MFAC14K1AA0001A Auxiliary variable speed relay ALSTOM

Relay in series RC circuit: This form is mainly used in circuits where the rated operating voltage of the relay is lower than the supply voltage. When the circuit is closed, the electromotive force generated by the self-inductance phenomenon of the relay coil will hinder the increase of current in the coil, thus prolonging the closing time. After the RC circuit is connected in series, the closing time can be shortened. The principle is that at the moment when the circuit is closed, the voltage at both ends of capacitor C can be regarded as a short circuit if it cannot be mutated. In this way, the power supply voltage higher than the rated working voltage of the relay coil is added to the coil, thus speeding up the increase of current in the coil and making the relay pull in quickly. After the power supply is stabilized, capacitor C does not work and resistance R acts as current limiting function.

2. Selection of rated working voltage of relay
The rated working voltage of relay is the most important technical parameter of relay. When using a relay, the working voltage of the circuit (that is, the circuit where the relay coil is located) should be considered first. The rated working voltage of the relay should be equal to the working voltage of the circuit. Generally, the working voltage of the circuit is 0.86 of the rated working voltage of the relay. Note that the workpiece voltage of the circuit must not exceed the rated working voltage of the relay, otherwise the relay coil is easy to burn. In addition, some integrated circuits, such as NE555 circuit can directly drive the relay work, and some integrated circuits, such as COMS circuit output current is small, need to add a transistor amplifier circuit to drive the relay, which should consider the transistor output current should be greater than the rated working current of the relay.

1, transistor drive circuit

When a transistor is used to drive a relay, its emitter must be grounded. The specific circuit is as follows:NPN transistor drive: when the transistor T1 base is input high voltage level, the transistor saturation conduction, the collector becomes low level, so the relay coil is energized, contact RL1 suction. When the transistor T1 base is input low level, the transistor shuts off, the relay coil is powered off, and the contact RL1 is disconnected.

Summary: This paper introduces the working principle of the relay and the driving circuit of the relay. The design of the driving circuit depends on the drawing voltage and current of the relay coil, which must be greater than the drawing current of the relay to make the relay work reliably.