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Old 18th April 2006, 01:41 PM   #1
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Default needed 317/337 double regulation

I need a schematics for LM317/337 double regulated power supply

Thanks in advance
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Old 18th April 2006, 02:16 PM   #2
Eva is offline Eva  Spain
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Have you checked the datasheets from National Semiconductor? They contain plenty of useful application examples.
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Old 18th April 2006, 02:42 PM   #3
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Quote:
Originally posted by Eva
Have you checked the datasheets from National Semiconductor? They contain plenty of useful application examples.

Yes I have it in hand. I guess I was kinda looking for tips.

This is what I have on paper

24,000uf+.1uf--[317]--.1uf+12,000uf___ .33ohm ___ 3300uf+.1uf--[317]--.1uf+1000uf___ .33ohm.___

each 317 has a pot(100uf cap in parallel) at adj pin to ground
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Old 18th April 2006, 03:00 PM   #4
Eva is offline Eva  Spain
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With such amounts of capacitance, remember to add diodes to protect the regulators from reverse biasing as the datasheet shows
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Old 19th April 2006, 08:53 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
Quote:
24,000uf+.1uf--[317]--.1uf+12,000uf___ .33ohm ___ 3300uf+.1uf--[317]--.1uf+1000uf___ .33ohm.___
That last 0.33ohm is going to ruin your regulation. Is that what you need?
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Old 19th April 2006, 09:36 AM   #6
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Hi AndrewT

I definitely donít want to ruin the regulation.

I have a power supply in a separate chassis and need to get 40volt down to 18volt and only using 317/337. I will use 3 regulators per rail to get the voltage to 18volts. The 18volt will feed a preamp with 48,000uf per rail. I didnít think the last .33ohm resistor would be a problem. Should I leave it or remove it?

Thanks
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Old 19th April 2006, 09:46 AM   #7
Did it Himself
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Sorry but that is a very inelegant solution. Why not use a single regulator, or simple emitter follower fed from zener reference?
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Old 19th April 2006, 09:58 AM   #8
Eva is offline Eva  Spain
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It's quite obvious that he is looking for something exotic while he has little or no knowledge on how to use a LM317/LM337 (two things that usually happen together, as the more electronics you understand, the more you laugh at exotic).

If he just wanted something functional, he would calculate the required capacitances depending on load current and on the maximum allowed input voltage ripple in order to obtain the desired output ripple (and the resulting values would be much smaller than the ones he mentioned).

I understand exotic trends quite well, we as humans are very prone to fill the knowledge gap with imagination when we don't have anything better to use.
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Old 19th April 2006, 10:47 AM   #9
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I was trying to put it in a less upfront way.
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Old 19th April 2006, 11:35 AM   #10
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Good, you know more about electronics.

richie00boy
Hereís the thing. I need to build the power supply with the parts I have but Thanks

Eva
I donít need the exotic, just the functional. I planed to do the capacitance calculations but I have the equation on paper somewhere. This is not my only hobby but it is the only one, as much as I love it, which is not going to put money in my pockets, so tend not to keep formulas and equations in my head.

Your first post was helpful, thank you. I really donít know how to take your second.
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