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'[EE] Power supply project'
2008\06\12@232912 by Jinx

face picon face
Wonder if anyone has a PSU project or schematic they'd like to
share or recommend

I'm rationalising all the smallish PSUs and wall-warts I use into
one case. I'll probably use two transformers. One is a 19V 150VA,
the other is a multi-tap, 10-0-10, 6 and 45. I'd like to have multiple
outputs for all those bench experiments that need doing and PICs
that need powering

Fixed, eg high-current 5V and 12V (perhaps include SLA charging
voltage too)

Variable voltage / variable current outputs

Variable tracking +/- for op-amps etc (10-0-10 will be useful for that)

High voltage, either/and from the 45V / 19V with SMPS boost

Digital readout - LED/LCD

All of which I'm capable of putting together but if there are good
links or existing circuits that I should take a look or something that
could be add I'd love to hear about it. I have many regulators and
SMPS controllers in stock so parts aren't really an issue

TIA

(apologies if this gets sent twice - OE is playing silly beggars)

2008\06\12@235147 by Richard Prosser

picon face
One suggestion, if you're putting a power supply together, is to make
it capable of control via a PC (RS232 etc.) While not needed every
day, a controlled power supply can make testing (some)  projects a
whole lot less tedious.

RP

2008/6/13 Jinx <spam_OUTjoecolquittTakeThisOuTspamclear.net.nz>:
{Quote hidden}

> -

2008\06\13@002149 by Jinx

face picon face
> One suggestion, if you're putting a power supply together, is to
> make it capable of control via a PC (RS232 etc.) While not needed
> every day, a controlled power supply can make testing (some)
> projects a whole lot less tedious

Sounds interesting. Got a fer instance ?

I'm also working on cross-linking my function generators to include
timed one-shots and tone bursts (eg clocking tests on shift routines)

2008\06\13@013858 by Apptech

face
flavicon
face
> Wonder if anyone has a PSU project or schematic they'd
> like to
> share or recommend ...

> ... or something that
> could be add I'd love to hear about it. I have many
> regulators and
> SMPS controllers in stock so parts aren't really an issue

Following wishlist based on my experiences:

These would not all be in all supplies but would be in a
premium bench supply.

1    Voltage viewable and settable with DC output turned
off. Extremely useful.

2    Voltage measurable to at least 1 mV resolution where
possible. At least 3.5 digits (1.999) and if possible 3.75
digits so called (2.999). 4 digits would be very useful in
many cases.

3    Current also measurable to 1 mA resolution.
One way to achieve 2 & 3 is an autoranging meter set to the
appropriate function.

4    Current limit settable with output off (just a
"shorting button upstream of the DC out switch will achieve
this.

5    Consider Kelvin sensing voltage inputs for optional
use. Can be extremely nice - especially if extra external
metering or current drops exist between psu and load.

6    Put current meter inside voltage loop so when you set a
voltage it stays set across a wide range of current drains.

7    Either reverse current protected OR reverse current
proof. Otherwise expensive smoke happens.

8    A bit more unusual - consider providing a load that
sinks current that tries to lift output above set voltage.
This current could eg be shunted to an external load
terminal to allow you to choose what loads it sees. This
allows rough simulation of a battery - voltage above Vbat
charges the battery at a load set by the specified load.
Also useful for handling eg motor regeneration. You may want
to clamp returned current to Vset or to allow an impedance
for it to dissipate into terminated either in ground or in
Vset.I can expand on this if wanted.

9 Either fold back or linear limit overcurrent protection
depending on what you want to achieve. Either can be a
nuisance depending on the application.

10    Delta / fine variable voltage set and perhaps current
set. Using breathing and Jedi mind control on a psu knob to
get eg 5.000 volts on an output when the slightest twitch
perturbs the output 0.1 V makes one feel like a real
engineer but is hard on productivity.

11    Getting harder - analog or digital presets so you can
jump between a set of presetablished voltages.

12    Extension off 11 perhaps - exterior control - RS232 or
USB or whatever with say setting of Vout, Ilim, type of
Ilim, return of V and I would allow various features to be
implemented in code AND allow logging of results. eg Run
this load at constant current and log V. Run this code at
constant power by varying either V or I. Step V from X to Y
in steps of Z and record current. (I would have made a lot
of use of that in the last 6 months). Terminate in
equivalent of X ohms for Vterminal > Vset. Sink all current
at Vset for Vterm > Vset. ...



       Russell







{Quote hidden}

2008\06\13@015456 by Jinx

face picon face
> Following wishlist based on my experiences:

Oh. Just those 12 then ? ;-)

Food for thought

2008\06\13@022331 by Apptech

face
flavicon
face
>> Following wishlist based on my experiences:

> Oh. Just those 12 then ? ;-)

No. Those are just the first 12 that came to mind :-).
I'll probably remember a few more in the next while.

> Food for thought

Aye.


       R


2008\06\13@024318 by Xiaofan Chen

face picon face
On 6/13/08, Apptech <.....apptechKILLspamspam@spam@paradise.net.nz> wrote:

> These would not all be in all supplies but would be in a
> premium bench supply.
>
> 1    Voltage viewable and settable with DC output turned
> off. Extremely useful.
>
> 4    Current limit settable with output off (just a
> "shorting button upstream of the DC out switch will achieve
> this.

