CN109788596B - Low-THD LED driver - Google Patents
Low-THD LED driver Download PDFInfo
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- CN109788596B CN109788596B CN201711113044.5A CN201711113044A CN109788596B CN 109788596 B CN109788596 B CN 109788596B CN 201711113044 A CN201711113044 A CN 201711113044A CN 109788596 B CN109788596 B CN 109788596B
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Abstract
A low THD LED driver comprising a transformer (102), a rectifier (101) and a chip drive power transistor (Q1); the input end of the rectifier (101) is electrically connected with the power supply end, the output end of the rectifier (101) is connected with the collector of the chip driving power tube (Q1) through the primary winding of the transformer (102), and the emitter of the driving power tube (Q1) is connected with the sampling resistor (R)CS) Grounding; the LED driver further comprises an LED driving chip (100); the LED driving chip (100) comprises a sampling module (111) which is electrically connected with an emitter of the driving power tube (Q1) and used for acquiring a peak voltage at the emitter of the driving power tube (Q1), and a BCM control module (117) which is electrically connected with a base of the driving power tube (Q1) and used for controlling the on and off of the driving power tube (Q1). The system architecture of the invention is simpler than the prior art, and the system cost can be optimized.
Description
Technical Field
The invention relates to the field of circuits, in particular to a low-THD LED driver.
Background
In the existing LED light source, a driving circuit is not a two-stage circuit topology scheme of a high power factor PF and a low harmonic distortion THD, and output ripples are very high. Because PF is generally not high, cause current harmonic distortion THD too big, this pollutes the electric wire netting seriously, the reactive power that the concrete expression was done to the electric wire netting is too big, the loss at the public line of electric wire netting is big. And power is because of PF is not high, and current harmonic distortion THD is too big, still can make output current ripple too big, seriously influences LED's light source characteristic, and this current ripple can make the fluorescent tube take place stroboscopic phenomenon, and it is very big to human eyes injury, seriously harm human health.
Disclosure of Invention
The invention provides an LED driver with low THD aiming at the technical problems.
The technical scheme provided by the invention is as follows:
the invention provides an LED driver, which comprises a transformer, a rectifier and a chip driving power tube, wherein the transformer is connected with the rectifier; the input end of the rectifier is electrically connected with a power supply end, the output end of the rectifier is connected with a collector of a power tube through a primary winding chip of a transformer, the power tube is driven (an emitter of a Q1 is grounded through a sampling resistor, a secondary winding of the transformer is connected with an LED load to form a load loop, the output end of the rectifier is grounded through a protection resistor, a voltage stabilizing diode and an auxiliary winding, and the anode of the voltage stabilizing diode is grounded after passing through a first voltage dividing resistor and a second voltage dividing resistor in sequence;
the LED driver also comprises an LED driving chip, the LED driving chip comprises a sampling module, a ZCD detection module, a first multiplier, an error amplifier and an input voltage detection module, wherein the sampling module is electrically connected with an emitting electrode of the driving power tube and used for acquiring peak voltage at the emitting electrode of the driving power tube, the ZCD detection module is electrically connected with a connecting point between the first voltage-dividing resistor and the second voltage-dividing resistor and used for detecting ZCD waveform of pin input voltage at the connecting point between the first voltage-dividing resistor and the second voltage-dividing resistor so as to output a duty ratio D, the first multiplier is respectively electrically connected with the sampling module and the ZCD detection module and used for multiplying the duty ratio D and the peak voltage, the error amplifier is electrically connected with the first multiplier and used for carrying out error operation on a calculation output result of the first multiplier and a chip reference voltage, and the input voltage detection module is electrically connected with a connecting point between the first voltage-dividing resistor and the second voltage-, the device comprises a triangular wave generator, a comparator and a BCM control module, wherein the triangular wave generator is electrically connected with the input voltage detection module and used for acquiring pin input voltage and outputting a triangular wave with a slope corresponding to the pin input voltage, the comparator is respectively electrically connected with the triangular wave generator and the error amplifier and used for comparing the triangular wave output by the triangular wave generator with an output result of the error amplifier, the BCM control module is electrically connected with the comparator and a base electrode of the driving power tube and used for controlling the conduction and the disconnection of the driving power tube according to the output result of the comparator.
