Laboratory Report Lab I Full Wave Rectifier. Submitted by. Date of Experiment June 16, 2016

Transcription

1 UM SJTU JOINT INSTITUTE Electronic Circuits (VE311) Laboratory Report Lab I Full Wave Rectifier Submitted by Xing Hua Section IV Huang Junhao Section IV Date of Experiment June 16, 2016 Date of Report June 26, 2016

2 VE311 Lab I Report 1 Introduction In this lab we are building a half-wave rectifier circuit, a full-wave bridge rectifier circuit without capacitance and a full-wave bridge rectifier circuit with capacitance. Multiple measurements are taken with various input signals. And we are performing calculations time constants τ, ripple voltage Vr conduction angle ω and LED current ID. Finally lab measurements are taken to verify calculation results. 2 Experimental Results 2.1 Half-Wave Rectifier Build the rectifier as shown in Figure 1. Figure 1: Half-Wave Rectifier Schematics without Capacitor1 and the circuit we built is shown in figure 2 Figure 2: Physical Circuit Layout for Half-Wave Rectifier without Capacitor 1 Image credit goes to VE311 SU2016 TA Group. Image digitally altered by the author of this document. 2 of 11

3 We intended to use V S = 20V pp as input source, but apparently source generator does not agree, as shown in Figure 3. Figure 3: Signal Generator Voltage Output Limit. 10 V pp max. With input V S = 10V pp, f = 100Hz sinusoidal AC, we have AC input (GREEN) and DC output (YELLOW) oscilloscope images in Figure 5 and??, respectively. Figure 4: Oscilloscope Image for V S = 10V pp, f = 100Hz input. Input applied on a half-wave rectifier. 3 of 11

4 Figure 5: Oscilloscope Image for half-wave rectifier output in response to a V S = 10V pp, f = 100Hz input. As expected, we are seeing identical input-output frequencies. And output peak-to-peak voltage is half that of input. 2.2 Full-Wave Bridge Rectifier without Capacitor Normal Operation Solder two additional diodes and build a full-wave rectifier as shown in Figure 6. and the circuit we built is shown in figure 7 Figure 6: Full-Wave Rectifier Schematics without Capacitor 2 2 Image credit goes to VE311 SU2016 TA Group. Image digitally altered by the author of this document. 4 of 11

5 VE311 Lab I Report Figure 7: Physical Circuit Layout for Full-Wave Rectifier without Capacitor With input VS = 10Vpp, f = 100Hz sinusoidal AC, we have AC input and DC output oscilloscope images in Figure?? and 9, respectively. Figure 8: Oscillator display for sinusoidal input with VS = 10Vpp, f = 100Hz. Such input signal is applied to a full-wave rectifier. 5 of 11

6 Figure 9: Oscillator display for full-wave rectifier circuit output under input V S = 10V pp, f = 100Hz. And as expected, we are seeing output peak-to-peak voltage half that of input, and output frequency double that of input. There is a bit of scribble at the bottom of Figure 9. We are attributing this anomaly to a loose connection or environmental noise Operating Below V on Now decrease source voltage to V S oscilloscope images in Figure 10. = 1V pp, f = 100Hz sinusoidal AC, we have AC input and DC output Figure 10: Oscilloscope display for sinusoidal input V S = 1V pp, f = 100Hz 6 of 11

7 But for output we are seeing a weird picture shown in Figure 11 Figure 11: Oscilloscope output measurement for full-wave rectifier without capacitor under sinusoidal input V S = 1V pp, f = 100Hz and we are seeing a non-regular periodic graph. What is most strange is peak-to-peak voltage. We are sourcing a 1 V pp input, so it would make sense to have an output peak-to-peak at 500mV. But instead, w are getting V pp = 271mV, only half the expected value. To figure out what happened, we removed emitted diode in series with R. Now output is shown in Figure 12. Figure 12: Oscilloscope output measurement for full-wave rectifier without capacitor and light-emitted diode under sinusoidal input V S = 1V pp, f = 100Hz With a peak-to-peak output voltage at 14.9mV, we are sure there is NO output signal at all. Notice we are 7 of 11

