Driver to drive?

Any PSU using a *shunt* regulator is hopelessly inefficent.
Click to expand...
Yeah, that's why I'm trying to get rid of it. I know the GM tube doesn't
draw much current - it spends most of its time not conducting at all. And
the polypropylene capacitors seem to hold a charge pretty well - I've been
zapped by one that had been charged and accidentally left lying on my bench
for at least half an hour.

What regulated voltage do you need ?
Click to expand...
For this application, 500 volts. Some tubes take 900 volts. I'm sticking
with 500 volts because it requires fewer components, most of the tubes I'm
considering are 500 volts, and Electronic Goldmine's selling tiny 500 volt
tubes (I'm using one in testing right now) for $35, which is a decent price
for single-unit quantities.

Scott
 
In article <Mwrqd.15346$9A.288232@news.xtra.co.nz>,
Terry Given <my_name@ieee.org> wrote:
[...]
IRC (the company, I do Recall Correctly) make some great smt resistors.
And have peak pulse power curves.
Click to expand...

IRC person: Hello, how may I help you?

Ken: I need some pulse rated resistors.

IRC person: Good how many box cars full, and where the siding.

Ken: I only need about 100

IRC: 100 Box cars full is a small order but I think we can do it.

Ken: No, I need 100 resistors


IRC: Ha-ha-ha
(Craching sound as he falls out of chair)

Phone: Click Buzzzzzzzzzzzzzzzz


Also IIRC, their spec was weirdly written. It was some time ago but I
remember talking to the technical help from some resistor company and
pointing out that according to the specs, the part could handle less power
for 16mS than it could handle forever.



--
--
kensmith@rahul.net forging knowledge
 
On a Geiger counter I built many years ago from scratch, I used the
recommended
idea of a string of series NE-2s. Worked great. I still have that Geiger
counter and, aside from replacing the tube once, it's still working just
fine!
Click to expand...
The neon lamp tubes? I've seen that done. I'm using 250v varistors
instead. Doesn't seem like it would be any more efficient - it's still a
shunt regulator, and will put a constant drain on the PSU even when the GM
tube's not conducting, right?

Scott
 
normanstrong wrote:

It appears to be a resistor/capacitor substitution box, not a decade
box.
Click to expand...
Nope. It's a decade box. It is set by binary switches thusly:

....
80K \
40K \___ This is a decade.
20K /
10K /
8K \
4K \___ This is another decade.
2K /
1K /
....

A pure binary box would go fron 8K to 16K, and the user would not
be able to independantly set each decade. With this design he can
independantly set each decade, so it is indeed a decade box.
 
Fred Bloggs wrote:

What is it used for? Didn't PC SPICE kill the market for these things?
Click to expand...
Nope. There are plenty of people setting up things in factories,
designing their first circuit, trying to decide exactly how bright
to make the LED they are using, etc.
 
You could do something like shown below with a JFET input OA. This circuit
uses a resistor string to convert the HV into a current, 10uA at HV=500V,
and then an operational amplifier current-to-voltage converter to produce
the A/D sample. The output impedance of the circuit is 10K which most
embedded A/D can handle. If you need less impedance then go to a TL082 and
use the other OA as a buffer. The output clamps at 5V until the input
exceeds approximately HV=400V, and for voltages greater than this the
output subtracts ~25mV from 5V per volt of HV input in excess of 400V-
landing you somewhere around Vout=2.5V for HV=500V.
Click to expand...
Hey, that's pretty slick. I'll have to try that. I know the A/D will work
with 10K impedance. I was also thinking of trying a comparator, but the
buffered A/D scheme only uses the one input pin, and at < 50 cents for the
TL081 that sounds like a cheap, flexible solution. Though it'd be nice to
find some cheap carbon film resistors in > 10 megohms to reduce the parts
count. The high-value thick film resistors go for about $4 at Digi-Key.

I'll do a full writeup on this project when I get a chance. Most of the
hobby kits and published designs I've seen have been pretty simplistic, with
just a speaker and maybe a meter, and the kits sell for about $150 and up.
Mine's got an LCD display and serial interface, and can be scrounged
together for under $50 in its current form.

Thanks for the input...

Scott
 
Joerg wrote:

Hi Graham,

Any PSU using a *shunt* regulator is hopelessly inefficent.


Yes. Should be a nice PWM control instead. Of course, when it is cold a
shunt regulator does have its merits ;-)
Click to expand...
Only if it's a multi kW supply !

;-)


Using 'spare cycles' on an MCU is a truly lousy way to do it btw. Far better a
dedicated controller chip.


Why is that lousy? If the MCU has spare horse power why spend the money
on a PWM chip? Of course, to be safe this would have to run reliably.
Within its own interrupt routine or something like that.
Click to expand...
That's the sort of thing I meant.

Graham
 
Nico Coesel wrote:
Guy Macon <http://www.guymacon.com> wrote:

Nico Coesel wrote:

Looks neat. But why screw-terminals? I would prefer the speaker like
terminals. No tools needed. Or even better: 4mm jacks with screw
posts. So you can connect loose wires or standard test leads without
tools.

