Re: 300 mA from a microcontroller pin

On Nov 30, 1:16 pm, DJ Delorie <d...@xxxxxxxxxxx> wrote:
CBFalconer <cbfalco...@xxxxxxxxx> writes:
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.

If you replace R1/R2 with the 1/2 Vcc op-amp circuit I posted earlier,
you can use a single resistor in series with the LED and reduce the
"off" leakage current.

That is actually a very elegant solution. It only requires a single
op-amp for the entire array, provided it can handle the current of
multiple LEDs at a time. Or you can use an op-amp for each channel.
But it does not directly provide for the multiplexing the OP wants.
However, I don't see your original post, so maybe you have a way of
dealing with that.

What is required is a switch between the LED and the 1/2 Vcc voltage
source output. I expect you could find an op-amp with a disable that
cuts off all output current, no? Then the only issue I see is the
fact that you will only have 2.5 volts to drive the LED. At the high
current the OP wants, there may not be enough head room to adequately
control the current with a load resistor. Or the LED voltage may be
higher than 2.5 volts limiting the max current. But with a slightly
higher Vcc, this is an excellent idea.
.

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