Performance of safety capacitor failure

The application of safety capacitors as electronic components on power circuit boards plays a protective role. It refers to the use in situations where the failure of a capacitor will not cause electric shock and will not endanger personal safety.

It includes two types of capacitors, X capacitor and Y capacitor. X capacitor is a capacitor that is connected across two lines (L-N) of a power line, and generally uses a metal thin film capacitor; Y capacitors are capacitors that are connected in pairs between two power lines and ground (L-E, N-E). Based on the limitation of leakage current, the Y capacitance value cannot be too large. Generally, the X capacitance is of uF level and the Y capacitance is of nF level. X capacitor suppresses differential mode interference, Y capacitor suppresses common mode interference.

What will happen if the safety capacitor is broken? How to confirm if the safety capacitor is damaged?

Generally speaking, if the safety capacitor is broken, the circuit will be cut off and not powered on.

The reasons for the failure of safety capacitors on the power circuit board are analyzed

1: The short circuit and open circuit inside the capacitor are damaged, and the fault phenomenon is the burning of switch tubes and other current limiting components, such as fuses and current limiting resistors in switching power supplies. Short capacitance and broken circuit damage: When the voltage of a filtering capacitor working in high voltage and high current (such as a switching power supply or row output circuit of a color TV) rises for some reason and exceeds its withstand voltage value, it will cause breakdown and short circuit damage, or when the rectifying diode is damaged, a polarized electrolytic capacitor is equivalent to working in an AC circuit, heating up under a large reverse leakage current and short circuit damage. Due to the high current flowing through the capacitor during a short circuit, the capacitor will generally burst or cause its sealing plug to expand. After a short circuit in the filtering capacitor, faults such as fuse or current limiting resistor burning out, power supply thick film blocks or switch tubes, and rectifier tube breakdown often occur. The main manifestation is the "three no" fault of the entire machine, which has commonality in various types of switching power supplies.

2: The inefficiency or slight leakage caused by the reduction of capacitor capacity is caused by the S-shaped distortion or asynchronous movement of the TV image. For current TVs using IIC bus, there are some special fault phenomena. If the synchronization board is in a critical state due to the impact, the accompanying sound can greatly affect the quality of the TV, causing the accompanying sound to appear at any time. The main reason is that the parameters of the capacitor have changed, but they have not completely failed, and to a certain extent, they still have an effect, but they cannot achieve the expected effect, resulting in the occurrence of existing fault phenomena. Moreover, such faults are difficult to diagnose and troubleshoot.

3: The failure, complete leakage, or bursting caused by the disappearance of capacitor capacity is the most difficult fault to distinguish and repair after capacitor failure in power supply. This is because measuring capacitor devices and testing everything with a multimeter is normal, but after installing the capacitor on the circuit, the capacity of the capacitor completely disappears. This is one of the most difficult soft faults to repair in the circuit, that is, the component cannot withstand voltage, and once there is voltage, it is easy to completely disappear.

The main function of safety capacitors on power circuit boards is to filter, pass through AC through DC, and store and boost power. If the safety capacitor is damaged, these functional failures will only cause the circuit to stop working, reduce work efficiency, or malfunction, without damaging other components. It will not pose any danger to the user.