Amplitude modulate variable regulator

Thu Jan 19, 2012 12:20 pm   

I have a few of these 0-30VDC variable power supply kits left over
from a previous project.

http://www.4shared.com/account/dir/6bfaqiMd/_online.html?rnd=24#dir=43926040

It uses a UA723 IC regulator.

Is it possible to modulate the output by inserting a control voltage
(via a function genrator), that would act the same way as manually
varying R10?

Any idea what the maximum modulating frequency might be?

I would like to know how so as not to damage the IC. Thank you for any
suggestions.

Glenn Myers

Thu Jan 19, 2012 12:45 pm   

On 1/19/2012 3:20 AM, Glenn Myers wrote:


You can modulate the control voltage.
So, yes, you can modulate the control voltage to make it work like
manually varying the voltage set pot.

But is that what you want????

Be aware that the output is typically unidirectional.
You have active current in one direction only. The speed of
the other direction depends on the load and the output capacitor.
If you use a current limit, trying to slew too fast into a capacitor
will put
it into current limit.

Thu Jan 19, 2012 4:03 pm   

On Thu, 19 Jan 2012 11:20:03 GMT, glennmyers_at_intergen.com (Glenn
Myers) wrote:


I get "The file link that you requested is not valid."


...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
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I love to cook with wine. Sometimes I even put it in the food.

Thu Jan 19, 2012 8:09 pm   

On Thu, 19 Jan 2012 08:03:34 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon_at_On-My-Web-Site.com> wrote:


Very (extemely) sorry about that. This one definitely works.

http://www.4shared.com/photo/tN1TX3ES/Power-Supply.html

The question was how to modulate the IC with a low frequency sinewave
.... and any downsides.

Many thanks for the comments so far, and for looking again.

Glenn

Thu Jan 19, 2012 8:30 pm   

On Thu, 19 Jan 2012 19:09:14 GMT, glennmyers_at_intergen.com (Glenn
Myers) wrote:


(1) Midpoint (setpoint) voltage?
(2) Desired amplitude of modulation (at OUT)?
(3) Frequency of modulation?
(4) Load value, resistive, reactive?

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

Thu Jan 19, 2012 11:24 pm   

On Thu, 19 Jan 2012 19:09:14 +0000, Glenn Myers wrote:



My experience of similar circuits using the 123/723 is that they have the
habit of going unstable in the low MHz range.

Commercial ones, too. The only cure in such cases was to reduce the loop
gain and accept a little poorer regulation.

Stay away from 723s ;-)

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)

Fri Jan 20, 2012 12:37 am   

On Thu, 19 Jan 2012 12:30:17 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon_at_On-My-Web-Site.com> wrote:



Even though the linked circut is shown operating from a 30VDC supply,
I will be using a single 12V lead acid battery. So anything close to
that.

BTW I am not using this circuit to charge a battery. Only as a high
current signal source.


As high as is practical without re-jigging the entire circuit. 5 or 6V
would be acceptable.


Between 1-60Hz is all I really need. But I would be interested to see
the upper limit.


Whatever current the circuit will comfortably sink ... preferably lots
given the TO-3 stage. Load, I assume, would be more or less resistive
at these low frequencies. Ceramic load resistor, solenoid, etc.

Thank you for your reply.

Glenn Myers

Fri Jan 20, 2012 1:13 am   

On Thu, 19 Jan 2012 11:20:03 GMT, glennmyers_at_intergen.com (Glenn
Myers) wrote:



Without thinking I tried to use it as a cheap and dirty speaker
amplifier. But it only will source current, not sink it, so you get a
horribly truncated wave into the speaker through the coupling
capacitor.

Jim

Fri Jan 20, 2012 1:19 am   

On Thursday, January 19, 2012 3:20:03 AM UTC-8, Glenn Myers wrote:

If you only need a small modulation, it suffices to put a transformer
secondary in series with the output; any signal you put into the primary,
will show up on the output. That's good for just about ANY frequency
except DC.

Otherwise, just sum the reference voltage of the uA723 with your signal,
and amplify it (any old op amp will do). Power supplies with uA723 aren't
terribly good at reproducing AC signals.

Fri Jan 20, 2012 1:24 am   

On Thu, 19 Jan 2012 23:37:36 GMT, glennmyers_at_intergen.com (Glenn
Myers) wrote:


Too vague. Write down your requirements as if you were composing an
RFQ for something you would buy if it met your specs.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

Fri Jan 20, 2012 2:14 am   

On Thu, 19 Jan 2012 17:24:10 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon_at_On-My-Web-Site.com> wrote:


This is just an experiment Jim, not a military contract I'll
settle for anyone's best guess ... expect mine.

Glenn

Fri Jan 20, 2012 2:44 am   

On 1/19/2012 4:13 PM, RST Engineering wrote:

Yep, but it does do what you asked..."it acts the same way as
manually varying R10."
As others have stated, just because it's not a military contract
doesn't relieve you from specifying exactly what you want it to do.
The hardest part of any project is specifying, IN DETAIL, the result you
expect.

Fri Jan 20, 2012 4:08 am   

"Glenn Myers" wrote in message news:4f18bf16.7071656_at_news.tpg.com.au...


If it's just an experiment, then you can just give it a try. You probably
won't damage anything, and if you do, and you have a bunch of these surplus,
it's no big deal. But as Jim points out, you should have some idea of what
you are trying to do, and for modulation up to 60 Hz into a resistor it
should work just fine. But a solenoid may be a different animal, and you
have to provide some way to deal with the inductive "kick" when the supply
is going low. A diode across the coil will probably be all that is needed.
But it is still a mystery what you have in mind.

If you really want a power amplifier or a function generator, then there are
some very inexpensive ICs that can do what you want MUCH better than the
723. It's been so long since I've used one I forgot they even existed. Even
for power supplies, ICs like the LM317 or LM2931 are much better and cheaper
(like 25 cents) and require less external components. And for about a dollar
you can get a 4 watt stereo amplifier TEA2025 in a DIP package:
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00000172.pdf

I know it is tempting to use parts you already have to build something, but
usually it is better (and cheaper) to get a more modern part that does
exactly what you want. And it's also futile to imagine possible alternate
uses for parts you have. I have thousands of surplus parts that are now so
old that they are obsolete, or damaged because of humid storage conditions.
I hate to throw them away, but I've had them for 20 years and I've only uses
a few of them and I've sold a few, and it really cost me more in time and
effort than I got from the sales.

If you want some parts really cheap, they are listed at:
http://www.pstech-inc.com/surplus.htm
and an even more complete listing at: http://www.pstech-inc.com/PARTS.txt or
http://www.pstech-inc.com/PARTS.xls

No guarantees on what I actually have or what condition, but I'd be happy to
find good homes for not much more than shipping costs from 21030.

Paul

Fri Jan 20, 2012 4:10 am   

"Glenn Myers"

** The minimum output voltage is 2.2 volts - not zero.



.... Phil

Fri Jan 20, 2012 4:15 am   

"Glenn Myers"



** The value of C1 is WAAAAYYY to low at 1000uF.

At 3 amps the ripple would be 25Vp-p.

10,000uF is more like it.



.... Phil