High Current Transistor Switch for DC Motor Control Circuit

One of our previous articles explained about the working of transistor acts as 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, relays we need another version of transistor switch circuit. Large current flow through the device is essential for power electronics applications. In this article we are going to explain about the basic working of transistor switching for inductive loads (relay, motor).This circuit is also called 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 better understanding of the working.

Also read: How to connect relay: Relays working with animation

Circuit diagram

Transistor as switch circuit

Components required

  1. Transistor
  2. Resistor
  3. 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 load current  flows from Vcc to ground through the transistor.
  • Hence the motor rotates. If we remove the base drive voltage, the transistor become OFF and no current flows though the load.
  • To drive high current inductive loads we often use this circuit.

Transistor acts as switch Animation/ Simulation

Hope this animation gives you enough explanation. Don’t forget to use the comment box below if this article was helpful to you. Also subscribe us, like our facebook page and follow us on Google plus. Cheers!
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3 thoughts on “High Current Transistor Switch for DC Motor Control Circuit

  1. How can I use a 12 volt automobile battery as a power source and automatically turn a 12 volt light on when it becomes dark which is connected to the same 12 volt battery?

    Please; keep it as simple as possible!
    Thanks

  2. Please can the remote control circuit for electric bulb be use in putting on and off a generator of 250watt?

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