Ultra-low-cost 1W high-power LED power supply and control circuit analysis

High-power LEDs have higher luminous efficiency and service life than fluorescent lamps. People should install a heat sink according to the actual usage. At present, the retail price of domestic 3W white light LED is 15 yuan, but because the quality of 3W high-power LED is not reliable enough, it is not suitable for use at present. 5W high-power LED is only imported, and the price is as high as 60 yuan each. It is only suitable for lighting projects with special requirements. The most suitable for people's home lighting is the domestic 1W LED.

Since the working voltage of high-power LED is only 3V, the voltage drop on the full bridge is about 1.8V when 220V AC is converted into DC through full-bridge rectification, and the energy efficiency of driving only one LED is only 60%. More than three LEDs must be connected in series to make the total energy efficiency exceed 80%.

According to the principle of synthesizing white light with three primary colors, by connecting three 1W high-power light-emitting diodes (red, green and blue) in series, you can get a brightness equivalent to that of a 3W white-light LED. At the same time, you can also combine six colors of light to meet people's preference for changing color lights. In order to avoid wasting electricity, capacitors should be used as voltage-reducing and current-limiting components when using AC power as an LED driver.

The conventional 4.7μ/AC400V capacitor used in washing machine motors can provide 325mA working current as a step-down current limiting component, which is exactly the same as the rated working current of a 1W high-power LED. It costs 20 yuan to buy three 1W high-power LEDs, red, green and blue, which is 5 yuan more expensive than buying a 3W white-light LED. However, the working current of a 3W high-power LED is three times that of a 1W high-power LED, so a 14μ capacitor is needed as a step-down current limiting component. Buying a 14μ/AC400V capacitor is 5 yuan more expensive than buying a 4.7μ/400V capacitor, so the overall cost is not cost-effective.

The practical driving power supply of 1W high-power light-emitting diode is shown in the attached figure, where: the main function of C3 capacitor is to prevent the instantaneous large current that may be produced from passing through the LED to damage it when the 220V mains is just connected, and the VS1 thyristor is to prevent the high voltage generated at both ends of C3 when the load is open, causing serious heating and explosion. The turning voltage of the VDS1 trigger diode is 30V~40V. Under normal conditions, the voltage at both ends of C3 does not exceed 10V, VDS1 is always cut off, and VS1 is also cut off. Only when the load circuit is disconnected or the LED is open-circuited, VS1 will be turned on immediately when the voltage at both ends of C3 just rises to 30V~40V and maintain the on state. After eliminating the fault and reconnecting the power supply, VS1 will automatically return to the off state.

If only three high-power LEDs are required to emit light together, VT1~VT9 and R3~R9 in the power drive circuit can be completely omitted. This part of the circuit is specially designed to control the light-emitting state of the three LEDs of red, green and blue. The three terminals A, B and C are suspended or connected to the relative midpoint of the negative terminal of the DC. VT1, VT4, VT7~VT9 are cut off, VT2, VT3, VT5 and VT6 are turned on, LED2 and LED3 are short-circuited by VT2 and VT3 respectively, and only LED1 works and emits light.

Connecting the B terminal to the DC positive terminal alone will turn on VT8, and VT5 and VT2 will be turned off, and LED2 will work and emit light. Connecting the C terminal to the DC positive terminal alone will turn on VT9, and VT6 and VT3 will be turned off, and LED3 will work and emit light. At the same time, connecting the B terminal or the C terminal to the DC positive terminal can turn on VT4 and VT1, and LED1 will be short-circuited by VT1 and will not work. However, connecting the A terminal to the DC positive terminal will turn on VT7, forcing BG4 to be turned off, and VT1 to be turned off, and LED1 will work and emit light. In this way, no matter what state the A, B, and C terminals are in, there is always at least one light-emitting tube working. By controlling the level added to the A, B, and C terminals, the three light-emitting tubes can be made to emit light according to the required combination.

The levels at the three terminals A, B, and C can be controlled by ordinary switches, or by using three D flip-flops and a button to achieve cyclic changes. Of course, you can also connect six LEDs in series and use a special color light control IC to achieve dynamic changes. Those who are interested can also further design the control circuit into an infrared remote control circuit, which will be more attractive when installed in the bedroom.