CN105338718B - Linear and PWM (pulse-width modulation) working mode-based L ED (light-emitting diode) constant current driving method and device - Google Patents
Linear and PWM (pulse-width modulation) working mode-based L ED (light-emitting diode) constant current driving method and device Download PDFInfo
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Abstract
本发明公开了一种基于线性与PWM工作模式的LED恒流驱动的方法和装置，该方法是在线性恒流的框架下，采用PWM控制技术，通过改变交流电经过整流以后的脉冲波形的占空比来控制LED负载的电流，能减少功率器件的发热量和提高转换效率，有效解决了现有技术中线性恒流驱动无功功耗大、允许电源电压波动范围小、转换效率低等缺陷，具有电路结构简单、无须电感元件、造价低廉、无EMI等优点。
The present invention discloses a method and device for driving an LED constant current based on a linear and PWM working mode. The method adopts PWM control technology under the framework of linear constant current, controls the current of an LED load by changing the duty cycle of a pulse waveform after rectification of alternating current, can reduce the heat generated by power devices and improve conversion efficiency, effectively solves the defects of linear constant current driving in the prior art, such as large reactive power consumption, small allowable power supply voltage fluctuation range, low conversion efficiency, etc., and has the advantages of simple circuit structure, no need for inductor components, low cost, no EMI, etc.
Description
技术领域technical field
本发明涉及一种照明灯驱动电源，特别是一种LED恒流驱动的方法和装置。The invention relates to a lighting lamp driving power supply, in particular to a LED constant current driving method and device.
背景技术Background technique
在以AC220V/50Hz市电为电源的LED照明灯具中，高压线性恒流驱动方案已经被广泛应用，线性恒流驱动器具有结构简单、造价低廉、无电磁辐射、可靠性高等优点而被业界认可，然而，线性恒流驱动器同时也具有如下不可回避的缺陷：In LED lighting fixtures powered by AC220V/50Hz mains power, the high-voltage linear constant current drive scheme has been widely used. The linear constant current drive has the advantages of simple structure, low cost, no electromagnetic radiation, and high reliability. It has been recognized by the industry. However, the linear constant current driver also has the following unavoidable defects:
1、线性恒流驱动器工作在线性的模式下，与负载(LED光源)串联使用，通过调节自身的压降来控制负载的电流，以达到恒流的目的，线性恒流驱动器自身的压降所产生的无功功率会导致器件发热，效率下降，在应用中必须选用高电压，小电流，低压差的光源，所以，在应用上受到一定程度的限制。1. The linear constant current driver works in the linear mode and is used in series with the load (LED light source). It controls the load current by adjusting its own voltage drop to achieve the purpose of constant current. The voltage drop of the linear constant current driver itself depends on the The reactive power generated will cause the device to heat up and the efficiency will drop. In the application, a light source with high voltage, low current and low dropout voltage must be selected, so the application is limited to a certain extent.
2、线性恒流驱动器允许电源电压的波动幅度比较小，一旦电源波动幅度超出允许范围，将造成效率下降甚至影响正常工作。2. The fluctuation range of the power supply voltage allowed by the linear constant current driver is relatively small. Once the fluctuation range of the power supply exceeds the allowable range, the efficiency will drop or even affect the normal operation.
3、现有的LED光源一般是由若干个LED芯片或灯珠串联而成，单个LED的正向电压为3.2V左右，如果使用线性驱动方案，厂家一般都会以增加灯珠的数量为代价来提高灯串的电压，降低压差，或采用价格较高的高压灯珠，这样导致产品的成本增高。3. The existing LED light source is generally composed of several LED chips or lamp beads in series. The forward voltage of a single LED is about 3.2V. If a linear drive scheme is used, the manufacturer will generally increase the number of lamp beads. Increase the voltage of the light string, reduce the differential pressure, or use higher-priced high-voltage lamp beads, which will increase the cost of the product.
发明内容Contents of the invention
为了克服现有技术的不足，本发明提供一种电路结构简单、无须电感元件、造价低廉、无EMI的基于线性与PWM工作模式的LED恒流驱动方法及装置。In order to overcome the deficiencies of the prior art, the present invention provides an LED constant current driving method and device based on linear and PWM working modes with simple circuit structure, no need for inductive elements, low cost, and no EMI.
本发明解决其技术问题所采用的技术方案是：The technical solution adopted by the present invention to solve its technical problems is:
一种基于线性与PWM工作模式的LED恒流驱动方法，在线性恒流的框架下，采用PWM控制技术，通过改变交流电经过整流以后的脉冲波形的占空比来控制LED负载的电流。A LED constant current driving method based on linear and PWM working modes. Under the framework of linear constant current, PWM control technology is used to control the current of LED load by changing the duty cycle of the pulse waveform after rectification of alternating current.
对交流电整流以后的脉冲波形进行取样，由脉冲控制器产生一组与整流以后的脉冲波形周期同步、频率相同的脉冲信号，通过改变占空比，控制与LED负载串联的半导体功率器件的通断时间，使LED负载电流恒定。Sampling the pulse waveform after AC rectification, and the pulse controller generates a group of pulse signals that are cycle-synchronous and of the same frequency as the rectified pulse waveform, and control the on-off of the semiconductor power device connected in series with the LED load by changing the duty cycle time to make the LED load current constant.
由脉冲控制器产生一组占空比可控的方波信号，对整流后的直流脉冲波形实施调制，通过调制脉冲的占空比去控制与LED负载串联的半导体功率器件的通断时间，使LED负载电流恒定。The pulse controller generates a set of square wave signals with controllable duty ratio, and modulates the rectified DC pulse waveform, and controls the on-off time of the semiconductor power device connected in series with the LED load by modulating the duty ratio of the pulse, so that The LED load current is constant.