A cheap solution to this is to add a controlled relay in
series with the power supply. Or an external switch.
;-)

Xiaofan

2008\06\13@035441 by Alan B. Pearce

face picon face
>1    Voltage viewable and settable with DC output turned
>off. Extremely useful.

and don't forget to have a pair of 4mm banana sockets do you can plug an
external DVM in to verify the voltage before turning on the output. For
minimal extra expense the monitoring facility can be a lifesaver at times.

2008\06\13@035805 by Apptech

face
flavicon
face
>> These would not all be in all supplies but would be in a
>> premium bench supply.

>> 1    Voltage viewable and settable with DC output turned
>> off. Extremely useful.
>>
>> 4    Current limit settable with output off (just a
>> "shorting button upstream of the DC out switch will
>> achieve
>> this.
>
> A cheap solution to this is to add a controlled relay in
> series with the power supply. Or an external switch.
> ;-)

Yes.
Many of the ideas that I suggested have "cheap solutions".
What Jinx is trying to do is to integrate all his psu needs
in one module so the various cheap solutions get integrated
therein.

One useful "cheap solution is accessing a supply and putting
an external socket in the main current path and inside the
voltage feed loop. If you short this the supply operates as
before. If you open circuit it an place an ammeter across it
you have an output meter that essentially does bot affect
output voltage when current is varied. Whereas, adding an
external series meter adds typically ohms to 10 ohms plus to
the supply output resistance and makes variable current
constant current use annoying.



       Russell

2008\06\13@042930 by Jinx

face picon face
> No. Those are just the first 12 that came to mind :-).

Oh good :-/

I think just for starters I'll build the rectifier board to get the plain
DC up and running, then start the scheming. This could turn into
a handy PIC project for everyone

I'd be interested to hear how you'd implement

8 A bit more unusual - consider providing a load that sinks
current that tries to lift output above set voltage

2008\06\13@052440 by Apptech

face
flavicon
face
> I'd be interested to hear how you'd implement

> 8 A bit more unusual - consider providing a load that
> sinks
> current that tries to lift output above set voltage

I've actually done this and there are several ways,
But, back of a brainvelope first thought.

- The output with a passive low load is usually driven by
what is effectively a high side driver.
- The feedback loop usually sees the output trying to droop
below set point and turns on the high side driver as
required.
- If the polarity of the feedback signal is reversed by
current coming INTO the supply you turn on a low side sink
to compensate.

So, what you have is a simple half bridge.
You can run it pure class B with either source or sink on or
you could add a whisper of Class AB so that eg there is a
trickle of current down through the sink at all times so
that you have the lower (sink) driver trembling on the edge
of it's seat waiting to turn on if the output is driven
high.

If response time to changeover and a wee bit of deadband is
OK, and it usually would be, then you don't need much
complexity at all.

A simple out of head example.

NFET,PFET.
connect gates
connect sources
P drain low to ground
N drain high to V+
LM324

Ref input set to V+/2 to start.
324 output to dual gates.
324 non inv to Ref
324 inv to sources.

Output from Sources.

Vary ref and output will track.

Load output and N channel will be driven on.

Sink current into output so Vout rises above ref and P
channel will be driven on.

Very rough but gives general idea. Range does not include
rails.

Add a power resistor in series with lower driver (P stage)
and you have a finite impedance supply. There are more
elegant ways to simulate that but ... .

E&OE. Brainvelope is tired and a long night beckons.
One standard sun of sorts is coming up (slowly) in the
basement and the solar panels are waiting to feel its
warmth. ...


       Russell


2008\06\13@053635 by Jinx

face picon face
What are your thoughts on the LM350 and LM317 ? I've got
a heap of them sitting around doing nothing except getting older

The NatSemi Databook has several circuits using them combined
as adjustable current regulators, and other topologies sharing current
for higher outputs

Now, for the measurement

Setting voltage, piece o'cake

Setting current. Hmmm. Still looking for a circuit that doesn't use
a meter

Current isn't there until you use it, so I presume there would be
at least two methods

(1) the pot used to set the current limit has a voltage across it that
corresponds to the current that needs to be set, and this voltage is
displayed in current terms. If selected digitally, transcription also

(2) ganged pot, with one setting current, the other used for display.
Unlikely

(3) ???

2008\06\13@055131 by Jake Anderson

flavicon
face
Jinx wrote:
>> No. Those are just the first 12 that came to mind :-).
>>    
>
> Oh good :-/
>
> I think just for starters I'll build the rectifier board to get the plain
> DC up and running, then start the scheming. This could turn into
> a handy PIC project for everyone
>
> I'd be interested to hear how you'd implement
>
> 8 A bit more unusual - consider providing a load that sinks
> current that tries to lift output above set voltage
>
>  
Personally I'd grab one of those 400W+ 36 volt power supplies off ebay
to give you a decent DC supply (~$30 each)
Then make up a set of switchmode stepdown modules that run in parallel
off that.
For extra credit make each supply isolated ;->

2008\06\13@060401 by William \Chops\ Westfield

face picon face

On Jun 13, 2008, at 2:35 AM, Jinx wrote:

> What are your thoughts on the LM350 and LM317 ? I've got
> a heap of them sitting around doing nothing except getting older
>
> The NatSemi Databook has several circuits using them combined
> as adjustable current regulators, and other topologies sharing current
> for higher outputs

Yeah, there are circuits that use 317 for both current and voltage  
regulation, circuits that use paralleled 317s for currents greater  
than 1A, and even circuits that use a 317 as the sorce of negative  
bias current for voltages down below 1.2V.  I've been annoyed for "a  
while" that there isn't one definitive circuit for a "lab" supply  
that uses 317s as THE major active element...

