From looking at Dr Dunk's assembly, and reading his posts, I'm guessing the current is picoamps. I was gonna propose a 200V shunt regulator that had a "virtual ground" made of a resistive divider, and four 1 Meg pots for the four lenses, but your design is probably simpler. My design does use a small 1:1 isolation transformer instead of an 80V transformer.

__________________
Ron (aka Rube)

 

Hi guys,
Many thanks to Roff, Hero, and all for the ongoing help. You guys are a treasure trove of resources!

One thing to consider. The +/-100V is a nominal value. I put this value, as I thought that any value would be possible to achieve, not realising that it would require a specialised transformer (as per Hero's post). If it simplifies things, then pick any maximum voltage over say 50V, up to 230 V..

Hopefully the value of 100V hasn't lead to head scratching on how to achieve it..

Also, to have four outputs, is it simply a matter of building four such circuits, or could they all be taken off the same transformer?

Cheers!

 

Is there some reason why the power supply out of a disposable camera won't work. In combination with a wall wart it has to be the simplest and cheapest solution. You can even buy the parts at the local grocery store.

Mike.
Edit, just looking around I found this site. Just remove everything to the right of the "large cap" and you have a 200V+ supply.

 

Beats me Mike! Thanks for your suggestion, and I will be sure to check it out tomorrow when I get to work (I have gone over my bigpond allowance at home, and I have been dropped to 64 kbit/s... )

 

You don't need four circuits, just four 20k potentiometers.

Notice that it forms a potential divider which is adjusted by the knob's position?

A capacitor charger might work but it isn't ideal since he wants a regulated supply and it also needs to be capable of producing both positive and negitive voltages.

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I also post at the following sites:
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Screen name: Aloone_Jonez
And http://www.silicontronics.com, same screen name as here.

 

Check out the attached circuit. give feedback on outcome.

Attached Images

Psupply.jpg (60.0 KB, 36 views)

 

A current limiting resistor and 4 * 51V zeners with a center tap on the zeners will give a totally isolated ±100V supply, you can earth the center tap if desired. Although the output voltage will be dependent on the tolerance of the zeners, it will be constant, that is, it may be 105V but will be a constant 105V. Multiple 1MΩ pots could be used to vary the output.

Mike.

 

I started out thinking zeners, but the tempco of the standard ones are higher than the OP was looking for. There are compensated zeners available, but I thought they might be difficult to obtain (or hard to get ).

__________________
Ron (aka Rube)

 

As the current is so low then the zeners shouldn't get hot and the Tc in the first data sheet I found (BZX79C51) was 40mV/°C. If you choose the current limiting resistor correctly then most of the current will flow through the output pots. If nothing else, it's cheap and can be tried easily.

DrDunk,
You state 0.1% variation over the day. Is this realistic as I doubt that you can position a pot to better than 1%.

Mike.

 

G'day Mike,

It is an ideal.. I suppose that +/- 1V would also be acceptable, however if it was to drift throughout the day, then this would not be good. As the electrostatic lenses are used to deflect a beam of ions, any drift in the voltage would mean that the ion beam would shift off axis and not pass through the machine..

BTW, in the interest of giving you all a better understanding, I have attached a pdf schematic of the machine I am building. The parts that we are discussing are in the "extraction chamber". The chambers shown are all vacuum chambers, with resting vacuum of better than 10^-6 torr (for reference you are sitting in around 760 torr right now)

Apologies that this is outside the scope of "electronics" however thought that you may be interested..

The machine is a time of flight (TOF) mass spectrometer coupled to a photoelectron spectrometer (the long tube). In a nut shell, ions and cluster ions are produced in the ion source, accelerated along the TOF axis, and overlapped with laser radiation in the "Laser interaction chamber". In this region, electrons are forced off the anion clusters, and are directed along the flight tube. We measure their energy, which is related to their molecular origin! With this machine it will be possible to follow the course of chemical reactions!

Anyway, as I said it is outside the scope of this forum, however it has some nice applications of electronics associated with it.

Cheers!

Attached Files

ModifiedSetup.2.pdf (19.4 KB, 22 views)

 

Hi all,

Thanks for all for your help. I will be starting construction on these things in the coming weeks, and will report back on how it goes.

Unbeknownst to me, the department had hired an electronics technician and he arrived today.. I just met with him, and showed him the designs, and he was mightily impressed (thanks again). He will build them, and then I will report back.

Cheers

 

Did you tell him about this forum or are you planning to take credit for the ideas?

I also forgot to mention that the absolute maximum input voltage from the transformer is 99VAC, any higher than this and the zeners across the LM317 and LM337 will start to conduct which will cause the output voltage to rise and if it's increased further the zeners will be toast. I chose an 80V transformer as assuming regulation of 10% (the output being 10% higher than the rating when unloaded) and a high mains voltage it should be alright.

You can buy the LM317 and LM337 in higher voltage rating of 60V, this will allow you to use 60V zeners and allow the input voltage to go up to 113V, you can also connect zeners in series with the rectifiers to further reduce the output.

If you can find a suitable 80V transformer then you don't need to worry about the above but I just thought I'd add those comments just incase you find yourself restricted to transformers with ratings of say 110V.

__________________
I also post at the following sites:
http://www.stop-microsoft.org http://www.heated-debates.com
Screen name: Aloone_Jonez
And http://www.silicontronics.com, same screen name as here.

 

The conversation went something like this;

Me: "Hi there Electronics guy, the name's DrDunk."
Him: "Hi DrDunk, nice to meet you, what can I do for you."
Me: "Ahhh, don't ask yourself what can you do for me, instead ask, what can I do for you..."
Him: "What the?"
Me: "We can make a shiteload of money off these great bipolar supplies that I have thought up"
Him: "Ya what?!? Top effort! My first day, and already on a winner..."
Me: "True... Here's my design."

Apologies, that was very lame. Of course I told him straight away about this excellent forum and the wonderful gurus there waiting to help. I am a scientist, and plagiarism is a big no no...

Thanks for the extra info, I will pass this on to him.

An interesting point, this guy has had a varied life. He actually patented a revolutionary technique to safeguard VCRs from being dubbed.. Apparently they were sold in Russia?!? However then it went belly up when the DVD came out...

Cheers!

 

Sounds like a cause for celebration, just open a few cans of Fosters and put another Quokka on the barbie.

JimB

__________________
Experience is directly proportional to the value of the equipment ruined.

 

Fosters!?!? Only tastes good in Europe. Over here it takes like run off from a peat bog...

And as for the quokka, can't eat them. Being endangered is not the problem, they are too stringy and hard to swallow..

Anyway, apologies for going off topic, thanks again for all the help!