this should be easy

[Mook Johnson]

I'm looking for a sine wave driver that can deliver 2 volts p-p 30Khz sine
wave into a 3 ohm load. +/- 4.5V rails are available and sine wave will be
the input. Distortion needs to be reasonable but not ultra tight. >1%
maybe.

I have a design using complementary NPN and PNP biased to class AB (audio
amplifier) with a opamp completing the loop and providing feedback to
minimize the residual xover distortion.

Thermal runaway is a high concern. I'm using large 2 ohm emitter resistors
on the output and diode biasing to compensate for temperature affects.
Anything else I should be looking at? both xisters will be mounted to a 6
layer PC board with lots of copper underneath.

This amp will be running above 125C (ambient) so the audio amp ICS with the
thermal cutoff will be of no use to me.

Just looking for different opinions..

thanks.


P.S. Class D is also out due to noise issues in the immediate areas.

 

[Mike Fields]

"Jim Thompson" <thegreatone@example.com> wrote in message
news:3bj7v058ov4d06s74qvp0hl1ql90nicaum@4ax.com...

On Sun, 23 Jan 2005 08:40:55 -0800, Luhan Monat <x@y.z> wrote:

Mook Johnson wrote:
I'm looking for a sine wave driver that can deliver 2 volts p-p 30Khz
sine
wave into a 3 ohm load. +/- 4.5V rails are available and sine wave
will be
the input. Distortion needs to be reasonable but not ultra tight. >1%
maybe.

I have a design using complementary NPN and PNP biased to class AB
(audio
amplifier) with a opamp completing the loop and providing feedback to
minimize the residual xover distortion.

Thermal runaway is a high concern. I'm using large 2 ohm emitter
resistors
on the output and diode biasing to compensate for temperature affects.
Anything else I should be looking at? both xisters will be mounted to
a 6
layer PC board with lots of copper underneath.

This amp will be running above 125C (ambient) so the audio amp ICS with
the
thermal cutoff will be of no use to me.

Just looking for different opinions..

thanks.


P.S. Class D is also out due to noise issues in the immediate areas.



Hi,

You have not said what this whole thing is for. From the description
you have given, it could be an electric cigar lighter. You get better
directions if you let people know just where you are going.

RS-232 to TTL??? You have something against 1488 and 1489 ?

...Jim Thompson
--

OK, sometimes I have trouble "reading between the lines", but how
did we get from a 30khz amp at 120 deg C to RS-232 ??????????

mikey

 

[Winfield Hill]

Mook Johnson wrote...

I'm looking for a sine wave driver that can deliver 2 volts p-p
30kHz sine wave into a 3 ohm load. +/- 4.5V rails are available ...
This amp will be running above 125C (ambient) so the audio amp ICS
with the thermal cutoff will be of no use to me.

That's 330mA delivered from a 4.5V supply with a 3.5V rail-to-output
drop allowed, right? What's wrong with unbiased NPN and PNP followers
inside an opamp feedback loop? There won't be any thermal runaway,
and < 1% distortion shouldn't be any problem with high opamp f_T.


--
Thanks,
- Win

 

[Ban]

Luhan Monat wrote:

This amp will be running above 125C (ambient) so the audio amp ICS
with the thermal cutoff will be of no use to me.


You have not said what this whole thing is for. From the description
you have given, it could be an electric cigar lighter. You get better
directions if you let people know just where you are going.

I once encountered a similar problem, but with 180°C temp spec. Impossible
to do reliably with silicon, I had to assemble these brittle GaAs chips on a
hybrid. It was supposed to be for "Telecommunications".
By chance I found out later that this circuit was mounted above the gates
of those F16 bunkers and was used to arm the atomic weapons in the last
possible moment. The afterburner was heating up that area, that is where
that spec came from. Well telecommunication was not exactly wrong...
--
ciao Ban
Bordighera, Italy

 

[Ken Smith]

In article <ct0mgv02j91@drn.newsguy.com>,
Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:
[...]

That's 330mA delivered from a 4.5V supply with a 3.5V rail-to-output
drop allowed, right? What's wrong with unbiased NPN and PNP followers
inside an opamp feedback loop? There won't be any thermal runaway,
and < 1% distortion shouldn't be any problem with high opamp f_T.

.... and highish frequency transistors. At these currents that should be
no problem. This is one application where you don't want the TIP35/36
pair.


--
--
kensmith@rahul.net forging knowledge

 

[Tony Williams]

In article <ct0mgv02j91@drn.newsguy.com>,
Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

That's 330mA delivered from a 4.5V supply with a 3.5V
rail-to-output drop allowed, right? What's wrong with unbiased
NPN and PNP followers inside an opamp feedback loop? There
won't be any thermal runaway, and < 1% distortion shouldn't be
any problem with high opamp f_T.

Maybe reduce the dissipation in the Tr's with a resistor in
series with each collector. Up to 10 ohms looks possible.

--
Tony Williams.