CN203722885U - High-power-factor and non-stroboscopic device capable of outputting constant current - Google Patents

Abstract

The embodiment of the utility model provides a high-power-factor and non-stroboscopic device capable of outputting constant current. The device comprises a high power factor processing circuit and a constant current control circuit, the high power factor processing circuit is used for receiving rectified input signals and receiving signals outputted by the constant current control circuit as driving signals, and the constant current control circuit is used for receiving constant voltage signals outputted by the high power factor processing circuit, outputting constant current and driving LED constant current loads. According to the technical solution of the device, the high power factor processing circuit receives the signals outputted by the constant current control circuit and regards the signals as the driving signals so that a high-power-factor and non-stroboscopic constant current circuit is realized.

Description

High Power Factor is without the device of stroboscopic output constant current

Technical field

The utility model relates to field of switch power, and particularly, the utility model relates to High Power Factor without the device of stroboscopic output constant current.

Background technology

As everyone knows, the High Power Factor LED constant current scheme of current trend is divided into two classes, and a class has power frequency flicker (abbreviation stroboscopic), another kind of without power frequency flicker (being called for short without stroboscopic).

The first kind has stroboscopic scheme, and output LED lamp stroboscopic scheme is often peripheral simple, and system BOM cost is lower.But study, show, LED lamp stroboscopic can have very large injury to human eye.If this type of scheme wants to alleviate stroboscopic, or strengthen input capacitance, or strengthen output filter capacitor.Strengthen input capacitance, the sacrifice High Power Factor of take is often cost, and stroboscopic alleviates better, and power factor is sacrificed greatlyr.Strengthen output filter capacitor, although can alleviate LED lamp stroboscopic, can not solve stroboscopic problem at all, and do like this meeting increase system BOM cost, that is to say the system BOM low-cost advantage that sacrifices this type of scheme.

Equations of The Second Kind is without stroboscopic scheme, although this type of scheme without stroboscopic, peripheral complicated, system BOM cost is high, the more similar scheme difficulty of PCB layout.Controller is inner needs integrated two to overlap modulation circuits, causes controller internal control circuit complicated, and the more general High Power Factor chip of price is expensive, causes system BOM cost high.

Therefore, be necessary to propose effective technical scheme, but solve in existing LED constant current scheme have stroboscopic or without stroboscopic control circuit complexity and the high problem of cost.

Utility model content

The purpose of this utility model is intended at least solve one of above-mentioned technological deficiency, particularly by High Power Factor treatment circuit and the signal that receives constant-current control circuit output as driving signal, realized High Power Factor and without the constant-current circuit of stroboscopic.

In order to achieve the above object, embodiment of the present utility model has proposed a kind of High Power Factor without the device of stroboscopic output constant current, comprises High Power Factor treatment circuit and constant-current control circuit;

Described High Power Factor treatment circuit, for receiving the input signal after rectification, and the signal that receives described constant-current control circuit output is as driving signal;

Described constant-current control circuit, for receiving the constant voltage signal of described High Power Factor treatment circuit output, and for exporting constant current, driving LED Constant Current Load.

The such scheme the utility model proposes, as driving signal, has realized High Power Factor and without the constant-current circuit of stroboscopic by High Power Factor treatment circuit and the signal that receives constant-current control circuit output.In addition, the technical scheme the utility model proposes is simple in structure, and the controller cost of control switch electric power outputting current is lower, is conducive to applying of technical solutions of the utility model, has very high practical value.

The such scheme the utility model proposes, very little to the change of existing system, can not affect the compatibility of system, and realize simple, efficient.

The aspect that the utility model is additional and advantage in the following description part provide, and these will become obviously from the following description, or recognize by practice of the present utility model.

Accompanying drawing explanation

Above-mentioned and/or the additional aspect of the utility model and advantage will become from the following description of the accompanying drawings of embodiments and obviously and easily understand, wherein:

Fig. 1 is that embodiment of the present invention High Power Factor is without the method flow diagram of stroboscopic output constant current;

Fig. 2 is the circuit theory diagrams schematic diagram of the utility model embodiment;

Fig. 3 is the whole principal diagram intention of the utility model embodiment;

Fig. 4 is the principle schematic of the utility model embodiment constant-current controller;

Fig. 5 is that the utility model embodiment constant current keeps and erasing time testing circuit schematic diagram;

Fig. 6 is the sequential chart of the utility model embodiment corresponding diagram 5 circuit;

Fig. 7 is the utility model embodiment clock generating and management circuit schematic diagram;

Fig. 8 be the utility model embodiment under BCM pattern, the input voltage phase variation schematic diagram after input average current and rectification;

Fig. 9 be the utility model embodiment under DCM pattern, the input voltage phase variation schematic diagram after input average current and rectification.

