Rail to Rail output stage for 2A 5V

[Clive Arthur]

I need a more-or-less (say <100mV) rail to rail output running from a 5V
supply and capable of sourcing and sinking 2A or so. Up to 50kHz.

It needs to work at >125'C and IC's like the OPA567 would get too hot.
I probably need op-amps around a discrete output stage, but what's the
best topology? Preferably no charge pumps used and no bias adjustments.

Cheers
--
Clive

 

[John Larkin]

On Wed, 5 Jun 2019 15:27:13 +0100, Clive Arthur
<cliveta@nowaytoday.co.uk> wrote:

I need a more-or-less (say <100mV) rail to rail output running from a 5V
supply and capable of sourcing and sinking 2A or so. Up to 50kHz.

Linear amplifier? Or switching to the rails?

It needs to work at >125'C and IC's like the OPA567 would get too hot.
I probably need op-amps around a discrete output stage, but what's the
best topology? Preferably no charge pumps used and no bias adjustments.

Cheers

Is 5V the only supply available?

Complementary follower mosfets would be easy but the gates would have
to be driven past the power rails. Flip the fets if only 5v is
available, but the bias gets a little trickier to avoid crossover
distortion.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[bitrex]

On 6/5/19 11:51 AM, John Larkin wrote:

On Wed, 5 Jun 2019 15:27:13 +0100, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

I need a more-or-less (say <100mV) rail to rail output running from a 5V
supply and capable of sourcing and sinking 2A or so. Up to 50kHz.

Linear amplifier? Or switching to the rails?


It needs to work at >125'C and IC's like the OPA567 would get too hot.
I probably need op-amps around a discrete output stage, but what's the
best topology? Preferably no charge pumps used and no bias adjustments.

Cheers

Is 5V the only supply available?

Complementary follower mosfets would be easy but the gates would have
to be driven past the power rails. Flip the fets if only 5v is
available, but the bias gets a little trickier to avoid crossover
distortion.

A classic op-amp power booster that should be able to go more-or-less
rail to rail is the op amp output feeding the emitters of a PNP and NPN,
connected like the output stage of a complimentary emitter follower, but
facing back towards the op amp and driven common-base, through a
resistor for V->I conversion. the bases are both grounded to the mid
point for a single supply.

then resistors in the collector lines of each, complimentary MOSFET
gates to the resistors, sources to the supply and ground, drains drive
the output. AC and DC feedback back to the op amp from the junction and
then couple the output thru a cap

 

[Winfield Hill]

John Larkin wrote...

On Wed, 5 Jun 2019, Clive Arthur wrote:

I need a more-or-less (say <100mV) rail to rail output
running from a 5V supply and capable of sourcing and
sinking 2A or so. Up to 50kHz.

It needs to work at >125'C and IC's like the OPA567
would get too hot. I probably need op-amps around a
discrete output stage, but what's the best topology?
Preferably no charge pumps used and no bias adjustments.

I'd consider a bank of OPA567, configured with small
series output resistors, to insure current sharing.
Are you serious about running the electronics at an
125C ambient? OK, time to add some active cooling.

Complementary follower mosfets would be easy but the
gates would have to be driven past the power rails.
Flip the fets if only 5v is available, but the bias
gets a little trickier to avoid crossover distortion.

And compensation would be painful.


--
Thanks,
- Win

 

[Clive Arthur]

On 06/06/2019 09:55, Winfield Hill wrote:

John Larkin wrote...

On Wed, 5 Jun 2019, Clive Arthur wrote:

I need a more-or-less (say <100mV) rail to rail output
running from a 5V supply and capable of sourcing and
sinking 2A or so. Up to 50kHz.

It needs to work at >125'C and IC's like the OPA567
would get too hot. I probably need op-amps around a
discrete output stage, but what's the best topology?
Preferably no charge pumps used and no bias adjustments.

I'd consider a bank of OPA567, configured with small
series output resistors, to insure current sharing.

