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'[EE] Digital adjustment of LM317'
2011\03\21@033208 by IVP

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part 1 1152 bytes content-type:text/plain; charset="iso-8859-1" (decoded quoted-printable)

Hi all,

could I have suggestions for controlling an LM317 please

In the attached diagram, the 10k pot is used to set the voltage
of the HV PWM outputs

What I need to add is a modulation control, which simulates
the pot being rotated left and right. The pot will stay, modulation
is just another mode

The frequency will be 10Hz at most, sinusoidal. That's not a
problem. Reading the LM317 datasheet, I see an example of
a Power Follower, using an LM195, but I don't think it's going
to be suitable

IF I'm right assuming that ADJ can't be directly voltage-controlled
(correct me if I'm wrong) then adding modulation will require either
grounding the pot through a FET, so that it can be switched out, or
paralleling it with some resistive element

Such as -

Digital pot
PWM-ed 4066 switch (effective R = Ton/Toff)
Linearly-driven FET

The first two imply some additional logic, perhaps a 12F. The
third seems simpler, if the FET could be is used as a resistor
with R (simply) controlled between Ron and 10k ohms. If the
pot is left in circuit, then R would be from Ron to Roff

Any other ideas ?

Joe

part 2 4384 bytes content-type:image/gif; name="LM317_adjust.gif" (decode)


part 3 181 bytes content-type:text/plain; name="ATT00001.txt"
(decoded base64)

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2011\03\21@034241 by Mark Rages

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On Mon, Mar 21, 2011 at 2:30 AM, IVP <spam_OUTjoecolquittTakeThisOuTspamclear.net.nz> wrote:
> Hi all,
>
> could I have suggestions for controlling an LM317 please
>
> In the attached diagram, the 10k pot is used to set the voltage
> of the HV PWM outputs
>
> What I need to add is a modulation control, which simulates
> the pot being rotated left and right. The pot will stay, modulation
> is just another mode
>
> IF I'm right assuming that ADJ can't be directly voltage-controlled
> (correct me if I'm wrong) then adding modulation will require either
> grounding the pot through a FET, so that it can be switched out, or
> paralleling it with some resistive element
>

How much modulation (in terms of output voltage) do you need?

Could you use digital pot, e.g. AD5290, with existing pot in series?
-- Mark Rages, Engineer
Midwest Telecine LLC
.....markragesKILLspamspam@spam@midwesttelecine.co

2011\03\21@040444 by IVP

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> How much modulation (in terms of output voltage) do you need?
>
> Could you use digital pot, e.g. AD5290, with existing pot in series?

Ah, sorry. Missed that detail. Adjustable modulation. That would be
from min (1.25V) to any voltage up to and including max (32.5V), so
the pot would have to be out of circuit or paralleled

Jo

2011\03\21@052101 by Manu Abraham

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On Mon, Mar 21, 2011 at 1:00 PM, IVP <joecolquittspamKILLspamclear.net.nz> wrote:
{Quote hidden}

Another thought that might work (not tested, but from a logical point of view)

The ADJ pin of the LM317 is one end of the ref. current source and
using a pot to vary the current sink, you vary the voltage; that's the
general application note.

What I think is possible: Use the PWM output of the PIC, use it to
drive a transistor: this should result in a variable voltage accross
the transistor. Low pass filter this to get a clean voltage reference
which is someway related to the PWM signal. Using this voltage
reference, convert it to a current source that can be scaled in some
way proportional to  you require, use this current source to sink
appropriately from the ADJ pin. I guess, this might work

2011\03\21@052546 by Manu Abraham

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On Mon, Mar 21, 2011 at 2:51 PM, Manu Abraham <.....abraham.manuKILLspamspam.....gmail.com> wrote:
{Quote hidden}

And oh, yes. I can confirm that would work. I did a simple google on
that aspect, which resulted thus

http://www.electro-tech-online.com/attachments/microcontrollers/32974d1251452611-digital-control-voltage-using-lm317-adjusting-regulator-output-digitally.gif

2011\03\21@064137 by RussellMc

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1. You MAY be able to modulate the MC34063 Vout fast enough to not
need output PWM, depending on application.

2. If you drive the LM317 adj terminal with a voltage which is stiff
wrt the pot load then Vout will be 1.25V above the drive voltage. You
could drive it with a less stiff voltage and lift the pot ground end
with the same result. Getting the changeover timing right is a good
idea.

3. For interest, why are there two identical but parallel HV PWM channels?

4. If a pot is setting VPWM source then adjusting the 34063 output
seems MUCH wiser unless you hav an unusual application. ie at 1.25V
out you get about 96% of your smps power dissipated in the LM317.