Embodiment

Describe embodiment of the present utility model below in detail, the example of described embodiment is shown in the drawings, and wherein same or similar label represents same or similar element or has the element of identical or similar functions from start to finish.Below by the embodiment being described with reference to the drawings, be exemplary, only for explaining the utility model, and can not be interpreted as restriction of the present utility model.

The scheme the utility model proposes, receives the input signal after rectification by High Power Factor treatment circuit, and the signal that receives constant-current control circuit output is as driving signal; High Power Factor treatment circuit output constant voltage signal, constant voltage signal input constant-current control circuit; Constant-current control circuit output constant current, driving LED Constant Current Load, has realized High Power Factor and without the constant-current circuit of stroboscopic.In addition, the technical scheme the utility model proposes is simple in structure, and the controller cost of control switch electric power outputting current is lower, is conducive to applying of technical solutions of the utility model, has very high practical value.

The utility model embodiment High Power Factor comprises High Power Factor treatment circuit 10 and constant-current control circuit 20 without the device of stroboscopic output constant current.

Particularly, High Power Factor treatment circuit 10, for receiving the input signal after rectification, and the signal that receives constant-current control circuit output is as driving signal.

Particularly, High Power Factor treatment circuit 10 comprises:

BOOST booster circuit or CUK chopper circuit.

Particularly, High Power Factor treatment circuit 10 inside have power switch.

Particularly, the power switch of High Power Factor treatment circuit 10 inside is metal-oxide-semiconductor or BJT bipolar transistor.

Constant-current control circuit 20, for receiving the constant voltage signal of High Power Factor treatment circuit 10 outputs, and for exporting constant current, driving LED Constant Current Load.

Particularly, constant-current control circuit 20 inside have power switch.

Particularly, the power switch of constant-current control circuit 20 inside is metal-oxide-semiconductor or BJT bipolar transistor.

Particularly, constant-current control circuit output constant current 20 is irrelevant with the input voltage of constant-current control circuit 10.

Particularly, constant-current control circuit 20 comprises:

BUCK-BOOST topology Switching Power Supply, BUCK topology Switching Power Supply, BOOST topology Switching Power Supply, flyback topology Switching Power Supply and forward topology Switching Power Supply.

Particularly, when constant-current control circuit 20 is flyback topology Switching Power Supply, constant-current control circuit 20 output constant currents comprise input circuit, controller, power switch, flyback transformer and output circuit,

Input circuit, for receiving the voltage of outside input, driving governor and power switch are in running order;

Controller, for power ratio control switch, makes the input current I of the current input terminal of power switch _ppeak value be steady state value, and the product of the switching frequency f of power ratio control switch and the erasing time Tdemag of flyback transformer is steady state value, makes Tdemag*f=c, c is constant;

Power switch, for control transformer primary current I _p, and current input terminal is connected with the primary coil of flyback transformer;

Flyback transformer, for from secondary coil output current, and is connected with input circuit from ancillary coil feedback;

Output circuit, for the electric current of the output winding of transformer is carried out to rectification and filtering, then exports constant output current.

The such scheme the utility model proposes, receives the input signal after rectification by High Power Factor treatment circuit, and the signal that receives constant-current control circuit output is as driving signal; High Power Factor treatment circuit output constant voltage signal, constant voltage signal input constant-current control circuit; Constant-current control circuit output constant current, driving LED Constant Current Load, has realized High Power Factor and without the constant-current circuit of stroboscopic.In addition, the technical scheme the utility model proposes is simple in structure, and the controller cost of control switch electric power outputting current is lower, is conducive to applying of technical solutions of the utility model, has very high practical value.

With respect to said apparatus, as shown in Figure 1, be the scheme flow chart of the utility model embodiment High Power Factor without stroboscopic output constant current, comprise the following steps:

S110: High Power Factor treatment circuit receives the input signal after rectification, and the signal that receives constant-current control circuit output is as driving signal.

As embodiment of the present utility model, High Power Factor treatment circuit comprises:

BOOST booster circuit or CUK chopper circuit.

