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FrozenGate by Avery

Is this a logical way to setup 2x LM317 in a driver?

rhd

rhd

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To accomplish ~1.6 to 1.7 A in an LM317 445nm build, does this setup make sense logically? Is this a proper parallel LM317 setup?

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Yes, that'll work. However, you'll save yourself some trouble if you just use a higher current-rated regulator (lm350 comes to mind).
 
Good point -

In reality though, I'm actually looking to go in the other direction and use LM1117s for their low voltage drop. They have a 1A limit (so even lower than LM317).

I just didn't indicate LM1117 above because I didn't want to confuse the issue I was seeking guidance on :)
 
rhd;

I agree with Cyparagon.

Don't use two parallel regulators.

There are single regulators that can handle 3 amps by themselves.
(National LMS1587CS-ADJ)

LarryDFW
 
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What would be an appropriate single regulator to use, with a low voltage drop similar to that of the LM1117?
 
I've been looking into this (superficially) as well the other day, and I've found out that
people advise against simply paralleling the output together.
The reason given was that, although equal in theory, in practice there will be slight differences in resistance between each lm317, so the load would not be equally
distributed, with possibly fatal (for the IC) consequences.
If I am not mistaken, two possible ways around this problems were proposed:
1. putting a capacitor between the output of each lm317 and ground, or
2. adding the same value balancing resistors in series after the output of each lm317.
these balancing resistors were supposed to be very low resistance, like 0.2 or 0.333Ohm.

Now, what I didn't quite catch correctly if this matters for our usage of lm317
as a current regulator, or if this applies when the IC is used to regulate voltage?:thinking:
In any case, I think it probably couldn't hurt to consider this, in case you end up
actually trying this.

There might even be a suitable circuit among the many examples on the online lm317 datasheet.
 
The differences in current are no issue at all!

You can rig current sources in paralel, even if they have totally different output currents, for example one 1.0A and one 0.5A can be combined to source 1.5 amps, even if they are of different design.

Using one regulator rated for a higher current can be more practical in construction, but from an electronics standpoint the circuit as you have drawn is fine.

The confusion comes from operating 2 voltage sources in paralel for more output current: That can cause problems if the voltages arent exactly the same.
 
Benm said:
The differences in current are no issue at all!
....
The confusion comes from operating 2 voltage sources in paralel for more output current: That can cause problems if the voltages arent exactly the same.
Click to expand...
Well thank you for clearing that up for me!:beer:
+1 internetz to you
My bait was successful and I'm off to slam a 2nd lm317 into my labby!:D:D
 
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rhd said:
...LM1117s for their low voltage drop.
Click to expand...

The minimum voltage drop is lower. If you power a 4V diode with 8V, it'll still drop the extra 4V. The only performance increase over the lm317 in this case is when the batteries are almost dead, it'll hold the current better.
 
Yes - that's what I meant. I mean, they'll both always drop the extra unnecessary voltage right? (within the limit of their capabilities)

I was under the impression that LM1117 would do a better job of running a 445nm on 2x Li-Ion cells.
 
Why not use the Current regulator to drive a pass transistor. That way you can pick a transistor that will handle whatever current your supply can handle and your load might demand?
 
A lower drop regulator like the 1117 will do a better job, and operate within specification. Obviously there are plenty of options to construct a driver with the required specifications, but the posed approach is still correct.
 
Has any one here tryed a LM 350 or a LM1117 I think they may not work as a current regulator !
 
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