COMSATS Institute of Information TechnologyAttock CampusPower Electronics LAB REPORT#06 Name:Mukhtar Hussain (FA15-BEE-004)Batch:BS(EE)- 5Department :Electrical EngineeringSubmitted to:Engineer AlamdarSubmission Date: 9/11/2017 LAB REPORT-06Introduction to Thyristor Objective:To demonstrate the use of power thyristor for switching DC and AC.To observe the signal waveforms in power circuits. Introduction:
Athyristoris asolid-statesemiconductor devicewith four layers of alternatingPandN-typematerials. It acts exclusively as abistableswitch, conducting when the gate receives a current trigger, and continuing to conduct while the voltage across the device is not reversed (forward-biased). A three-lead thyristor is designed to control the larger current of its two leads by combining that current with the smaller current of its other lead, known as its control lead.Power control in dc circuits is obtained by varying the duration of on-time and off-time of thedevice and such a mode of operation is called on-off control or chopper control.It has four alternating layer and three junctions J1, J2, J3of N type semiconductorand P type semiconductor material. A thyristor has three terminals. Namely anode, cathode and gate. Thyristor acts as a bistable switch, conducts when its anode is made positive with respect to cathode and gate signal (between gate terminal and cathode terminal) is applied. Once the SCR is in its fully conducting state, the voltage drop across the device is generally around 1 V for all values of anode current up to its rated value.The SCR then continues to conduct while the anode current remain above the holding current for the device which is normally denoted as IH. Below this value the SCR stops conducting. Therefore in DC and some highly inductive AC circuits there has to be a means of turning the device off as the SCR will continue conducting.In DC triggering, a sufficient DC voltage is applied between the gate and cathode terminals in such a way that the gate is made positive with respect to the cathode. The gate current drives the SCR into conduction mode. In this, a continuous gate signal is applied at the gate and hence causes the internal power dissipation (or more power loss).
Triggering means turning ON of a device from its off state. Turning ON of a thyristor