CN102916595B - Switching power supply and multi-threshold switching circuit thereof - Google Patents

Abstract

The invention is applicable to the technical field of switching power supplies, and provides a switching power supply and a multi-threshold switching circuit thereof. The multi-threshold switching circuit is characterized in that a sampling voltage judgment module is used for dividing voltage outputted by a power supply circuit, comparing the voltage with a first reference voltage, a second reference voltage and a third reference voltage outputted by a reference voltage generating module and outputting corresponding control signals to a voltage-controlled oscillation module according to comparison results; the voltage-controlled oscillation module is used for generating pulse signals with specific duty ratio according to a fourth reference voltage and a fifth reference voltage which are outputted by the reference voltage generating module and the control signals; and a power switch is used for high-frequency on-off switching with a corresponding frequency according to the pulse signals to enable a transformer to perform storage and release of electricity energy correspondingly, so that output voltage of the transformer is periodically modulated to achieve stable contact voltage output. The switching power supply is further simplified structurally by the aid of the multi-threshold switching circuit, and cost is reduced.

Description

A kind of Switching Power Supply and multi thresholds switching circuit thereof

Technical field

The invention belongs to switch power technology field, particularly relate to a kind of Switching Power Supply and multi thresholds switching circuit thereof.

Background technology

At present, along with development and the renewal of switch power technology, Switching Power Supply has possessed the advantage that efficiency is high, volume is little and cost is low, so it has been widely used in various electronic equipment.Particularly in charger for mobile phone or the power supply such as adapter or standby power, Switching Power Supply generally only needs to possess constant voltage output function.

Export to realize constant voltage in the power supply such as charger for mobile phone or adapter, prior art provides a kind of former limit feedback flyback Switching Power Supply, it needs the On current of switch tube to sample, and after output feedack voltage being sampled by the independent pin of internal controller, by controller according to certain duty ratio and switching frequency to adjust output voltage, after repeatedly adjustment, realize constant voltage export.Aforesaid prior art exports although can realize constant voltage, but cause the peripheral circuit structure relative complex of its controller because it needs the On current of sampling switch pipe and independent pin sampling output feedack voltage, cost increases, reduce the antijamming capability of whole switch power supply system simultaneously, have impact on the stability of a system and poor reliability.

Summary of the invention

The object of the present invention is to provide a kind of multi thresholds switching circuit of Switching Power Supply, be intended to solve switch power supply system stability existing for prior art and poor reliability, the complicated and problem that cost is high of circuit structure.

The present invention realizes like this, a kind of multi thresholds switching circuit of Switching Power Supply, with the sampling in Switching Power Supply and power supply circuits, start-up circuit and transformer T1 are connected, described sampling and power supply circuits are used for sampling to the output voltage of described Switching Power Supply and provide power supply for multi thresholds switching circuit, described start-up circuit is used at the beginning of described Switching Power Supply powers on for described multi thresholds switching circuit provides starting resistor, the output of described sampling and power supply circuits and the output of described start-up circuit connect altogether, described multi thresholds switching circuit has a power end, the power end of described multi thresholds switching circuit connects the output of described sampling and power supply circuits, described multi thresholds switching circuit comprises:

Sampled voltage judge module, VCO module, reference voltage generation module and power switch;

The power end of described sampled voltage judge module is the power end of described multi thresholds switching circuit, the power end of described VCO module and the power end of described reference voltage generation module are connected to the power end of described sampled voltage judge module altogether, control end and the output of described VCO module are connected the output of described sampled voltage judge module and the control end of described power switch respectively, first reference output of described reference voltage generation module, second reference output and the 3rd reference output connect the first benchmark input end of described sampled voltage judge module respectively, second benchmark input end and the 3rd benchmark input end, 4th reference output of described reference voltage generation module and the 5th reference output are connected with the first benchmark input end of described VCO module and the second benchmark input end respectively, input and the output of described power switch are connected the second end and the ground of the armature winding of described transformer T1 respectively,

The output voltage of described sampling and power supply circuits is carried out dividing potential drop and the first reference voltage exported with described reference voltage generation module by described sampled voltage judge module, second reference voltage and the 3rd reference voltage compare, and control signal to described VCO module accordingly according to comparative result output, described VCO module is according to described control signal, the 4th reference voltage that described reference voltage generation module exports and the 5th reference voltage generate the pulse signal accordingly with particular duty cycle, described power switch carries out the switching of high frequency break-make according to described pulse signal with corresponding frequency makes transformer T1 correspondingly carry out storage and the release of electric energy.

Another object of the present invention is also to provide a kind of Switching Power Supply, and described Switching Power Supply comprises current rectifying and wave filtering circuit, transformer T1, sampling and power supply circuits, start-up circuit, secondary current rectifying and wave filtering circuit and described multi thresholds switching circuit.

