TW201143516A - Driving circuit for single-string light-emitting diode (LED) lamp - Google Patents

Abstract

A driving circuit for a single-string light-emitting diode (LED) lamp includes a push-pull converter. The push-pull converter boosts an input low DC voltage of 12-19 volts to a high DC voltage of up to 200 volts for providing power to the single-string LED lamp. The driving circuit controls lamp current of the single-string LED lamp by means of constant current and modulates brightness of the single-string LED lamp by means of pulse-width modulation (PWM) dimming. In addition, the single-string LED lamp provides the standardization design for connectors of the driving circuit used to connect to the single-string LED lamp, so that the driving circuit has better common-use characteristic. Moreover, the driving circuit does not need a current balance circuit, and just needs a cheaper and general purpose integrated circuit to control the push-pull converter to reduce design cost of the driving circuit.

Description

201143516 VI. Description of the Invention: [Technical Field] The present invention relates to a driving circuit of a Light Emitting Diode (LED), and in particular to a single-string (four) lamp In the driving circuit of the tube, all the LEDs in the single string LED tube, that is, the I^D tube, are all coupled in series. [Prior Art] The current liquid crystal display (Liquid Crystal Display, referred to as (10), such as LCD screen (10) monitor), LCD TV (10) TV), the computer host integrated in the liquid screen - body computer (10) seven such as PC), etc., Start using (10) light ^^ backlight. The LEDs in this LED tube are usually combined in series and parallel. For example, the LEDs in the 灯 tube are connected in parallel with 8 groups and each group is consumed by 1 (H solid series connection. The driving circuit of the LED tube passes The power converter boosts the input low-voltage DC voltage (such as 12-19V) to a relatively high DC voltage (such as 3 (four) QV) to provide (10) the supply voltage required for lamp operation. This supply voltage is controlled by the LED tube. (10) The number of series is determined by 0. Since there are many parallel groups of LED tubes, for example, 4 sets of parallel, 6 sets of parallel, 8 sets of ^, etc. 'In order to make each group (10) output current equal, it must be adopted The dedicated integrated circuit of the current sharing function or the current sharing circuit of the current miscellaneous circuit makes the driving circuit of the (10) lamp tube = ten cost compared with the other 'currently each panel factory defines the way to the output input end of the (four) lamp tube" The number of groups is also different, so that the driving circuit 4 of the LED tube has no sister and is poor, resulting in waste of manpower and design cost. [Summary] 201143516 Road 'and circuit design can be standardized and better Sharing. The present invention proposes a single string The LED circuit of the LED tube, wherein the single string (10) tube has an input end and a transmission {±| terminal. The driving circuit of the single string tube includes at least a dimming control circuit, a current feedback circuit, and a pulse width modulation (Pulse-Width). Modulation 'abbreviation just】 control circuit and push-pull reading shop, in which the dimming control (four) way and the current feedback circuit are connected in series, between the output end of the single-string LED tube and the ground end, the control circuit is cut to the f-end And through the feedback end secret light control f road and money feedback circuit, the push-pull converter is consumed to the input end of the single string LED tube and the PWM control circuit. A dimming control circuit receives the dimming signal of the cis form Each period of the dimming signal includes a = start period and a close period. During the turn-on period, the dimming control circuit controls the single-string (10) lamp I's input it! end is coupled to the ground end, and the money touches the circuit to check the single string (4) The lamp current outputted from the output end of the lamp tube and according to the output of the first feedback voltage to the feedback end, the control circuit outputs two PWM signals of phase difference (10) degrees when the first feedback voltage is received, Pull-type, ancient change, according to the input of the first DC when receiving the PWM signal The voltage boost is second straight to output to the input end of the single string LED tube. During the off period, the dimming control circuit prepares the output end of the LED tube and the ground terminal _ and outputs the second feedback voltage to Feedback ^ 'The