In addition to being stable, efficient, and reliable, a good LED switching power supply must be carefully designed to avoid effective protection of power circuits and loads under complex environmental conditions. This article describes LED switches. Several common protection circuits for power supplies.
1. Overcurrent protection circuit
In the DC LED switching power supply circuit, in order to protect the adjusting tube from being short-circuited and the current is increased, it is not burned. The basic method is that when the output current exceeds a certain value, the adjustment tube is in a reverse bias state, thereby being turned off, and the circuit current is automatically cut off. As shown in Figure 1, the overcurrent protection circuit consists of a triode BG2 and voltage divider resistors R4, R5. When the circuit works normally, the base potential of BG2 is higher than the emitter potential through the pressure of R4 and R5, and the emitter junction is subjected to the reverse voltage. Therefore, BG2 is in the off state (equivalent to an open circuit) and has no effect on the voltage regulator circuit. When the circuit is short-circuited, the output voltage is zero, and the emitter of BG2 is equivalent to ground. BG2 is in a saturated conduction state (corresponding to a short circuit), so that the base and emitter of the adjustment tube BG1 are short-circuited and are in an off state. Cut off the circuit current for protection purposes.
Figure 2: LED switching power supply input overcurrent protection circuit
2. Overvoltage protection circuit
The overvoltage protection of the switching regulator in the DC LED switching power supply includes input overvoltage protection and output overvoltage protection. If the voltage of an unregulated DC power source (such as a battery and a rectifier) ​​used in a switching regulator is too high, it will cause the switching regulator to malfunction or even damage the internal components. Therefore, it is necessary to use the input in the LED switching power supply. Voltage protection circuit. Figure 3 is a protection circuit composed of a transistor and a relay. When the voltage of the input DC power supply is higher than the breakdown voltage of the Zener diode, the Zener diode breaks down and a current flows through the resistor R. Transistor T is turned on, the relay operates, the normally closed contact is disconnected, and the input is cut off. The polarity protection circuit of the input power supply can be combined with the input overvoltage protection to form a polarity protection identification and overvoltage protection circuit.
Figure 3: LED switching power supply input overvoltage protection circuit
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