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Old 26th September 2003, 01:57 AM   #1
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Default brdiged mode speaker impedance and power supply voltage question

going for a long and informative title.

i was just wondering what reasons there would be for not using a lower power supply voltage and using bridged loads in certain apps. mainly, i was thinking about building a car audio amplifer with power ICs. i mean it seems like a logical goal seeing how i have 2 large car amp heatsinks laying around, and may be able to get 2 more pretty cheap.

but i got to thinking:

a 4ohm BTL isn't listed as being reccomended for the lm4780 chips or any for that matter, unless chips are paralleled. but i was wondering if it would be possible to use maby a 30V supply and a bridged 4ohm load. wouldn't the results be the same as going with a single channel with a higher voltage. the power would be the same.

i guesst his is more a theoretical quesiton for now. it falls into what i want to do fro one of my personal projects though. i had wanted to use balenced inputs and just amplify the signal.
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Old 28th September 2003, 09:34 AM   #2
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When you make a bridged amplifier you get the double voltage -sving across you load, witch again give you (teoretical) four times the power.

(you now have 2 x the voltage drop across the chip-amp, so you will never reach the x4 power, but if your PSU and heatsink is up for the job, you will be close)

BUT, when you use a bridged amplifier each amplifier now "sees" half the load. So if you connect a 4 ohm load to your bridged amplifier each amplifier is now driving a 2 ohm load. This usually means more current and more heat to the chip-amp.
This is the reason paralleling are recommended since it "spread/distribute" the extra heat between the paralled amps.

You can use your LM4780 to a bridged amp, but you most be very carefull about the heatdistributioon. (lowering the voltage is one way).

Thomas
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