Re: LED Buffer Circuit

On May 13, 9:11 pm, D from BC <myrealaddr...@xxxxxxxxx> wrote:
On Tue, 13 May 2008 17:36:28 -0700 (PDT), sck0006 <skam...@xxxxxxxxx>
wrote:

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

How driving that LED with a mosfet driver instead?
Less parts, less math and less part shopping.http://ww1.microchip.com/downloads/en/DeviceDoc/21390D.pdf
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

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
.

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