Voltage Regulators in Parallel...

[Cursitor Doom]

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

 

[Tabby]

On Tuesday, 2 May 2023 at 00:20:44 UTC+1, Cursitor Doom wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

They shouldn\'t fight. If mismatched, one will carry all the current upto its inbuilt limit, then the 2nd will kick in. Prepare for that thermally.

 

[Phil Hobbs]

On 2023-05-01 19:25, Tabby wrote:

On Tuesday, 2 May 2023 at 00:20:44 UTC+1, Cursitor Doom wrote:
Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

They shouldn\'t fight. If mismatched, one will carry all the current
upto its inbuilt limit, then the 2nd will kick in. Prepare for that
thermally.

They won\'t fight the way op amps do, because they can\'t pull down, so
the highest-voltage one will provide most of the current. (Their loop
gain isn\'t super super high, so it may droop far enough for others to
contribute a bit.

When the hot one hits thermal limit, though, it\'ll abruptly shut off,
transferring the load to the next few in line. That\'s not a nice way to
treat the poor regulator, and depending on the quality of the heat
spreader, it may result in complete shutdown of the regulators.

Some power resistors in series before connecting them together would be
the ticket, if you have them laying around.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[bitrex]

On 5/1/2023 7:20 PM, Cursitor Doom wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

Here\'s an old chestnut:

<https://i.stack.imgur.com/PRnYU.png>

 

[bitrex]

On 5/1/2023 10:16 PM, bitrex wrote:

On 5/1/2023 7:20 PM, Cursitor Doom wrote:
Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

Here\'s an old chestnut:

https://i.stack.imgur.com/PRnYU.png

I have concerns about how this one behaves at temperature extremes,
though. Looks fine in the sim on a temp sweep, that is until you pick
two different type of series silicon diodes with similar ratings and
then it all goes side ways

 

[John Larkin]

On Mon, 1 May 2023 22:16:23 -0400, bitrex <user@example.net> wrote:

On 5/1/2023 7:20 PM, Cursitor Doom wrote:
Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

Here\'s an old chestnut:

https://i.stack.imgur.com/PRnYU.png

That\'s mega-lame. The 7812s will probably have different output
voltages (some are spec\'d at +-4%), and the diodes aren\'t good current
equalizers.

Why does he parallel two 78L12s when he could use one 7812?

Why would pass transistors need \"critical power resistors\" at their
collectors?

So many bypass caps that are not bypassing much.

At least use LM317s or 1117s to minimize the output voltage
differential, and resistors as the equalizers. 1% of 1.25 volts is a
lot less than 4% of 12 volts.

There is a simple way to boost a 3T reg with a PNP. Or an NPN! Or make
a good reg with an opamp and a giant mosfet.

 

[bitrex]

On 5/1/2023 10:59 PM, John Larkin wrote:

On Mon, 1 May 2023 22:16:23 -0400, bitrex <user@example.net> wrote:

On 5/1/2023 7:20 PM, Cursitor Doom wrote:
Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

Here\'s an old chestnut:

https://i.stack.imgur.com/PRnYU.png

That\'s mega-lame. The 7812s will probably have different output
voltages (some are spec\'d at +-4%), and the diodes aren\'t good current
equalizers.

I have concerns abut it

Why does he parallel two 78L12s when he could use one 7812?

Why would pass transistors need \"critical power resistors\" at their
collectors?

So many bypass caps that are not bypassing much.

I\'m not convinced it works great at operating temperature unless all the
devices are on a common heat sink, maybe not even then.

At least use LM317s or 1117s to minimize the output voltage
differential, and resistors as the equalizers. 1% of 1.25 volts is a
lot less than 4% of 12 volts.

LM3xx seem easier to parallel, they\'re basically op amps with an offset
and we know how to parallel op amps.

There is a simple way to boost a 3T reg with a PNP. Or an NPN! Or make
a good reg with an opamp and a giant mosfet.

Well, it wasn\'t the question..

