Objectives:

1. To verify the operation of SCR using DC triggering.

2. To demonstrate the phase control operation of SCR using AC triggering.

Procedures:

1. Research the datasheet of 2N1599 SCR and fill the following table 1 at 250C.

Table 1: Specifications of EC103D1 SCR

Part I: SCR Operation – DC Triggering

2. Construct the circuit as shown in the Figure 1. (use jumpers as a switch)

Figure 1: SCR DC Triggering

3. Connect the gate switch (S1) to R2, and then run the simulation. Do not stop the simulation until you complete table 2.

4. Measure the voltage at the gate terminal and record the measured value in the first row of the table 2 under gate voltage.

5. Measure the voltage between anode and cathode of the SCR and record the measured value in the first row of the table 2 under SCR voltage.

6. Indicate the condition of the SCR whether it is on or off based on the lamp condition.

7. Change the position of the switch in the order as indicated in table 2 below and repeat steps 4 through 6.

Table 2: Voltage measurements and condition of SCR

Part II: Phase control of SCR – AC Triggering

1. Modify the previous circuit as shown below.

Modify the number of turns to 12:0.5:0.5 by double clicking on the transformer

Figure 2: SCR Phase control – AC Triggering

2. Turn the potentiometer (R2) to 0%, which represents the firing angle to be approximately 1800. Then Run the simulation.

a. Since the firing angle is 1800, no power delivered to the lamp and it should be off.

3. The signals on the oscilloscope should be as shown below. Blue one across SCR & Red one across lamp (separate both signals so you can see them clearly).

Figure 3: Oscilloscope waveforms

4. Change the potentiometer in steps of 25%, take the screenshot of the oscilloscope image (use snipping tool), and insert below.

Potentiometer @ 25%:

Potentiometer @ 50%:

Potentiometer @ 75%:

Potentiometer @ 100%:

Answer the following Experiment Questions:

1. Before firing, the voltage from anode to the cathode is _____B______.

a. 0 V b. Approximately Equal to VCC.

2. If the gate is made ___B_____ when the anode and cathode are forward-biased, the SCR turns on.

a. Negative b. Positive

3. The SCR will ___A____ when the gate potential is removed and the anode/cathode are forward-biased.

a. Remain on b. Turn off

4. When the SCR is off, the voltage from the anode to ground is __B______.

a. Close to VCC b. Near 0

5. The SCR will turn off when the current flowing through it drops below the ___Holding Current__________ value.

(Students need to write this).