[Amps] 1N5408 vs 1N5553

[Jim Thomson]

Date: Tue, 8 Jun 2010 15:11:10 -0600
From: "Jim  Garland" <4cx250b at muohio.edu>
Subject: Re: [Amps] 1N5408 vs 1N5553

> >From a quick search it appears that the 1N5553 reverse current is 1ua,
and  the 1N5408 is 5ua, both at 25*C. Leakage goes up with temperature.
> 
> Carl
> KM1H
> 

I was surprised to learn that the 1N5408 is made by at least 29 different
manufacturers
(http://www.datasheetcatalog.com/datasheets_pdf/1/N/5/4/1N5408.shtml) , and
specs vary slightly among the group. General Semiconductor gives the reverse
leakage (25 degrees C) as 5 uA, while On Semiconductor specifies it as 10
uA.  On Semiconductor gives the 150C reverse current as 100uA, whereas
Semtech gives the 105C (not 150C) leakage current as 500 uA. Everbody agrees
the 1N5408 is rated at 3ADC (with leads of about 1/2 inch).

The 1N5553 also shows some variation among different manufacturers, though
most agree that the reverse leakage current at PIV is 1 uA at 25C, rising to
20uA at 100C.  All manufacturers specify the switching speed of the 1N5553
at 2 usec, and nobody specs the switching speed of the 1n5408. Don't know
why. The 1N5553 is rated at 5ADC with 3/8 in. leads, or 3A DC, with shorter
leads.

You can buy one 1N5408 from Mouser for $0.15 (Taiwan Semiconductors). Mouser
stocks tens of thousands of them.

## I remember buying 1N5408's  for 60 cents each.. back in 1977.  If you bought
40 or more.. they were down to 40 cents each.  I think HEP-170's  were aprx 10-12 cents
each... and don't think they were rated for 3A... and no 200A surge.  



 Mouser says the 1N5553 is now obsolete and
no longer stocks them. Newark still sells them, however, and prices have
plummeted to about $1/ea in quantities of 1000. A few months ago, when they
were still in production and "military approved," they were selling for
about $16/each.  Maybe Uncle Sam finally wised up!  (FYI, I bought fifty
from a local surplus dealer for $5. Nice little diodes.)

##  I used to be able to get 6A10's  for 25 cents each.. but the price has gone up/down
depending which brand, which day of the week, etc.  All I buy/use these days is 6A10's.
They will drop right in where a 1N5408 once stood.  Same 16 ga wire leads out each end,
same length.  The diam on the 6A10 is double.  [ 6A  and a 400A surge]    I think the 1N5408
will hi pot test to aprx 1400 v.. and ditto with a 6A10.  With 1 kv.. the leakage is really low..and
prob just as good as a megabuck 5553.  In any event.. just add a few extra diodes per
leg.. and leakage is a non issue. 

later... Jim  VE7RF 





73,
Jim W8ZR