current feedback circuit does not detect the lamp current and stops outputting the first feedback voltage. · ^ The circuit stops outputting the simple signal when receiving the second return, and the push-pull converter receives the PWM signal. The conversion is stopped and the second DC voltage is no longer output. The driving circuit of the single-string LED lamp of the present invention can be boosted to a voltage of 2 〇〇v or higher by inputting a low voltage/first DC voltage of 12V 19V. The high voltage / the second DC for a single string of LED lights, the power supply is light, and the current mode is controlled. The tube current of the LED tube and the section of the single string (10) tube are used in the shun dimming mode. The invention adopts a single string LED tube, which has the same input and output definition as the existing Cold Cathode Fluorescent Lamp (CCFL), and is used for receiving the input of the high/second DC current and For output lamp 201143516 current provides feedback control At the end, the driver circuit is lightly connected to the light tube. The connector design can be standardized and has better singularity, and only needs to use a cheap general-purpose integrated circuit to control the _current circuit. Push-pull converters make drive circuit design less expensive. The above and other objects, features and advantages of the present invention will become more <RTIgt; [Embodiment] FIG. 1 is a circuit block diagram showing an embodiment of a driving circuit of a single-string LED lamp of the present invention. Please refer to FIG. 1 'Single string LED tube 4 is composed of a plurality of LEDs DL1 DLDLn, which are all connected in series, that is, the cathode end of DLi is reduced to the anode of DL (^ +1), ' i is any positive integer in (6)), and the anode end of the leddli is the input end 41 of the single string LED tube 4, and the cathode end of the LED DLn is the output end 42 of the single string LED tube 4. The drive circuit 1 of the single-string LED lamp 4 includes a push-pull converter u, a dimming control circuit 12, a current feedback circuit 13, a just control circuit 14, an off control circuit 15, and an overvoltage protection circuit 16. The dimming control circuit 12 is coupled in series with the current feedback circuit 13 between the output terminal 42 of the single-string LED tube 4 and the ground terminal 18. The pwm control circuit 14 is coupled to the feedback terminal 17 and coupled via the feedback terminal 17. Connected to the dimming control circuit 12 and the current feedback circuit 13, the push-pull converter 11 is connected to the input terminal 41 of the single-string LED tube 4 and the control circuit 14, and the switch control circuit 15 is connected to the PWM control. The circuit 14, the over-protection circuit 16 is coupled to the input terminal 41 of the single-string LED tube 4 and the PWM control circuit 14. The dimming control circuit 12 receives the dimming signal dim in the form of PWM. Each period T of the dimming signal DIM includes an on period Ton and a off period T〇ff (described further in FIG. 5 below). The dimming control circuit 12 controls the output end 42 of the single-string LED tube 4 to be coupled to the ground terminal 18, and the current feedback circuit 13 detects the lamp current Hamp outputted from the output terminal 42 of the single-string LED tube 4 and The first feedback voltage Vfbl 6 201143516 is outputted to the feedback terminal Π, and the PWM control circuit 14 wakes up the two PWM signals with a difference of 180 degrees when receiving the first feedback voltage, and pushes out the =_* _ The input first DC voltage is boosted to ^ directly if 乂 output to the wheel end 4 of the single string LED tube 4 during the off period Toff, the path 12 controls the round end 42 of the single string L黯 tube 4 and The ground terminal 18 is disconnected, and the voltage Vfb2 is fed back to the feedback terminal 17. The current feedback circuit 13 stops the output of the first feedback voltage VfM, and the touch control circuit Μ receives the first-iS grant. When the voltage Vfb2 is stopped, the output of the pwm signal is stopped, and the subtraction converter 11 stops switching when the PWM signal 1 and PWM2 are not received. The second DC voltage Vout is further outputted. An additional 'switch control circuit 15 receives the switching signal 〇N/〇FF according to 〇_ controlling whether the PWM control circuit 15 operates. The overvoltage protection circuit 16 is when the voltage waste Vout is greater than the threshold voltage Vref2 The control pwM control circuit 14 stops outputting the touch signals PWM1 and PWM2 (which will be further described later in Fig. 6).

