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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 30th Oct 2014, 4:40 pm   #1
jim_jobe
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Default Variable HT regulator circuit.

Can anyone point me in the direction of a simple solid-state VV circuit giving up to 100mA or so for adding to an existing 300V valve power supply?
Many thanks,
Jim
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Old 30th Oct 2014, 5:52 pm   #2
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Default Re: Variable HT regulator circuit.

A simple MOSFET source follower will work well, keep in mind the SOA (safe operating area) of any FETs used, you (will?) need a few in parallel. I designed, and implemented, a constant current source at 450V and 10A maximum and ended up with 48 MOSFETs in parallel. OK they where cheap TO220 devices (50p each), in the end it worked out cheaper than a smaller number of bigger ones.
 
Old 30th Oct 2014, 6:35 pm   #3
woodchips
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Default Re: Variable HT regulator circuit.

A Variac with asuitable isolating transformer feeding a choke filter? Not much current limiting though.
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Old 30th Oct 2014, 7:16 pm   #4
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Default Re: Variable HT regulator circuit.

Thanks for those suggestions guys. The last Variac I used almost melted when a careless bystander managed to short it out!
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Old 30th Oct 2014, 7:38 pm   #5
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Default Re: Variable HT regulator circuit.

This may be useful. Plenty of MOSFETS to choose from.
http://www.eleccircuit.com/the-varia...supply-0-300v/
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Old 30th Oct 2014, 8:51 pm   #6
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Default Re: Variable HT regulator circuit.

Cheers,
I've got all those components!
Jim
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Old 31st Oct 2014, 12:23 am   #7
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Question Re: Variable HT regulator circuit.

Quote:
Originally Posted by jim_jobe View Post
. . . . a simple solid-state VV circuit . . .
Please excuse my ignorance, but what does the "VV" stand for?
I assume it is an abbreviation.

Al.
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Old 31st Oct 2014, 12:31 am   #8
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Default Re: Variable HT regulator circuit.

Variable Voltage?
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Old 31st Oct 2014, 10:48 am   #9
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Default Re: Variable HT regulator circuit.

Yes, that's right.
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Old 31st Oct 2014, 11:27 am   #10
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Post Re: Variable HT regulator circuit.

Thank you. I suspected as such - wasn't sure. I've never seen that abbreviation for "variable voltage" before.

Al.
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Old 31st Oct 2014, 1:46 pm   #11
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Default Re: Variable HT regulator circuit.

To make the output smoother decouple the gate to the FET with a resistor from the pot and a capacitor to ground, 100k and 1u would do fine.
 
Old 31st Oct 2014, 3:22 pm   #12
jim_jobe
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Default Re: Variable HT regulator circuit.

Cheers Merlin!
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Old 31st Oct 2014, 3:46 pm   #13
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Default Re: Variable HT regulator circuit.

This seems to fit the bill - pity it's not in English though!

http://www.jogis-roehrenbude.de/Roeh...fs_Pruefer.htm
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Old 31st Oct 2014, 4:06 pm   #14
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Default Re: Variable HT regulator circuit.

Use Google Translate :

https://translate.google.com/transla...htm&edit-text=
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Old 31st Oct 2014, 8:40 pm   #15
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Default Re: Variable HT regulator circuit.

Cheers, that's very useful!
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Old 1st Nov 2014, 11:18 am   #16
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Default Re: Variable HT regulator circuit.

When selecting the potentiometer, make sure it can withstand the voltage and power dissipation of your circuit. Most of the standard metal film resistors are only rated up to 350V.

Mosfets that are made with insulated packages like TO-220F are easier to fit to heatsinks.

Keep the wiring to the gate of the Mosfet as short as possible.
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Old 1st Nov 2014, 12:00 pm   #17
jim_jobe
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Default Re: Variable HT regulator circuit.

Thanks Silicon - I was wondering about the VR rating. I think I've some old wire wounds and I'll sort out one of those. Yes, it's a pity about the IRF840 not being insulated as I want to use the case as a heatsink, so it's useful to know about the TO-220Fs.
73
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Old 1st Nov 2014, 8:33 pm   #18
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Default Re: Variable HT regulator circuit.

Quote:
Originally Posted by jim_jobe View Post
Thanks Silicon - I was wondering about the VR rating. it's a pity about the IRF840 not being insulated
I built a nearly identical circuit using an ordinary 1M carbon potentiometer and an STP11NK40Z MOSFET which comes in an all-plastic package.
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Old 1st Nov 2014, 11:32 pm   #19
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Default Re: Variable HT regulator circuit.

Thanks David; I have some of those I think.
Jim
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Old 2nd Nov 2014, 10:34 pm   #20
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Default Re: Variable HT regulator circuit.

Quote:
Originally Posted by Restoration73 View Post
This may be useful. Plenty of MOSFETS to choose from.
http://www.eleccircuit.com/the-varia...supply-0-300v/
Could someone recommend a suitable (cheapish) transformer to use with this circuit?
Thanks
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