Good idea. Do you have a part number that you like (and won't cost
an arm and a leg)? We only made 100 of them, and doing a re-layout
isn't a problem.

Farnell 143-550 looks nice. Around EUR 1.15 if you buy 100.
Click to expand...
Thanks! I will look into it.
 
Blake wrote:

DIP switches are fine for use in set-and-forget applications, but as
controls on a piece of test equipment? I doubt they will hold up very long
in daily use.
Click to expand...
Set and forget is defitatly a target market for me. I have seen
many aerospace test setups where they set it up with a pile of
dec boxes in the test system, and leave them in for the next year
or so.
 
CBarn24050 wrote:

this is a product that is allready in the marketplace for decades
Click to expand...
Not at the price point I am aiming for. I can go as low as $30
each and (barely) make a profit. The lowest-price competition
in my niche is here: [ http://www.oselectronics.com/ose_p65.htm ].
 
From: Winfield Hill hill_a@t_rowland-dotties-harvard-dot.s-edu
Date: 11/28/04 10:44 AM Pacific Standard Time
Message-id: <cod6bb01ssa@drn.newsguy.com

BFoelsch wrote...

Try vodka and Milk of Magnesia some time.

I think that's called a Phillip's Screwdriver...................

................... rimshot!


Hkmm, does that also need OJ in it?

I did come across this,

Phillip's Head Screwdriver
- 3 oz Vodka
- 3 1/2 oz Orange Juice
- 3 1/2 oz Milk

If mixed wrong it tastes like curdled milk, if mixed right it
tastes like a creamsicle with Vodka.

I invented one too, it's black cherry soda and dark rum and it tastes, and
Click to expand...
works, just like Robitussein. I really enjoyed some dry gin and fresh squeezed
lime Friday night, delightful both to the taste buds and the numb buds too.

Rocky
 
Fred Bloggs wrote:

It's gone now- but was your BUY NOW price $199? That's the biggest ratio
of minimum bid I've ever seen.
Click to expand...
$99. I would love it if I could sell these for $99 each,
but two for $99 or three for $99 is more realistic.
 
On Sun, 28 Nov 2004 23:44:09 +0000, Guy Macon
<http://www.guymacon.com> wrote:

John Fields wrote:

Junk.

Translation: good job, Guy! You hit your market (low cost) spot on!
Click to expand...
---
You asked, I gave you my opinion.

That doesn't mean I don't wish you well, I do.

I just wouldn't buy one, that's all...

--
John Fields
 
Shunts are inefficient because they regulate by 'burning off' the excess.
I'd just use it just as a feedback. How to do that with a TLV431 is
explained in a TI app note about isolated flyback converters. I forgot the
number but you should be able to find it.
Click to expand...
I'll take a look.

minimum 'cathode' current of 100uA. Since your application appears not to
be an isolated one this feedback circuitry will become much simpler than
in the TI note.
Click to expand...
Isn't it? It's using a transformer with isolated windings. Doesn't that
make it an isolated flyback converter? Or does that not count because it
feeds back into the +9v rail through the shunt?

Scott
 
Well.... for next to no current draw you could choose a simple inverter.
Simply
choose the turns ratios to suit the supply and take into account Vce sat
on the
primary driver. Wind it so the primary takes next to no magnetisation
current.

Should do the trick. And you could still tickle it with your MCU !
Click to expand...
Gah... I think that went a bit over my head. You're saying to just use an
appropriate transformer to get the required output voltage without the
doubler? Not something I really want to do for cost and time reasons - the
CCFL transformer is a cheap, off-the-shelf part.

As for the primary driver, I replaced the one originally specified in the
design (no longer made) with a BS170 MOSFET set up as a low-side switch.
Not sure how that would affect what you're suggesting.

Scott
 
That shunt would drain your battery rather quickly. Q1 keeps pumping in
energy and the varistors just burn that off. Also, please note that the
metal oxide variety has a finite lifetime. They are like a bank account,
after so many joules they go kaputt.
Click to expand...
Indeed it does... draws about 40 or 50 ma, with < 10 of that being the MCU
and display. Didn't know that about MOVs - one more reason to find another
design.

Thanks,

Scott
 
The TL082 is still available from Radio Shack- as well as 10Meg 1/4W
carbon film 5-packs - so that's a plus, and why I chose that one.
Click to expand...
I'm luck if my local RS has ANY parts. No problem, I order from Digi-Key
almost every week, and I have 10Meg 1/4W resistors by the hundreds. Use 'em
for feedback in MCU clock oscillators.

If you go with the TL082 and don't need the buffer, then a good use for it
would be as low-pass filter and buffer for the 5V shown in the
schematic...this will eliminate your 5V switching noise from the MCU and
other digital switching you have going on there.
Click to expand...
I'll probably try out the direct version and see how much noise it's got.
Would a simple RC network make an acceptable filter if there's a lot of
noise on the op amp output?

Thanks,

Scott
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top