Amplifier IC selection

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Hi people it's been a long while since I posted in here.

I am after a little advice, I need a circuit to amplify a 1V pk 1KHz
Sine wave to 26VRMS.

10Watts is more than enough.

Not too concerned about THD.
I would prefer not to capacitively couple the load.
Stepping up with a Transformer is OK.
Short Circuit protection/thermal overload would be good.
Single supply rail whilst good is not imperative.

I've got a some theory but little experience so any help appreciated.
Cost is not a concern as I'll only be building a few circuits.

Cheers

Adam...

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Ahh probably should  clarify I'm not after a whole circuit design just a
suitable amplifier IC for the job, I can do the design (I hope)... :)

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http://www.national.com/mpf/LM/LM3886.html
is cheap, readily available and easy to work with.
Its used in "gainclone" audio power amplifiers
by a legion of audio DIYers.

Glenn.



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"glenbadd"
 Adam
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**  Delivering 26 volts rms  ( +/- 37 volts peak) into even a tame load will
stress the LM3886 to its limit.

The DC supply used will have to be +/- 40 volts under load and have very
little 100Hz ripple  -  also, it must not go above +/- 45 volts of the chip
will fry.

The OP must say what the load is ( a  Piezo driver ? ) or there is no way to
be sure it will work OK.



.......    Phil



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Is the '10W' based on a guess, or a firm knowledge of what load ipedence you
are hoping to drive ?

geoff



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It's driving a Resolver, the Sin & Cos outputs of the resolver are fed
into a Resolver to Digital Converter Card for which I have no input
impedance information. I know that 10W is heaps of headroom. I suspect
the input impedance is in the mid to upper kOhm range but can't be sure.

I have +24 and -24 rails available so it'd be nice to stick within
these. Hence the step up Transformer on the output.

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Yeah 10W was more so I can derate the IC and not have to stick a big
heatsink on it. Appologies for the confusion so far.

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"Adam"
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**  Not everyone is into "robotics" or servo control systems -  Adam.

For the uninitiated:

http://en.wikipedia.org/wiki/Resolver_ (electrical)


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**  Use the LM3886 and step up the output voltage with a transformer.

 A 15 volt, 1 amp multitapped,  2155  type should be OK.

 Just use the secondary as a 1:2 step up autotransformer and trim off and
insulate the primary wires.




......  Phil





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woops my bad.
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woohoo thanks Phil. It looks like a good chip.
I'll lurk in here and offer some help back now that i've got a news
reader set up again.

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Excellent Idea. Slightly off topic, I also have a need to amplify a
sinewave, but 3 phase 70hz, about 20v pk.
Its from a turbine tachometer generator with 3 phase output to drive a 3
phase tachometer indicator (gauge).
The reason I need to amplify the signals is because the gauge reads a bit
low.
Would 3 step up transformers work ok?



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If you mean 'amplify' in terms of provide more available power, then no,
transformers won't work. If it's a case of there's excess power available,
but the voltage is too low, then they may, depending on the numbers. 3
transformers, one per phase with star points commoned on each side.



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finger to keyboard and composed:

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What about a hybrid stereo audio amp, eg something in the STK series?
I've seen these with +/-30V, 40W ratings. Of course they're designed
for 4 or 8 ohm loads, but I can't foresee any problems driving into a
few Kohm, if that is indeed your load impedance. The cost should be of
the order of $15 - $25 (from WES).

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

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