CN103078478B - Controller for switching power supply and switching power supply - Google Patents
Controller for switching power supply and switching power supply Download PDFInfo
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- CN103078478B CN103078478B CN201310024632.7A CN201310024632A CN103078478B CN 103078478 B CN103078478 B CN 103078478B CN 201310024632 A CN201310024632 A CN 201310024632A CN 103078478 B CN103078478 B CN 103078478B
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Abstract
The invention discloses a controller for a switching power supply. The controller comprises a feedback (FB) detection circuit, wherein the output end of the FB detection circuit is connected with an oscillator circuit and an over-current protection circuit; the output ends of the oscillator circuit and the over-current protection circuit are connected with a pulse width modulation (PWM) logic control circuit respectively; and the output end of the PWM logic control circuit is connected with a driving circuit. The controller for the switching power supply is applied to a switching power supply circuit, the FB detection circuit can output different signals according to different load conditions, the oscillator circuit can control the working frequency of the switching power supply according to the output signals of the FB detection circuit, and the over-current protection circuit controls duty ratios of output signals of the oscillator circuit according to the output signals of the FB detection circuit, so that the working frequency can be adapted to different loads, and the energy consumption of the switching power supply is reduced.
Description
Technical field
The present invention relates to power technique fields, particularly a kind of switch power controller and apply the Switching Power Supply of this switch power controller.
Background technology
Switching Power Supply is the time ratio that a kind of control switch pipe connected sum turns off, and maintain the power supply of regulated output voltage, Switching Power Supply is widely used in electronic product with the feature such as small-sized, light weight, high efficiency.According to statistics, the stand-by power consumption of electronic product is 3%-13% at the electric power proportion in the whole world.Along with the development of power electronic technology and the enhancing of energy-conserving and environment-protective consciousness, the stand-by power consumption of electronic product becomes an important performance characteristic received much concern, and low standby power loss becomes the trend of electronic product inevitable development.
Inevitably there is energy loss in Switching Power Supply, such as switching loss, conduction loss and control circuit loss in the course of the work.Energy loss and the operating frequency of Switching Power Supply are proportional, and the trend of miniaturization of electronic products causes the operating frequency of Switching Power Supply to rise, and the energy of loss also constantly increases, and becomes the major part of Switching Power Supply energy loss under underloading or holding state.How to effectively reduce the operating frequency of Switching Power Supply, the operating frequency especially how reducing Switching Power Supply when underloading or zero load becomes current problem demanding prompt solution.
Summary of the invention
The object of the present invention is to provide a kind of switch power controller and apply the Switching Power Supply of this switch power controller, the operating frequency of Switching Power Supply can reduce along with the reduction of load, thus realizes Switching Power Supply low standby power loss.
In order to realize foregoing invention object, the invention provides following technical scheme:
A kind of switch power controller, comprise FB testing circuit, the output of described FB testing circuit is connected with pierce circuit and current foldback circuit, the output of described pierce circuit is connected PWM logic control circuit respectively with the output of current foldback circuit, and the output of described PWM logic control circuit is connected with drive circuit;
Described switch power controller is applied in switching power circuit, the MOS power tube in described drive circuit connecting valve power circuit, and described pierce circuit is according to the operating frequency of the output signal control switch power-supply controller of electric of FB testing circuit; Described current foldback circuit controls the duty ratio of pierce circuit output signal according to the output signal of FB testing circuit.
According to the embodiment of the present invention, the feedback voltage of the input access switch power source output voltage of FB testing circuit, and obtain the first feedback voltage and the second feedback voltage, export to current foldback circuit and pierce circuit respectively; The benchmark job frequency of the input access Switching Power Supply of pierce circuit, pierce circuit exports the clock signal of corresponding frequencies according to the second feedback voltage, the operating frequency of control switch power-supply controller of electric.
Further, when the second feedback voltage is in the reference voltage range set, the operating frequency of switch power controller is benchmark job frequency; When the second feedback voltage reduces and reaches the falling voltage threshold of switch power controller setting, the operating frequency of switch power controller reduces gradually along with the reduction of the second feedback voltage; When the second feedback voltage is less than or equal to the voltage stabilizing threshold value of setting, the operating frequency of switch power controller is the minimum frequency of operation maintaining Switching Power Supply work.
