Fast Recovery Diode

Hi Everybody,

Could someone please explain the use of a Fast Recovery Diode? I am particularly interested in:

  1. How is this diode different from a regular rectifier diode. 2. The role of these diodes in MOSFET circuits.

(Sorry, there is no Wiki for this.)

Thanks for your help.

Regards, Anand

Reply to
Anand P. Paralkar
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Muzaffer Kal

DSPIA INC.
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Reply to
Muzaffer Kal

Do you mean a step recovery diode?

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George H.

Reply to
George Herold

The difference is, a fast switching diode will become non conductive a lot sooner than a non-fast switching diode.

In non fast recovery diodes, the path between the anode and cathode is still some what conductive after the current that placed them in that state is gone. What this means is, reverse polarity on this diode will cause a conductive path in the reverse direction for a per scribed amount of time just after a completion of a forward path on the diode if not sufficient time given to have it recover before this reverse path appears across the nodes of the diode.

It acts like a cap that has been charged and when reverse voltage appears across it, it'll exert current. But don't get confused, it's not the same thing. It's all about electrons and the way they impact the surface of the materials between the anode and cathode used in the diode. Fast diodes are made a little differently to limit this problem.

TO get a better understanding, look up Ultra Fast Diodes or Switching diodes..

P.S. Transistors of many kinds are also spec'ed this way.

Reply to
Jamie

"Jamie" wrote in message news:NCrto.6026$ snipped-for-privacy@newsfe07.iad...

Actually, it acts more like, no, it acts exactly like a battery. The voltage is almost constant until the charge is gone -- that means the diode is actually producing energy (positive voltage, negative current) as the charge leaves.

FYI, a simulation of 1N4007 driven at If = 1A and turning off at -100A/us reaches a peak current I_rr of 6.978A in 69.7ns before turning off. A proper high speed diode like MUR420 does it in 1/3 the time, and accordingly about 1/9th the charge (Q_rr).

Real recovery time of a 1N4007 is probably a lot worse (4us+?).

Tim

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Reply to
Tim Williams

The higher-voltage power diodes, like a 4007, tend to act like PIN diodes. They can make decent drift step-recovery diodes, too.

Try this some time: apply 48 volts in the forward direction to a

1N4007 or 1N4009. The current will ramp up pretty linearly to numbers like 50 amps in 100 ns or so. Now apply a lot of reverse current, like 50 amps, through a small inductor. It will conduct in the reverse direction for maybe 50 ns then snap off, making a huge (kilovolt maybe) spike across the inductor, just a couple ns wide. Lotsa EMI.

Power rectifiers can do the step-recovery thing even at 60 Hz. That can cause mysterious problems elsewhere in a box.

A Russian guy, Grehkov, discovered the DSRD effect and another, even faster plasma breakdown effect, in common power diodes.

John

Reply to
John Larkin

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

Yep, lotsa EMI. Some tube amp builders have noticed this. So, instead of simply applying an RC damper, they go with high speed diodes. Usually the bigass FREDs. What they need 6A diodes for, I don't have a clue. The ones with deeper pockets even buy SiC schottkies.

The mind reels.

Tim

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Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

We just used some power mosfets. The forward bias supply was 48 volts and the reverse was 400. We used a different diode, something we could cool properly, to get the rep-rate up. But lots of cheap power diodes will snap like gangbusters.

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We designed this for the LEAP tomographic atom probe. Didn't sell many, but it was fun. Lots of things turn out to be fun but don't sell many.

John

Reply to
John Larkin

A step-recovery diode needs a hyperbolic doping profile, which regular diffusion can make, on purpose or not. The SRD was discovered accidentally by Boff at HP, in the 60s. There's some history in the old HP Journals. They were originally called "Boff diodes" but the name didn't catch on.

A modified doping profile can make a "soft recovery" power rectifier diode that still stores a lot of charge but doesn't snap.

John

Reply to
John Larkin

How the hell do you do that, for just the 100ns? Surely any device that could deliver the 48 volts and 50 amps would produce heaps of EMI all by itself?

Clifford Heath.

Reply to
Clifford Heath

I talked to someone yesterday who has a large collection of old HP Journals. I asked if I can borrow them to scan to PDF. I'm waiting for an answer. :)

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enough left over to pay them.
Reply to
Michael A. Terrell

They are all online!

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Here's the Boff diode one:

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I wonder if the GR Experimenters are available somewhere. Tek had a journal, too.

John

Reply to
John Larkin

Nice links! Thanks.

Ed

Reply to
ehsjr

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