I am considering just that, but these parts have such a small heatsink
pad area. It seems they're rated for 85'C ambient operation knowing
that the part itself will run much hotter.

Are you serious about running the electronics at an
125C ambient? OK, time to add some active cooling.

Active cooling is out of the question, it's in a well. 125'C is
minimum, 180'C is a better target. Luckily the OPA567 thermal shutdown
is optional

Complementary follower mosfets would be easy but the
gates would have to be driven past the power rails.
Flip the fets if only 5v is available, but the bias
gets a little trickier to avoid crossover distortion.

And compensation would be painful.

Yes. It's linear BTW.

Cheers
--
Clive

 

[Winfield Hill]

Clive Arthur wrote...

Active cooling is out of the question, it's in a well.
125'C is minimum, 180'C is a better target.

If you're down in a very deep hot well, how
is it you only have 5.0 volts? That's weird.


--
Thanks,
- Win

 

[Clive Arthur]

On 06/06/2019 12:02, Winfield Hill wrote:

Clive Arthur wrote...

Active cooling is out of the question, it's in a well.
125'C is minimum, 180'C is a better target.

If you're down in a very deep hot well, how
is it you only have 5.0 volts? That's weird.

I do have lots more volts and there's a step down SMPS.

I'm driving a low-impedance load. Normally, I'd use say a 30V supply for
the amplifier - conventional class AB - and a step-down transformer to
couple to the load, but I'd like to try direct coupling. This means a
lower supply voltage, and rail to rail becomes important.

Cheers
--
Clive

 

On Thursday, 6 June 2019 12:03:16 UTC+1, Winfield Hill wrote:

Clive Arthur wrote...

Active cooling is out of the question, it's in a well.
125'C is minimum, 180'C is a better target.

If you're down in a very deep hot well, how
is it you only have 5.0 volts? That's weird.

Maybe it's time to develop a valve IC for downhole use. I always wondered if a VFD could be rejigged to somewhat do that.


NT

 

[piglet]

On 06/06/2019 10:17 am, Clive Arthur wrote:

On 06/06/2019 09:55, Winfield Hill wrote:
John Larkin wrote...

On Wed, 5 Jun 2019, Clive Arthur wrote:

I need a more-or-less (say <100mV) rail to rail output
running from a 5V supply and capable of sourcing and
sinking 2A or so.  Up to 50kHz.

It needs to work at >125'C and IC's like the OPA567
would get too hot.  I probably need op-amps around a
discrete output stage, but what's the best topology?
Preferably no charge pumps used and no bias adjustments.

  I'd consider a bank of OPA567, configured with small
  series output resistors, to insure current sharing.

I am considering just that, but these parts have such a small heatsink
pad area.  It seems they're rated for 85'C ambient operation knowing
that the part itself will run much hotter.

  Are you serious about running the electronics at an
  125C ambient?  OK, time to add some active cooling.

Active cooling is out of the question, it's in a well.  125'C is
minimum, 180'C is a better target.  Luckily the OPA567 thermal shutdown
is optional

Complementary follower mosfets would be easy but the
gates would have to be driven past the power rails.
Flip the fets if only 5v is available, but the bias
gets a little trickier to avoid crossover distortion.

  And compensation would be painful.

Yes.  It's linear BTW.

Cheers

Larkin's complementary source follower is a great solution. Is the
objection to two low current charge pumped auxilliary rails
philosophical or is noise a worry?

piglet

 

[Clive Arthur]

On 06/06/2019 13:01, piglet wrote:

<snip>

Larkin's complementary source follower is a great solution. Is the
objection to two low current charge pumped auxilliary rails
philosophical or is noise a worry?

piglet

It's reliability - capacitors are best avoided at high temperatures and
high vibration if possible.