As embodiment of the present utility model, High Power Factor treatment circuit inside has power switch.

As embodiment of the present utility model, power switch is metal-oxide-semiconductor or BJT bipolar transistor.

S120: High Power Factor treatment circuit output constant voltage signal, constant voltage signal input constant-current control circuit.

As embodiment of the present utility model, constant-current control circuit inside has power switch.

As embodiment of the present utility model, power switch is metal-oxide-semiconductor or BJT bipolar transistor.

As embodiment of the present utility model, the mains input voltage transient change of constant-current control circuit output constant current and this device is irrelevant.

As embodiment of the present utility model, constant-current control circuit comprises:

BUCK-BOOST topology Switching Power Supply, BUCK topology Switching Power Supply, BOOST topology Switching Power Supply, flyback topology Switching Power Supply and forward topology Switching Power Supply.

As embodiment of the present utility model, when constant-current control circuit is flyback topology Switching Power Supply, output constant current comprises the following steps:

Input circuit receives the voltage of outside input, and driving governor and power switch are in running order;

Controller power ratio control switch, makes the input current I of the current input terminal of power switch _ppeak value be steady state value, and the product of the switching frequency f of power ratio control switch and the erasing time Tdemag of flyback transformer is steady state value, makes Tdemag*f=c, c is constant;

The current input terminal of power switch is connected with the primary coil of flyback transformer, and the primary current on primary coil is I _p, the ancillary coil signal back input circuit of flyback transformer;

The secondary coil output current of flyback transformer obtains constant output current after output circuit rectification and filtering.

S130: constant-current control circuit output constant current, driving LED Constant Current Load.

As embodiment of the present utility model, constant-current control circuit inside has power switch.

As embodiment of the present utility model, power switch is metal-oxide-semiconductor or BJT bipolar transistor.

As embodiment of the present utility model, the input voltage of constant-current control circuit output constant current and constant-current control circuit is irrelevant.

As embodiment of the present utility model, constant-current control circuit comprises:

BUCK-BOOST topology Switching Power Supply, BUCK topology Switching Power Supply, BOOST topology Switching Power Supply, flyback topology Switching Power Supply and forward topology Switching Power Supply.

As embodiment of the present utility model, when constant-current control circuit is flyback topology Switching Power Supply, output constant current comprises the following steps:

Input circuit receives the voltage of outside input, and driving governor and power switch are in running order;

Controller power ratio control switch, makes the input current I of the current input terminal of power switch _ppeak value be steady state value, and the product of the switching frequency f of power ratio control switch and the erasing time Tdemag of flyback transformer is steady state value, makes Tdemag*f=c, c is constant;

The current input terminal of power switch is connected with the primary coil of flyback transformer, and the primary current on primary coil is I _p, the ancillary coil signal back input circuit of flyback transformer;

The secondary coil output current of flyback transformer obtains constant output current after output circuit rectification and filtering.

The such scheme the utility model proposes, receives the input signal after rectification by High Power Factor treatment circuit, and the signal that receives constant-current control circuit output is as driving signal; High Power Factor treatment circuit output constant voltage signal, constant voltage signal input constant-current control circuit; Constant-current control circuit output constant current, driving LED Constant Current Load, has realized High Power Factor and without the constant-current circuit of stroboscopic.In addition, the technical scheme the utility model proposes is simple in structure, and the controller cost of control switch electric power outputting current is lower, is conducive to applying of technical solutions of the utility model, has very high practical value.

For the ease of understanding the utility model, below in conjunction with more specifically, more complete circuit devcie, the scheme of the above-mentioned proposition of the utility model or device are further elaborated.

Fig. 2 is the circuit theory diagrams schematic diagram of the utility model embodiment.By Fig. 2, can be known, High Power Factor of the present utility model is without the constant-current circuit of stroboscopic, and this circuit only needs one to drive signal, and a modulation circuit, to reach, simplifies circuit and cost-saving, improves PCB layout.

This circuit is to realize like this High Power Factor without stroboscopic, and gauze voltage, after rectification circuit, enters High Power Factor treatment circuit, then passes through constant-current control module, obtains constant current output, has High Power Factor simultaneously.

High Power Factor treatment circuit, the power tube (metal-oxide-semiconductor, BJT transistor) of this modular circuit of drive of employing constant-current control circuit.This modular circuit can be BOOST booster circuit, and cuk converter etc.

