Re: [EE] looking for negative 5V regulator or circuit

At 02:43 PM 2025-06-10, you wrote:
>Good day to all.
>
>I'm working on a project where I need a negative 5 Vdc rail relative to the
>incoming +12 Vdc rail.  My first thought was a bog-standard 7905B regulator
>(the "B" suffix denotes -40C operation) but this is a battery-powered
>system and the worst case bias current of 8mA is way too high.
>
>I spent some time looking at Digikey offerings but they all seem stupid
>expensive.  Can anyone suggest a part that is reasonably inexpensive and
>works down to -40C?  Current is fairly low - should be less than 20 mA
>worst case.  I sort of prefer a package larger than SOT-23 just because of
>the fairly minimal heat dissipated.
>
>My alternative is a 6.2V Zener diode feeding a PNP Darlington pass
>transistor.
>
>Suggestions and opinions greatly appreciated!
>
>dwayne

Hi, Dwayne:

Yes, negative regulators are a niche product these days.

Torex XC6902N251PR-G ?  100uA power consumption, but only -16V abs max input.

SOT-89

0.93 CAD in 100's  Digikey
0.41 USD (0.56 CAD) in 100's LCSC
0.90 CAD in 100's Mouser

Your Zener + pass transistor is not a bad solution if the tolerances and
tempcos work for you. 6.2V Zeners behave reasonably well (unlike low
voltage parts).

For a 1mA load. Efficiency is about 37% vs the theoretical maximum
of 42% for a linear regulator.

https://i.imgur.com/qsjgEfo.png


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