Re: 300 mA from a microcontroller pin

On Fri, 30 Nov 2007 11:39:52 -0500, the renowned CBFalconer
<cbfalconer@xxxxxxxxx> wrote:

Mark Borgerson wrote:
toe@xxxxxxxxxxx says...

A bi-colour LED that has only two pins (they're in parallel
facing in different directions). If the microcontroller pin is
high, then it'll be red. If low, it'll be green. If high
impedance, it'll be off.

... snip ...

You don't really need a tri-state driver, then. If both LED pins
are at the same level (either high or low), the LED will be off.

If total power dissipation isn't a concern, your circuit could
simplify to:

+5 +5
| |
R1 R2
| |
|---- LED ----|
| |
P1.1---T1 P1.2---T2
| |
| |
gnd gnd

T1 and T2 are logic-level N-channel mosfets controlled by
your MPU pins.

Ignoring total dissipation, a single tri-state driver will do:

+5
|
R1
|
tri state here >---|X|-----+
LED |
R2
|
GND

with R1 approximately equal to R2. The ratio controls brightness.

You sure about that?


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@xxxxxxxxxxxx Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
.

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