EEE-454, Power Electronics Laboratory

Experiment 1

Switching Mechanism of Unidirectional Power Switches

Final Part


ANSWERING QUESTION:


1.     1. What is the significance of using a transistor switch and a power electronic switch?

Ans: A transistor switch is more economical than other switches. It gives trouble-free service because of its solid-state nature. It has no moving parts and hence there is no tear and wear. It gives noiseless operation. In power electronics circuitry, these switches act in the saturation region and work in the linear region in the analogue circuitry such as in power amplifiers and linear regulators. This makes these switches highly efficient since there are lesser losses during the power processing.

 

2.     2. When will you understand that the switching device is switching the circuit?

Ans: An ideal transistor switch would have infinite circuit resistance between the Collector and Emitter when turned “fully OFF” resulting in zero current flowing through it and zero resistance between the Collector and Emitter when turned “fully ON”, resulting in maximum current flow.

Therefore, the transistor acts as an open circuit and the LED becomes OFF. When the switch is closed, the base current starts flowing through the transistor and then drives into saturation, resulting in the LED turning ON. Resistors are placed to limit the currents through the base and LED.

 

3.     3. What is the dissimilarity of switching between SCR and TRIAC?

Ans: The main difference between SCR and TRIAC is, that SCR is a Unidirectional Semiconductor Device, it is conducting current in only one direction so switching is possible in only one direction. But TRIAC is a Bi-Directional semiconductor device, it is conducting currents in both directions, so switching is possible in both directions. 

 

4.  4. Is there any difference between using the NPN structure and the PNP structure of the transistor for switching?

Ans: NPN structure transistor has a faster switching system Here, the direction of current is Collector to Emitter. PNP structure transistor has a slower switching system, here direction of current is Emitter to Collector. 




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