Diode Behavior

[Ducttape]

I thought I'd hook up a trivial diode circuit to the scope just to make sure it does what I'd expect it to (newbie). Had a symmetrical ramp at 1kHz powering a 1k resistor in series with a 1N4004 diode, per the attached schematic. Channel 3 is voltage across resistor (ch1 - ch2). Looked as expected.

Decided to up the frequency to 100kHz and got something not as pretty. What diode spec/characteristic is influencing the lagging voltage drop that allows reverse current flow?

[rfeecs]

Reverse recovery time.  Some datasheets list it:
http://global.oup.com/us/companion.websites/fdscontent/uscompanion/us/pdf/microcircuits/students/diode/1n4004-general.pdf

It is caused by minority carrier charge storage in PN junctions.  The amount of charge (and consequently the time) depends on the forward and reverse current.

[nugglix]

Hi!

Nice video about that:



Explains and shows whats going on.
Great stuff, as usual. 

[Ducttape]

Reverse recovery time.  Some datasheets list it:
http://global.oup.com/us/companion.websites/fdscontent/uscompanion/us/pdf/microcircuits/students/diode/1n4004-general.pdf

It is caused by minority carrier charge storage in PN junctions.  The amount of charge (and consequently the time) depends on the forward and reverse current.

Thanks. My 'ON Semiconductor' datasheet doesn't include it, although I wouldn't have understood its significance before now.

[Ducttape]

Hi!

Nice video about that:

Explains and shows whats going on.
Great stuff, as usual. 

Excellent. And since I didn't know the term 'reverse recovery time' I probably would have never found it.

[Audioguru]

The 1n400x are low frequency rectifiers (50Hz to 200Hz). The 1N4148 is a fast diode but it is smaller so its maximum current rating is lower.
There are fast high current diodes available but I have never needed one so I don't know their part numbers.

[David Hess]

Reverse recovery time.  Some datasheets list it:
http://global.oup.com/us/companion.websites/fdscontent/uscompanion/us/pdf/microcircuits/students/diode/1n4004-general.pdf

It is caused by minority carrier charge storage in PN junctions.  The amount of charge (and consequently the time) depends on the forward and reverse current.

Thanks. My 'ON Semiconductor' datasheet doesn't include it, although I wouldn't have understood its significance before now.

Huh, I was going to say that you must have missed it but I just checked and the ON Semiconductor datasheet is indeed missing any reverse recovery information for the 1N4004.

Diodes also have forward recovery where they do not turn on instantly but it is of lessor concern because it is so much faster making it rarely specified.