CN102105010A - LED drive circuit - Google Patents

Abstract

The invention relates to an LED drive circuit, comprising a rectifier bridge, a power factor correcting circuit, a control circuit and a constant current output circuit, wherein the output end of the rectifier bridge is connected with the power factor correcting circuit which is a flow-by-flow power factor correcting circuit; the control circuit comprises a controller, an Out end of which is connected with a control end of a switch element; a first conducting end of the switch element is connected with a cathode of a second diode through a first inductor, and a second conducting end of the switch element is connected with an CS end of the controller; a corresponding end of the first inductor is connected with an anode cathode of a sixth diode through a second inductor, and a cathode of the sixth diode is connected with an output negative end; a non-corresponding end of the first inductor is connected with an output positive end. The invention meets the requirements for power factor and harmonic wave and can output constant current, and has the advantages of high efficiency, high dependability, small volume and low cost; furthermore, the output capacitor can be a small capacitor and even is unnecessary.

Description

A kind of led drive circuit

Technical field

The present invention relates to the led drive circuit field, the led drive circuit of the non-isolation of particularly a kind of High Power Factor.

Background technology

The LED illumination is as a kind of new industry technology, and constantly developing is used widely.Led drive circuit is a key link of LED technology, uses the drive circuit based on inverse-excitation type (flyback) topological structure at present usually.

Fig. 1 is the systematic schematic diagram of existing drive circuit.This drive circuit comprises input rectifying filter circuit 11, ON-OFF control circuit 12, isolating transformer 13 and output rectifier and filter 14, the transformer that the auxiliary winding 107 of the former limit of transformer winding 105, transformer secondary winding 106 and transformer is formed, be coupled to the first control circuit 110 of the former limit of transformer winding 106, first control circuit 110 comprises drive circuit 111 and feedback control circuit 112.The base stage of power switch pipe 108 connects first control circuit 110, and collector electrode connects the different name end of the former limit of transformer winding 105, and emitter is by first resistance, 101 ground connection.Between two outputs of transformer secondary winding 106 and downlink connection first electric capacity 102 and second resistance 103.

This drive circuit is sent to energy the output of transformer secondary winding 106 by the turn-on and turn-off of the drive circuit 111 power controlling switching tubes 108 of first control circuit 110 by the former limit of transformer winding 105.Above-mentioned drive circuit adopts isolating transformer 13, and input rectifying filter circuit 11 and output rectifier and filter 14 are isolated, and can play certain safety effect.Do not need to isolate but partial L ED illumination is used, in drive circuit, use isolating transformer 3 can reduce the efficient of circuit.

Summary of the invention

Purpose of the present invention provides a kind of led drive circuit, and this drive circuit promptly satisfies power factor and harmonic requirement, and exportable again constant current has high efficiency, high reliability, little, the low cost and other advantages of volume.

A kind of led drive circuit of the present invention, comprise rectifier bridge, circuit of power factor correction, control circuit and constant current output circuit: the output of rectifier bridge is connected circuit of power factor correction, circuit of power factor correction is for pursuing the streaming circuit of power factor correction, control circuit comprises controller (U1), the Out end of controller (U1) connects the control end of switch element (Q1), first conduction terminal of switch element (Q1) is by the negative electrode of first inductance (L1) connection second diode (D2), and second conduction terminal of switch element (Q1) connects the CS end of controller (U1); The end of the same name of first inductance (L1) is by the anode of second inductance (L2) connection the 6th diode (D6), and the negative electrode of the 6th diode (D6) connects the output negative terminal, and the different name end of first inductance (L1) connects output plus terminal.

Preferably, circuit of power factor correction comprises second electric capacity (C2), second electric capacity (C2) anode connects an output of rectifier bridge, and negative terminal connects the negative electrode of the 3rd diode (D3), and the anode of the 3rd diode (D3) connects another output and the ground connection of rectifier bridge; The negative electrode of second diode (D2) connects the anode of second electric capacity (C2), and the anode of second diode (D2) connects the anode of the 3rd electric capacity (C3), the negativing ending grounding of the 3rd electric capacity (C3).

Preferably, also comprise the 4th diode (D4), the anode of the 4th diode (D4) connects the negative electrode of the 3rd diode (D3), and the negative electrode of the 4th diode (D4) connects the anode of second diode (D2).

Preferably, the anode of the 4th diode (D4) connects the negative electrode of the 3rd diode (D3) by the 9th resistance (R9).

