Multiple regulated voltages

P

Piotr Wyderski

Guest
I need +/-10V (about 1A), +/-2.5V (about 100mA) and 5V (about 60mA).
I was shocked that it is virtually impossible to find a negative voltage
LDO capable of hundreds of milliamps and reasonably cheap. It seems
that producing all these rails with a bunch of opamp-boosted emitter
followers will be cheaper than a single adjustable negative LDO.
I already have a decent 2.5V reference (LTC6655) in the project so why
exactly should I avoid the temptation of making this PSU out of discrete
elements? Noise properties should be comparable to that of an LDO and
I can shape thermal/max voltage issues with a proper transistor.

Best regards, Piotr
 
Piotr Wyderski wrote...
I need +/-10V (about 1A), +/-2.5V (about 100mA) and 5V
(about 60mA). I was shocked that it is virtually
impossible to find a negative voltage LDO capable of
hundreds of milliamps and reasonably cheap.
Click to expand...

I'm surprised you want to waste 1.8 watts on 5V and
2.5V linear regulators. It's easy to make negative
buck converters from positive boost converters.


--
Thanks,
- Win
 
On 13 Jun 2019 12:28:30 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

George Herold wrote...

On Thursday, June 13, 2019 at 2:14:08 PM UTC-4, Piotr Wyderski wrote:
I need +/-10V (about 1A), +/-2.5V (about 100mA) and 5V (about 60mA).
I was shocked that it is virtually impossible to find a negative voltage
LDO capable of hundreds of milliamps and reasonably cheap.

I guess the LM337 doesn't count as LDO.

Why would one need an LDO to go from -10V to -2.5V?
Click to expand...

Some people have taken to calling any linear regulator an LDO.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
George Herold wrote...
On Thursday, June 13, 2019 at 2:14:08 PM UTC-4, Piotr Wyderski wrote:
I need +/-10V (about 1A), +/-2.5V (about 100mA) and 5V (about 60mA).
I was shocked that it is virtually impossible to find a negative voltage
LDO capable of hundreds of milliamps and reasonably cheap.

I guess the LM337 doesn't count as LDO.
Click to expand...

Why would one need an LDO to go from -10V to -2.5V?


--
Thanks,
- Win
 
Winfield Hill <winfieldhill@yahoo.com> wrote in
news:qdu5ft0260h@drn.newsguy.com:

Piotr Wyderski wrote...

I need +/-10V (about 1A), +/-2.5V (about 100mA) and 5V
(about 60mA). I was shocked that it is virtually
impossible to find a negative voltage LDO capable of
hundreds of milliamps and reasonably cheap.

I'm surprised you want to waste 1.8 watts on 5V and
2.5V linear regulators. It's easy to make negative
buck converters from positive boost converters.
Click to expand...

Our oem lvsmps with multiple outputs were practically the same as
the single output jobs. Usually a bit smaller than a brick.

We made about 400V and then downconvert for the actual output
voltages. Running the 400V rail clean made the supply LV setpoints
easier to manage and keep clean.
 
On Thursday, June 13, 2019 at 2:14:08 PM UTC-4, Piotr Wyderski wrote:
I need +/-10V (about 1A), +/-2.5V (about 100mA) and 5V (about 60mA).
I was shocked that it is virtually impossible to find a negative voltage
LDO capable of hundreds of milliamps and reasonably cheap. It seems
that producing all these rails with a bunch of opamp-boosted emitter
followers will be cheaper than a single adjustable negative LDO.
I already have a decent 2.5V reference (LTC6655) in the project so why
exactly should I avoid the temptation of making this PSU out of discrete
elements? Noise properties should be comparable to that of an LDO and
I can shape thermal/max voltage issues with a proper transistor.

Best regards, Piotr
Click to expand...

What do you have for input voltage/current?
I guess the LM337 doesn't count as LDO.
Two wall warts for the +/- 10V? There are also a number of DC-DC converter
modules. But 1 amp may cost too much.

George H.
 
Winfield Hill wrote:

I'm surprised you want to waste 1.8 watts on 5V and
2.5V linear regulators. It's easy to make negative
buck converters from positive boost converters.
Click to expand...

