2
\$\begingroup\$

I'm trying to convert all relays and solenoids to transistors in a circuit to make it solid state. I have a small (150cc) 12V DC starter motor that is currently turned on by a small transistor turning on a solenoid, but now I want to use a larger transistor to be able to do the solenoid's work.

Would there be anything wrong in doing this? I realize I need to measure the motor's current draw while it is under load to pick an appropriate sized transistor. If this would work, would you recommend a MOSFET instead of a BJT for this application? I should also put a 1N4007 flyback diode on the motor's terminals as well, correct?

Thank you for your input.

\$\endgroup\$
3
  • \$\begingroup\$ A solenoid is typically used to convert electrical energy to physical motion, unlike a relay which uses electrical energy to operate an electrical switch. It may be reasonable to replace a relay with a transistor, but not a solenoid. \$\endgroup\$
    – DoxyLover
    Commented Oct 26, 2014 at 21:21
  • \$\begingroup\$ A solenoid can be many things, but in my question it is used as an electrical switch, is it not? \$\endgroup\$
    – klcjr89
    Commented Oct 26, 2014 at 21:55
  • \$\begingroup\$ A solenoid is typically a physical actuator which will push, pull or turn a physical object. For example, magnetschultz.co.uk/uploads/images/product_images/… \$\endgroup\$
    – DoxyLover
    Commented Oct 27, 2014 at 4:18

1 Answer 1

Reset to default
3
\$\begingroup\$

A MOSFET may be a better choice for the following reasons:

  • Today's power MOSFETs are amazing devices with options for extremely low ON resistance and quite high current capacity.

  • The MOSFET uses a voltage control input which can be easier to drive in a high speed manner to reduce switching time loss in the device.

  • There are even devices commonly referred to as Smart FETs that have built in gate drivers and fault control circuitry. Deploying these devices simplifies the driving aspects and helps to protect the high current FET device from overloads.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.