At 10:19 AM 2000-02-03 -0500, Phil T. (VA3UX) wrote:
>At 02:24 PM 2/3/2000 +0000, you wrote:
>>The Motorola web data sheet shows 200 amperes for NON-repetitive peak
>>current for the 1N5408; the 1N4007 is rated at 30 amperes. Neither data
>>sheet gives a repetitive peak current rating.
>>
>
>The 3 Amp rating is the repetitive rating Steve. I think its often listed
>as "Irep".
Pardon me: here's the exact wording from the Motorola 1N5408 data sheet,
both the present-day web page and from my old "Motorola Silicon Rectifier
Manual", Series A, copyright 1980:
"Average Rectified Forward Current
(Single Phase Resistive Load,
1/2" leads, T(L)=105 deg C) Io 3.0 Amp"
>From the manual, pp. 3-11:
"It is customary, as well as a JEDEC requirement, to rate rectifiers in
terms of average current delivered to a resistive load at a specified case
temperature in a 60 Hz half-wave circuit. The rated current is defined as Io."
The peak current in a fullwave rectifier depends upon the product
2*2*Pi*F(ripple)*C*R(L) (omit the first "2" for a halfwave rectifier), in
addition to the desired ripple percentage and source (transformer)
reactance and resistance. Calculating all these factors becomes
sufficiently complex that graphs published by Schade in the 1943
Proceedings of the IRE are normally used.
Back-of-the-envelope estimations that I've been doing since last night
indicate that the peak repetitive current is in the range of 15 to 20 times
the average dc output current. However, the actual increase in average
current due to this peak current depends upon the conduction angle of this
peak current due to the filter capacitance, desired ripple percentage, and
load resistance. This peak current is limited by the maximum allowable
diode junction temperature which depends upon the cooling method and
efficiency. The single-cycle peak current rating of 200 amperes given in
the data sheet is established by the allowable junction temperature and
power dissipation of the diode package.
73, Steve K0XP
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