对电源电压、LED负载电流、LED负载与电源之间的电压差同时进行信号采样，脉冲控制器根据采样信号，产生合适的脉冲宽度，以达到LED负载恒流目的。The power supply voltage, LED load current, and the voltage difference between the LED load and the power supply are simultaneously sampled, and the pulse controller generates a suitable pulse width according to the sampled signal to achieve the purpose of constant current of the LED load.
一种实现上述方法的基于线性与PWM工作模式的LED恒流驱动装置，该装置包括整流电路、LED负载、PWM控制器、开关电路、电压采样电路和电流采样电路；所述LED负载、开关电路和电流采样电路串联后一端接所述整流电路的正极，另一端接所述整流电路的负极；所述电压采样电路一端接所述整流电路的正极，另一端接所述整流电路的负极；所述PWM控制器的输入端接所述电压采样电路和电流采样电路，输出端接所述开关电路。A LED constant current drive device based on linear and PWM operating modes for realizing the above method, the device includes a rectifier circuit, an LED load, a PWM controller, a switch circuit, a voltage sampling circuit and a current sampling circuit; the LED load, the switch circuit After being connected in series with the current sampling circuit, one end is connected to the positive pole of the rectification circuit, and the other end is connected to the negative pole of the rectification circuit; one end of the voltage sampling circuit is connected to the positive pole of the rectification circuit, and the other end is connected to the negative pole of the rectification circuit; The input terminal of the PWM controller is connected to the voltage sampling circuit and the current sampling circuit, and the output terminal is connected to the switch circuit.
所述开关电路包括N沟道MOS管T1，所述MOS管T1的漏极D接所述LED负载，源极S接所述整流电路的负极，栅极G接所述PWM控制器的输出端；所述MOS管T1的漏极D和源极S之间并联有电阻R6。The switch circuit includes an N-channel MOS transistor T1, the drain D of the MOS transistor T1 is connected to the LED load, the source S is connected to the negative pole of the rectifier circuit, and the gate G is connected to the output terminal of the PWM controller ; A resistor R6 is connected in parallel between the drain D and the source S of the MOS transistor T1.
所述电流采样电路包括NPN型三极管T2和电阻RCS，所述电阻RCS的一端接所述MOS管T1的源极S，另一端接所述整流电路的负极，所述三极管T2的基极B接所述电阻RCS和MOS管T1源极S的结点，发射极E接所述整流电路的负极，集电极C通过电阻R5接所述PWM控制器。The current sampling circuit includes an NPN transistor T2 and a resistor RCS, one end of the resistor RCS is connected to the source S of the MOS transistor T1, the other end is connected to the negative pole of the rectifier circuit, and the base B of the transistor T2 is connected to The junction of the resistor RCS and the source S of the MOS transistor T1, the emitter E is connected to the negative pole of the rectification circuit, and the collector C is connected to the PWM controller through the resistor R5.
所述PWM控制器为电压比较器U1；电压采样电路包括电阻R1、电阻R2、电阻R3和稳压二极管Z1，所述电阻R1和电阻R2串接后一端接所述整流电路的正极，另一端接整所述流电路的负极，所述电阻R3和稳压二极管Z1串接后，电阻R3的另一端接所述整流电路的正极，稳压二极管Z1的另一端接所述流电路的负极，所述电压比较器U1的同相输入端分两路，一路接所述电阻R1和电阻R2的结点，另一路接所述电阻R5，所述电压比较器U1的反向输入端分两路，一路通过电阻R21接所述电阻R3和稳压二极管Z1的结点，另一路通过电阻R22接所述整流电路的负极，电压比较器U1的输出端接所述MOS管T1的栅极G；所述稳压二极管Z1的两端并联有电容C1。The PWM controller is a voltage comparator U1; the voltage sampling circuit includes a resistor R1, a resistor R2, a resistor R3 and a Zener diode Z1, and the resistor R1 and the resistor R2 are connected in series, and one end is connected to the positive pole of the rectifier circuit, and the other end Connect the negative pole of the rectifier circuit, after the resistor R3 and the Zener diode Z1 are connected in series, the other end of the resistor R3 is connected to the positive pole of the rectifier circuit, and the other end of the Zener diode Z1 is connected to the negative pole of the rectifier circuit, The non-inverting input terminal of the voltage comparator U1 is divided into two circuits, one of which is connected to the junction of the resistor R1 and the resistor R2, and the other is connected to the resistor R5, and the reverse input terminal of the voltage comparator U1 is divided into two circuits, One path is connected to the junction of the resistor R3 and the Zener diode Z1 through the resistor R21, the other path is connected to the negative pole of the rectifier circuit through the resistor R22, and the output terminal of the voltage comparator U1 is connected to the gate G of the MOS transistor T1; A capacitor C1 is connected in parallel with both ends of the Zener diode Z1.
所述整流电路的正负极之间连接有滤波电容C2；所述滤波电容C2与所述整流电路的正极之间连接有隔离二极管D5。A filter capacitor C2 is connected between the positive and negative electrodes of the rectifier circuit; an isolation diode D5 is connected between the filter capacitor C2 and the positive electrode of the rectifier circuit.
