Electronics > Projects, Designs, and Technical Stuff
Can I get -5V from an "isolated" DC-DC converter?
rea5245:
Hi. I have a +5V supply and I need to get -5V (low current, a few mA) for one part of my circuit. I'm looking at the PDME1-S5-S5-S DC-DC converter module (https://www.cui.com/product/resource/pdme1-s.pdf) which says it takes a +5V input and produces an isolated +5V output.
Am I correct that, since it's isolated, I can tie its +Voutput to my board's ground so that the 0V output is -5V relative to my ground?
Is there really a tiny transformer in that module, or is there another strategy for isolating power?
Thank you,
Bob
Siwastaja:
Yes, you can do that, and yes, it has a tiny transformer and a crappy driver driving it.
Note they are unregulated and the ripple and EMC may not be that great.
daqq:
--- Quote ---Is there really a tiny transformer in that module, or is there another strategy for isolating power?
--- End quote ---
Yup, it's a tiny transformer. See:
Isolated modules are generally more expensive than a non isolated solution and may have various issues (lack of regulation and feedback, minimum load requirements...). Also, that module looks like a massive overkill for a few mA. Maybe you could look at non-isolated solutions such as:
https://www.analog.com/en/technical-articles/micropower-sot23-inverting-dcdc-converter-extends-battery-life.html
MagicSmoker:
--- Quote from: Siwastaja on December 28, 2019, 04:16:16 pm ---Yes, you can do that, and yes, it has a tiny transformer and a crappy driver driving it.
Note they are unregulated and the ripple and EMC may not be that great.
--- End quote ---
Well, whaddya expect for $4? :P
OP: If the output doesn't need to be isolated and the load only draws a few mA then the obvious solution is the classic '7660 inverting charge pump. The original part number is ICL7660 but it has been second sourced by pretty much every semi manufacturer on the planet: https://www.mouser.com/Semiconductors/Power-Management-ICs/Voltage-Regulators-Voltage-Controllers/Switching-Voltage-Regulators/_/N-668jtZ1yzvvqx?Keyword=7660&FS=True
mariush:
For non isolated output, look up ratiometric / charge pump regulators.
Here's examples: https://www.digikey.com/short/zc8r13
Microchip makes one in DIP package, TC7660 : http://ww1.microchip.com/downloads/en/DeviceDoc/21465C.pdf
It's cheap and in the list above, for under 1$.
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