Summary of the invention
The invention provides that cost is low, reliability, stability is high and drive the high a kind of self-excited oscillation type high power LED constant-current driving circuit of efficient.This circuit does not adopt any chip for driving, only uses common discrete components such as less resistance, electric capacity, triode, constitutes a kind of self-oscillation structure, the driving switch circuit, and, realized the constant-current driving of great power LED in conjunction with current feedback.And, can change the luminosity of LED by regulating the resistance of foreign current sampling resistor.
The present invention adopts following technical scheme:
A kind of self-excited oscillation type high power LED constant-current driving circuit, comprise current rectifying and wave filtering circuit, switching circuit, the pressure-stabilizing constant flow output circuit, transformer, the self-excited oscillation type pulse-width modulation signal generating circuit, the current feedback disable circuit, electric main is converted to high-voltage dc signal through current rectifying and wave filtering circuit and is sent to switching circuit, switching circuit carries out pulse-width modulation with described high-voltage dc signal, obtain high frequency ac signal and transfer to transformer, the high-frequency alternating voltage that the secondary output winding of transformer passes over elementary winding is transported to the pressure-stabilizing constant flow output circuit, is that direct voltage output is in order to driving LED by the pressure-stabilizing constant flow output circuit with this high-frequency alternating voltage rectifying and wave-filtering, and export described direct voltage to the current feedback disable circuit in order to produce block signal and to export this signal to switching circuit in order to suppress pulse-width signal as current sampling signal, the control switch circuit working, the positive feedback winding of transformer exports the positive feedback voltage of responding to self-excited oscillation type pulse-width modulation signal generating circuit generation pulse-width signal and transports to switching circuit, and this signal control switch circuit produces high-frequency alternating voltage.
The present invention has following advantage:
1, drive circuit of the present invention is only used common discrete components such as less resistance, electric capacity, triode, constitute a kind of self-oscillation structure, the driving switch metal-oxide-semiconductor, therefore do not need special PWM (pulse-width modulation) chip, saved circuit cost greatly, and chip lost efficacy easily under such as situations such as, mechanical oscillation big in climate change, discrete device is affected by environment less, therefore, the reliability of circuit also is improved.
2, the present invention has added one group of positive feedback winding on transformer, the integration structure that cooperates resistance capacitance, produce self-oscillation, control the triode conducting and end, thereby the driving power metal-oxide-semiconductor carries out HF switch, make that switching circuit can operate as normal, the energy on former limit is passed to secondary by high frequency transformer.Because adopted the switching circuit structure, the efficient of whole drive circuit is improved greatly than traditional linear voltage stabilization structure, can reach more than 80%.
3, output of the present invention adopts the current-mode sampling feedback, formed a kind of disable circuit by conventional, electric-resistance, electric capacity, triode, photoelectrical coupler, when output current is higher than the setting constant current value, this disable circuit quits work switching circuit, when output current has just dropped to below the constant current value, disable circuit fails, and switching circuit works on; So just, can make the LED operating current of output be in the constant current state that very little ripple is only arranged; Thereby can realize constant current output, make great power LED reliably working more, luminous even, increase the service life.
4, circuit of the present invention can also further be regulated the brightness of LED, because the brightness of LED and the electric current that flows through are directly proportional, can carry out the brightness regulation of LED by regulating the foreign current sampling resistor, and is convenient and reliable.Because the disable circuit unlocking condition is that transistor base reaches 0.7V, this 0.7V is the pressure drop on the current sampling resistor, if change resistance value, flows through the electric current of sampling resistor in the time of just changing the 0.7V pressure drop, has promptly regulated the constant current set point when LED is luminous.
5, the input of circuit of the present invention adopts transformer and photoelectrical coupler to isolate, and the driving output of LED and high pressure civil power do not have directly and be electrically connected, disturb so little, reliability raising, the fail safe when also having strengthened circuit working in addition.
6, circuit of the present invention also by adding the auxiliary winding of transformer, provides operating voltage for optocoupler and triode, does not need additional power source, has saved circuit area and cost.
7, input circuit of the present invention utilizes inductance, electric capacity, resistance to constitute transition supression circuit, prevent the damage of surge voltage, electric current to late-class circuit, this structure also provides filter function simultaneously, can improve power factor, help the restraining line to carry the noise of noise and filter out power generation, improve reliability.
8, the price height of existing various great power LED chip for driving, quality is uneven, and the LED chip for driving power capacity of inner integrated switch pipe is limited, and carrying load ability is not strong, can't drive for some more high-power LED; And this circuit adopts external switching tube, can carry out freely selecting according to the actual power demand, can carry out more high-power LED and drive.