Constant-current control circuit, conservation of energy formula is released

$\mathrm{Iout}=\frac{\frac{1}{2}\×(I_{p1}^2-I_{p}2)\×L_p\×f\×\mathrm{\η}}{\mathrm{Uout}+U_D}---\left(1\right)$

Constant-current control circuit guarantees by modulation circuit

constant, transformer efficiency eta approximately constant, so constant, i.e. output constant current.This contactor electric source topology can be flyback topology, BUCK-BOOST is topological, BUCK is topological etc., and mode of operation can be interrupter duty (DCM) pattern, continuous operation (CCM) pattern and critical conduction (BCM) pattern.

Fig. 3 is the whole principal diagram intention of the utility model embodiment.In conjunction with Fig. 2, can understand more intuitively core concept of the present utility model, do not repeat them here, refer to the description to Fig. 2.

Fig. 4 shows the theory diagram of the controller of preferred specific embodiment of the present utility model.As shown in Figure 4, controller 20 comprises comparator 204, and comparator 204 is used for limiting the magnitude of voltage of CS end, thereby controls primary current I _pthe size of electric current; CS lead-edge-blanking circuit 205, lead-edge-blanking circuit is used for eliminating the abnormal of CS voltage that the factors such as noise at the beginning of each cycle conducting of switching tube NMOS cause; Also comprise that FB sampling keeps and erasing time testing circuit 206, clock generating and management circuit 207, d type flip flop 208, with door 209.

FB sampling maintenance and erasing time testing circuit are as shown in Figure 5.Sampling keeps the timing waveform corresponding with erasing time testing circuit as shown in Figure 6.Controller FB port receives the voltage feedback signal FB of power-supply system, FB is input to the in-phase end of comparator 1 and comparator 2, simultaneously, FB opens and turn-offs through sampling switch K0 is regular, in this example, K0 design is opened 200ns in FB erasing time (us magnitude) 2/3 time corresponding position, obviously also can design the instantaneous sampling finishing in the erasing time, or other times, on capacitor C2, obtain sampling and keep voltage VFB, the end of oppisite phase of VFB input comparator 1 and the comparison of FB signal, and VFB is used for controlling the frequency of oscillator.The end of oppisite phase of comparator 2 can ground connection (zero potential), and the output signal VF2 of the output signal VF1 of comparator 1 and comparator 2 is through obtaining signal Ft0 with gate logic, and Ft0 is input to the clock trigger end of d type flip flop; The output signal PFM of the internal module circuit 208 of the reset signal Time Controller 20 of d type flip flop, PFM signal is mainly used to control the conducting of switching tube NMOS and the signal of shutoff of power-supply system.The antilogical signal of Ft0 and Ft1 carry out NOR gate logic and obtain erasing time detection signal F_demag; The time representation of F_demag high level the erasing time of transformer each cycle.

Fig. 7 shows preferred clock generating and the management circuit 207 of the controller of preferred specific embodiment of the present utility model.Clock generating and management circuit 207 can be subdivided into two parts, FB voltage control current circuit 271, and frequency generates and logical circuit 272.Wherein, this constant-current control circuit belongs to reverse exciting switching voltage regulator topology, and this circuit working is in DCM pattern.Efficiency is generally constant, is assumed to 1, below theoretical derivation be all according to carrying out under the DCM mode of operation of flyback topology.

$\mathrm{Iout}=\frac{\mathrm{Pout}}{\mathrm{Vout}+V_D}=\frac{1}{2}*\mathrm{Lp}*{\mathrm{Ip}}^2*\frac{f}{\mathrm{Vout}+V_D}---\left(2\right)$

Known by power-supply system

$\mathrm{VFB}=\frac{R2}{R1+R2}*\mathrm{Vaux}---\left(3\right)$

Vaux=n*(Vout+V _D) （4）

That is:

$\mathrm{VFB}=\frac{R2}{R1+R2}*n*(\mathrm{Vout}+V_D)---\left(5\right)$

Formula represents VFB and Vout+V above _dbecome multiple relation, formula 5 substitution formula 2 can be obtained,

$\mathrm{Iout}=\frac{1}{2}*\mathrm{Lp}*{\mathrm{Ip}}^2*\frac{f}{\mathrm{VFB}}*\frac{n*R2}{R1+R2}---\left(6\right)$

From formula 6, when Lp, Ip fix, the frequency f of power-supply system and the ratio of VFB when (constant), power-supply system is exported constant electric current I out.

