LM317 Regulator Question

Thread Starter

NM2008

Joined Feb 9, 2008
135
Hi,
With regard to the LM317 regulator circuit attached below,
could somebody tell me is it possible to connect another LM317 regulator ic in parallel to the one in this diagram, to achieve a regulator circuit capable of handling 3A, instead of 1.5A.

Can LM317 regulators be connected directly in parallel to one another in order to handle more current?

Thanks for your help.
Regards NM
7Vdc1.5ARegulatedSupply.PNG
 
Hi NM,

The datasheet for the LM317 shows how to connect three in parallel to boost the current to 4A. Several additional components are necessary in order to keep them regulated and for compensating for output variations.

It also shows how to do it with one regulator and some bypass elements.

The datasheet can be found here: http://www.national.com/ds/LM/LM117.pdf
 

SgtWookie

Joined Jul 17, 2007
22,220
You could use an LM338 5A positive regulator: http://octopart.com/search?q=LM338
or an LM350 3A positive regulator: http://octopart.com/search?q=LM350

You'll need to watch your power dissipation. If you're considering using a circuit like this in an automotive application, the system voltage will be around 14. With a 7v output, the regulator will be dissipating as much power as the load; with a 3A draw, that's 21 Watts. You'll need a big heatsink.
 

yasir9909

Joined May 22, 2008
3
Why don't you better try LM2576.It can provide 3A output current.It has fixed 5v output voltage version as well as 3.3V, 5V, 12V, 15V, and adjustable output versions.
LM2576 Wide input voltage range, 40V up to 60V.

regards
m.yasir
 

Thread Starter

NM2008

Joined Feb 9, 2008
135
Why is the method ruleworld stated not recommended?

I take it that when
3 of them in parallel
is mentioned, he means setting up three lm317 regulator circuits, then paralleling their output pins.

Will the regulator break down after time, by doing it this way?

Could someone tell me why this is not done.
Regards NM
 

jvjtech

Joined Jan 26, 2008
23
Could someone tell me why this is not done.
Regards NM
Current hogging. In a parallel arrangement, if one regulator starts "hogging" the load current the other regulators may not carry their portion of the load current. The one that is "hogging" more than its share of the load current may overheat with unsatifactory results. The additional components in circuits with parallel series pass transistors, regulators, etc. are intended to balance the currents in the parallel branches. Regards. JJ
 
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