Embodiment
Below by specific embodiments of the invention also in conjunction with the accompanying drawings, purpose of the present invention, circuit structure and advantage are further described.
As shown in Figure 1, the present invention includes current rectifying and wave filtering circuit 1, switching circuit 2, self-excited oscillation type pulse-width modulation signal generating circuit 3, pressure-stabilizing constant flow output circuit 4, current feedback disable circuit 5, transformer 6.
Current rectifying and wave filtering circuit 1 is converted to high-voltage dc signal comparatively stably to electric main, exports the high-voltage dc signal input of switching circuit 2 to from its high-voltage dc signal output, as the energy supply of entire circuit; Switching circuit 2 is undertaken the high direct voltage signal that receives to change high frequency ac signal into after the pulse-width modulation by HF switch, energy delivery is given the elementary winding a of transformer 6 by its high frequency ac signal output; Simultaneously, switching circuit 2 pulse-width signal that is produced by self-oscillation by self-excited oscillation type pulse-width modulation signal generating circuit 3 that its signal input part is received or the block signal that sent by current feedback disable circuit 5 are in order to the switch of control switch S1; Transformer 6 is provided with elementary winding a, positive feedback winding b, secondary output winding c and accessory power supply winding d; The secondary output winding c of transformer 6 exports the high-frequency alternating voltage of sensing to the high-frequency alternating voltage input of pressure-stabilizing constant flow output circuit 4, dc voltage output end from pressure-stabilizing constant flow output circuit 4 after rectifying and wave-filtering is direct voltage is exported, in order to driving LED, and export this direct voltage the dc voltage input end of current feedback disable circuit 5 to, the current sample output of pressure-stabilizing constant flow output circuit 4 is transported to current sampling signal the current sampling signal input of current feedback disable circuit 5 simultaneously; The positive feedback winding b of transformer 6 outputs to the positive feedback voltage of sensing the positive feedback voltage input end of self-excited oscillation type pulse-width modulation signal generating circuit 3; The accessory power supply winding d of transformer 6 sends the high-frequency alternating voltage of sensing to the auxiliary high frequency alternating voltage input of current feedback disable circuit 5, current feedback disable circuit 5 is handled current sampling signal, when electric current surpasses the continuous current that sets, start disable circuit, force the power switch metal-oxide-semiconductor S1 in the stopcock circuit 2, make the LED current stabilization in the constant current set point.
As shown in Figure 2, described current rectifying and wave filtering circuit 1 comprises the first diode D1, the second diode D2, the 3rd diode D3, the 4th diode D4, first capacitor C 1, second capacitor C 2, first resistance R 1, inductance L 1; The first diode D1, the second diode D2, the 3rd diode D3, the 4th diode D4 form full-bridge rectifier, the 3rd diode D3 negative electrode connects the first diode D1 anode, the 4th diode D4 negative electrode connects the second diode D2 anode, and two tie points connect electric main; The first diode D1, the second diode D2 negative electrode link to each other, and output is connected with an end of inductance L 1 as the high direct voltage behind the commercial power rectification, and the 3rd diode D3, the continuous ground connection of the 4th diode D4 anode are as the input ground after the rectification; Inductance L 1 is in parallel with first resistance R 1, and an end connects first capacitor C, 1 positive pole simultaneously, another termination second capacitor C 2 positive poles, and first capacitor C 1, second capacitor C, 2 other ends are ground connection all, forms transition and suppress and the EMI filter circuit; Second capacitor C, 2 positive poles are as the high-voltage dc signal output of current rectifying and wave filtering circuit 1.
Described switching circuit 2 comprises the 5th diode D5, the 3rd capacitor C 3, the second resistance R 2, the 3rd resistance R 3, the 4th resistance R 4, the 5th resistance R 5, power switch metal-oxide-semiconductor S1; Second resistance R, 2 one ends are as the high-voltage dc signal input of switching circuit 2, one end of another termination the 3rd resistance R 3, the grid of another termination power switch metal-oxide-semiconductor S1 of the 3rd resistance R 3 and an end of the 4th resistance R 4, the other end ground connection of the 4th resistance R 4, second resistance R 2, the 3rd resistance R 3, the 4th resistance R 4 constitute the start-up circuit of power switch metal-oxide-semiconductor S1, and the intersection point of second resistance R 2, the 3rd resistance R 3 is as the pulse-width signal input of switching circuit 2; The source class ground connection of power switch metal-oxide-semiconductor S1, drain electrode connects the different name end of the elementary winding a of transformer 6, also connects the anode of the 5th diode D5 simultaneously; The 5th resistance R 5,3 parallel connections of the 3rd capacitor C, the negative electrode of one termination the 5th diode D5, the other end is as the end of the same name of the elementary winding a of the high frequency ac signal output connection transformer 6 of switching circuit 2, and the 5th resistance R 5, the 3rd capacitor C 3 and the 5th diode D5 constitute the RCD buffer.
Self-excited oscillation type pulse-width modulation signal generating circuit 3 comprises the 6th diode D6, the 4th capacitor C 4, the 5th capacitor C 5, the 6th resistance R 6, the 7th resistance R 7, the 8th resistance R 8, the 9th resistance R 9, the first triode Q1, the 6th resistance R 6 is connected with the 5th capacitor C 5, the other end of the 6th resistance R 6 is as the positive feedback voltage input end of self-excited oscillation type pulse-width modulation signal generating circuit 3, be connected with the end of the same name of the positive feedback winding b of transformer 6, the collector electrode of another termination first triode Q1 of the 5th capacitor C 5 and the negative electrode of the 6th diode D6, play clamping action, the plus earth of the emitter of the first triode Q1 and the 6th diode D6, the collector electrode of the first triode Q1 is as the pulse-width signal output of self-excited oscillation type pulse-width modulation signal generating circuit 3, pulse-width signal input with switching circuit 2, the block signal output of current feedback disable circuit 5 links to each other, one end ground connection of the 9th resistance R 9, the base stage of the first triode Q1 connects the other end of the 9th resistance R 9 and an end of the 8th resistance R 8, one end of another termination the 4th capacitor C 4 of the 8th resistance R 8 and an end of the 7th resistance R 7, the other end ground connection of the 4th capacitor C 4, the other end of the 7th resistance R 7 is as the positive feedback voltage input end of self-excited oscillation type pulse-width modulation signal generating circuit 3.The 7th resistance R 7, the 8th resistance R 8, the 9th resistance R 9 and the 4th capacitor C 4 have been formed the drive circuit to the first triode Q1 base stage.
Pressure-stabilizing constant flow output circuit 4 comprises the 7th diode D7, voltage stabilizing didoe D8, the 6th capacitor C 6, the 7th capacitor C 7, the 8th capacitor C 8, the ten resistance R 10, variable resistor RV1; The anode of the 7th diode D7 is as the high-frequency alternating voltage input of pressure-stabilizing constant flow output circuit 4, be connected with the different name end of the secondary output winding c of transformer 6, the negative electrode of the 7th diode D7 links to each other with the anode of LED load as the dc voltage output end of pressure-stabilizing constant flow output circuit 4; The 6th capacitor C 6 is in parallel with the 7th diode D7 with the tenth resistance R 10 polyphone backs, plays the buffer effect; Positive termination the 7th diode D7 negative electrode of the 7th capacitor C 7, another termination output ground plays filtering energy storage effect; The 8th capacitor C 8 one terminations the 7th diode D7 negative electrode, another termination LED negative electrode plays the effect of filter high frequency clutter; Voltage stabilizing didoe D8 negative electrode connects the 7th diode D7 negative electrode, and its anode connects the negative electrode of LED load, plays the overvoltage protection effect; Variable resistor RV1 one end is as the current sample output termination LED negative electrode of pressure-stabilizing constant flow output circuit 4, and another termination output ground plays the electric current sampling action.
Described current feedback disable circuit 5 comprises the 9th diode D9, the 9th capacitor C 9, the 11 resistance R the 11, the 12 resistance R the 12, the 13 resistance R the 13, the 14 resistance R the 14, the 15 resistance R 15, photoelectrical coupler OP1, the second triode Q2, the 3rd triode Q3; The anode of the 9th diode D9 is as the auxiliary high frequency alternating voltage input of current feedback disable circuit 5, connect the different name end of the accessory power supply winding d of transformer 6, the negative electrode of the 9th diode D9 connects the positive pole of the 9th capacitor C 9, the minus earth of the 9th capacitor C 9, the high-frequency alternating voltage rectifying and wave-filtering that both provide accessory power supply winding d is a direct voltage, as accessory power supply, supply with the photoelectrical coupler OP1 and second triode Q2 work; The end of the 13 electric capacity R13 is as the current sampling signal input of current feedback disable circuit 5, be connected with the dc voltage output end of pressure-stabilizing constant flow output circuit 4, the collector electrode of another termination the 3rd triode Q3 and the light-emitting diodes tube anode of photoelectrical coupler OP1 play metering function; The base stage of the 3rd triode Q3 is as the current sample output of the current sample input termination pressure-stabilizing constant flow output circuit 4 of current feedback disable circuit 5, the light-emitting diode minus earth of the emitter of the 3rd triode Q3 and photoelectrical coupler OP1, the positive pole of one termination the 9th capacitor C 9 of the 14 resistance R 14 and an end of the 15 resistance R 15, the phototriode collector electrode of another termination photoelectrical coupler OP1 of the 14 resistance R 14 plays metering function; The phototriode grounded emitter of photoelectrical coupler OP1,15 metering functions of the 15 resistance R, the collector electrode of its another termination second triode Q2, one end of the base stage of the second triode Q2 and the 12 resistance R 12, the other end of the 11 resistance R 11 connects, the phototriode collector electrode of one termination photoelectrical coupler OP1 of the 11 resistance R 11, the grounded emitter of the other end of the 12 resistance R 12 and the second triode Q2, the collector electrode of the second triode Q2 is as the block signal output of current feedback disable circuit 5, connect the pulse-width signal input of switching circuit 2, switch S 1 when the LED electric current reaches the setting constant current value in the positive closing circuit 2 is to reach the constant current effect.
