A linear constant current LED driver circuit design

Vz1, Vz2, VQ1, VQ2, R1, R2 form a linear constant current source, it ensures that only the current flow through each white LED same, uniform brightness.The LED driver using electric direct rectifying filter, get control of LED DC voltage, without the need to LED Fluorescent Manufacturer step-up or step-down treatment, so the power drive circuit is simple, and the power supply with high efficiency.Use LED high-brightness white LED (working voltage range: 3 ~ 3.2V), using 94 LED LED daylight lamp bulbs.rnHere, a linear constant current source circuit analysis of the working principle, circuit employing complementary ends of constant current source structure.rnComplementary ends of the constant current source circuitrnTransistor regulator tube VQ1, Vz1 and R1 consists of a constant current source, the constant current source to the zener diode Z2 is to LED Par Light provide a stable working current, and the transistor VQ2, a voltage stabilizing tube Vz2 and R2 constitute another constant current source to a voltage stabilizing tube Vz1 stable working current.Since the two constant current source are stable side voltage regulator tube operating point, so that the stable voltage Vz1 and Vz2 and flows through the constant current unit total current shall not change, which can ensure the working current flow through the LED constant.rnThe relationship between current and voltage:rnWe use the LED lamp is 0.06 W LED, working current of 20mA, for ease of design, selection of the circuit components are completely symmetrical, parameters are as follows:rnThe above parameter (1) type available:rnConstant current source circuit provides current of 20mA, meet the requirements for beads.rn2 experimental results and analysisrnTest wiring, by adjusting the autotransformer to change the voltage to simulate the change of the grid voltage.By simulating the fluctuation LED Flood Lamp of network voltage, test the constant current control circuit in the actual electric network operating characteristics, observed the LED working current whether with the external voltage fluctuations which occur large fluctuations, and this circuit under different voltage efficiency and LED junction temperature of the actual test.rnLED forward current varies with the input voltage changes in the characteristics ofrnLED lamp string working current and voltage relationship curve.