isolationpowerpower electronicspower supply
I need to equalize the ground voltage between the input and output of an isolated DC-DC power supply while still maintaining galvanic isolation. Is there a way to do this?
The reason I need this is so that I don't exceed the maximum isolation voltage rating on the DC-DC power supply.
You're looking for an isolation amplifier. These are great if you're looking for a monolithic solution that is easy to integrate, but might not be cost-optimized. Some even provide a little isolated (HV-side) power via an internal DC/DC converter to run scaling op-amps, etc.
I've had good luck with the Burr Brown ISO series of isolation amplifiers (acquired by TI a few years back). The ISO122 is a general use product, and the ISO124 has higher accuracy.
Analog Devices also makes a few general purpose isolation amps.
Just be aware that some sort of modulation is required to move the signal across the isolation barrier within an isolation amplifier. Some do it inductively, some optically. Either way, plan on a little ripple on the output signal. The specs usually do a good job of outlining the limitations.
Sure they have transformers: -
The transformer looks different to a regular AC type but it's still the largest single component on the PCB but a whole lot smaller than it would be for 50/60 Hz operation. The transformer is the big yellow taped thing in front of the heat sink at the back/left.
SMPSs also use opto-isolators for feeding back a measure of the output voltage so that it can be regulated. This is another significant isolation feature thus, output and input remain galvanically isolated to several kV and are therefore "safe".
Best Answer
If I had a black box with two wires going into it and was told that the two wires ARE NOT galvanically connected but, V1 always equals V2, then the only reasonable conclusion I could draw is that they ARE galvanically connected and they are indeed shorted.
Imagine putting your multimeter across the two wires - it would read zero ohms. It couldn't possibly read anything else because V1 = V2.