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Old 27th September 2004, 03:06 PM   #1
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Default power supply for car amp.

if i put the TL494 in this power supply it will work ?

http://www.diyaudio.com/forums/attac...&postid=399631

thanks.
tamir
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Old 27th September 2004, 09:34 PM   #2
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??? please
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Old 28th September 2004, 10:51 AM   #3
B.I.G is offline B.I.G  Romania
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no it will not work TL494 can not drive the gates of fet`s
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Old 28th September 2004, 11:02 AM   #4
djQUAN is offline djQUAN  Philippines
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my SMPS circuit uses the TL494 output to drive the gates to turn on and an emitter follower to turn the mosfets off.
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Old 29th September 2004, 12:49 AM   #5
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Can't you use the TL494 to drive a totem pole BJT configuration that drives the FET's? If I am not mistaken, this is how you should drive the FET anyway if you are going to switch at a high frequency. The capacitance from the gate of the mosfet will require a current spike, or lower impeadence to turn it on AND off quickly enough for SMPS frequencies.
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Old 29th September 2004, 02:44 AM   #6
djQUAN is offline djQUAN  Philippines
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I have done that before but I've run out of driver transistors to do that.

besides, this is the second PSU (500WRMS, three 110A mosfets per side) that I have done. the first one (200WRMS, two 95A mosfets per side) is still running in the car with no problems.

the gate capacitances are isolated by 100R resistors. I have checked the waveforms on my scope and they're fine. I run them at around 37kHZ and I've run them during testing at >50kHz without problems.
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Old 29th September 2004, 11:27 PM   #7
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Quote:
Originally posted by djQUAN
I have done that before but I've run out of driver transistors to do that.

besides, this is the second PSU (500WRMS, three 110A mosfets per side) that I have done. the first one (200WRMS, two 95A mosfets per side) is still running in the car with no problems.

500Wrms.... that is over 40A from a 12V source. Most stock alternators only put out around 40A - 60A depending on the car requirements. This extra current along with the normal load of the car electrical system might pop the rectifier diodes in the alternator. Suggest getting a high performance alternator at or around 100A at least!
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Old 29th September 2004, 11:48 PM   #8
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Quote:
Can't you use the TL494 to drive a totem pole BJT configuration that drives the FET's?
Yes, that is how it is typically done. The TL494 is often used in car amplifiers, moreso these days than the 90's. I'm not sure why the trend has gone that way, but I am sure that cost is at least partly to "blame" - the 3524/5 are more than double the cost of the '494.

I personally like the SG3525 because of its anti-shoot through logic protection. The 3524 had a tendency under certain circumstances to allow both outputs to turn on simultaneously. Plus, it has the Totem pole configuration built in. I still go with outboard pairs close to the FETs to minimize the effects of drive capacitance.

Boy, I am rambling on here. The gist of the situation is that there are several good chips to use - heck, I've even seen LM555's used in the worst of all amplifiers, namely some old Jensen and Fultron amps.
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Old 30th September 2004, 03:27 PM   #9
djQUAN is offline djQUAN  Philippines
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Quote:
500Wrms.... that is over 40A from a 12V source. Most stock alternators only put out around 40A - 60A depending on the car requirements. This extra current along with the normal load of the car electrical system might pop the rectifier diodes in the alternator. Suggest getting a high performance alternator at or around 100A at least!
actually, I designed the PSU to handle about 45A continuous and about 65A peak. it uses a 3" diameter ferrite toroid and it's going to power a monoblock P68 driving 2 ohms (two 4 ohm subs) with +/-50V rails. (about 500WRMS) also, this is not a car. I'm driving a nissan terrano (pathfinder in other countries). the stock alternator has proven to be powerful enough for the present system (total 540 watts RMS). except for slight headlight dimming at very very high volumes.

Quote:
Yes, that is how it is typically done. The TL494 is often used in car amplifiers, moreso these days than the 90's. I'm not sure why the trend has gone that way, but I am sure that cost is at least partly to "blame" - the 3524/5 are more than double the cost of the '494.
cost it is indeed! the 3525 also costs twice the 494 over here. that's why I used TL494 in my SMPS's, besides, TL494's are readily available in broken computer PSU's.
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Old 30th September 2004, 09:44 PM   #10
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Quote:
Originally posted by djQUAN


actually, I designed the PSU to handle about 45A continuous and about 65A peak. it uses a 3" diameter ferrite toroid and it's going to power a monoblock P68 driving 2 ohms (two 4 ohm subs) with +/-50V rails. (about 500WRMS)
What is the inner diameter and hight of your toroid core?
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