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Old 9th May 2012, 12:26 AM   #101
tomchr is offline tomchr  United States
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Quote:
Originally Posted by jackinnj View Post
The problem you get with transformer based current injectors is that they get saturated pretty quickly (unless it's a really, really expensive transformer) -- you're running the AC + DC current through it.
Yep. That's my guess on what happened as well.

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Originally Posted by jackinnj View Post
Had you seen Jan's article on the "T-Regulator" from Elektor March 2009
I did see the article. As I recall, it's a floating regulator -- not unlike my HV Reg 3.2, in fact. The T-Reg uses a pair of BJT's for the error amp as I remember. Such a regulator works pretty well as long as you can keep the reference voltage clean. That was the fundamental limitation in my design as far as ripple rejection goes, and I suspect it is in Jan's as well.

~Tom
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Old 15th May 2012, 05:11 PM   #102
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Hey there, anyone in germany up for sharing shipping cost?
PM me...
ich würde bestellen und dann weiterleiten, um versandkosten zu sparen
Yurgs
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Old 15th May 2012, 05:49 PM   #103
tomchr is offline tomchr  United States
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Originally Posted by yurgs View Post
Hey there, anyone in germany up for sharing shipping cost?
PM me...
ich würde bestellen und dann weiterleiten, um versandkosten zu sparen
Yurgs
European distributor! Great initiative. Thanks.

The shipping cost from the US to any international destination is $18 flat fee regardless of the number of boards purchased. So the distribution model should work pretty well if you can get a handful of people together in a group buy.

~Tom
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Old 16th May 2012, 05:33 PM   #104
7N7 is offline 7N7  United Kingdom
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Please let me know if anyone is to distribute these in UK or Europe.

Thanks in advance - and compliments Tom, for what looks to be a very fine job!
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Old 6th June 2012, 05:01 PM   #105
JZatopa is offline JZatopa  United States
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Is there any reason I couldn't use this regulator after the silicon ray tube smps?

RTP-15 Switching Mode Power Supply (SMPS) for Tube Amplifier - Boards | Kits | Components | Modules | Tools

Great design, I may try modding my zen select to try to use this regulator.
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Old 6th June 2012, 06:43 PM   #106
tomchr is offline tomchr  United States
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Originally Posted by DJNUBZ View Post
Is there any reason I couldn't use this regulator after the silicon ray tube smps?

Great design, I may try modding my zen select to try to use this regulator.
Thanks. I like my design as well...

Whether you can power the Universal Filament Regulator using the Silicon Ray supply or not depends on the output voltage that you desire. If you're aiming for filament voltages of 3.5 V (maybe 4 V) or below, you can run the regulator off of one 6.3 V output. For other filament voltages (up to near 10 V) you'll need two 6.3 V outputs in series. My Universal Filament Regulator is a buck (step-down) converter, hence, this limitation.

I strongly suggest using WebBench or my recommended values spreadsheet to confirm that the regulator will work for you.

~Tom
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Old 26th June 2012, 10:05 PM   #107
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hi tom,
i've looking for a HV regulator for a few weeks. every time i google about it this topic and your website hits the search. i'm not an audio guy, but i like your design and i'm a fan for obselete MC1466 which is ancestor of LT3080. i'm thinking about to make a HV power supply. maximum output voltage may be 900-1000V. but it must be adjustable in full range, ie 0-900V. also, floating output and short circuit protection is needed. as max nominal output current 10mA is enough for me. i'll use this PS for electrostatic deflection as in the CRT tubes. is it possible to use your design for my purpose? furthermore, consider to using a R-2R DAC as set input of LT3080. so that, an external voltage can control the output. what do you think about this?
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Old 27th June 2012, 12:08 AM   #108
tomchr is offline tomchr  United States
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Good to hear that my website is popular with the search engines...

In my design, the input voltage is limited by the input cap and the cascode device, Q1. I wouldn't go much beyond 800 V input with the values I have in the schematic. And not beyond 575~600 V on the output voltage. But I don't see any reason you couldn't use the topology of my design for higher voltages.

On the topic of current limiting, see my earlier post on the topic.

