Isolation on outputs

Question

To measure a voltage in a (potentially dangerous) external system, people typically use a differential amplifier or even an isolation amplifier, something like this:

^{simulate this circuit – Schematic created using CircuitLab}

This way, the voltage going into the safe system isn't directly connected to high voltages, and we can happily put our ADC there and supply it a safe input.

I want to do this the other way around. I am generating a voltage \$V_{out}\$ under 5V, and I would like to apply this voltage across an element of the other circuit.

1. Is there a typical setup for doing this?
2. I believe that the low side of my output will be connected to the ground of the external circuit. That means it would be possible to do this without a differential output - I could just put my regular ground-referenced output into the external circuit. Am I correct to think that it's unsafe to simply connect the two grounds together, or is this the much simpler solution?

Answer 1

The most common solution for your problem is to use an isolation amplifier such as Analog Devices AD210. Note that there are many different models available from many suppliers.

Isolation amplifiers are generally broken into two categories: 2-port & 3-port. The number of ports specifies how many isolated sections are in the amplifier. A 3-port isolation amplifier has the input separated from the output with both sections separated from the power supply input. A 2-port isolation amplifier has the power supply in the same section as either the input or output, depending on that particular model. Obviously, 2-port isloation amplifiers cost less than 3-port units.

Also be aware that the isolation voltage is different between ports. The AD210 that I mentioned earlier has higher isolation voltage rating between the input port and both other ports whereas the output port has a lower isolation voltage between itself and the power supply port.

A quick Google search for the search terms "isolation amplifier" will show you the plethora of options available.

Note also that I as speaking of Analog isolation amplifiers. If you have the ability to convert a digital bitstream into your desired result at the destination, there exists another plethora of digital isolation devices.