 

[John Larkin]

On Mon, 1 May 2023 23:26:31 -0400, bitrex <user@example.net> wrote:

On 5/1/2023 10:59 PM, John Larkin wrote:
On Mon, 1 May 2023 22:16:23 -0400, bitrex <user@example.net> wrote:

On 5/1/2023 7:20 PM, Cursitor Doom wrote:
Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

Here\'s an old chestnut:

https://i.stack.imgur.com/PRnYU.png

That\'s mega-lame. The 7812s will probably have different output
voltages (some are spec\'d at +-4%), and the diodes aren\'t good current
equalizers.

I have concerns abut it

Why does he parallel two 78L12s when he could use one 7812?

Why would pass transistors need \"critical power resistors\" at their
collectors?

So many bypass caps that are not bypassing much.

I\'m not convinced it works great at operating temperature unless all the
devices are on a common heat sink, maybe not even then.

At least use LM317s or 1117s to minimize the output voltage
differential, and resistors as the equalizers. 1% of 1.25 volts is a
lot less than 4% of 12 volts.

LM3xx seem easier to parallel, they\'re basically op amps with an offset
and we know how to parallel op amps.

There is a simple way to boost a 3T reg with a PNP. Or an NPN! Or make
a good reg with an opamp and a giant mosfet.

Well, it wasn\'t the question..

This is pleasingly goofy:

https://www.dropbox.com/s/ceawu3xk43byfzj/LM317s_in_parallel.jpg?raw=1

 

[whit3rd]

On Monday, May 1, 2023 at 8:38:34 PM UTC-7, John Larkin wrote:

On Mon, 1 May 2023 23:26:31 -0400, bitrex <us...@example.net> wrote:

On 5/1/2023 10:59 PM, John Larkin wrote:
On Mon, 1 May 2023 22:16:23 -0400, bitrex <us...@example.net> wrote:

On 5/1/2023 7:20 PM, Cursitor Doom wrote:
Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were?

This is pleasingly goofy:

https://www.dropbox.com/s/ceawu3xk43byfzj/LM317s_in_parallel.jpg?raw=1

Well, yeah, but... the regulators would take a heatsink to really deliver current.

LM317 and PNP pass transistor can get you from 1A to 5A pretty easily, as long
as you need the heatsink anyhow.

<https://sound-au.com/articles/vreg-f7.gif>
is the circuit I\'d prefer, other variants (setting R4 and R5 to zero) don\'t really benefit
from the current limit of the LM317.

 

[John Larkin]

On Tue, 02 May 2023 00:20:37 +0100, Cursitor Doom <cd@notformail.com>
wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

This is a little better maybe:

https://www.dropbox.com/s/0rf7274rlesc0mh/LM317s_parallel_2.jpg?raw=1

 

[Fred Bloggs]

On Monday, May 1, 2023 at 7:20:44 PM UTC-4, Cursitor Doom wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

They can be paralleled but you need ancillary circuitry and components. Generally any high current bipolar NPN emitter follower type of linear regulator can be adapted to the 3-terminals. The 3-terminals do have an advantage of internal reference, overtemperature foldback, and current limiting, so that\'s a plus, making them almost indestructible.

Thanks,

CD

 

[bitrex]

On 5/2/2023 10:19 AM, John Larkin wrote:

On Tue, 02 May 2023 00:20:37 +0100, Cursitor Doom <cd@notformail.com
wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

This is a little better maybe:

https://www.dropbox.com/s/0rf7274rlesc0mh/LM317s_parallel_2.jpg?raw=1

While we\'re being \"pleasingly goofy\":

<https://imgur.com/a/ZK8eitu>

Load regulation isn\'t great, but at leas it doesn\'t go crazy when you
use two different kinds of power diodes and do a temp sweep like the EDN
one does..

