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Old 13th February 2010, 06:30 PM   #971
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D5 & D6 are for transients by mishandling. Work for any Mosfet regardless of the circuit's DC levels, its for avoiding gate punch through. D1 is a 150V 5A Zener so to protect the CCS Mosfet when there is potential to see over 200V (its max spec), say in an accidental swift short. If your DC In is not over 200V in the first place, that Zener is redundant. That said, there are many examples of finely working Simplistic Regs in this thread for a long time without Zeners. Its for when plugging or unplugging carelessly or tweaking, recycling on/off etc. Just to know how to apply.
I wonder about the necessity of D6, since IRF840 has maximum VDSS of 500 Volt.
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Old 13th February 2010, 06:37 PM   #972
Salas is online now Salas  Greece
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You probably mean D5. The gates have an oxide layer that has about 20V max before they become Swiss cheese. Don't mix it with VDS max.
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Old 13th February 2010, 06:49 PM   #973
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Originally Posted by Salas View Post
You probably mean D5. The gates have an oxide layer that has about 20V max before they become Swiss cheese. Don't mix it with VDS max.
Indeed, I meant D5. If VDS Max. is 20V, then 150V Zener is as good as no Zener at all. May be it takes 18-19 Volt Zener?
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Old 13th February 2010, 06:55 PM   #974
Salas is online now Salas  Greece
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This is VGS we are talking, not VDS which is our Vout here. If an input transient hits a thin oxide gate, its history, regardless of the DC level of the circuit. You must have seen protection Zeners across G,S in some Mosfet amplifier schematics.
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Old 13th February 2010, 07:21 PM   #975
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Sorry. My confusion is cleared now – I didn't note at first that D5 and D6 are 12V Zeners.
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Old 13th February 2010, 08:44 PM   #976
Salas is online now Salas  Greece
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No worries. Essentially D1 may only be called for in real reg use anyway. 99% it is all protection it might come handy. D5 and D6 could be called for mainly when testing with probes. Fully deployed gate protection takes 2 at each gate, one towards negative too. Was just an example.
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Old 13th February 2010, 09:40 PM   #977
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Thanks.
I got what you said.
It seems to me that protection is very useful while testing and debugging the regulator.
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Old 15th February 2010, 09:38 AM   #978
massimo is offline massimo  Italy
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Salas, in your last Simpler Simplistic schematic, safety diodes aside, you added R10 (47 ohms) and change Q1 from IRFP9240 to IRF9610.....
What's the role of R10 and why a smaller Pmos now?
I remember since LV Simplistic Shunt you were always in favour of beefy TO247 mosfets over smaller TO220s.
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Old 15th February 2010, 04:57 PM   #979
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R10 helps the cap even out the performance in the VLF without making the component value big. I wanted to make it full TO-220 since its only few mA in HV and IRF840 is TO-220 already, and see if it holds. I tested it and it does. For same mounting in both elements, cheaper and faster part.
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Old 16th February 2010, 03:41 PM   #980
fnemick is offline fnemick  United States
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Hi guys, my first post on this site!

I've ordered parts to do a build, except for the 2sk170. I have a couple LSK 389a ( 0-4ma I Believe) and was hoping I could sub it. Any problems? Be forewarned I am pretty much a solid state newbie

Thanks Frank
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