need high dc voltage low constant current diagram

thanks for the answer

I am not good in electronics but i can make device by the diagram. If I make device by these first tree diagrams will I have drop of voltage like I had with those current limitation diodes? With those current limitation diodes I measured voltage before I drop electrodes into water and voltage between them was 56V after I put them in water voltage immediately was cut off on 22V and dropping after that when water starts to filling with ions from electrodes. Same thing happened when I tried this with 33V adapter from one old printer,those diodes cut my initial voltage at the same level of 22V. The 1n5283 diode can handle up to 100V but I did not try to make power source of 100V because I would probably got voltage cut on those 22V as well(which is not enough), I need a lot higher voltage in the start of process so the process last for couple of hours not days like it is now. I prefer fourth diagram but as I said before my load in circuit is not constant so what will happen when resistance of the distilled water drop? If I make device by the fourth diagram will the current stay constant as resistance start to drop? I am asking this because i can not stay near the process all the time and adjusting level of current by the pot.

We have a term for that issue with current sources, and it's called the compliance range. This is the operating-voltage range over which the current-source circuit correctly delivers the desired value. The compliance range for all four of these circuits is very good, since they only need a small minimum voltage for their own operation. I've listed the ranges below:

Ckt Vmin Vmax

1. 1.4V Vbreakdown

2. 0.8V Vbreakdown

3. 5v 85V

4. 3V 500V

As you can see, all the minimum requirements are well below 20 to 30V or whatever you might have struggled with.

Also, the LN150 would allow you to use a high-voltage supply, above 80 volts, which could be dangerous!

Please be careful. You should have a hinged safety enclosure with a breaker microswitch, which disconnects the high voltage unless the lid is closed. Another rule is, one hand behind your back. This is so you can avoid any dangerous through-the-chest shock currents.

thanks again for the info

I am aware of danger from high voltages and because i need higher voltage that I can get(higher voltage=faster process) using of lnd150 will be the best in this case. As i said before i am not good in electronics so can you tell me what will happen with the current in fourth circuit when resistance of load start to drop? Will I need to adjust it by the pot every time resistance is change or current will remain at the same level once I regulate it on the start of the process?

The two-terminal current-source circuit will increase or decrease its own voltage drop to maintain the current you set with the pot. That means as your load resistance changes, and its voltage drop changes, the current-source will take up the difference to maintain the correct current. The whole idea is that you should not have to re-adjust the pot.

Naturally, being as enamored of this scheme as I am, with my "favorite" LND150 part, and all, I've got bench data to show how well it works, or fails to work. Here's a plot that will appear in the third edition of The Art of Electronics, showing the accuracy of an LND150 with a self-biasing resistor to make a current source.

We show three different current values measured over a 1.5 volt to 500-volt operating range. As you can see, if we run the LND150 at 500uA the current increases by 1% as we go above 100 volts, but if we're running it lower at 100uA a 1% increase doesn't happen until we get above 300 volts. If we're running at 10uA we have to push all the way to its 500-volt rating to see a 1% change.

You haven't said how much accuracy you need, but this should help you to see if it'll meet your needs. As usual, there are ways to increase the accuracy by adding more parts.

Well, maximum level of current depends on a volume of anode, in my case maximum current should not bi higher than 0.4mA,it can be lower ten or more times than 0.4 mA but higher no.

So let say that I build power source that can give 480V (lnd150 can handle max 500V), and my current must always be under 0.4mA, it does not matter if current is for instance 0.010mA because with that current I will also get nano size of particles. I measured resistance of distilled water and before process it is around 1.5Mohms.How to calculate what resistance to put between pins of MOSFET(gate and source if I am right)?? I used your fourth circuit in multisim 10.0 and to get 0.15mA in the start of the process i must used resistor of 1.5 Mohm. So initial Voltage (according to multisim) drop from 480 to 215 Volts(which is high enough) and after I lower the resistance of the load to 150 Kohms Voltage drop to 50V and current rise to 0.28mA.. By the time when resistance of the water drops to some 50 Kohms I usually have enough particles in the water so I change the value of load resistance again, this time from 150 to 50 Kohms and mutisim showed me that voltage in the circuit will be 15Volts and current around 0.3 mA(which is less than 0.4 and OK). Do you have any formula to calculate what resistance i must use between pins and do you think that multisim was accurate in this case?

You cannot use Multisim or any other spice to analyze this circuit, unless you have an accurate model of the mosfet, which I'm pretty sure you don't. There are a number of reasons, but one is because spice models fail to work properly in the sub-threshold region. Anyway, you really don't need spice to understand the current source; I have shown you the performance curves. If you have a high-impedance load that can't draw 0.2mA, then the mosfet will sit turned on like a switch with no more than 1 to 2 volts across it, as the curves show, presenting nearly the full voltage of your power source to the load. When your load does finally start drawing current, when it reaches 0.2mA the mosfet will then start using up whatever voltage it needs in order to maintain 0.2mA as the maximum current.

OK

Thanks very much for your answers, you helped me to understand how circuit works!

Best regards

You're very welcome. Your work sounds interesting. There's more I would like to have said, but it could clog up the forum. I'd like to know more about your distilled-water application. Drop me an email, my address is my name, no spaces, at yahoo.com I can tell you a few more details, add a simple high-voltage high-impedance measuring scheme, and if you like send you a drawing of a relevant instrument we made in our lab.

I wrote you an e-mail on WinfieldHill@yahoo.com few days ago but did not got respond yet. Wrong e-mail?

Ooooops, you just posted my email address! Spam city!