所述PWM控制器包括三角波发生器U1A、电压比较器U1B，所述电压采样电路包括电阻R12、电阻R9、电阻R10、电阻R13、电阻R14、电阻R15、电阻R16、电阻R17、电阻R18、稳压二极管D6、电容C3和电容C4；所述电阻R12、电阻R9、电阻R10依次串联后，电阻R12的另一端接所述整流电路的正极，电阻R10的另一端接所述整流电路的负极；所述稳压二极管D6和电容C3并联后一端接所述电阻R12和电阻R9的结点，另一端接所述整流电路的负极；所述电阻R13、电阻R14串联后，电阻R13的另一端接所述电阻R12和电阻R9的结点，电阻R14的另一端接所述整流电路的负极；所述电阻R16、电阻R17和电容C4依次串联后，所述电阻R16的另一端接所述电阻R12和电阻R9的结点，所述电容C4的另一端接所述整流电路的负极；所述电阻R15的一端接所述电阻R13和电阻R14的结点，另一端接电阻R16和电阻R17的结点，所述三角波发生器U1A的同相输入端接电阻R13和电阻R14的结点，反向输入端接电阻R17和电容C4的结点，输出端接电阻R16和电阻R17的结点；所述电压比较器U1B的同相输入端接电阻R9和电阻R10的结点，反向输入端接电阻R17和电容C4的结点，输出端接所述开关电路的输入端，所述电阻R18的一端接所述电阻R12和电阻R9的结点，另一端接所述电压比较器U1B的输出端。The PWM controller includes a triangular wave generator U1A, a voltage comparator U1B, and the voltage sampling circuit includes a resistor R12, a resistor R9, a resistor R10, a resistor R13, a resistor R14, a resistor R15, a resistor R16, a resistor R17, a resistor R18, a stable A voltage diode D6, a capacitor C3 and a capacitor C4; after the resistor R12, the resistor R9, and the resistor R10 are connected in series in sequence, the other end of the resistor R12 is connected to the positive pole of the rectifier circuit, and the other end of the resistor R10 is connected to the negative pole of the rectifier circuit; After the voltage stabilizing diode D6 and the capacitor C3 are connected in parallel, one end is connected to the node of the resistor R12 and the resistor R9, and the other end is connected to the negative pole of the rectifier circuit; after the resistor R13 and the resistor R14 are connected in series, the other end of the resistor R13 is connected to The junction of the resistor R12 and the resistor R9, the other end of the resistor R14 is connected to the negative pole of the rectifier circuit; after the resistor R16, the resistor R17 and the capacitor C4 are connected in series, the other end of the resistor R16 is connected to the resistor R12 and the junction of the resistor R9, the other end of the capacitor C4 is connected to the negative pole of the rectifier circuit; one end of the resistor R15 is connected to the junction of the resistor R13 and the resistor R14, and the other end is connected to the junction of the resistor R16 and the resistor R17 point, the non-inverting input terminal of the triangular wave generator U1A is connected to the node of resistor R13 and resistor R14, the reverse input terminal is connected to the node of resistor R17 and capacitor C4, and the output terminal is connected to the node of resistor R16 and resistor R17; The non-inverting input terminal of the voltage comparator U1B is connected to the node of resistor R9 and resistor R10, the inverting input terminal is connected to the node of resistor R17 and capacitor C4, the output terminal is connected to the input terminal of the switch circuit, and one end of the resistor R18 is connected to The other end of the node of the resistor R12 and the resistor R9 is connected to the output end of the voltage comparator U1B.
所述电压采样电路和电流采样电路包括NPN型三极管Q1、电阻RCS1、电阻R7、电阻R8和电阻R20，所述电阻RCS1的一端接所述MOS管T1的源极S，另一端接所述整流电路的负极，所述电阻R7和电阻R8串联后，电阻R7的另一端接所述整流电路的正极，电阻R8接所述整流电路的负极，所述电阻R20的一端接所述电阻R7和电阻R8的结点，另一端分两路，一路接所述三极管Q1的基极，另一路接所述电阻RCS1和开关电路的结点，所述三极管Q1的集电极通过电阻R11接所述电阻R9和电阻R10的结点，集电极所述整流电路的负极。The voltage sampling circuit and the current sampling circuit include an NPN transistor Q1, a resistor RCS1, a resistor R7, a resistor R8 and a resistor R20, one end of the resistor RCS1 is connected to the source S of the MOS transistor T1, and the other end is connected to the rectifier The negative pole of the circuit, after the resistor R7 and the resistor R8 are connected in series, the other end of the resistor R7 is connected to the positive pole of the rectifier circuit, the resistor R8 is connected to the negative pole of the rectifier circuit, and one end of the resistor R20 is connected to the resistor R7 and the resistor The junction of R8, the other end is divided into two circuits, one is connected to the base of the triode Q1, the other is connected to the junction of the resistor RCS1 and the switch circuit, the collector of the triode Q1 is connected to the resistor R9 through the resistor R11 and the junction of resistor R10, the collector is the negative pole of the rectifier circuit.
本发明的有益效果是：本发明在线性恒流的框架下，采用PWM控制技术，通过改变交流电经过整流以后的脉冲波形的占空比来控制LED负载的电流，能减少功率器件的发热量和提高转换效率，有效解决了现有技术中线性恒流驱动无功功耗大、允许电源电压波动范围小、转换效率低等缺陷，具有电路结构简单、无须电感元件、造价低廉、无EMI(电磁辐射)等优点。The beneficial effects of the present invention are: under the framework of linear constant current, the present invention adopts PWM control technology to control the current of the LED load by changing the duty cycle of the pulse waveform after the alternating current is rectified, which can reduce the calorific value of the power device and Improve the conversion efficiency, effectively solve the defects of large reactive power consumption of linear constant current drive, small fluctuation range of allowable power supply voltage, and low conversion efficiency in the prior art. It has simple circuit structure, no inductive components, low cost, and no EMI (electromagnetic radiation) and so on.