5. Even as shown, shutting down the smps below 12V and using direct
feed seems liable to be useful.

6. Dropout of LM317 is such that you cannot guarantee to reach the Vmax shown.

7. Telling us what you are actually trying to do may result in (even)
better answers ;-)

8. You will have trouble reaching the high side current limit as shown :-)



On 21 March 2011 20:30, IVP <joecolquittspamspam_OUTclear.net.nz> wrote:
{Quote hidden}

>

2011\03\21@070615 by IVP

face picon face
> http://www.electro-tech-online.com/attachments/microcontrollers/32974d1251452611-digital-control-voltage-using-lm317-adjusting-regulator-output-digitally.gif

Thanks. I also Googled. Didn't find much apart from your link and

http://www.electro-tech-online.com/attachments/electronic-projects-design-ideas-reviews/18890d1209004583-lm317-control-pic-mcu-lm317.png

Will have to try them and see

Joe

2011\03\21@092028 by RussellMc

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>> http://www.electro-tech-online.com/attachments/microcontrollers/32974d1251452611-digital-control-voltage-using-lm317-adjusting-regulator-output-digitally.gif

This circuit is flawed.
It is semi oen loop.
It relies on the FET having an approximately constant Vturnon, so that
Vout = 1.25 + 2 x Vturnon + Vadc.
Minimum voltage is limited to 2 x Vturnon + 1.25.
Vtturnon (aka ~= Vth)(as at 10 mA) will vary between FETs and more.

> http://www.electro-tech-online.com/attachments/electronic-projects-design-ideas-reviews/18890d1209004583-lm317-control-pic-mcu-lm317.png

Looks entirely workable - essentially what I described. Some playing
will be needed. eg may oscillate as is. Adding a transistor output
driver will allow Vins > opamp Vdd max if desired.

Drive something like circuit 2 with the ADC or equivalent and 'you
have a ball game".
Circuit 2 Voutmax is limited by the op amp's Vmaxout but if you
operate the opamp Vdd supply from LM317 Vin you get almost max
possible swing as O amp max output needs only be
Vin - 1v* - 1.25V **  or 2.25V or more below Vin. Check Max Vdd wrt
out  of opamp used.


2011\03\21@110229 by Harold Hallikainen

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An LM317 is just a 1.2V regulator. The output is always 1.2V above the
adjust pin (as long as we're in regulation). So, you can drive the adjust
pin with a voltage source that is 1.2V below the output voltage you want.

Another interesting adjustable regulator is the LT3080 (
http://www.linear.com/product/LT3080 ). It uses a reference current source
instead of a reference voltage source. The voltage that is compared with
the output to set the regulated voltage is developed across a "set"
resistor with the internally generated reference current. This is
typically used as a fixed regulator with a set resistor. It can be an
adjustable regulator (down to 0V) with a pot for the set resistor. It can
be a programmable voltage regulator by driving the SET pin with the
desired voltage. The output voltage will be the same voltage, but with
higher current capability.

Harold



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2011\03\21@125009 by Dwayne Reid

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At 01:30 AM 3/21/2011, IVP wrote:
>Hi all,
>
>could I have suggestions for controlling an LM317 please
>
>IF I'm right assuming that ADJ can't be directly voltage-controlled
>(correct me if I'm wrong)

Sure it can.  You just have to use a stiff output on your voltage source such as an op-amp.

You can think of a LM317 as a beefy power transistor with an accurate 1.25V offset between the ADJ pin and the output.  You need the stiff output just to control the bias current coming out of the pin.  Doesn't need to handle much current (hundreds of uA, IIRC) - just needs to be stiff.

My early gell-cell battery chargers dating back from the late '80s uses LM317 regulators as pass devices in exactly that configuration.  Some of those are still in use to this day.

dwayne

-- Dwayne Reid   <@spam@dwaynerKILLspamspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
http://www.trinity-electronics.com
Custom Electronics Design and Manufacturing

2011\03\21@135356 by Marcel Duchamp

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On 3/21/2011 9:50 AM, Dwayne Reid wrote:
{Quote hidden}

One thing to keep in mind about the LM317 is the minimum load current needed to keep it happy.  It regulates well with 10mA or more load current and this is typically supplied with the resistor between the output and the adjust pin.  But it doesn't have to flow through the adjust network.  The minimum load current can be supplied through a resistor or some other current sink.

The adjust pin needs around 50uA of bias current, check your datasheet.   This is the current your control circuit needs to supply

2011\03\21@180627 by IVP

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part 1 1413 bytes content-type:text/plain; charset="iso-8859-1" (decoded quoted-printable)

>> .....-control-pic-mcu-lm317.png
>
> Looks entirely workable - essentially what I described. Some playing
> will be needed. eg may oscillate as is. Adding a transistor output
> driver will allow Vins > opamp Vdd max if desired.

