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Way to reduce rail voltage ? (wise type ?)
Way to reduce rail voltage ? (wise type ?)
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Old 6th March 2012, 07:32 AM   #11
guitar89 is offline guitar89  Malaysia
diyAudio Member
Join Date: Dec 2010
Location: Malaysia, Selangor
Originally Posted by ChrisA View Post
A regulator could work. But don't use anLM7818. Use the 317 adjustable reg and then adjust it to exactly what you want. Use one of those 15 turn trimmer pots to set the voltage. There is a negative version of the 317 also. But these chips will only pass about 1 amp. Is that enough. If not you will need a large size pass transistor and a large heat sink in addition to the regulator. So if this amp needs more then about an amp then I'd just replace the transformer.

Look at the data sheet for the LM317 it will have some good examples of how to do the above.

Also, you could simply use a resistor but I'd take advantage of it and put it to work rather then simply burning off power build a CRCRC" filter, This will not only drop volts but will dramaticaly cut the ripple voltage in the raw power. Not as much as a regulater would but it can handle more amps at lower cost. I'd use the CRCRC for larger currents and the LM317 for a smaller supply.

In the above "CRCRC" the lat "C" is the filter caps you have now, the two "Rs" are resistors to drop voltage use two of them to spead out the heat. the the other two "Cs" can be anything, say 100uF
Thanks for your advice, but in my case, it is either very low consumption (30mA MAX, without OPS) or high consumption (range from 4A to 8A, included OPS).
And because of the regulator needs external components, it increase components counts and complexity (tweaking for correct voltage or so) compare to a zener regulator.
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