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

AliExpress has a lot of similar converters for less than a dollar each.

The problem may be their quiescent consumption.


Cheers,

Isaac


Em 13/06/2025 13:40, doug metzler escreveu:
> 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
>>>>
>> --
>> O software antivírus Avast realizou uma checagem de vírus neste e-mail.
>> www.avast.com
>> --
>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> View/change your membership options at
>> https://mailman.mit.edu/mailman/listinfo/piclist
>>

-- 
O software antivírus Avast realizou uma checagem de vírus neste e-mail.
www.avast.com
-- 
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
https://mailman.mit.edu/mailman/listinfo/piclist