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Old 4th November 2004, 02:17 AM   #1
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Default OP-AMP based car amp power supply

Would I be able to use some kind of circuit generating a 60hz signal (possibly a 555 timer???), driving an opamp (such as an opa549 that will run off of a single 12V power supply), which is connected to a transformer? If I use this, I would get about 10A at 60hz output, and all I'd have to do is use a transformer to boost power, then bridge rectify it, and power my amps.

Would this work, or am I missing something?
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Old 4th November 2004, 02:21 AM   #2
Stocker is offline Stocker  United States
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Default could work?

It's not the usual way, to say the least, but I guess...
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Old 4th November 2004, 02:23 AM   #3
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Yes, thats what I figured

But I don't want to mess with the complexity of switching supplies, yet am pretty familiar with opamps.
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Old 4th November 2004, 03:25 AM   #4
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Rod Elliott has a switcher which works, note too that National Semiconductor, Infineon and On-Semi have PCB layouts for some of their switching chips -- don't be bashful about trying these -- at least an automotive environment you won't have to mind the switching noise.

...and if you build a switcher for a car -- the first thing to do is get an inverter from WalMart and throw out everything except the transformer and case.
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Old 4th November 2004, 05:23 AM   #5
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if the point was to get 120V 60Hz in the car, why not just keep the walmart unit, if you are going to buy it anyhow?
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Old 4th November 2004, 05:38 AM   #6
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Default Is that really a 600 Watt amp?

This would really let you know if the amp can deliver rated power continuously.

If the amp is a Class AB, you will draw more power than you care to from the battery. A Class D amp, sure.

You can use a 32,768Hz crystal to extract a time base. You can divide it down to get 64Hz very easily, and filter it as well. Or, use a Wein Bridge Oscillator, Google will find a schematic and equations.

I would file this under EXERCISE, and when I got it working, go down to Walmart and but the unit with twice the power, half the size, lower price, and reliability.
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Old 4th November 2004, 12:52 PM   #7
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I don't know where 600W came from.

the amp would be 2 549's that can be bridged to a sub or drive 2 stereo speakers.

It would run at +/-25VDC, not 120VAC.

Would I be able to modify the walmart inverter to put out +/-25VDC?
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Old 4th November 2004, 01:43 PM   #8
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Default Re: OP-AMP based car amp power supply

Quote:
Originally posted by soundNERD
...or am I missing something?
Yes. The fact that as you scale up the voltage output from the transformer also scale up the current required to feed it. A chip amp will simply not be able to drive the transformer.

And you can't get a sinewave from a 555 timer.

And it's an extremely inefficient and bulky way to do it.
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Old 4th November 2004, 08:43 PM   #9
azira is offline azira  United States
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Default Re: Re: OP-AMP based car amp power supply

Quote:
Originally posted by richie00boy


And you can't get a sinewave from a 555 timer.

You could lowpass filter the 555 signal through a high order active filter first before delivering it to your opamp if you wanted more of a sin wave. There'll still be some garbage on it but could be made significantly attenuated. Your squarewave should have the fundamental plus every odd harmonic and nothing else, so you don't care about filter response below the fundamental and you won't need to worry about a peaking response at the fundamental but you do want as sharp of a cutoff as possible. I would think that some kind of Chebychev filter with a large slope would be a good.

The only thing you're missing is that power is going to be conserved. So if your OPA549 can deliver 60W of output power, then that's at most what you're going to get out of your circuit no matter what. With lossy devices like your transformer, you'll probably get less output power.
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Old 5th November 2004, 12:32 AM   #10
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To modify the walmart inverter to give you 25VDC is the same as modifying your house to get 25VDC. Use a little transformer and a bridge rectifier.
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