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Several overcurrent protection methods in power modules

Article Source：Kinri Energy | Author：Kinri Energy | Issuing Time：2024.05.20
With the widespread application of modular power supplies in various electronic devices, it is inevitable that overcurrent, overvoltage, or short circuit phenomena may occur due to other factors during use. In order to protect product performance, modular power supplies are designed with overcurrent and short circuit protection functions. Below are several methods of overcurrent protection.


AC DC POWER MODULE

First type: rated current droop type

Hiccup style, self-healing. The principle is to check the circuit to see if there is any overcurrent, and then provide feedback to the control circuit to turn off the output. If overcurrent is still detected after a certain period of time, then provide feedback to the control until the overcurrent disappears.

Second type: constant current type

The product maintains a constant current value, and since the current value is larger than the full load, the design power margin needs to be larger than the nominal value.

Third type: constant power type

When overcurrent occurs, the output power remains unchanged and the current increases, which is protected by reducing the output voltage.

Overcurrent protection is the protection of the module power supply or load when the output is short circuited or overloaded. The principle of overcurrent protection is that when a phase to phase short circuit fault occurs in the power grid, the current will suddenly increase and the voltage will suddenly decrease. According to the requirements of line selectivity, the operating current of the current relay is set. When the fault current in the circuit reaches the operating value of the current relay, the current relay will selectively cut off the faulty circuit according to the selective requirements of the protection device.

For circuit overcurrent protection, the general control method is to turn off or limit the current. Overcurrent circuits generally use fuse current limiting protection or adopt sampling resistors to obtain circuit signals. Fused current limiting protection is widely used in circuits such as switching power supplies and power modules. Fuses have both self recovery and non recovery, and PPTC is one of the non recovery types. The working principle of a fuse is that when the current is abnormal and the power rises to a certain strength, the current causes the temperature to overheat, causing the fuse to melt and the input circuit to disconnect.

The sampling resistor is used to obtain current limiting signal protection. As shown in the above figure, the LM317 current limiting protection circuit is connected to the load through the 2P connector, where R is the sampling resistor. Once the current is too high, the capacitor MC1 is charged, and the charging is greater than the conduction voltage of the transistor 9013. The output voltage of LM317 drops below its reference voltage, which can be around 1.25V, to protect the load.

Overcurrent protection mainly includes two types: short circuit protection and overload protection. The characteristics of short circuit protection are high setting current and instantaneous action. Electromagnetic current releases, relays, and fuses are commonly used as short-circuit protection components. The characteristics of overload protection are small set current and inverse time action. Thermal relays and delay type electromagnetic current relays are commonly used as overload protection components.
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