According to the embodiment of the present invention; current foldback circuit input access MOS power tube conducting time sampled voltage; current foldback circuit compensates sampled voltage; sampled voltage is made to increase set point; when the sampled voltage after compensating reaches the first feedback voltage, current foldback circuit output signal control PWM logical circuit turns off MOS power tube.
Preferably, the input of current foldback circuit is also connected with overcurrent protection compensating circuit, the input access input current of described overcurrent protection compensating circuit, input current forms overcurrent protection bucking voltage through overcurrent protection compensating circuit, overcurrent protection bucking voltage input overcurrent protection circuit; When the sampled voltage after compensating reaches overcurrent protection bucking voltage, current foldback circuit output signal control PWM logical circuit turns off MOS power tube.In MOS power tube conduction period, sampled voltage increases gradually.If but load is very heavy, the first feedback voltage is then very large, if the sampled voltage after compensating always is less than the first feedback voltage, then uncontrollable MOS power tube turns off.Therefore overcurrent protection compensating circuit is set, is turned off by overcurrent protection bucking voltage control MOS power tube, effectively ensured the shutoff of MOS power tube.
Preferably, switch power controller also comprises temperature protection circuit, and the output of temperature protection circuit connects the input of PWM logic control circuit, and the input of temperature protection circuit connects photo resistance; When the input voltage of temperature protection circuit is lower than setting voltage threshold value, temperature protection circuit exports the signal for turning off MOS power tube to PWM logic control circuit.
Preferably, switch power controller also comprises start-up circuit, described start-up circuit comprises charging circuit, the power input VIN of the input connecting valve power-supply controller of electric of described charging circuit, the feeder ear VDD of the output connecting valve power-supply controller of electric of charging circuit, described power input VIN accesses input voltage and charges, and the starting switch power-supply controller of electric when charging voltage reaches the starting resistor of switch power controller stops charging simultaneously.
Present invention also offers a kind of AC-DC Switching Power Supply applying above-mentioned switch power controller, comprise switch power controller and transformer, in switch power controller, the output of drive circuit connects the grid of MOS power tube, the armature winding of the drain electrode connection transformer of MOS power tube, the armature winding of transformer is also connected with rectification circuit, the two ends of primary winding are connected with RCD absorption circuit, the source electrode of MOS power tube is by sampling resistor ground connection, in switch power controller, the input of current foldback circuit connects the source electrode of MOS power tube, the power supply port VDD of switch power controller passes through the auxiliary winding of diode connection transformer, the secondary winding of transformer is connected with output voltage feedback circuit, the input of FB testing circuit in optical coupler connecting valve power-supply controller of electric in described output voltage feedback circuit, in switch power controller, the input connection reference frequency of pierce circuit arranges resistance, and described reference frequency arranges the other end ground connection of resistance.
According to the embodiment of the present invention; in MOS power tube conduction period; AC-input voltage accesses the armature winding of transformer after rectifier circuit rectifies with DC input voitage; primary winding is formed the inductive current increased gradually; this inductive current flows through sampling resistor, forms sampled voltage and the current foldback circuit accessed in switch power controller.At MOS power tube blocking interval, the armature winding of transformer is released to the magnetic energy stored by RCD absorption circuit: the secondary winding of transformer is connected with the first rectifier diode, and the secondary winding of transformer provides output voltage by the first rectifier diode; The auxiliary winding switching of transformer has the second rectifier diode, and the auxiliary winding of transformer is powered by the power supply port VDD that the second rectifier diode is switch power controller.
Further, described output voltage feedback circuit also comprises the first resistance and second resistance of series connection, the 3rd resistance of series connection, diode and TL431, and the first resistance is connected with the secondary winding of transformer respectively with the 3rd resistance; Output voltage feedback circuit by series connection the first resistance and the second resistance output voltage is sampled; and generate feedback current by the 3rd resistance, diode and the TL431 connected; feedback current is transferred to FB testing circuit in switch power controller by optical coupler again; feedback current generates the first feedback voltage and the second feedback voltage through FB testing circuit, exports to current foldback circuit and pierce circuit respectively.