Cheers
--
Clive

 

[John Larkin]

On Thu, 6 Jun 2019 12:29:30 +0100, Clive Arthur
<cliveta@nowaytoday.co.uk> wrote:

On 06/06/2019 12:02, Winfield Hill wrote:
Clive Arthur wrote...

Active cooling is out of the question, it's in a well.
125'C is minimum, 180'C is a better target.

If you're down in a very deep hot well, how
is it you only have 5.0 volts? That's weird.

I do have lots more volts and there's a step down SMPS.

I'm driving a low-impedance load. Normally, I'd use say a 30V supply for
the amplifier - conventional class AB - and a step-down transformer to
couple to the load, but I'd like to try direct coupling. This means a
lower supply voltage, and rail to rail becomes important.

Cheers

If you can power a small opamp from, say, +10 and -5, it could drive
complimentary mosfet followers powered by the big +5/0 rails.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On 6 Jun 2019 01:55:45 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

John Larkin wrote...

On Wed, 5 Jun 2019, Clive Arthur wrote:

I need a more-or-less (say <100mV) rail to rail output
running from a 5V supply and capable of sourcing and
sinking 2A or so. Up to 50kHz.

It needs to work at >125'C and IC's like the OPA567
would get too hot. I probably need op-amps around a
discrete output stage, but what's the best topology?
Preferably no charge pumps used and no bias adjustments.

I'd consider a bank of OPA567, configured with small
series output resistors, to insure current sharing.
Are you serious about running the electronics at an
125C ambient? OK, time to add some active cooling.

Complementary follower mosfets would be easy but the
gates would have to be driven past the power rails.
Flip the fets if only 5v is available, but the bias
gets a little trickier to avoid crossover distortion.

And compensation would be painful.

Probably not hard at 50 KHz.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[bitrex]

On 6/6/19 7:40 AM, tabbypurr@gmail.com wrote:

On Thursday, 6 June 2019 12:03:16 UTC+1, Winfield Hill wrote:
Clive Arthur wrote...

Active cooling is out of the question, it's in a well.
125'C is minimum, 180'C is a better target.

If you're down in a very deep hot well, how
is it you only have 5.0 volts? That's weird.

Maybe it's time to develop a valve IC for downhole use. I always wondered if a VFD could be rejigged to somewhat do that.


NT

Korg makes a VFD-based dual triode:

<https://www.youtube.com/watch?v=raYGrKWSKRE>

 

piglet <erichpwagner@hotmail.com> wrote in
news:qdbe30$797$1@dont-email.me:

On 06/06/2019 13:14, Clive Arthur wrote:
On 06/06/2019 13:01, piglet wrote:

snip

Larkin's complementary source follower is a great solution. Is
the objection to two low current charge pumped auxilliary rails
philosophical or is noise a worry?

piglet

It's reliability - capacitors are best avoided at high
temperatures and high vibration if possible.

Cheers

Interesting. Thanks. What are the best capacitor types for that
kind of environment?

piglet

up to 260C

<https://www.mouser.com/new/Kemet-Electronics/kemet-high-temp-
capacitors/>

 

[piglet]

On 06/06/2019 13:14, Clive Arthur wrote:

On 06/06/2019 13:01, piglet wrote:

snip

Larkin's complementary source follower is a great solution. Is the
objection to two low current charge pumped auxilliary rails
philosophical or is noise a worry?

piglet

It's reliability - capacitors are best avoided at high temperatures and
high vibration if possible.

Cheers

Interesting. Thanks. What are the best capacitor types for that kind of
environment?

piglet

 

On Thursday, 6 June 2019 17:39:24 UTC+1, bitrex wrote:

On 6/6/19 7:40 AM, tabbypurr wrote:
On Thursday, 6 June 2019 12:03:16 UTC+1, Winfield Hill wrote:
Clive Arthur wrote...

Active cooling is out of the question, it's in a well.
125'C is minimum, 180'C is a better target.

If you're down in a very deep hot well, how
is it you only have 5.0 volts? That's weird.

