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Old 20th January 2013, 11:50 AM   #1
FOXYE is offline FOXYE  Israel
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Default Led + emitter follower regulator

Hello,
Trying to change the power supply circuit is based on the following:
Click the image to open in full size.

But instead of using a zener diode aim to use LEDs.

Edit:
Circuit works.

Last edited by FOXYE; 20th January 2013 at 03:49 PM.
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Old 20th January 2013, 12:15 PM   #2
Mooly is offline Mooly  United Kingdom
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Its normal because this is a "regulator" with no error correction or error amplifier.
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Old 20th January 2013, 12:23 PM   #3
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Way better the simple circuit with the zener, if you want i will post my implementation to that regulator, better regulation and noise but not useful for few mA's...
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Old 20th January 2013, 01:37 PM   #4
Ketje is offline Ketje  Belgium
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Happely it's only simulation,otherwise those poor LED's, 250mA !
If you need 5V stabilised,why not use the LM117 with to resistors,that's it.
Mona
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Old 20th January 2013, 03:03 PM   #5
FOXYE is offline FOXYE  Israel
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Thanks for the information,

Because of this:

Using 3-pin regulators off-piste: part 1

"For 5V output, a useful substitution is to use two green LEDs in series. These will drop about 1.94v each, or 3.9v across the two, with lower impedance than a 3.9v zener - which makes the output voltage setting more accurate, and with lower noise since the leds are forward-biased PN junctions. You also get bright green light to let you know the reg is working..."
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Old 21st June 2013, 07:59 PM   #6
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What is the max current this regulator can supply?
What demands has the circuit for heat dissipation?

gianxdiy can you post your implementation?
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Old 22nd June 2013, 01:47 AM   #7
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Quote:
Originally Posted by FOXYE View Post
Thanks for the information,

Because of this:

Using 3-pin regulators off-piste: part 1
That page was very specifically written (by me) for LM317 and similar adjustable 3-pin regulators.

Your circuit is not comparable; it will need informed revision to use LEDs instead, and infact in the circuit you post using LEDs would offer very minimal gains.
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Old 22nd June 2013, 09:40 AM   #8
Elvee is offline Elvee  Belgium
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With one additional transistor, you can retain the advantages of a LED, but with added benefits, like much better static and dynamic performance, approximate temperature compensation, flexibility in output voltage setting and low drop-out feature.
Note that a real life circuit will need some kind of start-up method for a deterministic behavior. The exact implementation depends on the context.
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