The course of work of circuit of the present invention and principle:
Circuit of the present invention is as long as the incoming transport civil power gets final product operate as normal.Because the input voltage that switching circuit 2 requires is a direct current, so must carry out rectifying and wave-filtering to electric main earlier, this function is finished by current rectifying and wave filtering circuit 1.The full-wave rectification bridge input that electric main is made up of first diode to the, four diodes, rectification is an all-wave voltage, through being high voltage direct current behind transition inhibition and the EMI filter circuit, is input to switching circuit 2 again.This filter circuit construction helps the restraining line to carry the noise of noise and filter out power generation; Except that filter function, the transient impedance of inductance L 1 is very high, makes up the surge current that the polyphone impedance that can provide necessary limits transient state, the protection late-class circuit with first resistance R 1.First capacitor C 1, second capacitor C 2 also play the effect of energy storage except that filtering.
Power switch metal-oxide-semiconductor S1 carries out HF switch under pulse-width signal control, high direct voltage is modulated to the high-frequency alternating voltage on the elementary winding a of transformer 6, utilizes transformer to give secondary output winding energy delivery.When power switch metal-oxide-semiconductor S1 conducting, high direct voltage-elementary winding a-power switch metal-oxide-semiconductor S1-ground constitutes the loop, and electric current flows through elementary winding a, energy is stored on the elementary winding a, this moment, end of the same name was for just, and the different name end is a power switch metal-oxide-semiconductor S1 drain voltage, near 0V.According to transformer character, this moment secondary output winding c end of the same name also for just, the different name end is for negative, the 7th diode D7 oppositely ends, LED powers by the energy of storage on the 7th capacitor C 7.When power switch metal-oxide-semiconductor S1 ends, elementary winding a produces induced potential, and end of the same name is for negative, and the different name end is for just, after then secondary output winding c senses, it is negative that its different name end becomes, and end of the same name is being for just, the 7th diode D7 forward conduction, energy is delivered to secondary output winding c from elementary winding a by transformer, secondary output winding c electric current flows into energy storage the 7th capacitor C 7, to its charging, powers to LED simultaneously.Because when power switch metal-oxide-semiconductor S1 turn-offs, elementary winding a goes up the reflected voltage of wanting inductive secondary output winding c, voltage in the power switch metal-oxide-semiconductor S1 drain electrode is that high direct voltage adds reflected voltage, if consider factors such as winding leakage inductance spike, the withstand voltage that might surpass power switch metal-oxide-semiconductor S1 is with its damage.The 5th diode D5, the 3rd capacitor C 3, the 5th resistance R 5 have been formed a RCD buffer, in order to the peak voltage that reduces to produce when power switch metal-oxide-semiconductor S1 turn-offs, and protection power switch metal-oxide-semiconductor S1.When diode reverse is ended, also can produce the high pressure spike on it, the 6th capacitor C 6,10 cushioning effects of the tenth resistance R reduce this peak voltage, protect the 7th Rectigon D7.Second resistance R 2, the 3rd resistance R 3, the 4th resistance R 4 are formed the start-up circuit of power switch metal-oxide-semiconductor S1, and when rigidly connecting civil power, circuit does not totally also bring into operation, and directly utilizes high direct voltage this moment, through opening power switch metal-oxide-semiconductor S1 after the dividing potential drop.The 3rd resistance R 3 also plays the metering function to power switch metal-oxide-semiconductor S1 grid.The 8th capacitor C 8 in the output circuit is high frequency noise components of filtering output voltage.If at some state, LED driving voltage moment of output is too high, and voltage stabilizing didoe D8 plays pressure stabilization function, and protection LED can not damage.The same on the electric current that variable resistor RV1 goes up process and the LED, its pressure drop can be represented the size of electric current, as the sampling of electric current, offers current feedback disable circuit 5.
