Objective: The objective of this exercise is to examine the Zener diode's V-I characteristic curve on an oscilloscope. Components needed: Resistors: 220 £2, 1.0 k 2, 2.2 k Four rectifier diodes 1N4001 1.0k 2 potentiometer 5 V Zener, (1N4733A or equivalent) 12.6 V ac center-tapped transformer with fused line cord Schematic: 1/4 A R. 1.0 ΚΩΣ 12.6 V IN4733AZ 20000 44 이히 이런 Invert Y Channel Figure 3-1 Procedure: Important safety note: You are connecting a 12.6 VAC transformer into the ac utility voltage. Be certain the line cord is insulated and fused. At no time should you touch the circuit when it is connected. You will make no connections or measurements on the primary side of the transformer. 1. Measure and record the values of the resistors listed in Table 3-1 2. Observe the Zener characteristics curve by setting up the circuit shown in Figure 3-1. Put scope in the X-Y mode. Sketch the V-I curve using "IntuiLink" software (installed on the lab desktops). The 1.0 k2 resistor changes the scope's y-axis into a current axis (1mA per volt). Label your plot for current and voltage. 3. Investigate the effect of a Zener regulator as the source voltage is varied. Connect the circuit shown in Figure 3-2. Set V, to each voltage listed in Table 3-2 and measure the output (load) voltage, Vout Vs R₁ ww 220 Ω VOUT 1/2 W IN4733A R₁ 2.2 ΚΩ Figure 3-2 4. From the measurements in step 3, complete Table 3-2. Apply Ohm's Law to compute the load current, I, for each setting of the source of voltage. The voltage across R₁ (VR1) can be found by applying Kirchhoff's Voltage Law (KVL) to the outside loop. It is the difference between the source voltage, V, and the output voltage, Vout. Note that I, is through R₁ and can be found using Ohm's law. Find the zener current, Iz, by applying Kirchhoff's Current law (KCL) to the junction at the top of the zener diode. What happens to the zener current after the breakdown voltage is reached? 5. Test the effect of a variable load resistance on a zener regulator. Construct the circuit shown in Figure 3-3. Set the power supply to a fixed +12.0 V output and adjust the potentiometer (R) for maximum resistance. Vs R₁ ww 220 Ω 1/2 W VOUT IN4733A R₁₂ 3 1.0 ΚΩ Figure 3-3 6. With the potentiometer set to 1.0 k2 (maximum resistance), measure the load voltage (Vout) and record the voltage in Table 3-3. Compute the other parameters listed on the first row as before. (Use Ohm's law for IL, KVL for VR1, Ohm's law for Is, and KCL for Iz). 7. Set the potentiometer to each value listed in Table 3-3 and repeat step 6. 8. From the data in the Table 3-3, plot the output voltage as a function of load resistance using "IntuiLink" software. Choose a reasonable scale factor for each axis and add labels and a title to the plot. Data: Table 3-1: Resistor Table 3-2: Listed value Measured value R₁ 220 Ω R₂ 1.0 ΚΩ 220 1.00 An RL 2.2 ΚΩ 2.00 A Vs Vout IL VR1 Is Iz (measured) (computed) (computed) (computed) (computed) 2.0 V 1.82V 4.0 V 3.6V 6.0 V 4.45V 8.0 V 10.0 V 5.68V 5.76V Table 3-3: RL Vout IL (measured) (computed) VR1 (computed) Is (computed) Iz (computed) 1.0 ΚΩ 5.31 750 Ω 5.30 500 Ω 5.20 250 Ω 5.10 100 Ω 3.70