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Topic: 3 volt regulator (Read 840 times) previous topic - next topic

elico

hi all

I need a 3 volts simple regulator IC like the 7805 .
  A 3 legs regulator IC that with several resitors it will be adjusted to 3 volts output .

Any suggestions ?

Thanks
Elico

cjdelphi

#1
Nov 16, 2012, 10:42 am Last Edit: Nov 16, 2012, 10:45 am by cjdelphi Reason: 1
if worst comes to worse just build your own voltage regulator if you're desperate with just old circuit boards...





Bajdi

Is 3.3V ok? The LM1117 is the most common 3.3V regulator in TO220 package, and it is a low drop out regulator.
www.bajdi.com

dhenry

Quote
it is a low drop out regulator.


They are marketed as LDOs but they are really not LDOs.

Bajdi

#4
Nov 16, 2012, 12:59 pm Last Edit: Nov 16, 2012, 01:01 pm by Bajdi Reason: 1
The LM1117 has a drop out voltage of 1.1 to 1.4V according to the National Semiconductor datasheet. The datasheet is from 2001, these days you can find newer regulators with much lower drop out voltages, all depends what you need it for. I use the LM1117 because they are easy to find and cheap...
www.bajdi.com

majenko

What is your incoming voltage?  How much current will you be drawing?

Given enough incoming voltage headroom, and low enough current draw, you could very easily use an LM317T regulator.  It's far from perfect, but a handy one to have lying around (I have lots here) as they can be adjusted to create a wide range of output voltages with just 2 resistors and a couple of capacitors.  They can even be wired up in a constant current arrangement, which is useful for driving LEDs.
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dhenry

It is very easy to tell. The 1117 has emitter output, like 7805. Thus the high drop out.

A typical LDO has collector output, and has a drop out voltage of less than 0.5v - and many times much lower, because of its collector output toplogy.

dhenry

Quote
They can even be wired up in a constant current arrangement,


Any voltage regulators can be wired to do that.

majenko


Quote
They can even be wired up in a constant current arrangement,


Any voltage regulators can be wired to do that.


Yes, but these ones are commonly wired up like that, so there are plenty of resources and schematics on the web for the "user" to get.
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dhenry

Quote
these ones are commonly wired up like that,


Which ones are "those ones"?

lm317 has an advantage in this application because of its low Vref - so lower losses on the current-setting resistor.

majenko


Quote
these ones are commonly wired up like that,


Which ones are "those ones"?

The LM317T of course - can you not follow a simple thread of conversation?
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dhenry

It is hard to follow. Just because lm317s are common wired for ccs doesn't mean others cannot be wired for ccs - the basics are the same.

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