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Author Topic: Floatable power supply one side of isolation amplifier  (Read 613 times)


  • Chipper
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Floatable power supply one side of isolation amplifier
« on: November 07, 2017, 04:50:31 AM »

I am making a circuit where I need to float one part of the circuit with (-200V) I am using isolating amplifiers ISO124 to isolate that part of the circuit.

An image below should explain what I am trying to say.

The part in the orange box is isolated and floated to -200V (floating ground, FGND). The problem I am having is finding power supply for the op amps on the floatable side of the circuit. The parts outside the orange box can be floated easily with any +- 15V power supply. What do I do with the part inside the orange box?

I have researched a bit and found several DC-DC isolated power supplies, but I am not sure how to float them so that I can have 200+15 V and 200-15 V power supply for the opamps in the floatable region.

I guess what I am asking is if there is a isolating power supply device something like

Where there are three terminals on the output side ( right) and I can float it to whatever I want. If not? what other choices do I have. I have seen many people using optocouplers and isolating amps, there has to be something people do to power opamps in the floating side.

I can use the DC-DC isolated power supplies, but I not only have to float the FGND, but also the rail voltages of the op-amps relative to FGND like so:

I want the rail voltages to be FGND+15V and FGND-15V and not, FGND+30V and FGND.


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Re: Floatable power supply one side of isolation amplifier
« Reply #1 on: November 07, 2017, 11:46:55 AM »

Take a page from a zillion SMPS designs and make the -15v from the -200v rail.  A couple resistors to a zener.   MAybe?


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Re: Floatable power supply one side of isolation amplifier
« Reply #2 on: November 08, 2017, 11:01:37 PM »

Search a site like Mouser for DC-DC converters. You can choose isolated or non-isolated, you want isolated. The next most important selection is the input Voltage. 5V and 48V are common but other Voltages are available. You probably want +/- 15V for output but you need to know how much current is needed. Most DC-DC converters come in some kind of brick form but there are also small PC board and DIP packages. The data sheet for the supply will specify a maximum isolation Voltage.

DC-DC converters can be quite expensive. They get used in military and industrial products. They can be found at surplus stores, but you will need to dig up the proper data sheet to get all the data.
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