EEE-454, Power Electronics Laboratory

Experiment 1

Switching Mechanism of Unidirectional Power Switches

Part 01


OBJECTIVE: To experiment with the switching mechanism of unidirectional power switches.


INTRODUCTION: Unidirectional switches are used when the circuit can develop a voltage polarity in one direction only and the switch must be able to block current flow in that direction until switched on.

Some circuits can develop a voltage polarity in both directions and the switch must be able to block current in both directions. However, when switched on, the switch must be able to conduct current in one specific direction only and shall never conduct in the reverse direction. Sometimes, a series-connected diode is needed with the semiconductor switch to be able to meet this requirement.


EXPERIMENT: The following circuits have been constructed in the laboratory.


1. BJT AS A Switch:


EQUIPMENT:

  1. BJT - [Model: BD243C].
  2. Resistor - [1K].
  3. Ceramic Resistor - [220Ω]
  4. Power Supply - [10V].                                
  5. Connecting Wire.
  6. Multimeter.
  7. Trainer Board.
  8. Variable DC Power Supply.


CIRCUIT DIAGRAM:




IB = (VBB - VBE)/1k, Ic = (VCC - VCE)/RL

RL= 200 Ohm (ceramic resistor), VCC = 30V, VBB from 0 to 10V in step of 1and recorded VBB, VBE, VCC, IB, IC, VCE. The switch is ON when VCE = 0. After the switch ON, Ic= (Vcc — 0)/Rc becomes constant (does not increase as Ic = βIB) indicating saturation of the transistor.


DATA TABLE:


VBB

VBE

VCE

IB­ = (VBB­ - VBE)/1K

IC = (VCC – VCE)/RL

0.1 V

45.8 mV

9.98 V

0.0542 mA

0.09 mA

1.11 V

0.644 V

4.3 V

0.465 mA

25.9 mA

1.5 V

0.644 V

120.3 mV

0.856 mA

44.9 mA

3.1 V

0.683 V

32.1 mV

2.415 mA

45.3 mA



PRACTICAL WORK:




DISCUSSION: This lab is related to how BJT works as a switch. We can use a BJT as a switch. By using a BJT as a switch, we can automate the process of switching or switching on or off the load remotely operated instead of using an electromechanical switch that is operated by hand. While doing this experiment, we follow all the rules of the laboratory. First of all, we connect all equipment by following a circuit diagram. Then we connect all the equipment with the AC supply for our experiment. We observe something in our experiment. Our first two BJT was at fault. That’s why we can't complete our experiment. Then we choose another one and that was good. Then we complete our experiment successfully. We take all the values perfectly and put them on the table. We are very careful to take the value of voltages and currents. Sometimes multimeter was not capable to read the short-range value of current. So, we take an effective ammeter to measure the short range of the current value. Finally, we disconnect all the connections carefully and return the equipment to the lab assistant.



PART - 02 CLICK HERE