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In Reply to: RE: Cree Schottky diodes : ( posted by Lowrider on March 15, 2008 at 05:22:47
...
Antonio Melo Ribeiro
Follow Ups:
Must be a bad diode??? I've been using Cree, both the 600v (for the 250v and lower voltages) and the 1200v (the TO-220 package, from partsconnexion) in most of my gears and never had such failures (hopefully, I won't ever...) They're really good. While other diodes would have these little quigglings at the top of the ripple voltage, the Cree shows up smooth.
Found the courage to install them, no problems so far...
Sounds more easy, floating, if you know what I mean, subtle but good improvement... ;)
Antonio Melo Ribeiro
Shouldnt I be able to measure current in one direction, as I do with the "normal" diodes, 4002 and FR307 ?
Thanks,
Antonio Melo Ribeiro
Yes, you should be able to see conduction with a "normal" DMM ohmmeter. Such a device forces a constant current through the DUT, and reads the voltage across it. Unless the diode has a lower breakdown voltage than the DMM's current source maximum compliance voltage, there should be an extremely large difference between the low forward voltage and "off-scale" reverse voltage.
Schottky diodes have a Forward (Vf) voltage much less than normal Silicone rectifier doides so they are not always a 'direct drop in' replacement part over a normal Si Diode. Cree Schottky diodes have a very small forward voltage drop as compared to normal rectifier diodes and will also require "heat-sinks" as they do get very hot. To make matters worse, Schottky diodes have a typical max junction temp of 175º C as compared to the Standard 200ºC for normal rectifier diodes, making heat dissipation one more element to deal with.
Apart from this, unless the power transformer secondary winding resistance is so darn low that these diodes "mis-behave", I cannot see why they are not able to perform properly. The TO-220 version has Pin 1 as the Anode a(+) and pin 2/Metal Tab as the Cathode k (-).
Also reverse current leakage of Schottky diodes is larger than most typical regular Si rectifiers, sometimes causing issues.
Cree have designed their Schottky diodes to feature unusually high reverse bias voltages. Typical Schottky Vr = 150 Volts, and Cree has them at 600V and 1200 V, similar to standard Silicon rectifiers.
I have personally not used these, but I have heard from other people locally that these diodes get very hot and some have failed w/o a heatsink installed.
Shall I try the 5A 1200V on B+, or write them off...
Antonio Melo Ribeiro
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