Lab 3 - Uni-Junction Transistor (UJT) Operation Objectives: 1. To verify and plot the switching characteristics of UJT. 2. To demonstrate the operation of UJT as a relaxation oscillator. 3. To Measure the frequency of oscillations. Procedures: Part I: UJT Characteristics: 1. Construct the circuit as shown in the figure 1 using multisim. V1 -9V R5 500Ω Key=A 0% |: -- PR4 I (p-p): -- R1 15ΚΩ R3 470Ω Q1 I(rms): -- I(dc): -- I(freq): -- Current Probe Voltage Probe PR1 V: -- V(p-p): -- 2N6027 R2 51ΚΩ R4 470Ω V(rms): -- V(dc): -- V(freq): -- Transsitors >> UJT >> 2N6027 Figure 1: UJT test circuit 2. Adjust the R5 potentiometer to 0%. 3. Place current and voltage probes at the anode of the UJT as shown above. 4. Run the simulation and fill the following table by varying the potentiometer as listed under column 1. Potentiometer VA ΤΑ setting 0% 10% 20% 30% 40% 50% 60% 70% 80% 85% 95% 100% Table 1: Measured voltage and current values at the anode 5. Compare the values of VA and lÅ before and after firing (firing implying when UJT is ON). a. Prior to firing, as the VA increases ↳ increases until a voltage called as the peak voltage. From table 1, the peak voltage is b. After firing, là continues to increase whereas VA drops to a lower value called as the valley voltage. From table 1, the valley voltage is C. Since voltage decreases when current increases, this region of operation of UJT is referred as negative resistance region. 6. Based on the readings from the table 1, plot the graph between Anode current (IA) on X-axis and Anode voltage (VA) on the Y-axis. Note: Use word or Excel to plot the graph. Properly indicate the titles for each axis. Part II: UJT as Relaxation Oscillator 1. Modify the previous circuit as shown below. 5 500 V1 .9V R1 16ΚΩ Anode 33 R3 47ΚΩ PR1 Gate Q1 2N6027 V: -- V(p-p): -- V(rms): -- Cathode V(dc): V(freq): -- C1 R2 27ΚΩ R4 = 0.1μF 200 XSC1 B Ext Trig Figure 2: UJT Relaxation Oscillator 2. Record the frequency of oscillations in the table below by modifying the values of R3 and C₁ as listed below. Use the voltage probe to measure the frequency. Measured R3 C1 Frequency 47 ΚΩ 0.1 µF 68ΚΩ 0.1 μF 75ΚΩ 0.1 µF 75ΚΩ 0.01 μF 91 ΚΩ 0.01 µF Table 2: Measured frequency values 3. Connect the oscilloscope at Anode, cathode and gate and insert the waveform snippets (at least 3 cycles) for each of the terminal below using the values in the first row of table 2. Experiment Questions: 1. After UJT fires, VA 2. a. Increases A positive pulse train is found at a. Anode and IA b. Cathode b. decreases of a UJT oscillator c. Gate 3. The voltage waveform at is a sawtooth. a. Anode b. Cathode c. Gate 4. If the value of RE increases, the oscillator frequency a. Increases b. decreases