Full voltage LED fluorescent switch constant current source circuit diagram

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

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Basic characteristics AC non-isolated high-frequency switching step-down constant current mode AC 85 ~ 245V, 50 ~ 60Hz working range series charging, parallel discharge passive power factor correction can be built in 28 mm lamp installation working environment temperature 0 ~ 75 ° C Meet the requirements of IEC61000-3-2:2001

Circuit principle AC mains inlet is connected with 1A fuse FS1 and anti-surge negative temperature coefficient thermistor NTC. This is followed by an EMI filter consisting of L1, L2 and CX1. The BD1 is a rectified full bridge with four high voltage silicon diodes inside.

C1, C2, R1, D1~D3 form passive power factor correction. For the working principle, see the article "Optimization Method of Designing LED Fluorescent Lamp with PT4107". PWM control chip U1 and power MOS transistor Q1, ballast inductor L3, and freewheeling diode D5 form a Buck step-down converter. U1 collects the peak current on the sense resistors R6-R9. The internal logic controls the pulse duty of the GAte pin signal. Constant current control.

The chip is powered by the electronic filter consisting of T1, D4, C4, and R2~R4. The internal resistance of this filter is very high, the output impedance is very small, and it can provide a stable voltage of about 16V to ensure stable operation of the chip in the full voltage range. . R5 is part of the chip oscillator circuit, changing it will adjust the oscillation frequency. The potentiometer RT is not used for dimming in this circuit, but is used to fine tune the current of the constant current source to make the circuit reach the design power.

The parameters of this circuit are 22 LEDs in series, 15 series parallel, driving 330 60 mW white LEDs, each string current is 17.8 mA.