Sigh.
BillW

2008\06\13@061046 by cllow2020(gmail)

picon face
have somelink info: www.freewebs.com/acselectronics/buildregs.html
switcher using LM317

--------------------------------------------------
From: "Jinx" <joecolquittspamKILLspamclear.net.nz>
Sent: Friday, June 13, 2008 5:35 PM
To: "Microcontroller discussion list - Public." <.....piclistKILLspamspam.....mit.edu>
Subject: Re: [EE] Power supply project

{Quote hidden}

> --

2008\06\13@062005 by Jinx

face picon face
> Personally I'd grab one of those 400W+ 36 volt power supplies off
> ebay to give you a decent DC supply (~$30 each)

Yes, I have thought about the NZ second-hand market (US is a little
bit distant). But that won't reduce the pile of transformers and rectifiers
sitting around here, which is part of the exercise. A few projects lately
have pushed me into areas I normally wouldn't dabble (get my fingers
burned ?) in, and I'm getting the hang of this learning-new-stuff

> Then make up a set of switchmode stepdown modules that run
> in parallel off that

Switchmode is certainly one thing I'll be adding, but I was thinking
up, not down. I've enough linears to cover stepdown, and they are
simple. And there

> For extra credit make each supply isolated ;->

Hmmm. Wind my own transformers eh ? What could possibligh
go wrong.....


2008\06\13@062811 by Jinx

face picon face
> have somelink info:
> www.freewebs.com/acselectronics/buildregs.html
> switcher using LM317

Thanks ! All grist to the mill


2008\06\13@104150 by Mark Rages

face picon face
On Fri, Jun 13, 2008 at 5:27 AM, Jinx <EraseMEjoecolquittspam_OUTspamTakeThisOuTclear.net.nz> wrote:
>> have somelink info:
>> www.freewebs.com/acselectronics/buildregs.html
>> switcher using LM317
>
> Thanks ! All grist to the mill
>

Agilent (née HP) has manuals for some of their older linear supplies
online, including schematics.  These are some nice supplies and worthy
of study.

If I ever build myself a supply I'll have an analog meter for current
and a digital meter for voltage.   Why?  I usually run the supply in
constant-voltage mode, so the voltage doesn't change much.  The
current does change and it's easier to watch an analog meter out of
the corner of your eye.  If you do a lot of low-power design a
multiple-range current meter might be useful.

Regards,
Mark
markrages@gmail
--
Mark Rages, Engineer
Midwest Telecine LLC
markragesspamspam_OUTmidwesttelecine.com

2008\06\13@113424 by Alan B. Pearce

face picon face
>Agilent (née HP) has manuals for some of their older linear supplies
>online, including schematics.  These are some nice supplies and worthy
>of study.

The other place to look for those is HP journals, which often have block
diagrams and pretty good descriptions of how the circuits work. Someone
posted a link here a few months ago to a scan depository of old HP journals
which can be downloaded as pdfs. Many happy hours of viewing later .....

2008\06\13@153225 by Marcel

picon face
William "Chops" Westfield wrote:
> I've been annoyed for "a  
> while" that there isn't one definitive circuit for a "lab" supply  
> that uses 317s as THE major active element...
>
> Sigh.
> BillW
>

A [definitive circuit for a "lab" supply] does not exist because there
is no lab supply that addresses all needs.  One that tries to will be:

a) too large
b) too expensive
c) too heavy
d) too ....

One person doing pic development work wants a wall wart supply; another
wants HP-IB to control it from their computer.  Someone else wants just
enough current for 'simple' stuff; another wants to be able to arc weld
with it.  And so it goes.

For experimenters learning electronics, LM317's are quite useful; I've
gotten lots of miles out of them.  But after a while, people get tired
of re-inventing the wheel and just buy a suitable bench supply.

2008\06\14@042128 by William \Chops\ Westfield

face picon face

On Jun 13, 2008, at 12:31 PM, Marcel wrote:

> A [definitive circuit for a "lab" supply] does not exist because there
> is no lab supply that addresses all needs.

I want a copy of the ubiquitous 0-30V 0-3A (or 5A) CCCV "bench  
supply" that pretty near all the test equipment suppliers supply.  
They all seem to be about the same size, too, though they're probably  
limited by transformer, meters, knobs, and power dissipation issues  
rather than electronics complexity...

(So has anyone else noticed that surplus switching supplies are  
hitting price parity with 60Hz transformers of similar capacity?  For  
instance, you can get a 16VDC 3.75A switching supply for about $15,  
while a 12.6VAC 3A transformer is about $11...  The difference being  
that the 16VDC supplies show up in the trash after each generation of  
laptop "refreshes", while the 12.6VAC transformers are getting hard  
to find...)


> people get tired of re-inventing the wheel and just buy a suitable  
> bench supply.

Indeed.  My bench supply has been among the most useful of my impulse  
purchases, and when the first one broke I bought a new one right  
away.  But it would be nice to have a reference schematic to fix the  
old one using my stock of 317s...

BillW

2008\06\14@044825 by Apptech

face
flavicon
face
>> people get tired of re-inventing the wheel and just buy a
>> suitable
>> bench supply.

