[sdiy] Driving an LED with an NPN via -15

[Scott Bernardi]

That should work, as long as you have a resistor in series with the base, also
(i.e., don't drive the base directly). The npn only cares about the voltages
across it, not what their ground reference is.

Peter Grenader wrote:

> Peoples,
>
> I have a quicky qustion for yooz guys:
>
> I've got an avalaible voltage swing between -15 and ground.  I have an
> unnused section of a NPN transistor array, I want to use it to drive an LED.
>
> I'm thinking....
>
> -15 to the emitter of the NPN, the collector to the cathode of the LED via a
> current limit resistor, the anode to ground.  As the base swings up from -15
> toward ground, the NPN conducts, passed the -15, MR. LED lights up.
>
> yes?
>
> Sorry for the simpleton questions.  As you know, I am a dweeb when it comes
> to this stuff.  A dweeb who has only used NPN to pass ground signals.
>
> let me know when you can,
>
> P