First, the design features Second, the working principle The AC input is rectified and filtered by BR1, C1 and C2. Inductor L1, together with C1 and C2, forms a π-shaped filter and provides EMI filtering. Fuse F1 provides protection in the event of a serious fault. In order to operate the power supply under no load without damage, the Zener diode VR2 is used for constant voltage adjustment and the voltage is maintained at approximately 21 V.
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1, for high ambient temperature (75 degrees)
2, high energy efficiency
3, EU CoC / CEC 2008 / ENERGY STAR 2.0 requirements, the load mode is high efficiency (up to 86%, the requirement is 79.6%); the no-load input power < 250 mW at 265 VAC input, the requirement is 300 mW
4, hysteresis shutdown protection
5, load disconnect protection
6, the foot EN55015B conduction EMI limit, EMI margin > 8 dB microvolts
Figure 1 shows a typical 20 V, 14 W constant voltage (CV), constant current (CV) output power supply circuit. The amount of light output from the LED array is proportional to the amount of current flowing through it. Therefore, the LED driver should have a constant current output instead of a constant voltage output. In this design, the DC output is not isolated from the AC input, so the LED array and housing should be safely isolated from the user. 
