How to isolate 5V and 12V circuit

Hello everyone,

I have extend existing circuit design by adding a 12V relay to it. AT the moment both 5V and 12V circuit are side by side. This doesn't work well. Intermitent device failure happen.

I would appreciate opinion and instruction on how to isolate these two circuit. I already have some idea to put the relay and it 12V voltage supply on another board. But I have no idea whether this will work or not.

Thanks in advance

Reply to
Loading thread data ...

The most important points are:

The 12 volt supply and the 5 volt supply commons connect at one point, only, at the relay driver

The relay supply be bypassed to this common point with a capacitor, before the power heads for the relay coil.

The relay coils have reverse voltage suppression connected across them. This can be a diode, a diode in series with a zener or resistor, or a series RC (or some other choices). The point is that if a driver turns off the relay coil current and there is no place for the inductive current to go, the coil produces a very high voltage pulse.

These 3 solve most relay next to logic problems.

John Popelish
Reply to
John Popelish

If I could add one more to Mr. Popelish's list:

  • Do what you can to minimize arcing at the relay contacts, especially if you're switching an inductive load.. The EMI can cause upsets on logic level lines.

One good way to do tis is to put an R-C snubber across the inductive load. What this does is reduce the rate of rise in voltage across the load so the relay contacts can get far enough apart to avoid arcing.

Good luck Chris

Reply to

I have always totally isolated, using split planes and creepage distances, any area of my boards that drive relay coils. Yes, snubbers on the load and diodes (TVS) on the coil help. I would still supply an isolated 12V to the relay-driving side of my circuit and communicate through optocouplers to it.

As an alternative, you might consider solid state relays. They might be a bit more expensive than the mechanical one you are using, but they won't kill the rest of your circuit with +/- spikes. They come in big and small sizes (I use them to drive 6A motors!).

Reply to
Andrew DeWeerd

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.