Relay is an electronic circuit element commonly used in general by the transistors, relays and other components of the composition of the electronic switch driver circuit, often have to add some additional circuitry to change the operating characteristics of the relay or protective effect. Additional relay circuit mainly has the following three forms:
1. Relay series RC circuit: the circuit in the form shown in Figure 1, this form is mainly used in the relay rated voltage below the supply voltage circuit. When the circuit is closed, the relay coil will produce the phenomenon of the self-inductance emf hinder the increase of current in the coil, thus extending the pull-time series on the RC circuit can be reduced after the pull time. Closed circuit principle is the moment, the voltage across capacitor C mutation can not be regarded as short-circuit, so that the relay coil than the high voltage power supply rated coil voltage is applied, thereby speeding up the rate of coil current increases, so quickly pull the relay. Capacitance C does not work after the power and stability, resistance R from the limiting effect.
2. Relay parallel RC circuit: the circuit in the form shown in Figure 2, the circuit is closed, when the current stable RC circuit does not work, disconnect the circuit, the relay coil inductance and the induced electromotive force generated by the RC circuit is discharged, so that slow decay of current in the coil, the relay armature to extend the release time, play time delay effect.
3. Relay parallel diode circuit: circuit in the form shown in Figure 3, mainly to protect the transistors and other drive components. When the figure turns the transistor into cutoff by the VT, the current flowing through the relay coil will decrease rapidly, when the self-inductance of the coil will produce a high electromotive force and the supply voltage in the VT’s stacked Jiahou Jia c, e between two poles will lead to transistor breakdown, the diodes in parallel, you can force the self-inductance of the coil in the clamp diode forward voltage, the value of silicon tube of about 0.7V, germanium tube of about 0.2V, transistor and other drivers to avoid breakdown components. Parallel diode must pay attention to the diode polarity is not reversed, or easy to damage the transistors and other drive components.