Re: 300 mA from a microcontroller pin


Mark Borgerson <mborgerson@xxxxxxxxxxx> writes:
+5V +5V
| |
10K |---P-Chan
| | |
P1.1-----------------| |------------- Output
| | |
10K |---N-Chan
| |
GND GND

This only works if the Vg cutoff is more than 2.5v. I've tried all
sorts of these types of drivers, and they just don't work. For
MOSFETs, the Ids at Vg=2.5v (or even 1.65v) is too much - both
transistors conduct. For NPN/PNP pairs, the Ibe leakage causes both
transistors to be on no matter what.

If you knew you were working with 5v (I was working with 3.3v) you
could use 2.5v zeners to make your "floating" Vgs close enough to zero
to keep the mosfets off, but you'd need a second stage to do level
shifting.

Here's one half, as an example:

+5v
|
+5V zener
| |
10K |---P-Chan *----------
| | | |
P1.1-----------------* *-----N-Chan
| | |
10K 10K |
| | |
GND GND GND

Alernately, use a single op-amp follower to produce a regulated 2.5v reference,
and tie the first stage sources to that.

+5V
|
10K
|
*-------|+\
| | >---*---- 2.5v
10K *-|-/ |
| | |
GND `--------'
.

Relevant Pages