[Noisebridge-discuss] Homework Help?

[Daniel Pitts]

Hey Circuit Hackers.

So, I'm taking a Linear Circuits class (at Diablo Valley College in 
Pleasant Hill), but due to scheduling constraints I skipped the "AC" 
electronics course.  I have one particular homework problem that I think 
I've gotten correct, but I'd like to have someone with more experience 
confirm.  Unfortunately most of my classmates finish the homework on the 
due-date, so I can't compare notes.

The problem as stated:

Find the peak and average power delivered to Rl in the figure:(view 
fixed-width font)


.--o^-._-^-* -.  2:1  .---->|---o--.
|  Fuse ^     |      |  Diode^     |
o             S* || *S             \
               S  ||  S/
120V rms      S  ||  S\ 220 ohm
               S  ||  S/
o             |      |\
|             |      |             |
`-------------.      .------.---o--.
|
-----
                            ---
-


My approach to solving this is:

120v rms becomes 60v rms on the secondary of the transformer. Assuming a 
sine waveform, the peak voltage is 60v*sqrt(2), approx 85v.

Using the "ideal" model, the diode only conducts one direction, which 
cuts the Vrms in half.
Pavg = 30v^2/220ohm ~= 4watts
Ppeak = 85v^2/220ohm ~= 33watts

Does this look correct?

Thanks,
Daniel.