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

TL;DR but I have one of these sitting right in front of me.

https://www.digikey.com/en/products/detail/digilent-inc/410-294-A/5730865?s=N4IgjCBcpgrATANiqAxlAZgQwDYGcBTAGhAHsoBtEeAFgE4wB2eEAXRIAcAXKEAZS4AnAJYA7AOYgAvlJItIVACbDxwnAVFcABB1IB3AoIBGI1AGstbKUA

but maybe that exceeds your "not stupid expensive" requirement :-)



On Thu, Jun 12, 2025 at 12:18 PM Isaac Marino Bavaresco <
[email protected]> wrote:

> If the OP needs several of such circuits, the number of components grow
> rapidly.
>
> With his original idea, a few components can be saved for each circuit.
>
> Cheers,
>
> Isaac
>
>
>
> Em 12/06/2025 11:03, Dmitriy Kiryashov escreveu:
> >   Hi Dwayne.
> >
> > If you goal is to switch hi-side ( +12V ) on and off to some load ( in
> reference to the ground )
> > why don't you try pair P-FET on high side ( instead of PNP ) and N-FET
> to ground controlling
> > that P-FET ( plus few resistors ).
> >
> > What is benefit of creating that artifical "-5 below incoming +12" level
> instead of doing control
> > in reference to the ground ?
> >
> >
> > Dmitriy.
> >       On Wednesday, June 11, 2025 at 09:37:44 AM PDT, Dwayne Reid <
> [email protected]> wrote:
> >
> >   I see that I was not sufficiently clear about what I am doing.  My
> > apologies.
> >
> > I am doing hi-side switching from the incoming +12 Vdc supply.  It looks
> > like the easiest and least expensive way to do this is to use 74HC595
> shift
> > registers driving MMBT4403 transistors.  THe emitters of the transistors
> > are tied to the incoming +12V rail.  So are the VDD pins of the shift
> > register and the PIC that is driving the shift register.
> >
> > So - I need to create a -5V rail with respect to that +12V rail.  In
> other
> > words, about 7 Vdc.  My initial thought was to use a 7905B regulator with
> > its input tied to incoming ground and the bias pin tied to the +12V rail.
> > That gives me -5 Vdc with respect to the incoming +12V rail.  The
> problem I
> > have is that the 7905 data sheet says that worst case bias current is 8
> mA
> > which is really high for a vehicle that might be sitting idle (turned
> OFF)
> > for weeks on end.
> >
> > So - I'm looking for a -5 Vdc regulator that has significantly-lower
> > quiescent current than the 7905.  My fall-back position is something
> like a
> > MPSA63 voltage-follower being fed with a 6.2V Zener or, as was suggested
> > here, one of the low-current TL431 variants.  I would use something a bit
> > beefier than the MPSa63 but you get the idea.  I'm wanting to get the
> > quiescent current down to a couple of hundred uA.
> >
> > I estimate the total current on that -5V supply is less than 50 mA,
> > depending on how many shift register / transistor stages I need.  Might
> be
> > as many as 16 outputs, each transistor getting a bit more than 2 mA
> drive.
> >
> > As always, suggestions and comments gratefully accepted!
> >
> > dwayne
> >
> > On Tue, Jun 10, 2025 at 12:43 PM Dwayne Reid <[email protected]>
> 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
> >>
>
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