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Old 14th March 2007, 03:02 AM   #11
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Quote:
Originally posted by Brian Beck
Ah yes, the LM317"H". Of course that's the old TO-5 style can, which I think is now long obsolete. With a mere 60mW of dissipation, it needed no heatsink.
There's a TO-220 LM317HV currently available, rated for 60Vdiff, that's what I've used.
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Old 14th March 2007, 11:20 AM   #12
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Be mindful that when you go over 600V on a printed circuit board -- high voltages really like to creep, there is a high probability of dielectric breakdown, you have to take special care to protect yourself from any accidental, lethal contact.
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Old 14th March 2007, 01:22 PM   #13
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Quote:
Originally posted by leadbelly
There's a TO-220 LM317HV currently available, rated for 60Vdiff, that's what I've used.
Leadbelly,

Thanks, I haven't used that one before. Of course, once you decide you need an additional HV transistor(s) to stretch the voltage out, you can set the voltage across the 317 to anything you want by the zener choice.

By the way, the 317 is an old stalwart that I refer to it out of habit, and because I still have a parts bin full of them. But there are other, even better, 3-terminal floating regulators out there. I'm thinking of the LM108x/LT108x series in particular, which feature lower drop-out voltages and higher current (neither feature is an advantage in most HV tube supplies). The Maida design works for them too.

Jackinnj, Good advice. For HV traces on PC boards, keep lots of copper-free distance between traces, and of course safety should always be a concern when using HV with either PCBs or point-to-point wiring.
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Old 14th March 2007, 02:54 PM   #14
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Quote:
Originally posted by jackinnj
Be mindful that when you go over 600V on a printed circuit board -- high voltages really like to creep, there is a high probability of dielectric breakdown, you have to take special care to protect yourself from any accidental, lethal contact.
I usually allow 1mm per 100V, rounding up,as a rough rule of thumb, so 240v =3mm, 110v=2mm etc.
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Old 14th March 2007, 03:46 PM   #15
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A solder mask will help as well.
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Old 23rd September 2007, 03:19 PM   #16
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Quote:
Originally posted by SY
Use a 1kV transistor or MOSFET and it will work fine and forever.
Being far away from my hobby room, I do spend my DIY hours trying to understand working principles of things: on the agenda for this week is a higher voltage / high current Maida: le't target 600V and 300mA. Quite serious and dangerous, I know!

From what I understood, due to lower beta of HV transistors, the 300mA figure can not be supplied by a simple transistor without implying in some serious current drawn by the base, and a Darlington will have to be used. I searched for a 'complete package' and found the NTE2558, listed at about US$ 20,00, but not found in the Netherlands (neither in Chile, where I reside for the moment). But still, could this one be used? (datasheet attached)

The second option is to make a Darlington. Although one of the transistors may be smaller, it's hard to find small, HV transistors. The smallest (and cheapest at euro 1.20) I sourced is the 2SC3886A (NPN transistor 1500V 8A 50W). I think this one could be used in both positions!?

But now, the main question. SY mention the use of a 1kV MOSFET. Is it possible to just substitute the single HV transistor for a MOSFET, and would the MOSFET be able to pass the 300mA without problems? I mean, won't it suffer from the same limitations as the single transistor? Sorry, I am not very familiar with SS stuff. The MOSFET I have in mind is the 2SK1119 (N channel MosFet 1000V 4A 100W).

I thank you for the attention and comments!

Erik
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