In the LED driver of the present invention, the two ends of the primary winding of the transformer are connected in parallel to the clamping circuit.
In the above LED driver of the present invention, the clamping circuit includes a clamping capacitor, a clamping diode and a clamping resistor, the cathode of the clamping diode is connected to the output end of the rectifier through the clamping resistor, and the anode of the clamping diode is connected to the collector of the driving power transistor; the clamp capacitor is connected in parallel to both ends of the clamp resistor.
In the LED driver of the present invention, the output terminal of the error amplifier is grounded after passing through the compensation capacitor.
The LED driver changes the comparison object of the comparator by adopting the triangular wave generator and the input voltage detection module, so that the secondary side current and the voltage output by the rectifier keep a better linear relation, thereby achieving the purposes of reducing THD and improving PF.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
fig. 1 shows a circuit diagram of a prior art isolated LED driver;
FIG. 2 shows a functional block diagram of the LED driver chip of the isolated LED driver shown in FIG. 1;
FIG. 3 shows a schematic diagram of a ZCD waveform detected by the ZCD detection module of the LED driver chip shown in FIG. 2;
fig. 4 shows a schematic diagram of input currents of a prior art LED driver and a preferred embodiment of the present embodiment;
fig. 5 shows a circuit diagram of an LED driver according to a preferred embodiment of the present invention;
fig. 6 illustrates a functional block diagram of an LED driving chip of the LED driver shown in fig. 5;
fig. 7 is a schematic diagram of THD results of the LED driver of the prior art and the present embodiment;
fig. 8 is a graph showing PF results of the LED driver of the prior art and the present embodiment.
Detailed Description
As shown in fig. 1 and 2, fig. 1 shows a circuit diagram of a prior art isolated LED driver; fig. 2 shows a functional block diagram of an LED driving chip of the isolated LED driver shown in fig. 1. The specific working process of the isolated LED driver is as follows: when the chip-driven power tube Q1 is turned on, the primary current I of the transformer 102PWith VinThe slope of/L (L is the inductance of the primary winding of transformer 102) begins to increase, and the voltage V begins to increasecsThen the size is increased; sampling module 111 of LED driving chip 100 detects voltage VCSPeak voltage V ofPKI.e. primary side current IPPeak current I ofPKAnd a resistor RCSThe product of (a); the ZCD detection module 112 detects ZCD waveforms through the auxiliary winding 103, the first voltage dividing resistor R2, and the second voltage dividing resistor R3, so as to obtain information of the duty ratio D; the first multiplier 113 combines the duty ratio D with the peak voltage V detected by the sampling module 111PKThe multiplication is performed to obtain a result V1, i.e., V1 ═ VPKX D; error amplifier 114 couples V1 to chip reference voltage VREFCarrying out error operational amplification to obtain a result VCOMP(ii) a The second multiplier 115 multiplies VCOMPAnd MT (MT is V)inPartial pressure of) is multiplied to obtain a result V2; comparator 116 couples V2 with voltage VcsMaking a comparison when VcsWhen the voltage reaches the value of V2, the chip drives the power tube Q1 to be switched off; when the chip drives the power tube Q1 to be switched off, the primary side current IPWhen the voltage becomes 0, the secondary side of the transformer 102 starts to discharge, and when the secondary side of the transformer 102 discharges, the secondary side current I is caused to flowsWhen the current reaches 0, the LED driving chip 100 determines by detecting the falling edge of the ZCD waveform to obtain the information, so as to start the next cycle, even if the chip driving power transistor Q1 is turned on again, the operating waveform is as shown in fig. 3. When the system is operating steadily, the error amplifier 114 is balanced, and V1 is equal to VREFIs then VPK×D＝VREFBy designing the primary to secondary turns ratio N of the transformer 102PSAnd a resistance RCSThe output current can be obtained:
because the external capacitor C3 at the COMP end of the LED driving chip is relatively large (generally more than 1 uF), the loop bandwidth is very low (only 10Hz), which is much lower than 50Hz of the AC input voltage, so that the voltage at the COMP end is approximately constant in one AC cycle, and then:
VCS,PK＝V2＝MT*VCOMP＝VIN(θ)*VCOMP (2)
wherein, VmIs a Vin(θ) maximum value;
Vm、k、Vcompcan be approximated as a constant over one AC cycle, thus:
When V isacVery big, due to k<<sin (θ), then Iin(θ) ≈ A, approximately constant, as shown in FIG. 4, with the existing isolated LED driver at 264VacUnder input conditions, input current IinIt is approximately constant most of the time and thus THD will become poor.