2 and 3 are circuit diagrams of the first and second embodiments of the push-pull converter u shown in Fig. 1, respectively. Please refer to FIG. 2 'Push-pull converter 21 includes two power switches (composed of transistor Q1 and diode DQ1 and composed of transistor Q2 and diode _, respectively), transformer Ή, output rectifier circuit (by The diodes D1 to D4 are composed of an output filter circuit (composed of the inductor L1 and the electric grid C1). One end of the two windings on the primary side of the transformer τ1 receives the first-direct current light Vin, and the other end is connected to the 汲 terminal of the two transistors Q1 and Q2. The source terminals of the two transistors Q1 and Q2 are coupled to the ground terminal 18. The two transistors are respectively coupled to the gate terminals of Q2 to receive the two phase difference p signals p er 1 and PWM 2 . The two transistors Q1 and Q2 are alternately turned on by the PWM signals pwM1 and pwM2, respectively, so that a low-voltage pulse square wave is generated between the two windings on the primary side of the transformer T1, and the transformer T1 uses the primary-side low-voltage pulse square wave as a transformer. The number of turns is higher than the primary multiple. The pulse square wave. The output rectifier circuit rectifies the high voltage pulse 201143516 square wave outputted by the surface device T1 into a high voltage pulsating DC voltage, and finally the high voltage pulsating DC voltage is finally filtered by the output filter circuit into a high voltage low chopping second DC voltage Vout to provide a single string LED lamp. The supply voltage required for the operation of tube 4. Referring to Fig. 3, the push-pull converter 31 and the push-pull converter 21 shown in Fig. 2 differ mainly in the output rectifier circuit. The output rectifying circuit of the push-pull converter 21 is a bridge rectifying circuit composed of diodes D1 to D4, in which diodes D1 and D2 are used for rectification, and diodes D3 and D4 are used for freewheeling. The output rectification circuit of the push-pull converter 31 is composed of diodes D1 and D2 for rectification and is then supplied to ground terminal 18 through the secondary side of the transformer T1 to provide a current path for freewheeling. 4 is a circuit diagram of an embodiment of the dimming control circuit 12, the current feedback circuit 13, and the pWM control circuit 14 shown in FIG. 1, and FIG. 5 is a p(10) (dimming control timing chart) of the circuit shown in FIG. Referring to FIG. 4 and FIG. 5, the dimming control circuit 22 includes a first unidirectional conduction component (composed of the diode D5) and a first inverter circuit (composed of the transistor Q3 and the resistors R1 RR4). a second inverter circuit (composed of transistor Q4 and resistor R5 and cyst) and a switch (composed of transistor Q5). The first inverter circuit receives the dimming signal dim and outputs the output to the dimming signal DIM The inverting dimming signal DIM1, wherein the dimming signal dim includes an on period Ton and a off period Toff. The inverting dimming signal dimi is coupled to the feedback terminal 17 through the first one-way conducting element to During the turn-on period, τ〇η stops outputting the second feedback voltage Vfb2 to the feedback terminal 17' during the off period Toff, and outputs the second feedback voltage Vfb2 to the feedback terminal 17. The second inverter circuit is coupled to the first inversion phase. The circuit receives the inverting dimming "No. DIM1 ' and outputs the in phase with the inverted phase s of the inverted light s KIM DIM1 The optical signal is connected to the current feedback circuit 23 in series between the output end 42 of the single-string le:D lamp tube 4 and the ground terminal 18. The switch is turned on according to the in-phase dimming signal DIM2 during the opening period to control the output end. The resistor R7 of the current feedback circuit 23 is coupled to the ground terminal 18, and Toff is turned off during the off period to control the output terminal 42 to be disconnected from the ground terminal 18. During the on period Ton, the dimming signal DIM is at a high level voltage. Let the transistor (10) lead 8 201143516 'pass, the transistor Q3 turns on, the inverted dimming signal DIM1 is low level voltage (voltage is $), and then the transistor Q4 is turned off, the transistor Q4 is cut off to make the in-phase dimming signal The high-level voltage (voltage is R6/(R5+R6)xVdc2), and then the transistor q5 is turned on, the transistor Q5 is turned on to make the switch open and the control output 42 is coupled to the ground terminal 18, at this time, the single-string LED The lamp current Ilamp of the lamp tube 4 is not zero and will emit light (bright), wherein Vdc2 is a DC voltage. During the off period, the Toff 'dimming signal DIM is a low level voltage and the transistor (10) is turned off, and the transistor Q3 is turned off. Making the inverting dimming signal DIM1 a high level voltage (voltage is (R3+R4)/(R2+R3+R4)xVdcl) 'In turn, the transistor Q4 is turned on, and the transistor q4 is turned on to make the in-phase dimming signal DIM2 a low level voltage (voltage is zero), thereby making the transistor milk Φ cutoff, the transistor Q5 is cut off, the switch is closed and the control output 42 is disconnected from the ground terminal 18. At this time, the lamp current I lamp of the single string LED tube 4 is zero without illuminating (dark), wherein Vdcl is DC voltage. Therefore, the single-string LED tube 4 is bright during the turn-on period and Toff is