The pulse-width signal of S1 is produced by self-excited oscillation type pulse-width modulation signal generating circuit 3 in the driving switch circuit 2.When power switch metal-oxide-semiconductor S1 began conducting, the end of the same name of positive feedback winding b was sensed as positive voltage, was added on the grid of power switch metal-oxide-semiconductor S1 via the path of the 6th resistance R 6, the 5th capacitor C 5, the 3rd resistance R 3, impelled its conducting more, was positive feedback.Simultaneously; positive feedback voltage is by 4 chargings of 7 pairs the 4th capacitor C of the 7th resistance R; when voltage on the 4th capacitor C 4 is not enough to make the first triode Q1 base stage to reach 0.7V-1V; the first triode Q1 turn-offs; do not influence its conducting; the 8th resistance R 8 is current-limiting resistances of the first triode Q1 base drive, and the 9th resistance R 9 plays the effect of protection base stage.When the continuous charging along with the 4th capacitor C 4, after the first triode Q1 base stage reached 0.7V-1V, the first triode Q1 was conducting, power switch metal-oxide-semiconductor S1 grid drawn be low level, on-off switching tube.When power switch metal-oxide-semiconductor S1 turn-offs, secondary output winding c output energy, the voltage reversal of positive feedback winding b, its end of the same name is sensed as negative voltage, the 6th diode D6 conducting this moment, with the collector electrode clamper of the first triode Q1 at the current potential that hangs down a diode drop than ground, promptly-0.7V, the pass off-state of holding power switch MOS pipe S1.At this moment, be approximate 0 current potential because the 5th capacitor C 5 connects the first triode Q1 collector electrode, one end, the other end is a negative pressure, and the 5th capacitor C 5 is recharged.When secondary winding c release energy finish after, the voltage of each winding of transformer 6 tends to 0 level, the positive feedback voltage output end that is positive feedback winding b trends towards 0V, because the voltage of the 5th capacitor C 5 can not suddenly change, then the end that links to each other with the 3rd resistance R 3 of the 5th capacitor C 5 is a positive voltage, this will impel power switch metal-oxide-semiconductor S1 conducting again, a little after the conducting, can quicken its conducting by positive feedback again, repeat above-mentioned steps, this is a self-oscillatory process, has so just obtained the pulse-width modulation control signal of high frequency.Power switch metal-oxide-semiconductor S1 is in switching process, and ON time was decided by the charging interval of the 4th capacitor C 4, and the shut-in time equals secondary output winding c, and the phase has discharged time of energy weekly.
Ifs circuit does not add the feedback adjusting module, and then output voltage can raise always, can not pressure-stabilizing constant flow.So the present invention has added current feedback disable circuit 5, be pressure-stabilizing constant flow output in order to guarantee circuit.What flow through on the electric current that flows through on the variable resistor RV1 and the LED is the same, its pressure drop can be represented the size of output current, when the pressure drop of variable resistor RV1 less than 0.7V, when promptly the 3rd triode Q3 base emitter voltage is less than 0.7V, the 3rd triode Q3 turn-offs, and output voltage has electric current to flow through through current limliting the 13 resistance R 13 on the light-emitting diode of photoelectrical coupler OP1, according to the characteristic of optocoupler, also flow through electric current on its phototriode.Accessory power supply winding d, the 9th diode D9 and the 9th capacitor C 9 are formed accessory power supplys, power supply when being the phototriode work of the second triode Q2 and optocoupler OP1, and the 15 resistance R the 15, the 14 resistance R 14 is a current-limiting resistance.Because electric current is flow through in the phototriode conducting of optocoupler OP1, its collector electrode is pulled to earth potential, and promptly the second triode Q2 base stage is a low level, not conducting, and this moment, current feedback disable circuit 5 disconnected with switching circuit 2, did not play blocking action.When the output current that flows through LED reaches the setting constant current value, the sampled value of variable resistor RV1 equals 0.7V, the 3rd triode Q3 conducting, the electric current major part is passed through from the 3rd triode Q3, it is 0 substantially that light-emitting diode flows through electric current, electric current also is 0 substantially on the phototriode, and its collector potential is no longer drawn to be low level.Accessory power supply is by the 11 resistance R 11, the dividing potential drop of the 14 resistance R 14 and the 12 resistance R 12 is added on the second triode Q2 base stage, its conducting, power switch metal-oxide-semiconductor S1 grid is forced to draw for low level and turn-offs, play blocking action, switching circuit 2 stops to transmit energy, output voltage and electric current will descend, when output current reduces slightly, sampled value a little less than 0.7V after, the second triode Q2 just is turned off at once, blocking action is removed, power switch metal-oxide-semiconductor S1 proceeds switch, transmit energy, electric current and voltage bottom out again is the stationary value that sets, and so circulation is gone down.So export to the driving voltage electric current substantially constant of LED, have only very little ripple, belong to constant current control.In addition, change the resistance of variable resistor RV1, just can change the current value when making its pressure drop be 0.7V, promptly changed the constant current set point of driving LED electric current, because the brightness of LED is directly proportional with the electric current that flows through, so just can change the luminosity of institute's driving LED by regulating the resistance of variable resistor RV1.
