WO2015096753A1 - 一种led恒流驱动器 - Google Patents

一种led恒流驱动器 Download PDF

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Publication number
WO2015096753A1
WO2015096753A1 PCT/CN2014/094878 CN2014094878W WO2015096753A1 WO 2015096753 A1 WO2015096753 A1 WO 2015096753A1 CN 2014094878 W CN2014094878 W CN 2014094878W WO 2015096753 A1 WO2015096753 A1 WO 2015096753A1
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Prior art keywords
control unit
constant current
voltage
constant
led
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PCT/CN2014/094878
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English (en)
French (fr)
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余世伟
朱元
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欧普照明股份有限公司
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Publication of WO2015096753A1 publication Critical patent/WO2015096753A1/zh

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/395—Linear regulators
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
    • Y02B20/30—Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Definitions

  • the invention relates to a constant current driver, in particular to a constant current driving circuit of a lighting device.
  • LED has long life, high luminous efficiency and low power.
  • Single-pole power factor adjustment (PFC) circuits are often used to drive LEDs in LED driver power supplies. Such circuits are simple and low cost.
  • Existing unipolar PFC circuits are typically used in two ways. The first type is a direct output constant current. In this way, the output current has a large ripple, which requires large-capacity electrolytic capacitor filtering, resulting in an increase in the size and cost of the circuit.
  • the second type as disclosed in Chinese Patent Application Publication No. CN102843808A, discloses a light-emitting diode constant current driver comprising a single-stage PFC circuit, an adjustment tube, and a control unit.
  • the input end of the single-stage PFC circuit is connected to the power source, and the light-emitting diode and the adjusting tube are connected in series between the first output end and the second output end, the anode of the LED is connected to the first output end, and the cathode is connected to the first end of the adjusting tube.
  • the second end of the adjustment tube is connected to the second output end of the single-stage PFC circuit, and the control end is connected to the control unit.
  • the control unit can control the current flowing in the adjustment tube to stabilize, change the load characteristic of the single-stage PFC circuit connection, reduce the load current ripple of the single-stage PFC circuit, thereby reducing the output signal feedback of the single-stage PFC circuit to
  • the error at the input of the current closed-loop control circuit also reduces the error of the reference reference signal at the input of the current control circuit in the single-stage PFC control circuit, ultimately improving the power factor of the single-stage PFC circuit.
  • the LED load voltage changes, the loss of the regulating tube and the control unit increases, which makes the efficiency of the constant current driver decrease.
  • an LED constant current driver Providing constant current driving for the LED load, comprising a power factor correction unit, a constant voltage control unit and a constant current control unit, the first end of the constant current control unit is connected to the negative end of the LED load, and the constant voltage control unit One end is connected between the constant current control unit and a negative end of the LED load, the constant current control unit controls flow of the LED load current, and the constant voltage control unit controls the first of the constant current control unit The voltage at one end.
  • the constant current control unit includes a switching element and a control circuit of the switching element, the control circuit controlling a current flowing through the switching element to be constant.
  • the switching element of the constant current control unit is a triode
  • the control circuit is connected to the base of the triode, and the control circuit provides a stable voltage such that the triode is linearly turned on.
  • the constant voltage control unit includes a sampling circuit, a first end of the sampling circuit is connected to a collector of the triode, and the constant voltage control unit controls a voltage of the collector of the triode.
  • the constant current control unit further includes at least one sampling resistor, the first end of the sampling resistor is connected to the emitter of the triode, and the second end is grounded.
  • the control circuit of the constant current control unit includes a voltage stabilizing tube and a current limiting circuit, the first end of the voltage stabilizing tube is connected to the base of the triode, and the second end is connected to the second end of the sampling resistor.
  • the first end of the current limiting circuit is connected to the base of the triode and the first end of the voltage stabilizing tube, and the second end is connected to a voltage.
  • control circuit of the constant current control unit includes an operational amplifier and a current limiting circuit, and the constant voltage control unit and the constant current control unit share an operational amplifier.
