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4hv.org :: Forums :: High Voltage
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Putting many diodes in series for a HV diode.

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Antonio
Wed Jun 22 2011, 12:36AM
Antonio Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
I have used strings of 1N4007 diodes for low-frequency applications without equalization, and they work as expected or better, with low leakage, and very uniform maximum voltage. One string failed, probably due to excessive reverse current, since they are not avalanche rated. The failed diodes look normal, but their leakage current is measured as much higher that the normal.
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Patrick
Wed Jun 22 2011, 01:41AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ash Small wrote ...

Proud Mary wrote ...


I think all EE courses should have an industrial economics module, because 99% of real world EE is concerned with manufacturing products or providing services which must compete in the marketplace.


It's called 'Production Engineering' (part of most engineering courses), something which most 'academics' have little time for... smile
Unfortunatley I have to agree.
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cedric
Wed Jun 22 2011, 10:14AM
cedric Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143
Patrick wrote ...

Ive seen a few mentions here on the forum about putting many diodes in series to make a single Hv diode, my question is...

[Given a square wave of 100kHz at Hv with a steep V rise and fall at 10-20kV,at a Duty cycle of about 50%.]

(2) Would the HER108 be a good chioce? I have 700+ Pcs.
(says nothing about avalanche, so I presume its not rated.)

I check your reference diode and it's not gonna work at 500 khz or at list it's gonna get very hot witch is bad for avalanche rating...
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Patrick
Wed Jun 22 2011, 05:34PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
cedric wrote ...

I check your reference diode and it's not gonna work at 500 khz or at list it's gonna get very hot witch is bad for avalanche rating...
I didnt say 500kHz, and I dont think the HER108 has avavalanche capability.
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Pinky's Brain
Wed Jun 22 2011, 07:27PM
Pinky's Brain Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837
Resistors only take care of the static voltage sharing any way ... not the dynamic voltage sharing during turn off.

If you didn't have all those diodes I'd say just go for avalanche rated ones ... since you do, just add more and hope for the best. Given all the dynamic processes inside the string (lots of Ls, lots of Cs, lots of diodes snapping off suddenly and at different times) trying to calculate anything by hand would be futile ... and diode models in simulators aren't generally accurate enough to model reverse recovery.
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Patrick
Wed Jun 22 2011, 07:28PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Pinky's Brain wrote ...

Resistors only take care of the static voltage sharing any way ... not the dynamic voltage sharing during turn off.

If you didn't have all those diodes I'd say just go for avalanche rated ones ... since you do, just add more and hope for the best. Given all the dynamic processes inside the string (lots of Ls, lots of Cs, lots of diodes snapping off suddenly) trying to calculate anything would be futile ... and diode models in simulators aren't generally accurate enough to model reverse recovery.
These are the things I worry about, and why I ask for many oppinons.
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Proud Mary
Wed Jun 22 2011, 07:33PM
Proud Mary Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Patrick wrote ...

cedric wrote ...

I check your reference diode and it's not gonna work at 500 khz or at list it's gonna get very hot witch is bad for avalanche rating...
I didnt say 500kHz, and I dont think the HER108 has avavalanche capability.

Of ten manufacturer's data sheets I checked, MRRT is given as either 70 or 75 nS.

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Patrick
Thu Jun 23 2011, 12:15AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Proud Mary wrote ...

Patrick wrote ...

cedric wrote ...

I check your reference diode and it's not gonna work at 500 khz or at list it's gonna get very hot witch is bad for avalanche rating...
I didnt say 500kHz, and I dont think the HER108 has avavalanche capability.

Of ten manufacturer's data sheets I checked, MRRT is given as either 70 or 75 nS.


The way i see it 100kHz shouldnt be a problem at 75nS.
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jpsmith123
Thu Jun 23 2011, 03:10AM
jpsmith123 Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
I would've liked to use strings of diodes-in-series too...but for the PITA of making the circuit boards and drilling so many holes and having to solder so many pieces...I decided not to.

Too bad someone doesn't sell circuit boards designed for this purpose, already etched and drilled.

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cedric
Thu Jun 23 2011, 12:48PM
cedric Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143
Patrick wrote ...

cedric wrote ...

I check your reference diode and it's not gonna work at 500 khz or at list it's gonna get very hot witch is bad for avalanche rating...
I didnt say 500kHz, and I dont think the HER108 has avavalanche capability.
sorry I miss read ,100khz ,it's still a lot .

I have the idea that if your diode can not avalanche at all you need to balance them with resistor,but I might be wrong.
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