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Department OF Electrical and Electronics Engineering

This document provides instructions for determining the holding current, latching current, and break over voltage of a silicon controlled rectifier (SCR). The experiment involves applying gate current and varying anode voltage to obtain the static voltage-current characteristics of the SCR. Key steps include reducing anode voltage to find the latching and holding currents, at which points the SCR switches off with and without gate current respectively. Anode voltage and current values are recorded to plot the forward and reverse static characteristics and determine the SCR's forward resistance. The aim is to experimentally analyze the three operating modes of an SCR from its static V-I curve.

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Rishi Raj Kanojia
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399 views4 pages

Department OF Electrical and Electronics Engineering

This document provides instructions for determining the holding current, latching current, and break over voltage of a silicon controlled rectifier (SCR). The experiment involves applying gate current and varying anode voltage to obtain the static voltage-current characteristics of the SCR. Key steps include reducing anode voltage to find the latching and holding currents, at which points the SCR switches off with and without gate current respectively. Anode voltage and current values are recorded to plot the forward and reverse static characteristics and determine the SCR's forward resistance. The aim is to experimentally analyze the three operating modes of an SCR from its static V-I curve.

Uploaded by

Rishi Raj Kanojia
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOCX, PDF, TXT or read online on Scribd
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DEPARTMENT

OF
ELECTRICAL AND ELECTRONICS ENGINEERING

POWER ELECTRONICS LABORATORY

LAB INSTRUCTIONS FOR CARRYING OUT PRACTICAL

ON

TO DETERMINE HOLDING, LATCHING CURRENT AND BREAK


OVER VOLTAGE OF GIVEN SCR.

SARALA BIRLA UNIVERSITY, RANCHI


AIM: To determine holding, latching current and break over voltage of given SCR.

APPARATUS REQUIRED:
1. Trainer Kit
2. Patch Cords
3. Multimeter
4. CRO

THEORY:
An elementary circuit diagram for obtaining static V-I characteristics of a thyristor is
shown in Fig. The anode and cathode are connected to main source through the load. The
gate and cathode are fed from a source Es which provides positive gate current from gate to
cathode fig. shows static V-I characteristics of a thyristor. Here Va is the anode voltage
across thyristor terminals A, K and Ia is the anode current. Typical SCR V-I characteristic
shown in fig. reveals that a thyristor has three basic modes of operation; namely, reverse
blocking mode, forward blocking (off-state) mode and forward conduction (on state) mode.
These three modes of operation are now discussed below:

CIRCUIT DIAGRAM:
PROCEDURE:

Finding Latching Current


1. Ensure that the SCR is in the state of conduction.
2. Start reducing (VAK) anode voltage in steps of 2V; simultaneously check the state of SCR by
switching off gate supply V2. If SCR switches off just by removing gate terminal, and
switches on by connecting gate supply, then the corresponding anode current IA is the
latching current (IL) for the SCR.

Finding Holding Current


1. Ensure that the SCR is in the state of conduction.
2. Switch off the gate supply permanently.
3. Start reducing (VAK) anode voltage in steps of 2V; simultaneously check the state of SCR. If
SCR switches off. Note down the anode current (I A) just before it drops to zero, which will be
IH.
4. Reverse the anode voltage polarity.
5. Vary VAK in steps of 5V till 25V and note down VAK and IA values at each step
6. Plot forward and reverse characteristics using the above-tabulated values. Find the SCR
forward resistance using the graph.
7. Repeat the above procedure for the forward and reverse characteristics of SCR for a gate
current Ig = Ig2.

OBSERVATION TABLE:

Gate current IG = IG1 =…..mA

Sl. No VG (Volts) IA (mA)


CHARACTERISTIC CURVE:

Latching & Holding Current of SCR


RESULT:

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