> Indeed.

I wish it were so.
If you look at my 12 point list you'll find that most of the
features don't appear on most bench supplies. If you are
willing to pay enough you'll get some of them. Probably not
all.

Maybe I should market a proper power supply :-)



       Russell


2008\06\14@070745 by Dennis Crawley

picon face
On Friday, June 13, 2008 6:22 AM [GMT-3=CET],
Apptech  wrote:

> Add a power resistor in series with lower driver (P stage)
> and you have a finite impedance supply. There are more
> elegant ways to simulate that but ... .
>         Russell

GICs ?

I´ve used for audio control but I've never imagine this useage.

Dennis
-.. --- .--. ..- -- .- ...

2008\06\14@074417 by Dennis Crawley

picon face
On Friday, June 13, 2008 6:35 AM [GMT-3=CET],
Jinx  wrote:

> What are your thoughts on the LM350 and LM317 ? I've got
> a heap of them sitting around doing nothing except getting older

I made one of those with LM317/337. (1.2A only, the 350 3A)
If you need more current and your transformer allows you can add some 3055
or TIP35 with a calculated R in series with each emmiter.

Rgs.
Dennis.




2008\06\29@082256 by Jinx

face picon face
(question at bottom)

Been gathering parts for a few days. As mentioned originally I
want to consolidate a whole pile of transformers into one case
as a general-purpose PSU. So far I've made up some rectifier
boards with raw DC out. +/- 30V 2A, 70V 1A, 26V 15A
and 38V 10A

The low-current outputs aren't a particular problem, based on
LM317/LM350/LM78xx

As a bonus, I found two things whilst looking for something else.
The first was a bag of a few dozen 50V 6800uF caps that I was
given a long time ago and completely forgot about . The second
was a PSU of uncertain origin in a great case, 0-25V 5A it says
on the front, but the transformer says 10A, with 2 x 10-turn 10k
pots for V and I control. The LED display is not there unfortunately
but can be replaced easily enough. The active control is an SFC2723C
in 10-pin can. Research suggests this is an old old precision voltage
controller or reference. All semis have 1980 date codes, and overall
it's in good condition. The non-assuming front panel says VOEDING
25V 5A, with the pots marked I and U. A black and a red binding
post, and that's it

This circuit caught my eye for the higher outputs

http://www.electronics-lab.com/projects/power/003/

It has independently settable voltage and current. One reason it
appeals is that both pots, P1/P2, have an earthy end and the voltage
on the wiper is the control, so it should be fairly simple to interface
these to a PIC for display purposes. They are also both 10k, so a
common digital pot could be used

One question I have is about the bypass transistor Q4, a 2N3055

I'd like to parallel 3 x 2N3055, as in this circuit

http://www.freewebs.com/acselectronics/buildregs.html

How would I best parallel 2N3055 in the electronics-lab link ?

2008\06\29@111244 by Dennis Crawley

picon face
On Sunday, June 29, 2008 9:22 AM [GMT-3=CET],
Jinx  wrote:

> One question I have is about the bypass transistor Q4, a 2N3055
>
> I'd like to parallel 3 x 2N3055, as in this circuit
>
> http://www.freewebs.com/acselectronics/buildregs.html
>
> How would I best parallel 2N3055 in the electronics-lab link ?

The real problem you have to face is the drop Base-emitter and the gain of
each transistor

You can have a bunch of transistors produced the same day in the same batch
but they can have different VBE drop.
As you know this can make one or more Transistors to deliver more current
than other producing a lot of effects or its destruction... and this is
valid as well for the gain.

Assuming you will connect 4 transistors your ideal current in each branch
would be Io/4.
The conection is all collector in common to the source, all bases in common
to the driver with NO resistor.

Some ideas about this:
1.- A resistor in the base only cures the Beta effect but not the unbalance
drop out.
2.- Choose a resistor and connect it between the emitter and the
load(degenerative resistance;)
3.- There is a trade off between the unbalance percentage you allow and the
efficiency you get.
4.- You can use that resistance placing an opto diode with a resistor in
parallel so you can sense that drop.
5.- The main criteria to choose the RE resistor is 10 times Base
resistance/Hfe. (must confirm doing thevenin)

.... or

a dirver for each transistor with a very small resistance just to sens a
drop and to get a feedback.

it is very interesting.

Dennis.




2008\06\29@221019 by Jinx

face picon face
> it is very interesting.

Some very helpful discussions, tips from people who've built one,
modifications etc, on the 0-30V 3A circuit

http://www.electronics-lab.com/forum/index.php?topic=7317.0

2008\06\30@022458 by Jinx

face picon face
part 1 1378 bytes content-type:text/plain; (decoded 7bit)

Trying to work out some components for boosting the
current output of

http://www.electronics-lab.com/projects/power/003/

Attached shows original output stage and what I thin should work

Couple of questions -

Some components around Q1 are part of the shut-down including,
presumably, D10 and R16. Their function isn't explained

Dennis Crawley sent me an OnSemi pdf, thanks again, which suggests,
and has calculations for, emitter resistors for current-sharing, but all the
practical examples I've seen for PSUs have resistors on the bases, none
on the emitters. Which makes sense if you don't want to restrict current
flow

So, does the TIP31 look a suitable substitution for the 2N2219 ? It
has similar gain but higher Ic

If the original 1k 2N2219 base resistor was kept, would a TIP121
be better ? National are quite fond of the LM195 as bypasses. They're
a power Darlington that needs very low base current

Any other thoughts ?

