Tomas -

What I use for this is MICREL MIC2981.  =

Similar to ULN2003 but for hi-side switching.
 =

 Foster


> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of Tom=E1s =D3 h=C9ilidhe
> Sent: Monday, June 16, 2008 4:23 PM
> To: Microcontroller discussion list - Public.
> Subject: [EE] Bread-and-butter transistor as switch
> =

> =

> I need a transistor to use as a switch. One side of the switch will go
> to Vcc, the other will go to the anode of an LED which then goes to a
> resistor and then to ground. I'll need 12 of these on my board (I've
got
> twelve 12 different LED's).
> =

> Normally I use the ULN2003 driver chip for this purpose, but I can't
> find a PNP version of it (i.e. a version that will provide a path to
Vcc
> rather than to ground).
> =

> The current through the switch won't be more than 30 mA.
> =

> I could use a simple bi-polar junction transistor such as a BC327 but
> then I'd need a resistor for the base. And because I've got 12 of
these
> LED's, that would mean 12 more resistors on my board, so I'd rather go
> for an option that doesn't require a resistor.
> =

> So I'm thinking along the lines of a NMOS transistor. The gate will be
> connected to an output pin on a PIC chip. The source will go to Vcc
and
> the drain will go to an LED's anode.
> =

> Can anyone suggest a very simple NMOS transistor that's on at 5 V and
> off at 0 V, and that can pass 30 mA? Or if you've got another idea,
> please throw it out there :-D
> =

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