According to the embodiment of the present invention, current foldback circuit receives sampled voltage and compensates sampled voltage, sampled voltage is made to increase set point, when the sampled voltage after compensating reaches the first feedback voltage, current foldback circuit generating output signal control PWM logic control circuit exports the signal for turning off MOS power tube; MOS power tube ON time
, wherein,
represent MOS power tube ON time size,
the primary winding inductance amount size of indication transformer 104,
represent that MOS power tube conduction period flows through the maximum current of the armature winding of transformer,
represent the DC input voitage value of AC-input voltage after rectifier circuit rectifies.
According to the embodiment of the present invention, pierce circuit regulates the frequency of its clock signal generated automatically according to the second feedback voltage of input: when the second feedback voltage is in the reference voltage range set, and the frequency of the clock signal that pierce circuit exports is the benchmark job frequency being arranged resistance setting in advance by reference frequency; When the second feedback voltage reduces gradually and reaches falling voltage threshold, the frequency of clock signal reduces continuously along with the reduction of the second feedback voltage; When the second feedback voltage is less than or equal to voltage stabilizing threshold value, the frequency of clock signal is the minimum frequency of operation maintaining Switching Power Supply work.The transformable clock signal generated is exported to PWM logic control circuit, the work period of the FREQUENCY CONTROL MOS power tube of the clock signal that PWM logic control circuit exports according to pierce circuit by pierce circuit.
The power input port VIN of switch power controller connects the output of rectification circuit by current-limiting resistance.In switch power controller, the input of temperature protection circuit connects photo resistance NTC.When the resistance of external photo resistance reduces along with the rising of ambient temperature; the input voltage of temperature protection circuit also declines thereupon; when dropping to the voltage threshold that temperature protection circuit is established; PWM logic control circuit sends the signal for turning off MOS power tube to drive circuit, turns off MOS power tube.
compared with prior art, beneficial effect of the present invention:
The feedback voltage of switch power source output voltage has reacted the loading condition in switching power circuit, switch power controller of the present invention can according to the feedback voltage gathering switch power source output voltage, the operating frequency of dynamic conditioning Switching Power Supply and the ON time of MOS power tube in the work period, the operating frequency of Switching Power Supply is reduced along with the reduction of load, and then reduces the energy loss of Switching Power Supply.
Switching Power Supply provided by the invention applies switch power controller of the present invention, the feedback circuit for gathering output voltage is provided with in switching power circuit, generate feedback voltage, switch power controller can according to operating frequency and the ON time of MOS power tube in the work period opening feedback voltage dynamic conditioning Switching Power Supply, the operating frequency of Switching Power Supply is reduced along with the reduction of load, and then reduces the energy loss of Switching Power Supply.
Accompanying drawing illustrates:
Fig. 1 is the theory structure block diagram of switch power controller of the present invention.
Fig. 2 is the switching power circuit figure of switch power controller shown in a kind of application drawing 1.
Mark in figure: 101-Switching Power Supply control chip, 102-rectification circuit, 103-RCD absorption circuit; 104-transformer circuit, 105-optical coupler, 106-MOS power tube; 107-thermistor; 201-start-up circuit, 202-current foldback circuit, 203-FB testing circuit; 204-pierce circuit; 205-PWM logic control circuit, 206-drive circuit, 207-temperature protection circuit.
Embodiment
Below in conjunction with test example and embodiment, the present invention is described in further detail.But this should be interpreted as that the scope of the above-mentioned theme of the present invention is only limitted to following embodiment, all technology realized based on content of the present invention all belong to scope of the present invention.
With reference to figure 1, switch power controller of the present invention comprises FB testing circuit 203, pierce circuit (OSC) 204, current foldback circuit (OCP) 202 and PWM logic control circuit 205, the output input of connection oscillator circuit 204 and the input of current foldback circuit 202 respectively of described FB testing circuit 203, the output of pierce circuit 204 is connected the input of PWM logic control circuit 205 respectively with the output of current foldback circuit 202, the output of PWM logic control circuit 205 is connected with drive circuit 206, described drive circuit 206 is for the shutoff of the MOS power tube in control switch power circuit.Described pierce circuit 204 is according to the operating frequency of the output signal control switch power supply of FB testing circuit 203; Described current foldback circuit 202 controls the duty ratio of pierce circuit output signal according to the output signal of FB testing circuit 203, namely controls the ON time of MOS power tube in the work period.