 

[bitrex]

On 5/2/2023 11:31 AM, bitrex wrote:

On 5/2/2023 10:19 AM, John Larkin wrote:
On Tue, 02 May 2023 00:20:37 +0100, Cursitor Doom <cd@notformail.com
wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

This is a little better maybe:

https://www.dropbox.com/s/0rf7274rlesc0mh/LM317s_parallel_2.jpg?raw=1



While we\'re being \"pleasingly goofy\":

https://imgur.com/a/ZK8eitu

oops, it works better when you use the right number of diodes:

<https://imgur.com/a/ElVxiJb>

 

[Cursitor Doom]

On Tue, 2 May 2023 11:37:42 -0400, bitrex <user@example.net> wrote:

On 5/2/2023 11:31 AM, bitrex wrote:
On 5/2/2023 10:19 AM, John Larkin wrote:
On Tue, 02 May 2023 00:20:37 +0100, Cursitor Doom <cd@notformail.com
wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

This is a little better maybe:

https://www.dropbox.com/s/0rf7274rlesc0mh/LM317s_parallel_2.jpg?raw=1



While we\'re being \"pleasingly goofy\":

https://imgur.com/a/ZK8eitu

oops, it works better when you use the right number of diodes:

https://imgur.com/a/ElVxiJb

Naw... \"Goofy\" is transformerless power supplies when you use a
handful of diodes, resistors and caps to take 240VAC and turn it into
5VDC stabilised. Okay, the final \"5VDC stabilised\" comes courtesy of a
linear IC, but the rest of it is discretes.
Transformerless keeps costs way down, but you need to know the load
parameters within *very* tight tolerances as the source resistance of
these suckers is quite high. The lack of galvanic isolation provided
can also be concerning. Best to troubleshoot with a low VA mains
isolation transformer. ;->

 

[John Larkin]

On Tue, 2 May 2023 11:31:07 -0400, bitrex <user@example.net> wrote:

On 5/2/2023 10:19 AM, John Larkin wrote:
On Tue, 02 May 2023 00:20:37 +0100, Cursitor Doom <cd@notformail.com
wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

This is a little better maybe:

https://www.dropbox.com/s/0rf7274rlesc0mh/LM317s_parallel_2.jpg?raw=1



While we\'re being \"pleasingly goofy\":

https://imgur.com/a/ZK8eitu

Load regulation isn\'t great, but at leas it doesn\'t go crazy when you
use two different kinds of power diodes and do a temp sweep like the EDN
one does..

OK, that wins the goofy prize. Why use diodes to merge the two reg
outputs?

Looks like someone was trying to maximize the current imbalance.

 

[bitrex]

On 5/2/2023 7:14 PM, John Larkin wrote:

On Tue, 2 May 2023 11:31:07 -0400, bitrex <user@example.net> wrote:

On 5/2/2023 10:19 AM, John Larkin wrote:
On Tue, 02 May 2023 00:20:37 +0100, Cursitor Doom <cd@notformail.com
wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

This is a little better maybe:

https://www.dropbox.com/s/0rf7274rlesc0mh/LM317s_parallel_2.jpg?raw=1



While we\'re being \"pleasingly goofy\":

https://imgur.com/a/ZK8eitu

Load regulation isn\'t great, but at leas it doesn\'t go crazy when you
use two different kinds of power diodes and do a temp sweep like the EDN
one does..

OK, that wins the goofy prize. Why use diodes to merge the two reg
outputs?

Paralleling fixed regulators is annoying, since you don\'t have access to
the feedback terminal, and can\'t connect it to the \"real\" output after
the ballast resistors. So the only thing that can bring a regulator\'s
output into line is current against the ballast resistors. But if you
use ballast resistors large enough to ensure tight current sharing you
end up with a large voltage drop at max output.

I think the diodes were a hack basically to try to limit the max voltage
drop at max output while ensuring there\'s always _some_ amount of
current sharing. vs if you just connect them directly together they\'re
guaranteed to hog.

