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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Power Supply Rectifier Diode Specs Question posted by rwalton on May 8, 2002 at 20:44:24:
This means that it can do the first line cycle (8.3 msec) at 55A. Your capacitor is not even close to charged in that short period (one half line cycle)! It will take multiple cycles to do that. The next (or second) REPETITIVE cycle must be down to 10A which is the repetitive current rating of the BYQ28E that you are using. I am surprised you are only getting this every 20 times you turn it on (likely there is more margin than the guaranteed specs...but specs is specs)Even when fully charged, you are likely to have >10A repetitive peaks for very short periods (probably less than 0.8 msec but likely in the 15A range) at the very top of the AC line cycle.
The BYQ diodes are intended for (and rated for) high frequency switching transformer output where the output waveform is square wave not sine wave allowing the charge to be delivered to the output cap in a much more uniform fashion (the Philips spec is 10A square wave with a duty cycle of 50%).
I hope this explains more the phenomenon involved. Once you get your sense resistor installed you will witness this on the scope.
Anyway look closely at the Nonrepetitive and Repetitive rating on your diode below:
http://www.semiconductors.philips.com/acrobat/datasheets/BYQ28E_SERIES_3.pdf
Best regards
Joe...
G.
Crank it up...
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Follow Ups
- Rick it is because the 55A is a NON REPETITIVE rating... - Gepetto 15:31:14 05/09/02 (1)
- Re: Rick it is because the 55A is a NON REPETITIVE rating... - rwalton 12:19:59 05/10/02 (0)
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