Re: Best way to get 2.5 volts from somewhere? (Vcc = 5 volts)

Tomás Ó hÉilidhe wrote:

I have a question...

If I have an LED that has about 2 volts across it, then is it OK to
put a 2 volt power supply across it without a current limiting
resistor?

My overall power supply would be 9 V coming from a square battery, but
I'll be putting it thru a voltage regulator to give me out 2 V.

I'll then be putting the 2 V across the LED.

Can I leave out the LED's current-limiting resistor, or is there still
a chance of there being too much current that would fry components?

Go to the data ***.
Find the V/I curves, and include the temperature coefficent.
Now find the MIN and MAX specs, and draw those load-lines for
2V drive.

The real world is a little more forgiving than the corner cases,
and you will find LEDs within a batch match better than random
scattering MIN-MAX.
[SMD leds on a tape, are actually very well Vf matched]

Your practical problems will be brightness matching (well before
your current variations hit damage levels), and thermal tracking.

-jg

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