  • the operational amplifier includes a first output connected to the first end of the constant voltage control unit, a first input negative terminal connected to the second end of the constant voltage control unit, and a first input connected to a first reference voltage.
  • the terminal is positive, thereby feeding back a signal to the constant voltage control unit to control the power factor correction unit.
  • the operational amplifier further includes a voltage source input connected to a stable voltage source, a second input positive terminal connected to a second reference voltage, and a sampling resistor connected to the constant current control unit. a second input terminal and a second output end of the current limiting circuit connected to the constant current control unit, the first end of the current limiting circuit is connected to the second output end of the operational amplifier, and the second end is connected to the triode The base of the.
  • the LED constant current driver of the present invention has the following advantages: high efficiency and low ripple of the constant current LED driver are realized by a simple circuit.
  • FIG. 1 is a schematic structural view of an LED constant current driver according to the present invention.
  • FIG. 2 is a circuit diagram of a first preferred embodiment of an LED constant current driver of the present invention.
  • FIG. 3 is a circuit diagram of a second preferred embodiment of the LED constant current driver of the present invention.
  • an LED constant current driver of the present invention provides constant current driving for an LED load, including a power factor correction unit, a constant voltage control unit, and a constant current control unit.
  • the first end of the constant current control unit is connected to the negative end of the LED load, and one end of the constant voltage control unit is connected between the constant current control unit and the negative end of the LED load, and the constant current control unit controls the current flowing through the LED load, and the constant voltage control The unit controls the voltage at the first end of the constant current control unit.
  • the LED constant current driver of the invention uses a power factor correction unit to supply voltage to the LED load, and provides a constant current control unit to connect the negative end of the LED load to control the current constant current flowing through the LED load, and the constant current control unit can effectively suppress the flow. Current ripple across the LED load.
  • a constant voltage control unit is provided to control the voltage between the constant current control unit and the negative terminal of the LED load, so that the voltage of the constant current control unit does not change with the change of the LED load voltage, thereby enabling constant current control.
  • the power consumption of the unit is constant, which improves the efficiency of the LED constant current driver.
  • the LED constant current driver of the invention realizes high efficiency and low ripple for the power factor adjustment circuit by using a simple circuit.
  • FIG. 2 is an LED constant current driver 1 according to a first preferred embodiment of the present invention, which provides constant current driving for the LED load.
  • LED constant current driver 1 includes power factor correction Element 10, constant voltage control unit 11 and constant current control unit 12.
  • the first end of the constant current control unit 12 is connected to the negative end of the LED load, and one end of the constant voltage control unit 11 is connected between the constant current control unit 12 and the negative end of the LED load.
  • the constant current control unit 12 controls the flow of the LED load current, and the constant voltage control unit 11 controls the voltage of the first end of the constant current control unit 12.
  • the constant current control unit 12 includes a switching element Q3 and a control circuit 120 of the switching element Q3.
  • the control circuit 120 controls the current flowing through the switching element Q3 to be constant.
  • the switching element Q3 of the constant current control unit 12 is a linear adjustment tube.
  • the switching element Q3 is a triode.
  • the switching element Q3 may also be a MOS tube or other type of adjustment tube.
  • the control circuit 120 is connected to the base of the switching element Q3, and the control circuit 120 provides a stable voltage so that the switching element Q3 is linearly turned on.
  • the constant voltage control unit 11 includes a sampling circuit 110, the first end of which is connected to the collector of the switching element Q3, and the constant voltage control unit 12 controls the voltage of the collector of the switching element Q3.
  • the constant current control unit 12 also includes at least one sampling resistor R30.
  • the first end of the sampling resistor R30 is connected to the emitter of the switching element Q3, and the second end is grounded.
  • the control circuit 120 includes a Zener diode Z1 and a current limiting circuit 121.
  • the first end of the Zener diode Z1 is connected to the base of the switching element Q3, and the second end is connected to the second end of the sampling resistor R30.
