[AMPS] Diodes

Rich Measures measures@vc.net
Thu, 29 Jul 1999 10:13:40 -0700




>
>I think my message bounced. 
>
>Marv says that recovery time isn't important, based on the slow 
>slew rate of powerline frequencies.
>
>What then makes sure the diodes all share equal voltages while 
>turing off? 

€  Avalanche threshold.  They don't need to share the reverse potential 
equally.  For example, if you had a 800piv diode in series with a 1200piv 
diode, and a 1900v reverse pulse came along, would you want the diodes to 
share it equally?  //  . Without "equalization", the sharing will be 
according to ability.  Add external "Equalization" and the 800v unit gets 
gaffed.  (see p. 11-9 in ARRL Handbook) 

>If it is junction capacitance, you are in trouble. 

€  not as long as the capacitance of the P/N junction is in parallel with 
a limiter -- i.e., the avalanche characteristic of the P/N junction.  .  

>
>The capacitance is not only not matched, it changes with reverse 
>voltage. The lowest capacitance diode will turn off quickest, and 
>that will lower capacitance even more in that diode compared to 
>higher capacitance (slower) diodes.
>
>Reverse leakage current, unless you take the diode to the 
>threshold, is extremely low. Are people claiming one diode goes to 
>threshold and then the others start being forced to threshold as 
>that single diode avalanches? Is that the mechanism that causes 
>voltages to be "shared"?
>
€  I think he's got it!.  
>
-  cheers, Tom


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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