~Tom
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Old 9th September 2012, 12:33 PM   #109
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Default MOSFET SOA problems

I have been trying to build the design from this thread for a target output of 500V at 500mA approx. for a KT88 parallel push pull amplifier and have come up against many problems.
As far as I can see any linear regulator using recent MOSFET designs other than a very few specific devices will probably fail if the pass element exceeds as few tens of watts dissipation at any time during start-up.
I am not an expert in power electronics but it appears that the extreme optimisation of MOSFETs for switching applications has caused them to become unable to function at even moderate currents at high voltages as the devices have a positive temperature coefficient when operated in linear mode (this means the saturated region of the MOSFET characteristic).
A good description of this topic is found in: http://www.ixys.com/Documents/AppNotes/IXAN0068.pdf or search for 'MOSFET FSBOA' (forward bias safe operating area).
Here’s how I figured out (dumbly and slowly) what was going on …
I first of all tried building a Swenson / Gary Pimm regulator for 500V 500mA and after a cup full of dead MOSFETs turned to the 21st Century Maida design. Same result; my confusion was immense as I was using 24A 800V 600W (!) IXFH 24N80P pass devices (and the TO220 version of the LDO) and as a test load 2 off 60W 240V light bulbs in series (i.e. a 250mA load at 480V output). I looked for RF oscillations, and pondered LTSpice models to no avail.
Trying different loads start-up into anything above a few 10’s of watts of light bulb caused the pass MOSFET to fail for any Vin over 400V. Improving the thermal interface to the large fan cooled heat sink I was using for testing helped – I did this by removing the insulating pad (not a long term plan!), cleaning the heat sink and MOSFET mounting surfaces, using the right size bolt and a big washer and a torque wrench to avoid deforming the transistor package. This got me to being able to start-up at 240V out with 300V in into a single 60W light bulb with the IXFH 24N80P, but at any voltage above that the pass device would fail.
I then theorised that in some way the current limit circuit wasn’t working and hence a current spike on start-up was frying the MOSFET (although I could not see how), or that the gate was getting spiked despite being protected by a Tranzorb diode. Looking at the voltages across the MOSFET on start-up with a high voltage differential probe provided the answer; the MOSFET was breaking down a few hundred milliseconds into start-up at around Id=100mA, Vds=300V with single digit volts Vdg - a power level of only 30W for a 600W device..! At first I suspected a faulty device and tried another batch of IXFH 24N80P’s and then a different MOSFET of similar specification with similar results.
I then discovered the IXYS application note posted, and product advisories from International Rectifier and others setting out the same problem, which the semiconductor fabricators appear none too keen to publicise. Vendors either now don't publish SOA curves for power MOSFETS or if they do they show serious derating for DC operation to no more than 5-10% of theoretical maximum dissipation regardless of case temperature! The problem is according to the various published studies caused by recent (last few years) changes in device geometries.
I thought about IGBTs briefly as an alternative route and then discovered these are even less well understood operating at DC than MOSFETS.
The same IXYS documentation that explained what was going on pointed me to their ‘L’ and L2 ranges of devices as being designed specifically for linear mode operation. The (very expensive ) IXYS IXTK22N100L is specified for substantial dissipations in linear mode and I have now built a (Swenson) regulator using this device which happily starts up into light bulbs and other difficult loads etc at my target power levels. I incidentally want this to work in case the amp is power cycled with hot tubes. In the production build I will use two of these devices paralleled on an earthed fan cooled heat sink with a high performance silicone insulator pad.
Some of the MOSFETS I experimented with also showed very strange partial failure modes – ‘dying’ in the sense that they would go into continuous conduction and then recovering when power-cycled but failing shortly afterwards - spooky eh? I think these failures come about from the fact that all big MOSFETS consisting of many parallel devices, some of which go short-circuit in the initial failure and others of which continue to work. The positive tempco which underlies the problem of linear mode operation means that the hotter devices on the die get more current, and hence the failure of the whole device follows progressively.
Incidentally anybody out there trying to build something like this - wear safety glasses. A number of the MOSFETs detonated quite impressively with lots of flying plastic and device legs.
I've also now build the 21st Century Maida design with the IXYS IXTK22N100L and it works fine too starting up into difficult loads.
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Old 9th September 2012, 01:21 PM   #110
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Quote:
Originally Posted by Kronecker Delta View Post
it must be adjustable in full range, ie 0-900V. also, floating output and short circuit protection is needed. as max nominal output current 10mA is enough for me.
You need a quiet h.v. switching regulator -- the late Jim Williams of Linear Technologies wrote an application note for this, and made a video which is on youtube. https://www.youtube.com/watch?v=e9RX_UPownc
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