  • the first end of the current limiting circuit 121 is connected to the base of the switching element Q3 and the first of the Zener Z1 The second end is connected to a voltage source VCC to access a voltage.
  • the current limiting circuit 121 includes a resistor R26. In other embodiments, the current limiting circuit 121 may also include multiple resistors or be composed of more electronic components.
  • the LED load is composed of a plurality of LED particles, and the resistor R26, the Zener diode Z1, and the voltage source VCC provide a reference stable voltage Vref for the switching element Q3.
  • the voltage source VCC is a stable voltage source, and the resistor R26 and the voltage source VCC supply the operating current of the Zener diode Z1 and the switching element Q3.
  • the sampling resistor R30 is a current sampling resistor.
  • the capacitor C13, the resistors R27, R29, the capacitor C14, and the Zener diode U3 constitute a constant voltage control unit to control the power factor correction unit 10 to thereby control the constant current control unit 12.
  • the voltage so that the negative voltage of the LED load remains unchanged in any case, is Vc.
  • the base emitter voltage difference of the switching element Q3 is Vbe.
  • the current flowing through the LED load and the collector current Ic Ir+Ib of the switching element Q3, Ib is the driving current of the switching element Q3, and the value is negligibly small and remains unchanged. Then Ic remains unchanged, and finally the drive current Io flowing through the LED load remains constant.
  • the constant voltage control circuit 11 controls the collector voltage Vc of the switching element Q3.
  • Vc (R27/R29+1)*Vr
  • the collector voltage Vc can be changed according to changes in the resistors R27 and R29 and the Zener diode U3.
  • the constant current control unit 12 can well control the power frequency ripple of the current flowing through the LED load, and on the other hand, the LED is sampled by the constant voltage control unit 11.
  • the negative voltage of the load that is, the voltage of the constant current control circuit 12, effectively controls the loss of the constant current control circuit 12, and the efficiency of the entire LED driver is increased.
  • FIG. 3 is an LED constant current driver 2 according to a second preferred embodiment of the present invention, which provides constant current driving for the LED load.
  • the LED constant current driver 2 includes a power factor correction unit 20, a constant voltage control unit 21, and a constant current control unit 22.
  • the first end of the constant current control unit 22 is connected to the negative end of the LED load, and one end of the constant voltage control unit 21 is connected between the constant current control unit 22 and the negative end of the LED load.
  • the constant current control unit 22 controls the flow of the LED load current, and the constant voltage control unit 21 controls the voltage of the first end of the constant current control unit 22.
  • the constant current control unit 22 includes a switching element Q3 and a control circuit 220 of the switching element Q3.
  • the control circuit 220 controls the current flowing through the switching element Q3 to be constant.
  • the switching element Q3 of the constant current control unit 22 is a linear adjustment tube.
  • the switching element Q3 is a triode.
  • the switching element Q3 may also be a MOS tube or other type of adjustment tube.
  • the control circuit 220 is connected to the base of the switching element Q3, and the control circuit 220 supplies a stable voltage so that the switching element Q3 is linearly turned on.
  • the constant voltage control unit 21 includes a sampling circuit 210, the first end of which is connected to the collector of the switching element Q3, and the constant voltage control unit 22 controls the voltage of the collector of the switching element Q3.
  • the constant current control unit 22 also includes at least one sampling resistor R30.
  • the first end of the sampling resistor R30 is connected to the emitter of the switching element Q3, and the second end is grounded.
  • the control circuit 220 of the constant current control unit 22 includes an operational amplifier U4 and a current limiting circuit 221.
  • the constant voltage control unit 21 and the constant current control unit 22 share the operational amplifier U4.
  • the current limiting circuit 221 includes a resistor R24.
  • the current limiting circuit 221 may further include a plurality of resistors or other current limiting components.
