Can someone solve this problem for me.
Thanks in advance.
Thanks in advance.
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An ideal diode still only conducts in one direction doesn't it? That smells highly nonlinear to me...@ericgibbs
@blah2222
The question speaks of an ideal diode so I don't think factors such as harmonics and non-linearity of diode are required to be taken into account. Even if I did assume practical factors it doesn't explain the huge difference between MikeML's answer and mine.....
I use the approximation that the charge time (time the diode conducts) is so short that the discharge time is the entire duration until the next charge pulse comes along. At 50Hz AC, the period between successive pulses is 1/50 = 20ms. If you want, you could say that the charge time is ~2ms and the discharge time is ~18ms. This is borne out by the LTSpice sim... My way, you calculate that you need a slightly larger filter capacitor, so the error is not significant.@ericgibbs
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@MikeML
In your calculation of capacitor discharge you have taken t=20ms. The capacitor doesn't discharge during the entire cycle right?
Also if avg. resistor current is 90mA how does that make avg.diode current as 90mA ?
Thank you MikeML for your answer.Lets see how the method does:
Peak cap voltage is 10-0.7 = 9.3V
Initial Discharge (resistor) current = 9.3/100 = 93mA
Sag (ΔV) = i*t/C= 93m*20m/4m = 0.465V
Av. Cap Voltage = 9.3-0.465/2 = 9.067V
Ave Resistor current = 9.067/100 = 90mA
Therefore average diode current = 90mA.
Now look at a simulation:
LTSpice says average diode current is 89.9mA. I'd say the method works...
Note the peak diode current; Note the duration that current actually flows through the diode...
I think for this question, 'ideal' is referring to the on-diode as a short. Most textbooks describe 'ideal' diodes in this way. The Shockley model seems a bit complex for this type of question.Which begs the question: What is an ideal diode? The one I linked to, or one that has a forward voltage drop of zero?
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