Author Topic: Low power redundant power supply switch???  (Read 855 times)

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Offline dazz1Topic starter

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Low power redundant power supply switch???
« on: May 01, 2019, 01:49:10 pm »
Hi
I have a project that has a small module that draws 30mA @ 3.3VDC. I need the module to be able to select it's power supply. One supply is 3.3VDC, and the other supply is nominally a 12VDC LiFe battery. I need to be able to seamlessly switch between the 2 supplies. 

All the search words I try to use to find a suitable circuit/device don't have the right outcome. Any suggestions  c


Please help.
Dazz

Over Engineering: Why make something simple when you can make it really complicated AND get it to work?
 

Offline dazz1Topic starter

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Re: Low power redundant power supply switch???
« Reply #1 on: May 07, 2019, 05:27:49 am »
Hi
I figured out I can do this with ideal diodes.

Dazz
Dazz

Over Engineering: Why make something simple when you can make it really complicated AND get it to work?
 

Offline Ian.M

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Re: Low power redundant power supply switch???
« Reply #2 on: May 07, 2019, 06:09:26 am »
I presume you are regulating the battery supply down to 3.3V.  A pair of ideal diodes wont do what you want reliably as the supply with the fractionally higher voltage always 'wins'.   e.g. if 3v3in=3.30V  and 3V3batt=3.31V, it will never draw current from the 3.3V input, so will flatten the battery.

What you actually need ts a circuit that monitors the 3.3V input, and if present connects it to the load via a mosfet and simultaneously disconnects the battery via another MOSFET, or possibly by disabling the battery 3.3V regulator via its enable pin, (but that regulator must then tolerate 3.3V on its output when disabled - check datasheets carefully).

 

Offline dazz1Topic starter

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Re: Low power redundant power supply switch???
« Reply #3 on: June 07, 2019, 10:08:24 am »
Hi
I have a new solution.
Drive a single 3V3 LDO through 2 diodes from 2 separate 5V supplies. 
I need the LDO anyway.


Dazz
Dazz

Over Engineering: Why make something simple when you can make it really complicated AND get it to work?
 


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