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?
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.
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.
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.
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?
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?
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.
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.
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.
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
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.
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.
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.
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?