Need 1 amp, 24volt from a 25KVDC supply

[Zaphappy]

I have an application for remote operation of equipment. The only source available is 25KVDC. Is it possible to configure
a string of mosfet current sources well over the total Vdss rating of the fets or is this a ridiculous approach ?

I would of course follow this with a voltage regulator to power the low voltage electronics.

Any thoughts ?

 

[barry]

I can't believe 25KV is the "only" source available. Where does the 25KV source get its input, from a 25KV wall outlet?

But if 25KV is really the only source, I would let somebody else test my circuit.

Obviously, you are not going to get 1 amp from any kind of linear approach, you would have to use some kind of switching regulator. It all sounds just too scary to me.

 

[Zaphappy]

25KV scary ?? Nah:grin: But I see mosfets with ratings of hundreds of amps and volts so is it really that crazy ? How about some clues on the impossibleness of this approach.

 

[FvM]

Cascaded converters (primary series - secondary parallel connected) are quite common for the MW power range, e.g. in electrical traction applications. For low power, the overall effeciency will be most likely low and the effort uncomfortably high. But basically feasible.

 

[barry]

25KV scary ?? Nah:grin: But I see mosfets with ratings of hundreds of amps and volts so is it really that crazy ? How about some clues on the impossibleness of this approach.

Hundreds of amps? Pulsed, maybe. 25KV, I don't think so. But I'll defer to others here, my voltage limits don't go that high. If it can arc, I don't want to know about it.:wink:

 

[goldsmith]

Hi ZapHappy
As Barry said it seems a bit more unusual ! but i can imagine that you have a source such as that . can you tell us what is it's base source ? cells ? a generator ???!!!!!! ( this option is impossible ) . solar cells ? ( many many solar cells ? ) if you can't tell us , the main source because of each reason ( i know why this high rate voltage and current can be used , but i don't think that your field is what is in my mind ! )
Anywhere , consider that you have that , a notice : that voltage with that current can be pretty dangerous if you walk near by it , it will be your latest time to be in this world alive ! ( each kilo volt , needs at least one mm gap ( if it is DC ) but because it is high current source and if it is under load , the filed of it , can be pretty dangerous ( more that you can think about it ) . a reasonable solution for your aim , can be a vacuum tube oscillator , ( tuned with transformer ) and a perfect isolator ! if you tell us more about it , perhaps we can help you more !
Best Wishes
Goldsmith

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By the way , series arrangement of mosfets can be ok too , but it needs more experience .

 

[jeffrey samuel]

getting power from 1 A and 25 V supply of about 25 kW is i think impossible kindly rephrase the question

power = V*I

the power can never exceed 25 W in your need

 

[goldsmith]

Hi Jeffrey

getting power from 1 A and 25 V supply of about 25 kW is i think impossible kindly rephrase the question

For my opinion it is not impossible , but it needs more experience . ( if He / she has ! )

the power can never exceed 25 W in your need

He/she told that that power is required ( 24 v 1 A =24 VA ) .
Best Regards
Goldsmith

 

[jeffrey samuel]

my pal when i go fro MOS then can i get some ckt which can be tried out

thanks strange though to learn to limit current and voltage but deliver such high power

how will this power be dissipated then ?????????

 

[goldsmith]

Jeffrey
He/she told 24 volts 1 A from 25000 volts .

getting power from 1 A and 25 V supply of about 25 kW is i think impossible kindly rephrase the question

power = V*I

the power can never exceed 25 W in your need

 

[jeffrey samuel]

Jeffrey
He/she told 24 volts 1 A from 25000 volts .

thanks for clearing me sir sorry guys for the misconception

sorry again

 

[goldsmith]

thanks for clearing me sir sorry guys for the misconception

sorry again

Don't worry ! sometimes , i misunderstand somethings too ! :wink:

 

[jeffrey samuel]

dropping such a large power is not economically viable even if we use such a ckt the initial current op from the setup will be high this has to be reduced furthur using current limiters

this involves too much circuitory that may not be so pleasant to watch and build

 

[FvM]

The "string of mosfet current sources" point in the original post suggests a linear voltage regulator which is completely unrealistic because it involves 25 kW power dissipation. A switching regulator is basically feasible, but no fun.

 

[jeffrey samuel]

i don't think this is really advisable to carry out in real practise the losses will be too much and this is really a waste to practise it out

 

[goldsmith]

i don't think this is really advisable to carry out in real practise the losses will be too much and this is really a waste to practise it out

Hi Jeffrey
Loss ? if you go through SMPS with frequency around 2 KHZ , or less , it will be ok , current is just 1 amperes , if you use mosfets in series together with 0.5 ohms or less Rdson you will have around 28 ohms .
Dissipation will be negligible ! because of pretty low duty cycle .
Best Luck
Goldsmith

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By the , way , to prevent some bad effects it is better to use multistage SMPS ( step by step reduction )

 

[betwixt]

goldsmith, please tell us where to get SMPS switching transistors, MOS or bipolar which are rated at 25KV.

Brian.

 

[goldsmith]

Hi Brian
No , you can't find switches with 25KV rating , if you read my latest posts , carefully , you will see that i have mentioned mosfets as series together . i told 0.5 ohms as Rdson ( for IRFP450LC is 0.27 ohms ) and then will have equally 28ohms it means some of them in series together . perhaps my words were not as clear as enough .
However i agree it is a bit time consuming to match them together , but if it is important to do this project , it is one of the best ways . ( it needs some advanced feed back loops to be sure that mosfets have overlap and all of them are in )
Best Regards
Goldsmith ;-)

 

[FvM]

The necessity to use cascaded transistors has been already recognized in the original post ("a string of MOSFET"(s)).

I have no doubts that a switched mode supply with similar parameters can be implemented. But I won't suggest it to anyone without profound knowledge in power electronics and HV techniques.

 

[goldsmith]

Hi again
Yes i'm agree with FvM . High voltages with ability of high current handling will be pretty dangerous , and i saw some explosions ! humans ! burning or something worst ( i was in HV laboratories for some month but i couldn't tolerate events there ! consider your friend be dead and you see his dead and you can't do anything for him i have many bad experiences with 5KV but 25 KV is very higher and more dangerous . and at last i preferred to leave that group ) . hence , i think it needs deep knowledge too . and after that some precise equipments and an isolated room . and some other specific materials .
And a thing for more fun , but i believe it is terrible , i saw a man , that became powder with an Arc of 400 KV . he was a friend ! after those events , hardly i can work with these systems . hence when i'm typing on this thread , my fingers are shaking .
Good luck and be careful .
Goldsmith