As shown in fig. 5-6, fig. 5 shows a circuit diagram of an LED driver according to a preferred embodiment of the present invention; fig. 6 illustrates a functional block diagram of an LED driving chip of the LED driver shown in fig. 5. Specifically, the LED driver includes a transformer 102 and a rectifier 101, an input terminal of the rectifier 101 is electrically connected to a power supply terminal, an output terminal of the rectifier 101 drives a collector of a power transistor Q1 through a primary winding chip of the transformer 102, and an emitter of a driving power transistor Q1 drives a collector of the power transistor Q3578 through a sampling resistor RCSGrounding; the secondary winding of the transformer 102 is connected with the LED load to form a load loop; the output end of the rectifier 101 passes through a protective resistor R4, reversely passes through a voltage stabilizing diode D2 and then is grounded through an auxiliary winding 103; the anode of the voltage stabilizing diode D2 is grounded after passing through the first voltage dividing resistor R2 and the second voltage dividing resistor R3 in sequence;
the LED driver further comprises an LED driving chip 100, wherein the LED driving chip 100 is electrically connected with the emitter of the driving power tube Q1 and used for obtaining the peak voltage V at the emitter of the driving power tube Q1PKIs electrically connected with the connection point between the first voltage-dividing resistor R2 and the second voltage-dividing resistor R3, and is used for detecting the pin input voltage F at the connection point between the first voltage-dividing resistor R2 and the second voltage-dividing resistor R3(in) ZCD waveform to output duty ratio D ZCD detection module 112, which is electrically connected with sampling module 111 and ZCD detection module 112 respectively and used for comparing duty ratio D with peak voltage VPKA first multiplier 113 electrically connected to the first multiplier 113 for performing multiplication operation, and used for calculating the output result of the first multiplier 113 and the chip reference voltage VREFAn error amplifier 114 for performing error operation, an input voltage detection module 119 electrically connected to a connection point between the first voltage-dividing resistor R2 and the second voltage-dividing resistor R3 for detecting a pin input voltage f (in), a triangular wave generator 118 electrically connected to the input voltage detection module 119 for obtaining the pin input voltage f (in) and outputting a triangular wave having a slope corresponding to the pin input voltage f (in), and a triangular wave generator 118 electrically connected to the triangular wave generator 118 and the error amplifier 114 for outputting the triangular wave output by the triangular wave generator 118 and an output result V of the error amplifier 114COMPA comparator 116 for performing comparison, and a BCM control module 117 electrically connected to the comparator 116, electrically connected to the base of the driving power transistor Q1, and configured to control the on/off of the driving power transistor Q1 according to an output result of the comparator 116. Here, compared to the existing isolated LED driver as shown in fig. 1 and 2, the LED driver of the present embodiment reduces