Switch power controller is applied in switching power circuit; the feedback current of the input access sampling switch electric power output voltage of FB testing circuit 203; FB testing circuit 203 detects the feedback current of input; and obtain the first feedback voltage and the second feedback voltage, export to current foldback circuit 202 and pierce circuit 204 respectively.The benchmark job frequency of the input access Switching Power Supply of pierce circuit 204, pierce circuit 204 exports the clock signal of corresponding frequencies according to the second feedback voltage, and transfer to PWM logic control circuit 205, transfer to drive circuit 206 through PWM logic control circuit 205 again, drive circuit 206 turns off according to the output signal control MOS power tube of PWM logic control circuit 205.When the second feedback voltage is in normal range (NR), under switch power controller is operated in benchmark job frequency; When load reduces, when namely the second feedback voltage reduces and reaches the falling voltage threshold of switch power controller setting, the operating frequency of Switching Power Supply reduces gradually along with the reduction of the second feedback voltage; When the second feedback voltage continues the voltage stabilizing threshold value being reduced to setting, the operating frequency of Switching Power Supply reaches minimum frequency of operation and to maintain this minimum frequency of operation constant, to ensure that Switching Power Supply normally works.
MOS power tube conduction period, sampling is carried out to the voltage flowing through MOS power tube and generates sampled voltage.The input access sampled voltage of current foldback circuit 202, and sampled voltage is compensated, make sampled voltage increase set point.In MOS power tube conduction period, sampled voltage increases gradually, and the sampled voltage after compensation is also corresponding to be increased gradually.When the sampled voltage after compensating reaches the first feedback voltage, current foldback circuit 202 outputs signal control PWM logical circuit 205 and turns off MOS power tube.Namely current foldback circuit 202 is according to the ON time of the first feedback voltage control switch power-supply controller of electric MOS power tube within a work period.
Current foldback circuit 202 can also be turned off by another kind of mode control MOS power tube.The input of current foldback circuit 202 also connects the output of overcurrent protection compensating circuit, the power input port VIN of the input connecting valve power-supply controller of electric of overcurrent protection compensating circuit.The input current of the power input port VIN of switch power controller flows into overcurrent protection compensating circuit, forms overcurrent protection bucking voltage, overcurrent protection bucking voltage input overcurrent protection circuit 202.Sampled voltage after compensating reaches the overcurrent protection bucking voltage of generation, and current foldback circuit 202 outputs signal control PWM logical circuit 205 and turns off MOS power tube.Load is very heavy, and the first feedback voltage is then comparatively large, if the sampled voltage after compensating always is less than the first feedback voltage, is then turned off by overcurrent protection bucking voltage control MOS power tube, has effectively ensured the shutoff of MOS power tube.
Switch power controller of the present invention is according to the feedback voltage of switch power source output voltage, the operating frequency of dynamic adjustment switch power controller and the ON time of metal-oxide-semiconductor in the work period, the operating frequency of Switching Power Supply is reduced along with the reduction of load, and then reduces the energy loss of Switching Power Supply.
As a kind of preferred implementation of switch power controller of the present invention; switch power controller also comprises temperature protection circuit (OTP protection) 207; the output of temperature protection circuit 207 connects the input of PWM logic control circuit 205; in switching power circuit, the external photo resistance of input of temperature protection circuit 207.It is too high and cannot normally work that temperature protection circuit 207 is unlikely to Yin Wendu for the protection of the components and parts in switching power circuit.
As the another kind of preferred implementation of switch power controller of the present invention, switch power controller also comprises start-up circuit 201, start-up circuit 201 comprises charging circuit, the power input port VIN of the input connecting valve power-supply controller of electric of charging circuit, access input voltage charges, the power supply port VDD of the output connecting valve power-supply controller of electric of charging circuit, when charging voltage reaches the starting resistor of switch power controller, switch power controller is started working, and stops charging simultaneously.
With reference to figure 2, above-mentioned switch power controller is packaged into Switching Power Supply control chip, is applied in switching power circuit.Switching Power Supply control chip comprises eight pins, be respectively and start the power input port that namely pin VIN(startup pin VIN is switch power controller), namely supply power voltage pin VDD(supply power voltage pin VDD is the power supply port of switch power controller), grounding pin GND, feedback pin FB, sampling pin CS, temperature monitoring pin RT, benchmark job set of frequency pin RI, and export control pin GATE.Wherein, starting pin VIN is the input of charging circuit; supply power voltage pin VDD is the output of charging circuit; feedback pin FB is the input of FB testing circuit 203; sampling pin CS is the input of current foldback circuit 202; temperature monitoring pin RT is the input of temperature protection circuit 207, and benchmark job set of frequency pin RI is the input of pierce circuit 204, exports and controls the output that pin GATE is drive circuit 206.As shown in Figure 1.