Supplemental question - have some large filter caps, 63V 10,000uF.
As they haven't been used for a while I thought that a bit of charge
might go some way to re-forming them if they need it. After applying
current-limited 25V to them, I removed that and checked voltage
over a period. After a day, they measure 23V. Is this a meaningful
indicator of their health ? Seems a fairly low leakage for big caps


part 2 7124 bytes content-type:image/gif; (decode)


part 3 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2008\06\30@043841 by Picbits Sales

flavicon
face
Be warned about that power supply. It has a number of faults (aparrently).

There has been lots of talk about it on http://www.electro-tech-online.com about
how its badly designed and doesn't work properly and one of the guys on
there was a moderator and got kicked off for trying to fix it etc etc.

It crops up every now and again on there and posters are told not to build
it.

Never tried it myself but its worth nipping over to the electro tech forums
and reading some of the comments yourself.

Dom
{Original Message removed}

2008\06\30@053514 by Jinx

face picon face
> Be warned about that power supply. It has a number of faults
> (apparently).
>
> There has been lots of talk about it on http://www.electro-tech-online.com
> about how its badly designed and doesn't work properly and one of
> the guys on there was a moderator and got kicked off for trying to fix
> it etc etc

I found, after almost giving up searching

www.electro-tech-online.com/general-electronics-chat/37867-wouldl-lik
e-make-benctop-varible-power-supply.html

Thanks for the heads-up. Sounds like the improved version is worth
a look at, forget the 003 original

2008\06\30@081536 by Enki

picon face

       I remember an old Elektor Magazine article from December 1982 titled
"Precision Power Supply" that used a LM723.
       I built that circuit and it is still in use today.
       It has current and voltage adjust.

       Mark Jordan
       

On 30 Jun 2008 at 21:34, Jinx wrote:

{Quote hidden}

> --

2008\06\30@084604 by Jinx

face picon face
> "Precision Power Supply" that used a LM723

I'm looking at LM723 designs right now

Very surprised that it's been so difficult to find a complete public
domain PSU with adjustable voltage and current

2008\06\30@092406 by Michael Rigby-Jones

picon face


> -----Original Message-----
> From: @spam@piclist-bouncesKILLspamspammit.edu [KILLspampiclist-bouncesKILLspamspammit.edu] On
Behalf
{Quote hidden}

fix
> > it etc etc
>
> I found, after almost giving up searching
>
>
www.electro-tech-online.com/general-electronics-chat/37867-wouldl
-
> lik
> e-make-benctop-varible-power-supply.html
>
> Thanks for the heads-up. Sounds like the improved version is worth
> a look at, forget the 003 original

Joe,

Some years back I started building a bench PSU with this kit (sold by
Quasar in the UK <http://www.quasarelectronics.com/1138.htm> ) but never
got around to properly finishing it.  Sounds like it might not be worth
it either!

Two parts that will probably need upgrading for higher currents are the
bridge rectifier and smoothing cap; I suspect the ripple current rating
of the cap is pretty marginal even for 3A.  I used a 25Amp bridge and a
big computer grade electrolytic I had lying around, probably overkill as
I only wanted about 5-6Amps.

Regards

Mike

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'[EE] Power supply project'
2008\07\01@063351 by Jinx
face picon face
> Quasar in the UK <http://www.quasarelectronics.com/1138.htm> )
>
> Two parts that will probably need upgrading for higher currents are the
> bridge rectifier and smoothing cap; I suspect the ripple current rating
> of the cap is pretty marginal even for 3A.  I used a 25Amp bridge and a
> big computer grade electrolytic I had lying around, probably overkill as
> I only wanted about 5-6Amps.

I haven't had time to track down all the amendments made to the original
electronics-lab project (which, AYK, is the Quasar kit above), but the
base complaint is that the 24VAC of the transformer is way too high, and
particularly so for the op-amps and the SOAR of the single 2N3055

I've written to Silicon Chip, mentioning the dearth of public domain *good*
bench supply schematics, and suggested they might consider a PSU linear
or SMPS project or tutorial. The last they did was way back in 2000, a
1.23V - 40V @ 1.2A switchmode

http://www.siliconchip.com.au/cms/A_102445/article.html

2008\07\13@090747 by Jinx

face picon face
Re the 30V 3A variable V and I supply

http://www.electronics-lab.com/projects/power/003/

I've tracked down the amendments

http://home.clear.net.nz/pages/joecolquitt/30V_mods_notes.gif

http://home.clear.net.nz/pages/joecolquitt/30V_mods1.gif

http://home.clear.net.nz/pages/joecolquitt/30V_mods2.gif

http://home.clear.net.nz/pages/joecolquitt/30V_mods3.gif

http://home.clear.net.nz/pages/joecolquitt/30V_mods4.gif

2008\07\13@125001 by Dennis Crawley

picon face
On Sunday, July 13, 2008 10:05 AM [GMT-3=CET],
Jinx  wrote:

> Re the 30V 3A variable V and I supply
>
> http://www.electronics-lab.com/projects/power/003/
>
> I've tracked down the amendments
>
> http://home.clear.net.nz/pages/joecolquitt/30V_mods_notes.gif
>
> http://home.clear.net.nz/pages/joecolquitt/30V_mods1.gif
>
> http://home.clear.net.nz/pages/joecolquitt/30V_mods2.gif

This link appears to be missing...

