LED industry develops very fast due to its environmental protection, long service life, high efficiency etc advantages. LED light service life is more than 100000 hours, but in fact, LED is very easy to damage if the power supply design has problem.
Before designing LED power supply, it is necessary to know about the characteristics of LED current and voltage. Take white LED for example, its forward voltage is about 3.0-3.6V, output voltage is 3.3V, current is 20mA. When the forward voltage exceeds 3.6V and even it increase a little, the current will be doubled. It will cause LED light temperature rise too fast and light attenuation, LED light service life will decrease a lot, even broken. So LED power supply is critical.
Many manufacturers use capacitor unit to step down voltage and a diode to stabilize voltage in their power supply, it has much problems. Firstly, low efficiency. Capacitor unit consume much power even more than the consumption of LED light, it can't supply high current because the higher current the more consumption on capacitor unit. So many manufactures take the series connection in LED products. Secondly, stabilize voltage ability is very bad, it can't ensure the current doesn't exceed to normal, manufacturers lower voltage in design, but it is at the cost of LED brightness decrease. This kind of power supply can't stabilize LED brightness well, when voltage is low, brightness reduced; when voltage is high, brightness increased. Thirdly, the most important advantage of this kind of power supply is cost saving. According to the characteristics of LED current and voltage, it is feasible to use constant voltage power supply.