LED Buffer Circuit

I need help designing a circuit, it will be a tachometer calibrator. It will input 5V square wave signals from a Fluke 741B, nothing higher than 3kHz & it can't draw much current from the input. It will have a high intensity LED and a battery pack, something along the lines of 4 D Cells. The LED I have has a VF of 3.1V with a current draw of .2A (no P/N on this guy, just found it in my drawer). Is something as simple as a Darlington pair & voltage regulator sufficient for this, say a 2N3904 feeding a TIP31? Is a common emitter or common collector configuration better suited for this application? I have a very hard time designing circuits, I'm just looking for a little guidance.

Thanks for the time, Steve

Reply to
sck0006
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How driving that LED with a mosfet driver instead? Less parts, less math and less part shopping.

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TC1411 8 pin chip. Spec'd down to 4.5V TTL compatible input. It's about $1.00 from Digikey..

mosfet driver + resistor + LED ...done..??

But..If you want to maintain LED current while the 6V of batteries die right down to 3.1V ...That's another design.

D from BC British Columbia Canada

Reply to
D from BC

shopping.http://ww1.microchip.com/downloads/en/DeviceDoc/21390D.pdf

Brilliant. I'll just replace the batteries if they start to die. This design is about pure simplicity, you've hit the nail on the head with your suggestion. Thanks for the great reply.

Steve

Reply to
sck0006

a
r

I think with the output resistance of the TC1411, I don't even need a resistor at 5V, it shows typical resistance of 10 ohms, which with the

3V drop of the diode would be a 2V drop across the chip, which will work out to approximately .2A, which is perfect for the LED. Now, I'd just like to add a 5V regulator to the entire circuit. Of course, I'll use more batteries to give the regulator headroom. Is there an easy to use switching regulator with few components? I hate to just put a linear device in there & give up that battery life to heat. It just needs to be rated for say, 9-15VDC input, 5V output, .3A max current. Any ideas?

Thanks again, Steve

Reply to
eletlabs

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tor

rd

We're going to use the TL2575

Reply to
eletlabs

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Dude! We don't hear gushing praise like this from googlers very often - did you get an "A" or what? ;-D

Cheers! Rich

Reply to
Rich Grise

I actually use Google at work for ease, the company doesn't have a news server, use Agent at home. Actually, I've been out of college for a few years now, this is for work. Unfortunately, I don't get graded on my effort at work and no one will even notice besides the guy I'm building this for. This is to replace our old GenRad 1531A which has managed to finally give out.

Best,

Steve

Reply to
Steve

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