[sdiy] Power Supplies

[Pete Hartman]

That's all well and good, but I think it's more common for simple supplies
using 78XX and 79XX parts to simply be victim of part variability.  I can't
think of the last time I threw one of these together that I was getting
"rated" voltage out even under no (real) load (i.e. LEDs only).  If you
want exact voltages, use an adjustable regulator.  That has little to do
with sensing and load regulation....

(ps, lights drop at your house when taking a shower?? Hopefully it's not an
electric shower! :-) ).

Thanks

Pete

On Sat, Oct 10, 2015 at 1:06 PM, Richie Burnett <
rburnett at richieburnett.co.uk> wrote:

> Remember that regulation using negative feedback only guarantees the
> correct voltage at the point where the negative feedback is being taken
> from, (often at the output terminal block or posts of the power supply.)  A
> synth module at the opposite end of an enclosure from the power supply is
> going to see less voltage because of the voltage drop in the cable or PCB
> tracking, due to this module's current draw and all the other modules
> connected to that length of cable.  Current draw *will* cause a local
> voltage drop.  It's the same behaviour that makes the lights dim in your
> house when someone takes a shower.
>
> On expensive power supplies with external sensing terminals, you can run
> another two wires to sense the voltage at the far end of a long power
> cable. This would keep the regulation very tight at this point, but the
> voltage at the power supply end would then go higher than spec when there's
> a heavy load near the end of the cable.  Maybe a "ring main" type of wiring
> arrangement would be best!?!?  I don't know, this might even be common
> practice in modular synths for all I know!
>
> -Richie,
>
>
> -----Original Message----- From: Mattias Rickardsson
> Sent: Saturday, October 10, 2015 6:13 PM
> To: mskala at ansuz.sooke.bc.ca
> Cc: synth-diy diy
> Subject: Re: [sdiy] Power Supplies
>
>
> On 10 October 2015 at 12:38,  <mskala at ansuz.sooke.bc.ca> wrote:
>
>> On Sat, 10 Oct 2015, Tom Wiltshire wrote:
>>
>>> What's the evidence that drawing more current from a linear regulator
>>> causes its output voltage to fall? I thought that was exactly the
>>> problem regulators were supposed to solve?
>>>
>>
>> If the output voltage doesn't decrease when the current increases, then
>> the real part of the regulator's output impedance is zero or negative,
>> which is very likely to create stability problems.  You want to to have a
>> small, positive, and almost purely resistive output impedance.
>>
>
> Is this the reason why synth power supplies seem to be a little bit off?
> Almost all +/- 15 V rails I've measured so far have been something
> like +14.9 V and -15.1 V.
>
> /mr
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2014.0.4830 / Virus Database: 4365/10792 - Release Date: 10/10/15
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20151010/98fe0ebe/attachment.htm>