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Etmax
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re: Green LED replaces LDO regulator
Etmax   9/26/2011 1:49:27 AM
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Given that it light up in ise, that may be difficuly :-)

Etmax
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re: Green LED replaces LDO regulator
Etmax   9/26/2011 1:47:29 AM
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Hmm I get 3 diodes at a cost of 4-5 cents. Compare that to 15 cents for an LED. What are you paying for LED's??

numberone2
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re: Green LED replaces LDO regulator
numberone2   9/28/2010 6:03:48 AM
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I disagree that the LED replaces 3 components compared with using an LDO. In this case the LDO would share bypassing with the other IC so this solution really only saves a few cents and marginal board space, ie an 0402 LED vs an SOT323 LDO. I would personally take the peace of mind and go with the LDO.

GREAT-Terry
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re: Green LED replaces LDO regulator
GREAT-Terry   9/16/2010 6:23:41 PM
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This is a trick that students usually come up with. I may say this is a simple trick but not always be useful. It may only work well if the load is really light and the tempco. (in other words, the output voltage accuracy) is not an issue. To nowadays demanding digital stuff, it surely is not a good idea. However, for many low voltage consumer stuff, it is still a viable solution but need to be used with great care.

NATRON
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re: Green LED replaces LDO regulator
NATRON   9/15/2010 6:51:32 PM
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You might consider leaving the led in the dark...they tend to generate a voltage when exposed to strong light...

loggie
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re: Green LED replaces LDO regulator
loggie   9/15/2010 4:03:07 PM
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I would be concerned about the variation in forward voltage drop across the LED over temperature range (0 to 80 C for a typical consumer device). Typically, core logic operating at 1.8V requires a +/-10% regulated supply voltage. Given that the 3.6V supply has its own tempco and adding this to the LED tempco, it is possible that the 1.8V supply could have a variation over temperature exceeding 10%.

Jack Bauer
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re: Green LED replaces LDO regulator
Jack Bauer   9/15/2010 1:12:00 PM
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This assumes the VCC current is relatively fixed to generate a nearly constant forward voltage in the green LED. It also assumes the larger supply is exactly a diode drop greater than the logic supply needs to be. That almost never happens. Interesting trick, but not exactly a universal solution.

BicycleBill
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re: Green LED replaces LDO regulator
BicycleBill   9/13/2010 2:55:57 AM
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t.alex: I'll pass your query to the author. Of course, the circuit is so simple you could try it with and without the resitor, and see for for yourself! What have you got to lose, except an inexpensive LED?

t.alex
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re: Green LED replaces LDO regulator
t.alex   9/10/2010 12:25:35 AM
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Ah nice trick! The only factor is we need to select good-grade led as it is always ON. Do we need to have a current-limiting resistor?

Avatar Engineer
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re: Green LED replaces LDO regulator
Avatar Engineer   9/9/2010 2:16:00 AM
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Why not? it's cheaper than 3 diodes in series!

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