  • the operational amplifier U4 includes a first output terminal OUT1 (pin 1) connected to the first end of the constant voltage control unit 21, a first input terminal negative terminal IN1- (pin 2) connected to the second end of the constant voltage control unit 21, and a first connection
  • the first input terminal of the reference voltage REF is positively charged IN1+ (pin 3), thereby feeding back a signal to the constant voltage control unit 21 to control the power factor correction unit 20.
  • the operational amplifier U4 further includes a voltage source input terminal VCC (pin 8) connected to a stable voltage source VCC, a second input terminal positive terminal IN2+ (pin 5) connected to a second reference voltage REF2, and a constant current control unit 22 connected thereto.
  • the second input terminal of the sampling resistor R30, the negative terminal IN2-(pin 6) and the second output terminal OUT2 (pin 7) of the current limiting circuit 221 of the constant current control unit 22 are connected.
  • the first end of the current limiting circuit 221 is connected to the second output terminal OUT2 of the operational amplifier U4, and the second end is connected to the base of the transistor Q3.
  • the constant current control circuit 22 further includes a filter circuit 222, and the filter circuit 222 includes a capacitor C23 and a resistor R28.
  • the filter circuit 222 is connected to the connection of the operational amplifier U4. Between pin 6 and sampling resistor R30. Pin 4 of operational amplifier U4 is grounded.
  • the operational amplifier U4 controls the switching element Q3 to be turned on
  • the first reference voltage REF is an externally stable voltage reference source.
  • the stable voltage source VCC supplies power to the operational amplifier U4, and supplies a drive current to the switching element Q3 through the current limiting circuit 221.
  • the current Ir on the sampling resistor R30 flows through the sampling resistor R30 to generate a voltage signal Vr.