And in the sim they do share very nicely, at 25 degrees C, with ideal
7812s and ideal diodes, but just start swapping diode types around and
it goes sideways over temperature. My goofy idea isn\'t really much
better. The LM7812 is +/- 5% over temperature and the temp sweep doesn\'t
take that into account, you\'d have to monte carlo that.

Looks like someone was trying to maximize the current imbalance.

Any solution for fixed regulators has to take into account the output of
one regulator could be sitting at 12.5 and the other at 11.5 and be
within spec, and none of the simple ideas I\'ve played with can do much
with that. You could actively monitor the input current to each and do
something with that maybe, but that seems like a waste of time.

 

[John Larkin]

On Wed, 3 May 2023 12:07:44 -0400, bitrex <user@example.net> wrote:

On 5/2/2023 7:14 PM, John Larkin wrote:
On Tue, 2 May 2023 11:31:07 -0400, bitrex <user@example.net> wrote:

On 5/2/2023 10:19 AM, John Larkin wrote:
On Tue, 02 May 2023 00:20:37 +0100, Cursitor Doom <cd@notformail.com
wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

This is a little better maybe:

https://www.dropbox.com/s/0rf7274rlesc0mh/LM317s_parallel_2.jpg?raw=1



While we\'re being \"pleasingly goofy\":

https://imgur.com/a/ZK8eitu

Load regulation isn\'t great, but at leas it doesn\'t go crazy when you
use two different kinds of power diodes and do a temp sweep like the EDN
one does..

OK, that wins the goofy prize. Why use diodes to merge the two reg
outputs?

Paralleling fixed regulators is annoying, since you don\'t have access to
the feedback terminal, and can\'t connect it to the \"real\" output after
the ballast resistors. So the only thing that can bring a regulator\'s
output into line is current against the ballast resistors. But if you
use ballast resistors large enough to ensure tight current sharing you
end up with a large voltage drop at max output.

I think the diodes were a hack basically to try to limit the max voltage
drop at max output while ensuring there\'s always _some_ amount of
current sharing. vs if you just connect them directly together they\'re
guaranteed to hog.

The diodes probably make the sharing worse than resistors. Diode
behavior is complex, NTC at low currents and PTC at high currents.

And in the sim they do share very nicely, at 25 degrees C, with ideal
7812s and ideal diodes, but just start swapping diode types around and
it goes sideways over temperature. My goofy idea isn\'t really much
better. The LM7812 is +/- 5% over temperature and the temp sweep doesn\'t
take that into account, you\'d have to monte carlo that.

Sims share nicely with no sharing parts at all! Just slap the regs in
parallel.

Looks like someone was trying to maximize the current imbalance.


Any solution for fixed regulators has to take into account the output of
one regulator could be sitting at 12.5 and the other at 11.5 and be
within spec, and none of the simple ideas I\'ve played with can do much
with that. You could actively monitor the input current to each and do
something with that maybe, but that seems like a waste of time.

That\'s one reason to use LM317s or 1117s. They will share to
millivolts.

Or add opamps.

 

[Phil Hobbs]

On 2023-05-03 13:31, John Larkin wrote:

On Wed, 3 May 2023 12:07:44 -0400, bitrex <user@example.net> wrote:

On 5/2/2023 7:14 PM, John Larkin wrote:
On Tue, 2 May 2023 11:31:07 -0400, bitrex <user@example.net> wrote:

On 5/2/2023 10:19 AM, John Larkin wrote:
On Tue, 02 May 2023 00:20:37 +0100, Cursitor Doom <cd@notformail.com
wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

This is a little better maybe:

https://www.dropbox.com/s/0rf7274rlesc0mh/LM317s_parallel_2.jpg?raw=1



While we\'re being \"pleasingly goofy\":

https://imgur.com/a/ZK8eitu

Load regulation isn\'t great, but at leas it doesn\'t go crazy when you
use two different kinds of power diodes and do a temp sweep like the EDN
one does..

OK, that wins the goofy prize. Why use diodes to merge the two reg
outputs?