>
> http://home.clear.net.nz/pages/joecolquitt/30V_mods3.gif
>
> http://home.clear.net.nz/pages/joecolquitt/30V_mods4.gif


Thank you for post your findings, Jinx. I like the Re resistor, I think with
5W is enough according to your maximum current (3A)...
BR,
Dennis


2008\07\13@144604 by David P Harris

picon face
Dennis Crawley wrote:
{Quote hidden}

Yes, thanks for that Jinx.  What's the next step?  Are pcbs still
available?  Maybe we should add a PIC and V&A monitoring LCD?

David



2008\07\13@144635 by David P Harris

picon face
Dennis Crawley wrote:
{Quote hidden}

Yes, thanks for that Jinx.  What's the next step?  Are pcbs still
available?  Maybe we should add a PIC and V&A monitoring LCD?

David



2008\07\13@170032 by Jinx

face picon face
> home.clear.net.nz/pages/joecolquitt/30V_mods2.gif
>    
> This link appears to be missing...

Sorry about that boss. Should be there now

> Yes, thanks for that Jinx.  What's the next step?  Are pcbs still
> available?  Maybe we should add a PIC and V&A monitoring
> LCD?

That's the intention

Electronics Lab suggest this, using a TQFP ATMega (a bit OTT)

http://www.electronics-lab.com/projects/test/022/index.html

http://www.electronics-lab.com/projects/test/022/schematic.jpg

I'm undecided what display to use. I want to have several PSUs in
one box, possibly 4 or 5, so an LCD each seems a little extravagant.
OTOH, I've a box of 4-digit 1/2" displays and drivers, and plenty of
7-segment LEDs (even a few old 1/8" calculator displays !!!)

First things first - get one of these beasties made up and see how
it performs

2008\07\13@171702 by Jinx

face picon face
BTW, in

http://www.electronics-lab.com/projects/test/022/index.html

the author is making a voltage measurement across the current sense
resistor to get the 'current flowing' display. It might be desirable to
take a measurement at the current-limiting pot also and display that
as well. And/or an LED to show that current out >= limit set

2008\07\13@205002 by Dennis Crawley

picon face
On Sunday, July 13, 2008 5:59 PM [GMT-3=CET],
Jinx  wrote:

> I'm undecided what display to use. I want to have several PSUs in
> one box, possibly 4 or 5, so an LCD each seems a little extravagant.
> OTOH, I've a box of 4-digit 1/2" displays and drivers, and plenty of
> 7-segment LEDs (even a few old 1/8" calculator displays !!!)

I'll use the 7 segments. When things are going wrong I want to clearly see
the
Amps or the Volts. (summer project)

> First things first - get one of these beasties made up and see how
> it performs

I have the negative side also. In the same cabinet I've installed a PC power
supply with all the outputs in the front pannel 3.3,±5,±12, One 9V output
for the PicstartPlus :)

BR,
Dennis


2008\07\16@045010 by Vasile Surducan

face picon face
On 7/13/08, Jinx <RemoveMEjoecolquittTakeThisOuTspamclear.net.nz> wrote:
> Re the 30V 3A variable V and I supply
>
> http://www.electronics-lab.com/projects/power/003/
>
> I've tracked down the amendments
>
> http://home.clear.net.nz/pages/joecolquitt/30V_mods_notes.gif
>
> http://home.clear.net.nz/pages/joecolquitt/30V_mods1.gif
>
> http://home.clear.net.nz/pages/joecolquitt/30V_mods2.gif
>
> http://home.clear.net.nz/pages/joecolquitt/30V_mods3.gif
>
> http://home.clear.net.nz/pages/joecolquitt/30V_mods4.gif

Assuming we need someday 3.3V and 3A from this power supply, the
thermal dissipation on Q4 and Q5 will be around 90-100W. I think from
this perspective that is a pour design. Imagine how would be at +30C
ambient and four hours of running. Even power supplies designed back
in 1980 have two good solutions for this problem:
1. switchable trafo windings using relays
2. a controlled bridge using two thyristors and two diodes (sometimes
four thyristors).

2008\07\16@061728 by Jinx

face picon face
> Assuming we need someday 3.3V and 3A from this power supply,
> the thermal dissipation on Q4 and Q5 will be around 90-100W

That is a significant disadvantage of linear PSUs. For a drop like that
you'd expect to need fan cooling. I have a product that needs 4.1V @
3A for extended periods and for that I use an LM2576 switcher, which
of course hardly heats up at all. So you do use what's appropriate when
necessary

One of my musty-smelling old books is the GE SCR Manual and they
go into switched bridges in some depth

One reason for this project though is that I'd like to build and share
something that could be put together from spare parts that most
would have or could get cheaply, even if it does double as a heater
sometimes

Rummaging around through many years' worth of hoarding has
turned up some useful finds. Parts that I'd completely forgotten were
there. LM338, 2N3055, MJ15003 and even MJ11016 power
Darlingtons, all unused. Even really old LM309 in steel TO3. I
think I inherited a lot from a friend who closed his repair shop many
years ago

2008\07\16@064529 by William \Chops\ Westfield

face picon face

>> Assuming we need someday 3.3V and 3A from this power supply,
>> the thermal dissipation on Q4 and Q5 will be around 90-100W

I've had two commercial "lab" linear power supplies, and they both  
seem to engage relays (audible clicks) at set voltage points along  
their range.  The 50V supply that's working now clicks at about 15  
and 30V...