  • the constant voltage control unit 21 includes a PI adjusting circuit composed of capacitors C22, C14, and R36, and further includes resistors R21 and R31.
  • Capacitor C14 and operational amplifier U4 form a CV control unit that controls power factor correction unit 20 such that the lower terminal voltage of the LED load remains constant in any case, at voltage Vc.
  • the resistors R21 and R31 are sampling resistors of the voltage Vc, and the first reference voltage REF is an externally stable voltage reference source.
  • the voltage Vc (R21 / R31 + 1) * REF, wherein changing the resistances R21, R31 can change the set value of the voltage Vc.
  • the constant current control circuit 22 effectively suppresses the ripple of the current flowing through the LED load.
  • the collector voltage Vc of the switching element Q3 is controlled to be (R21/R31+1)*REF, and the voltage Vc can be changed according to the change of the resistors R21, R31 and the first reference voltage REF, and the circuit can be operated normally.
  • the second reference voltage REF2 is an applied voltage reference source

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Abstract

本发明公开了一种LED恒流驱动器，为LED负载提供恒流驱动，包括功率因数校正单元、恒压控制单元以及恒流控制单元，所述恒流控制单元的第一端连接所述LED负载的负端，所述恒压控制单元的一端连接所述恒流控制单元与所述LED负载的负端之间，所述恒流控制单元控制流过所述LED负载电流，所述恒压控制单元控制所述恒流控制单元的第一端的电压。

Description

一种LED恒流驱动器 技术领域
本发明涉及一种恒流驱动器，尤其指一种照明装置的恒流驱动电路。
背景技术
LED具有寿命长，光效高，低功率等特点。在LED驱动电源中常采用单极功率因数调整(PFC)电路来驱动LED，这样的电路简单，成本低。现有的单极PFC电路通常采用两种方式。第一种为直接输出恒流，这种方式输出电流的纹波大，需要大容量的电解电容滤波，从而导致电路的体积和成本增大。第二种，如中国专利申请公开第CN102843808A号公开了一种发光二极管恒流驱动器，该驱动器包括单级PFC电路、调整管、以及控制单元。单级PFC电路的输入端与电源连接，第一输出端和第二输出端之间串接有发光二极管和调整管，LED的阳极与第一输出端相连，阴极与调整管的第一端相连，调整管的第二端与单级PFC电路的第二输出端相连，控制端与控制单元相连。该控制单元能够控制调整管中流过的电流达到稳定，改变了单级PFC电路连接的负载特性，减小单级PFC电路的负载电流纹波，从而减小了单级PFC电路的输出信号反馈至电流闭环控制电路的输入端的误差，也减小了单级PFC控制电路中电流控制电路输入端的基准参考信号的误差，最终提高了单级PFC电路的功率因数。然而这种恒流驱动器在LED负载电压变化时，调整管及控制单元的损耗会增大，使得恒流驱动器的效率降低。
因此，为了克服上述缺陷，有必要提供一种改进的LED恒流驱动器。
