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Comments on Converting 5V to ±12V

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Converting 5V to ±12V

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I would like to convert 5V rail I have on PCB to ±12V. Existing solution is using boost converter 5V to 12V, and a buck for 5V to -12V. This feels bulky for what it's needed - here are the requirements:

  • +12V and -12V rail shall serve for powering opamp only
  • Ripple of the ±12V rails is not of a concern, as the opamp is used in comparator mode(something I would like to swap with the comparator in the future but keeping it for now in the design)
  • +12V and -12V rail should be within ±5% ie. acceptable voltage range of rail is (11.4V, 12.6V) both for positive and negative
  • ±12V rails shall be capable of providing no more than 5mA of current
  • There is a 3V3 powered uC on board with available PWM output which could be used for charge pumps

Everything mentioned so far asks for a charge pump, the way how I see it.

Some options I found:

  • Maxim/Analog have +5V to ±10V converter IC MAX680/681, with VCC max of 6.2V and V+/V- being +12V/-12V in absolute maximum ratings, I feel like stretching it + it is not within acceptable voltage range
  • Do a DIY charge pump using PWM uC output - haven't done this earlier so if someone could explain a concept with jellybean components that would be a useful answer as well.
  • Use a standalone 5V to ±12V converter like a Murata one
  • Use 2x dedicated charge pumps - 5V to 12V(to be found) and 12V to -12V(TC1044S)

Questions:

  • Could charge pump 5V to ±12V be implemented with 1xPWM output from the uC, how would the circuit look like and what would be the component values(capacitor size, diodes, etc.)?
  • Are there some other way how to do this which I have not covered?
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1 comment thread

You could use a RS232 driver IC. Set one TTL input to 0 the other to 5V. Then you may have +12V and -... (3 comments)
You could use a RS232 driver IC. Set one TTL input to 0 the other to 5V. Then you may have +12V and -...
H_H‭ wrote 11 months ago

You could use a RS232 driver IC. Set one TTL input to 0 the other to 5V. Then you may have +12V and -12V on the output pins. RS232 ICs often need to generate 12V from 5V or 3.3V for their output signals.

But not sure if that is enough and what advantage you have compared to a DC-DC IC.

Olin Lathrop‭ wrote 11 months ago

Those ICs don't usually make +-12 V, even with 5 V in. They usually have a two-stage charge pump, so you'll get +-10 V minus a little loss.

TonyStewart‭ wrote 11 months ago

Charge pumps suffer from high very impedance output impedance leakage issues and are not worth the effort. Murata package is my best recommendation. https://www.digikey.ca/en/products/detail/murata-power-solutions-inc/NMV0512DC/5799183