BillW

2008\07\16@211232 by Jinx

face picon face
> I've had two commercial "lab" linear power supplies, and they
> both seem to engage relays (audible clicks) at set voltage points
> along their range.  The 50V supply that's working now clicks at
> about 15 and 30V...

What do you think they would be switching ?

2008\07\16@212354 by Marcel Birthelmer

flavicon
face
My guess is they have a few secondary windings from the mains transformer
that get rectified to a few different DC voltages, and going between output
ranges switches between the input signals. That way, you the output
regulator doesn't have to deal with dissipating I x 29V when you want a 1V
output, but instead just up to the next stage.
- Marcel

On Wed, Jul 16, 2008 at 5:47 PM, Jinx <spamBeGonejoecolquittspamBeGonespamclear.net.nz> wrote:

> > I've had two commercial "lab" linear power supplies, and they
> > both seem to engage relays (audible clicks) at set voltage points
> > along their range.  The 50V supply that's working now clicks at
> > about 15 and 30V...
>
> What do you think they would be switching ?
>
> -

2008\07\16@224242 by Jinx

face picon face
> My guess is they have a few secondary windings from the mains
> transformer

Hmmm. There's a thought. One transformer I'd probably use has
secondary taps. I guess for using the control circuit I've posted you
could add a boost switcher so that the control circuit always has a
constant V+, no matter what DC is going through the main bridge to
the output transistors, unless the PSU has a small secondary just for
the electronics. LED displays are pretty hungry so it actually would
be a good idea to have a separate supply for them rather than waste
capacity of the main winding. And changing the secondary would
certainly go some way to reducing losses at low output voltages

2008\07\17@223248 by Sean Breheny

face picon face
The guess is correct. That is pretty standard in bench supplies.

Sean


On Wed, Jul 16, 2008 at 10:39 PM, Jinx <TakeThisOuTjoecolquittEraseMEspamspam_OUTclear.net.nz> wrote:
{Quote hidden}

> -

2008\07\18@110641 by Martin

face
flavicon
face
I wonder if it would be a good design to have a buck pre-regulator SMPS
that was heavily filtered followed by a linear regulator dropping a few
volts. The buck supply would have a slow feedback response because of
the filtering but the floating linear reg could make up for it.
-
Martin

2008\07\18@122339 by Sean Breheny

face picon face
That sounds like a decent idea, although it may still have some of the
disadvantages of a switcher (switchers are blamed for being noisy, but
often this noise is very high frequency which a linear regulator
cannot reject very well. So, the way to fix it is to design the SMPS
correctly in the first place and add shielding/filtering.

Sean


On Fri, Jul 18, 2008 at 11:06 AM, Martin <RemoveMEmartinspamTakeThisOuTnnytech.net> wrote:
> I wonder if it would be a good design to have a buck pre-regulator SMPS
> that was heavily filtered followed by a linear regulator dropping a few
> volts. The buck supply would have a slow feedback response because of
> the filtering but the floating linear reg could make up for it.
> -
> Martin
> -

2008\07\18@203027 by Jinx

face picon face
> I wonder if it would be a good design to have a buck pre-regulator
> SMPS that was heavily filtered followed by a linear regulator dropping
> a few volts. The buck supply would have a slow feedback response
> because of the filtering but the floating linear reg could make up for it

Seems to me that, like the relays which switch secondaries, at certain
voltage points you could change the SMPS's feedback resistor ratio
to minimise the voltage drop across the following linear section (if you
have one)

How would you effect adjustable current-limiting in a simple SMPS ?

> switchers are blamed for being noisy, but often this noise is very high
> frequency

Sean, a modem I use specifies a very low noise tolerance so I looked
at SMPS ripple output. AFAICT it was pretty low, under mV at least,
and I didn't take any special precautions to remove it. A schematic
straight out of the datasheet actually. A filter (cap and small series
inductor) is a common 'dashed line' option in many d/s schematics

2008\07\18@205230 by John La Rooy

flavicon
face
On Sat, Jul 19, 2008 at 10:28 AM, Jinx <joecolquittEraseMEspam.....clear.net.nz> wrote:

>
> Seems to me that, like the relays which switch secondaries, at certain
> voltage points you could change the SMPS's feedback resistor ratio
> to minimise the voltage drop across the following linear section (if you
> have one)
>
> Could you not just add a zener in the feedback leg of the SMPS so it always
tries to output Vzener volts above the voltage you have dialed?

Then you always have 3V (or 5V or whatever you choose) headroom for the
linear to operate.

John

2008\07\18@212828 by Jinx

face picon face
> Could you not just add a zener in the feedback leg of the SMPS
> so it always tries to output Vzener volts above the voltage you have
> dialed?

Hmmm, so it's tracking but somewhat higher than the required output

I'll look into that. The feedback divider reduces the output voltage
to that of the controller's internal reference, and the controller
switching works to maintain the output voltage by comparing that
feedback voltage to the reference

Possibly a TL431 adjustable Zener might be used ? If voltage setting
is to be done in the linear stage then that information has to go back
into the SMPS section for tracking. Perhaps

Time to open up some app notes ......

