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Old 2nd June 2010, 04:18 PM   #1
semi932 is offline semi932  United States
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Default Will this work with regulators?

Using the regulators in the link and the diagram on pg. 25, will this circuit work if powered with 18v dc from batteries?

I know it's not ideal but just learning and have got some different ideas in my head.
This is to power a phono stage board so not much current required.

Thanks.

Last edited by semi932; 2nd June 2010 at 04:18 PM. Reason: forgot the link http://www.fairchildsemi.com/ds/KA%2FKA7815E.pdf
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Old 2nd June 2010, 04:57 PM   #2
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The data sheet says the drop out voltage is typically 2 volts. If you are talking about a 15 volt output, this will be marginal; espically when you consider that the battery voltage may be less than 18 volts.
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Old 2nd June 2010, 07:33 PM   #3
semi932 is offline semi932  United States
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Quote:
Originally Posted by sawreyrw View Post
The data sheet says the drop out voltage is typically 2 volts. If you are talking about a 15 volt output, this will be marginal; espically when you consider that the battery voltage may be less than 18 volts.
Thanks for the reply.

I'm not sure exactly what to do. Today while at a thrift I picked up a 30vdc adaptor. Looks like it was from computer supply.
Also a 32v plus 15v wall wart from a printer.

Saw something on Rod Elliot's site about splitting wall wart out to = and - supplies. Going to study that a little and see what develops.
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Old 2nd June 2010, 08:04 PM   #4
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Quote:
Originally Posted by semi932 View Post
Thanks for the reply.

I'm not sure exactly what to do. Today while at a thrift I picked up a 30vdc adaptor. Looks like it was from computer supply.
Also a 32v plus 15v wall wart from a printer.

Saw something on Rod Elliot's site about splitting wall wart out to = and - supplies. Going to study that a little and see what develops.
What exactly do you need? +/- 15VDC? How much current?

jd
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Old 3rd June 2010, 03:44 AM   #5
semi932 is offline semi932  United States
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Quote:
Originally Posted by janneman View Post
What exactly do you need? +/- 15VDC? How much current?

jd
Yes + and - 15vdc.

As far as current I'm not exactly sure but both AC converters I picked are good for 500ma.
Will be using it for a phono stage which I haven't received yet. I'm thinking current should not be a problem.
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Old 3rd June 2010, 03:52 AM   #6
semi932 is offline semi932  United States
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Also I was just experimenting for my education using this link Project 43 - Simple DC Adapter Power Supply
and building the simple voltage divider to turn the 30v adaptor to two 15vdc rails.

Everything was fine until I started taking some voltage readings and one of the 25v 1000uf caps blew.
Fortunately for me I had the board component side down. No flying missles just had to make a quick powder room run!!!!!!!

I'm not sure why that happened though. I would have thought 25v would have been enough for caps.
In the morning hopefully I'll recheck my wiring and soldering and use some higher voltage caps.
Hopefully it was just a solder bridge or something similar.
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Old 3rd June 2010, 07:02 AM   #7
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Quote:
Originally Posted by semi932 View Post
Also I was just experimenting for my education using this link Project 43 - Simple DC Adapter Power Supply
and building the simple voltage divider to turn the 30v adaptor to two 15vdc rails.

Everything was fine until I started taking some voltage readings and one of the 25v 1000uf caps blew.
Fortunately for me I had the board component side down. No flying missles just had to make a quick powder room run!!!!!!!

I'm not sure why that happened though. I would have thought 25v would have been enough for caps.
In the morning hopefully I'll recheck my wiring and soldering and use some higher voltage caps.
Hopefully it was just a solder bridge or something similar.
It's much easier to comment on what might have happened if you can show a circuit of what you were doing, even hand-drafted & scanned.

Note that for a +/-15V set of regs you need at least 2*17 or 18V 'raw' DC inputs; the regs need some headroom to work with. That's worst case, lowest mains, highest current etc. So conservatively you'd want a raw 2*20VDC or thereabouts.
The problem with dividing a single 30V into two 15V is that any imbalance in current may skew the division. You'r much better served with a traditional transformer/rectifier solution.

jd
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Old 3rd June 2010, 05:41 PM   #8
semi932 is offline semi932  United States
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I was using this layout Project 43 - Simple DC Adapter Power Supply

I know it's not optimum and I'm planning on building a genuine PS but am awaiting parts.

As far as blowing caps yesterday it was my rookie ignorance as the adaptor plug is not polarized. I must have plugged it opposite and fed the caps wrong way.
Everything in order now.

BANG. Small caps so no real damage done.

Thanks

Everything you says is helpful to me and I appreciate it.
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