发明内容
本发明的目的在于提供一种LED恒流驱动器。
为了实现上述目的，本发明采用如下技术方案：一种LED恒流驱动器， 为LED负载提供恒流驱动，包括功率因数校正单元、恒压控制单元以及恒流控制单元，所述恒流控制单元的第一端连接所述LED负载的负端，所述恒压控制单元的一端连接于所述恒流控制单元与所述LED负载的负端之间，所述恒流控制单元控制流过所述LED负载电流，所述恒压控制单元控制所述恒流控制单元的第一端的电压。
优选地，所述恒流控制单元包括开关元件以及开关元件的控制电路，所述控制电路控制流过所述开关元件的电流恒定。
优选地，所述恒流控制单元的开关元件为三极管，所述控制电路连接所述三极管的基极，所述控制电路提供稳定电压使得所述三极管线性导通。
优选地，所述恒压控制单元包括采样电路，所述采样电路的第一端连接所述三极管的集电极，所述恒压控制单元控制所述三极管集电极的电压。
优选地，所述恒流控制单元还包括至少一采样电阻，所述采样电阻的第一端连接所述三极管的发射极，第二端接地。
优选地，所述恒流控制单元的控制电路包括稳压管以及限流电路，所述稳压管第一端连接所述三极管的基极，第二端连接所述采样电阻的第二端，所述限流电路的第一端连接所述三极管的基极以及所述稳压管的第一端，所述第二端接入一电压。
优选地，所述恒流控制单元的控制电路包括运算放大器以及限流电路，所述恒压控制单元和恒流控制单元共用一运算放大器。
优选地，所述运算放大器包括连接所述恒压控制单元第一端的第一输出端、连接所述恒压控制单元第二端的第一输入端负极以及连接一第一参考电压的第一输入端正极，从而给所述恒压控制单元反馈信号以控制所述功率因数校正单元。
优选地，所述运算放大器还包括连接一稳定电压源的电压源输入端、连接一第二参考电压的第二输入端正极、连接所述恒流控制单元的采样电阻的 第二输入端负极以及连接所述恒流控制单元的限流电路的第二输出端，所述限流电路的第一端连接所述运算放大器的第二输出端，第二端连接所述三极管的基极。
相较于现有技术，本发明LED恒流驱动器有以下优点：利用简单的电路实现了恒流LED驱动器的高效率低纹波。
附图说明
图1为本发明LED恒流驱动器的结构示意图。
图2为本发明LED恒流驱动器的第一较佳实施例的电路图。
图3为本发明LED恒流驱动器的第二较佳实施例的电路图。
具体实施方式
请参考图1所示，本发明一种LED恒流驱动器，为LED负载提供恒流驱动，包括功率因数校正单元、恒压控制单元以及恒流控制单元。恒流控制单元的第一端连接LED负载的负端，恒压控制单元的一端连接恒流控制单元与LED负载的负端之间，恒流控制单元控制流过LED负载的电流，恒压控制单元控制恒流控制单元的第一端的电压。本发明LED恒流驱动器利用功率因数校正单元为LED负载提供电压，一方面提供恒流控制单元连接LED负载的负端，以控制流过LED负载的电流恒流，恒流控制单元可以有效抑制流过LED负载的电流纹波。另一方面，提供了恒压控制单元控制恒流控制单元与LED负载负端之间的电压，从而使得恒流控制单元的电压不会随着LED负载电压的变化而变化，从而使得恒流控制单元的功耗一定，提高了LED恒流驱动器的效率。本发明LED恒流驱动器利用简单的电路，针对功率因数调整电路实现了高效低纹波。
具体的，请参考图2所示，为本发明第一较佳实施例的LED恒流驱动器1，为LED负载提供恒流驱动。LED恒流驱动器1包括功率因数校正单 元10、恒压控制单元11以及恒流控制单元12。恒流控制单元12的第一端连接LED负载的负端，恒压控制单元11的一端连接恒流控制单元12与LED负载的负端之间。恒流控制单元12控制流过LED负载电流，恒压控制单元11控制恒流控制单元12的第一端的电压。
恒流控制单元12包括开关元件Q3以及开关元件Q3的控制电路120。控制电路120控制流过开关元件Q3的电流恒定。
恒流控制单元12的开关元件Q3为线性调整管。本实施例中开关元件Q3为三极管，其他实施例中，开关元件Q3也可以为MOS管或其他类型的调整管。控制电路120连接开关元件Q3的基极，控制电路120提供稳定电压使得开关元件Q3线性导通。
恒压控制单元11包括采样电路110，采样电路110的第一端连接开关元件Q3的集电极，恒压控制单元12控制开关元件Q3集电极的电压。
恒流控制单元12还包括至少一采样电阻R30。采样电阻R30的第一端连接开关元件Q3的发射极，第二端接地。
控制电路120包括稳压管Z1以及限流电路121。稳压管Z1第一端连接开关元件Q3的基极，第二端连接采样电阻R30的第二端，限流电路121的第一端连接开关元件Q3的基极以及稳压管Z1的第一端，第二端连接一电压源VCC从而接入一电压。本实施例中限流电路121包括电阻R26，其他实施例中，限流电路121也可以包括多个电阻或由更多的电子元件组成。
