Reference no: EM131135536

Lab- Switching Transistors and Optical Devices

Part A-Switching Devices

Week seven activities introduce the concept of electronic switching. Transistors can be used to turn on and off devices such as LEDs. The Silicon Controlled Rectifies (SCR) is another semiconductor that can be used as a switch. Controlling small dc motors is a common requirements and a special IC called an H-bridge is used.

Given a DC switching application such as driving a motor in one and two directions use a SCR and a transistor and an H-bridge driver to successfully perform the operation, calculate and measure the operating voltages and currents.

A. Briefly describe how a transistor is used as an electronic switch including conditions of cutoff and saturation.

a. Write one to two paragraphs describing how a BJT is used as a switch.

b. Write one to two paragraphs describing how a JFET is used as a switch.

B. Given a transistor switch, calculate the saturation voltages and currents and simulate the circuit to verify proper operations.

a. Using the specification sheet, determine the maximum collector current for a 2N3904.

b. Given the circuit, calculate I_{C (sat)} if V_{CE (sat)} = 0.2V.

c. Calculate I_{B (sat)} = __________

d. Determine the value of R_B required to drive the transistor into saturation if V_{BE (sat)}.

e. If you have a different version of Multisim, use your version to create the circuit below. Verify the simulated results against the calculated values. 

V_{CE (sat)} =_______

I_{C (sat)}= _________

I_D = _________

Notice the series LED and a 2kΩ resistor in parallel with R_C. Determine why the LED is not on. Use the Multisim specifications for the LED (Left double click). Explain why the LED will not turn on. Correct the problem and verify the circuit's operation. 

f. Prototype the simulated circuit. Verify the operation of the LED. Measure the following values

V_{CE (sat)} =_______

I_{C (sat)}= _________

I_D = _________

Compare them to the calculated and simulated values.

C. Describe an SCR's structure and operation.

a. Draw the pn structure of a SCR.

b. Draw the schematic symbol and label each terminal.

c. Briefly describe the SCR's operation.

D. Given the data sheet of a typical SCR such as a 2N5060, determine the electrical characteristics and ratings and determine its on-off conditions.

a. Use the specification sheet to determine the Gate, Cathode and Anode terminals. Draw the diagram.

b. Record the following values:

V_RRM= _________

I_T(AV)= _________

V_TM= _________

V_GT= _________

I_GT= _________

I_H= _________

E. Simulate a circuit using an SCR to control a motor or LED.

a. The Multisim circuit below uses a 2N5060 SCR to control an LED with V_CC= 10V, V_TRIG = 3V and R_A = 1kΩ. Use the specification sheet for additional information and determine the value of R_G needed to trigger the SCR. Calculate the expected anode current.

b. If you have a different version of Multisim, create the circuit below. Start the simulation. Closing SW1 should activate the SCR and the LED. The circuit does not work properly. Beginning with the SCR circuit, use the DMMs to troubleshoot the SCR and determine why it will not trigger. Explain why the circuit is not working and what changes are needed.

c. Make the changes. Use the DMMs to verify that the problem has been corrected.

d. Now troubleshoot the LED circuit. Use Multisim to determine the properties of the LED, double click on the diode.

e. Use the DMMs to troubleshoot the LED circuit and determine why it will not illuminate. Explain why the circuit is not working and what changes are needed.

F. Calculate the gate and anode current, prototype and test the circuit and measure the operating values of a SCR used to control a motor or LED. Compare the results with the simulated values.

a. Prototype the working circuit used in the simulation.

b. Verify that the circuit will turn the LED on and off.

c. Measure the following values:

V_GK =_______

I_A = _________

I_ON = _________ LED Current

V_F = _________

How do these values compare to the calculated and simulated results.

G. Given a data sheet of an H driver integrated circuit such as a L293D determine the operating parameters and use drawing software such as Visio to create a schematic of a reversible motor control circuit.

a. Use the specification sheet for an H-Bridge IC driver such as the L293D or L293D and draw the package layout. Label the pins and their functions. For each pin, specify its function.

b. Record the maximum ratings for

V_CC1 =_______

V_CC2 =_______

I_O = _________

c. Draw a schematic of a bi-directional dc motor circuit controlled by mechanical switches and explain how the circuit allows bi-directional operations.

H. Prototype a reversible motor control circuit then measure and record the operating parameters and troubleshoot any faults.

a. Given a dc motor determine the following.

Operating voltage V_M = _________

Operating current I_M = _________

Static dc winding resistance R_static = _________

b. Prototype a motor control circuit using an H-bridge IC. The schematic below contains the LS7404 and the L293D motor driver. Will the L293D support the motor's current requirements? Yes/No.

c. Confirm the motors bi-directional operations

I. Discuss the need for back EMF protection when switching motor circuits.

a. Draw the schematic of a transistor switch used to control a small dc motor. Include a protection circuit for reverse voltage spikes.

b. Explain the need for the protection circuit and how it works.

Part B-Optical Devices

Given an application that requires electrical isolation choose an appropriate optical isolation device to provide the necessary isolation for that particular application.

A. Explain the operation of a 4N25 optical coupler.

a. Draw the internal layout for an optical coupler such as a 4N25. Label the pin numbers and functions.

b. Describe briefly the operation of an optical coupler.

B. Use the specification sheet for typical optical couplers such as the 4N25 and determine suitable operating parameters.

a. Use the specification sheet to determine the following values

Diode forward voltage

Diode forward current

Collector output current

Isolation voltage

Collector to emitter voltage

C. Simulate a circuit that will provide the isolation between two different supply voltages, such as a 5V TTL control circuit and a 12V motor circuit.

a. Using the circuit below, calculate the value of R₁ that allows the switch (Sw) to operate the motor. V_C= 5V, V_M = 6V, I_M = 60mA, Q₂ = 2N3904, U₁ = 4N25, D₁ = 1N4001. Use I(LED) of 2mA

R₁ = __________

b. Simulate the circuit. If you have a different version of Multisim, use your version to create the circuit.

c. Record the following values from the simulation.

I_{C (sat)}= _________

V_{CE (sat)} =_______

I_D = _________ LED Current

D. Prototype a circuit that will provide the isolation between two different supply voltages, such as a 5V TTL control circuit and a 6V motor circuit and compare the simulated values with the measured ones.

a. Prototype the circuit above. 

b. Record the following values.

I_{C (sat)}= _________

V_{CE (sat)} =_______

I_D = _________ LED Current

c. Compare the measured values to the simulated and calculated results.

Part C-Internet Device Searches

1. Use the Internet to locate information on the SN754410 Quadruple Half-H Driver. Download the specification sheet. Specify its package layout. Write a brief description of the device. Is it compatible with the L293D? Why or why not.

2. Use the Internet to locate information on the 4N33 optically coupled isolator. Download the data sheet. Give a brief description of the device. What is its package configuration? How does it differ from a 4N25? Can it directly substitute for a 4N25? Why or why not.