A good LED switching power supply not only needs to be stable, efficient and reliable, but also all kinds of protection measures of the circuit must be carefully designed to avoid the effective protection of the switching power supply circuit and load quickly under complex environmental conditions. This paper introduces several common protection circuits of LED switching power supply.

Overcurrent protection circuit
In the DC LED switching power supply circuit, in order to protect the adjustment tube in the circuit short circuit, increase the current will not be burned. The basic method is that when the output current exceeds a certain value, the regulating tube is in the reverse bias state, so as to cut off the circuit current automatically. As shown in Figure 1, the overcurrent protection circuit is composed of triode BG2 and divider resistors R4 and R5. When the circuit is working normally, the voltage effect of R4 and R5 makes the base potential of BG2 higher than that of the emitter, and the emitter junction bears the reverse voltage. Therefore, BG2 is in the cut-off state (equivalent to open circuit) and has no effect on the voltage regulator circuit. When the circuit shorts, the output voltage is zero, the emitter of BG2 is equivalent to ground, and BG2 is in saturation conduction state (equivalent to short circuit), so that the base pole and emitter of adjusting tube BG1 are close to short circuit, but in the cut-off state, and the circuit current is cut off, so as to achieve the purpose of protection.
LED switching power supply input overcurrent protection circuit

Overvoltage protection circuit
The overvoltage protection of switching regulators in DC LED switching power supply includes input overvoltage protection and output overvoltage protection. If the voltage of the unstabilized DC power supply (such as accumulator and rectifier) used by the switching regulator is too high, it will lead to the failure of the switching regulator and even damage the internal devices. Therefore, it is necessary to use the input overvoltage protection circuit in the LED switching power supply. In this circuit, when the voltage of the input DC power supply is higher than the breakdown voltage of the regulator diode, the regulator tube is broken down, and a current flows through the resistance R, making the transistor T conduction, relay action, normally closed contact disconnect, cut off the input. The polarity protection circuit of the input power supply can be combined with the input overvoltage protection to form the polarity identification and overvoltage protection circuit.

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