附图说明Description of drawings
下面结合附图和实施例对本发明进一步说明。The present invention will be further described below in conjunction with the accompanying drawings and embodiments.
图1是本发明的第一种实施方式电路原理图；Fig. 1 is the schematic circuit diagram of the first embodiment of the present invention;
图2是本发明的第二种实施方式电路原理图.Fig. 2 is the schematic circuit diagram of the second embodiment of the present invention.
具体实施方式Detailed ways
参照图1、图2，一种基于线性与PWM工作模式的LED恒流驱动方法，在线性恒流的框架下，采用PWM控制技术，通过改变交流电经过整流以后的脉冲波形的占空比来控制LED负载的电流。Referring to Figure 1 and Figure 2, a LED constant current driving method based on linear and PWM working modes, under the framework of linear constant current, uses PWM control technology to control by changing the duty cycle of the pulse waveform after the AC power is rectified. LED load current.
对交流电整流以后的脉冲波形进行取样，由脉冲控制器产生一组与整流以后的脉冲波形周期同步、频率相同的脉冲信号，通过改变占空比，控制与LED负载串联的半导体功率器件的通断时间，使LED负载电流恒定。Sampling the pulse waveform after AC rectification, and the pulse controller generates a group of pulse signals that are cycle-synchronous and of the same frequency as the rectified pulse waveform, and control the on-off of the semiconductor power device connected in series with the LED load by changing the duty cycle time to make the LED load current constant.
由脉冲控制器产生一组占空比可控的方波信号，对整流后的直流脉冲波形实施调制，通过调制脉冲的占空比去控制与LED负载串联的半导体功率器件的通断时间，使LED负载电流恒定。The pulse controller generates a set of square wave signals with controllable duty ratio, and modulates the rectified DC pulse waveform, and controls the on-off time of the semiconductor power device connected in series with the LED load by modulating the duty ratio of the pulse, so that The LED load current is constant.
对电源电压、LED负载电流、LED负载与电源之间的电压差同时进行信号采样，脉冲控制器根据采样信号，产生合适的脉冲宽度，以达到LED负载恒流目的。The power supply voltage, LED load current, and the voltage difference between the LED load and the power supply are simultaneously sampled, and the pulse controller generates a suitable pulse width according to the sampled signal to achieve the purpose of constant current of the LED load.
一种实现上述方法的基于线性与PWM工作模式的LED恒流驱动器，包括整流电路、LED负载、PWM控制器、开关电路、电压采样电路和电流采样电路；所述LED负载、开关电路和电流采样电路串联后一端接所述整流电路的正极，另一端接所述整流电路的负极；所述电压采样电路一端接所述整流电路的正极，另一端接所述整流电路的负极；所述PWM控制器的输入端接所述电压采样电路和电流采样电路，输出端接所述开关电路。A LED constant current driver based on linear and PWM operating modes for realizing the above method, including a rectifier circuit, an LED load, a PWM controller, a switch circuit, a voltage sampling circuit and a current sampling circuit; the LED load, the switch circuit and the current sampling After the circuits are connected in series, one end is connected to the positive pole of the rectification circuit, and the other end is connected to the negative pole of the rectification circuit; one end of the voltage sampling circuit is connected to the positive pole of the rectification circuit, and the other end is connected to the negative pole of the rectification circuit; the PWM control The input terminal of the device is connected with the voltage sampling circuit and the current sampling circuit, and the output terminal is connected with the switch circuit.
第一种实施方式参见图1，所述开关电路包括N沟道MOS管T1，所述MOS管T1的漏极D接所述LED负载，源极S接所述整流电路的负极，栅极G接所述PWM控制器的输出端，所述MOS管T1的漏极D和源极S之间并联有电阻R6。Referring to Figure 1 for the first implementation mode, the switch circuit includes an N-channel MOS transistor T1, the drain D of the MOS transistor T1 is connected to the LED load, the source S is connected to the negative pole of the rectifier circuit, and the gate G Connected to the output terminal of the PWM controller, a resistor R6 is connected in parallel between the drain D and the source S of the MOS transistor T1.
所述电流采样电路包括NPN型三极管T2和电阻RCS，所述电阻RCS的一端接所述MOS管T1的源极S，另一端接所述整流电路的负极，所述三极管T2的基极B接所述电阻RCS和MOS管T1源极S的结点，发射极E接所述整流电路的负极，集电极C通过电阻R5接所述PWM控制器。The current sampling circuit includes an NPN transistor T2 and a resistor RCS, one end of the resistor RCS is connected to the source S of the MOS transistor T1, the other end is connected to the negative pole of the rectifier circuit, and the base B of the transistor T2 is connected to The junction of the resistor RCS and the source S of the MOS transistor T1, the emitter E is connected to the negative pole of the rectification circuit, and the collector C is connected to the PWM controller through the resistor R5.
