In recent years, the number of people engaged in LED manufacturing and R&D has increased significantly. LED companies are also growing like mushrooms. Due to the large number of enterprises and people engaged in the research and development of LED drivers , their technical level is uneven, and the quality of LED driver circuits developed is mixed. The failure of LED lamps often occurs, which hinders the frequent promotion of LED lighting. LED lamp failure is caused by failure of power supply and drive, and secondly by failure of LED device itself. This paper tries to analyze the working principle of the circuit from the actual LED power supply circuit, and then tries to analyze the failure effect of various working sensitive parameters from the LED driving circuit under different environments to perform the failure mode. The analysis, finally, verified the results by simulation. And theoretically give a solution to failure.
2. LED drive circuit principle
LED is a kind of semiconductor material made of light-emitting diode, which can only be single-pass, and its conduction voltage is not high, and the forward conduction current can not be too large, so there is a certain requirement for the LED power supply, then LED The drive circuit came into being. In actual use, most of the LED products use an alternating current power supply as the power input of the LED driving circuit, and the driving circuit becomes a circuit of a regulated output form or a constant current output form. The LED driver circuit can be divided into many types according to different division criteria. At present, according to the driving principle of the circuit, it can be divided into two categories: one is a linear driving circuit, and the other is a switching driving circuit.
2.1 linear drive circuit
The schematic diagram of the linear drive circuit is shown in Figure 1. The structure generally includes the following parts, the rectifier circuit, the filter circuit, and the voltage regulator circuit.
The figure uses full-wave bridge rectification to rectify the alternating power supply into a unidirectional ripple voltage. The filter circuit adopts RC filtering, and the voltage value filtered by the filter circuit is relatively close to the DC power supply. However, due to the voltage fluctuation on the power grid, the output voltage of the driving circuit fluctuates, which is fatal for the LED. Therefore, the voltage after filtering needs to be added with a voltage regulator circuit. So that the linear drive circuit can maintain a relatively smooth voltage to drive the LED.
In a linear drive circuit, the brightness of the LED is a function of the pass current, independent of the voltage drop applied across the LED. As can be seen from the above circuit schematic, the linear LED driver circuit is simple in structure, easy to implement, short in development cycle, low in production cost, small in size, and, because no large-capacity capacitors and inductors are used, circuit design is not required. Consider EMI issues. Can be applied to low current lighting systems.
2.2 Switching drive circuit
The schematic diagram of the switch-type drive circuit is shown in Figure 2. After the input alternating voltage is rectified and filtered by the rectifier circuit, the current or voltage of the LED is controlled by the switch state, so that the LED can illuminate smoothly. A typical switch-type drive circuit is given below to gradually analyze the operating state of the switch-type drive circuit.
As can be seen from FIG. 2, the switch type LED driving circuit can be divided into the following parts: a low frequency rectification filter circuit, a self-oscillation circuit, a voltage stabilization circuit, a sampling pulse width adjustment circuit, and a high frequency rectification filter circuit.
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