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'Diode Turn-on Time (was MOSFET)'
2007\12\29@191002 by Jack Smith

picon face
After reading the discussion concerning protecting MOSFETs from
inductive spikes with diodes, I've just finished turn-on and turn-off
time measurements for four power diodes; two 1N400x type, one high speed
silicon and one Schottky diode.  Discussion and 'scope photos at
http://www.cliftonlaboratories.com/diode_turn-on_time.htm

I see the expected difference in reverse recovery time, but all four
diodes have very short transitions from reverse to forward bias. Perhaps
I'm misunderstanding what is going on, or perhaps there's an issue with
my test setup, but all four diodes look like they transition in a few
nanoseconds. Certainly well under 100 ns. I didn't drag my 400 MHz
digital 'scope over to the other side of the shop for the data, so it's
taken with a 100 MHz analog scope, but I don't think that's the reason.

To me, all four diodes look as if they would provide more than fast
enough transition from reverse to forward  bias conditions. What am I
doing wrong here?

Jack

2007\12\29@191237 by Jack Smith

picon face
(Sorry - sent originally without the [EE] tag.)


After reading the discussion concerning protecting MOSFETs from
inductive spikes with diodes, I've just finished turn-on and turn-off
time measurements for four power diodes; two 1N400x type, one high speed
silicon and one Schottky diode.  Discussion and 'scope photos at
http://www.cliftonlaboratories.com/diode_turn-on_time.htm

I see the expected difference in reverse recovery time, but all four
diodes have very short transitions from reverse to forward bias. Perhaps
I'm misunderstanding what is going on, or perhaps there's an issue with
my test setup, but all four diodes look like they transition in a few
nanoseconds. Certainly well under 100 ns. I didn't drag my 400 MHz
digital 'scope over to the other side of the shop for the data, so it's
taken with a 100 MHz analog scope, but I don't think that's the reason.

To me, all four diodes look as if they would provide more than fast
enough transition from reverse to forward  bias conditions. What am I
doing wrong here?

Jack


2007\12\29@192852 by William Beckman

flavicon
face
Some food for thought.
I used to do diode measurements and recall this:
di/dt.
Specs are written at a specific current.
The effective transition directly relates to the impedance.
I believe di/dt is ignored. Physics Rules.
.
-Bill
.
{Original Message removed}

2007\12\29@222246 by William \Chops\ Westfield

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On Dec 29, 2007, at 4:09 PM, Jack Smith wrote:

> I've just finished turn-on and turn-off
> time measurements for four power diodes; two 1N400x type, one high  
> speed
> silicon and one Schottky diode.  Discussion and 'scope photos at
> http://www.cliftonlaboratories.com/diode_turn-on_time.htm

Nicely done, and quite interesting.  Thanks for the effort!

BillW

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