Just for kicks, I decided to do a quick bench test of a 1N4004 and =
compare
it to a UF4004 to see the reverse recovery times (trr) first hand.  I =
used
an HP3314A signal generator to drive the rectifier connected in series =
with
a 50 ohm load and measured the trr with a Tex 2456DMS scope.  The signal =
was
a square wave at 100KHz at 10 volts p-p.

The results:

1N4004  4 microseconds trr (!)
UF4004  55 nanoseconds trr

Interesting.

Dave Challis

-----Original Message-----
From: pic microcontroller discussion list =
[mailto:PICLIST@MITVMA.MIT.EDU] On
Behalf Of Spehro Pefhany
Sent: Monday, January 26, 2004 9:55 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [OT ] Quick 1N400? question


At 05:28 PM 1/26/2004 +0000, you wrote:


>OK, the capacitance does change with the amount of reverse voltage on=20
>the diode and there are specific diodes that exploit this effect, but=20
>in the original question he is asking if he can use a 1N4006 in place=20
>of a 1N4001 where the reverse voltage shouldn't go above the rating for =

>the 1N4001.  In this case there shouldn't be any change as all the=20
>other characteristics of the diode are the same.

The recovery times are longer and the capacitance less for 1N4006 and =
1N4007
(compared to 1N4001..1N4005) under the *exact same* conditions. This
"typical" characteristic information (and PAGES of related
curves) have been excised from newer data sheets. (Of course it's also
possible that the process has changed and none of the older information =
is
relevant, but there is much less information on current data sheets.)

Of course one should endeavor to use only guaranteed information in a
design, HOWEVER note that on modern data sheets the reverse recovery =
time
just is not guaranteed at all. We just "hope" it isn't 50 milliseconds =
or
something on 1% of the units, that would likely cause the product to =
explode
or burst into flames, incinerating the hapless customer. Same with =
junction
capacitance.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the
reward"
speff@interlog.com             Info for manufacturers: =
http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  =
http://www.speff.com

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