[sdiy] psu negative too high

[Ove Ridé]

I don't think anyone suggested connecting the LED without a resistor.
And furthermore, a LED on each rail has the added benefit of
indicating that power is on and working. Having 2 or even 3 resistors
in series could be useful for distributing the wasted heat. And also
perhaps to revisit the classical method of lifting the resistor a bit
above the PCB to improve air flow.

On 17 November 2015 at 19:03,  <rsdio at audiobanshee.com> wrote:
> Yikes, no! Never connect an LED to a voltage source without the appropriate current-limiting resistor. You risk burning out the LED. For a -15 V supply, you'd need at least 600 to 700 Ohms.
>
> Of course, by the time you find a resistor to protect the LED, you could just load down your supply with the resistor alone. A 600 Ohm resistor will draw 25 mA from the -15 V supply, but you'd better have a 1/2 Watt resistor because it's going to get warm. Also, don't put anything that will melt near that resistor - like your multimeter test probes.
>
> A 1 kOhm resistor will only draw 15 mA, so you'd only need the standard 1/4 Watt resistor. It still might get hot.
>
> Brian Willoughby
> Sound Consulting
>
>
> On Nov 17, 2015, at 6:01 AM, Carlos Portela <carlosrochaportela at gmail.com> wrote:
>> you mean like a led?
>>
>> 2015-11-17 15:00 GMT+01:00 Werner Flügel <werner.fluegel at b-tu.de>:
>>> Am 17.11.2015 um 14:47 schrieb Carlos Portela:
>>>> Hi all,
>>>>
>>>> Im having a problem with my psu.
>>>> Its a 15v dual psu + 5v. The 15V and the 5V are working; the negative
>>>> outputs around 30V.
>>>
>>> Put a little load on the negative rail - a multimeter has too high input
>>> impedance. Had the same effect recently ;-)
>
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-- 
/Ove

Blog: <http://blog.gg8.se/>

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