Preferably, the anode of the 4th diode (D4) connects the negative electrode of the 3rd diode (D3) by the 9th inductance (L9).

Preferably, the anode of the 5th electric capacity (C5) connects the output negative terminal, and the negative terminal of the 5th electric capacity (C5) connects output plus terminal.

Preferably, the anode of the 5th diode (D5) is by the 3rd inductance (L3) ground connection, and the negative electrode of the 5th diode (D5) connects the Vcc end of controller (U1).

Preferably, the FB of controller (U1) end also connects the anode of the 5th diode (D5) by the 7th resistance (R7) ground connection by the 6th resistance (R6).

Preferably, the emitter of triode Q1 is by second resistance (R2) ground connection.

Preferably, the Vcc of controller (U1) end connects the negative electrode of second diode (D2) by first resistance (R1), and passes through the 4th electric capacity (C4) even.

Preferably, also comprise filter circuit, filter circuit comprises the 8th inductance (L8) and first electric capacity (C1), and the 8th inductance (L8) end connects the electric current positive input terminal, and the other end connects rectifier bridge one input; First electric capacity (C1) end connects the 8th inductance (L8), and the other end connects the interchange negative input end.

Preferably, exchange positive input terminal and insert filter circuit by fuse (F1).

Compared with prior art, the present invention has the following advantages:

The present invention adopts former limit switch control mode, does not need output voltage current detection circuit and optocoupler, only needs to detect former limit switching current and auxiliary winding voltage, realizes the constant current constant voltage control of output.The present invention solves the problem that existing low-power LED drive circuit can not satisfy power factor and harmonic requirement, promptly satisfies power factor and harmonic requirement, and exportable again constant current has the efficient of doing, high reliability, little, the low cost and other advantages of volume.

Description of drawings

Fig. 1 is existing driving circuit structure figure;

Fig. 2 is driving circuit structure figure of the present invention;

Fig. 3 is the voltage oscillogram of circuit node A point to ground;

Fig. 4 is the current waveform figure of diode D6;

Fig. 5 is the built-in function block diagram of controller U1 one embodiment;

Fig. 6 is circuit of power factor correction one example structure figure;

Fig. 7 is another example structure of circuit of power factor correction figure.

Embodiment

For above-mentioned purpose of the present invention, feature and advantage can be become apparent more, the present invention is further detailed explanation below in conjunction with the drawings and specific embodiments.

Referring to Fig. 2, driving circuit structure of the present invention is shown, drive circuit comprises input filter circuit 21, rectifier bridge 22, circuit of power factor correction 23, control circuit 14 and constant current output circuit 25.

Exchange the input anode and insert filter circuit 21 by fuse F1, filter circuit 21 comprises inductance L 1 and capacitor C 1, and inductance L 1 one ends connect fuse F1, and the other end connects rectifier bridge 22 1 inputs; Capacitor C 1 one ends connect the common port of inductance L 1 and fuse F1, and the other end connects the common port that exchanges input negative terminal and rectifier bridge 22;

Alternating current again through filter circuit 21 filtering, is input to rectifier bridge 22 rectifications after the insurance of fuse F1 overcurrent.

Rectifier bridge 22 is made up of four diodes of series connection successively, the output of rectifier bridge 22 connects circuit of power factor correction 23, circuit of power factor correction 23 comprises capacitor C 2, capacitor C 2 anodes connect an output of rectifier bridge 22, negative terminal connects the negative electrode of diode D3, and the anode of diode D 3 connects another output and the ground connection of rectifier bridge 23; The negative electrode of diode D2 connects the anode of capacitor C 2, and the anode of diode D2 connects the anode of capacitor C 3, the negativing ending grounding of capacitor C 3;

The electric current of 23 pairs of inputs of circuit of power factor correction carries out power factor correction, and circuit node A point to the voltage waveform on ground as shown in Figure 3.The A point voltage is not a straight direct voltage, but a fluctuation voltage, this voltage fluctuates between the input ac voltage peak value at 1/2 of input ac voltage peak value, and frequency is 2 times of input ac voltage frequency.

It is 48% that circuit of power factor correction 23 can make input current total harmonic distortion THD, and power factor PF reaches 0.8, satisfies the IEC61000-3-2 standard.