The present invention comprises described sampled voltage judge module by adopting in Switching Power Supply, described VCO module, the multi thresholds switching circuit of described reference voltage generation module and described power switch, the voltage exported by described sampling and power supply circuits is carried out dividing potential drop and the first reference voltage exported with described reference voltage generation module by described sampled voltage judge module, second reference voltage and the 3rd reference voltage compare, and control signal to described VCO module accordingly according to comparative result output, described VCO module is according to described control signal, the 4th reference voltage that described reference voltage generation module exports and the 5th reference voltage generate the pulse signal accordingly with particular duty cycle, described power switch carries out the switching of high frequency break-make according to described pulse signal with corresponding frequency makes transformer T1 correspondingly carry out storage and the release of electric energy, and then realize carrying out periodic modulation to the output voltage of described transformer T1, to reach the object stably realizing constant voltage and export, and the employing of described multi thresholds switching circuit makes the circuit structure of Switching Power Supply simplify further, reduce cost, solve the switch power supply system stability existing for prior art and poor reliability, complicated and the problem that cost is high of circuit structure.

Accompanying drawing explanation

Fig. 1 is the function structure chart of the multi thresholds switching circuit of the Switching Power Supply that the embodiment of the present invention provides;

Fig. 2 is the exemplary circuit structure chart of the multi thresholds switching circuit of the Switching Power Supply that the embodiment of the present invention provides.

Embodiment

In order to make object of the present invention, technical scheme and advantage clearly understand, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, be not intended to limit the present invention.

The embodiment of the present invention comprises sampled voltage judge module by adopting in Switching Power Supply, VCO module, the multi thresholds switching circuit of reference voltage generation module and power switch, the voltage that sampling and power supply circuits 300 export is carried out dividing potential drop and the first reference voltage exported with reference voltage generation module by sampled voltage judge module, second reference voltage and the 3rd reference voltage compare, and control signal to VCO module accordingly according to comparative result output, VCO module is according to described control signal, the 4th reference voltage that reference voltage generation module exports and the 5th reference voltage generate the pulse signal accordingly with particular duty cycle, power switch carries out the switching of high frequency break-make according to described pulse signal with corresponding frequency makes transformer T1 correspondingly carry out storage and the release of electric energy, and then realize carrying out periodic modulation to the output voltage of transformer T1, to reach the object stably realizing constant voltage and export, and the employing of multi thresholds switching circuit makes the circuit structure of Switching Power Supply simplify further, reduce cost.

Fig. 1 shows the modular structure of the multi thresholds switching circuit of the Switching Power Supply that the embodiment of the present invention provides, and for convenience of explanation, illustrate only part related to the present invention, details are as follows:

In embodiments of the present invention, Switching Power Supply comprises multi thresholds switching circuit 100, current rectifying and wave filtering circuit 200, transformer T1, sampling and power supply circuits 300, start-up circuit 400 and secondary current rectifying and wave filtering circuit 500, the input incoming transport civil power AC of current rectifying and wave filtering circuit 200, the output of current rectifying and wave filtering circuit 200 is connected with the first end 1 of the armature winding of transformer T1, the first end 3 connecting secondary current rectifying and wave filtering circuit 500 of the secondary winding of transformer T1, the output of secondary current rectifying and wave filtering circuit 500 exports DC powered loaded work piece, second end 4 of the secondary winding of transformer T1 connects and exports ground, sampling and power supply circuits 300 are for sampling to the output voltage of Switching Power Supply and providing power supply for multi thresholds switching circuit 100, and sampling and power supply circuits 300 comprise the auxiliary winding of transformer T1, rectifier diode D0 and filter capacitor C0, from the characteristic of transformer, the output voltage of transformer T1 level becomes turn ratio relation with auxiliary winding voltage, therefore realize the sampling to the output voltage of transformer T1 level by the voltage of the auxiliary winding of sampling transformer T1, and then realize the sampling to switch power source output voltage, the input of start-up circuit 400 is connected with the output of current rectifying and wave filtering circuit 200, and it comprises a resistance R0, at the beginning of powering in Switching Power Supply for multi thresholds switching circuit 100 provides starting resistor, secondary current rectifying and wave filtering circuit 500 comprises rectifier diode D1 and electric capacity C2.

