+/- 15VDC from +/-75Vdc Is there a better way? - Page 2 - diyAudio
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Old 14th May 2005, 07:22 AM   #11
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What do you need to power with +/- 15 V? Wouldn't a separate trafo make more sense?

dave
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Old 14th May 2005, 10:19 AM   #12
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Apart from the switching option suggested by anatech, all the other options will produce the same, or more heat. You might get a better quality of power supply though.

I would just get some ali clad power resistors, and bolt them to the chassis somewhere near, then just conect up with flying leads.

Cheap and easy.
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Old 14th May 2005, 01:50 PM   #13
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The whole front end is powered off the +/-15VDC a preamp section and 2 parametric eq sections.

I am adding the vertical board anyway to the amp as there are no fuses on the B+/- anyway. if one channel should fail (which it did) there is nothing to protect the thing from totally destroying itself except the 10amp line fuse!!! So i am adding a board in there with fuses between the power supply and each amp board just to try and help save the thing a little bit should it ever fail again. at least try and save the PCB board and traces from burning up.

So i have a small amount of room in there between the fuse holders where i could put a regulator that uses TO-220 pass devices mounted on small heatsinks. OR, i may just use some larger resistors or maybe parallel several together to reduce the tempurature of each down a little bit. the total heat will be the same, but each one will run cooler.

But before i went that route, i thought i would explore what possibilitys are out there and the PASS regulator looks like it would do the trick nicely and fun to build and experiment with.

A small transformer really would be the best option. and im still looking to see if i can somehow squeeze one in there, but i think the regulation would actually be worse then. as there would be no regulation at all. i would have to add some regulators and a small trafo. but i could at least then use off the shelf 78xx devices.

BUT,... would that be better?


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Old 14th May 2005, 02:17 PM   #14
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IŽd definitely vote for the extra transformer.
You might fight a defective satellite-tuner or similar where you can find the right one or just buy a little 15VA which should be sufficient and easy to squeeze in somewhere!?
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Old 14th May 2005, 02:50 PM   #15
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Check out my website. A full design including board layout to do exactly what you need www.readresearch.co.uk click on High Voltage PSU.
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Old 14th May 2005, 03:18 PM   #16
anatech is offline anatech  Canada
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I'd vote for the transformer plus regulator IC's. Failing that, run the 555 at higher frequencies and it'll be clean. Say 10KHz~40KHz, filtering that isn't too hard.

There are more elegant designs out there. Possibly a module or all-in-one chip you can use.

Richie00boy's circuit has additional filtering which is good. I just don't like extra heat, like the original design.

-Chris
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Old 19th May 2005, 10:02 AM   #17
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Default Auxilliary supplies regulator

Hi all

Here's the schematic of the auxilliary supplies regulator I used on my PowerDAC1 digital amplifier. It runs off 75Vdc provided by the main SMPS converter, and outputs +3.3V, +5V, +12V, -12V, plus a floating +12V for hi-side gate drive powering of an external sync reg, all from a single switchmode, with quite reasonable cross regulation. It's a simple forward converter with a core reset winding and a coupled output inductor. TI has a plethora of app notes and design guides on coupled inductors. Max total output power is 30-35W and the transformer is an RM series coreset, as I recall.

All the circuitry associated with Q16 is for locking the switching frequency and may be omitted if not required. The regulator powers itself initially from the +75V through Q18, but once the +12V rail is up and running, it extracts power from this and D40/42 are backbiased. All unneeded rail output circuits can be omitted.

The circuit posted is not the latest version, as it doesn't have the -12V rail output, which I added later. I'll try to dig up the latest schematic as well as some transformer details and post these if there's any interest. In practice this it has worked well for 5 years, has low ripple and is robust towards secondary abuse.
Also it uses simple, cheap components.

JohnH
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Old 1st July 2005, 06:56 AM   #18
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I looked in the power supply section of "Success in Electronics" and found what it calls an "emitter follower stabilizer".

It's a power transistor whose base voltage is controlled by a Zener diode. The output voltage is the Zener voltage minus the base voltage. Apart from the transistor and Zener diode, the circuit has two resistors.
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Old 1st July 2005, 08:47 AM   #19
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Tim: This circuit is OK provided your current drain from the +15V is very small. But it is simply a linear regulator, and if you were to draw, say 50mA to power a lot of op-amps in a preamp or something, the power transistor would dissipate 2.25W and would require a heatsink.

John
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Old 1st July 2005, 12:41 PM   #20
Eva is offline Eva  Spain
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This is an old thread so I suppose that ZeroCool has already solved his problem. But anyway, I think that the smartest solution is to wrap two auxiliary 18V AC windings around the main toroid transformer (in case it's a toroid and it's not encapsulated).

This will provide about 27V DC max. to the front-end PSU so dissipation will be strongly reduced and IC regulators are suitable.

The SMPS is also a very smart solution, altough it has a great degree of complexity and uses additional space.
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