Because the pressure drop of different LED is not quite similar, and also different according to the LED number of reality requirement polyphone, the present invention is by revising design of transformer, change the turn ratio of primary and secondary winding, change a small amount of components and parts, just can produce the output of different driving voltage, adapt to various designing requirements.
Data with a specific embodiment (referring to Fig. 3) 4,5 illustrate advantage of the present invention in conjunction with the accompanying drawings below:
Drive two polyphone great power LEDs, each LED normal when luminous the constant-current driving electric current be 1A, single tube voltage drop is 4.5V, the output voltage that then requires this drive circuit is 9V, 1A, and holding current is constant, the current ripples scope is in positive and negative 5%.
Input: 220V electric main
Output: 9V, the 1A constant current, 9W drives two polyphone LED
The parameter of rectifier bridge is selected main consider withstand voltage and current capacity, for the application system of 220V, considers due to voltage spikes in particular cases, generally chooses the rectifier bridge of withstand voltage 1000V.Electric current is decided according to the input current of side circuit, also will leave certain surplus, and for led drive circuit of the present invention, under the situation that maximum power is used, input current can not surpass 1A yet, thus can choose the rectifier bridge of 2A, such as KBP210.
The parameter of first capacitor C 1, second capacitor C 2, inductance L 1 will decide according to actual filtering requirements and circuit test, roughly can be with reference to following formula: L=Z/ (2 π * fc), C=1/ (2 π * fc * Z), wherein Z is that filter inputs or outputs the impedance under cut-off frequency, fc is a filter cutoff frequency, and is relevant with designing requirement.First resistance R 1 is in parallel with inductance L 1, assists to suppress surge current, shields, and generally gets 10K ohm.
Because power switch metal-oxide-semiconductor S1 is in turn off process, drain electrode can be born the high pressure about 500V, considers to leave certain safe clearance, generally selects the metal-oxide-semiconductor of withstand voltage 600V or 700V.In addition, also will be the peak current that flows through transformer 6 elementary winding a as standard, selection can be born the power switch metal-oxide-semiconductor S1 of this current peak.For the drive circuit of most of great power LED, according to the power difference, this peak current is generally between 1A~5A.
Resistance R 3 is current-limiting resistances of power switch metal-oxide-semiconductor S1 gate driving, and the electric current when discharging and recharging in order to restriction S1 grid is generally got about 10 ohm.Second resistance R 2 and the 4th resistance R 4 are connected between high direct voltage and the ground, gate drive voltage is provided during for the startup of power switch metal-oxide-semiconductor S1, its partial pressure value will satisfy the voltage when making power switch metal-oxide-semiconductor S1 grid reach the metal-oxide-semiconductor conducting, for power MOS pipe, generally this driving voltage is 10V~15V.Be Vdc * R4/ (R2+R4)=10V-15V, Vdc is the value of high direct voltage.Second resistance R 2 and the 4th resistance R 4 resistances can not be too little in addition, otherwise when the circuit operate as normal, power consumption is bigger, generally get tens K ohms to K ohms up to a hundred.Because the 3rd resistance R 3 resistances are less relatively, can ignore in the dividing potential drop process.
The fundamental formular that the
5th resistance R 5 is selected is
V wherein
C3Be the
3rd capacitor C 3 both end voltage, be generally
nV
o2~2.5 times, L
Lk1Be the leakage inductance of elementary winding a, i
PeakBe the peak current on the elementary winding a, n is the turn ratio of elementary winding a and secondary output winding c, V
oBe output voltage, f
sSwitching frequency for power switch metal-oxide-semiconductor S1.The fundamental formular that the
3rd capacitor C 3 is selected is
Wherein
Be V
C3Ripple, generally get 5%~10%.The reverse withstand voltage of the 5th diode D5 is greater than the withstand voltage of power switch metal-oxide-semiconductor S1, and general employing can be flow through the fast recovery diode of 1A electric current.