That would have been something like my original plan. A DC amp to
drive ADJ. As I'm busy with other parts of the project I thought to
ask here and get some suggestions first

> 3. For interest, why are there two identical but parallel HV PWM
> channels?
>
> 7. Telling us what you are actually trying to do may result in (even) > better answers ;-)
>

It's a modification to a confidential product belonging to someone else,
so I can't divulge too much

Basically it's a drive system for two specialised sensors. The first draft
of the circuit is pot controlled, manual or motorised. The customer has
asked for a swell function, pot and/or micro controlled, so the output
would now look like an old-time wooden rollercoaster with the area
under the curve filled in with adjustable PWM

The attached shows one of the H-bridge controllers. 'IR' accepts both
remote control and data. Unfortunately the motors are too slow for
anything but a very slow swell so that's why I need to look at electronic
control, probably using the 675's spare i/o as RC'd PWM -> linear
voltage for the op-amp
Joe



part 2 3336 bytes content-type:image/gif; name="ir_h-bridge_675.gif" (decode)


part 3 181 bytes content-type:text/plain; name="ATT00001.txt"
(decoded base64)

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2011\03\22@093343 by Olin Lathrop

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RussellMc wrote:
>>
http://www.electro-tech-online.com/attachments/electronic-projects-design-ideas-reviews/18890d1209004583-lm317-control-pic-mcu-lm317.png
>
> Looks entirely workable - essentially what I described.

If you're going to go so far as adding a opamp to control the LM317, you
might as well just have the opamp drive something like a PNP pass
transistor.  The fancy electronics in the LM317 isn't doing much for you at
this point.  You're mostly using the LM317 as a pass element anyway.

Stability might be a little better with the '317 since things can be
arranged to be more linear, but you have to think about stability in either
case, and it's not that hard to drive a PNP or PFET directly.

Again though, does the PWM high side really need to be varied at all?  It
would be simpler and more efficient if this modulation could be performed
with duty cycle control and the LM317 dispensed with altogether.  If the
user input via the pot still needs to be there, wire the pot between the PIC
Vdd and Vss driving a A/D input, then have the result modify the duty cycle
inside the PIC.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2011\03\22@093343 by Olin Lathrop

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IVP wrote:
> Basically it's a drive system for two specialised sensors. The first
> draft of the circuit is pot controlled, manual or motorised. The
> customer has asked for a swell function, pot and/or micro
> controlled, so the output would now look like an old-time wooden
> rollercoaster with the area
> under the curve filled in with adjustable PWM

I suggested this yesterday, but some messages apparently got sucked into the
black hole of the list server.

Anyway, there is no need for adjusting the high side of the PWM at all, as
long as the load only "sees" the average value.  Always use the full (35V
was it?) and take care of everything else by modulating the duty cycle
appropriately.  This includes the user control.  Ditch the LM317 linear
regulator altogether and wire the pot into a PIC A/D pin.  This becomes one
more input to the final duty cycle calculation.

> The attached shows one of the H-bridge controllers.

Now I'm even more confused.  Your previous schematic was modulating the high
side of the PWM pulses, up to a high of something like 35V.  This shows the
H bridge and the motors all running from 5V only.  Presumably the previous
PWM outputs were for driving the H bride?  They had pullup resistors and
certainly weren't suitable for driving the motor directly.  But why do you
want to modulate the high side voltage of these pulses since they always
need to just saturate the transistors?

Another problem is that there is no place for the inductive energy of the
motor to go during the off phase.  The normal catch diodes are missing.
There should be four schottky diodes, one string of two from ground to power
on each side of the H bridge.  Perhaps you can argue that the top NPN
transistors will provide the low side clamp, but you still need diodes to
the power rail.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2011\03\22@093343 by Olin Lathrop

face picon face
IVP wrote:
> could I have suggestions for controlling an LM317 please
>
> In the attached diagram, the 10k pot is used to set the voltage
> of the HV PWM outputs
>
> What I need to add is a modulation control, which simulates
> the pot being rotated left and right. The pot will stay, modulation
> is just another mode

Instead of modulating the high side voltage of the PWM, how about folding
that into the duty cycle so that you can always run with a fixed high
voltage, 33.5V in your case?  Instead of linearly dropping half that, for
example, in the LM317, reduce the duty cycle by half instead.

How will these PWM signals be used?  What are they driving?  Is the ultimate
load only going to "see" the average value?  If so, then all modulation can
be combined into a duty cycle value.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2011\03\22@154426 by IVP

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> How will these PWM signals be used?  What are they driving?  Is
> the ultimate load only going to "see" the average value?

