Usually people want to control a larger voltage with a smaller one using a microcontroller of some sort. Here I've found myself needed to allow current to flow threw a 5V wire only when there is power going through a 12V wire on a completely different circuit.

Quick recap. If there is 12V power flowing, allow the 5V source to pass through. If there is no 12V source present, flip the switch and shut that 5V source off. (There is always power going threw the 5V source but not always threw the 12V source).

Let me know what you guys think would work the best. Please provide a specific product name (LMxxxx) and don't just say MOSFET or SSR, etc.

 

Are you averse to using a relay?
Using AC or DC?
The device will depend on the power requirement.
Max.

 

As @MaxHeadRoom notes, the choice depends on the details of the sources and loads. Voltage, AC or DC, current or wattage, etc.

Assuming 5V and 12V DC, do they share a common ground or are they completely isolated from each other?

 

Let me know what you guys think would work the best. Please provide a specific product name (LMxxxx) and don't just say MOSFET or SSR, etc.

It makes a big difference if it's 5 V 200 AMPs or 5V 100 mA. Do you know what kind of voltage drop the 5V can tolerate?

 

Are you averse to using a relay?
Using AC or DC?
The device will depend on the power requirement.
Max.

As @MaxHeadRoom notes, the choice depends on the details of the sources and loads. Voltage, AC or DC, current or wattage, etc.

Assuming 5V and 12V DC, do they share a common ground or are they completely isolated from each other?

It makes a big difference if it's 5 V 200 AMPs or 5V 100 mA. Do you know what kind of voltage drop the 5V can tolerate?

It's a 5V DC and 12V DC. The current draw on the 5V is no greater than a amp. The current on the 12V is about 200mA. This is all automotive wiring and the 12V is a remote turn on wire.

I want to use the remote turn on wire to allow and disallow power to a add on 5V device.

 

Perhaps this or something similar is a suitable solution:

5V regulator with remote shutdown

 

Perhaps this or something similar is a suitable solution:

5V regulator with remote shutdown

Here is a image that I made that showed the two "circuits" I'm working with. I don't need any voltage regulators as the red wire in the diagram is 5V and the blue wire is 12V. Both have current that is less than 1A.

I am trying to find a device that would resemble the yellow box or something similar.

 

Did you read post #2?

http://uk.rs-online.com/web/p/produ...s_iFRQSpQZEJ8sdQSw9PZQ8FTgsuc7Mzo8BoC9Rzw_wcB

 

That's a good solution. If power for the coil is an issue you can probably use a low threshold voltage low on resistance P-channel MOSFET, but the relay would be a very robust solution.

 

Did you read post #2?

http://uk.rs-online.com/web/p/produ...s_iFRQSpQZEJ8sdQSw9PZQ8FTgsuc7Mzo8BoC9Rzw_wcB

That's a good solution. If power for the coil is an issue you can probably use a low threshold voltage low on resistance P-channel MOSFET, but the relay would be a very robust solution.

I definitely can use a relay! That's what I figured I might end up using but was looking for a specific part like the link above. Is there by chance a site that sells that in the USA that may have reasonable shipping times / prices. I searched the same item on Amazon and it was 5 times the price and had a two week shipping time.

 

These relays are available just about everywhere, it's a standard 12V automotive relay.

 

Automotive relays are pretty standard and only come in a few variations. The can be had in about any automotive parts store including any required connectors or sockets. Here is an Amazon example:
Car Auto Truck Relay & Socket SPDT 12V 12 Volt DC 40A AMP 5Pin
That is really all you need. Now if you want to go solid state and use electronic switching with a MOSFET type device SparkFun sells the FQP27P06 P Channel and the 30N06 N Channel for about a buck each. Personally I would walk into any auto parts store and buy an off the shelf relay. Actually you only need a SPST not a DPDT as I linked to. Either would work actually but all you need is SPST.

Ron

 

You can use any varient of these OPTOMOS parts, Here https://www.digikey.com/products/en?keywords=CLA249CT-ND is one such part.

You would have to mount on a small PCB which you can buy, add a resistor and package into a large piece of heat shrink. The LED drops about 1.5 V and uses 10 mA, Some m=need as low as 1 mA.

R would be <= (12-1.5)/10e-3; You might want to pick 10 V as the design value. 13.8 would be the engine running value.