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Old 22nd August 2008, 02:08 PM   #1
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Join Date: Dec 2007
Default need help in building 24v power supply

I am newbie. i need help in building a dc power supply for my dac. the dac is powered using plug pack dc adaptor.

i would like better power supply that can output 24v and at least 300mA

i have 4 rectifier diodes. money no object as building this power supply wont cost me a bomb i suppose.

any help on schematic and parts? thanks a lot in advance

regards, Erwin
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Old 24th August 2008, 04:30 PM   #2
Minion is offline Minion  Canada
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Very simple....Just use a diode Bridge ,then Filter the DC outout with a 1000uF cap then use a LM317 regulator to regulate to 24v then add another 1000uF cap after the regulator....That is it...

Look at the LM317 datasheet for examples....

http://cache.national.com/ds/LM/LM117.pdf



Cheers
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Old 24th August 2008, 05:52 PM   #3
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Hi Minion, i suppose that i need 18v 0v transformer

from below attachment, to output 24vdc. how to calculate R1 and R2?

need another RC to reduce hum or something? whats the recommended value for this RC? 100ohm 2200uF?

thx
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File Type: jpg lm117.jpg (13.0 KB, 249 views)
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Old 24th August 2008, 07:55 PM   #4
Minion is offline Minion  Canada
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Here is a calculator for the LM317...

http://www.muzique.com/schem/lm317.htm

A 18v Transformer might be cutting it close as you will get about 26v DC from 18v AC, and the regulator needs a couple volts above the regulated voltage to maintain proper regulation.....You should be OK as long as your Transformer is big enough to not have Voltage sag under high current demand....
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Old 24th August 2008, 08:08 PM   #5
AndrewT is offline AndrewT  Scotland
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use a 24Vac transformer for a regulated 24Vdc.
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regards Andrew T.
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Old 25th August 2008, 02:39 AM   #6
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Just to make thing certain. using 24 Vac transformer for a regulated 24Vdc

R1=240 Ohm and R2=4560Ohm independent of the supply VAC voltage from the transformer. is this right? thanks alot
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Old 25th August 2008, 04:09 PM   #7
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hi there

actually, whats the different between regulated and unregulated power supply unit?

whats the advantage of regulated? if regulated psu provide better result, why some still use unregulated psu?

for dac application, which one is preferable? thx
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Old 25th August 2008, 04:56 PM   #8
AndrewT is offline AndrewT  Scotland
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that question is 6 posts too late.
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Old 25th August 2008, 05:49 PM   #9
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lol i know its too late. but im learning. In ealier 6 post i dont even have any idea whats regulated psu until minion suggest lm317. try to google but too broad and not audio specific. thx
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Old 25th August 2008, 06:22 PM   #10
paulb is offline paulb  Canada
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An unregulated supply has an output whose voltage will vary with the load that is attached to it. A regulated supply will keep roughly the same output voltage over a wide range of loads.
Whether you need one or not depends on what your DAC requires. Is your current dc adapter regulated or not?
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