the resistors R5 and R6, and at the same time, adds the triangular wave generator 118 and the input voltage detection module 119 in the LED driving chip 100. The working process of the LED driver of this embodiment is as follows: the chip drives the power tube Q1 to conduct, and the voltage of the primary winding of the transformer 102 is approximately equal to the input voltage Vin，VD2＝-Vin/NPAWherein N isPAIs the turns ratio of the primary winding of transformer 102 and the auxiliary winding 103; vD2Is the voltage at the anode of the zener diode D2; the input voltage detection module 119 clamps the pin input voltage f (in) to about 0, and at this time, a current flows from the ZCD terminal to the zener diode D2, and the magnitude of the current is Vin/(NPA×R2) Wherein R is2Is the resistance value of the first voltage divider resistor R2; thus, the pin input voltage f (in) has: f (in) ═ α Vin/(NPA×R2) Wherein α is a constant. Further, the slope of the triangular wave is coupled to the input voltage F (in)In this way, the triangular wave has information on the pin input voltage f (in). At the first multiplier 113, its output result V1 ═ VPKAnd (2) x D. Error amplifier 114 then couples V1 and VREFAre compared to obtain VCOMP(ii) a Comparator 116 then couples VCOMPComparing with the triangular wave when the voltage of the triangular wave is greater than VCOMPWhen the power transistor Q1 is turned off, the BCM control module 117 controls the driving power transistor Q1 to be turned off.
Further, in the present embodiment, a clamping circuit is connected in parallel to both ends of the primary winding of the transformer 102, and specifically, the clamping circuit includes a clamping capacitor C4, a clamping diode D3, and a clamping resistor R7, a cathode of the clamping diode D3 is connected to the output end of the rectifier 101 via the clamping resistor R7, and an anode of the clamping diode D3 is connected to a collector of the driving power transistor Q1; a clamp capacitor C4 is connected in parallel to both ends of the clamp resistor R7.
Further, in the present embodiment, as shown in fig. 5 and 6, the output terminal of the error amplifier 114 is grounded via the compensation capacitor C3.
Assuming that the slope of the triangular wave is A-F (in), and referring to FIG. 2, there are:
VmIs a Vin(θ) maximum value;
thus, the primary side current IPPeak current I ofPK(θ) has:
where L is the inductance of the primary winding of transformer 102;
input current Iin(θ) has:
wherein
Is approximately constant
It can be seen that the above formula is one more term of 1/(A- β sin (θ)) than formula (3), and as the AC input of the sine wave increases, Iin(theta) also increases accordingly, as shown in FIG. 4 as 264VacUnder the condition, compared with the averaged input current waveforms, it can be obviously seen that the input current waveform of the embodiment is closer to a sine wave compared with the prior art. FIGS. 7-8 show the THD and PF results of the prior art and this example, respectively, for the present invention at 264VacThe THD is only 8 percent and is obviously better than 13.5 percent of the prior art; on the other hand, the system architecture of the invention is simpler than the prior art, and the system cost can be optimized.
It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.
