bipolar voltage supply with zero crossing (+/- 100V)

[DrDunk]

Hi all,
Apologies in advance is this may seem a naive question, or if it has been covered before.

I am a Physical Chemist, working at a Uni in Australia, and I need to have some voltage supplies for electrostatic lenses of a mass spectrometer. The supplies need to be bipolar, and be tunable from -100V to 100V out of the one channel (i.e. not unplugging the leads). In all I need four independent supplies. The current would be very low, as the electrostatic lenses are isolated from ground.

A group I worked with in Germany had six electronics gurus who made these things, however here I have not much support!

What I am looking for is an answer to the question, can these be made easily? Does anyone have an idea on how this can be done?

I would really appreciate your help!

 

[DrDunk]

By the way, I said that I was a Physical Chemist to highlight the fact that I am a simpleton when it comes to electronics!

 

[Nigel Goodwin]

Can you get the circuit diagram from the previous electronics guys?, as it's a proven working design it seems silly to reinvent the wheel?.

 

[DrDunk]

Hi Nigel,
thanks for getting back to me. Unfortunately, they are not being very forthcoming with the schematics. I have asked a few times, and been fobbed off. I will ask again, however I am not hopeful!

Just wanted to see if anyone had an idea of how to do it, as I am challenged when it comes to these things.

 

[specie]

Hi all,
The supplies need to be bipolar, and be tunable from -100V to 100V out of the one channel (i.e. not unplugging the leads). In all I need four independent supplies. The current would be very low, as the electrostatic lenses are isolated from ground.

Can be done, how low (ie current) are we talking here?

 

[DrDunk]

G'day specie,

Thanks for your post! Here I will show my lack of knowledge... As the plates that I wish to apply the voltage to are isolated from ground, am I right in thinking that the only current flow will be due to the slight capacitance that the plates will have? By this I mean that the current will flow only during the initial charging of the plates?

I have not calculated the capacitance, however I have a journal article that has some equations for doing this for different plate shapes etc (i.e. whether they are circular, rectangular, etc)
Yuanshun Chi, European Journal of Physics, volume 17 pages 363-364

For a different application, with bigger plates than the ones I plan to use here, I calculated a capacitance of 5.5 pico Farad.

From this, I would imagine that the current flow would be negligible.

Cheers!

 

[DrDunk]

G'day again,

Apologies for the next "stupid" question, however can I get a feeling from you all of what is considered to be a "low current"? My thinking would be that 500µA or below would be a low current, am I right?

Cheers!

 

[Roff]

G'day again,

Apologies for the next "stupid" question, however can I get a feeling from you all of what is considered to be a "low current"? My thinking would be that 500µA or below would be a low current, am I right?

Cheers!

That's pretty low, but the lower it is, the easier it is to do. What sort of temperature stability do you need (ppm/deg C or %/deg C)?

 

[DrDunk]

G'day Roff,

Thanks for your reply. By temperature stability, do you mean the stability of the voltage output with respect to environmental temperature (i.e. of the lab), or the stability of the components?

I would think that as long as the voltage did not change by 0.1% over the day, then this would be fine.

Cheers!

 

[Roff]

G'day Roff,

Thanks for your reply. By temperature stability, do you mean the stability of the voltage output with respect to environmental temperature (i.e. of the lab), or the stability of the components?

I would think that as long as the voltage did not change by 0.1% over the day, then this would be fine.

Cheers!

Is it being used in a stable temperature environment? I'm assuming that a lab would be air conditioned (or whatever the local term is ).

 

[DrDunk]

The lab is air conditioned, and will not change much throughout the day.

What would you consider stable? +/- 5 degs?

 

[Roff]

The lab is air conditioned, and will not change much throughout the day.

What would you consider stable? +/- 5 degs?

That's good enough. Do you have 220V mains? I think you can see I'm leading up to something here.

 

[DrDunk]

Yep I do (have 220V), and how much does the unit you produce cost?? Or is this not what you were leading up to??

(Apologies if this appears cheeky..)

 

[Roff]

Yep I do (have 220V), and how much does the unit you produce cost?? Or is this not what you were leading up to??

(Apologies if this appears cheeky..)

LOL!
No, I don't produce anything. I just have a fairly simple design that might work.
I have it designed, but I need to do a little research on components before I post it, and unfortunately it's past my bed time.
I'll get back to it some time tomorrow.

 

[specie]

Hey DrDunk,
You do not come across as a complete ignorant in electronics . Anyway, with the conditions you specified, it will not be much of a problem. Will get back to you with a circuit latest monday. I do not have access to the net on weekends

 

[DrDunk]

Thanks to both of you! I really appreciate the effort.

It will be great to have some circuit diagrams, as I have a couple of 3rd year students who would love to give it a go building them.

 

[Hero999]

In all I need four independent supplies. The current would be very low, as the electrostatic lenses are isolated from ground.

How much electronics do you know?

Do all of the channels need to be isolated from each other?

If so it would be a pain as each power supply would need to be run from a separate isolation transformer, unless you can find a transformer with four separate 0-75V windings.

 

[DrDunk]

How much electronics do you know?

Do all of the channels need to be isolated from each other?

If so it would be a pain as each power supply would need to be run from a separate isolation transformer, unless you can find a transformer with four separate 0-75V windings.

When you say isolated from one another, do you mean with separate grounds? I think that if all four channels had a common ground then that would be fine. In fact, what I have done with the supplies I used before in Germany was to take the ground from each channel, and actually ground it to the mass spectrometer.

 

[Hero999]

Yes, that's exactly what I meant.

I'm thinking you could use a 75V transformer and some sort of linear regulator with a push-pull output to give +-100V but I'll wait until Roff comes back before I have a go at sketching a design for you.

 

[Roff]

Yes, that's exactly what I meant.

I'm thinking you could use a 75V transformer and some sort of linear regulator with a push-pull output to give +-100V but I'll wait until Roff comes back before I have a go at sketching a design for you.

Hero, go for it if you want to. I'm struggling with the following issue...
Dr. Dunk, if the lenses draw zero DC current, the solution should be relatively simple. If not, it seems like it gets complicated.
Don't you have a specification on these lenses?