8 passing through 2 diodes from positive to negative every single time. With V on = 0.6V, we need at least V i > 1.2V to make currents flow through both diodes from positive to negative. Since input peal-to-peak voltage is only 1V, no current went through the circuitry, hence the noise we are seeing in Figure 12. And the output in Figure 11 must have been because circuit characteristics altered because of an additional diode (light-emitting notwithstanding, it is still a diode). 2.3 Full-Wave Bridge Rectifier with Capacitor Input f = 100Hz Solder capacitor onto the circuitry and build a rectifier as shown in Figure 13. Figure 13: Full-Wave Rectifier Schematics with a 1mF Capacitor 3 With input V S = 10V pp, f = 100Hz sinusoidal AC, we have AC input and DC output oscilloscope images in Figure 14 and 15, respectively. Figure 14: Input signal feeding into a full-wave rectifier with capacitor. Input set at V S = 10V pp, f = 100Hz. 3 Image credit goes to VE311 SU2016 TA Group. Image digitally altered by the author of this document. 8 of 11

9 Figure 15: Output signal fed from a full-wave rectifier with capacitor, with input set at V S = 10V pp, f = 100Hz. And now we are looking at a straight line. The reason behind this is that we are supplying too fast of an input frequency, leading to an extra-short conduction time and extra-small ripple voltage. Calculation in Section III shows those value to be 225.1µs and 0.11 V. That is small compared to input 20V peak-to-peak voltage value and 10ms period. Thus oscilloscope was not able to discern such a small ripple voltage and short conduction time, and that is why we are seeing a flat output line Input f = 1Hz Now slow frequency down to f = 1Hz sinusoidal AC, we have AC input and DC output oscilloscope images in Figure 16 and 17, respectively. Figure 16: Oscilloscope Display on Input Signal into a full-wave rectifier. Signal parameter is V S = 10V pp, f = 1Hz 9 of 11

10 Figure 17: Oscilloscope Display on Output Signal picked up from a full-wave rectifier. V S = 10V pp, f = 1Hz Signal parameter is Compared with Figure 15, we are getting a proper full-wave rectifier output graph. Ripple voltage is clearly visible in Figure 17. This corroborates with our guess that Figure 15 is a dead straight line because input frequency is way too high, leading to conduction time and ripple voltage too small to be discernible. 3 Calculations Estimate full-wave bridge rectifier parameters time constants of charging and discharging τ, ripple voltage V r, conduction time δt, conduction angle θ c and finally, LED current i D, with parameters R = 2kΩ C = 220µF V pp = 10V f = 100Hz V on = 0.6V Adhering to the convention set by signal source device in the lab, we interpret V pp as maximum amplitude of voltage source, rather than a peak-to-peak, two times the swing. And we have τ = R C = 2 kω 220 µf = 0.44 s (1) V r = V pp 2 V on T 10V 2 0.6V 1 = = 0.1V (2) R 2C 2kΩ 2 100Hz 220µF δt = 1 ω 2V r = 1 V pp 2πf 2V r V = V pp 2π 100Hz = s = 225.1µs (3) 10V 2V r 2 0.1V θ c = ω T = = = (4) V pp 10V 10 of 11

11 NOTE: i D is calculated under the assumption that LED carries no internal capacitance. And since i D varies through time, the value we have is an average value. i D = I dc V pp 2 V on R = 10V 2 0.6V 2 kω = 4.4 ma (5) 4 Conclusion We completed the construction and measurement of a half-wave rectifier and a full-wave rectifier. For the fullwave version, we experimented with the removal of the capacitor and observed resulting signal. And for the full-wave rectifier without a capacitor, we experimented feeding the circuit with insufficient input voltage to overcome diode V on. Pure noise was observed as a result. With regard to the full-wave rectifier circuit, different frequencies were applied in input. While 1Hz input generated visible ripple voltage, the 100Hz input generated a straight output line. We concluded that the higher frequency caused conduction time and ripple voltage too small to be discernible by oscilloscope. And in the end calculations on time constant, conduction time, conduction angle and LED current are performed on the full-wave rectifier with capacitor installed. Calculation result corroborated with our earlier guess of high frequency reducing rectifier ripples to a dead flat line. In conclusion, we built three rectifier circuits and fed them input of varying voltage and frequency to observe circuit response. Calculations were carried out to quantitively explain qualitative observations. And a final note: measure capacitance and resistance in lab on the actual module you are suing. Marked value might diverge from actual value. And that is going to have a huge impact on calculations. 11 of 11