Simplistic Mosfet HV Shunt Regs - Page 275 - diyAudio
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Old 6th February 2012, 05:59 PM   #2741
stajo is offline stajo  Sweden
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Default Safety question

Hello

This might be slightly OT as a general question but as it concerns this build that might be built by many people that like me is not educated in all saftey rules and regulations, I thought it might be proper to ask here. Eventual answer might even serve as a reminder for others.

Regarding a high voltage FET as IRF840 in this case and the outboard placement of the fairly big sink. What is considered enough saftey rearding that? Is it mandatory to place it completely inside and insulated from a grounded metal case or can the sink be touchable from outside the case if both the sink and the case is properly grounded?

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Staffan
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Old 6th February 2012, 06:38 PM   #2742
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That is what was advised to do. You dont want HV in reach.
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Old 6th February 2012, 07:10 PM   #2743
Salas is offline Salas  Greece
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Read this sticky thread from tubes forum regarding safety. Will link it in post#1 here too.
Safety Practices, General and Ultra-High Voltage
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Old 6th February 2012, 07:55 PM   #2744
stajo is offline stajo  Sweden
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Quote:
Originally Posted by Salas View Post
Read this sticky thread from tubes forum regarding safety. Will link it in post#1 here too.
Safety Practices, General and Ultra-High Voltage
Yes, thats wise. Its a long and mixed thread with various tips, trix and examples tho and maybe its not self-given for everyone not to mount a HV FET, even with isolation pads so its sink is touchable even if grounded.

When reading I came to #49 that said: "UL specifies a minimum of a 4 mm spacing across a surface (PCB) between any "energized" part up to 400 V Peak and a part of opposite polarity or a "dead metal part" (earth). UL then specifies a 8 mm spacing for any voltage up to, I believe 1000 V peak.
"

I dont know what UL is, some countrys recommendations maybe but I think that clearly specifies that also isolation of the sink from being exposed to small fingers or whatever is mandatory.

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Old 10th February 2012, 06:05 PM   #2745
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Salas,
Does this look OK? IT will fir on a standard PCB etch board available here through Radio Shack.
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Old 10th February 2012, 06:21 PM   #2746
Salas is offline Salas  Greece
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Quote:
Originally Posted by stajo View Post
Yes, thats wise.
Staffan
This one from George is a nice electrical safety writeup also:
Electrical Safety
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Old 10th February 2012, 06:25 PM   #2747
Salas is offline Salas  Greece
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Originally Posted by buzzforb View Post
Salas,
Does this look OK? IT will fir on a standard PCB etch board available here through Radio Shack.
Can't foretell if it will have practical problems. Looks a bit wide loop area for one. Is there no sense/force?
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Old 10th February 2012, 07:18 PM   #2748
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I have the sense and force tied together at output. In theory aren't they joined at the same point on the B+ and G rails? Here is alternate.
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Old 10th February 2012, 07:33 PM   #2749
Salas is offline Salas  Greece
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They should be tied at the respective load points after covering the wiring distance. Else you got no ''remote'' but ''local'' sensing. I.e. A classic two wire connection susceptible to wiring length deviations in measuring and counteracting the correct impedance point by the regulator's error amplifier.
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Old 10th February 2012, 07:40 PM   #2750
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Ok. I am going to try the second layout. Well see how it goes.
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