Author Topic: Do I need any extra circuitry for a basic power relay?  (Read 650 times)

0 Members and 1 Guest are viewing this topic.

Offline MarmottaTopic starter

  • Contributor
  • Posts: 37
  • Country: gb
Do I need any extra circuitry for a basic power relay?
« on: January 01, 2020, 06:42:27 pm »
I'm building a low powered PC with an external graphics card and noticed while testing everything for the first time that the graphics card would be constantly powered on, regardless of the state of the PC motherboard. As the motherboard and graphics card both run off separate 12V inputs, I'd thought I'd put a power relay on the input of the graphics card and connect the coil to a low-current 5V signal from the motherboard which would only be active when the PC was powered on.

Since the 5V signal will only ever be present when I want the power passing through the relay to the graphics card, is there any reason to add any further circuitry to the relay for practical or safety purposes?
 

Offline David Hess

  • Super Contributor
  • ***
  • Posts: 17429
  • Country: us
  • DavidH
Re: Do I need any extra circuitry for a basic power relay?
« Reply #1 on: January 01, 2020, 11:49:51 pm »
That should work fine.
 

Offline JustMeHere

  • Frequent Contributor
  • **
  • Posts: 827
  • Country: us
Re: Do I need any extra circuitry for a basic power relay?
« Reply #2 on: January 02, 2020, 12:03:46 am »
You need a fly back diode on the coil. 
 

Offline David Hess

  • Super Contributor
  • ***
  • Posts: 17429
  • Country: us
  • DavidH
Re: Do I need any extra circuitry for a basic power relay?
« Reply #3 on: January 02, 2020, 12:57:50 am »
You need a fly back diode on the coil.

The flyback diode will not hurt but the bulk output capacitance on the 5 volt supply will absorb the back EMF.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf