Power-saving LED dimming circuit

This energy-saving LED dimming desk lamp light source changes the traditional incandescent bulb and adopts a hybrid component of 1W high-power and φ5mm low-power light-emitting diodes. The dimming circuit is also unique, which is a trigger dimming circuit. It has a simple structure and adds an operational amplifier. The actual illumination is no less than a 25W incandescent lamp. It has the characteristics of energy saving, reliability and long service life.

Circuit Principle

The power supply is taken from transformer T and bridge rectifier D1~D4 to convert the 220V mains power into a 14V DC working power supply. The operational amplifier Al and the voltage regulator IC1 form a reference voltage for the operational amplifier A2 and the peripheral resistors R3~R6 to form the in-phase input reference voltage of the trigger circuit, and the inverting input is sampled by resistor R9 and compared with the in-phase input, so that the pulse width at its output end is adjusted by the reference potentiometer RP, and after amplification by the driving transistor BG1 and the power transistor BC2, the LED1-LED15 light-emitting diode components are lit. The current size can be controlled by controlling the potentiometer RP to complete the actual dimming function. Here, the freewheeling diode D5 and the energy storage inductor make the output current stable.

Component requirements

T is a power transformer, which can be substituted with the commercially available specification of 8W9V. The light-emitting diode components LED1-LED6 and LED10~LED15 are φ5 mm straw hat-shaped natural light colors, with 12 pieces on each side, 6 pieces less, a total of 24 pieces: LED7~LED8 are 1W high-power and natural light colors, with heat sinks, and the market price has dropped significantly to 7 yuan, which is worthwhile. However, when assembling, the three pieces are combined into one, and suitable strip aluminum materials are added to increase the heat dissipation effect. Op amps Al and A2 are dual op amps LM358. If there is LM324, it is completely universal. There are only two more op amps. IC1 voltage regulator is TL431, the voltage regulation value is 2.5V, and the other resistors and capacitors are conventional configurations. The inductor L1 is selected as a high-frequency magnetic ring with an outer diameter of φ15mm, and φ0.25mm enameled wire is wound with 40T. The current limiting resistor R9 has a power of 1W. The resistance value is selected from 2.2Ω-3.OΩ.

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After turning on the power supply, a DC voltage of 14V can be measured across capacitor Cl, and 10.5V at full load. The total current of the light-emitting diode assembly is determined by R9. Select an appropriate value to ensure that the working current flowing through LED7~LED9 is not less than 350mA. The working current of each path of the 4.5 mm straw hat shape on both sides is not more than 20mA. A small resistor of 20Ω can be connected in series with LED1~LED6 and LED10~LED15 to keep the working current normal. A power switch should be installed at the mains input end, and the specifications are optional.