LED负载由若干LED颗粒组成，电阻R26、稳压管Z1、以及电压源VCC为开关元件Q3提供基准稳定电压Vref。电压源VCC为一稳定的电压源，电阻R26和电压源VCC提供稳压管Z1和开关元件Q3的工作电流。采样电阻R30为电流采样电阻。
本实施例中，电容C13、电阻R27、R29、电容C14以及稳压管U3构成恒压控制单元，以控制功率因数校正单元10从而控制恒流控制单元12的 电压，使LED负载的负端电压在任何情况下保持不变，为Vc。稳压管U3提供一个稳定的电压参考Vr，电阻R27、R29为电压Vc的采样电阻。其中Vc＝(R27/R29+1)*Vr，因此改变电阻R27、R29即可以改变电压Vc的设定值。开关元件Q3基极发射极电压差为Vbe。
在系统稳定状态时，采样电阻R30上的电流为Ir＝(Vref-Vbe)/R30，基准稳定电压Vref及开关元件Q3的基极发射极电压差Vbe以及采样电阻R30均为恒定参数，则采样电阻R30上电流Ir保持恒定。此时流过LED负载的电流与开关元件Q3的集电极电流Ic＝Ir+Ib，Ib为开关元件Q3的驱动电流，数值很小可忽略，且保持不变。则Ic保持不变，最终流过LED负载的驱动电流Io保持恒定不变。
另一方面，恒压控制电路11控制开关元件Q3的集电极电压Vc。Vc＝(R27/R29+1)*Vr，根据电阻R27、R29及稳压管U3的改变，可以改变集电极电压Vc。在满足电路能正常工作时，集电极电压Vc取值可设置的很小，则恒流控制单元12的损耗P＝Vc×Io很小，为恒定值，并且和LED负载电压变化无关。
以上可以看出，通过控制开关元件Q3工作于线性工作状态，使得恒流控制单元12能够很好的控制流过LED负载的电流的工频纹波，另一方面通过恒压控制单元11采样LED负载负端即恒流控制电路12的电压，有效控制了恒流控制电路12的损耗，整个LED驱动器的效率增高。
具体地，请参考图3所示，为本发明第二较佳实施例的LED恒流驱动器2，为LED负载提供恒流驱动。LED恒流驱动器2包括功率因数校正单元20、恒压控制单元21以及恒流控制单元22。恒流控制单元22的第一端连接LED负载的负端，恒压控制单元21的一端连接恒流控制单元22与LED负载的负端之间。恒流控制单元22控制流过LED负载电流，恒压控制单元21控制恒流控制单元22的第一端的电压。
恒流控制单元22包括开关元件Q3以及开关元件Q3的控制电路220。控制电路220控制流过开关元件Q3的电流恒定。
恒流控制单元22的开关元件Q3为线性调整管。本实施例中开关元件Q3为三极管，其他实施例中，开关元件Q3也可以为MOS管或其他类型的调整管。控制电路220连接开关元件Q3的基极，控制电路220提供稳定电压使得开关元件Q3线性导通。
恒压控制单元21包括采样电路210，采样电路210的第一端连接开关元件Q3的集电极，恒压控制单元22控制开关元件Q3集电极的电压。
恒流控制单元22还包括至少一采样电阻R30。采样电阻R30的第一端连接开关元件Q3的发射极，第二端接地。
恒流控制单元22的控制电路220包括运算放大器U4以及限流电路221。恒压控制单元21和恒流控制单元22共用运算放大器U4。本实施例中，限流电路221包括电阻R24，其他实施例中，限流电路221还可以包括多个电阻或者其他限流元件。
运算放大器U4包括连接恒压控制单元21第一端的第一输出端OUT1(接脚1)、连接恒压控制单元21第二端的第一输入端负极IN1-(接脚2)以及连接第一参考电压REF的第一输入端正极IN1+(接脚3)，从而给恒压控制单元21反馈信号以控制功率因数校正单元20。
运算放大器U4还包括连接一稳定电压源VCC的电压源输入端VCC(接脚8)、连接一第二参考电压REF2的第二输入端正极IN2+(接脚5)、连接恒流控制单元22的采样电阻R30的第二输入端负极IN2-(接脚6)以及连接恒流控制单元22的限流电路221的第二输出端OUT2(接脚7)。限流电路221的第一端连接运算放大器U4的第二输出端OUT2，第二端连接三极管Q3的基极。本实施例中，恒流控制电路22还包括滤波电路222，滤波电路222包括电容C23及电阻R28。滤波电路222连接于运算放大器U4的接 脚6和采样电阻R30之间。运算放大器U4的接脚4接地。
本实施例中，运算放大器U4控制开关元件Q3导通，第一参考电压REF为外加稳定的电压参考源。稳定电压源VCC给运算放大器U4供电，并通过限流电路221给开关元件Q3提供驱动电流。采样电阻R30上的电流Ir流过采样电阻R30，而产生电压信号Vr。电压信号Vr与运算放大器U4的第二参考电压REF2比较运算，产生驱动信号从而控制开关元件Q3，使Vr＝REF2，从而使得采样电阻R30上的电流Ir＝REF2/R30，为恒定值。