Multi thresholds switching circuit 100 is connected with power supply circuits 300, start-up circuit 400 and transformer T1 with the sampling in Switching Power Supply, sampling connects altogether with the output of power supply circuits 300 and the output of start-up circuit 400, multi thresholds switching circuit 100 has a power end, the power end of multi thresholds switching circuit 100 connects the output of sampling and power supply circuits 300, and multi thresholds switching circuit 100 comprises:

Sampled voltage judge module 101, VCO module 102, reference voltage generation module 103 and power switch 104;

The power end of sampled voltage judge module 101 is the power end of multi thresholds switching circuit 100, the power end of VCO module 102 and the power end of reference voltage generation module 103 are connected to the power end of sampled voltage judge module 101 altogether, control end and the output of VCO module 102 are connected the output of sampled voltage judge module 101 and the control end of power switch 104 respectively, first reference output V1 of reference voltage generation module 103, second reference output V2 and the 3rd reference output V3 connects the first benchmark input end Vin1 of sampled voltage judge module 101 respectively, second benchmark input end Vin2 and the 3rd benchmark input end Vin3, 4th reference output V4 of reference voltage generation module 103 and the 5th reference output V5 is connected with the first benchmark input end Vin1 of VCO module 102 and the second benchmark input end Vin2 respectively, second end 2 of the armature winding of the input of power switch 104 and output difference connection transformer T1 and ground,

Sampling is carried out dividing potential drop with the output voltage Vg of power supply circuits 300 and the first reference voltage V r1 exported with reference voltage generation module 103 by sampled voltage judge module 101, second reference voltage V r2 and the 3rd reference voltage V r3 compares, and export corresponding control signal Vctrl to VCO module 102 according to comparative result, VCO module 102 is according to control signal Vctrl, the 4th reference voltage V l that reference voltage generation module 103 exports and the 5th reference voltage V h generates the pulse signal Vgf accordingly with particular duty cycle, power switch 104 carries out the switching of high frequency (if frequency is for 60kHz) break-make according to pulse signal Vgf with corresponding frequency makes transformer T1 correspondingly carry out storage and the release of electric energy, and then realize modulating the output voltage of transformer T1.Wherein, the 4th reference voltage V l is less than the 5th reference voltage V h.

Fig. 2 shows the exemplary circuit structure of the multi thresholds switching circuit of the Switching Power Supply that the embodiment of the present invention provides, and for convenience of explanation, illustrate only part related to the present invention, details are as follows:

As one embodiment of the present invention, sampled voltage judge module 101 comprises:

Resistance R1, resistance R2, resistance R3, resistance R4, the first comparator COMP1, the second comparator COMP2, the 3rd comparator COMP3, the first NOR gate NOR1, the second NOR gate NOR2, the first inverter INV1, delay circuit 1011, NMOS tube NM1, PMOS PM1 and first and door AND1;

The first end of resistance R1 is the power end of sampled voltage judge module 101, second end of resistance R1 and the first end of resistance R2 are connected to the in-phase input end of the first comparator COMP1 altogether, second end of resistance R2 and the first end of resistance R3 are connected to the inverting input of the second comparator COMP2 altogether, second end of resistance R3 and the first end of resistance R4 are connected to the inverting input of the 3rd comparator COMP3 altogether, the second end ground connection of resistance R4, the inverting input of the first comparator COMP1, the in-phase input end of the second comparator COMP2 and the in-phase input end of the 3rd comparator COMP3 are respectively the first benchmark input end Vin1 of sampled voltage judge module 101, second benchmark input end Vin2 and the 3rd benchmark input end Vin3, first input end 1 and second input 2 of the first NOR gate NOR1 are connected the output of the first comparator COMP1 and the output of the second NOR gate NOR2 respectively, the first input end 1 of the second NOR gate NOR2 and the output 3 of the first NOR gate NOR1 are connected to the input of the first inverter INV1 altogether, second input 2 of the second NOR gate NOR2 connects the output of the 3rd comparator COMP3, the output of the first inverter INV1 is connected with second input 2 of door AND1 with the input and first of delay circuit 1011 simultaneously, the output of delay circuit 1011 is connected with the grid of NMOS tube NM1 and the grid of PMOS PM1 simultaneously, the source electrode of NMOS tube NM1 connects the output of the second comparator COMP2, the first end of the drain electrode connecting resistance R1 of PMOS PM1, the drain electrode of NMOS tube NM1 and the source electrode of PMOS PM1 are connected to the first input end 1 of first and door AND1 altogether, first is the output of sampled voltage judge module 101 with the output 3 of door AND1.Wherein, delay circuit 1011 is the delay circuits be made up of multiple delayer, can adjust arbitrarily the quantity of delayer according to the difference of delay time.

