Lab 6 - GilesVolmir/Skylar-Scott--308L-Junior-Lab GitHub Wiki

2/29/12

AFTER CLOSING THE TAB AND LOSING MY NOTEBOOK TO THIS POINT.

in recap: II. the two 15VAC on either side of the center tap are 2pi out of phase and have an amplitude of 22 volts.

III. after wiring it like it said, i got a wave that is just the positive portion of the sine wave with the negative portions just sitting at ground. it was also attenuated

THIS PREVIOUS PORTION OF THE NOTEBOOK WAS FROM MEMORY AFTER I LOST MY DATA.

IV. After adding the diode and connection to the out of phase coil my graph looks like an attenuated absolute value of a sign wave.

V. I added the 100microF capacitor as shown. the capacitor measures 19.5 VDC across it. this makes sense even though the rms voltage is less than this because the amplitude is 22 volts. The capacitor is approaching that voltage. When the scope zooms in I can see what looks like a sawtooth wave (almost vertical straight rising edge, slowly dropping straight falling edge) on top of the ~20 volts with amplitude 0.75 volts and same period as the ~60Hz input from the transformer. In comparison to the amplitude of the signal, the unstable top is very small voltage.

VI: added the zener diode in parallel to the 1k resistor as shown (forward biased to the capacitor). The voltage across the resistor is now ~0.86 volts, but when examined with the oscilloscope the sawtooth wave on top is now only ~0.02 volts (down from 0.75 volts). The zener diode is serving to bleed the current from the capacitor when it reaches the capacitor's breakdown voltage. since this is a sharp curve, the voltage resulting is sharp.
I just realized I had my zener diode the wrong direction, in this case the wave on top is ~0.05 volts.

VII: I connected the LED in with the 1k resistor.

3/7/12

My circuit was, understandable, changed during the week. rebuilding it now. Circuit rebuilt, with easier to reach 1k resistor since I'm going to have to change it out soon here. When the power is turned on the LED turns on so I think I have the circuit right. I noticed that back in part VI I forgot to mention the voltage after forward biasing the zener diode. This voltage (with just the 1k resistor) is 11.90 volts. I tried switching out the 1k for a 5.1k resistor as was suggested, and with the 5.1k I could see a decrease in the amount of light. With the 1k resistor I measure 9.9 volts across the resistor and 2.03 volts across the LED. With the 5.1k resistor I measure 10.4 volts across the resistor and 1.87 volts across the LED. Since the resistor and LED are in series they will have the same current running through them. V/R=I For the 1k: 9.9/1k=9.9mA For the 5.1k: 10.4/5.1k=2.0mA These numbers indicate the luminance is a function of the current rather than voltage since the change in brightness is easily visible, probably a change closer to 500% than 9%. (which are the percent changes in current and voltage, respectively) This also agrees with what I would expect from the model (each electron falling through the gap releases a photon) and what I've been taught about LEDs.

VIII: The full bridge A ~13 volt biased asymmetric wave with amplitude of ~1.5 volts. The scope says it's a 60Hz wave. The leading edge is much steeper and shorter than the falling edge. Ok, everything I just said is totally wrong. I can't look at the wave with the scope because the ground on the scope is the same as the ground on the proto-board. So there is a ground conflict which messes up all the waves. I'll just measure with the Fluke Multimeter. The multimeter measures ~13 volts across the resistor. Can't tell anything about the amplitude of the ridge on top without an isolated ground scope.