Claims (4)
1. An LED driver is characterized by comprising a transformer (102), a rectifier (101) and a chip driving power tube (Q1); the input end of the rectifier (101) is electrically connected with the power supply end, the output end of the rectifier (101) is connected with the collector of the chip driving power tube (Q1) through the primary winding of the transformer (102), and the emitter of the driving power tube (Q1) is connected with the sampling resistor (R)CS) Grounding; the secondary winding of the transformer (102) is connected with the LED load to form a load loop; the output end of the rectifier (101) is grounded through the auxiliary winding (103) after passing through a protective resistor (R4) and then reversely passing through a voltage-stabilizing diode (D2); the anode of the voltage stabilizing diode (D2) is grounded after passing through the first voltage dividing resistor (R2) and the second voltage dividing resistor (R3) in sequence;
the LED driver also comprises an LED driving chip (100), the LED driving chip (100) comprises a sampling module (111) which is electrically connected with an emitter of the driving power tube (Q1) and used for acquiring the peak voltage at the emitter of the driving power tube (Q1), a ZCD detection module (112) which is electrically connected with a connection point between a first voltage division resistor (R2) and a second voltage division resistor (R3) and used for detecting the ZCD waveform of a pin input voltage at the connection point between the first voltage division resistor (R2) and the second voltage division resistor (R3) so as to output a duty ratio D, a first multiplier (113) which is electrically connected with the sampling module (111) and the ZCD detection module (112) respectively and used for multiplying the duty ratio D and the peak voltage, an error amplifier (114) which is electrically connected with the first multiplier (113) and used for carrying out error operation on the calculation output result of the first multiplier (113) and the chip reference voltage, the device comprises an input voltage detection module (119) which is electrically connected with a connection point between a first voltage division resistor (R2) and a second voltage division resistor (R3) and used for detecting pin input voltage, a triangular wave generator (118) which is electrically connected with the input voltage detection module (119) and used for acquiring the pin input voltage and outputting a triangular wave with the slope corresponding to the pin input voltage, a comparator (116) which is respectively electrically connected with the triangular wave generator (118) and an error amplifier (114) and used for comparing the triangular wave output by the triangular wave generator (118) with the output result of the error amplifier (114), and a BCM control module (117) which is electrically connected with the comparator (116), electrically connected with the base of a driving power tube (Q1) and used for controlling the on and off of the driving power tube (Q1) according to the output result of the comparator (116).
2. The LED driver of claim 1, wherein a clamping circuit is connected in parallel across the primary winding of the transformer (102).
3. The LED driver of claim 2, wherein the clamping circuit comprises a clamping capacitor (C4), a clamping diode (D3) and a clamping resistor (R7), the cathode of the clamping diode (D3) is connected to the output terminal of the rectifier (101) via the clamping resistor (R7), and the anode of the clamping diode (D3) is connected to the collector of the driving power transistor (Q1); a clamp capacitor (C4) is connected in parallel to both ends of the clamp resistor (R7).
4. The LED driver of claim 1, wherein the output of the error amplifier (114) is grounded via a compensation capacitor (C3).
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| CN111586929A (en) * | 2020-05-28 | 2020-08-25 | 成都航天凯特机电科技有限公司 | Infrared light filling lamp circuit of VCSEL without red explosion |
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| CN102447381B (en) * | 2010-10-11 | 2014-07-16 | 辉芒微电子（深圳）有限公司 | Power factor correcting device and controller and THD attenuator used in the device |
| CN102612229B (en) * | 2012-03-13 | 2014-10-22 | 辉芒微电子（深圳）有限公司 | LED (light emitting diode) light adjusting device and LED light adjusting driving circuit |
| EP2878074A1 (en) * | 2012-07-26 | 2015-06-03 | Osram Sylvania Inc. | Flyback ac-to-dc converter |
| CN109247042B (en) * | 2016-03-31 | 2020-11-10 | 昕诺飞控股有限公司 | AC/DC PFC converter, conversion method and LED driver |
| CN106304500A (en) * | 2016-09-23 | 2017-01-04 | 厦门矿通科技有限公司 | A kind of driving chip for LED illumination power management and drive circuit |
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Non-Patent Citations (1)
| Title |
|---|
| An Improved Current Compensation Method for High PF and Low THD in Digital Boost Power Factor Corrector;Park, MH等;《2017 IEEE 3RD INTERNATIONAL FUTURE ENERGY ELECTRONICS CONFERENCE AND ECCE ASIA (IFEEC 2017-ECCE ASIA)》;20170607;1065-1070页 * |
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Address after: 518057, room 10, building 5-8, Changhong science and technology building, twelve South tech Road, Nanshan District Science Park, Shenzhen, Guangdong Patentee after: Huimang Microelectronics (Shenzhen) Co.,Ltd. Address before: 518057, room 10, building 5-8, Changhong science and technology building, twelve South tech Road, Nanshan District Science Park, Shenzhen, Guangdong Patentee before: FREMONT MICRO DEVICES (SZ) Ltd. |
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