Electric current is input to control circuit 4 and constant current output circuit 5 after power factor correction.Control circuit 4 comprises controller U1, and the Vcc end of controller U1 connects the negative electrode of diode D2 by resistance R 1, and passes through capacitor C 4 even; The Out end of controller U1 connects the base stage of triode Q1, and the collector electrode of triode Q1 is by the negative electrode of inductance L 1 connection diode D2, and the emitter of triode Q1 connects the CS end of controller U1, and by resistance R 2 ground connection; The FB end of controller U1 also connects the anode of diode D5 by resistance R 7 ground connection by resistance R 6, the anode of diode D5 is also by inductance L 3 ground connection, and the negative electrode of diode D5 connects the Vcc end of controller U1; 2 ends of inductance L 1 are by the anode of inductance L 2 connection diode D6, and the negative electrode of diode D6 connects the output negative terminal, and 1 end of inductance L 1 connects output plus terminal; The anode of capacitor C 5 connects the output negative terminal, and the negative terminal of capacitor C 5 connects output plus terminal.

Among this embodiment, resistance R 1 is the starting resistance of controller U1, is connected to the VCC pin of controller U1, and controller U1 is provided after circuit powers on a certain size starting current.Inductance L 3 is auxiliary winding, with the current supply circuit of diode D5, capacitor C 4 formation controller U1.Simultaneously, inductance L 3 voltages are connected to the FB pin of controller U1, as the detection and the protective circuit of output voltage through resistance R 6, resistance R 7 dividing potential drops.Resistance R 2 is the current sense resistor of triode Q1, is connected to the CS pin of controller U1, the current sample pin.The GND pin of controller U1 is connected to earth potential, and the Out pin drives pin for output, exports the pwm signal of certain pulsewidth, and control triode Q1 turns on and off.

Triode Q1 of the present invention also can adopt other switch elements, as semiconductor switch devices such as power MOSFET tubes.

Controller U1 realizes the switch control functions of constant current output circuit 5.Inductance L 1, L2 intercouple by magnetic core.Electric current is exported constant current after control circuit 4 and constant current output circuit 5 bucks.

Be set in the switch periods, the ON time of output diode D6 is Tons, and the turn-off time is Toffs, and the output current peak value is Ipk, coupling inductance L1 umber of turn N1, coupling inductance L2 umber of turn N2.Controller U1 control switch duty ratio keeps ON time Tons and the turn-off time Toffs proportions constant of output diode D6, and then in switch periods, the mean value of output current is:

$I_{\mathrm{out}}=\frac{1}{2}\·I_{\mathrm{pks}}\·\frac{T_{\mathrm{ons}}}{T_{\mathrm{ons}}+T_{\mathrm{offs}}}---\left(1\right)$

Fig. 4 is the current waveform through diode D6.

According to Ampere theorem, output current peak I pks and triode Q1 current peak Ipk have following relation during the firm conducting of output diode D6:

$I_{\mathrm{pks}}=\frac{N1}{N1+\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="HDA0000052169710000012.png"\; state="\{\{state\}\}">N</figure-callout>}2}\&CenterDot;I_{\mathrm{pk}}---\left(2\right)$

Therefore, the mean value of output current is:

$I_{\mathrm{out}}=\frac{1}{2}\&CenterDot;\frac{N1}{N1+\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="HDA0000052169710000012.png"\; state="\{\{state\}\}">N</figure-callout>}2}\&CenterDot;I_{\mathrm{pk}}\&CenterDot;\frac{T_{\mathrm{ons}}}{T_{\mathrm{ons}}+T_{\mathrm{offs}}}---\left(3\right)$

Control chip U1 is by detecting former limit switching current, and it is constant to control former limit switching current peak I pk, while control switch duty ratio, and ON time Tons and the turn-off time Toffs proportions constant of maintenance output diode D6 have realized the constant of output current.

Control mode of the present invention is lower to the parameter request of capacitor C 5, like this can the relatively low electric capacity of selected parameter, and this electric capacity volume is little, and cost is low, makes things convenient for circuit layout, and cost-saved.And can in circuit shown in Figure 2, not use this capacitor C 5 according to actual needs, do not influence the realization of above-mentioned functions.

Fig. 5 is the built-in function block diagram of controller U1 one embodiment, comprises constant voltage control unit, peak current control unit, constant current control unit, inner voltage stabilizing and bias unit and output driver element etc.

Among this embodiment, triode Q1 also can adopt other semiconductor switch devices such as power MOSFET.Controller U1 also can be packaged together with triode Q1 is integrated.