As one embodiment of the present invention, VCO module 102 comprises:

Second with door AND2, the first current source I1, PMOS PM2, NMOS tube NM2, the second current source I2, the 4th comparator COMP4, the 5th comparator COMP5, electric capacity C1, the first NAND gate NAND1, the second NAND gate NAND2, the second inverter INV2 and the 3rd inverter INV3;

Second is the control end of VCO module 102 with the first input end 1 of door AND2, the input of the first current source I1 is the power end of VCO module 102, the drain electrode of the output termination PMOS PM2 of the first current source I1, the grid of PMOS PM2 and the grid of NMOS tube NM2 are connected to the output 3 of second and door AND2 altogether, the common contact of the source electrode of PMOS PM2 and the drain electrode of NMOS tube NM2 simultaneously with the in-phase input end of the 4th comparator COMP4, the inverting input of the 5th comparator COMP5 and the first end of electric capacity C1, the source electrode of NMOS tube NM2 connects the input of the second current source I2, the output of the second current source I2 and second end of electric capacity C1 are connected to ground altogether, the inverting input of the 4th comparator COMP4 and the in-phase input end of the 5th comparator COMP5 are respectively the first benchmark input end Vin1 and the second benchmark input end Vin2 of VCO module 102, output and the output of the 5th comparator COMP5 of the 4th comparator COMP4 are connected the first input end 1 of the first NAND gate NAND1 and second input 2 of the second NAND gate NAND2 respectively, second input 2 of the first NAND gate NAND1 connects the output 3 of the second NAND gate NAND2, the first input end 1 of the second NAND gate NAND2 and the output 3 of the first NAND gate NAND1 are connected to the input of the second inverter INV2 altogether, the input of the 3rd inverter INV3 and second and second input of door AND2 be connected to the output of the second inverter INV2 altogether, the output of the 3rd inverter INV3 is the output of VCO module 102.

As one embodiment of the present invention, reference voltage generation module 103 is conventional band-gap reference circuit, in embodiments of the present invention, it is except providing reference voltage for sampled voltage judge module 101 and VCO module 102, also for the first current source I1 in VCO module 102 and the second current source I2 provides reference current, and provide bias current for the 4th comparator COMP4 and the 5th comparator COMP5.

As one embodiment of the present invention, power switch 104 is high pressure NMOS pipe NM3, and the grid of high pressure NMOS pipe NM3, drain electrode and source electrode are respectively the control end of power switch 104, input and output.In other embodiments of the present invention, power switch 104 can also be high voltage PMOS pipe, and the grid of high pressure NMOS pipe, drain electrode and source electrode are respectively the control end of power switch 104, input and output equally.

In actual applications, multi thresholds switching circuit 100 can be integrated in a chip according to said structure and annexation, and the power end of sampled voltage judge module 101, the input of power switch 104 and output are respectively as three pins of constant-voltage controller, and the On current of sampled power switch 104 need not be removed by independent circuit, also pin that need not be independent and independent circuit remove the output voltage of sampling switch power supply, chip pin can be reduced like this, improve integrated level, three pin packaging structures of TO92 or SOT89-3 can be adopted, thus effectively reduce packaging cost.

Below the operation principle of multi thresholds switching circuit 100 in Switching Power Supply is described further:

At the beginning of Switching Power Supply powers on, exporting high voltage direct current after current rectifying and wave filtering circuit 200 pairs of electric mains carry out rectifying and wave-filtering divides two-way to enter start-up circuit 400 and transformer T1, power supply is provided to multi thresholds switching circuit 100 by the resistance R0 of start-up circuit 400, then the input voltage of multi thresholds switching circuit 100 can raise gradually, thus drive multi thresholds switching circuit 100 to start working, power switch 104 starts the break-make switch operating of high frequency, but because the resistance of the resistance R0 in start-up circuit 400 is larger, the electric current that start-up circuit 400 provides cannot meet the consumption of the multi thresholds switching circuit 100 after startup, namely when after the break-make switch operating of power switch 104 at high frequency, the power end of sampled voltage judge module 101 (is also the power end of multi thresholds switching circuit 100, the i.e. first end of resistance R1) voltage can reduce, therefore after starting, be contained in sampling and can provide energy to the power end of sampled voltage judge module 101 (that is to say the power end of multi thresholds switching circuit 100) with the auxiliary winding of the transformer T1 in power supply circuits 300.