Paralleling fixed regulators is annoying, since you don\'t have access to
the feedback terminal, and can\'t connect it to the \"real\" output after
the ballast resistors. So the only thing that can bring a regulator\'s
output into line is current against the ballast resistors. But if you
use ballast resistors large enough to ensure tight current sharing you
end up with a large voltage drop at max output.

I think the diodes were a hack basically to try to limit the max voltage
drop at max output while ensuring there\'s always _some_ amount of
current sharing. vs if you just connect them directly together they\'re
guaranteed to hog.

The diodes probably make the sharing worse than resistors. Diode
behavior is complex, NTC at low currents and PTC at high currents.


And in the sim they do share very nicely, at 25 degrees C, with ideal
7812s and ideal diodes, but just start swapping diode types around and
it goes sideways over temperature. My goofy idea isn\'t really much
better. The LM7812 is +/- 5% over temperature and the temp sweep doesn\'t
take that into account, you\'d have to monte carlo that.

Sims share nicely with no sharing parts at all! Just slap the regs in
parallel.

Those spherical cows don\'t know how good they\'ve got it, for sure.

Looks like someone was trying to maximize the current imbalance.


Any solution for fixed regulators has to take into account the output of
one regulator could be sitting at 12.5 and the other at 11.5 and be
within spec, and none of the simple ideas I\'ve played with can do much
with that. You could actively monitor the input current to each and do
something with that maybe, but that seems like a waste of time.

That\'s one reason to use LM317s or 1117s. They will share to
millivolts.

Or add opamps.

Yeah, at some point you might as well build the regulator you actually
want.

One op amp, one Darlington or MOS pass transistor, a voltage reference,
and a small BJT plus a few resistors to make a foldback current limiter
to stay within the SOA and thermal limits.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[bitrex]

On 5/3/2023 1:31 PM, John Larkin wrote:

On Wed, 3 May 2023 12:07:44 -0400, bitrex <user@example.net> wrote:

On 5/2/2023 7:14 PM, John Larkin wrote:
On Tue, 2 May 2023 11:31:07 -0400, bitrex <user@example.net> wrote:

On 5/2/2023 10:19 AM, John Larkin wrote:
On Tue, 02 May 2023 00:20:37 +0100, Cursitor Doom <cd@notformail.com
wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

This is a little better maybe:

https://www.dropbox.com/s/0rf7274rlesc0mh/LM317s_parallel_2.jpg?raw=1



While we\'re being \"pleasingly goofy\":

https://imgur.com/a/ZK8eitu

Load regulation isn\'t great, but at leas it doesn\'t go crazy when you
use two different kinds of power diodes and do a temp sweep like the EDN
one does..

OK, that wins the goofy prize. Why use diodes to merge the two reg
outputs?

Paralleling fixed regulators is annoying, since you don\'t have access to
the feedback terminal, and can\'t connect it to the \"real\" output after
the ballast resistors. So the only thing that can bring a regulator\'s
output into line is current against the ballast resistors. But if you
use ballast resistors large enough to ensure tight current sharing you
end up with a large voltage drop at max output.

I think the diodes were a hack basically to try to limit the max voltage
drop at max output while ensuring there\'s always _some_ amount of
current sharing. vs if you just connect them directly together they\'re
guaranteed to hog.

The diodes probably make the sharing worse than resistors. Diode
behavior is complex, NTC at low currents and PTC at high currents.


And in the sim they do share very nicely, at 25 degrees C, with ideal
7812s and ideal diodes, but just start swapping diode types around and
it goes sideways over temperature. My goofy idea isn\'t really much
better. The LM7812 is +/- 5% over temperature and the temp sweep doesn\'t
take that into account, you\'d have to monte carlo that.

Sims share nicely with no sharing parts at all! Just slap the regs in
parallel.



Looks like someone was trying to maximize the current imbalance.