Maybe it's time to develop a valve IC for downhole use. I always wondered if a VFD could be rejigged to somewhat do that.


NT


Korg makes a VFD-based dual triode:

https://www.youtube.com/watch?v=raYGrKWSKRE

How to make triodes much more expensive for no known reason.


NT

 

[Jasen Betts]

On 2019-06-06, tabbypurr@gmail.com <tabbypurr@gmail.com> wrote:

On Thursday, 6 June 2019 12:03:16 UTC+1, Winfield Hill wrote:
Clive Arthur wrote...

Active cooling is out of the question, it's in a well.
125'C is minimum, 180'C is a better target.

If you're down in a very deep hot well, how
is it you only have 5.0 volts? That's weird.

Maybe it's time to develop a valve IC for downhole use. I always wondered if a VFD could be rejigged to somewhat do that.

no. cylindical tubes handle pressure much better than flat-sided ones.



--
When I tried casting out nines I made a hash of it.

 

On Friday, 7 June 2019 07:31:15 UTC+1, Jasen Betts wrote:

On 2019-06-06, tabbypurr wrote:
On Thursday, 6 June 2019 12:03:16 UTC+1, Winfield Hill wrote:
Clive Arthur wrote...

Active cooling is out of the question, it's in a well.
125'C is minimum, 180'C is a better target.

If you're down in a very deep hot well, how
is it you only have 5.0 volts? That's weird.

Maybe it's time to develop a valve IC for downhole use. I always wondered if a VFD could be rejigged to somewhat do that.

no. cylindical tubes handle pressure much better than flat-sided ones.

both form factors are well established & handle it without any difficulty. That has simply nothing to do with developing an IC


NT

 

[Jasen Betts]

On 2019-06-07, tabbypurr@gmail.com <tabbypurr@gmail.com> wrote:

On Friday, 7 June 2019 07:31:15 UTC+1, Jasen Betts wrote:
On 2019-06-06, tabbypurr wrote:
On Thursday, 6 June 2019 12:03:16 UTC+1, Winfield Hill wrote:
Clive Arthur wrote...

Active cooling is out of the question, it's in a well.
125'C is minimum, 180'C is a better target.

If you're down in a very deep hot well, how
is it you only have 5.0 volts? That's weird.

Maybe it's time to develop a valve IC for downhole use. I always wondered if a VFD could be rejigged to somewhat do that.

no. cylindical tubes handle pressure much better than flat-sided ones.

both form factors are well established & handle it without any difficulty. That has simply nothing to do with developing an IC

neither were designed to handle downhole pressure, but the box shape is
particularly vulnerable.

--
When I tried casting out nines I made a hash of it.

 

On Friday, 7 June 2019 13:01:08 UTC+1, Jasen Betts wrote:

On 2019-06-07, <tabbypurr> wrote:
On Friday, 7 June 2019 07:31:15 UTC+1, Jasen Betts wrote:
On 2019-06-06, tabbypurr wrote:
On Thursday, 6 June 2019 12:03:16 UTC+1, Winfield Hill wrote:
Clive Arthur wrote...

Active cooling is out of the question, it's in a well.
125'C is minimum, 180'C is a better target.

If you're down in a very deep hot well, how
is it you only have 5.0 volts? That's weird.

Maybe it's time to develop a valve IC for downhole use. I always wondered if a VFD could be rejigged to somewhat do that.

no. cylindical tubes handle pressure much better than flat-sided ones.

both form factors are well established & handle it without any difficulty. That has simply nothing to do with developing an IC

neither were designed to handle downhole pressure, but the box shape is
particularly vulnerable.

more so per given quantity of glass. Hence it uses thicker glass.
Anyway the enclosure shape of an IC-like array is not a challenge. Plenty of tiny VFD style triodes can fit in a short tube if you so want, and of course VFDs can be made with thick glass. It doesn't strike me as a problem.


NT