Need cheap 40V supply OpAmp with >500mA peak output

[Robert Latest]

Hi folks,

for a low-noise floating +/- 15V-supply running off +/- 18V I'm
looking for a simple integrated power amplifier that can
deliver about 1.5W rms power into the transformer (~15kHz
sine). Interestingly there seems to be a "gap" in available
amps: There are plenty of cheap 1-2W audio amps running off 5V,
and then there are the big 3A L165 and friends (which, at 36V
total supply, burns more than 2W quiescent power).

Of course I can go discrete; I'm just asking if I'm missing the
obvious candidate.

Thanks,
robert

 

[Winfield Hill]

Robert Latest wrote...

for a low-noise floating +/- 15V-supply running off +/- 18V
I'm looking for a simple integrated power amplifier that can
deliver about 1.5W rms power into the transformer (~15kHz
sine). Interestingly there seems to be a "gap" in available
amps: There are plenty of cheap 1-2W audio amps running off 5V,
and then there are the big 3A L165 and friends (which, at 36V
total supply, burns more than 2W quiescent power).

Of course I can go discrete; I'm just asking if I'm missing
the obvious candidate.

It's the cheap part that'll get you into trouble. For example,
consider the buf634 at $4.12 qty 100 in the miniDIP package,
with a low-noise opamp of your choice. Just how cheap do
you want it to be?

 

[Robert Latest]

On 12 Dec 2006 07:09:20 -0800,

Robert Latest wrote...

It's the cheap part that'll get you into trouble. For example,
consider the buf634 at $4.12 qty 100 in the miniDIP package,
with a low-noise opamp of your choice. Just how cheap do
you want it to be?

Well, ON Semi's TCA0372 fits the bill nicely for .95 at DigiKey.
Except that DK is a bit difficult to order from if you're in
Europe and you're ordering for a government agency (lots of red
tape and steep shipping fee because of overseas order). I've added
the chip to my continuously growing "DigiKey-Only" list which
hasn't yet reached the threshold at which I think placing an
order is justified.

robert

 

[Winfield Hill]

Robert Latest wrote...

Winfield Hill wrote

Well, ON Semi's TCA0372 fits the bill nicely for .95 at DigiKey.
Except that DK is a bit difficult to order from if you're in
Europe and you're ordering for a government agency (lots of red
tape and steep shipping fee because of overseas order). I've added
the chip to my continuously growing "DigiKey-Only" list which
hasn't yet reached the threshold at which I think placing an
order is justified.

Farnell doesn't have it?

 

[[email protected]]

Robert Latest wrote...

Farnell doesn't have it?

They say they do but at their US sister company Newark, so it is either

pay ~35$ to get it in 3 days or 10$ to get it in 14 days

-Lasse

 

[Helmut Sennewald]

Hi folks,

for a low-noise floating +/- 15V-supply running off +/- 18V I'm
looking for a simple integrated power amplifier that can
deliver about 1.5W rms power into the transformer (~15kHz
sine). Interestingly there seems to be a "gap" in available
amps: There are plenty of cheap 1-2W audio amps running off 5V,
and then there are the big 3A L165 and friends (which, at 36V
total supply, burns more than 2W quiescent power).

Of course I can go discrete; I'm just asking if I'm missing the
obvious candidate.

Thanks,
robert

Hello Robert,

The LM675 from National or the OPA544 from TI will be your best choice.
As far as I remember, the OPA544 is easier to tame.

Best regards,
Helmut

 

[Tony Williams]

for a low-noise floating +/- 15V-supply running off +/- 18V I'm
looking for a simple integrated power amplifier that can
deliver about 1.5W rms power into the transformer (~15kHz
sine). Interestingly there seems to be a "gap" in available
amps: There are plenty of cheap 1-2W audio amps running off 5V,
and then there are the big 3A L165 and friends (which, at 36V
total supply, burns more than 2W quiescent power).

I remember reading a US DoD note on the requirements
of AC power amplifiers feeding rectifier loads. They
recommended a peak current capability equivalent to
4x to 6x the apparent VA requirement.

It might be useful to LTspice the transformer and
rectifying load first, in order to see the demands
placed on the driving amplifier.

 

[Robert Latest]

On Wed, 13 Dec 2006 09:13:11 +0000 (GMT),

It might be useful to LTspice the transformer and
rectifying load first, in order to see the demands
placed on the driving amplifier.

Good tip. Done it and it came out pretty much like I had figured with
pencil and paper as I haven't really made friends with simulators yet.
But it's great to be able to see the startup process!

robert

 

[Tony Williams]

It might be useful to LTspice the transformer and
rectifying load first, in order to see the demands
placed on the driving amplifier.

[/QUOTE]

Good tip. Done it and it came out pretty much like I had figured
with pencil and paper as I haven't really made friends with
simulators yet. But it's great to be able to see the startup
process!

What was your rectifier/smoothing/load, and what
sort of current waveshape did it draw into the
primary of the transformer?

 

[Chris Jones]

Hi folks,

for a low-noise floating +/- 15V-supply running off +/- 18V I'm
looking for a simple integrated power amplifier that can
deliver about 1.5W rms power into the transformer (~15kHz
sine). Interestingly there seems to be a "gap" in available
amps: There are plenty of cheap 1-2W audio amps running off 5V,
and then there are the big 3A L165 and friends (which, at 36V
total supply, burns more than 2W quiescent power).

Of course I can go discrete; I'm just asking if I'm missing the
obvious candidate.

Thanks,
robert

I would have recommended the very cheap TDA2030A (although it might have
more quiescent current than you want), but here in the UK Farnell reckons
that ST have stopped making it, even though the ST website says it is still
"active" and available. The TDA2040 has less supply voltage rating and
draws more current and costs more but Farnell do admit to having some.

Chris