Hi Mario,

An emitter follower will always introduce a Vbe drop, and it will spoil
the regulation.  A much better solution is to use a PNP transistor as
described in many of the 3 terminal regulator application notes e.g.

http://www.onsemi.com/pub_link/Collateral/MC7800-D.PDF

Note that this will defeat the current limiting built into the
regulator, so if this is important you will need a slightly more complex
circuit which is also described in this datasheet.

Mike

> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of Electron
> Sent: 05 December 2011 11:23
> To: Microcontroller discussion list - Public.
> Subject: [EE] Linear regulator pass transistor
>=20
>=20
> Howdy,
> to get more current out of a linear regulator, is a NPN pass
transistor
> (collector
> to VReg input, base to VReg output, and emitter to circuit) a good
idea?
> From my
> experiments it introduced a voltage drop... is it me or it's an
intrinsic
> and
> unavoidable defect of this simple solution?
>=20
> Thanks,
> Mario
>=20
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