what is the meaning of the term 'reverse recovery time" for diode? - Electronic Circuits Projects Diagrams Free

wkyong · 2nd May 2008, 01:53 AM

what is the meaning of the term 'reverse recovery time" for diode?What is soft & fast recovery ?Are they same?

dknguyen · 2nd May 2008, 01:57 AM

Reverse recovery time is the time it takes for the diode to turn on if it is fully reversed bias (so it's off) and then suddenly is forward biased (so it's on).

THe soft and hard recovery has to do with the way current decays in the diode whenever it turns off. FOr soft recovery the current will gradually (smoothly) approach the zero. Snap recovery it will just approach it directly. Soft is more desireable for power applications as it makes less noise and the di/dt is smaller so there are less inductive voltage spikes and things like that.

All of that and more in detail is here:
http://www.powerdesigners.com/InfoWe...es/diodes.shtm

dknguyen · 2nd May 2008, 02:46 AM

Quote:

Originally Posted by Sceadwian

I thought reverse recovery time was the time a diode would conduct in the reverse direction when abruply switched from forward to reverse bias? I think it's related to the capacitance of the diode junction. Schotky and Pin diodes are supposed to be 'hard' or 'fast' recovery diodes. Power supply diodes don't need to be fast, they're only switched at 50-60hz so they're 'soft' recovery diodes, can be made with a simplier semiconductor layout.

Ah, yeah. From my link that appears to be what it is. THe time it takes for the diode to turn off. My definition must have been creeping a bit to "the time that it takes to turn off and on" or vice versa because I use that spec to try and guess how fast the diode will turn on when reversed bias since I only ever use it for flyback diodes.

By power applications, I'm talking about switched power supplies and inverter drives. Not AC rectifiers.

Sceadwian · 2nd May 2008, 03:01 AM

Even a 'general purpose diode' s time constant is around 50khz with a reverse recovery at 20us, so the general electronics user doesn't have to worry about it until ultrasonic or low RF switching frequencies.

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2nd May 2008, 01:53 AM	(permalink)
wkyong	what is the meaning of the term 'reverse recovery time" for diode? what is the meaning of the term 'reverse recovery time" for diode?What is soft & fast recovery ?Are they same?

2nd May 2008, 01:57 AM	(permalink)
dknguyen	Reverse recovery time is the time it takes for the diode to turn on if it is fully reversed bias (so it's off) and then suddenly is forward biased (so it's on). THe soft and hard recovery has to do with the way current decays in the diode whenever it turns off. FOr soft recovery the current will gradually (smoothly) approach the zero. Snap recovery it will just approach it directly. Soft is more desireable for power applications as it makes less noise and the di/dt is smaller so there are less inductive voltage spikes and things like that. All of that and more in detail is here: http://www.powerdesigners.com/InfoWe...es/diodes.shtm __________________ NO, that picture isn't me so don't bother asking if we can be friends. Last edited by dknguyen; 2nd May 2008 at 01:59 AM.

2nd May 2008, 03:01 AM	(permalink)
Sceadwian	Even a 'general purpose diode' s time constant is around 50khz with a reverse recovery at 20us, so the general electronics user doesn't have to worry about it until ultrasonic or low RF switching frequencies. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."