dark during the turn-off period. When the frequency of the dimming signal DIM is above 15 Hz, the human eye will feel the effect of persistence of vision. If the brightness of the lamp 4 is not changed, the average value of the change can only be felt. Therefore, the dimming effect of adjusting the brightness of the kneading surface can be achieved by adjusting the ratio of light and dark (ie, adjusting the duty cycle of the dimming signal DIM). This dimming method is called dimming or burst mode dimming. • In addition, the inverting dimming signal DIM1 is first divided into DIM1 through resistors R3 and R4, and then connected to the feedback terminal 17 through a pole D5. During the turn-on period τ〇η, the voltage of the inverted dimming signal DIM1 is zero, so the inverted dimming signal DIM1, the voltage is also zero, and the diode turns off, thus stopping outputting the second feedback voltage Vfb2 to the feedback terminal 17 . During the off period Toff, the voltage of the inverting dimming signal DIM1 is (R3+R4)/(R2+R3+R4)xVdcl, so the voltage of the inverted dimming signal DIM1' is R4/(R2+R3+R4)xVdd' The diode D5 is turned on, thereby outputting a second feedback voltage Vfb2 (voltage is R4/(R2+R3+R4)xVdcl-Vd5) to the feedback terminal 17, where Vd5 is the diode D5 conduction voltage drop, and the resistance is known The R3 and R4 are used to adjust the feedback amount of the second feedback voltage Vfb2. 9 201143516 The square mine includes a second unidirectional conduction element (consisting of diode d6) with a switch of light control circuit 22 (consisting of transistor Q5) ^ output terminal 42 and ground terminal 18 of ray (10) lamp tube 4 between. Current Detection = (consisting of resistor R7) Detects the lamp current of a single string (10) of lamps 4! Ia, and according to the = detection voltage Vr7, the detection voltage ·通 · two single (four) pass element secret to the feedback end 17, in order to open the first feedback · coffee to the feedback end 17 during the opening period, in the ugly Toff stops outputting the first feedback voltage to the feedback terminal 1?. The current feedback circuit 23 further includes resistors R8 and R9 and a capacitor C2, wherein the resistor (10) and the feedback amount used to divide the voltage to adjust the first feedback voltage are generally selected for the resistor shape and the R9 The resistance value must be much larger than the resistance value of the current detector R7 to ensure that the lamp current Ilamp flows almost all through the current detector R7, and the capacitor C2 is used to filter out high frequency noise. During the on period Ton, the transistor Q5 is turned on, the lamp current η_ is not zero, and a voltage drop is generated on the current detecting resistor R7. This voltage drop is the detection voltage Vr7 ' with the lamp current 1 _ magnitude. The one-pole body D6 is turned on, so that the detection voltage vr7 is first divided by the resistors R8 and R9 into a first feedback voltage Vfbl (voltage is (Vr7-Vd6)xR9/(R8+R9)) with an appropriate level and then output to The feedback terminal π, which is the conduction voltage drop of the diode D6. During the off period Toff, the lamp current Hamp is zero and the detection voltage Vr7 is zero, causing the diode D6 to be turned off, thereby stopping the output of the first feedback power -Vfbl to the feedback terminal 17. Therefore, the voltage of the feedback terminal π, that is, the feedback terminal signal FB, is equal to the first feedback voltage Vfbl during the turn-on period (voltage is (Vr7-Vd6)xR9/(R8+R9)), during the off period Toff It is equal to the second feedback voltage Vfb2 (voltage is R4/(10)+R3+R4)xVdcl-Vd5), and in this example, the first feedback voltage Vfbl is smaller than the second feedback voltage Vfb2. The PWM control circuit 24 includes a PWM controller ΙΠ, an output drive circuit 241, and a resistor-capacitor compensation circuit (composed of a resistor R10 and a capacitor C3). The PWM controller U1 is, for example, a TL494 integrated circuit, and the first to third pins are respectively the non-201143516 of the error amplifier eai, the inverting input terminal, the inverting input terminal, and the output terminal 'the ninth and the first ones The pins are used to output PWM signals PWM1 and PWM2, respectively. The PWM controller m includes an error amplifier EM. The error amplifier EA1 has two input terminals (ie, a non-inverting input terminal and an inverting input terminal) and an output terminal, wherein the - input terminal (ie, the non-inverting input terminal) is juxtaposed to the feedback terminal 17, and the other input terminal ( That is, the inverting input terminal receives the reference voltage Vref1. The resistor R1〇 and the capacitor C3 of the resistor-capacitor compensation circuit are connected in series between one round-in terminal (ie, the inverting input terminal) of the error amplifier EA1 and the output terminal of the error amplifier EA1, so that the error amplifier is a negative feedback architecture. Since the error amplification H EA1 is a negative feedback architecture, the two inputs have a virtual short-circuit characteristic, so during the turn-on period Ton will force the feedback terminal signal FB (when its voltage is equal to the first feedback voltage Vfbl) equal to the reference voltage VreH. At this time, since the lamp current Ilamp is Vr7/R7 and the first-return power M Vfbl is (Vr7-Vd6)xK9/(10) side), the voltage value of the reference voltage Vref1 and the resistance value of the resistor R7 can be achieved. Set the lamp current to the current value. In