Turn ratio principle according to transformer:

$\frac{\mathrm{Vg}+\mathrm{Vd}0}{\mathrm{Vout}+\mathrm{Vd}1}=\frac{\mathrm{Nf}}{\mathrm{Ns}}---\left(1\right)$

Wherein, Nf and Ns is the auxiliary winding of transformer and the turn ratio of secondary winding respectively, Vd0 and Vd1 is rectifier diode D0 with the forward conduction voltage drop of rectifier diode D1 (because both are the diodes belonging to identical type respectively, so both forward voltage drops are also identical), Vg and Vout is respectively sampling and the output voltage of power supply circuits 300 and the output voltage of Switching Power Supply, so the output voltage Vout of Switching Power Supply can be expressed as

$\mathrm{Vout}=\frac{\mathrm{Nf}}{\mathrm{Ns}}\·(\mathrm{Vg}+\mathrm{Vd}0)-\mathrm{Vd}1---\left(2\right)$

Therefore, from relational expression (2), constant by control voltage Vg, just can so that control Vout constant.

The first end 1 of direct current to the armature winding of transformer T1 is exported after current rectifying and wave filtering circuit 200 pairs of electric mains carry out rectifying and wave-filtering, transformer T1 starts working and exports direct current to secondary current rectifying and wave filtering circuit 400, simultaneously, sampling and power supply circuits 300 provide voltage Vg to the first end of resistance R1, then by resistance R1, resistance R2, resistance R3 and resistance R4 carries out dividing potential drop to Vg, be respectively the in-phase input end of the first comparator COMP1, the inverting input of the second comparator COMP2 and the inverting input of the 3rd comparator COMP3 input the first branch pressure voltage Vg1, second branch pressure voltage Vg2 and the 3rd branch pressure voltage Vg3, first branch pressure voltage Vg1, the voltage relationship of the second branch pressure voltage Vg2 and the 3rd branch pressure voltage Vg3 and sampled voltage Vg is expressed as:

$\mathrm{Vg}1=\frac{R1+R2+R3+R4}{R2+R3+R4}\·\mathrm{Vg}1---\left(3\right)$

$\mathrm{Vg}=\frac{R1+R2+R3+R4}{R3+R4}\·\mathrm{Vg}2---\left(4\right)$

$\mathrm{Vg}=\frac{R1+R2+R3+R4}{R4}\·\mathrm{Vg}3---\left(5\right)$

The magnitude of voltage of the first reference voltage V r1, the second reference voltage V r2 and the 3rd reference voltage V r3 reduces (i.e. Vr1>Vr2>Vr3) successively, introduce the first reference voltage Vt1, the second reference voltage Vt2 and the 3rd reference voltage Vt3 herein, and the first reference voltage Vt1, the second reference voltage Vt2 and the 3rd reference voltage Vt3 and the first reference voltage V r1, the second reference voltage V r2 and the 3rd reference voltage V r3 relation separately as follows:

$\mathrm{Vt}1=\frac{R1+R2+R3+R4}{R2+R3+R4}\·\mathrm{Vr}1---\left(6\right)$

$\mathrm{Vt}2=\frac{R1+R2+R3+R4}{R3+R4}\·\mathrm{Vr}2---\left(7\right)$

$\mathrm{Vt}3=\frac{R1+R2+R3+R4}{R4}\·\mathrm{Vr}3---\left(8\right)$

At the beginning of Switching Power Supply powers on, sampled voltage Vg is less than the first reference voltage Vt1(Vg<Vt1), then the first control signal Vctrl exported with door AND1 is low level, VCO module 102 does not start and the pulse signal Vgf exported is also low level, so power switch 104 ends.

After Switching Power Supply powers on, the first dividing potential drop Vg1 of voltage Vg is greater than the first reference voltage V r1, and namely voltage Vg is greater than the first reference voltage Vt1(Vg>Vt1).Now the output of the first comparator COMP1 exports high level, 3rd comparator COMP3 output low level, then the first inverter INV1 exports high level, output low level is set as at the beginning of delay circuit 1011 powers on, then NMOS tube NM1 cut-off, PMOS PM1 conducting, first obtains high level with the first input end 1 of door AND1, so first exports high level opening pressure control oscillation module 102 work with door AND1, the 3rd inverter INV3 in VCO module 102 exports the pulse signal Vgf driving power switch 104 with fixed duty cycle realizes high frequency break-make alternation with corresponding frequency.

After delay circuit 1011 time delay in sampled voltage judge module 101, voltage Vg is greater than the 3rd reference voltage Vt3(Vg>Vt3), the output of delay circuit 1011 becomes high level from low level, so, the height of the output level of the second comparator COMP2 is depended in the change of the first control signal Vctrl exported with door AND1, that is:

If Vg2>Vr2(and Vg>Vt2), second comparator COMP2 output low level, control signal Vctrl is also low level, and VCO module 102 is closed, the pulse signal Vgf that 3rd inverter INV3 exports is low level, and power switch 104 ends;

If Vr3<Vg2<Vr2(and Vt3<Vg<Vt2), second comparator COMP2 exports high level, control signal Vctrl is also high level, VCO module 102 is opened and is vibrated and make the 3rd inverter INV3 export the pulse signal Vgf with fixed duty cycle, then power switch 104 realizes the alternation of high frequency break-make with the switching frequency corresponding to pulse signal Vgf.