Power factor of the present invention is adjusted circuit 23 can increase resistance or inductance again, as Fig. 6, shown in Figure 7.Among Fig. 6, the anode of diode D4 connects the negative electrode of diode D3 by resistance R 9; Among Fig. 7, the anode of diode D4 connects the negative electrode of diode D3 by inductance L 9.Can further improve input power factor by resistance R 9 or inductance L 9, reduce total harmonic distortion.

The present invention adopts former limit switch control mode, does not need output voltage current detection circuit and optocoupler, only needs to detect former limit switching current and auxiliary winding voltage, realizes the constant current constant voltage control of output.

According to the present invention, the high performance lED drive circuit of having formed the non-isolation of High Power Factor by the streaming circuit of power factor correction and the combination of the Buck-boost switching power circuit that adopts former limit switch control mode, this circuit has High Power Factor, control mode is simply novel, output need not big capacity electrochemical capacitor, component number is few, and volume is little, the advantage that cost performance is high.。

The above only is a preferred implementation of the present invention, does not constitute the qualification to protection range of the present invention.Any any modification of being done within the spirit and principles in the present invention, be equal to and replace and improvement etc., all should be included within the claim protection range of the present invention.

Claims (12)

1. led drive circuit, it is characterized in that, comprise rectifier bridge, circuit of power factor correction, control circuit and constant current output circuit: the output of rectifier bridge is connected circuit of power factor correction, circuit of power factor correction is for pursuing the streaming circuit of power factor correction, control circuit comprises controller (U1), the Out end of controller (U1) connects the control end of switch element (Q1), first conduction terminal of switch element (Q1) is by the negative electrode of first inductance (L1) connection second diode (D2), and second conduction terminal of switch element (Q1) connects the CS end of controller (U1); The end of the same name of first inductance (L1) is by the anode of second inductance (L2) connection the 6th diode (D6), and the negative electrode of the 6th diode (D6) connects the output negative terminal, and the different name end of first inductance (L1) connects output plus terminal.

2. circuit as claimed in claim 1, it is characterized in that, circuit of power factor correction comprises second electric capacity (C2), second electric capacity (C2) anode connects an output of rectifier bridge, negative terminal connects the negative electrode of the 3rd diode (D3), and the anode of the 3rd diode (D3) connects another output and the ground connection of rectifier bridge; The negative electrode of second diode (D2) connects the anode of second electric capacity (C2), and the anode of second diode (D2) connects the anode of the 3rd electric capacity (C3), the negativing ending grounding of the 3rd electric capacity (C3).

3. circuit as claimed in claim 2 is characterized in that, also comprises the 4th diode (D4), and the anode of the 4th diode (D4) connects the negative electrode of the 3rd diode (D3), and the negative electrode of the 4th diode (D4) connects the anode of second diode (D2).

4. circuit as claimed in claim 3 is characterized in that, the anode of the 4th diode (D4) connects the negative electrode of the 3rd diode (D3) by the 9th resistance (R9).

5. circuit as claimed in claim 3 is characterized in that, the anode of the 4th diode (D4) connects the negative electrode of the 3rd diode (D3) by the 9th inductance (L9).

6. circuit as claimed in claim 1 is characterized in that, the anode of the 5th electric capacity (C5) connects the output negative terminal, and the negative terminal of the 5th electric capacity (C5) connects output plus terminal.

7. circuit as claimed in claim 1 is characterized in that, the anode of the 5th diode (D5) is by the 3rd inductance (L3) ground connection, and the negative electrode of the 5th diode (D5) connects the Vcc end of controller (U1).

8. circuit as claimed in claim 7 is characterized in that, the FB end of controller (U1) also connects the anode of the 5th diode (D5) by the 7th resistance (R7) ground connection by the 6th resistance (R6).

9. circuit as claimed in claim 1 is characterized in that, the emitter of triode Q1 is by second resistance (R2) ground connection.

10. circuit as claimed in claim 1 is characterized in that, the Vcc end of controller (U1) connects the negative electrode of second diode (D2) by first resistance (R1), and passes through the 4th electric capacity (C4) even.

11. circuit as claimed in claim 1 is characterized in that, comprises that also filter circuit, filter circuit comprise the 8th inductance (L8) and first electric capacity (C1), the 8th inductance (L8) end connects the electric current positive input terminal, and the other end connects rectifier bridge one input; First electric capacity (C1) end connects the 8th inductance (L8), and the other end connects the interchange negative input end.

12. circuit as claimed in claim 1 is characterized in that, exchanges positive input terminal and inserts filter circuit by fuse (F1).

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