A simple and practical LED table lamp scheme is shown in Figure 1. The AC220V provides a stable 12V DC power supply to the LED desk lamp via a safe step-down converter outside the luminaire. A constant current source power supply board is placed in the base of the lamp base to convert the DC voltage into a stable DC constant current source to meet the LED light source. Technical requirements for luminescence. A power switch can be added before the DC constant current source to turn off the DC power when the desk lamp is not used, but the 220V AC power supply cannot be turned off. Therefore, the power plug of the adapter should be removed from the wall when not in use. This is also the practical solution. The only "disadvantage". If you don't want to use mechanical switches, and you want a more creative selling point, you can use electronic touch switch, such as finger tap to realize the opening of the desk lamp -> full bright, semi-dark, off; due to the rapid advancement of electronic technology, electronic touch Switches are now a low-cost device.
LED light source driving circuit
The driving circuit of the LED light source converts the 12V DC voltage into a stable constant current source. The design of the circuit is based on the principle of simple and cost-saving, and should be selected from a large number of LED driver chips that can complete the design requirements of this circuit. A chip that is better, has a simple application circuit, and has a relatively low price/performance ratio. Therefore, selecting a driver chip with few peripheral components of the driver circuit is the primary consideration for production cost.
The constant current accuracy of the LED light source driving chip is very important for the LED lamp manufacturer. At present, the constant current precision mass production of the LED light source driving IC will have a certain dispersion, and the LED lamp manufacturer is in mass production debugging. The same power supply, the same LED light source load, and the same constant current source power supply board, the difference in the constant current accuracy of the different drive ICs of the same model will cause the constant current source power board output current to have a certain tolerance, so that the same LED light source The brightness of the load varies, which increases the time for on-line debugging of high-current source power boards during mass production, affecting productivity. Therefore, the constant current source power board manufacturer should use a driver IC with high constant current accuracy, and the constant current accuracy should be at least ±3%. If it is ±1%, the price will be higher than ±3%.
Inductor selection
Adapter selection
EMI conduction and radiation
The overall design of this LED desk lamp solution should consider the conduction and radiation that can pass EMI. The key to the conduction and radiation of EMI is the power converter. Therefore, it is necessary to use the adapter that can pass EMI and even CE and UL to support the production. The LED table lamp can be exported to the European, American and Japanese markets. The constant current source power supply board is a DC/DC switching device. The switching frequency generates radiation during operation. Therefore, it can be effectively reduced in the metal case of the lamp base. The mechanical structure should be considered in the mechanical structure of the metal base. shield.
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