Output rectification the 7th diode D7 generally adopts fast recovery diode, and perhaps Schottky diode disturbs for preventing the spike that reverse recovery current brings, and maximum current drives the surplus of constant current value high 30% than the LED that sets.The
6th capacitor C 6 is generally got 3 * Cout, and Cout is the output capacitance of the 7th diode D7, calculates the following formula of the tenth resistance R 10
f
dThe resonance frequency of winding c leakage inductance and the 7th diode D7 output capacitance when not adding the RC buffer circuit.The computing formula of RC buffer circuit as a reference, reality also needs to carry out optimal selection by test.The 7th capacitor C 7 is an output capacitance, and its minimum value computing formula is,
Wherein, t
OffBe the turn-off time of the 7th diode D7, I
DCBe LED load current, V
PpBe desired maximum output ripple voltage peak-to-peak value.The
8th capacitor C 8 is to consider to remove output voltage high frequency clutter, generally gets 1uF.Voltage stabilizing didoe D8 is the voltage stabilizing didoe that prevents output overvoltage, generally chooses the voltage stabilizing value and gets final product than the normal LED driving voltage of exporting high 10%.Variable resistor RV1 is as current sampling resistor, and it will guarantee that when reaching needed constant drive current pressure drop is 0.7V, promptly
The
5th capacitor C 5 is when circuit carries out self-oscillation, its both end voltage will keep constant substantially, because frequency of oscillation is higher, so the appearance value selects 50nF to get final product, current-limiting resistance when the
6th resistance R 6 is positive feedback winding b to 5 chargings of the 5th capacitor C is generally selected 100 ohm.The first triode Q1 does not have specific (special) requirements, select common NPN type triode for example S9013 get final product.The 6th diode D6 that plays clamping action selects the most frequently used 1N4007.The
8th resistance R 8 is the current-limiting resistances that drive the first triode Q1 base stage, generally gets 100 ohm.Protective resistance the 9th resistance R 9 is not in order to influence the circuit operate as normal, and general value is bigger, between 50K ohm-100K ohm.The 7th resistance R 7 and the
4th capacitor C 4 have been formed the RC charging structure, when the
4th capacitor C 4 upper ends are charged to 0.7V-1V, the first triode Q1 will open, and this charging interval is exactly the pulse duration of pulse-width signal that self-maintained circuit produces, and pass therebetween is:
U wherein
cBe the voltage on the
4th capacitor C 4, U
0Initial voltage during for the firm conducting of phase power switch metal-oxide-semiconductor S1 weekly on the
4th capacitor C 4 generally is negative value in this circuit, U
sBe the RC charging voltage, i.e. the voltage of positive feedback winding b generation, R, C are respectively the value of the 7th resistance R 7, the
4th capacitor C 4, and t is the charging interval.When getting u
cThe pulse duration that=0.7V-1V, t=set, U
0, U
sUnder the known situation, just can calculate the value of RC.
Because the output current of accessory power supply is less, its output rectification the 9th diode D9 generally adopts the fast recovery diode of 1A, and the size of filtering the 9th capacitor C 9 is that 1uF gets final product.Optocoupler OP1 employing current transfer ratio is 1: 1 PC817B.The second triode Q2, the 3rd triode Q3 operate mainly in conducting and cut-off state, adopt general NPN type triode just passable, as S9013.The 13 resistance R 13 will satisfy for for making optocoupler OP1 energy operate as normal
V
oLED driving voltage for output.The 14 resistance R 14 is current-limiting resistances of phototriode among the optocoupler OP1, because optocoupler OP1 current transfer ratio is 1: 1, the difference between current that flows through in phototriode and the light-emitting diode is few, so have
V
sOutput voltage for accessory power supply.The 15 resistance R 15 is the current-limiting resistance between the second triode Q2 collector electrode and accessory power supply, gets about 80K ohm to get final product.The 11 resistance R 11 is the current-limiting resistance of the second triode Q2 base drive, 100 ohm of values.The selection of the 12 resistance R 12 resistances will guarantee that the dividing potential drop of itself and the 11 resistance R 11, the 14 resistance R 14 is enough to make the basic emitter-base bandgap grading conducting of the second triode Q2, promptly
Turn ratio during
transformer 6 designs between each winding has following relation: for the 220V system, high voltage direct current behind the rectifying and wave-filtering is about 310V, the output voltage of positive feedback winding b is generally 20V, could effectively open by guaranteed output switch MOS pipe S1 like this, so the turn ratio between elementary winding a and the positive feedback winding b is na: nb=310: 20, be about 15~16.The turn ratio of secondary output winding c and elementary winding a will be according to output voltage V
oDifference and difference, when preventing that S1 from turn-offing, the drain electrode peak voltage is too high, the general requirement is
V
DCBe the high voltage direct current behind the rectifying and wave-filtering.The turn ratio of accessory power supply winding d and secondary output winding c is both voltage ratios, has
Accessory power supply V
sBe generally 10V~15V.After the turn ratio is determined, when design, be also noted that and select the suitable number of turn (decision inductance value) and line footpath, in order to avoid magnetic core of transformer is saturated or temperature rise is too high.
