10-15A regulated supply - any options and/or tips? - diyAudio
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Old 6th May 2005, 02:47 AM   #1
cjd is offline cjd  United States
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Default 10-15A regulated supply - any options and/or tips?

I've gotten to that point where I realize I only understand enough to know that this is not something I'm going to be able to figure out on my own - I've spent the last few weeks digging through information and reading.

I would like to try regulated power on the SuperSymmetry chip-amp I'm working up. I'm using two LM4780 chips per channel which should have a 10-15A capable supply. These will be monoblocks.

Worst case, I'll build it without regulation. However, I would very much like to try a regulated supply.

The LM338 datasheet has a couple outlined, but they use obsolete chips in the circuit or are not recommended for more than 25V at best (though, I am not entirely clear where that voltage limit is being derived).

One of the things that has crossed my mind would be to supply each chip with its own regulator and not have a common power source (though I would still use one transformer and one rectifier bridge, and thus one capacitor bank behind the regulators). But I don't know if this is a good idea.

Other ideas and options are welcome.

Thanks!

C
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Old 6th May 2005, 04:22 AM   #2
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You can parrallel LT1083s without using an opamp, just 2 feet of 18g wire as ballast on each one (how do you make that look nice, i do not know )


http://www.linear.com/pc/downloadDoc...55,P1281,D3741

on page 12

that resistor with the arrow pointing to the chips output means that the resistor must be physically connected as close as possible to that pin.

that chip is a bit harder to find and more expensive than a 338.
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Old 6th May 2005, 08:46 AM   #3
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Because it's easyer to get the LM338 regulator chip, here's the schematic of paralleling three items to get a 15A voltage supply from the original datasheet :LM138/338 Datasheet
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File Type: jpg lm338x3.jpg (28.8 KB, 504 views)
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Old 6th May 2005, 01:00 PM   #4
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Are you bridging the chips?

I'm having the same dilemma. If you are bridging
you should be able to use one set of lm338 per chip.
If you are paralleling them then the V of the power supplies should
be close to each other.

I'm planning to do this by using 0.1% resistor and using
a trim pot to get the voltages within a few mV.
I don't know if this works but I don't see why not.

Harry
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Old 6th May 2005, 01:34 PM   #5
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if you must, use an external pass transistor with the LM338 (National has the details on their site) -- much less expensive than paralleling multiple discrete regulators -- you can also use a much less expensive regulator -- like an LM317 with an external pass device -- the approximate current that the "regulator" will have to bear is just the base drive (something approximating the output current by the beta of the pass transistor). the LM317 is less expensive than the LM338 and may be less noisy (although each device can be "cleaned up" if you read the application note by Wenzel Associates.)

be advised that you are adding another feedback loop into your circuitry when you "regulate" -- "not necessarily a good thing" to paraphrase Martha Stewart with her orange jumper and ankle bracelet.
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Old 6th May 2005, 03:43 PM   #6
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Quote:
Originally posted by slackman
Because it's easyer to get the LM338 regulator chip, here's the schematic of paralleling three items to get a 15A voltage supply from the original datasheet :LM138/338 Datasheet
Do you really want 15A capacity? Remember that an unregulated supply has basically zero Amps capacity except for the capacitors at the supply output. The amp runs on those caps except for the 20% of the time that the diodes conduct to recharge the caps and supply the amp if necessary.

So a very efficient regulated setup would be say one 338 with 5A capacity with say 10.000 uF of capacitance at the output. The amp will run 95% of the time on the regulated supply, and when you really need very high output pulses for bass drums etc the caps will provide that. A full 15A or more supply is a prime example of overkill.

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Old 6th May 2005, 06:28 PM   #7
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Quote:
Originally posted by janneman
So a very efficient regulated setup would be say one 338 with 5A capacity with say 10.000 uF of capacitance at the output.
Jan, I'm using 2,200uf on the LM3886 chips (after the LM338 regs).
This works very well.
But 10,000uf can kill a regulator at power-on, no?

Anyway, I think that the regs are fast enough to keep up with the demands, and 2,200uf seems ok.
They need some capacitance before them and around 10V difference between input and output so that they can regulate in the most demanding conditions, even accounting with some voltage sag (in this case they can give 12A peak current).

cjd, the LM338 regs can regulate at much higher voltages.
The limitation is the input to output voltage differential, not the regulated voltage.

PS: I would not parallel regulators. Better use a pass transistor.
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Old 6th May 2005, 06:56 PM   #8
cjd is offline cjd  United States
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Quote:
Originally posted by carlosfm

cjd, the LM338 regs can regulate at much higher voltages.
The limitation is the input to output voltage differential, not the regulated voltage.

PS: I would not parallel regulators. Better use a pass transistor.
I knew the 338's could regulate high voltages - the one example from the data-sheet that was posted here suggests 25V max, which I assumed was not due to the 338 but something else in the circuit. But, being unsure of WHAT is causing the 25V limit (if it's even a fair limit), and not really enjoying the thought of blowing something up in discovery, I decided it was better to admit my lack of knowledge and ask.

Pass transistor gives me something to look into. A couple of you have mentioned this and it seems to make sense if I understand the concept correctly. Now I just get to figure out how to actually implement it.

janneman: I don't need 15A probably, though it never hurts to have more capacity than needed. 5A seems to me to be too little though, even though I may never use it. The fact that the chips *could* draw more than 5A though...

C
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Old 6th May 2005, 10:32 PM   #9
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Quote:
Originally posted by cjd
5A seems to me to be too little though, even though I may never use it. The fact that the chips *could* draw more than 5A though...

C
5A continuous, 12A peak "for short periods of time", 7A "guaranteed peak output current".

in
LM138/LM338 datasheet
National Semiconductor
May 1998

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Old 6th May 2005, 11:57 PM   #10
cjd is offline cjd  United States
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Is 5A/7A/12A going to never have problems supplying power to two LM4780 chips?

(do you now have to ask "how loud do you play"? :P )

I'm actually having trouble finding documentation that explains anything enough (for me, given my level of understanding) regarding an external pass transistor. I can probably put the basic circuit together, just can't tell what parts go where. As if that's importnant.

C
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