FB voltage control current circuit 271 adopts LDO structure, and the voltage at the positive and negative two ends of error amplifier is equal, and the voltage of R5 equals VFB, has

$I3=\frac{\mathrm{VFB}}{R5}---\left(7\right)$

FB carrys out the variation of control frequency by controlling electric current I 3.

3 couples of capacitor C5 of electric current I that frequency generates and logical circuit 272 utilizes FB voltage control current circuit 271 to produce discharge and recharge, wherein charging current

I4=k3*I3 （8）

Discharging current

I5=k1*I3 （9）

According to electric weight formula,

I4*Tr=C5*ΔV （10）

I5*Tf=C5*ΔV （11）

Wherein,

Tr, represents the charging interval;

Tf, represents discharge time;

Δ V, the absolute value of the difference of expression reference voltage V ref1 and Vref0, can be set as 2.5V in this example.

The cycle T 0 discharging and recharging so:

T0=Tr+Tf （12）

Formula (8), (9), (10), (11) substitution formula (12) are obtained,

$T0=\frac{C5*\mathrm{\ΔV}}{k3*I3}+\frac{C5*\mathrm{\ΔV}}{k1I3}---\left(13\right)$

By formula (7), (8) substitution above formula, what can obtain C5 discharges and recharges frequency f 0,

$f0=\frac{1}{T0}=\frac{\frac{k1*\mathrm{VFB}}{R5}}{C5*\mathrm{\ΔV}}*\frac{(k3*\frac{\mathrm{VFB}}{R5})}{(k1+k3)*\frac{\mathrm{VFB}}{R5}}---\left(14\right)$

Power-supply system clock f is that the frequency f 0 that discharges and recharges of C5 obtains through two divided-frequency, that is:

$f=\frac{f0}{2}=\frac{\frac{k1*\mathrm{VFB}}{R5}}{2*C5*\mathrm{\ΔV}}*\frac{(k3*\frac{\mathrm{VFB}}{R5})}{(k1+k3)*\frac{\mathrm{VFB}}{R5}}---\left(15\right)$

So,

$\frac{f}{\mathrm{VFB}}=\frac{k1}{2*R5*C5*\mathrm{\ΔV}}*\frac{(k3*\frac{\mathrm{VFB}}{R5})}{(k1+k3)*\frac{\mathrm{VFB}}{R5}}---\left(16\right)$

So

Known in conjunction with formula (6), output current is constant.

Through above theory analysis, system output current is constant.After constant-current control circuit steady operation, constant-current controller OUT exports control signal, and the switch periods T of this control signal fixes, high level time, and the ON time Ton of constant-current control circuit fixes.This control signal is controlled two power switchs, and one is the power switch of constant-current control circuit, and one is the power switch of BOOST High Power Factor treatment circuit.This control signal Ton time is not subject to the modulation of BOOST High Power Factor treatment circuit, therefore High Power Factor treatment circuit belongs to modulated.

Fig. 8 shows the utility model embodiment and is operated under BCM pattern, and the input voltage phase after input average current and rectification changes schematic diagram.

Suppose that BOOST circuit working is at critical conduction mode.Suppose that the input voltage of electric main Vac after rectifier circuit rectification is U _{in (t)}, the inductance value of inductance T1 is L _t1, peak current I _t1, the switching tube ON time of BOOST circuit and the ON time T of constant-current control circuit _onequate,

$\mathrm{Imavg}\left(t\right)=\frac{1}{2}\×I_{T1}---\left(17\right)$

U _in(t)×T _on=L _T1×I _T1 （18）

$\mathrm{Imavg}\left(t\right)=\frac{1}{2}\×\frac{U_{\mathrm{in}\left(t\right)}\×T_{\mathrm{on}}}{L_{T1}}---\left(19\right)$

After system stability work, ON time T _onfixing, Lp is the sensibility reciprocal value of inductance T1, also fixes, so the input voltage U after input average current Imavg (t) and rectification _{in (t)}same-phase changes, thereby realizes High Power Factor.

Fig. 9 shows the utility model embodiment and is operated under DCM pattern, and the input voltage phase after input average current and rectification changes schematic diagram.In the case,

BOOST circuit working is in DCM mode of operation, so

$\mathrm{Imavg}\left(t\right)=\frac{1}{2}\&times;m\&times;\frac{U_{\mathrm{in}\left(t\right)}\&times;T_{\mathrm{on}}}{L_{T1}},$ Wherein, 0 < m < 1 (20)

Same, the input voltage U after input average current Imavg (t) and rectification _{in (t)}same-phase changes, and realizes High Power Factor.

