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Old 03-29-2009, 04:42 PM #1
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Default reference voltage

ONe more annoying question .......

What the hell is ref voltage and why should it always be 1.25 ?

thanks.


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Old 03-29-2009, 04:54 PM #2
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Default Re: reference voltage

That is what the regulated voltage is on the LM317. (between the sense pins)

It is actually a voltage regulator. We use it to regulate current, which it does by regulating the voltage very precisely to 1.25 volts.

To figure current...

1.25/ohms of resistance = current.

Example:

1.25/10 ohms = 125mA's
1.25/5 ohms = 250mA's

And so on...

The LM317 will take up to 37 volts supply. For a red build, you will want to supply the driver with more than 6 volts. Which is why you would use 2 X 3.6 volt batteries. Because 2 X 3.0 volt batteries will start to drop below 6 volts very soon. Then the LM317 will 'drop out' and not regulate the current.

For a blu-ray build using a DDL driver like this, you would want 9 to 12 volts supply...
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Old 03-29-2009, 04:59 PM #3
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Default Re: reference voltage

On a need to know basis you don't need to know . All you need to do is measure it with a DVM. if it is 1.25v you circuit is working correctly.

If you realy cannot live without that piece of knowledge read the data sheet which was linked for you on another thread.

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