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Old 31st December 2005, 10:24 AM   #11
Eva is offline Eva  Spain
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Put the N-channel MOSFET in the negative side and use a PNP transistor with its base connected to the negative (regulated) output, the emitter connected to the positive (fixed) output through a suitable zener and resistor, and its collector driving the gate with a bleeder resistor to the negative unregulated input. I've employed that kind of regulator in the past and it works fine, not to talk about its awesome simplicity and the convenient grounding of the tab of the power MOSFET.
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Old 31st December 2005, 11:02 AM   #12
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Hi Eva,
you're giving me a hard time...
Are you talking about something like
borbely link see Page 5 with Q2 and Q4 omitted? Seems to be very cool indeed!
Rüdiger
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Old 31st December 2005, 11:08 AM   #13
Eva is offline Eva  Spain
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Something like that, but with a bipolar transistor driving the MOSFET. It yields very good performance for a 7 part discrete design...
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Old 31st December 2005, 11:47 AM   #14
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Quote:
Originally posted by Eva
Something like that, but with a bipolar transistor driving the MOSFET. It yields very good performance for a 7 part discrete design...
Well, you just mentioned 5. I guess you need a resistor from Drain to Ground and a feedback res between Drain and Base?
You don't happen to have a schematic handy? I'm eager to try it out!

@Onra:
The Mosfet was in my parts bin. Some people reported a sonically well performance, I'll try it out. It's clear to me that a non 3-pin regulator should sound better than say a LM317, else it makes no sense to try other options. So, if you know a good bjt suitable for this job, just tell me...
Another option to try would be the TL431 as a reference.

thanks,
Rüdiger
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Old 31st December 2005, 03:06 PM   #15
Eva is offline Eva  Spain
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It's five components plus input and output capacitors
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Old 31st December 2005, 04:23 PM   #16
Onra is offline Onra  Germany
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Hi,
there is a similar basic circuit i found at:
http://www.mikrocontroller.net/attac.../Schaltung.png
You can use a P-MOSFET instead of the darlington power stage.
Voltage is controlled by the Resistor divider across the output.
To improve regulation (?) and output noise you can try a LED instead the zener.
The negative rail is then mirrored with respect to the polarity of active devices.
I asked for the need of IRF610 because of its high RDSOn and low current capability.
What is your current range the PSU should supply?
Onra
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Old 1st February 2006, 01:54 PM   #17
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Quote:
Originally posted by Eva
...output through a suitable zener and resistor...
[voice from off:] What is suitable for around 24V?
I do not really get what happens there.
Rüdiger
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Old 1st February 2006, 11:08 PM   #18
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Quote:
Originally posted by Onvinyl

I do not really get what happens there.
Rüdiger
I made a quick breadboard. With +/- 12Vin all goes fine, with 8Vout.
I used a 6.8V Zener, BC550/560, and IRF(9)610.
With +/- 24Vin one of the bipolars explodes, even with 13.6V Zener. I have no clue why, since I see no exeeding of voltages.




Rüdiger
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Old 2nd February 2006, 07:27 AM   #19
AndrewT is online now AndrewT  Scotland
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Hi Onvinyl,
you are calling up both pnp & npn transistors.
Which schematic did you use?

That one in post1 is wrong.
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Old 2nd February 2006, 07:48 AM   #20
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Hi,
I use the one eva mentioned. A corrected version of posting #1 works ok, which is no big surprise...
Rüdiger
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