Shunt Based Smart Solenoid "Diode" for Battery Isolation

[curtis.perrin]

Hi there

I'm wondering if anyone knows of a product that is essentially a circuit that only lets current flow in one direction using a relay.

I'm thinking its a simple IC that boots up, closes a relay then watches the direction of current flow and if the flow goes one way it opens the relay. We're trying to charge a 12V battery from a DCDC powered bus but need to ensure that the battery doesn't back power the bus when the DCDC is turned off. Looked a little at battery isolators or just straight diodes but those have leakage and power loss. Something as described above would essentially cut power to itself and have 0 parasitic load.

Curtis

 

[amberwolf]

Well, there are "ideal diodes" made of FETs, maybe they would do what you want without the complications?

There's a few versions discussed on ES / etc
https://www.google.com/search?newwindow=1&q=ebike+%22ideal+diode%22&oq=ebike+%22ideal+diode%22

This is a commercial unit:
http://www.ti.com/lit/gpn/LM74700-Q1


There may also be something out there that is closer to or exactly what you want, but it would be more complex. If you really want a chip to boot up and do it, you could use a small MCU, atttiny, or pic, and a small shunt, but you'd need a regulator for the MCU's power (3.3v or 5v).

It might be simpler to use as a relay-control a small transistor that's kept on only by current flowing thru a small diode/resistor string, where the current flow has to be into the battery for it to work, and if it's not then it doesn't have enough voltage across the resistor to turn the transistor on. If the transistor isn't on, it's collector isn't grounded, and it doesn't engage the relay coil anymore.



Everything you use will have *some* power loss, though not as much as a straight diode might.