2008\07\18@231319 by Apptech

face
flavicon
face
>> Could you not just add a zener in the feedback leg of the
>> SMPS
>> so it always tries to output Vzener volts above the
>> voltage you have
>> dialed?

> Hmmm, so it's tracking but somewhat higher than the
> required output

At the minimum the tracking "preregulator" needs to be a
Vdropout above the linear output.

I used an arrangement a few years ago which I saw also used
recently in a circuit from AFAIR Olin. I had a very nice LDO
linear regulator  with a dropout of a few tenths of a volt.
I placed a transistor across the regulator (say NPN for the
following example) with emitter to ouput and base via  a
resistor to input. Collector via a resistor to a higher
voltage. When across-regulator voltage exceeds Vbe the
transistor turns on and pulls the collector down to Vout. Or
use a PNP and reverese base+R and emitter connections and
collector will pull high from ground when regulator drop is
> 1 x Vbe. Use this to control smps pre-regulator. Worked
very well..
In this case the smps was a CD40106 hex Schmitt trigger
driving an NPN switch to produce 5 volts from 4 x C cells.
When batteries were new the batteries fed via the inductor
to the linear regulaor and the smps was gated off. As
batteries aged *OR* when the local motor load loaded the
batteries below about 5.2V the smps ran. So the logic always
saw 5V. Off state quiescent current was well under 100 uA
including 2 x LDO following.

The regulator was an AIC1722. Taiwanese sourced. Better than
most and very low cost. (??? $US0.10 in volume)

Data sheet
http://others.servebeer.com/misc/ds_aic1722.pdf



   Russell


2008\07\19@081704 by olin piclist

face picon face
John La Rooy wrote:
> Could you not just add a zener in the feedback leg of the SMPS so it
> always
> tries to output Vzener volts above the voltage you have dialed?

I usually use a PNP transistor so that it turns on when the switcher output
is the E-B drop above the linear output.  The collector signal is then the
output high/low feedback into the switcher controller.


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

2008\07\19@091101 by olin piclist

face picon face
Apptech wrote:
> I used an arrangement a few years ago which I saw also used
> recently in a circuit from AFAIR Olin. I had a very nice LDO
> linear regulator  with a dropout of a few tenths of a volt.
> I placed a transistor across the regulator (say NPN for the
> following example) with emitter to ouput and base via  a
> resistor to input. Collector via a resistor to a higher
> voltage. When across-regulator voltage exceeds Vbe the
> transistor turns on and pulls the collector down to Vout. Or
> use a PNP and reverese base+R and emitter connections and
> collector will pull high from ground when regulator drop is
>  > 1 x Vbe. Use this to control smps pre-regulator. Worked
> very well..

Yep, I've done this a bunch of times and it's always worked well.  One
example I can show publicly is in the new ReadyBoard-02
(http://www.embedinc.com/products/ready02/index.htm) schematic.  You can see
the PNP transistor around the 5V LDO on page 1 and the same topology around
the 3.3V LDO on page 3.  The feedback signal from page 1 is also used to
control the buck switcher on page 2 as either of these could be producing
the 6.3V main power rail.

One additional wrinkle in this case is that you have to consider the
behavior of the linear regulator with partial input power.  This is
generally not specified.  It is possible that the output stays off until the
input gets to some threshold.  In that case the PNP would come on because
the input is more than the E-B drop, which would prevent the output from
ever coming up.

There are several strategies to get around this.  One obvious one from
looking at the schematic are the dividers on the PNP collectors.  The output
of the dividers go into a the comparators in the 10F, with the other side of
the comparators tied to the internal 600mV fixed reference.  So for the
switcher output to be considered high, not only must the PNP transistor
conduct, but the switcher output must be high enough to be 600mV after the
divider.  This guarantees that the linear regulator input is reasonably
close to its valid range where it should be producing some output.  In
practise I know these MCP1700 regulators have FET pass elements, and
essentially pass input to output even if the input is a few 100mV less than
the regulation voltage.


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

2008\07\22@094742 by Martin

face
flavicon
face
I'm having trouble visualizing this circuit, could I possibly get you to
draw a schematic?
-
Martin

Apptech wrote:

{Quote hidden}

2008\07\22@095420 by Martin

face
flavicon
face
I posted too soon I just saw Olin's schematic.
-
Martin

2008\07\22@101345 by Apptech

face
flavicon
face
> I'm having trouble visualizing this circuit, could I
> possibly get you to
> draw a schematic?

You could.
BUT I'm about to go to bed (2:15am here) and if you drew
exactly what I described you will probably end up with a
schematic that is correct far sooner than if you wait for me
to draw it for you. If that doesn't work pse advise and I'll
draw it for you.

>> I used an arrangement a few years ago which I saw also
>> used
>> recently in a circuit from AFAIR Olin. I had a very nice
>> LDO
>> linear regulator  with a dropout of a few tenths of a
>> volt.
>> I placed a transistor across the regulator (say NPN for
>> the
>> following example)

This sounds pretty clear -

- with emitter to ouput and
- base via  a resistor to input.
- Collector via a resistor to a higher voltage.

>> When across-regulator voltage exceeds Vbe the
>> transistor turns on and pulls the collector down to Vout.
- Or use a PNP and reverese base+R and emitter connections
and
>> collector will pull high from ground when regulator drop
>> is
>>  > 1 x Vbe. Use this to control smps pre-regulator.
>> Worked
>> very well..



       Russell



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