I have a coil that has the following specs:

  • Coil Resistance: 123 ohms
  • Coil Current: 97.5 mA
  • Switching Voltage: 14 VDC

I am trying to use a 5V PWM output from an ECU to switch the relay. I know I need to use a transistor but I am way over my head in regards to how to decide the part and design the ciruit.

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    \$\begingroup\$ You want to switch it at the PWM frequency, or at what point in the duty cycle? What is the on-level and off-level? \$\endgroup\$ – Ron Beyer Jul 21 '20 at 21:35
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    \$\begingroup\$ Take a look here: electronics.stackexchange.com/questions/146499/… \$\endgroup\$ – winny Jul 21 '20 at 21:38
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    \$\begingroup\$ As soon as I receive any PWM signal. 0 for off, everything else is on. So I think I found a schematic of the circuit I need, just need to know if this makes sense: supramania.com/photobucket/post-1847585-1-8c7b18af.jpg \$\endgroup\$ – SideSwipe PB Jul 21 '20 at 21:39
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    \$\begingroup\$ I assume you want the relay to switch when the PWM duty cycle goes above or below a certain duty cycle? Not that you want to actually switch the relay directly with the PWM? Because relays can't switch that fast. \$\endgroup\$ – DKNguyen Jul 21 '20 at 21:39
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    \$\begingroup\$ @SideSwipePB Yeah, that circuit should work. There will be a delay between when the PWM starts and when the relay activates, and especially when the signal tops and the relay deactivates. Take mind of potential overheating of the MOSFET as it switches on or off since it may do so very slowly producing heat in the process. It depends how slow and how frequently you do it. \$\endgroup\$ – DKNguyen Jul 21 '20 at 21:40

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