addition, the error amplifier EA1 controls the PWM controller to output PWM signals PWM1 and PWM2 during the turn-on period τ〇η because the voltage FB of the feedback terminal 17 is equal to the reference voltage Vref1, and the voltage FB of the feedback terminal π during the off period When the voltage is equal to the second feedback voltage Vfb2) is greater than the reference voltage Vref1, the control PWM controller U1 stops outputting the PWM signals PWM1 and PWM2 〇1. The PWM signals PWM1 and PWM2 output by the PWM controller U1 may not be able to drive because of insufficient driving capability. The two transistors Q1 and Q2 in the push-pull converter 21 or 31 shown in FIG. 2 or FIG. 3, therefore, the PWM signals PWM1 and PWM2 output from the PWM controller U1 are usually also boosted by the output driving circuit 241. . Fig. 6 is a circuit diagram showing a first embodiment of the switch control circuit 15, the overvoltage protection circuit 16 &amp; pwM control circuit 14 shown in Fig. 1. Referring to FIG. 6, the control unit U1 of the control circuit is, for example, a TL494 integrated circuit with two error amplifiers EA1 and EA2' built therein. The 16th and 15th pins are non-inverting of the error amplifier EA2, respectively. The input terminal and the inverting input terminal, the 12th pin is used to receive the power supply 201143516 required to provide the PWM controller U1. The error amplifier EAI of the PWM controller U1 is used for the lamp current Ilamp feedback control and PWM dimming as shown in Figs. 4 and 5, and the error amplifier M2 is used for overvoltage protection. The control circuit 25 includes transistors q6 and Q?. When the switch QN/QFF is high and the bit voltage is turned on, the transistor is turned on, so that the transistor Q7 is turned on and the DC can be transferred to the pwm controller μ to supply the supply voltage required for its operation. When the switch domain 0N/0FF is low level and indicates off, the transistor (10) is turned off to turn off the transistor, the DC voltage Vdc3 cannot be transmitted to the PWM controller m, and the pWM controller stops working, so the PWM control circuit 24 stops. jobs. The switch control circuit 25 can be used to control whether or not the drive circuit i of the single-string LED lamp 4 is to be operated, and the drive circuit 1 is turned off in a standby power-saving mode or the like, so that the LED lamp 4 is stopped. . The overvoltage protection circuit 26 includes resistors n R11 and R12 and a capacitor C4, wherein the -R of the resistor R11 is drained to the input 41 of the single string Led bulb 4 to receive the second DC voltage =out, resistors RU and R12 Used to divide the voltage to adjust the sampling amount of the second DC voltage. Capacitor G4 uses (4) to remove high noise interference. The overvoltage protection circuit 26 outputs the sampled first DC voltage Vout to the error amplifier EA2 called by the controller for comparison with the threshold voltage Vref2. When the sampled second DC voltage (4) is less than the interval value Vrei2, 'the second DC voltage v〇ut is not overvoltage, so the control simple control circuit 24 is working*, and the sampled second DC voltage v〇ut is greater than When the threshold voltage vreu indicates that the second DC voltage V0ut has an overvoltage, the control circuit (4) stops outputting the PWM signals PWM1 and PWM2. The overvoltage protection circuit sink can provide a first DC voltage Vout _ input to the (10) lamp tube 4 within a certain safety voltage to prevent a second DC voltage when an abnormal problem occurs in the single string (10) lamp tube 4 or its driving circuit 1 _ is too high and may cause the LED tube 4 or its driving circuit to burn out. Fig. 7 is a circuit diagram showing a first example of the overvoltage protection circuit 16 and the compensation control circuit of Fig. 1. Referring to FIG. 7, the PWM control circuit 34 includes a compensation control (4), an output drive circuit 341, and a resistor-capacitor compensation circuit (from the resistor_and capacitor group 12 201143516). The PWM controller U2 is, for example, an SG3525 integrated body EM 1^2. EAf, its 11th and 14th pins are used to output the signal voltage. The universal differential / pin is used to receive the PWM controller u2 to work with two inputs (ie non-inverting input and inverting input (6) rain, wheel-in (ie, inverting input) coupling To the feedback terminal 17, another input f: non-t input) receives the reference power Vrefi. The resistor Μ container Ο of the resistor-capacitor compensation circuit is connected in series with an input terminal of the error amplifier EA1 (ie, the output terminal of the inverting input 々 amplifier EA1, so that the error amplifier EM is a negative feedback architecture and the controller U2 outputs The simple signal 1 and PWM2 enhance their driving capability by the output driving circuit 341 to drive the two transistors in the push-pull converter 21 or 31 shown in Fig. 2 or Fig. 3. Since the PWM control circuit 34 only There is an error amplifier, so the overvoltage protection circuit 36 includes, in addition to the resistors RU and R12 and the capacitor shown in FIG. 6, an operational amplifier OP1 and a transistor q-core overvoltage protection circuit 36 which will pass through the resistor R11. And the second DC voltage v〇ut sampled by R12 is output to the operational amplifier 〇ρι for comparison with the threshold voltage Vref2. When the sampled second DC voltage v〇ut is less than the threshold voltage, the second DC voltage v〇 is expressed. Ut no overvoltage, op amp 〇pi control transistor

