35v to 18v

purpf · 23rd June 2009, 07:29 PM

Hi,
What's the best way to drop the voltage of a PSU from 35v to 18v? Im thinking about a shunt voltage stabilizer.
What's your opinion?

mjf · 23rd June 2009, 08:11 PM

hello.
do you want to use the psu with a preamp.......or something else?
current consumption?
greetings..........

acid_k2 · 23rd June 2009, 08:58 PM

Other questions:
Do you need stable voltage? intermittent or continuos load? low ripple? low noise? low heat dissipation? small space available? other specification?

sawreyrw · 23rd June 2009, 09:08 PM

There is no way to give you a good answer without knowing your requirements: power level, regulation, noise and ripple, overload protection, efficiency, etc. Nonetheless, a current mode buck regulator would be a good choice.

Conrad Hoffman · 24th June 2009, 12:20 AM

Going from 35V to 18V is a 17V drop. If you want to draw even a measly 200mA, you'll dissipate 3.4W. Maybe that's ok, but the suggestion of a switching buck regulator is a very good one if you need any significant amount of current. There's a reason you'll almost never find a shunt regulator in commercial equipment (non-audio) other than as a voltage reference- they're a bad choice in almost any imaginable application.

jackinnj · 24th June 2009, 02:24 AM

Quote:

Originally posted by Conrad Hoffman
There's a reason you'll almost never find a shunt regulator in commercial equipment (non-audio) other than as a voltage reference- they're a bad choice in almost any imaginable application.

Except to save yourself warm in upstate NY winters.

purpf · 24th June 2009, 10:50 PM

I'm thinking of using a 2x24v toroidal core transformer with 2 PS units. 1 PSU to power an LM3875 chip amp and the other to power a preamp. Unless I can find a preamp powered by ~35v, I need to lover the voltage to about 18v.

purpf · 24th June 2009, 10:50 PM

I need stable DC current, the simplest solution is always the best

Conrad Hoffman · 24th June 2009, 11:49 PM

Though I don't have schematics handy, I think there have been a variety of discrete preamps over the years that ran on 35 and higher voltish single ended supplies. The claimed advantage was headroom on transients.

wwenze · 25th June 2009, 12:32 AM

Hmm? I know of op-amps that can handle +-17V. You can get a rail splitter to split the +35V to +-17V

23rd June 2009, 07:29 PM	#1
purpf diyAudio Member Join Date: Jun 2009	35v to 18v Hi, What's the best way to drop the voltage of a PSU from 35v to 18v? Im thinking about a shunt voltage stabilizer. What's your opinion?

24th June 2009, 12:20 AM	#5
Conrad Hoffman diyAudio Member Join Date: Mar 2007 Location: Canandaigua, NY USA	Going from 35V to 18V is a 17V drop. If you want to draw even a measly 200mA, you'll dissipate 3.4W. Maybe that's ok, but the suggestion of a switching buck regulator is a very good one if you need any significant amount of current. There's a reason you'll almost never find a shunt regulator in commercial equipment (non-audio) other than as a voltage reference- they're a bad choice in almost any imaginable application. __________________ I used to be an audiophool like you but then I took an arrow to the knee.

24th June 2009, 11:49 PM	#9
Conrad Hoffman diyAudio Member Join Date: Mar 2007 Location: Canandaigua, NY USA	Though I don't have schematics handy, I think there have been a variety of discrete preamps over the years that ran on 35 and higher voltish single ended supplies. The claimed advantage was headroom on transients. __________________ I used to be an audiophool like you but then I took an arrow to the knee.

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23rd June 2009, 08:11 PM	#2
mjf diyAudio Member Join Date: Jan 2009 Location: upper austria/near linz	hello. do you want to use the psu with a preamp.......or something else? current consumption? greetings..........

23rd June 2009, 08:58 PM	#3
acid_k2 diyAudio Member Join Date: Oct 2006	Other questions: Do you need stable voltage? intermittent or continuos load? low ripple? low noise? low heat dissipation? small space available? other specification?

23rd June 2009, 09:08 PM	#4
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	There is no way to give you a good answer without knowing your requirements: power level, regulation, noise and ripple, overload protection, efficiency, etc. Nonetheless, a current mode buck regulator would be a good choice.

24th June 2009, 10:50 PM	#7
purpf diyAudio Member Join Date: Jun 2009	I'm thinking of using a 2x24v toroidal core transformer with 2 PS units. 1 PSU to power an LM3875 chip amp and the other to power a preamp. Unless I can find a preamp powered by ~35v, I need to lover the voltage to about 18v.

25th June 2009, 12:32 AM	#10
wwenze diyAudio Member Join Date: Mar 2008	Hmm? I know of op-amps that can handle +-17V. You can get a rail splitter to split the +35V to +-17V

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