If Vg2<Vr3(and Vg<Vt3), then the first comparator COMP1 and the equal output low level of the second comparator COMP2,3rd comparator COMP3 exports and becomes high level, then control signal Vctrl is low level, VCO module 102 is closed, the pulse signal Vgf that 3rd inverter INV3 exports is low level, and power switch 104 ends.

When above-mentioned power switch 104 is in high frequency break-make switch operating, its energy exported is in gathering, the output voltage of transformer T1 level can raise, voltage Vg also raises simultaneously, and when voltage Vg is greater than the second reference voltage Vt2, power switch 104 enters closedown cut-off state, then along with load is to the consumption of output voltage Vout, voltage Vg can reduce again, and when voltage Vg is less than the second reference voltage Vt2, so power switch 104 starts again the break-make alternation carrying out high frequency.Through the adjustment repeatedly in multiple like this cycle, when Switching Power Supply stable output, voltage Vg can fluctuate near the second reference voltage Vt2, approximately equal, and namely voltage Vg is constant, and therefore the output voltage of Switching Power Supply is also constant, thus achieves constant voltage output.

The embodiment of the present invention comprises sampled voltage judge module by adopting in Switching Power Supply, VCO module, the multi thresholds switching circuit of reference voltage generation module and power switch, the voltage that sampling and power supply circuits export is carried out dividing potential drop and the first reference voltage exported with reference voltage generation module by sampled voltage judge module, second reference voltage and the 3rd reference voltage compare, and control signal to VCO module accordingly according to comparative result output, VCO module is according to described control signal, the 4th reference voltage that reference voltage generation module exports and the 5th reference voltage generate the pulse signal accordingly with particular duty cycle, the work of (as 60kHz) conducting and closedown that power switch carries out high frequency according to described pulse signal with corresponding frequency realizes storage and the release of the energy of transformer T1, and then realize modulating the output voltage of transformer T1, to reach the object stably realizing constant voltage and export, and the employing of multi thresholds switching circuit makes the circuit structure of Switching Power Supply simplify further, reduce cost, solve the switch power supply system stability existing for prior art and poor reliability, complicated and the problem that cost is high of circuit structure.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, all any amendments done within the spirit and principles in the present invention, equivalent replacement and improvement etc., all should be included within protection scope of the present invention.

Claims (8)

1. the multi thresholds switching circuit of a Switching Power Supply, with the sampling in Switching Power Supply and power supply circuits, start-up circuit and transformer T1 are connected, described sampling and power supply circuits are used for sampling to the output voltage of described Switching Power Supply and provide power supply for multi thresholds switching circuit, described start-up circuit is used at the beginning of described Switching Power Supply powers on for described multi thresholds switching circuit provides starting resistor, the output of described sampling and power supply circuits and the output of described start-up circuit connect altogether, described multi thresholds switching circuit has a power end, the power end of described multi thresholds switching circuit connects the output of described sampling and power supply circuits, it is characterized in that, described multi thresholds switching circuit comprises:

Sampled voltage judge module, VCO module, reference voltage generation module and power switch;

The power end of described sampled voltage judge module is the power end of described multi thresholds switching circuit, the power end of described VCO module and the power end of described reference voltage generation module are connected to the power end of described sampled voltage judge module altogether, control end and the output of described VCO module are connected the output of described sampled voltage judge module and the control end of described power switch respectively, first reference output of described reference voltage generation module, second reference output and the 3rd reference output connect the first benchmark input end of described sampled voltage judge module respectively, second benchmark input end and the 3rd benchmark input end, 4th reference output of described reference voltage generation module and the 5th reference output are connected with the first benchmark input end of described VCO module and the second benchmark input end respectively, input and the output of described power switch are connected the second end and the ground of the armature winding of described transformer T1 respectively,

The output voltage of described sampling and power supply circuits is carried out dividing potential drop and the first reference voltage exported with described reference voltage generation module by described sampled voltage judge module, second reference voltage and the 3rd reference voltage compare, and control signal to described VCO module accordingly according to comparative result output, described VCO module is according to described control signal, the 4th reference voltage that described reference voltage generation module exports and the 5th reference voltage generate the pulse signal accordingly with particular duty cycle, described power switch carries out the switching of high frequency break-make according to described pulse signal with corresponding frequency makes transformer T1 correspondingly carry out storage and the release of electric energy.

