High-power LEDs have higher luminous efficiency and longer life than fluorescent lamps. People should add additional heat sinks according to the actual use. At present, the domestic 3W white LED retail price is 15 yuan, but because the 3W high power LED quality is not reliable enough, it is not suitable for use. 5W high-power LEDs are only imported, each selling for up to 60 yuan, only suitable for special requirements of lighting projects, the most suitable for people to use for home lighting is the domestic 1W LED.
In view of the high-power LED operating voltage of only 3V, 220V AC is converted to DC by full-bridge rectification, the voltage drop across the bridge is about 1.8V, and the power utilization efficiency of driving only one LED is only 60%. More than three LEDs must be connected in series to achieve a total power utilization efficiency of more than 80%.
According to the principle of 3 primary color synthetic white light, three 1W high-power LEDs of red, green and blue are connected in series, and the brightness achieved by the LED equivalent to 3W white light can be obtained. At the same time, it can also combine 6 kinds of colored light to satisfy people's preference for changing color light. In order to avoid waste of power, the use of the mains as the LED driver should use capacitors as the buck current limiting component.
The conventional 4.7μ/AC400V capacitor used in the washing machine motor can be used as a buck current limiting component to provide 325mA operating current, which is exactly the same as the rated operating current of 1W high power LED. Buying 3, 1W high-power LEDs of red, green and blue requires 20 yuan, which is 5 yuan more than the purchase of 1 3W white LED. However, the operating current of 3W high-power LED is 3 times that of 1W high-power LDE. It is necessary to use a capacitor with a capacity of 14μ as a step-down current limiting component. Buying a 14μ/AC400V capacitor is more important than purchasing a 4.7μ/400V capacitor. If the price is 5 yuan higher, the comprehensive cost is not cost effective.
The practical driving power supply of 1W high-power LED is shown in the figure. The main function of C3 capacitor is to prevent the instantaneous high current that may be generated from being damaged by the LED when the 220V mains is turned on. The VS1 thyristor is Prevent high voltage from being generated at both ends of C3 when the load is open, causing serious heat and explosion. The corner voltage of the VDS1 trigger diode is 30V~40V. Under normal conditions, the voltage across C3 does not exceed 10V, VDS1 is always off, and VS1 is also cut off. Only when the load circuit is broken or the LED is internally open, VS1 is immediately turned on and maintains the conduction state when the voltage across C3 rises to 30V~40V. When the fault is re-powered, VS1 automatically resumes the cutoff state.
If only three high-power LEDs are required to emit light together, VT1 to VT9 and R3 to R9 in the power supply driving circuit can be eliminated. The part of the circuit is specially designed to control the illumination state of three LDEs of red, green and blue. The three ends of A, B and C are suspended or connected to the negative center of the DC negative terminal, and VT1, VT4, VT7 to VT9 are cut off, VT2. VT3, VT5, and VT6 are turned on, and LED2 and LED3 are short-circuited by VT2 and VT3, respectively, and only LED1 operates to emit light.
Connecting B to the DC positive terminal alone will turn VT8 on, VT5 and VT2 will turn off, and LED2 will work. Connecting the C terminal to the DC positive terminal alone will turn VT9 on, VT6 and VT3 will turn off, and LED3 will work. At the same time, the B terminal or the C terminal is connected to the DC positive terminal, and the VT4 is turned on, and the VT1 is turned on, and the LED 1 is short-circuited by the VT1. But connecting the A terminal to the DC positive terminal will make VT7 turn on, forcing BG4 to turn off, VT1 will be cut off, and LED1 will work. Thus, no matter what state the three ends of A, B, and C are, there is always at least one light pipe working. By controlling the levels applied to the three ends of A, B, and C, it is possible to illuminate the three illuminations in a desired combination.
The levels on the three ends of A, B, and C can be controlled by ordinary switches, or three D flip-flops and one button can be used to achieve cyclic conversion. Of course, it is also possible to connect 6 LEDs in series, and use a special lantern control IC to achieve dynamic changes. Interested parties can also further design the control circuit into an infrared remote control circuit, which has a taste in the bedroom.
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NTC thermistors and sensors are everywhere in our daily life and will have a wider range of uses in the future which have been used in automotive, household appliances, computers, medical equipment, electronic thermometer, digital thermostats, portable heaters, printer, air conditioners and refrigerators...
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