No. The PWM waveform needs to be retained, so the voltage of
it really does have to be variable. Initially I chose the LM317
because of the simplicity of just a pot between ADJ and 0

2011\03\22@154426 by IVP

face picon face
>> The attached shows one of the H-bridge controllers.
>
> Presumably the previous PWM outputs were for driving the H bridge ?

The HV PWM is for something else. That was just a diagram
showing the DC drive for the 4.5V pot motor. Although that
drive has been in service for some time without problems, I
note your point about catch diodes

Jo

2011\03\22@212803 by William \Chops\ Westfield

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On Mar 21, 2011, at 6:48 AM, Olin Lathrop wrote:

> If you're going to go so far as adding a opamp to control the LM317,  
> you
> might as well just have the opamp drive something like a PNP pass
> transistor.  The fancy electronics in the LM317 isn't doing much for  
> you at
> this point.  You're mostly using the LM317 as a pass element anyway.

A *fancy* pass element with features like overcurrent and overtemp  shutdown.  And pretty cheap, too.

I have a desire to build a general purpose lab-style power supply  using multiple 317s.  Several in parallel for increased output.  One  for the negative-voltage-driven current source that permits voltages  below 1.25V.  Maybe one as the regulation element in a switching pre- regulator.  Probably because of that eBay deal I got on a box of  317s... :-)

BillW

2011\03\23@061552 by Michael Rigby-Jones

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> -----Original Message-----
> From: KILLspampiclist-bouncesKILLspamspammit.edu [RemoveMEpiclist-bouncesTakeThisOuTspammit.edu] On
Behalf
{Quote hidden}

LM317's have some disadvantages for a lab supply:

1) Minimum output of 1.25v unless you can have a regulated, negative
rail you can use to pull the reference pin below ground.
2) To add any kind of variable current limiting means adding a bunch of
extra components
3) Not easy to add remote sense.

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2011\03\23@073005 by IVP

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> I have a desire to build a general purpose lab-style power supply  
> using multiple 317s.  Several in parallel for increased output.  One  
> for the negative-voltage-driven current source that permits voltages  
> below 1.25V

I've just about finished putting this together, perhaps make more

http://home.clear.net.nz/pages/joecolquitt/PSU_schematic.gif

PCB pattern can be got from Silicon Chip's Downloads section, 6/10

Maybe VG would do you a board ;-)

One modification will be an F88 and 16 x 2 LCD to display more
information than the 3 1/2 digit panel meter. The one specified for
the PSU is ICL7106-based

http://www.intersil.com/data/fn/fn3082.pdf

with a 200mV input. I've made a board with six DC amps for the
F88 ADCs. Nothing powered up yet, awaiting a 79L15

Jo

2011\03\23@081236 by alan.b.pearce

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> One modification will be an F88 and 16 x 2 LCD to display more
> information than the 3 1/2 digit panel meter. The one specified for
> the PSU is ICL7106-based

You may want to look at the PIC24FV family of chips that has just had the datasheet issued, the FV version runs of 2.5-5.5V (the F version is 1.8-3.6V IIRC) and they have a 12 bit ADC. Some versions come in 20 pin package, DIP, SOIC or SSOP.

I found the datasheet under 'What's new' at the MChip homepage

-- Scanned by iCritical.

2011\03\23@142754 by IVP

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> PIC24FV family of chips that has just had the datasheet issued

Thank

2011\03\24@031926 by cdb

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:: LM317's have some disadvantages for a lab supply:

I rather like the L200, though it has a minimum output of 2v85, but using two L200's a 0 to x supply can be made with output current in the 4A range if required.

See http://www.st.com/stonline/books/pdf/docs/1678.pdf for L200 circuits.

Can even be digitally controlled.

Colin
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'[EE] Digital adjustment of LM317'
2011\04\19@232823 by IVP
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part 1 734 bytes content-type:text/plain; charset="iso-8859-1" (decoded quoted-printable)

Attached is what I've got around to making. Components are pretty
much finalised. At this stage the LM317 can output any steady DC
voltage from 1.9 - 32.5V, 32.5V amplitude AC or any combination
of DC + AC to a maximum of 32.5V

The PIC and summing amp make a stepped sine wave from about
0.3Hz to 10Hz (my desired range), as set by the pot. A motorised
pot sets the DC Level, but this could also be PIC-derived. After
filtering, the shape is pretty good at the higher frequencies, a little
lumpy at the lower

This 'swell' voltage passes through to a second summer so that the
DC component can be added, and then on to the LM317

The LED indicates only frequency, not amplitude

Joe




part 2 6749 bytes content-type:image/gif; name="swell.gif" (decode)


part 3 181 bytes content-type:text/plain; name="ATT00001.txt"
(decoded base64)

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