所述PWM控制器为电压比较器U1；电压采样电路包括电阻R1、电阻R2、电阻R3和稳压二极管Z1，所述电阻R1和电阻R2串接后一端接所述整流电路的正极，另一端接整所述流电路的负极，所述电阻R3和稳压二极管Z1串接后，电阻R3的另一端接所述整流电路的正极，稳压二极管Z1的另一端接所述流电路的负极，所述电压比较器U1的同相输入端分两路，一路接所述电阻R1和电阻R2的结点，另一路接所述电阻R5，所述电压比较器U1的反向输入端分两路，一路通过电阻R21接所述电阻R3和稳压二极管Z1的结点，另一路通过电阻R22接所述整流电路的负极，电压比较器U1的输出端接所述MOS管T1的栅极G；所述稳压二极管Z1的两端并联有电容C1，电阻R1和电阻R2的结点与电阻R5连接。The PWM controller is a voltage comparator U1; the voltage sampling circuit includes a resistor R1, a resistor R2, a resistor R3 and a Zener diode Z1, and the resistor R1 and the resistor R2 are connected in series, and one end is connected to the positive pole of the rectifier circuit, and the other end Connect the negative pole of the rectifier circuit, after the resistor R3 and the Zener diode Z1 are connected in series, the other end of the resistor R3 is connected to the positive pole of the rectifier circuit, and the other end of the Zener diode Z1 is connected to the negative pole of the rectifier circuit, The non-inverting input terminal of the voltage comparator U1 is divided into two circuits, one of which is connected to the junction of the resistor R1 and the resistor R2, and the other is connected to the resistor R5, and the reverse input terminal of the voltage comparator U1 is divided into two circuits, One path is connected to the junction of the resistor R3 and the Zener diode Z1 through the resistor R21, the other path is connected to the negative pole of the rectifier circuit through the resistor R22, and the output terminal of the voltage comparator U1 is connected to the gate G of the MOS transistor T1; A capacitor C1 is connected in parallel between the two ends of the Zener diode Z1, and the junction of the resistor R1 and the resistor R2 is connected to the resistor R5.
220V、50Hz交流市电经过由二极管D1、D2、D3、D4组成的桥式整流电路后，变成峰值为311V、100Hz的单向脉冲电压，经过电阻R1、电阻R2分压后作为取样电压V1，接电压比较器U1的同相输入端“+”，取样电压V1的波形和分压前的波形是一致的。电阻R3、稳压二极管Z1和电容C1组成一个简单的稳压电路，提供一个稳定的工作电压供电压比较器U1使用，电阻R3和稳压二极管Z1的结点通过电阻R22、电阻R21分压后作为基准电压V2提供给电压比较器U1的反向输入端“-”。After the 220V, 50Hz AC mains passes through the bridge rectifier circuit composed of diodes D1, D2, D3, D4, it becomes a unidirectional pulse voltage with a peak value of 311V, 100Hz, which is divided by the resistors R1 and R2 as the sampling voltage V1 , connected to the non-inverting input terminal "+" of the voltage comparator U1, the waveform of the sampling voltage V1 is consistent with the waveform before the voltage division. Resistor R3, Zener diode Z1 and capacitor C1 form a simple voltage regulator circuit to provide a stable working voltage for voltage comparator U1. The junction of resistor R3 and Zener diode Z1 is divided by resistor R22 and resistor R21. As the reference voltage V2, it is provided to the inverting input terminal "-" of the voltage comparator U1.
工作时，输入电压在0点时，V1＜V2，故，电压比较器U1的输出端电压为低电平L，接着，随着输入电压波形的爬升，V1的电压也往上爬升，当V1＞V2时，电压比较器U1输出端翻转，输出为高电平H,经过5ms的时间，脉冲波形达到峰点，V1的电平也达到了最高点，随后，输入电压脉冲波形开始下滑，V1也跟着下降，当电压下降到V1＜V2时，电压比较器U1输出端翻转，输出端为低电平L,从脉冲峰点到整个脉冲周期完成，也历时5ms，这样，就完成了一个脉冲周期的转换，接下来进入下一个脉冲周期，也同样重复前面的过程，在电压比较器U1的输出端，就得到一串与输入电压同步的方波信号。基准电压V2决定了电压比较器U1的翻转阀值，改变V2的电压，就可以改变输出脉冲的宽度，也就改变了输出脉冲的占空比。When working, when the input voltage is at 0, V1<V2, therefore, the voltage at the output terminal of the voltage comparator U1 is low level L, and then, as the input voltage waveform rises, the voltage of V1 also climbs up, when V1 When >V2, the output terminal of the voltage comparator U1 flips, and the output is a high level H. After 5ms, the pulse waveform reaches the peak point, and the level of V1 also reaches the highest point. Then, the input voltage pulse waveform begins to decline, and V1 It also decreases. When the voltage drops to V1<V2, the output terminal of the voltage comparator U1 is reversed, and the output terminal is low level L. It takes 5ms from the peak point of the pulse to the completion of the entire pulse cycle. In this way, a pulse is completed Cycle conversion, and then enter the next pulse cycle, and repeat the previous process. At the output terminal of the voltage comparator U1, a series of square wave signals synchronous with the input voltage are obtained. The reference voltage V2 determines the flipping threshold of the voltage comparator U1. Changing the voltage of V2 can change the width of the output pulse, which also changes the duty cycle of the output pulse.
