LM317 voltage regulator parallel connection - Electronic Circuits Projects Diagrams Free

Haas · 16th November 2008, 10:19 PM

Hi

Since each LM317 volt. reg IC can supply only a maximum of 1.5amps, how could i connect 2 or more LM317 voltage reg. ICs in parallel in order to increase the current output capability at the output to supply 3-4 amps at the same variable voltage output.

Thanx

saturn1bguy · 16th November 2008, 10:28 PM

Use an LM350 for 3A, or a LM338 for 5A.

flat5 · 16th November 2008, 10:33 PM

Use a pass transistor.

http://ourworld.compuserve.com/homep...den/page12.htm

Willbe · 16th November 2008, 10:39 PM

Quote:

Originally Posted by Haas

Hi

Since each LM317 volt. reg IC can supply only a maximum of 1.5amps, how could i connect 2 or more LM317 voltage reg. ICs in parallel in order to increase the current output capability at the output to supply 3-4 amps at the same variable voltage output.

Thanx

You can use current sharing resistors on the outputs, and maybe output diodes so that the regulators only source current, but then you sacrifice the low output impedance regulators provide you, in return for simplicity.

microtexan · 17th November 2008, 01:11 AM

There is a 5 amp version, but it's in a different package than the 1.5 amp version.

saturn1bguy · 17th November 2008, 02:26 AM

Quote:

Originally Posted by microtexan

There is a 5 amp version, but it's in a different package than the 1.5 amp version.

The LM338 is the 5A version, as mentioned above. And the LM317 and LM338 are both offered in similar packages, namely the TO-220 (LM317T/LM338T) and the TO-3 (LM317K/LM338K).

gramo · 17th November 2008, 05:04 AM

Quote:

Originally Posted by Haas

how could i connect 2 or more LM317 voltage reg. ICs in parallel

Although a solution is already covered, hooking up two V regs in parallel is bad juju in general, as which ever is slightly biased higher, it will supply all of the current

Willbe · 17th November 2008, 04:14 PM

Quote:

Originally Posted by gramo

Although a solution is already covered, hooking up two V regs in parallel is bad juju in general, as which ever is slightly biased higher, it will supply all of the current

Juju or mojo?

Try it on paper. It's two loops with 3 resistors, one resistor being the load resistor. Assume a 0.1v difference in the IC outputs.

The real problem comes if you remove the load resistor, so if this is a possibility then I recommend output diodes.

Haas · 18th November 2008, 06:16 AM

Thanks for all your responses.

Then can't they have the same adjust pin? with a diode also connected in the adj pin to compensate for the output diodes?

Haas · 18th November 2008, 06:19 AM

The LM338T and LM350 are not available where i'm at. That's why i thought of a way to accomplish the same job using the LM317Ts - which are readily available here.

saturn1bguy · 18th November 2008, 06:59 AM

Quote:

Originally Posted by Haas

The LM338T and LM350 are not available where i'm at.

You can't get an LM338T in "does it matter?" Wow. (It's called go to Jameco or DigiKey online and order some

)

If you really can't get one then I'd stick with using a pass transistor on a single LM317, as previously suggested by someone...

Willbe · 19th November 2008, 06:39 PM

Electronic Design Welcome for 11.17.08 has an article [ED online 20023] where the author, Bruhns, parallels two LT3080 regulators.

Sort of. . .

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16th November 2008, 10:19 PM	#1 (permalink)
Haas	LM317 voltage regulator parallel connection Hi Since each LM317 volt. reg IC can supply only a maximum of 1.5amps, how could i connect 2 or more LM317 voltage reg. ICs in parallel in order to increase the current output capability at the output to supply 3-4 amps at the same variable voltage output. Thanx

16th November 2008, 10:28 PM	#2 (permalink)
saturn1bguy	Use an LM350 for 3A, or a LM338 for 5A. __________________ Go Trojans!

16th November 2008, 10:33 PM	#3 (permalink)
flat5	Use a pass transistor. http://ourworld.compuserve.com/homep...den/page12.htm Last edited by flat5; 16th November 2008 at 11:08 PM.

17th November 2008, 01:11 AM	#5 (permalink)
microtexan	lm327 There is a 5 amp version, but it's in a different package than the 1.5 amp version.

18th November 2008, 06:16 AM	#9 (permalink)
Haas	Thanks for all your responses. Then can't they have the same adjust pin? with a diode also connected in the adj pin to compensate for the output diodes? Last edited by Haas; 18th November 2008 at 06:20 AM.

18th November 2008, 06:19 AM	#10 (permalink)
Haas	The LM338T and LM350 are not available where i'm at. That's why i thought of a way to accomplish the same job using the LM317Ts - which are readily available here.

19th November 2008, 06:39 PM	#12 (permalink)
Willbe	speaking of parallel. . . Electronic Design Welcome for 11.17.08 has an article [ED online 20023] where the author, Bruhns, parallels two LT3080 regulators. Sort of. . .