regulated relay latch

Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=107480
Printed Date: July 14, 2025 at 11:50 AM

Topic: regulated relay latch

Posted By: zzachattack2
Subject: regulated relay latch
Date Posted: September 16, 2008 at 12:43 AM

Lets say i have a relay that is powered by the ignition wire, however when the ignition is turned off, I want that relay to stay closed by a regulated 12v source. This source will come from a power supply unit for a CarPC. To protect the electronics on the +12v rail of the power supply, I should use a diode correct? I imagined a circuit like the picture. Will this work correct, and will I have to worry about any electronics on the +12 V rail of the PSU being damaged from the larger/smaller voltages of the ignition line?

posted_image

Replies:

Posted By: i am an idiot
Date Posted: September 16, 2008 at 7:11 AM

The banded end of the diode goes at the bottom. As drawn in your diagram.

Your diagram is exactly what you need.

Posted By: dualsport
Date Posted: September 17, 2008 at 7:05 PM

The diodes you show will isolate between the different supply voltages, but if you're at all worried about voltage spikes damaging your PSU drive circuit, you should add a diode across the coil, in addition to the other two.