How to protect the circuit through relay contacts?

Release time：

2022-10-31 09:47

Under normal temperature and pressure, the key dielectric breakdown voltage in the air is 200~300V Therefore, our goal is generally to control the voltage below 200V or less. Through relay contact protection circuit, we generally have the following centralized methods to suppress:
1. Relay series RC circuit
This form is mainly applicable to circuits with rated working voltage of relay lower than power supply voltage. After the circuit is closed, the current of the relay coil interfered by the electromotive force increases due to the magnetic induction phenomenon, thus prolonging the suction time. After the RC circuit is connected in series, the suction time is shortened. The principle is that when the circuit is closed, the voltage at both ends of capacitor c cannot be considered as a sudden short circuit. In this way, the power supply voltage higher than the rated working voltage of the relay coil is added to the coil, so as to speed up the increase of current in the coil and make the relay absorb quickly. When the power supply is stable, capacitor c cannot work, and resistance r acts as a current limitation.
2. Relay parallel RC circuit
When the circuit is closed, the RC circuit cannot work when the current is stable. When the circuit is separated, the relay coil generates electromotive force through magnetic induction, discharges through the RC circuit, slows down the current attenuation of the coil, extends the relay armature release time, and plays a delay role.
3. Relay shunt diode circuit
It is mainly used to protect the drive components such as transistors. When the transistor VT is changed from the deflector to the cutoff, the current through the relay coil decreases rapidly. The coil can destroy the transistor by superposing the high magnetic induction electromotive force and the power supply voltage between the c and e poles of the VT. After the diode is raised in parallel, the magnetic induction clamp of the coil can be placed in the forward conduction voltage of the diode, which is about 0.7V for the silicon tube and 0.2V for the germanium tube, to avoid damaging the drive components such as the transistor. When manufacturing diodes in parallel, it shall be noted that the polarity of the diode shall not be reversed. Otherwise, it is easy to damage the transistor and other drive components.

contact,Relay contact

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