One of our previous articles explained about the working transistor acts as a switch, but that circuit was suitable only for logic level (to generate 0 or 1) and LED applications. For applications with inductive loads (high current, high power) such as DC motors, and relays we need another version of the transistor switch circuit. Large current flow through the device is essential for power electronics applications. In this article, we are going to explain the basic working of transistor switching for inductive loads (relay, motor). This circuit is also called a motor driver circuit or relay driver circuit if the motor in the below circuit diagram is replaced by a relay. We have also provided a small animation for a better understanding of the work.
- Power supply
Working of Relay Driver Circuit Using Transistor
- As we know, the threshold voltage required at the base terminal of an NPN transistor is 0.6V for silicon and 0.3 for germanium.
- Above the cut in voltage, the transistor turns ON (current flow from collector to emitter). In the circuit diagram, our load is a motor (Inductive load).
- We have applied the threshold voltage via a switch. When the switch is closed the transistor becomes ON and the motor loads current flows from Vcc to the ground through the transistor.
- Hence the motor rotates. If we remove the base drive voltage, the transistor becomes OFF, and no current flows through the load.
- To drive high current inductive loads we often use this circuit.
Hope this tutorial gives you enough explanation. You can try this at your home and use it as a control circuit for any DC motor.