the full voltage range, protects the safety of the electrical appliances, and simplifies User's switching power supply system design.

The limit power fluctuation curve waveforms of the switching power supply system of the present utility model and the traditional switching power supply system in the full voltage input range are shown in FIG. 5 . It can be seen from the curve in Figure 5 that the maximum output power of the switching power supply system of the present invention fluctuates close to 0 in the full voltage input range, which can be considered as a constant maximum power value, while the maximum power value of the traditional switching power supply system fluctuates System design safety specifications are exceeded.

The utility model also provides a switching power supply using the above-mentioned advanced limiting power constant value circuit, which includes a transformer, a switching power supply controller for generating a switching signal for adjusting the pulse width of the transformer, and a power switching tube M1 The switching power supply controller is coupled to a feedback unit located at the output end of the transformer; the first end of the power switching tube is connected to the input end of the transformer, and the second end of the power switching tube is respectively connected to the switching power supply controller and the limiter. The first end of the current resistance Rs, the third end of the power switch tube is connected to the switching power supply controller; the switching power supply controller includes an undervoltage lockout circuit, an advanced limiting power constant value circuit, a pulse width modulator and A driving circuit; the driving circuit is respectively connected with the undervoltage lockout circuit, the advanced limiting power constant value circuit and the pulse width modulator; the advanced limiting power constant value circuit is connected with the pulse width modulator.

As shown in Figure 3, it is a switching power supply using the advanced limit power constant value circuit in Figure 2, including a transformer and a switch controller, and the switch controller is coupled to a feedback unit located at the output end of the transformer to generate a switch The signal adjusts the pulse width of the transformer, and the switch controller is composed of an undervoltage lockout circuit, the advanced limit power constant value circuit, a pulse width modulator and a drive circuit coupled. The advanced limit power constant value circuit is embedded in a pulse width modulation controller integrated circuit, the VCC port of the advanced limit power constant value circuit is connected to the power supply VCC, and the GATE port of the advanced limit power constant value circuit is connected to The gate of the external power switch tube M1, the output signal of the OCP port of the advanced limiting power constant value circuit is sent to the third input terminal of the pulse width modulator, and the SNSE port of the advanced limiting power constant value circuit is connected to the first of the external sampling resistor Rs end and the source of a power tube M1, the CLK port of the advanced limiting power constant value circuit is connected to the fifth end of the pulse width modulator; the first input end of the pulse width modulator is connected to the first end of a sampling resistor Rs and the source of a power transistor M1, the second input terminal of the pulse width modulator is connected to the feedback terminal of the feedback unit, and the third terminal is connected to the third terminal OCP of the advanced limiting power constant value circuit, and the pulse width is The fourth terminal of the modulator is connected to the first terminal of the driving circuit, the fifth terminal of the pulse width modulator is connected to the fifth terminal CLK of the advanced limit power constant value circuit; the second input terminal of the driving circuit is connected to the power supply VCC , the third terminal of the drive circuit is connected to the gate of the power transistor M1; the second terminal of the sampling resistor Rs is grounded; the input terminal of the undervoltage lockout circuit is connected to the power supply VCC; the drain terminal of the power switch tube is connected to the transformer the primary coil.

Preferably, the undervoltage lockout circuit, the advanced limit power constant value circuit, the pulse width modulator and the driving circuit are embedded in an integrated circuit to save external components.

Although the present invention is disclosed above with preferred embodiments, it should not limit the present invention. Any person familiar with this field can make some changes and substitutions without departing from the spirit and scope of the present invention. For example, the utility model can be applied to the secondary side feedback switching power supply system, and is also suitable for the primary side feedback switching power supply system. The EMI of the switching power supply system using the utility model is obviously better than other traditional switching power supply systems, which can save users Cost, reduce the design difficulty of switching power supply system. Therefore, the protection scope of the present utility model should be defined by the appended patent scope.