Q8 OFF' At this time, whether or not the DC voltage Vdc3 is supplied to the PWM controller U2 is controlled by the switching signal ΟΝ/OFF to control whether the pwm controller U2 or the PWM control circuit 34 operates. When the sampled second DC voltage Vout is greater than the threshold voltage Vref2, it indicates that the second DC voltage Vout has an overvoltage. The operational amplifier 〇ρι controls the transistor Q8 to be turned on, so that the switching signal 〇N/〇FF is pulled low to a low level voltage. On the other hand, the switch is turned off, and the switch signal ON/OFF controls the PWM control circuit 34 to stop operating. Figure 8 is a circuit block diagram of an embodiment of a liquid crystal display of the present invention. Referring to Figure 8, the liquid helium display 5 includes AC to DC (Alternating-Current to Direct- 13 201143516 ♦ &lt;

Current, abbreviated as AC/DC converter 5], main board control circuit 52, panel drive circuit 53 j and single string LED tube 4 and its driving circuit 1 as shown in FIG. 1 , wherein single string LED tube 4 is used as liquid crystal The backlight of the display 3. The liquid crystal display 5 is, for example, a liquid crystal screen, a liquid crystal television, an all-in-one computer in which a computer main body is integrated in a liquid crystal screen, and the like. The AC/DC converter 5^ converts the input AC voltage Vac into DC voltages of different levels and provides (4) Secret 1 and the motherboard control circuit 52. A DC-to-DC (DG/DG) converter is built into the main circuit 52 to convert the input DC voltage to a DC voltage Vdc5 to provide the supply voltage required for the panel drive circuit 53 to operate. The mainboard control circuit 52 outputs a signal (10) and a dimming signal DIM to control the driving circuit 1 to drive the single string LED tube 4, and also outputs a control LVDS control board.

