---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Thu 06/03/21: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:44 PM - Re: Diode Failure Current vs Time Graph (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 05:44:23 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Diode Failure Current vs Time Graph At 11:35 AM 6/1/2021, you wrote: >Hey BobN, > >In your vast array of data & test results, do you have a current >vs time graph of a solenoid spike-suppression diode (1N5004?) short circuit? > >I'm wondering what the peak current is before it is destroyed. Interesting question and one that can probably be deduced by experiment. Setting up the experiment would be tricky. It's not so much a "peak current" as it is a "watt-seconds" issue . . . very much time dependent. To destroy a diode you need to either (1) MELT the barrier-hill layer between the p/n elements. This requires a watts/second injection of energy at some rate that exceeds the devices ability to reject the resulting generated heat. For our 1N400X series friends, this could be something on the order of 5A for Seconds . . . or 100A for milliseconds. (2) you can punch out the barrier-hill layer with reverse voltage that exceeds that layer's ability to stand it off. Again, it's an energy rate function, how much reverse current flows at the junction's breakdown voltage (watts) for sufficient time and rate to produce melting. Most people don't know it but ordinary junction diodes can be pressed into service as high voltage zeners. I used to use them as 700VDC regulators to bias up Geiger Muller tubes in radiation detectors. I had to hand select diodes from a lot to find the ones that offered 700V operation at about 50 microamps . . . or about 35 milliwatts dissipation. Well below the thermal threshold for damage. Getting back to your question: Download this data sheet . . . http://www.aeroelectric.com/Mfgr_Data/Semiconductors/1N4001.pdf Here we see a forward surge current rating of 50A with an interval of 1/2 of the 60H sine wave of 8.3 milliseconds. The data sheet says you can do this one time (generally interpreted to mean very low duty cycle). You could probably hit the device with this pulse once every second for a duty cycle of less than 1%. On this same data sheet we see thermal ratings citing 3W maximum dissipation. 175C maximum junction temperature and 50C/W thermal resistance to ambient. 50C/W X 3W is a 150C rise which is added to 25C ambient to get to the 175C max operating temperature. My hypothetical 5A 'overload' cited above would probably produce a voltage drop of over 1V. That's 5 Watts dissipation for a potential 275C junction temperature. Somewhere above 175C the junction will fail after sufficient time to produce the rise. The 30A rated surge pulse would obviously heat it up much faster but the 8.3Ms limit would be conservative. These numbers suggest some parameters for setting up your experiment. They also validate our selection of the 1N400x series devices as contactor coil spike catchers. A charged capacitor will deliver discharge voltage at no higher value than the capacitor was charged to. Similarly, an inductor delivers discharge current at the same value to which it was chaged. A 3A starter contactor coil would 'hammer' its catch diode at 3A peak for no more than 5-10 Milliseconds. Well inside the surge current limits suggested by the data sheet. Bob . . . Un impeachable logic: George Carlin asked, "If black boxes survive crashes, why don't they make the whole airplane out of that stuff?" ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.