Above-mentioned switch power controller is applied in switching power circuit, such as, is applied in the AC-DC Switching Power Supply that the present embodiment enumerates by being packaged into Switching Power Supply control chip, as shown in Figure 2.The output of Switching Power Supply control chip 101 controls pin GATE, and to connect MOS power tube in MOS power tube 106(the present embodiment be N-type MOS power tube) grid, the source electrode of MOS power tube is by sampling resistor R5 ground connection, the sampling pin CS of Switching Power Supply control chip 101 connects the source electrode of MOS power tube, for receiving the sampled voltage at sampling resistor R5 two ends, the armature winding of the drain electrode connection transformer 104 of MOS power tube, the two ends of transformer 104 armature winding connect RCD absorption circuit 103.The supply power voltage pin VDD of Switching Power Supply control chip 101 passes through the auxiliary winding of diode D3 connection transformer 104, the secondary winding (i.e. the output of transformer 104) of transformer 104 connects output voltage feedback circuit, the feedback pin FB of the optical coupler 105 connecting valve power supply control chip 101 in output voltage feedback circuit.The startup pin VIN of Switching Power Supply control chip 101 connects rectification circuit 102 by current-limiting resistance R1, and the benchmark job set of frequency pin RI of Switching Power Supply control chip connects reference frequency and arranges resistance R6, and reference frequency arranges the other end ground connection of resistance R6.The grounding pin GND ground connection of Switching Power Supply control chip.The temperature monitoring pin RT of Switching Power Supply control chip connects photo resistance 107.
The startup pin VIN of Switching Power Supply control chip 101 is connected with supply power voltage pin VDD by charging circuit.AC-input voltage AC is by rectification circuit 102 rectification, form DC input voitage, DC input voitage is accessed by current-limiting resistance R1 and starts pin VIN, start pin VIN to be charged to supply power voltage pin VDD by charging circuit, when voltage reaches the starting resistor of Switching Power Supply control chip 101 inner setting, Switching Power Supply control chip 101 is started working, and starts pin VIN simultaneously and stops charging to supply power voltage pin VDD.
Exporting output signal control MOS power tube 106 conduction period controlling pin GATE; the armature winding of the DC input voitage access transformer 104 of AC-input voltage AC after rectification; control the rate of rise flowing through the inductive current of the armature winding of transformer 104; this inductive current flows through sampling resistor R5; and produce the sampled voltage of fixed slope rising at sampling pin CS end, the current foldback circuit 202 of sampled voltage access Switching Power Supply control chip 101 inside.At MOS power tube 106 blocking interval, the armature winding of transformer 104 is released to the magnetic energy stored by RCD absorption circuit 103, secondary winding provides energy to output voltage together with the output rectifier diode D2 be attached thereto, simultaneously the auxiliary winding of transformer 104 and the VDD rectifier diode D3 that is attached thereto provide energy to VDD, to work required energy to maintain Switching Power Supply control chip 101.
In the whole course of work of Switching Power Supply control chip 101, feedback pin FB judges the loading condition of Switching Power Supply by the signal that optical coupler 105 feeds back, and regulates the operating frequency of Switching Power Supply.Output voltage feedback circuit is sampled to output voltage by divider resistance R3 and R4; and generate feedback current by the series connection of TL431, resistance R2 and diode; feedback current is transferred to the feedback pin FB of Switching Power Supply control chip 101 again by optical coupler 105; namely feedback current is transferred to the input of FB testing circuit again by optical coupler 105; feedback current generates the first feedback voltage and the second feedback voltage by FB testing circuit again, exports to current foldback circuit 202 and pierce circuit 204 respectively.