Input voltage U _{in (t)}after rectification, then pass through High Power Factor treatment circuit, i.e. BOOST topological circuit, so High Power Factor treatment circuit, except realizing High Power Factor, also has boosting, BOOST output capacitance E ₁obtain a fixing voltage U _out1.

Making the erasing time is Tdemag1,

(U _out1-U _in(t))×T _on=U _in(t)×T _demag1 （21）

$U_{\mathrm{out}1}=U_{\mathrm{in}\left(t\right)}\&times;(1+\frac{T_{\mathrm{on}}}{T_{\mathrm{demag}1}})---\left(22\right)$

BOOST booster circuit output voltage U _out1be a fluctuation voltage, work as U _{in (t)}when the lowest point, T _demag1minimum, maximum, U _out1also relatively little; Work as U _{in (t)}when peak value, T _demag1maximum, minimum, U _out1larger.Can be L by regulating the inductance value of inductance T1 _t1come adjusting erasing time T _demag1, and obtain a suitable BOOST circuit output U _out1.

Because constant-current control circuit output current

(referring to constant-current controller formula (6)), wherein output current I _outirrelevant with the mains input voltage transient change of this device, can not produce power current ripple, so this system can realize output current without stroboscopic.

Those skilled in the art are appreciated that realizing all or part of step that above-described embodiment scheme carries is to come the hardware that instruction is relevant to complete by program, described program can be stored in a kind of computer-readable recording medium, this program, when carrying out, comprises step of scheme implementation example one or a combination set of.

In addition, each functional unit in each embodiment of the utility model can be integrated in a processing module, can be also that the independent physics of unit exists, and also can be integrated in a module two or more unit.Above-mentioned integrated module both can adopt the form of hardware to realize, and also can adopt the form of software function module to realize.If described integrated module usings that the form of software function module realizes and during as production marketing independently or use, also can be stored in a computer read/write memory medium.

The above-mentioned storage medium of mentioning can be read-only memory, disk or CD etc.

The above is only part execution mode of the present utility model; it should be pointed out that for those skilled in the art, do not departing under the prerequisite of the utility model principle; can also make some improvements and modifications, these improvements and modifications also should be considered as protection range of the present utility model.

Claims (4)

1. High Power Factor, without a device for stroboscopic output constant current, is characterized in that, comprises High Power Factor treatment circuit and constant-current control circuit;

Described High Power Factor treatment circuit, for receiving the input signal after rectification, and the signal that receives described constant-current control circuit output is as driving signal;

Described constant-current control circuit, for receiving the constant voltage signal of described High Power Factor treatment circuit output, and for exporting constant current, driving LED Constant Current Load.

2. High Power Factor according to claim 1, without the device of stroboscopic output constant current, is characterized in that, described High Power Factor treatment circuit comprises:

BOOST booster circuit or CUK chopper circuit.

3. High Power Factor according to claim 1, without the device of stroboscopic output constant current, is characterized in that, described constant-current control circuit comprises:

BUCK-BOOST topology Switching Power Supply, BUCK topology Switching Power Supply, BOOST topology Switching Power Supply, flyback topology Switching Power Supply and forward topology Switching Power Supply.

4. High Power Factor according to claim 3 is without the device of stroboscopic output constant current, it is characterized in that, when described constant-current control circuit is flyback topology Switching Power Supply, described constant-current control circuit output constant current comprises input circuit, controller, power switch, flyback transformer and output circuit

Described input circuit, for receiving the voltage of outside input, drives described controller and described power switch in running order;

Described controller, for controlling described power switch, makes the input current I of the current input terminal of described power switch _ppeak value be steady state value, and the product of controlling the switching frequency f of described power switch and the erasing time Tdemag of described flyback transformer is steady state value, makes Tdemag*f=c, c is constant;

Described power switch, for control transformer primary current I _p, and current input terminal is connected with the primary coil of described flyback transformer;

Described flyback transformer, for from secondary coil output current, and is connected with described input circuit from ancillary coil feedback;

Described output circuit, for the electric current of the output winding of transformer is carried out to rectification and filtering, then exports constant output current.