The drive panel displays the image (4). %(四)W The driving circuit of the single string lamp of the present invention uses a push-pull converter = boosts the input low voltage/first DC voltage of 12V-19V into a high DC voltage of the bribe above Providing the power supply required for a single string of LED fresh work, and controlling the current of the single-string LED tube by the current mode and adjusting the brightness of the simple (10) tube; in addition, the present invention uses a single string (10) lamp; Side output and input terminal definition, secret receiving high voltage / second direct current =, input &amp; and · output lamp current is provided back to the control _ output, so that the connector design of the drive circuit can be standardized and better Commonality, and ==:=price_integrated circuit to pull-to-turn, apply the fiber as above, but it is not limited to the spirit and scope of the present invention, when it can be used BRIEF DESCRIPTION OF THE DRAWINGS 201143516 FIG. 1 is a circuit block diagram showing an embodiment of a driving circuit of a single string LED lamp of the present invention. 2 and 3 are circuit diagrams of the first and second embodiments of the push-pull converter u shown in Fig. 1, respectively. Fig. 4 is a circuit diagram showing an embodiment of the dimming control circuit, the current feedback circuit, and the pWM control circuit shown in Fig. 1. Fig. 5 is a timing chart of PWM dimming control of the dimming control circuit, the current feedback circuit, and the pWM control circuit shown in Fig. 4. 6 and 7 are circuit diagrams of the first and second embodiments of the switch control circuit, the overvoltage protection circuit, and the just control circuit shown in Fig. 1, respectively. Figure 8 is a circuit block diagram of an embodiment of a liquid crystal display of the present invention. [Main component symbol description]