用电压比较器U1输出的脉冲信号控制MOS管T1，在电压比较器U1输出低电平L时，MOS管T1截止，LED负载没有电流流过，在电压比较器U1输出高电平H时，MOS管T1导通，给LED负载提供工作电流。LED负载的工作电流通过电阻RCS时，会在其两端产生一个电压VCS，VCS的大小与通过电阻RCS的电流成正比，VCS接到三极管T2的基极B，直接影响了T2的集电极C的电压，也就直接影响了电压比较器U1的取样电压V1。假设，某种原因使负载电流增大(如输入市电电压升高等原因)，则通过电阻RCS的电流也同样增大，电压VCS也随着增大，由于三极管T2的放大作用，集电极C的电位也同时随之下降，通过电阻R5，把电压比较器U1的取样电压V1拉低，结果，电压比较器U1输出端的导通时间向后推移、截止时间提前，从而使输出脉冲宽度变窄；反之，如果某种原因使LED负载电流变小，通过电阻RCS的电流也同样变小，电压VCS下降，此时，三极管T2的集电极C点的电位上升，电压比较器U1的取样电压V1上升而使导通翻转时间提前、截止时间滞后，使输出脉冲宽度变大，这样，就可以把LED负载的电流自动控制在某个设定值上。Use the pulse signal output by the voltage comparator U1 to control the MOS transistor T1. When the voltage comparator U1 outputs a low level L, the MOS transistor T1 is turned off, and no current flows through the LED load. When the voltage comparator U1 outputs a high level H, The MOS transistor T1 is turned on to provide working current to the LED load. When the working current of the LED load passes through the resistor RCS, a voltage VCS will be generated at both ends of it. The magnitude of VCS is proportional to the current passing through the resistor RCS. VCS is connected to the base B of the triode T2, which directly affects the collector C of T2. The voltage directly affects the sampling voltage V1 of the voltage comparator U1. Assuming that some reason increases the load current (such as the increase of the input mains voltage, etc.), the current through the resistor RCS also increases, and the voltage VCS also increases. Due to the amplification effect of the transistor T2, the collector C At the same time, the potential of the voltage comparator U1 also decreases, and the sampling voltage V1 of the voltage comparator U1 is pulled down through the resistor R5. As a result, the conduction time of the output terminal of the voltage comparator U1 is pushed back and the cut-off time is advanced, so that the output pulse width is narrowed. Conversely, if the load current of the LED becomes smaller for some reason, the current through the resistor RCS also becomes smaller, and the voltage VCS drops. At this time, the potential of the collector point C of the triode T2 rises, and the sampling voltage V1 Rise to advance the turn-on inversion time and delay the cut-off time, so that the output pulse width becomes larger, so that the current of the LED load can be automatically controlled at a certain set value.
所述电阻R6的作用是检测MOS管T1的源极S与漏极D之间的电压，这个电压其实就是LED负载电压和电源电压(整流电路的输出端电压)之间的电压差，称为压差，在线性方案中，压差越小，效率就越高。当电源电压发生变化时，压差会随之改变，所以，电阻R6能将这个压差信号及时反馈给三极管T2，当电源电压上升时，MOS管T1的源极S与漏极D之间的电压也随之升高，通过电阻R6，VCS也随之升高，通过三极管T2、电阻R5，把电压比较器U1的取样电压拉低而使输出脉冲宽度变窄，反之，则输出脉冲宽度变大，这样，就一定程度的维持了LED负载的电流恒定。The function of the resistor R6 is to detect the voltage between the source S and the drain D of the MOS transistor T1. This voltage is actually the voltage difference between the LED load voltage and the power supply voltage (the output terminal voltage of the rectifier circuit), which is called Pressure difference, in a linear scheme, the smaller the pressure difference, the higher the efficiency. When the power supply voltage changes, the voltage difference will change accordingly. Therefore, the resistor R6 can feed back the voltage difference signal to the transistor T2 in time. When the power supply voltage rises, the voltage between the source S and the drain D of the MOS transistor T1 The voltage also rises accordingly, through the resistor R6, VCS also rises accordingly, through the triode T2 and resistor R5, the sampling voltage of the voltage comparator U1 is pulled down to narrow the output pulse width, otherwise, the output pulse width becomes narrower. In this way, the current of the LED load is maintained constant to a certain extent.
适当选用电阻R1、电阻R2、电阻R3、电阻R5、电阻R6和稳压二极管Z1的参数，可以设定脉冲宽度的变化窗口，可以使脉冲占空比从10％-95％的范围内变化，从而适应较大范围的电源电压波动，甚至，在电源电压低于一定幅度时，使脉冲宽度大于99，使MOS管T1直接工作在纯线性状态，改变电阻RCS的阻值，则可以设定恒流电流的大小。上述的电压比较器U1型号为LM393,也可以选用其他任何型号的比较器或运算放大器，如LM311、LM358等；MOS管T1为高压场效应功率管，如型号为2N60等。Appropriate selection of the parameters of resistor R1, resistor R2, resistor R3, resistor R5, resistor R6 and Zener diode Z1 can set the change window of the pulse width, and the pulse duty cycle can be changed from 10% to 95%. In order to adapt to a wide range of power supply voltage fluctuations, even when the power supply voltage is lower than a certain range, make the pulse width greater than 99, make the MOS tube T1 directly work in a pure linear state, and change the resistance value of the resistor RCS, then you can set a constant The magnitude of the current flowing. The model of the voltage comparator U1 mentioned above is LM393, and any other type of comparator or operational amplifier can also be used, such as LM311, LM358, etc.; the MOS transistor T1 is a high-voltage field effect power transistor, such as the model is 2N60.
在上述的基础上，在电路中增加滤波电容C2和隔离二极管D5，隔离二极管D5把电阻R1、电阻R3和LED负载单向隔离，使电压比较器U1的电压V1保持为100Hz的脉冲信号，基准电压V2和LED负载工作在纯直流的状态下，由于加入了滤波电容C2，电容C1可以省略。On the basis of the above, filter capacitor C2 and isolation diode D5 are added to the circuit. The isolation diode D5 isolates the resistors R1, R3 and the LED load in one direction, so that the voltage V1 of the voltage comparator U1 is maintained as a 100Hz pulse signal, the reference The voltage V2 and the LED load work in the state of pure direct current, because the filter capacitor C2 is added, the capacitor C1 can be omitted.
