Did these a while ago, but didn’t get a chance to post them.
Not much to say about them, other than, again, paying attention to impedance matching and loading is key. 10:1, for this low frequency stuff. Can’t impedance match 1:1 like I’m used to with radio stuff.
3L.1.1 The LC resonant circuit worked as predicted, but I didn’t get any photos. A 0.01uF capacitor and 10mH inductor predicted a resonant frequency of 5kHz and the actual measured frequency was 4.85kHz. That’s 3% error, well within the 10% capacitor tolerances.
3L.1.2 The f3db values were found to be 5.18 and 4.59kHz, for an average delta-f of .3 kHz, giving a Q of 15.3.
3L.1.6 To get the ringing I had to change the current limit resistor from 100k to 10k. Otherwise, there just didn’t seem to be enough current to do this exercise well. Using the decay ringing to estimate Q I found about 3 cycles before the voltage dropped below 6%, for a Q value of 19. Probably close enough to the 15.3 above.
3L.2 The half-wave rectifier worked as expected. Vpeak was 10V, meaning the transformer was a little high (the rated 6.3Vrms of the transformer should have given me 8.9Vpeak).
3L.3 Full wave bridge rectifier was assembled on a breadboard, and, as predicted, I blew a pair of diodes before I got it right. I begin to dislike solderless bread boards more and more. But can’t exactly roll a custom PCB for each project. Once it was built right, it behaved as expected:
The full wave rectifier gave me a 9.3Vpeak, exactly consistent with one extra voltage drop.
3L.3.1 The ripple amplitude without filtering was the full 9.3V at 120Hz. Once a 15uF capacitor was added, it settled down to 1.52Vpp. Calculated ripple should have been 2.24Vpp. Not sure why that much discrepancy. Maybe stray capacitance in the breadboard? Stray inductance in the leads?
3L.3.2 To design a filter for 1Vpp ripple at 20mA current, I found I needed an R of 465Ohm and a C of 160uF. Built up, this system worked too well – actual ripple was about 840mV.
This makes sense, since the design rests on Assumptions 1 and 2 which err on the side of less ripple.