After current foldback circuit 202 receives sampled voltage, by internal circuit, sampled voltage is compensated, make sampled voltage increase set point, then by the sampled voltage after compensation compared with the first feedback voltage.When the sampled voltage after compensating rises to the first feedback voltage, current foldback circuit 202 outputs signal control PWM logical circuit 205 and turns off MOS power tube.Current foldback circuit 202 controls the duty ratio of the output signal of pin GATE end according to sampled voltage, namely control the ON time of MOS power tube in the work period, MOS power tube ON time
, wherein:
represent MOS power tube ON time size;
the primary winding inductance amount size of indication transformer 104;
represent that MOS power tube conduction period flows through the maximum current of the armature winding of transformer 104;
represent the DC input voitage value of AC-input voltage AC after rectification circuit 102.
In MOS power tube conduction period, sampled voltage linearly increases.If but the load that Switching Power Supply connects is comparatively large, then the first feedback voltage is comparatively large, if the sampled voltage after compensating cannot reach the first feedback voltage, then uncontrollable MOS power tube turns off.Therefore; start pin VIN to be also connected with current foldback circuit 202 by overcurrent protection compensating circuit; flow through the electric current starting pin VIN and generate overcurrent protection bucking voltage through overcurrent protection compensating circuit, overcurrent protection bucking voltage input overcurrent protection circuit 202.When the sampled voltage after compensating reaches the overcurrent protection bucking voltage of generation, current foldback circuit 202 outputs signal control PWM logical circuit 205 and turns off MOS power tube.
Described second feedback voltage reduces along with the reduction of output voltage, second feedback voltage reflects the situation of change of output voltage, pierce circuit 204 regulates the frequency of its clock signal generated automatically according to the second feedback voltage of input, namely the operating frequency of AC-DC Switching Power Supply is regulated, the namely work period of control MOS power tube.Pierce circuit 204 regulates the method for the frequency of its clock signal generated to be automatically: when the second feedback voltage is when normal range (NR) (reference voltage range that namely normal range (NR) sets), and the frequency of the clock signal that pierce circuit 204 exports is in advance by benchmark job frequency that benchmark job set of frequency pin RI holds the resistance R6 connected to arrange; When load reduces, when the second feedback voltage is reduced to falling voltage threshold (described falling voltage threshold is the magnitude of voltage of a setting) gradually, the frequency of clock signal reduces continuously along with the reduction of the second feedback voltage; When the second feedback voltage is reduced to voltage stabilizing threshold value (described voltage stabilizing threshold value is the magnitude of voltage of another setting) always, it is constant that the frequency of clock signal maintains a very low value (i.e. minimum frequency of operation), thus guarantee Switching Power Supply normally works.The transformable clock signal generated is exported to PWM logic control circuit by pierce circuit 204, the work period (work period of described MOS power tube is that this shutoff of MOS power tube terminated to the time turning off end next time) of the FREQUENCY CONTROL MOS power tube of the clock signal that PWM logic control circuit exports according to pierce circuit 204, thus frequency adjustment is carried out to the output voltage of Switching Power Supply.
The external photo resistance 107(NTC of temperature monitoring pin RT of Switching Power Supply control chip 101).Switching Power Supply control chip 101 is inner, is connected with PWM logic control circuit 205 by temperature protection circuit 207.When the resistance of external photo resistance 107 reduces along with the rising of switch power supply system temperature; the voltage of temperature monitoring pin RT port also will decline thereupon; when dropping to the voltage threshold that temperature protection circuit is established; PWM logic control circuit 205 sends the signal for turning off MOS power tube to drive circuit; drive circuit controls by exporting the signal that pin GATE exports shutoff MOS power tube, turns off MOS power tube.
Switch power controller of the present invention can be applicable to the switching power circuit of various types of pwm pattern, is not limited to the AC-DC switching power circuit enumerated in the present embodiment.
