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Old 9th April 2009, 07:44 PM   #1
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Default LM3886 on 14.6 volts

I have seen alot of good reviews on this chip, and was wondering how well it will do on 14.6V into 4 ohms, I have a massive regulated 14.6 volt power supply, 50A continuous, have used it to run car amps in the past, also, are the LM3886's isolated from the case? (can multiple ones be mounted on same HS)
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Old 9th April 2009, 08:20 PM   #2
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I assume you mean a single +14.6VDC output? You could probably rig it up to work with the +14.6V connected as a ground, the 0V output connected as V- supply, and a big capacitor at the output. And your reward for that effort would be about 1 W of power.

You might want to do a bit of reading up on the basics of chipamps in this forum. Quite a lot of good stuff.
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Old 9th April 2009, 09:17 PM   #3
Bone is offline Bone  United Kingdom
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It appears from the Datasheet that at voltages less than +/- 9v i.e.18v the iC shuts down. This is detected as the voltage between pin 7 (earth or half supply voltage) and the -V pin 4.
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Old 9th April 2009, 09:24 PM   #4
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Quote:
Originally posted by Bone
It appears from the Datasheet that at voltages less than +/- 9v i.e.18v the iC shuts down. This is detected as the voltage between pin 7 (earth or half supply voltage) and the -V pin 4.
The detection circuit is only looking for pin 4 to be -9V from pin 7, it does not check for pin 5 to be +9V from pin 7, so you are wrong to insist that the supply need be +/- 9V.
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Old 9th April 2009, 09:29 PM   #5
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sorry for the misunderstanding, I had read elsewhere on the forum about someone running it from a car batt. with a modification to the circuit, I know that they are normally ran from CT transformers to get the standard V+ 0 V-, (I'm not that much of a noob javascript:smilie('') was just looking for a cost effective way to use existing power supply.
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Old 9th April 2009, 09:40 PM   #6
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About the lowest you can run an LM3886 is 16V total. The -9V must be met and the datasheet does indeed say minimum of 18V meaning +/-9V. But, if you test (as I did) you will find that if you run the negative rail at -10V and then the positive only needs about 6V to kick on. I made a simple circuit to create an asymmetrical supply to see how low it could go for an application using a 24V battery. You might find some parts that operate lower but you'd have to just buy a bunch and try them. Besides, THD improves quite a bit going from +/-12V to +/-15V. At 16V total you will have very little output power, not really worth it.

-TH
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Old 9th April 2009, 10:51 PM   #7
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any suggestions for chip amps that will run at 14.6V?? this is for a regulated, non CT power supply, only V+ and V-, same as a battery.
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Old 9th April 2009, 11:24 PM   #8
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Quote:
Originally posted by leadbelly
The detection circuit is only looking for pin 4 to be -9V from pin 7, it does not check for pin 5 to be +9V from pin 7, so you are wrong to insist that the supply need be +/- 9V.
According to AN-898 the voltage between negative rail and ground must be 9 V or higher and the voltage between negative and positive rail must be 14 V or higher.

Sasmit reports that the undervoltage protection has not worked reliable for him, however.
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Old 10th April 2009, 12:58 PM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
why would National fit an automatic shutdown on low supply voltage?

Could it be that the chip does not perform to specification if the single polarity supply voltage goes below 18Vdc?
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Old 10th April 2009, 02:40 PM   #10
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AN-898 claims that the purpose of the undervoltage protection is to avoid pops and DC at the output during power-up/down. In that case Rm should be chosen as big as possible, not the wide-spread 10k that activate the output, as soon as Vee is above 7,6 V or so.
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