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-   -   LM3886 at very low load < = ohm (http://www.diyaudio.com/forums/chip-amps/225062-lm3886-very-low-load-ohm.html)

rikkitikkitavi 5th December 2012 07:15 PM

LM3886 at very low load < = ohm
 
I was thinking of using a LM3886 as a power amplifier for loads of up to 1 ohm aboutish, and up to about 30 kHz, with a gain of 10 times, given the fact that THD is not an issue do you see any issues?

I dont expect to use more than a few volts of swing, at maximum 3-4 V peak.


This is not for audio.

Edit: I forgot, it will be powered by +-12 V .

Mooly 5th December 2012 07:39 PM

You mean loads down to about 1 ohm rather than up to 1 ohm.

I think if you ran it at the lower end of it's supply range (from -/+10 volts) then it would probably be OK. The current is well within its limits at 4 volts across 1ohm

I think it would work.

kiekefretter 5th December 2012 07:43 PM

1 Attachment(s)
Well,if you see this graph,it seems rather hopeless :(

rikkitikkitavi 5th December 2012 09:52 PM

Quote:

Originally Posted by Mooly (Post 3271837)
You mean loads down to about 1 ohm rather than up to 1 ohm.

I think if you ran it at the lower end of it's supply range (from -/+10 volts) then it would probably be OK. The current is well within its limits at 4 volts across 1ohm

I think it would work.

Yes thanks I meant down to 1 ohm as lowest.
I could not find any reasons why it should not work either.

With regard to the diagram from the datasheet, this is for higher voltage supply and quite stringent demands on THD and not valid for my applikation. But thanks for the effort.

Mooly 6th December 2012 07:50 AM

Quote:

Originally Posted by rikkitikkitavi (Post 3272011)
Yes thanks I meant down to 1 ohm as lowest.
I could not find any reasons why it should not work either.

With regard to the diagram from the datasheet, this is for higher voltage supply and quite stringent demands on THD and not valid for my applikation. But thanks for the effort.

That's why I think it would work if you used a low supply voltage.

Another idea... untried... would be to add a series output resistor of a few ohms in series with the load but take the feedback from the load. That way the IC drives a higher impedance but the feedback keeps the series resistor out of things. You would need a slightly higher voltage supply for that.

rikkitikkitavi 6th December 2012 07:45 PM

I was thinking about that too, but after some rethinking I realised that I actually need an non-infinite output impedance of about 1 ohm

( I will use a precision resistor with 1 ohm, 10W (or so) , 1%) because one of the things I will use it for is making impedance measurments of reactive loads (from about 50 mOhm to a couple of Ohms , depending on frequency)

Actually a current source instead of a voltage source is what I need.

AndrewT 6th December 2012 07:48 PM

The 3886 does not operate at low supply voltages.

Mooly 6th December 2012 07:53 PM

Quote:

Originally Posted by AndrewT (Post 3273552)
The 3886 does not operate at low supply voltages.

Quote:

Originally Posted by Mooly (Post 3271837)
.....................I think if you ran it at the lower end of it's supply range (from -/+10 volts) then it would probably be OK...........

Low as in 20volts (-/+10) going off the data sheet.

rikkitikkitavi 6th December 2012 07:57 PM

O well, then I guess the datasheet is incorrect when it states that it is operational from +-10V to +-84V (albeit with some restrictions on load and output power )

And I had no problems powering it from two car batteries when I climbed to the top of the hayloft at my wifes mothers old farm to do some SERIOUS acoustical measurments (sorry no pics) , and yes she really thought I was crazy but in Sweden the hayloft is not that high...

AndrewT 6th December 2012 08:02 PM

+-10V as a minimum, is met by your two 12V car batteries.
But you must ensure that the chipamp does not drop out if the voltage AT THE PINs droops to near 10V. I think one pin has a cut out set to ~ 9V.


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