Re: PMOS in parallel with NMOS

On May 7, 5:14 am, "robertwess...@xxxxxxxxx" <robertwess...@xxxxxxxxx>
wrote:

That won't work.  There will be some voltage leaking from the high
impedance device, and exactly what that is, and how much current there
is, will dictate exactly what the two drive transistors are going to
do.


With the PIC microcontroller, if you put a volt meter across a high
impedence pin, I think you measure about 3 V. Of course, it's behind a
massive resistance, but I think that 3 V might be enough to turn on an
NMOS transistor.


What are you trying to do?  Build a high output tristate device?  Are
you trying to drive a multi-color LED or something?


I have a bi-colour LED that has 3 pins. Within the LED package there
are two LED's, and they have a common cathode. Their anodes are
separate.

When my microcontroller pin is high, I want it to be green. When low,
red. When high impedence, off.

To do this, I want to use a p-type and a n-type transistor that have a
common gate/base. When the microcontroller pin is high, the n-type
transistor will be turned on and it will put five volts onto the red
anode. When the microcontroller pin is low, the p-type transistor will
be turned on and it will put five volts onto the green anode.

I might end up doing it with bi-polars instead of mosfets...

.

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