Claims (2)
1. a switch power controller, it is characterized in that, comprise FB testing circuit, the output of described FB testing circuit is connected with pierce circuit and current foldback circuit, the output of described pierce circuit is connected PWM logic control circuit respectively with the output of current foldback circuit, and the output of described PWM logic control circuit is connected with drive circuit;
Described switch power controller is applied in switching power circuit, the MOS power tube in described drive circuit connecting valve power circuit, and described pierce circuit is according to the operating frequency of the output signal control switch power-supply controller of electric of FB testing circuit; Described current foldback circuit controls the duty ratio of pierce circuit output signal according to the output signal of FB testing circuit;
The feedback voltage of the input access switch power source output voltage of FB testing circuit, and obtain the first feedback voltage and the second feedback voltage, export to current foldback circuit and pierce circuit respectively; The benchmark job frequency of the input access Switching Power Supply of pierce circuit, pierce circuit exports the clock signal of corresponding frequencies according to the second feedback voltage, the operating frequency of control switch power-supply controller of electric;
When the second feedback voltage is in the reference voltage range set, the operating frequency of switch power controller is benchmark job frequency; When the second feedback voltage reduces and reaches the falling voltage threshold of switch power controller setting, the operating frequency of switch power controller reduces gradually along with the reduction of the second feedback voltage; When the second feedback voltage is less than or equal to the voltage stabilizing threshold value of setting, the operating frequency of switch power controller is the minimum frequency of operation maintaining Switching Power Supply work;
Current foldback circuit input access MOS power tube conducting time sampled voltage, current foldback circuit compensates sampled voltage, sampled voltage is made to increase set point, when the sampled voltage after compensating reaches the first feedback voltage, current foldback circuit output signal control PWM logical circuit turns off MOS power tube;
The input of current foldback circuit is also connected with overcurrent protection compensating circuit, the input access input current of described overcurrent protection compensating circuit, input current forms overcurrent protection bucking voltage through overcurrent protection compensating circuit, overcurrent protection bucking voltage input overcurrent protection circuit; When the sampled voltage after compensating reaches overcurrent protection bucking voltage, current foldback circuit output signal control PWM logical circuit turns off MOS power tube;
Switch power controller also comprises temperature protection circuit, and the output of temperature protection circuit connects the input of PWM logic control circuit, and the input of temperature protection circuit connects photo resistance; When the input voltage of temperature protection circuit is lower than setting voltage threshold value, temperature protection circuit exports the signal for turning off MOS power tube to PWM logic control circuit;
Switch power controller also comprises start-up circuit, described start-up circuit comprises charging circuit, the power input VIN of the input connecting valve power-supply controller of electric of described charging circuit, the feeder ear VDD of the output connecting valve power-supply controller of electric of charging circuit, described power input VIN accesses input voltage and charges, the starting switch power-supply controller of electric when charging voltage reaches the starting resistor of switch power controller, stops charging simultaneously.
2. the AC-DC Switching Power Supply of the switch power controller of an application rights requirement described in 1, it is characterized in that, comprise switch power controller and transformer, in switch power controller, the output of drive circuit connects the grid of MOS power tube, the armature winding of the drain electrode connection transformer of MOS power tube, the armature winding of transformer is also connected with rectification circuit, the two ends of primary winding are connected with RCD absorption circuit, the source electrode of MOS power tube is by sampling resistor ground connection, in switch power controller, the input of current foldback circuit connects the source electrode of MOS power tube, the power supply port VDD of switch power controller passes through the auxiliary winding of diode connection transformer, the secondary winding of transformer is connected with output voltage feedback circuit, the input of FB testing circuit in optical coupler connecting valve power-supply controller of electric in described output voltage feedback circuit, in switch power controller, the input connection reference frequency of pierce circuit arranges resistance, and described reference frequency arranges the other end ground connection of resistance,
In MOS power tube conduction period, AC-input voltage accesses the armature winding of transformer after rectifier circuit rectifies with DC input voitage, primary winding is formed the inductive current increased gradually, this inductive current flows through sampling resistor, forms sampled voltage and the current foldback circuit accessed in switch power controller; At MOS power tube blocking interval, the armature winding of transformer is released to the magnetic energy stored by RCD absorption circuit: the secondary winding of transformer is connected with the first rectifier diode, and the secondary winding of transformer provides output voltage by the first rectifier diode; The auxiliary winding switching of transformer has the second rectifier diode, and the auxiliary winding of transformer is powered by the power supply port VDD that the second rectifier diode is switch power controller;
Described output voltage feedback circuit comprises the first resistance and second resistance of series connection, the 3rd resistance of series connection, diode and TL431, and the first resistance is connected with the secondary winding of transformer respectively with the 3rd resistance; Output voltage feedback circuit by series connection the first resistance and the second resistance output voltage is sampled; and generate feedback current by the 3rd resistance, diode and the TL431 connected; feedback current is transferred to FB testing circuit in switch power controller by optical coupler again; feedback current passed through FB testing circuit and generated the first feedback voltage and the second feedback voltage, exported to current foldback circuit and pierce circuit respectively.
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