恒压控制单元21包括电容C22、C14、R36组成的PI调节电路，还包括电阻R21、R31。电容C14和运算放大器U4构成CV控制单元，控制功率因数校正单元20，使LED负载的下端电压在任何情况下保持不变，为电压Vc。电阻R21、R31为电压Vc的采样电阻，第一参考电压REF为外加稳定的电压参考源。从而电压Vc＝(R21/R31+1)*REF，其中改变电阻R21、R31可以改变电压Vc的设定值。
在系统稳定状态时，采样电阻R30上的电流为Ir＝REF2/R30，第二参考电压REF2和采样电阻R30均为恒定参数，因而采样电阻R30上电流Ir保持恒定。LED负载的电流与开关元件Q3的集电极电流Ic＝Ir+Ib，(其中Ib为开关元件Q3基极驱动电流，数值很小可忽略，且保持不变)。则Ic保持不变，最终LED负载的驱动电流Io＝REF2/R30保持恒定不变。以上可以看出，恒流控制电路22有效抑制流过LED负载的电流的纹波。
另一方面，控制开关元件Q3的集电极电压Vc＝(R21/R31+1)*REF，根据电阻R21、R31、第一参考电压REF的改变，可改变电压Vc，且在满足电路能正常工作时，电压Vc取值可设置值很小。因此可以看出通过恒压控制电路21控制LED负载负端的电压，恒流控制电路22的损耗P＝Vc×Io很小，为恒定值，且和LED负载电压变化无关。
并且本实施例中，由于第二参考电压REF2为外加电压参考源，该参考 源值可以自由设定，而LED负载的驱动电流Io＝REF2/R30，第二参考电压REF2和电阻R30的精度直接影响LED的电流精度。因此提供一个高精度的第二参考电压REF2，则可以很容易的保证LED负载的电流高精度。
应当注意的是，本发明的实施例有较佳的实施性，且并非对本发明作任何形式的限制，任何熟悉该领域的技术人员可能利用上述揭示的技术内容变更或修饰为等同的有效实施例，但凡未脱离本发明技术方案的内容，依据本发明的技术实质对以上实施例所作的任何修改或等同变化及修饰，均仍属于本发明技术方案的范围内。

Claims (9)

  1. 一种LED恒流驱动器，为LED负载提供恒流驱动，包括功率因数校正单元、恒压控制单元以及恒流控制单元，所述恒流控制单元的第一端连接所述LED负载的负端，所述恒压控制单元的一端连接于所述恒流控制单元与所述LED负载的负端之间，所述恒流控制单元控制流过所述LED负载电流，所述恒压控制单元控制所述恒流控制单元的第一端的电压。
  2. 如权利要求1所述的LED恒流驱动器，其特征在于：所述恒流控制单元包括开关元件以及开关元件的控制电路，所述控制电路控制流过所述开关元件的电流恒定。
  3. 如权利要求2所述的LED恒流驱动器，其特征在于：所述恒流控制单元的开关元件为三极管，所述控制电路连接所述三极管的基极，所述控制电路提供稳定电压使得所述三极管线性导通。
  4. 如权利要求3所述的LED恒流驱动器，其特征在于：所述恒压控制单元包括采样电路，所述采样电路的第一端连接所述三极管的集电极，所述恒压控制单元控制所述三极管集电极的电压。
  5. 如权利要求4所述的LED恒流驱动器，其特征在于：所述恒流控制单元还包括至少一采样电阻，所述采样电阻的第一端连接所述三极管的发射极，第二端接地。
  6. 如权利要求5所述的LED恒流驱动器，其特征在于：所述恒流控制单元的控制电路包括稳压管以及限流电路，所述稳压管第一端连接所述三极管的基极，第二端连接所述采样电阻的第二端，所述限流电路的第一端连接所述三极管的基极以及所述稳压管的第一端，所述第二端接入一电压。
  7. 如权利要求5所述的LED恒流驱动器，其特征在于：所述恒流控制单元 的控制电路包括运算放大器以及限流电路，所述恒压控制单元和恒流控制单元共用一运算放大器。
  8. 如权利要求7所述的LED恒流驱动器，其特征在于：所述运算放大器包括连接所述恒压控制单元第一端的第一输出端、连接所述恒压控制单元第二端的第一输入端负极以及连接一第一参考电压的第一输入端正极，从而给所述恒压控制单元反馈信号以控制所述功率因数校正单元。
  9. 如权利要求8所述的LED恒流驱动器，其特征在于：所述运算放大器还包括连接一稳定电压源的电压源输入端、连接一第二参考电压的第二输入端正极、连接所述恒流控制单元的采样电阻的第二输入端负极以及连接所述恒流控制单元的限流电路的第二输出端，所述限流电路的第一端连接所述运算放大器的第二输出端，第二端连接所述三极管的基极。
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