Any solution for fixed regulators has to take into account the output of
one regulator could be sitting at 12.5 and the other at 11.5 and be
within spec, and none of the simple ideas I\'ve played with can do much
with that. You could actively monitor the input current to each and do
something with that maybe, but that seems like a waste of time.

That\'s one reason to use LM317s or 1117s. They will share to
millivolts.

Or add opamps.

You can parallel 78xxs with a few op amps and transistors, but you have
to play the leap frog game:

<https://imgur.com/a/3z7qwXH>

 

[John Larkin]

On Wed, 3 May 2023 14:28:43 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-03 13:31, John Larkin wrote:
On Wed, 3 May 2023 12:07:44 -0400, bitrex <user@example.net> wrote:

On 5/2/2023 7:14 PM, John Larkin wrote:
On Tue, 2 May 2023 11:31:07 -0400, bitrex <user@example.net> wrote:

On 5/2/2023 10:19 AM, John Larkin wrote:
On Tue, 02 May 2023 00:20:37 +0100, Cursitor Doom <cd@notformail.com
wrote:

Gentlemen,

I have a bunch of 12VDC and 5VDC voltage regulator ICs in TO-220
packages. IIRC, I think they\'re about 1A each. Could they be
paralleled-up to get more current or would they have a tendency to
\'fight each other\' as it were? It would be nice if they further
*stablised* each other but I\'m guessing I wouldn\'t be that lucky.

Thanks,

CD

This is a little better maybe:

https://www.dropbox.com/s/0rf7274rlesc0mh/LM317s_parallel_2.jpg?raw=1



While we\'re being \"pleasingly goofy\":

https://imgur.com/a/ZK8eitu

Load regulation isn\'t great, but at leas it doesn\'t go crazy when you
use two different kinds of power diodes and do a temp sweep like the EDN
one does..

OK, that wins the goofy prize. Why use diodes to merge the two reg
outputs?

Paralleling fixed regulators is annoying, since you don\'t have access to
the feedback terminal, and can\'t connect it to the \"real\" output after
the ballast resistors. So the only thing that can bring a regulator\'s
output into line is current against the ballast resistors. But if you
use ballast resistors large enough to ensure tight current sharing you
end up with a large voltage drop at max output.

I think the diodes were a hack basically to try to limit the max voltage
drop at max output while ensuring there\'s always _some_ amount of
current sharing. vs if you just connect them directly together they\'re
guaranteed to hog.

The diodes probably make the sharing worse than resistors. Diode
behavior is complex, NTC at low currents and PTC at high currents.


And in the sim they do share very nicely, at 25 degrees C, with ideal
7812s and ideal diodes, but just start swapping diode types around and
it goes sideways over temperature. My goofy idea isn\'t really much
better. The LM7812 is +/- 5% over temperature and the temp sweep doesn\'t
take that into account, you\'d have to monte carlo that.

Sims share nicely with no sharing parts at all! Just slap the regs in
parallel.

Those spherical cows don\'t know how good they\'ve got it, for sure.

Looks like someone was trying to maximize the current imbalance.


Any solution for fixed regulators has to take into account the output of
one regulator could be sitting at 12.5 and the other at 11.5 and be
within spec, and none of the simple ideas I\'ve played with can do much
with that. You could actively monitor the input current to each and do
something with that maybe, but that seems like a waste of time.

That\'s one reason to use LM317s or 1117s. They will share to
millivolts.

Or add opamps.


Yeah, at some point you might as well build the regulator you actually
want.

One op amp, one Darlington or MOS pass transistor, a voltage reference,
and a small BJT plus a few resistors to make a foldback current limiter
to stay within the SOA and thermal limits.

Cheers

Phil Hobbs

I\'ve done super low dropout regs with a big n-fet and an opamp, which
is great if you have a higher opamp voltage supply somewhere to
overdrive the fet gate.

I\'ve seen a few new low-dropout current limiter chips lately, which
could go upstream. Or use one of the shunt sensors, like INA281 or
similar, to sense current if you really need to.