Pages: [1]   Go Down
Author Topic: 3 volt regulator  (Read 809 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Full Member
***
Karma: 2
Posts: 158
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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
 
Logged

Offline Offline
Faraday Member
**
Karma: 30
Posts: 2501
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

if worst comes to worse just build your own voltage regulator if you're desperate with just old circuit boards...




« Last Edit: November 16, 2012, 04:45:20 am by cjdelphi » Logged

Belgium
Offline Offline
Sr. Member
****
Karma: 1
Posts: 283
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

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


Offline Offline
Edison Member
*
Karma: 116
Posts: 2205
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
it is a low drop out regulator.

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

Belgium
Offline Offline
Sr. Member
****
Karma: 1
Posts: 283
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

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...
« Last Edit: November 16, 2012, 07:01:36 am by Bajdi » Logged


UK
Offline Offline
Faraday Member
**
Karma: 100
Posts: 4153
Where is your SSCCE?!?!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Get 10% off all 4D Systems TFT screens this month: use discount code MAJENKO10

Offline Offline
Edison Member
*
Karma: 116
Posts: 2205
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Offline Offline
Edison Member
*
Karma: 116
Posts: 2205
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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

Any voltage regulators can be wired to do that.
Logged

UK
Offline Offline
Faraday Member
**
Karma: 100
Posts: 4153
Where is your SSCCE?!?!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Get 10% off all 4D Systems TFT screens this month: use discount code MAJENKO10

Offline Offline
Edison Member
*
Karma: 116
Posts: 2205
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

UK
Offline Offline
Faraday Member
**
Karma: 100
Posts: 4153
Where is your SSCCE?!?!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

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?
Logged

Get 10% off all 4D Systems TFT screens this month: use discount code MAJENKO10

Offline Offline
Edison Member
*
Karma: 116
Posts: 2205
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Pages: [1]   Go Up
Jump to: