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Thread: Inverting IR LED driver with 1 transistor
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face BY : Russell McMahon email (remove spam text)



Now the men have had their input :-) - there is an interesting variation you
can use here.
Instead of putting both LED and resistor in the collector lead, place the
resistor in the emitter. This then becomes a VERY rough current source as
the current is limited to (Vdrive-0.6)/R

E --> resistor --> +5V
C --> LED --> GND
B --> resistor --> TTL output from uP

Odds are its not much different in result than the other arrangement in this
case.
This would be of more affect if you drove the LED from a different voltage
source than the cpu - eg with an NPN drive & the LED supplied from the
unregulated battery supply while the processor runs on a regulated supply.

Have a look at the circuit inside typcal IR remotes and see what they do
(will vary no doubt)


           RM

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Subject (change) Inverting IR LED driver with 1 transistor

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