Building split power supply - can't find regulator chip

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Mike
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Building split power supply - can't find regulator chip

Post by Mike » Sun Oct 26, 2003 5:41 am

In my post about the LM3886 subwoofer and trying to parallel transformers, I decided that I might just go and buy a 5 or 6A transformer. I thought also that the circuit would benifit from a cleaner supply, so I want to build one with regulators. The thing is, though, that I cannot find any regualator that puts out over 3A, and has a posiive and a negative chip availiable (for split supply). I want a chip that can take maybe an amp over 6A, so that nothing can happen to it, possibly 8A. The voltage in is about 30-33V +, 30-33V - and ground. The voltage out needs to be about 25-30V + and -. Are there any regulators that can do this?<p>Thanks, Mike

cato
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Re: Building split power supply - can't find regulator chip

Post by cato » Sun Oct 26, 2003 6:47 am

Consider using/building switching power supplies. The alternative is to piss away a lot of power as heat.<p>If you want to use a linear regulator, consider adding power a power transistor at the output of the regulators you were going to use. I'm sure you can find application notes showing sample designs. For example, the output pin of the regulator would go to the base of the transistor and the feedback signal would be taken from the output (e.g., emitter). The iput of the transistor (e.g., collector) is, of course, tied to the unregulated input voltage.<p>[ October 26, 2003: Message edited by: cato ]</p>

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Externet
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Re: Building split power supply - can't find regulator chip

Post by Externet » Sun Oct 26, 2003 6:19 pm

Hi.<p>You do not need to regulate the power supply with linear regulators. What you really want is good filtering.
Switching power supplies are the least recommended type of power source for audio.
They are brutally noisy.
Miguel
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k7elp60
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Re: Building split power supply - can't find regulator chip

Post by k7elp60 » Mon Oct 27, 2003 7:40 am

There are two linear regulators that I know of that are postive. Bothe of these regulators have built in current limiting and only require two external resistors to set the output voltage, and as I recall they have over temperature shutdown as well as the over current protection They are the LM338K by National Semiconductor and LT1083 by Linear Technology.
If you need more info about them let me know.<p>If you use brute force filtering for the power supply the rule of thumb is 3000uf per amp of load current. <p>When choosing a transformer on thing to keep in mind is that with brute force full wave filtering(transformer,rectifier,filter) the transformer will only supply .566 of the current rating with out overheating. This is because of peak charging current for the filter capacitor.<p>One solution for your power supply is to build two positive regulated power supplys. That is use two transfomers, two rectifiers, two filter capacitors,and two positive regulators. On one you put the + output to the common ground of your amp and the - output to the - of the amplifier. The other power supply is hooked up + to + of the amp, and - to the common of the power supply.
Ned :)

Mike
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Re: Building split power supply - can't find regulator chip

Post by Mike » Tue Oct 28, 2003 6:48 pm

What are the different types of supplies? Right now I use a 48VCT transformer, a rectifier and 2 1000uf caps.

Chris Foley
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Re: Building split power supply - can't find regulator chip

Post by Chris Foley » Tue Oct 28, 2003 9:15 pm

<quote>What are the different types of supplies? Right now I use a 48VCT transformer, a rectifier and 2 1000uf caps.<p>You definitely need more capacitance. The "rule of thumb" is that, for a power supply with 120Hz ripple, you need 8300uF to keep the ripple down to 1V for every amp of current. That means that, for 6A and 1000uF, you will "theoretically" have 1V p.p. * 6A * 8300/1000) = almost 50V of ripple. Of course, that won't happen with a 33VDC power supply, because current drain will go down as the voltage decreases (the 8300uF is based on a constant current load), but I wouldn't be too shocked if your ripple drops you more than halfway to GND, maybe most all the way.<p>If you want to use a straight capacitive filter, figure 50,000 uF for 1V p.p. of ripple at 6A, 25,000uF for 2V p.p., 17,000uF for 3V p.p., and so on. Try for 2V p.p. or less, and you probably won't need the regulators.<p>Most all high power audio amps have unregulated power supplies, anyway. And if you do decide to go for regulated power, you'll need the caps anyway -- V(out) can't be greater than V(in) for a linear P.S., and usually V(in) has to be quite a bit higher (dropout voltage).<p>Good luck (and, as always, double-check my maths, please!)
Chris<p>[ October 28, 2003: Message edited by: Chris Foley ]</p>

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Re: Building split power supply - can't find regulator chip

Post by bodgy » Wed Oct 29, 2003 2:59 am

C= (Vripple * CurrentRequired)/ T in the US T=8.33mS.<p>To check I=CV/T<p>In 50Hz countries T= 10mS<p>Colin
On a clear disk you can seek forever.

Timothy Rasch
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Re: Building split power supply - can't find regulator chip

Post by Timothy Rasch » Thu Nov 20, 2003 9:57 pm

With the 50000 uf the surge current will be huge so you will need a time delay heavy duty dual relay control circuit[use 555 timer ic with diode protection across relay coil] to switch in the dual amps power supplies after the caps above are fully charged [maybe 10 sec.]to avoid damaging voltage thump in speakers . The power transformer,the bridge,and relay contacts may have to handle about 20amps surge current. I don't know the equation of surge current for capacitors of this size but it's very large. Don't forget bleeder resistors across the big caps [maybe 10k,2w] P=eXe/r r=e/I always for your safety when you unplug the power supply .Good Luck!!!!

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