Claims (7)

1. a kind of advanced power limit constant circuit, it is characterised in that: including transistor Q1~Q7, resistor R1~R3, electricity Container Csh, amplifier A1~A2, comparator C1, for providing the low of internal power supply VDD and internal reference voltage Vref1 Press power supply module, logical conversion module, oscillator OSC and five ports；

Five ports include first end VCC, second end GATE, third end OCP, the 4th end SENSE and the 5th end CLK；

The first end of the transistor Q1 meets the third end of transistor Q2, the third end of transistor Q3, transistor Q3 respectively Second end, the second end of transistor Q1 connect the first end of the negative input end of amplifier A1, resistance R1, the third of transistor Q1 respectively Terminate the output end of amplifier A1；

The second end of the first termination low-voltage power supply module of the transistor Q2, transistor Q2 second end distinguish connecting resistance R3's First end, the second end of transistor Q7, the second end of transistor Q4；

The second end of the first termination low-voltage power supply module of the transistor Q3；

The first end of the transistor Q4 connects the second end of the first end of transistor Q5, low-voltage power supply module, transistor respectively The third end of Q4 connect respectively the second end of transistor Q5, the third end of transistor Q5, transistor Q6 first end；

The second end of the transistor Q6 distinguishes the negative input end of the first end of connecting resistance R2, amplifier A2, transistor Q6's The output end of third termination amplifier A2；

The first end of the transistor Q7 connects the first end of the first end of capacitor Csh, comparator C1 respectively, and the of transistor Q7 The second end of three terminating logic conversion modules；

The second end of the resistance R1, the second end of R2, the second end of the second end of R3 and capacitor Csh are grounded respectively；

The second end of the positive input termination oscillator OSC of the amplifier A1；

The third end of the positive input termination low-voltage power supply module of the amplifier A2；

The second end of the first termination low-voltage power supply module of the oscillator OSC；The third of oscillator OSC terminates the 5th end CLK；

First termination first end VCC of the low-voltage power supply module；

First termination first end VCC of the logic variation module, the third that logic changes module terminate second end GATE；

The positive input of the comparator C1 terminates the 4th end SENSE, and the output of the comparator C1 terminates third end OCP.

2. advanced power limit constant circuit according to claim 1, it is characterised in that: transistor Q1, Q6, Q7 are NPN transistor or NMOS transistor, the first end collector of NPN transistor, second end are emitter, and third end is base stage, The first end of NMOS transistor is drain electrode, second end is source electrode, and third end is grid；Transistor Q2~Q5 is PNP transistor Or PMOS transistor, the first end emitter of PNP transistor, second end are collector, third end is base stage, PMOS transistor First end be source electrode, second end is drain electrode, third end is grid.

3. a kind of Switching Power Supply using advanced power limit constant circuit described in claim 1, it is characterised in that: including The switch power controller and a power of the switching signal of transformer, one for generating the pulse width for adjusting the transformer are opened Close pipe M1；

The switch power controller coupling one is set to the feedback unit of transformer output end；The power switch tube first end Transformer inputs are connect, the second end of power switch tube connects the first of the switch power controller and current-limiting resistance Rs respectively End, the third termination of the power switch tube switch power controller；

The switch power controller include undervoltage lockout circuit, advanced power limit constant circuit, pulse width modulator with Driving circuit；The driving circuit connects with undervoltage lockout circuit, advanced power limit constant circuit, pulse width modulator respectively It connects；

The advanced power limit constant circuit is connect with pulse width modulator.

4. Switching Power Supply according to claim 3, it is characterised in that: the first termination pulsewidth tune of the driving circuit The third of 4th end PWM of device processed, the second termination power VCC of driving circuit, driving circuit terminate the power switch tube M1 Third end；

The first end SENSE of the pulse width modulator connects the first end of a sampling resistor Rs, the second end of power tube M1, arteries and veins respectively The second end FB of wide modulator connects the feedback end of the feedback unit, and the third of pulse width modulator terminates the advanced limit function The third end OCP of rate constant circuit, the 5th end of the 5th termination advanced power limit constant circuit of pulse width modulator CLK；

The first end VCC of the advanced power limit constant circuit meets power supply VCC, and the of advanced power limit constant circuit Two end GATE connect the third end of the power switch tube M1, and the 4th end SENSE of advanced power limit constant circuit connects respectively First end, the second end of power tube M1 of external sampling resistance Rs；

The first end VCC of the first termination power limit constant circuit of the undervoltage lockout circuit；

The second end of the sampling resistor Rs is grounded.

5. Switching Power Supply according to claim 3 or 4, it is characterised in that: the power switch tube M1 is power crystal Pipe, the first end of power switch tube M1 are drain electrode, and second end is source electrode, and third end is grid.

6. Switching Power Supply according to claim 3, it is characterised in that: the undervoltage lockout circuit, advanced power limit Constant circuit, pulse width modulator, driving circuit are embedded in an integrated circuit.

7. a kind of Switching Power Supply using advanced power limit constant circuit described in claim 1, it is characterised in that: described Switching Power Supply is secondary side feedback formula Switching Power Supply or primary side feedback formula Switching Power Supply.