AG10 battery.Several common protection circuit designs for LED switching power supplies

　　In addition to being stable, efficient, and reliable, a good LED switching power supply must also have various circuit protection measures carefully designed to effectively protect the switching power supply circuit and load quickly under complex environmental conditions. This article introduces 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 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 biased state and thus cuts off, automatically cutting off the circuit current. As shown in Figure 1, the overcurrent protection circuit consists of transistor BG2 and voltage dividing resistors R4 and R5. When the circuit is working normally, the base potential of BG2 is higher than the emitter potential through the pressure effect of R4 and R5, and the emitter junction withstands the reverse voltage. So BG2 is in a cut-off state (equivalent to an open circuit) and has no impact on the voltage stabilizing 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 protection purposes.

　　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 the unregulated DC power supply (such as batteries and rectifiers) used by the switching regulator is too high, it will cause the switching regulator to not work properly or even damage the internal components. Therefore, it is necessary to use an input voltage regulator in the LED switching power supply. voltage protection circuit. Figure 3 shows a protection circuit composed of a transistor and a relay. 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 current flows through the resistor R, causing The 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.

　　3. Soft start protection circuit

　　The switching regulator circuit is relatively complex. The input terminal of the switching regulator is generally connected to an input filter with a small inductor and a large capacitor. At the moment of power-on, a large surge current will flow through the filter capacitor, which can be several times the normal input current. Such a large surge current can melt the contacts of a regular power switch or relay and blow the input fuse. In addition, surge current will also damage the capacitor, shortening its life and causing premature failure. 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 to prevent the current-limiting resistor from consuming too much power and affecting the normal operation of the switching regulator, a relay is used to automatically short-circuit it after the startup transient process, so that the DC power supply directly supplies power to the switching regulator. , this kind of circuit is called the soft-start circuit of DC LED switching power supply.

　　4. Overheating protection circuit

　　The high integration and light weight and small size of the switching regulator in the DC LED switching power supply have greatly increased the power density per unit volume. Therefore, if the requirements for the working environment temperature of the components inside the power supply device do not increase accordingly, it will inevitably This will cause circuit performance to deteriorate and components to fail prematurely. Therefore, an overheat protection circuit should be installed in the high-power DC LED switching power supply.

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