The fans consume 65W, so there is no real reason to care about 2
additional watts. And the rails will be quiet, which is a nice feature
in the vincinity of a 24-bit ADC.


Best regards, Piotr
 
On Thursday, June 13, 2019 at 3:28:53 PM UTC-4, Winfield Hill wrote:
George Herold wrote...

On Thursday, June 13, 2019 at 2:14:08 PM UTC-4, Piotr Wyderski wrote:
I need +/-10V (about 1A), +/-2.5V (about 100mA) and 5V (about 60mA).
I was shocked that it is virtually impossible to find a negative voltage
LDO capable of hundreds of milliamps and reasonably cheap.

I guess the LM337 doesn't count as LDO.

Why would one need an LDO to go from -10V to -2.5V?

Grin you wouldn't. I assumed the LDO was for the -10 V.
Click to expand...

George h.
--
Thanks,
- Win
Click to expand...
 
On a sunny day (Thu, 13 Jun 2019 20:14:06 +0200) it happened Piotr Wyderski
<peter.pan@neverland.mil> wrote in <qdu3pb$vnn$1@node2.news.atman.pl>:

I need +/-10V (about 1A), +/-2.5V (about 100mA) and 5V (about 60mA).
I was shocked that it is virtually impossible to find a negative voltage
LDO capable of hundreds of milliamps and reasonably cheap. It seems
that producing all these rails with a bunch of opamp-boosted emitter
followers will be cheaper than a single adjustable negative LDO.
I already have a decent 2.5V reference (LTC6655) in the project so why
exactly should I avoid the temptation of making this PSU out of discrete
elements? Noise properties should be comparable to that of an LDO and
I can shape thermal/max voltage issues with a proper transistor.

Best regards, Piotr
Click to expand...

As long as you do not specify tolerances and ripple,
you may as well use a tapped transformer
a few diodes and capacitors
and some oscillator.
That is how PC power supplies work.
 
On Thursday, June 13, 2019 at 3:40:36 PM UTC-4, John Larkin wrote:
On 13 Jun 2019 12:28:30 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

George Herold wrote...

On Thursday, June 13, 2019 at 2:14:08 PM UTC-4, Piotr Wyderski wrote:
I need +/-10V (about 1A), +/-2.5V (about 100mA) and 5V (about 60mA).
I was shocked that it is virtually impossible to find a negative voltage
LDO capable of hundreds of milliamps and reasonably cheap.

I guess the LM337 doesn't count as LDO.

Why would one need an LDO to go from -10V to -2.5V?

Some people have taken to calling any linear regulator an LDO.
Click to expand...

Right, I have no idea what an LDO is or isn't. I use the LT3080,
called an LDO, but typical app has a drop out of 1.2 V.

George h.
--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Click to expand...
 
George Herold wrote:

> What do you have for input voltage/current?

LT3439, located far, far away and shielded by a several centimeters
thick aluminum block (227mm, but with slots).

> Two wall warts for the +/- 10V?

Not even close to the required insulation.

Best regards, Piotr
 
Jan Panteltje wrote:

> As long as you do not specify tolerances and ripple

These rails are needed for a 16-bit DAC and 16 24-bit sigma-delta ADCs
(2x ADS131E08). PSRR is decent and I don't insist on the last possible
resolution bit, but nonetheless it would be best to keep the PSU quiet.

One strange discovery is that I can buy all the components for such
a 5-way PSU at the price of a negative LDO for the -10V rail.

Best regards, Piotr
 
George Herold wrote:

> Grin you wouldn't. I assumed the LDO was for the -10 V.

Exactly. And it turns out there are no such fixed voltage LDOs, curious
on its own. There are many for +10V.

Best regards, Piotr
 
torsdag den 13. juni 2019 kl. 22.04.01 UTC+2 skrev George Herold:
On Thursday, June 13, 2019 at 3:40:36 PM UTC-4, John Larkin wrote:
On 13 Jun 2019 12:28:30 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

George Herold wrote...

