Subject:
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re: ztx614
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Wed, 19 Mar 1997 17:34:27 GMT
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Original-From:
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Stefano Nardone <stefanon@promos.^NoMoreSpam^it>
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Viewed:
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1585 times
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>
> How are you gonna get 100 ma through a 1k resistor biased by 5volts??
> The max would be 5ma. I have *never* heard of a LED this size that can
> handle more than 20ma!! This LED is tiny. I don't know where pin one of
> the jumper goes to or its use but I know you can't pull more than 5ma
> through that 1k resistor when the whole board has a supply of 5 volts.
I just looked back to the IR transmitter schematic...
The 1K res + RED LED you see there is for the only purpose of having a visible
feedback of IR transmission. The IR Led and it's limiting resistor (if the
case) will be connected in series between pin 3 and 1 of J7. So R5 (1K) will be
used to limit the current in the visible RED led, but you can get a more
high current in the IR LED, limited by Q1 VCEsat, and IR led voltage
drop and additional limiting resistor. IR LEDs have fairly high Imax (pulsed)
reaching 1A (for very short times...)
stefano nardone
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Message is in Reply To:
 | | re: ztx614
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| (...) I think it must better be a darlinghton and it must support enough current: if you want to get 0.1A or more pulsed current in the IR led, the transistor must have a rather high current gain, more than that of an ordinary npn trans (by the way (...) (28 years ago, 19-Mar-97, to lugnet.robotics.handyboard)
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