2. multi thresholds switching circuit as claimed in claim 1, it is characterized in that, described sampled voltage judge module comprises:

Resistance R1, resistance R2, resistance R3, resistance R4, the first comparator, the second comparator, the 3rd comparator, the first NOR gate, the second NOR gate, the first inverter, delay circuit, NMOS tube NM1, PMOS PM1 and first and door;

The first end of described resistance R1 is the power end of described sampled voltage judge module, second end of described resistance R1 and the first end of described resistance R2 are connected to the in-phase input end of described first comparator altogether, second end of described resistance R2 and the first end of described resistance R3 are connected to the inverting input of described second comparator altogether, second end of described resistance R3 and the first end of described resistance R4 are connected to the inverting input of described 3rd comparator altogether, the second end ground connection of described resistance R4, the inverting input of described first comparator, the in-phase input end of described second comparator and the in-phase input end of described 3rd comparator are respectively the first benchmark input end of described sampled voltage judge module, second benchmark input end and the 3rd benchmark input end, first input end and second input of described first NOR gate are connected the output of described first comparator and the output of described second NOR gate respectively, the first input end of described second NOR gate and the output of described first NOR gate are connected to the input of described first inverter altogether, the output of the 3rd comparator described in second input termination of described second NOR gate, the output of described first inverter is connected with the second input of door with the input and described first of described delay circuit simultaneously, the output of described delay circuit is connected with the grid of described NMOS tube NM1 and the grid of described PMOS PM1 simultaneously, the source electrode of described NMOS tube NM1 connects the output of described second comparator, the drain electrode of described PMOS PM1 connects the first end of described resistance R1, the drain electrode of described NMOS tube NM1 and the source electrode of described PMOS PM1 are connected to the first input end of described first and door altogether, described first is the output of described sampled voltage judge module with the output of door.

3. multi thresholds switching circuit as claimed in claim 1, it is characterized in that, described VCO module comprises:

Second with door, the first current source, PMOS PM2, NMOS tube NM2, the second current source, the 4th comparator, the 5th comparator, electric capacity C1, the first NAND gate, the second NAND gate, the second inverter and the 3rd inverter;

Described second is the control end of described VCO module with the first input end of door, the input of described first current source is the power end of described VCO module, the drain electrode of PMOS PM2 described in the output termination of described first current source, the grid of described PMOS PM2 and the grid of described NMOS tube NM2 are connected to the output of described second and door altogether, the common contact of the source electrode of described PMOS PM2 and the drain electrode of described NMOS tube NM2 simultaneously with the in-phase input end of described 4th comparator, the inverting input of described 5th comparator and the first end of described electric capacity C1 connect, the source electrode of described NMOS tube NM2 connects the input of described second current source, the output of described second current source and second end of described electric capacity C1 are connected to ground altogether, the inverting input of described 4th comparator and the in-phase input end of described 5th comparator are respectively the first benchmark input end and second benchmark input end of described VCO module, the output of described 4th comparator is connected the first input end of described first NAND gate and the second input of the second NAND gate respectively with the output of described 5th comparator, the output of the second NAND gate described in second input termination of described first NAND gate, the first input end of described second NAND gate and the output of described first NAND gate are connected to the input of described second inverter altogether, the input of described 3rd inverter and described second is connected to the output of described second inverter altogether with the second input of door, the output of described 3rd inverter is the output of described VCO module.

4. multi thresholds switching circuit as claimed in claim 1, it is characterized in that, described power switch is high pressure NMOS pipe NM3, and the grid of described high pressure NMOS pipe NM3, drain electrode and source electrode are respectively the control end of described power switch, input and output.

5. a Switching Power Supply, it is characterized in that, described Switching Power Supply comprises current rectifying and wave filtering circuit, transformer T1, sampling and power supply circuits, start-up circuit, secondary current rectifying and wave filtering circuit and multi thresholds switching circuit, sampling in described multi thresholds switching circuit and Switching Power Supply and power supply circuits, start-up circuit and transformer T1 are connected, described sampling and power supply circuits are used for sampling to the output voltage of described Switching Power Supply and provide power supply for multi thresholds switching circuit, described start-up circuit is used at the beginning of described Switching Power Supply powers on for described multi thresholds switching circuit provides starting resistor, the output of described sampling and power supply circuits and the output of described start-up circuit connect altogether, described multi thresholds switching circuit has a power end, the power end of described multi thresholds switching circuit connects the output of described sampling and power supply circuits, it is characterized in that, described multi thresholds switching circuit comprises:

Sampled voltage judge module, VCO module, reference voltage generation module and power switch;

