Lab 9 Diodes

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Electrical Engineering

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Dec 6, 2023

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ECE 2200/2210 Lab 9: Diodes Possible Points: 56 Lab Equipment List:  Resistors: 56 Ω (green, blue, black), 510 Ω (green, brown, brown), 100 Ω (brown, black, brown), 1 k Ω (brown, black, red ), 22 k Ω (red, red, orange), and 100 k Ω (brown, black, yellow)  0.22 μ F (224) and a 47 to 220 μ F capacitor (use this capacitor where schematic calls for or 100 μ F)  IN4002 or 1N4004 diode (black plastic)  Red, green, or yellow light emitting diodes (LEDs)  IN4734 5.6 V Zener diode (gray) (we can also use 1N4730) Partnering:  Everyone must create their own lab report (fill out this document).  Groups are allowed to be maximum of 2 except in a class of odd numbers; in that case one group will be allowed to be 3. A group may use the same measurement equipment.  Discussions are encouraged, and you are also encouraged to answer each other’s questions!  Seek out the TA if you get stuck or need help. Lab Procedures: Today we’ll be exploring the use of diodes. Fig. 1 Diode image and schematic. Fig. 1 shows a diagram of a diode. Note the dark bar indicates the side of the diode that has the cathode. In the circuit schematic for the diode at the bottom of Fig. 1, the cathode side is represented by a line. Part 1: AC to DC Converter (A Half-Wave Rectifier) (39pts) 1. Let’s start out by creating a half-wave rectifier, which converts an AC current (+ and -) to DC (+ only). In this case, we want the DC current to be a constant voltage (flat line). An example scenario where we want to convert an AC current to a DC current is from a wall outlet to some DC circuitry in a laptop, for example. 1 UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu

ECE 2200/2210 Start by building the circuit shown in Fig 2 on your breadboard (don’t turn on the signal generator yet). The 1N4002 parts are power diodes and they have large leads. These leads may be hard to get into the breadboard holes. If you look closely at the lead ends, you’ll see that many are cut with a wire cutter that leaves a beveled end. If you line the bevel up with the holes that are connected inside the board, they go in a lot easier. Otherwise, wiggle and twist them as you push them into the board. Fig. 2 Schematic of the first circuit. 2. If we were to hook up a oscilloscope with Channels 1 & 2 connected as shown in Fig. 2 what would you expect to see? Consider this before going on to the next page. (3pts) <A CH2 positive wave will generate > 2 UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu

ECE 2200/2210 3. Now hook up the scope as shown in Fig. 2 (with the grounds connected to ground), Make sure that both scope inputs are set to “DC” coupling (it is probably already set to this by default, but make sure by pressing “mode coupling”, then press “coupling,” and check that DC is selected; repeat this for both channels 1 and 2 by first pressing the “1” and “2” buttons). 4. Turn on the signal generator. Set the signal generator to a sine wave with an amplitude of 4 Vpp (which will actually give 8 Vpp) and a frequency of 100 Hz. 5. Add an image below of the two waveforms that you observe (V S and V RL ). Note the half-wave rectification. The load voltage (V RL ) is now “DC” (since the current only flows in one direction now, the positive direction). However, the DC signal is not very “pure,” i.e. it not a flat constant line. (4pts) <add your plots here> 3 UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu

ECE 2200/2210 Fig. 3 6. How much lower in amplitude is the V RL result relative to the V S result? Does this make sense? (2pts) <Vs is 7.1V and Vrl is 2.19V> 7. What might we add to the circuit to change V RL so that it is an “always on” DC signal (i.e. a flat line)? Is there a component we studied this semester (resistors, op-amps, capacitors, inductors, diodes) that we could add to this circuit? If so, where might we put this component and how would it work? Consider this before going to the next page. (3pts) < A capacitor in parallel with R L > 8. A capacitor in parallel with R L as shown in Fig. 4 is a good candidate because it can store energy. That is, during the positive portion of the source sine wave, the capacitor can charge up. Then, during the negative portion of the sine wave, the source is “turned off” from the viewpoint of R L and the capacitor (due to the presence of the diode). During this time, the capacitor will discharge into the resistor (the voltage across the capacitor can’t change instantaneously, so it slowly decreases). 4 UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu

ECE 2200/2210 Fig. 4. This figure shows the same circuit as in Fig. 2, except now there is a capacitor in parallel with R L . We will want the time constant of the RC circuit in Fig. 4 to be relatively long so that the discharging of the capacitor will be slow enough to yield a nearly constant DC signal applied to R L . The time constant of an RC circuit is τ = RC . Calculate what you think we should set C equal to. (7pts) < C should be between 45  F to 55  F > 9. If your source is set to 100 Hz, then the period of the wave is 1/100 = 0.01 seconds. We need the capacitor to discharge during half of the period, or 0.01 / 2 seconds = 0.005 seconds. This means we want τ to be much larger than 0.005 seconds. Let’s try making the time constant 10 times larger than the time that no source voltage is applied to the RC circuit, i.e. τ = 10 ∗( sourceisoff ) . Then we can solve for C to yield this time constant: C = 10 ∗( sourceis off ) R = 10 ∗ 0.005 1k Ω = 50 μ F. As a result, try placing a 47 to 220 μF capacitor in parallel with the load resistor as shown in Fig. 4 (remember the capacitor polarity—you don’t want to blow up the capacitor). 10. Observe and plot the effect of the capacitor. You may notice that the load voltage is better than it was, but it’s still not great. The DC voltage still has significant “ripple” like the one shown in Fig. 5. 5 UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu

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