Power supply of LEDs from a network of 120-230 volts. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting. Control schemes
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When using LED garlands for window dressing, sign lighting, etc., it is convenient to power them directly from the mains through a rectifier and a ballast resistor so as not to install an additional low-voltage power supply. But in the pauses between half-cycles of the rectified mains voltage, the LEDs are not powered, which leads to their unpleasant flickering.
The proposed device (Fig. 1) eliminates flicker, operates on AC voltage 120...230 V and allows you to adjust the output voltage.
The operation of the circuit is based on controlling the opening time of the key transistor VT2. When the rectified voltage is below the threshold Upor set by the zener diode VD5, the zener diode is closed, respectively, the transistor VT1 is also closed. The rectified voltage through R4 is applied to the gate VT2, and it turns on. Zener diode VD6 limits the voltage at the gate VT2. Through the open VT2, the storage capacitor C2 is charged and the chain of LEDs HL1 ... HL11 is powered.
When the rectified voltage exceeds Upor, the zener diode VD5 breaks through and opens the transistor VT1, which shunts the gate VT2, and the latter closes. The LEDs are powered by a charged capacitor C2, the voltage on it gradually decreases (Fig. 2). Diode VD7 prevents the discharge of C2 through the control circuit.
The duration of the output voltage drop is determined by the load current and capacitance C2. For the normal glow of the LEDs, the voltage on C2 should not fall below the ignition threshold of the garland. The VT2 key opens only at low voltage, due to which the power dissipated on it is small. Resistor - fuse R1 protects the circuit and limits the inrush current when the AC voltage is turned on. The L1-C1 filter eliminates high-frequency noise that occurs during the operation of the circuit.
Author: TA Babu, India; Publication: rlocman.ru
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