Powerful Short-circuit protected DC supply

Discussion in 'The Projects Forum' started by EnthusiasticStudent, May 5, 2011.

  1. EnthusiasticStudent

    Thread Starter New Member

    May 5, 2011
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    I'm building my end-of-year project which is a requirement for graduation, but I'm having a lot of difficulties finding a short-circuit protected DC dual rail power supply for my project.
    I am building an amplifier with six channels, each powered by its own amplifier circuit at about 150W. Each amp requires 35V at 5A, so that's 30A minimum I need this circuit to push out. Space is a problem, as this is my first project at this scale and complexity, I am almost completely lost. Also to be powered by this supply are a few LEDs, two 5 band equalizers and a thermistor control circuit. So, to be safe I need about 35A at 35V.

    I've tried to design a circuit by adding short circuit protection components, but I'm afraid to order the parts for it because if it doesn't work, it'll just be a waste, and shipping is expensive to where I live. Also, I'm pressed for time as my project is due the 24th of May, or thereabout.

    I would be eternally grateful for any ideas, thanks.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    To Power that much amps you will need a transformer of around 1.3KVA
    Beside Building the project, where do you think you can find the transformer.

    As for shipping, we dunno where you are at.
     
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  4. wayneh

    Expert

    Sep 9, 2010
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    I don't know if this is relevant, but modern amplifiers generally have higher specs for each channel than their power supply is capable of delivering to all channels simultaneously. This is simply because music and movie content rarely drives all channels to the same level at the same time. So building the power supply - the costliest part of the amp - to do that, is just overkill. I don't know if there are any hard guidelines for this, but I've seen power supplies capable of maybe only 70% of the sum of all the individual channels.
     
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  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    It begs the question what kind of short circuit protection do you need?

    Current limit?
    Voltage fold back?
    Self recovery or user input required?
    Can I put a penny into it when I want to go to eleven?
     
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  6. EnthusiasticStudent

    Thread Starter New Member

    May 5, 2011
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    Thanks for the quick response everyone.

    I did a bit of reading on the net about short circuit protection, and I read that fuses generally don't react in time, So I threw that idea out. On that notion, I set about to find a circuit - and I did. But I didn't know if they were applicable because not many of these electronics websites give enough information for me to work with. They don't say how much current and Voltage the circuit can handle, and this has had me running around quite a lot.

    However, I am a total novice, and any advice thrown out will be eagerly accepted, and if fuses can work, then I'll have to use em, cuz I'm really out of time as I'm being pressed to finish my ordering today.

    This project is really dear to me, and important. I am a total music lover, and usually my first in anything is very dear. Also, i need to rank an A in this project if I wanna graduate with the best grade possible.

    About powering the six amps with one power supply - I thought it was kind of farfetched, because the more I searched for a commercial one of this capability, the more elusive it seemed. However, I was hoping and praying that it was possible. If it is not, I have two choices, either I do multiple power supplies, probably one P.s.u to every 2 or 3 amplifiers - totaling up to about 2-4 power supplies; or I could just use two amps instead of six, making the project smaller for now, and probably build two other stereo amplifiers.

    I had intended to build six amps; two each (Left and Right) for tweeters, Midrange and (sub)woofer - I decided on this after a bit of reading on the net.

    About the type of shortcircuit protecton I need. I didn't know about the different types, I just threw out the barebones that I knew, and hoped for some enlightenment on the topic. Thanks. I just googled 'em, and I think that self-recovery or Voltage foldback sound best. I don't think I have enough know-how to use user-input.

    Thanks everyone for such quick response, I really was floating with this all, and if I didn't check here, I'd probably be on the ropes when the parts did arrive and things started smokin' in the lab.

    I'm sitting on the computer waiting on your responses. Thank you.

    Oh, here are two things I think you guys should know, since you sound knowledgeable on the topic I might be saved some problems when it comes to building the project.

    1. I was initially following up on an amp with short circuit protection, however, the circuit details didn't specify the power ratings of the components, and before I knew it, I threw the idea out and had ordered a few of the parts for this really simple on I found here, http://electroschematics.com/79/high-power-200w-audio-amplifier-circuit-schematic/.

    This one doesn't have built in short circuit protection, so I had to put it into the power supply to ensure the speakers are not held at ransom by the BJTs in the amplifier. If you have any suggestions about this schematic, or its use, I'd appreciate it greatly.

    2. I did not add any pre-amplfication stage. I thought that the levels coming out of the equalizer would be within the range of the input of the amplfiier. However, if it isn't, I'd probably be floating when I discover this. If it is a must that I include pre-amplfiication, it's not too late to throw one in. I have about four hours until I must order, and my time is up.

    Here's a quick run through of the project.

    I had intended to take the outputs of the equalizer in the different ranges, and send them to their respective amplifiers. So probably for the five band equalizer, one or two of the outputs might have went to bass, another two to midrange, and the last to the tweeters. I intended to omit the recombination IC, so that I'd have these five outputs to send to the respective amps.

    I'm really full of questions, because books and blogs tend to be a bit vague, and i don't to run with my own ideas I come up with because of a hint I pick up on the Internet.

    So here's my last question for now.

    I was reading on this page, to help me design the power supply - http://www.tnt-audio.com/clinica/ssps1_e.html. The writer says not to use a regulated power supply for the driver and output stages of the Amp. Could anyone shed some light on what type of p.s.u I should use?
     
  7. EnthusiasticStudent

    Thread Starter New Member

    May 5, 2011
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    I think I'd go with voltage foldback or self recovery. How do I go about it?
     
  8. EnthusiasticStudent

    Thread Starter New Member

    May 5, 2011
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    I live in the Caribbean - Grenada to be specific. Customs kill us down here, plus DHL and Fedex are really expensive.
     
  9. EnthusiasticStudent

    Thread Starter New Member

    May 5, 2011
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    This article on wikipedia sounds great. This may just be the answer. Thanks. I'll do some reading on it.
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    If you use the new generation of amp ICs they have built in short circuit and over temperature protection inside the chip, it's pretty impressive.

    That makes them almost indestructable as they won't be hurt by speaker cable shorts or teenagers turning them right up. ;)

    Then just use a fuse between the PSU and each amp chip.
     
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  11. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    As I understand, you already have an amplifier based on the TDA2030 and you already have a basic bridge rectifier & cap power supply. You wish some protection between them.

    You also have 6 amplifiers. If all 6 run off the same supply then you can't set the trip point below 6 times the max normal current, or you need 6 limit circuits, and each limit circuit has 2 halves so you will need between 2 and 12 pass transistors.

    Then you have to figure out just how much and for how long you can let "a lot" of current flow. If you limit too fast the music will suffer, too slow and parts die. You wouldn't know how much current is too much until something breaks, so expect to kill your amps several times until you find the sweet spot.

    Or, you could just put in the fuses the TDA2030 schematic suggests.

    But as you can't design your solution you're best to buy it, and convert to a recently designed chip with built in limiting as theRB suggested.
     
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