basic BTL design needed 28VDC military job - diyAudio
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Old 27th May 2008, 10:37 PM   #1
opcom is offline opcom  United States
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Join Date: May 2008
Location: Texas
Default basic BTL design needed 28VDC military job

Looking for a basic BTL design to use single supply 27.5VDC nominal supply from a military truck, and drive a 2 Ohm public address horn load to about 175W RMS. Must not need capacitor in series with speaker.

This is to replace a class-B BTL design using a stack of 15 amp germanium power tranistors. unfortunately, the silly person that designed that end item saw fit to pot the driver modules so that the equipment cannot be repaired. If you are bell Helicopter, you just buy a new one. Me, I have to make a new one.

Any help pointing me to a decent schematic would be appreciated. Thank you very much.
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Old 28th May 2008, 12:04 AM   #2
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Join Date: Nov 2007
Location: Dallas

Mind you, the linked document is just the power stage.
You need another chip to generate the PWM... You have
a lot more choices of PWM driver than the one suggested.

The PWM interface is pretty basic....

Your schematic is probably Figure 17
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Old 30th May 2008, 06:49 AM   #3
opcom is offline opcom  United States
diyAudio Member
Join Date: May 2008
Location: Texas

I should have said I was looking for a discrete solution, but that IC is pretty attractive, and with 65W>4Ohm@28VDC, it would be in the power range if both channels were employed.

Not much difference between 130W and 175W from a listener's point of view when someone is yelling into a mike.

The loudspeaker is a pair of 4 Ohm units wired for 2 Ohms. Could be separated out.
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Old 2nd June 2008, 02:37 AM   #4
diyAudio Member
Join Date: Nov 2007
Location: Dallas
Default PBTL Fig 12

You may be looking at the wrong graph. See Fig 12:
Parallel BTL into 2 ohms....

If you venture back to the TI Link of the previous post,
you will see they now suggest a newer "more efficient"
version with a slightly different part #... I havn't had
time to yet investigate in what way the difference may
be significant?

The TI chips I've gotten to play with are all less'n 40W/CH.
Havn't seen one of the true monsters cross my desk (yet).
Its only a matter of time.

I won't comment on anything that isn't on the websight.
The chips I test might not be the same as what you buy.
Don't get me to lying about anything I can't reveal.
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