Protection design scheme based on a LED regulated switching power supply
LED switching power supply overcurrent protection circuit, LED switching power supply overvoltage protection circuit, LED switching power supply soft start protection circuit, LED switching power supply overheating protection circuit... Insiders contribute several practical circuit diagrams, and do a good job in the protection design of LED switching power supply with you .
LED switching power supply overcurrent protection circuit
In the DC LED switching power supply circuit, in order to protect the adjustment tube from being burned when the circuit is short-circuited and the current increases. The basic method is that when the output current exceeds a certain value, the adjustment tube is in a reverse bias state, so that it is cut 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 dividing resistors R4 and R5.
When the circuit works normally, the base potential of BG2 is higher than the emitter potential through the voltage action of R4 and R5, and the emitter junction bears the reverse voltage. So BG2 is in a cut-off state (equivalent to an open circuit), which 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 grounding, then BG2 is in a saturated conduction state (equivalent to a short circuit), so that the base and emitter of the adjustment tube BG1 are close to a short circuit, and are in a cut-off state. Cut off the circuit current to achieve the purpose of protection.
LED switching power supply 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 the unregulated DC power supply (such as battery and rectifier) used by the switching voltage regulator is too high, it will cause the switching voltage regulator to fail to work normally, and even damage the internal devices. voltage protection circuit.
A protection circuit composed of transistors and relays. In this circuit, when the voltage of the input DC power supply is higher than the breakdown voltage value of the Zener diode, the Zener diode breaks down, and a current flows through the resistor R, causing the transistor T to conduct On, the relay acts, the normally closed contact opens, 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.
LED switching power supply soft start protection circuit
The circuit of the switching regulated power supply is relatively complicated, and the input terminal of the switching regulator is generally connected with an input filter with a small inductance and a large capacitance. At the moment of power-on, the filter capacitor will flow a large surge current, which can be several times the normal input current. Such a large inrush current can melt the contacts of a normal power switch or the contacts of a relay and blow the input fuse. In addition, surge currents can damage capacitors, shortening their life and prematurely failing them. For this reason, a current-limiting resistor should be connected when starting up, and the capacitor will be charged through this current-limiting resistor. In order not to cause the current limiting resistor to consume too much power, so as to affect the normal operation of the switching regulator, a relay is used to automatically short-circuit it after the start-up transient process is over, so that the DC power supply directly supplies power to the switching regulator. , This circuit is called the "soft start" circuit of the DC LED switching power supply.
