LM317 voltage regulator parallel connection

[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

 

[saturn1bguy]

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

 

[flat5]

Use a pass transistor.

**broken link removed**

 

[Willbe]

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]

lm327

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

 

[saturn1bguy]

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]

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]

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]

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]

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]

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]

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. . .