第二种实施方式参见图2，图2所示的电路与图1所示的电路的区别在于：采用了一个三角波发生器和一个电压比较器，具体电路如下：See Figure 2 for the second embodiment. The difference between the circuit shown in Figure 2 and the circuit shown in Figure 1 is that a triangular wave generator and a voltage comparator are used, and the specific circuit is as follows:
所述PWM控制器包括三角波发生器U1A、电压比较器U1B，电压采样电路包括电阻R12、电阻R9、电阻R10、电阻R13、电阻R14、电阻R15、电阻R16、电阻R17、电阻R18、稳压二极管D6、电容C3和电容C4；所述电阻R12、电阻R9、电阻R10依次串联后，电阻R12的另一端接所述整流电路的正极，电阻R10的另一端接所述整流电路的负极；所述稳压二极管D6和电容C3并联后一端接所述电阻R12和电阻R9的结点，另一端接所述整流电路的负极；所述电阻R13、电阻R14串联后，电阻R13的另一端接所述电阻R12和电阻R9的结点，电阻R14的另一端接所述整流电路的负极；所述电阻R16、电阻R17和电容C4依次串联后，所述电阻R16的另一端接所述电阻R12和电阻R9的结点，所述电容C4的另一端接所述整流电路的负极；所述电阻R15的一端接所述电阻R13和电阻R14的结点，另一端接电阻R16和电阻R17的结点，所述三角波发生器U1A的同相输入端接电阻R13和电阻R14的结点，反向输入端接电阻R17和电容C4的结点，输出端接电阻R16和电阻R17的结点；所述电压比较器U1B的同相输入端接电阻R9和电阻R10的结点，反向输入端接电阻R17和电容C4的结点，输出端接所述开关电路的输入端，所述电阻R18的一端接所述电阻R12和电阻R9的结点，另一端接所述电压比较器U1B的输出端。The PWM controller includes a triangular wave generator U1A, a voltage comparator U1B, and the voltage sampling circuit includes a resistor R12, a resistor R9, a resistor R10, a resistor R13, a resistor R14, a resistor R15, a resistor R16, a resistor R17, a resistor R18, and a Zener diode D6, capacitor C3 and capacitor C4; after the resistor R12, resistor R9, and resistor R10 are connected in series in sequence, the other end of the resistor R12 is connected to the positive pole of the rectifier circuit, and the other end of the resistor R10 is connected to the negative pole of the rectifier circuit; After the Zener diode D6 and the capacitor C3 are connected in parallel, one end is connected to the node of the resistor R12 and the resistor R9, and the other end is connected to the negative pole of the rectifier circuit; after the resistor R13 and the resistor R14 are connected in series, the other end of the resistor R13 is connected to the The junction of the resistor R12 and the resistor R9, the other end of the resistor R14 is connected to the negative pole of the rectifier circuit; after the resistor R16, the resistor R17 and the capacitor C4 are connected in series in sequence, the other end of the resistor R16 is connected to the resistor R12 and the resistor The node of R9, the other end of the capacitor C4 is connected to the negative pole of the rectifier circuit; one end of the resistor R15 is connected to the node of the resistor R13 and the resistor R14, and the other end is connected to the node of the resistor R16 and the resistor R17, The noninverting input terminal of the triangular wave generator U1A is connected to the node of resistor R13 and resistor R14, the reverse input terminal is connected to the node of resistor R17 and capacitor C4, and the output terminal is connected to the node of resistor R16 and resistor R17; the voltage comparison The non-inverting input terminal of the device U1B is connected to the node of the resistor R9 and the resistor R10, the reverse input terminal is connected to the node of the resistor R17 and the capacitor C4, the output terminal is connected to the input terminal of the switch circuit, and one end of the resistor R18 is connected to the The other end of the node of the resistor R12 and the resistor R9 is connected to the output end of the voltage comparator U1B.
所述电压采样电路和电流采样电路包括NPN型三极管Q1、电阻RCS1、电阻R7、电阻R8和电阻R20，所述电阻RCS1的一端接所述MOS管T1的源极S，另一端接所述整流电路的负极，所述电阻R7和电阻R8串联后，电阻R7的另一端接所述整流电路的正极，电阻R8接所述整流电路的负极，所述电阻R20的一端接所述电阻R7和电阻R8的结点，另一端分两路，一路接所述三极管Q1的基极，另一路接所述电阻RCS1和开关电路的结点，所述三极管Q1的集电极通过电阻R11接所述电阻R9和电阻R10的结点，集电极所述整流电路的负极。The voltage sampling circuit and the current sampling circuit include an NPN transistor Q1, a resistor RCS1, a resistor R7, a resistor R8 and a resistor R20, one end of the resistor RCS1 is connected to the source S of the MOS transistor T1, and the other end is connected to the rectifier The negative pole of the circuit, after the resistor R7 and the resistor R8 are connected in series, the other end of the resistor R7 is connected to the positive pole of the rectifier circuit, the resistor R8 is connected to the negative pole of the rectifier circuit, and one end of the resistor R20 is connected to the resistor R7 and the resistor The junction of R8, the other end is divided into two circuits, one is connected to the base of the triode Q1, the other is connected to the junction of the resistor RCS1 and the switch circuit, the collector of the triode Q1 is connected to the resistor R9 through the resistor R11 and the junction of resistor R10, the collector is the negative pole of the rectifier circuit.
