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Old 27th January 2011, 01:54 PM   #11
superR is offline superR  Netherlands
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Something like this but with lm317 337 instead of 78xx 79xx regulators?
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Old 27th January 2011, 02:36 PM   #12
Boofers is offline Boofers  Canada
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Quote:
Originally Posted by superR View Post
I have been googling, but I can't seem to find a good example of a symmetric "cap multiplier using mosfet"-based psu. Can you tell me where to look for more information?

Check out this link, figure 6 on page 3.

http://passdiy.com/pdf/zen-ver3.pdf
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Old 27th January 2011, 06:15 PM   #13
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Quote:
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You know I am the guy who just built your LM4780 SS pcb right?

Yup, I was just joking with you!

You can run a 4780 on 42v rails, (just), but it will need huge heatsinks and will only drive 8ohm loads, any lower and it will go bang. I know, I was that soldier...
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Old 27th January 2011, 06:45 PM   #14
CBS240 is offline CBS240  United States
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What is the VA rating of the power transformer? Have you thought of using a second smaller transformer to buck the primary? (connect the primary of the second smaller transformer on the line, then its secondary in series with the primary of the power transformer in oposite phase.) I assume you have 240V mains. If the second transformer has a secondary of 40VAC and can handle the current on the primary side of the transformer (1/4 secondary current rating since total secondary voltage is 60V) This will cause a de-ration of the transformer but would bring the secondarys' voltage down to 25VAC + 25VAC for ~ +/-34VDC after rectifier.

I have seen this technique used to boost the line voltage after a long stretch of wire. Say you have a well pump that is far from the house breaker box, you can use a buck boost transformer to retrieve the lost voltage in the long wire so the pump motor would not run undervolts and destroy itself. It can also be used the other way around to reduce line voltage.

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Old 27th January 2011, 06:45 PM   #15
paulb is offline paulb  Canada
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Try this (Fig. 3) with zener diodes across the 12K resistors. You may need to calculate a new value for the second set of 220 ohm resistors.
Capacitance Multiplier Power Supply Filter
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Old 27th January 2011, 06:52 PM   #16
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Not a great idea to use a cap multiplier with an AB amp.

Here's what I'd use:

1.png

I have all these parts though, so it might be cheaper to just buy the correct transformer. That is, if cheap is what you are after.
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Old 28th January 2011, 12:15 AM   #17
Minion is offline Minion  Canada
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Maybe use the TDA7293 , it will run fine at 42VDC into 8 ohms .....
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Old 7th February 2011, 09:45 PM   #18
Boofers is offline Boofers  Canada
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I just came across this article about using the LM117 family as high voltage regulators. Apparently referred to on the forum as the Maida supply after this article's author.

http://www.national.com/an/LB/LB-47.pdf
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