The power end of described sampled voltage judge module is the power end of described multi thresholds switching circuit, the power end of described VCO module and the power end of described reference voltage generation module are connected to the power end of described sampled voltage judge module altogether, control end and the output of described VCO module are connected the output of described sampled voltage judge module and the control end of described power switch respectively, first reference output of described reference voltage generation module, second reference output and the 3rd reference output connect the first benchmark input end of described sampled voltage judge module respectively, second benchmark input end and the 3rd benchmark input end, 4th reference output of described reference voltage generation module and the 5th reference output are connected with the first benchmark input end of described VCO module and the second benchmark input end respectively, input and the output of described power switch are connected the second end and the ground of the armature winding of described transformer T1 respectively,

The output voltage of described sampling and power supply circuits is carried out dividing potential drop and the first reference voltage exported with described reference voltage generation module by described sampled voltage judge module, second reference voltage and the 3rd reference voltage compare, and control signal to described VCO module accordingly according to comparative result output, described VCO module is according to described control signal, the 4th reference voltage that described reference voltage generation module exports and the 5th reference voltage generate the pulse signal accordingly with particular duty cycle, described power switch carries out the switching of high frequency break-make according to described pulse signal with corresponding frequency makes transformer T1 correspondingly carry out storage and the release of electric energy.

6. Switching Power Supply as claimed in claim 5, it is characterized in that, described sampled voltage judge module comprises:

Resistance R1, resistance R2, resistance R3, resistance R4, the first comparator, the second comparator, the 3rd comparator, the first NOR gate, the second NOR gate, the first inverter, delay circuit, NMOS tube NM1, PMOS PM1 and first and door;

The first end of described resistance R1 is the power end of described sampled voltage judge module, second end of described resistance R1 and the first end of described resistance R2 are connected to the in-phase input end of described first comparator altogether, second end of described resistance R2 and the first end of described resistance R3 are connected to the inverting input of described second comparator altogether, second end of described resistance R3 and the first end of described resistance R4 are connected to the inverting input of described 3rd comparator altogether, the second end ground connection of described resistance R4, the inverting input of described first comparator, the in-phase input end of described second comparator and the in-phase input end of described 3rd comparator are respectively the first benchmark input end of described sampled voltage judge module, second benchmark input end and the 3rd benchmark input end, first input end and second input of described first NOR gate are connected the output of described first comparator and the output of described second NOR gate respectively, the first input end of described second NOR gate and the output of described first NOR gate are connected to the input of described first inverter altogether, the output of the 3rd comparator described in second input termination of described second NOR gate, the output of described first inverter is connected with the second input of door with the input and described first of described delay circuit simultaneously, the output of described delay circuit is connected with the grid of described NMOS tube NM1 and the grid of described PMOS PM1 simultaneously, the source electrode of described NMOS tube NM1 connects the output of described second comparator, the drain electrode of described PMOS PM1 connects the first end of described resistance R1, the drain electrode of described NMOS tube NM1 and the source electrode of described PMOS PM1 are connected to the first input end of described first and door altogether, described first is the output of described sampled voltage judge module with the output of door.

7. as right wants the Switching Power Supply as described in 5, it is characterized in that, described VCO module comprises:

Second with door, the first current source, PMOS PM2, NMOS tube NM2, the second current source, the 4th comparator, the 5th comparator, electric capacity C1, the first NAND gate, the second NAND gate, the second inverter and the 3rd inverter;

Described second is the control end of described VCO module with the first input end of door, the input of described first current source is the power end of described VCO module, the drain electrode of PMOS PM2 described in the output termination of described first current source, the grid of described PMOS PM2 and the grid of described NMOS tube NM2 are connected to the output of described second and door altogether, the common contact of the source electrode of described PMOS PM2 and the drain electrode of described NMOS tube NM2 simultaneously with the in-phase input end of described 4th comparator, the inverting input of described 5th comparator and the first end of described electric capacity C1 connect, the source electrode of described NMOS tube NM2 connects the input of described second current source, the output of described second current source and second end of described electric capacity C1 are connected to ground altogether, the inverting input of described 4th comparator and the in-phase input end of described 5th comparator are respectively the first benchmark input end and second benchmark input end of described VCO module, the output of described 4th comparator is connected the first input end of described first NAND gate and the second input of the second NAND gate respectively with the output of described 5th comparator, the output of the second NAND gate described in second input termination of described first NAND gate, the first input end of described second NAND gate and the output of described first NAND gate are connected to the input of described second inverter altogether, the input of described 3rd inverter and described second is connected to the output of described second inverter altogether with the second input of door, the output of described 3rd inverter is the output of described VCO module.

8. Switching Power Supply as claimed in claim 5, it is characterized in that, described power switch is high pressure NMOS pipe NM3, and the grid of described high pressure NMOS pipe NM3, drain electrode and source electrode are respectively the control end of described power switch, input and output.