AC220V、50Hz的交流市电，经整流二极管D1、D2、D3、D4组成的桥式整流器整流以后，变成峰值为311V、频率为100Hz的高压直流脉冲，输出正极接到LED负载的正极端，LED负载的负极连接到MOS管T1的漏极D。由电阻R12、稳压二极管D6、电容C3组成一个简单的直流降压稳压电路，提供了一个稳定的电压给三角波发生器U1A、电压比较器U1B、电阻R13、电阻R14、电阻R15、电阻R16、电阻R17和电容C4组成一个通用的三角波发生器，其脉冲频率取决于电阻R17、电容C4的充放电时间常数，三角波信号从电容C4与电阻R17的结点输出，送入电压比较器U1B的反向输入端，三角波发生器U1A的基准电压由电阻R13和电阻R14分压所得，电压比较器U1B的取样电压由电阻R9和电阻R10从12V电源上分压所得，三角波发生器U1A输出的三角波通过电压比较器U1B被整形为一组方波信号，该方波信号送到MOS管T1的栅极G，控制MOS管T1导通和截止。AC220V, 50Hz AC mains, after being rectified by the bridge rectifier composed of rectifier diodes D1, D2, D3, D4, becomes a high-voltage DC pulse with a peak value of 311V and a frequency of 100Hz, and the output positive pole is connected to the positive pole of the LED load. The negative electrode of the LED load is connected to the drain D of the MOS transistor T1. A simple DC step-down regulator circuit is composed of resistor R12, Zener diode D6, and capacitor C3, providing a stable voltage to the triangle wave generator U1A, voltage comparator U1B, resistor R13, resistor R14, resistor R15, and resistor R16 , resistor R17 and capacitor C4 form a general triangular wave generator, its pulse frequency depends on the charge and discharge time constant of resistor R17 and capacitor C4, the triangular wave signal is output from the junction of capacitor C4 and resistor R17, and sent to the voltage comparator U1B Inverting input terminal, the reference voltage of the triangular wave generator U1A is obtained by dividing the voltage of the resistor R13 and the resistor R14, the sampling voltage of the voltage comparator U1B is obtained by dividing the voltage of the 12V power supply by the resistor R9 and the resistor R10, and the triangular wave output by the triangular wave generator U1A The voltage comparator U1B is shaped into a group of square wave signals, and the square wave signals are sent to the gate G of the MOS transistor T1 to control the MOS transistor T1 to be turned on and off.
工作中，在电阻RCS1的两端就会产生一个电压VCS1，VCS1的大小与通过LED负载的电流大小成正比，VCS1被连接到三极管Q1的基极，由于三极管Q1的放大作用，VCS1的微小变化，会使三极管Q1的集电极电位同时发生变化，也就使电压比较器U1B的取样电压发生变化，而取样电压的变化就意味着门限电压发生改变，此时，其输出的脉冲占空比也就同时发生改变。比如，在一定的工作电流条件下，电压比较器U1B输出的脉冲占空比是80％，如果某种原因(如电源电压升高等)使LED负载的电流加大，此时，VCS1就由于电流的增大而跟着升高，这时，三极管Q1的基极电位升高就引起了集电极电流的增大，而把集电极电位拉低，通过电阻R6，把电压比较器U1B的同相输入端电位拉低，使电压比较器U1B的输出占空比变小，比如下降为70％、60％等，从而控制了MOS管T1的导通时间而使LED负载的电流变小，使通过LED负载的电流稳定在设定的范围内。During operation, a voltage VCS1 will be generated at both ends of the resistor RCS1. The magnitude of VCS1 is proportional to the magnitude of the current passing through the LED load. VCS1 is connected to the base of the transistor Q1. Due to the amplification effect of the transistor Q1, the slight change of VCS1 , the collector potential of the transistor Q1 will change at the same time, which will also change the sampling voltage of the voltage comparator U1B, and the change of the sampling voltage means that the threshold voltage will change. At this time, the pulse duty ratio of its output will also change. change at the same time. For example, under a certain operating current condition, the duty cycle of the output pulse of the voltage comparator U1B is 80%, if some reason (such as the increase of the power supply voltage, etc.) causes the current of the LED load to increase, at this time, VCS1 is due to the current At this time, the increase of the base potential of the triode Q1 causes the increase of the collector current, and the collector potential is pulled down, and the non-inverting input terminal of the voltage comparator U1B is connected to the voltage through the resistor R6. The potential is pulled down, so that the output duty cycle of the voltage comparator U1B becomes smaller, such as 70%, 60%, etc., thereby controlling the conduction time of the MOS transistor T1 and reducing the current of the LED load, so that the current through the LED load The current is stable within the set range.
如果需要使LED负载工作电压处于纯直流的状态，可以在电路中加入一只电解电容和一只隔离二极管来实现。If you need to make the LED load operating voltage in a pure DC state, you can add an electrolytic capacitor and an isolation diode to the circuit to achieve it.
以上的实施例只是为了说明本发明创造的工作原理，实施例中电路的具体结构不能构成对本发明创造保护范围的限定，专业技术领域的人员也可以根据电路的特性，将MOS管T1更换为P沟道的MOS管，将三极管T2、三极管Q1更换成PNP型等，并对器件的连接方式做适应的调整，PWM控制器也可以为单片机等，只要是依照本发明创造的整体构思所做的变化与改进，均仍属于本发明创造涵盖的范围之内。The above embodiments are just to illustrate the working principle of the present invention. The specific structure of the circuit in the embodiment cannot constitute a limit to the scope of protection of the present invention. Personnel in the professional technical field can also replace the MOS transistor T1 with P according to the characteristics of the circuit. For the MOS tube of the channel, the triode T2 and the triode Q1 are replaced with PNP type, etc., and the connection mode of the device is adjusted. Changes and improvements still fall within the scope of the invention.
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