According to above-mentioned foundation, each component parameters is calculated as follows in this example:
The first resistance R 1:10K Ω; The second resistance R 2:990K Ω; The 3rd resistance R 3:6.8 Ω; The 4th resistance R 4:56K Ω; The 5th resistance R 5:130K Ω; The 6th resistance R 6:100 Ω; The 7th resistance R 7:7.5K Ω; The 8th resistance R 8:100 Ω; The 9th resistance R 9:56K Ω; The tenth resistance R 10:10 Ω; The 11 resistance R 11:100 Ω; The 12 resistance R 12:3.3K Ω; The 13 resistance R 13:1K Ω; The 14 resistance R 14:1K Ω; The 15 resistance R 15:80K Ω;
Slide rheostat RV1:0~1 Ω when bright (normal be 0.7 Ω);
The first capacitor C 1:5.6uF; The second capacitor C 2:10uF; The 3rd capacitor C 3:2.2nF; The 4th capacitor C 4:3.3nF; The 5th capacitor C 5:50nF; The 6th capacitor C 6:2.2nF; The 7th capacitor C 7:1000uF; The 8th capacitor C 8:1uF; The 9th capacitor C 9:1uF;
The rectifier bridge first diode D1~the 4th diode D4:KBP210; The 5th diode D5:HER108; The 6th diode D6:1N4007; The 7th diode D7:SF22;
Voltage stabilizing didoe D8:9.8V voltage-stabiliser tube; The 9th diode D9:SF14; Inductance L 1:100uH; The NPN type triode first triode Q1~the 3rd triode Q3:S9013; Power switch metal-oxide-semiconductor S1:1N60; Photoelectrical coupler OP1:PC817B;
Transformer 6: each umber of turn is than na: nb: nc: nd=14: 1: 1: 2, elementary winding electric sensibility reciprocal was the 2.12mH interpretation of result:
In Fig. 4, Vo, Io are respectively the voltage and currents of circuit output driving LED, and Vgs1 is the pulse-width signal on the power switch metal-oxide-semiconductor S1 grid.When self-oscillation produced, power switch metal-oxide-semiconductor S1 grid was controlled by pulse-width signal, and switching circuit carries out HF switch, and energy is passed to secondary output by transformer.As can be seen, when pulse-width modulation, because energy delivery is arranged, output voltage and electric current progressively raise, when output current Io reaches a certain set point, be about 1.05A among the figure, disable circuit begins to work, and forces to make power switch metal-oxide-semiconductor S1 grid put low, turn-off it, switching circuit stops to transmit energy, and secondary output current and voltage progressively descend, when Io drops to a certain value, be about 0.98A among the figure, disable circuit fails, and power switch metal-oxide-semiconductor S1 grid continues to be subjected to pulse-width signal to control Vo, Io restarts to rise, so repeatedly, having guaranteed that finally output current Io has only very little ripple, is the stabling current of 1A substantially, and circuit plays the constant-current driving LED effect.
In Fig. 5, Vn2 is the voltage of positive feedback winding b, and Vc4 is the voltage of the 4th capacitor C 4 upper ends, and Vgs1, Vds1 are respectively the signal in power switch metal-oxide-semiconductor S1 grid and the drain electrode.In self-oscillation process, power switch metal-oxide-semiconductor S1 grid begins conducting when being high, Vds1 is about 0V, positive feedback winding b is the 20V high level at this moment, and by 4 chargings of 7 pairs the 4th capacitor C of the 7th resistance R, terminal voltage improves gradually on the 4th capacitor C 4, when being charged between 0.7V-1V, the NPN type first triode Q1 begins conducting, the grid of power switch metal-oxide-semiconductor S1 is drawn be low level switch-off power switch MOS pipe S1.This moment, elementary winding a was reverse, and Vds1 is the high pressure about 450V, positive feedback winding b also is reversed-10V about, 4 reverse chargings of the 4th capacitor C are to the-3V.Behind secondary output winding c discharge off, power switch metal-oxide-semiconductor S1 by the above-mentioned steps circulation, has constituted self-maintained circuit again by open-minded again.