On Thursday, June 13, 2019 at 2:14:08 PM UTC-4, Piotr Wyderski wrote:
I need +/-10V (about 1A), +/-2.5V (about 100mA) and 5V (about 60mA).
I was shocked that it is virtually impossible to find a negative voltage
LDO capable of hundreds of milliamps and reasonably cheap.

I guess the LM337 doesn't count as LDO.

Why would one need an LDO to go from -10V to -2.5V?

Some people have taken to calling any linear regulator an LDO.

Right, I have no idea what an LDO is or isn't. I use the LT3080,
called an LDO, but typical app has a drop out of 1.2 V.
Click to expand...

it is a bit special, it is emitter follower output so in principal
not an LDO, but it has extra input for a higher control voltage so
it can have a low drop out
 
Winfield Hill wrote:

I'm surprised you want to waste 1.8 watts on 5V and
2.5V linear regulators.
Click to expand...

To be honest, heatsinking is not exactly a problem in this case:

https://i.postimg.cc/bvq5RvjB/20190613-232726.jpg
https://i.postimg.cc/tgDMvHqC/20190613-232755.jpg
https://i.postimg.cc/4yH237zm/20190613-232817.jpg

5kg of high-performance alu + some 800 cubic meters per hour of forced
airflow. I am enchanted by the sound of this unit at its full rated
speed. Now just don't want to mess the analog front-end.

Best regards, Piotr
 
Piotr Wyderski wrote...
To be honest, heatsinking is not exactly a problem in this case:

https://i.postimg.cc/bvq5RvjB/20190613-232726.jpg
https://i.postimg.cc/tgDMvHqC/20190613-232755.jpg
https://i.postimg.cc/4yH237zm/20190613-232817.jpg

5kg of high-performance alu + some 800 cubic meters per hour of forced
airflow. I am enchanted by the sound of this unit at its full rated
speed. Now just don't want to mess the analog front-end.
Click to expand...

What in the world are those fans cooling?


--
Thanks,
- Win
 
Winfield Hill <winfieldhill@yahoo.com> wrote in
news:qdus310fln@drn.newsguy.com:

Piotr Wyderski wrote...

To be honest, heatsinking is not exactly a problem in this case:

https://i.postimg.cc/bvq5RvjB/20190613-232726.jpg
https://i.postimg.cc/tgDMvHqC/20190613-232755.jpg
https://i.postimg.cc/4yH237zm/20190613-232817.jpg

5kg of high-performance alu + some 800 cubic meters per hour of
forced airflow. I am enchanted by the sound of this unit at its
full rated speed. Now just don't want to mess the analog
front-end.

What in the world are those fans cooling?
Click to expand...

Probably better off putting two of the CPU self contained water
coolers under a quarter inch thick Al plate with the parts on it..
Quiet, small fans, and extremely good cooling characteristics. Much
smaller end product. Oh, and the fans and radiator are remote to
the actual cooling plates. Far easier to enclose and service.

Quieter electrically too. Especially proximal to the electronics.
 
Lasse Langwadt Christensen wrote:

it is a bit special, it is emitter follower output so in principal
not an LDO, but it has extra input for a higher control voltage so
it can have a low drop out
Click to expand...

LM1117 has 1.2V dropout in the worst case and it is counted as an LDO.
One VBE drop is absolutely fine.

Best regards, Piotr
 
Winfield Hill wrote:

> What in the world are those fans cooling?

A mother of Godzilla dual linear electronic load.

Best regards, Piotr
 
DecadentLinuxUserNumeroUno@decadence.org wrote:

Probably better off putting two of the CPU self contained water
coolers under a quarter inch thick Al plate with the parts on it..
Click to expand...

That was one of the considered options, but a more conservative design
won. You have to dump the kW-level amount of heat somewhere anyway and
it is better not to have any fluids nearby when it is operating in HV mode.

> Quiet

It turned out it is not exactly an advantage. It is very quiet at
moderate loads (the fans are PWM-capable) and you can hear every watt
of its capabilities at full load. This audio feedback is in fact
a post-design discovery that turned out to be a very useful and desired
feature. I would do it consciously that way in a fresh design.

And sexy. More or less this pitch:

https://www.youtube.com/watch?v=ifMUefCAEbo&feature=youtu.be&t=59

Best regards, Piotr
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top