Based on a design scheme for protecting an LED switching power supply
LED switching power supply over-current protection circuit, LED switching power supply over-voltage protection circuit, LED switching power supply soft-start protection circuit, LED switching power supply overheating protection circuit ...... industry insiders to contribute to several practical circuit diagrams, with you to do a good job in the protection design of LED switching power supply.
LED switching power supply overcurrent protection circuit
In the DC LED switching power supply circuit, in order to protect the regulator tube in the circuit short-circuit, the current increases not to be burned. The basic method is, when the output current exceeds a certain value, the adjustment tube is in reverse bias state, and cut off, automatically cut off the circuit current. As shown in Figure 1, the overcurrent protection circuit consists of transistor BG2 and voltage divider resistors R4 and R5.
Circuit normal operation, through the pressure of R4 and R5, making the base of BG2 potential than the emitter potential is high, the emitter junction to withstand the reverse voltage. So BG2 is in the cut-off state (equivalent to open circuit), no effect on the voltage regulator circuit. When the circuit is short-circuited, the output voltage is zero, the emitter of BG2 is equivalent to ground, then BG2 is saturated conduction state (equivalent to a short circuit), so that the regulator BG1 base and emitter near short-circuit, and is in the cut-off state, cut off the circuit current, so as to achieve the purpose of protection.
LED switching power supply overvoltage protection circuit
DC LED switching power supply switching regulator overvoltage protection including input overvoltage protection and output overvoltage protection. If the switching regulator used by the unregulated DC power supply (such as batteries and rectifiers) if the voltage is too high, will lead to the switching regulator can not work properly, or even damage to the internal devices, so the LED switching power supply there is a need to use the input overvoltage protection circuit.
Figure 3 for the transistor and relay protection circuit, in the circuit, when the input DC power supply voltage is higher than the breakdown voltage of the regulator diode value, the regulator breakdown, there is a current flow through the resistor R, so that the transistor T conductive, 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 a polarity protection identification and overvoltage protection circuit.
LED switching power supply soft start protection circuit
Switching regulated power supply circuit is more complex, the input of the switching regulator is generally connected to a small inductor, large capacitor input filter. At the moment of switching on, the filter capacitor will flow a large inrush current, the inrush current can be several times the normal input current. Such a high inrush current can melt the contacts of a normal power switch or relay and blow the input fuse. In addition, inrush currents can also damage capacitors, reducing their life span and causing premature damage. For this reason, a current limiting resistor should be connected at switch-on, through which the capacitor is charged. In order not to make the current limiting resistor consume too much power, so as not to affect the normal operation of the switching regulator, and at the end of the power-on transient process, use a relay to automatically short it, so that the DC power supply directly to the switching regulator power supply, this circuit is known as DC LED switching power supply "soft start" circuit.
LED switching power supply overheating protection circuit
DC LED switching power supply in the switching regulator of high integration and lightweight small volume, so that the power density per unit volume greatly improved, so if the power supply device components within the working environment temperature requirements are not correspondingly improved, will inevitably make the circuit performance bad, premature failure of components. Therefore, in the high-power DC LED switching power supply should be set up overheating protection circuit.
