In recent years, with the development of LED technique, LED light has several advantages to widely use, such as low voltage power supply, low energy dissipation, better applicability, high stability, short response time, multicolor shine, etc. LED power supply usually adopts switching power supply technique, constant driver which changes with the depreciation of LED forward voltage drop. According to the LED volt-ampere characteristics, the voltage changes a little, which maybe lead to the current changing too much and even damaging LED. It is complicated for switching power supply to control circuits. Because the electronic tolerance and heat impact ability of transistor and integrated device is poor. So the reliability of driver power supply influences LED products’ lifespan. In order to protect the safety of switching power supply and extend working life, we should design safe and reliable protective circuits.
First one is direct transmission circuit. Switching power supply often uses half-bridge and full-bridge topological structure. In the commutation period, it is easy distracted to generate direct transmission. Large direct transmission current can damage the contravariant power electronic devices. Once it occurs direct transmission, we should test and turn-off driver as soon as possible to avoid switching devices burnout with overlarge heat.
Second one is over-current protective circuit. The LED power supply occur load short circuit, overload or control circuit failure accident, which gives rise to the switching tube over-current and increasing power dissipation and emitting heat of tube. If there is no over-current protective device, large power switching tube maybe damage. Over-current protection is tested by sample resistance and Hall sensor to realize protection.
Third one is startup and shutdown current overshoot protective circuits.It is very easy for stable switching power supply to generate current overshoot when starting up and shutting down. Instant large current maybe damage LED device. So we should strictly prevent current overshoot.
Fourth one is overvoltage protective circuits. The load of stable power supply occurs circuit breaking. Two ends of resistor’s voltage drops to zero. Once the value is not zero, the output voltage of regulator will increase the maximum value, which is very dangerous for the poor load connector.
In order to solve above the questions, there are two protective methods we should use at the same time. Firstly, we can place bidirectional TVS to protect the instant impulse voltage. Secondly, we should shut up LED power supply as soon as possible when the load circuit breaking.