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Foundations of Technology SCR (Silicon-Controlled Rectifier) Teacher Resource Unit 4 Lesson 4 © 2013 International Technology and Engineering Educators Association, STEMCenter for Teaching and Learning™ Foundations of Technology Objectives: 1. 2. You will build a simple circuit to show that an SCR conducts only after a positive pulse is applied to its gate. You will be able to observe an LED will light until the power is removed from the anode or cathode of the SCR. Gate Anode Cathode You will need the following parts from your kit: 1. 2. 3. 4. 5. 6. 7. 8. Breadboard 220 ohms resistor (red, red, brown, gold) 1000 ohms resistor (brown, black, red, gold) SCR LED (light emitting diode) 9 volt battery lead 3 wires 9 volt battery Use this schematic to construct the experiment. anode 220 Ohms 1K Ohms 9 volts cathode + gate - Beveled Edge front Gate Anode Cathode Quick Check: Your circuit should like this one. This circuit will light the LED after a pulse to the gate. 1. The SCR acts like a switch. 2. When a positive pulse is applied to the gate, it allows current to flow through the rest of the circuit. 3. An SCR is very sensitive to a lot of electrical energy, we use a 1000 ohm resistor to protect the SCR from burning out. 4. An SCR is used in computers and an alarm systems. 1. 2. 3. 4. Connect the 9 volt battery. Observe the brightness of the LED. Briefly touch the “loose” wire to the gate. Observe the brightness of the LED. Troubleshooting: 1. If the LED does not light up, check to make sure it is in correctly. 2. Check the battery. Does it have voltage? 3. Are there any breaks in the circuit? 4. Are you touching the “gate”? By completing this experiment, you should have noticed that current will flow through the SCR only after you put a positive pulse to the gate. In complete sentences, write what you learned about an SCR in a circuit.