Power adapter output overvoltage failure

　　For output over-voltage faults, the over-voltage sharp protection circuit works as follows: When the output voltage rises to exceed the operating voltage set by the over-voltage sharp protection circuit, the Zener diode ZD is turned on, and the driving current passes through R to the gate of the thyristor. The delay capacitor C1 is charged.

　　After a short time delay determined by the capacitors C1 and R4, the voltage on C1 will be charged to the gate turn-on voltage (0.6V) of the thyristor. At this time, the thyristor is turned on and the current is limited by the smaller resistance. Resistor R3 short-circuits the output terminal. At this moment, there is a large current flowing through the unadjusted DC input terminal. The overvoltage of the bypass connection is abruptly protecting the thyristor. In order to prevent excessive power consumption of the thyristor, in the linear regulator, the generally adopted method is to add a fuse or a circuit breaker to the unregulated DC power adapter.

　　If the above-mentioned short-circuit fault occurs in the series regulator Q1, the fuse or circuit breaker is disconnected, and the connection between the main power adapter and the output will be cut off before the thyristor for rapid overvoltage protection is damaged.

　　For such a system, its design conditions have been well defined, but it is only required to select the overvoltage protection thyristor or other bypass devices to ensure that the selected device can bear more energy than the fuse or circuit breaker. The energy is even greater.

　　For thyristors and fuses, the "let-through" energy is usually defined as Pt, where I is the fault current and t is the operating time of the fuse or circuit breaker.

　　Because system engineers assume that the overvoltage surge protection circuit can provide adequate protection (even if an overvoltage condition is caused externally), they have a soft spot for it. However, this kind of protection circuit does not always provide adequate protection. System engineers should be aware of abnormal situations that may occur.

　　In the standard "off-the-shelf" power adapter design, the overvoltage protection thyristor is generally selected to protect the load from the failure of the internal power adapter. In most of these situations, the maximum let-through power under fault conditions has been determined by a suitable, selected internal fuse. Therefore, the power adapter and load are 100% protected against internal faults. In a complete power adapter system, there may be an external power adapter, and the power adapter may also be connected to a thyristor to protect the end face of the power adapter and cause some system failures. Obviously, in the event of a fault, the current flowing through the protection device used for overvoltage protection may exceed its rated current. At this time, the overvoltage protection device may fail, such as an open circuit, which will also cause the load to be overvoltage. State.

　　It is impossible for the power adapter designer to predict these external fault load conditions. This is the responsibility of the system engineer or user. They should determine the worst-case fault state, so as to provide the most suitable overvoltage protection device.https://powerstation-gf.com/prodcuts/SPS-001-wall-mounted-home-energy-storage_283.html

　　Power adapter overvoltage protection

　　In the event of a failure, the output voltage of most power adapters may be higher than the specified or required value. In a power adapter without a protection circuit, excessive output voltage may damage the internal or external equipment of the power adapter. In order to protect the power adapter equipment under such abnormal working conditions, the generally adopted method is to add an overvoltage protection circuit to the power adapter.

　　Because TTL circuits and other logic circuits are easily damaged by overvoltage, providing overvoltage protection to the output of such circuits has become a common practice in industrial applications. As for other output voltage protection functions, they are usually added according to the needs of system engineers or users.

Read recommendations:

DC 5V high power switching power supply board AC DC inverter 5V 2A converter bare cir

Low power adapter 3.6W

24W desktop

Is the power adapter a switching power supply?

Maintenance Methods for 12V Switching Power Supply