Simplistic Mosfet HV Shunt Regs - Page 384 - diyAudio
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Old 16th March 2013, 07:04 AM   #3831
Salas is online now Salas  Greece
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For such conditions I see no reason to change Q3 in the first place.
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Old 16th March 2013, 05:44 PM   #3832
Alex M is offline Alex M  United Kingdom
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As I mentioned a few days ago, I have completed a couple of SSHV2s on matrix board and installed them on the chassis of my RTP3. These are working almost fine at the required current and voltage.

I have one question: the heatsinks for the current regulators (Q1) get quite hot, even though they are passing only 70mA with an input of 345V and a regulated output of 300V, which I calculate should only dissipate just over 3W. The sinks on the CCS device are rated at 3.9C/W, so should be only 12 degrees or so above ambient, but are uncomfortably hot to the touch, and are definitely hotter than the ones on the shunt MOSFETs, which I reckon are dissipating 4.5W at the shunt current of 15 mA. Is this indicative of some FR instability?

Alex
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Old 16th March 2013, 06:27 PM   #3833
Salas is online now Salas  Greece
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Probably. Use 0.1uF directly across the regs input to decouple them and see if something changes. I would expect 15C above ambient, 20C the most if convection isn't optimal.
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Old 16th March 2013, 08:46 PM   #3834
Alex M is offline Alex M  United Kingdom
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Quote:
Originally Posted by Salas View Post
Probably. Use 0.1uF directly across the regs input to decouple them and see if something changes. I would expect 15C above ambient, 20C the most if convection isn't optimal.
I had another look at your construction instructions and realised I had missed the vital phrase "Keep last raw DC filter capacitor near the regulator's input"...

I have put a 0.22uF cap (what I had at hand) right at the regulator input and all seems rather more stable.

Many thanks!

Alex
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Old 16th March 2013, 08:51 PM   #3835
Alex M is offline Alex M  United Kingdom
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Another question: is the function of the network R6/C1 as a low-pass filter, or is it an impedance correction for stability? How critical are the component values here?

I wonder whether a 1/4W resistor for R6 will have a high enough voltage specification in this position in some applications - the 0.6W MF parts I use have a rating of 250V, which doesn't seem enough for a 300V output, and I'm tempted to upgrade this to a 2W resistor with a commensurately higher voltage rating. I have no real feeling for what the maximum voltage will be across this component - I guess it will depend on the rise time of the raw DC input.

Alex

Last edited by Alex M; 16th March 2013 at 09:15 PM.
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Old 17th March 2013, 03:40 AM   #3836
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Its the latter. A "snubber" or Zobel network more precisely. Voltage drop across that resistor will be insignificant because it just poses "ESR" there. That capacitor has all of it across in essence. The values are critical enough and better not be altered unless someone optimizes damping for a specific load evaluating with lab gear. In general its a little wonder how this design interfaces with so many people's stuff without a multitude of major drama stories. One thing is I don't push the spec too far on purpose, it could be impressive to have 1/3 the now Zo and 3x the now bandwidth, but it would not be generally easy to get widely applied with simple means and no deeper understanding effort. There is a point of diminishing returns subjectively also, so its a juggling act to make a useful general purpose solid state HV shunt reg with some field success. Until now it seems serving the goals rather satisfactorily is my impression. The main purpose is to bring good tonality regulation in compact space with better damping for little money and weight VS iron clad traditional passive filtering cells. A rail hum killer with added value and good sonics in other words.
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Old 17th March 2013, 08:14 AM   #3837
stajo is offline stajo  Sweden
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Is it any electrical downsides to be mounting both the DN2540 CSS and the shunt mosfet on the same sink, underneath, if its fairly big?
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Old 17th March 2013, 08:28 AM   #3838
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I don't think so, but insulation will have to be perfect with pads that are well rated. Now if an oddity occurs with some parasitic against the big sink and its level reference, can't predict.
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Old 17th March 2013, 08:35 AM   #3839
vgeorge is online now vgeorge  Greece
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In my first built point to point I put everything in the same sink and could not see anything wrong with it on the scope, except not being very elegant!
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Old 17th March 2013, 09:19 AM   #3840
stajo is offline stajo  Sweden
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Thick aluoxide pads I guess is minimum at those voltages. And even that doesnt live up to electrical norms and standard which I think say like tou have to keep some 1,5 mm distance between hot and ground. And that is hard with a thru hole metal screw. Clamps would be the most appropriate I guess.
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