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Old 7th January 2011, 06:21 AM   #1
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Default Getting down to a regulated 150V

See if you can help me with this. I'm building a cute little output transformerless headphone amp. The design calls for a 150V power supply.

Here's the deal. I have a 140V transformer going into a bridge rectifier, and a 220μF filter, this gives about 180VDC. I need to get it down to ~150. I've got zeners, a few power MOSFETs, and an assortment of regulator ICs. I'd like to have a regulated supply, specifically one I can adjust with a trimmer to dial in the voltage, but I'm not sure of the best way to go about it. I'm really terrible at HV power supply design, so I need pointed in the right direction before I blow up any more resistors.
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Old 7th January 2011, 07:06 AM   #2
Elvee is offline Elvee  Belgium
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You can use one of the circuits I gave in this message and the subsequent ones:
Need Negative High Voltage Regulator Circuit
You simply have to adjust one resistor value for your voltage, and you will end up with an excellent regulator, safer than any integrated one without compromising on performance.
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Old 7th January 2011, 07:09 AM   #3
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One possibility is a Maida LM317 regulated supply.
Morgan Jones extensively discusses regulated supplies in Valve Amplifiers.
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Old 7th January 2011, 08:00 AM   #4
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Tres cool. I think I can work either one of those.
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Old 7th January 2011, 08:09 AM   #5
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While I'm here, is there any way to make this circuit:
http://hem.passagen.se/ebcpecz/Tube/...schematics.gif
work with a transformer without a center tap? I threw one together on a tagboard with a diode bridge in place of D2/D5/C6/C5/R9/R11 and literally vaporized R14. I'm certain that I did something positively hilarious, but as I said I suck at power supplies. (I do promise to spend the next few months reading up on them)
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Old 7th January 2011, 08:39 AM   #6
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The link seems to be missing an _ to work properly.
Maybe this helps to answer your question: Elliott Sound Products - Linear Power Supply Design
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Old 7th January 2011, 12:00 PM   #7
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by AudioFox View Post
While I'm here, is there any way to make this circuit:
http://hem.passagen.se/ebcpecz/Tube/...schematics.gif
work with a transformer without a center tap? I threw one together on a tagboard with a diode bridge in place of D2/D5/C6/C5/R9/R11 and literally vaporized R14. I'm certain that I did something positively hilarious,
No, you didn't. But the author of the schematic did: R14 is most probably 560K.
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Old 8th January 2011, 04:41 AM   #8
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Thanks for all your help guys. I think I've got a better handle on it now.
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Old 9th January 2011, 05:33 AM   #9
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Here's what I've gotten so far. Starting from the design in the LM317 datasheet I worked this out from parts I had laying around. I'm not entirely sure about it, so I thought I'd run it by you guys first. I had to substitute a lot of parts, I have a bunch of Darlington transistors but couldn't find them so I used an N-channel MOSFET (IRF840), which I'm not sure I did right. I'm also unsure about the value of R6, the voltage adjustment resistor. 4.7K produces 150V but putting such a low resistance across the output makes me nervous, it seems like it would pass too much current.
I don't stock many power resistors, so in the testing stage I used a 0.25W metal film just to see what would happen (smoke, is what happened). Needless to say that did little to allay my fears.
So what do you guys think? Any suggestion is welcome.
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Old 9th January 2011, 10:47 AM   #10
AndrewT is offline AndrewT  Scotland
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Hi,
what is the tolerance on your mains supply?
What is the range of current drawn by your H/P amp?
What is the worst case range of voltage available from the PSU smoothing cap?

You cannot design your PSU until you have at least got a clue about all of those topics.
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