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发表于 2013-5-21 07:49:41
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to help you understand it, here is a quick simulation.
V1 is the ac source, 220v rms (220v*1.4=308v peak) @ 50hz. R1 is the current limit diode, and D1/D2 are two diodes (2.5v Vfwd).
The peak current going through D1, in blue, has a peak current of 1.4ma (=1ma rms) during the positive cycle and 0ma during the negative cycle. So the rms current through the whole cycle is 0.5*(1ma+0ma)=0.5ma. The voltage drop over D1 is 2.5v during the positive cycle and -2.5v during the negative cycle. Total power dissipation is 2.5v*1ma+(-2.5v)*0ma = 2.5mw.
Consistent with what we discussed earlier.
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