11, 2b 31: Push-pull converter 13, 23: current feedback circuit 15, 25: switch control circuit 17: feedback terminal 241, 341: output drive circuit 41: input terminal 5: liquid crystal display 52: main board control Circuits C1 to C4: Capacitors DL1 to DLn: LEDs 1. Single-string LED lamp drive circuit 12' 22: Dimming control circuits 14, 24, 34: PWM control circuits 16, 26, 36: Overvoltage protection circuit 18: Ground terminal 4: Single string LED tube 42: Output terminal 51: AC/DC converter: Panel drive circuit D1~D6, DQ Bu DQ2: Diode 15 201143516 EAl, EA2: Error amplifier 0P1: Operational amplifier R1~ R12: resistor

Ul, U2: PWM controller

Vac : AC voltage

Vfbl: the first feedback voltage

Vin: the first DC voltage

Vr7: detection voltage

Vref2: threshold voltage DIM1, DIM1': inverting dimming signal FB: feedback terminal signal 0N/0FF: switching signal T: dimming period

Toff: off period L1: inductor Q1~Q8: transistor T1: transformer I lamp : lamp current

Vdcl~Vdc5: DC voltage

Vfb2: second feedback voltage

Vout: second DC voltage

Vrefl : Reference voltage Call DIM : Dimming signal DIM2 : In-phase dimming signal LVDS : Control signal PWM1, PWM2 : PWM signal

Ton: On period 16

Claims (1)

201143516 VII. Patent application scope: 1. The drive circuit of the early string light-emitting diode lamp f, the single input end and one round of the 矬 九 九 九 九 一 具有 具有 该 该 该 该 该 该 该 该The driving circuit of the tube comprises: a dimming control circuit, and receiving the pulse width modulation one cycle includes: during the opening period and the second closing period, the current signal feedback circuit is connected in series with the dimming control circuit During the opening period, the dimming control circuit controls the:=== detecting the single-string LED lamp=the dimming control circuit controls the output terminal and the grounding=:off=current feedback circuit is not detected _ The lamp current ramp control circuit 'reduced to the feedback terminal, in the receiving position - feedback voltage temple, the phase i (10) degree wide modulation signal, stop receiving output when receiving the second feedback a pulse width modulation signal; and a push-pull converter, which is connected to the input terminal and the pulse width modulation control circuit, and receives a first DC power when receiving the pulse width modulation signals Boost to a second DC voltage to output to the input The terminal 'stops switching when the pulse width modulation signals are not received and no longer outputs the second DC voltage. σ, 2. The driving circuit of the single-string LED lamp according to the above-mentioned patent application, wherein the pulse width modulation control circuit comprises: ^ - pulse width modulation control H 'including-error amplification II The error has a two-input and an output, wherein one input is coupled to the feedback terminal, and the other input receives a reference voltage, the reference voltage being equal to the first feedback voltage and less than the The second feedback 17 201143516 voltage 'the error amplifier controls the pulse width modulation controller to output the pulse width modulation signals when the voltage of the feedback terminal is equal to the reference voltage, and the voltage at the feedback terminal is greater than the » reference voltage The control δ Xuan pulse width modulation controller is shut down to output the pulse width modulation signals; and a &quot; resistor-capacitor compensation circuit is secreted to the error input || the input terminal and the output end of the error amplifier Between, the error amplifier is made into a negative feedback architecture. 3. The single-light-emitting diode lamp 嶋 circuit, a first one-way conduction component; one mesh=, receiving the dimming signal, and outputting a dimming signal inverting the dimming signal through the first - the unidirectional conduction element is lightly connected to the end ^ the 嶋 to the feedback first-class feedback string is connected between the output end and the ground end, according to the phase dimming signal is turned on during the opening period to win __^__^= t The current is fed back to the flat-line LED 2 _ tube _ dynamic circuit, a second unidirectional conduction element; and the ground end - __ = ^ = 201143516 a feedback voltage Up to the feedback terminal 'stops outputting the first feedback voltage to the feedback terminal during the shutdown period. 5. The driving circuit of the single-string LED lamp according to claim 1, further comprising a switch control circuit that is lightly connected to the pulse width modulation control circuit to receive a switch signal 'Control whether the pulse width modulation control circuit operates according to the switching signal. 6. The driving circuit of the single-string LED lamp of claim 1, further comprising an overvoltage protection circuit coupled to the input terminal and the pulse width modulation control The circuit 'controls the pulse width modulation control circuit to stop outputting the pulse width modulation signals when the second DC voltage is greater than a threshold voltage. 7. The driving circuit of the single-string LED lamp of claim 1, wherein the single-string LED lamp is suitable for backlighting of a liquid crystal display. 8. The driving circuit of a single-string light-emitting diode lamp according to claim 7, wherein the liquid crystal display comprises a liquid crystal screen. 9. The first diode lamp _ road, its A driving circuit, wherein the liquid crystal display of the single-string LED lamp of the seventh aspect of the invention comprises an all-in-one computer.