VI CHARACTERISTICS OF SCR (Model No : PEC16M1B)
User Manual
Version 1.0
Technical Clarification /Suggestion : N / F Technical Support Division,
Vi Microsystems Pvt. Ltd., Plot No :75, Electronics Estate, Perungudi, Perungudi, Chennai - 600 096, INDIA. Ph: 91- 44-2496 3142, 91-44-2496 1852 Mail :
[email protected], Web : www.vimicrosystem
CONTENTS
CHAPTER - 1 1.1 CHAPTER - 1
INTRODUCTION
1
Introduction
2
ABOUT OUR TRAINER
3
2.1
About Our Trainer
4
2.2
Front Panel View
5
2.3
Front Panel Description
6
2.4
Specification
6
CHAPTER - 3 3.1
Vi Characteristics of SCR
CHAPTER - 4 4.1 4.2 4.3 4.4
EXPERIMENTAL SECTION
THEORETICAL CONCEPT
SCR Power Circuit SCR Characteristics Device Testing Procedure Precautions
7 8 11 12 13 15 16
VI CHARACTERISTICS OF SCR
PEC16M1B
Chapter - 1
Introduction
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VI CHARACTERISTICS OF SCR 1.1
PEC16M1B
INTRODUCTION
Power electronics deals with the applications of solid-state electronics for the control and conversion of electrical power. Conversion techniques require the switching ON and OFF of power semiconductor device. An ideal power device should have no switching-ON and OFF limitations in terms of turn-ON time, turn-OFF time, current and voltage handling capabilities. Power semiconductor technology is rapidly developing with development in fast switching power devices with increased voltage and current limits. Power switching devices such as power BJTs, power SCRs, GTOs and other semiconductor devices find increasing applications in a wide range of products. The applications of modern microprocessors in synthesizing the control strategy for gating power devices to meet the conversion specifications are widening the scope of power electronics. In this manual we shall discuss about the VI characteristics of SCR.
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VI CHARACTERISTICS OF SCR
PEC16M1B
Chapter - 2
About Our Trainer
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VI CHARACTERISTICS OF SCR 2.1
PEC16M1B
ABOUT OUR TRAINER
The following is front panel of the PEC16M1B module. The Module PEC16M1B consist of SCR VI-characteristics circuit.
Fig - 1. Pictorial View of PEC16M1B
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VI CHARACTERISTICS OF SCR 2.2
PEC16M1B
FRONT PANEL VIEW
Fig - 2. Front Panel View
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VI CHARACTERISTICS OF SCR 2.3
PEC16M1B
FRONT PANEL DESCRIPTION
SCR VI characteristics Trainer module consists of 1. SCR power circuit. 2. SCR power supply circuit. 3. Gate trigger voltage circuit.
2.4
*
Input AC voltage is stepped down to 24V AC and rectified to DC voltage signal.
*
Variable input (0 - 24V) DC is given using the VOLT. ADJUST POT provided on the front panel. Switch (SW2) controls VDC2 input voltage.
*
Input AC voltage is stepped down to 18V and rectified. The rectified voltage signal is regulated to provide (0-15V) DC to the gate of SCR.
*
The gate current adjustment can be made using the coarse and fine adjustment POT. Switch (SW1) controls the VDC1 input voltage.
*
Ammeter between P5 and P7 is to read the gate current (I g). Ammeter between P8 and P11 is to read the device current (IA).
*
Voltmeter across SCR (between P9 and P10) is to read the device voltage (VAK ).
SPECIFICATION
*
Gate voltage (VDC1 )
-
0 to 15V
*
Supply Voltage (VDC2)
-
0 to 24V
*
SCR
-
TYN612 (600V/12A)
*
Load Resistance (R L)
-
220 S / 50W
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VI CHARACTERISTICS OF SCR
PEC16M1B
Chapter-3
Experiment Section
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VI CHARACTERISTICS OF SCR 3.1
PEC16M1B
EXPERIMENTAL SECTION
EXPERIMENT - 1 AIM
To study the VI characteristics of SCR with positive gate current by using PEC16M1B trainer module. APPARATUS REQUIRED
i. PEC16M1B Module. ii. Ammeter (0 to 20 mA)mc -1 No Ammeter (0 to 200 mA)mc-1 No iii. Voltmeter (0 - 30V) - 1 No. iv. Patch Chords. CONNECTION PROCEDURE
i.
Connect connector P1 to P3 and P 2 to P 4.
ii. Connect the ammeter between P5 and P7 connectors. iii. Connect the voltmeter between P8 and P9 connectors. iv. Connect the ammeter between P10 and P11 connectors. v. Connect connector P12 to P 14 and P 13 to P 15. EXPERIMENTAL PROCEDURE
i.
Switch on the 230V AC supply.
ii. Now vary pot3 and set the gate current (IG) in the range of 3mA to 4mA. iii. Now slowly increase the anode-cathode voltage (VAK ) by varying the pot 4 till the thyristor get turned on, note down the ammeter (IA), Voltmeter (VAK ) readings. iv. Now find out Break over voltage(VBR ). v. For various gate current take the reading and tabulate in table 1. vi. Plot the graph VAK Vs IA in a graph sheet.
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VI CHARACTERISTICS OF SCR
PEC16M1B
vii. After note down the max anode current remove the gate current by switch OFF the switch S 1. viii. Now reduce the anode cathode voltage(Vak ) gradually, at on stage the anode current will suddenly reach zero value. The current at this stage is holding current (IH). ix. Now switch ON the switch S 1 and increase anode cathode voltage (Vak ) slightly, now again switch OFF S1. a. If the anode current shows zero value again switch ON S1 and vary the anode cathode voltage. b. If the anode current shows some value, that is the latching current of the SCR. TABLE IL =
(mA)
IH =
(mA) Ig =
S.No
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VAK (V)
(mA) IA (mA)
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VI CHARACTERISTICS OF SCR
PEC16M1B
MODEL GRAPH
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VI CHARACTERISTICS OF SCR
PEC16M1B
Chapter - 4
Theoretical Concept
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VI CHARACTERISTICS OF SCR 4.1
PEC16M1B
SCR POWER CIRCUIT
A thyristor is one of the most important types of power semiconductor devices. Thyristors are used extensively in power electronic circuit. They are operated as bistable switches, operating from non conducting state to conducting state. Thyristor can also called as SCR (silicon controlled Rectifier). A SCR is a four layer three terminal semiconductor switching device of PNPN structure with three PN-Junctions. The three terminals are anode, cathode and gate The thyristor symbol and the sectional view of PN junctions are shown below. SCRs are manufactured by diffusion.
Cross section view of thyristor
Symbol of thyristor
When the anode voltage is made positive with respect to the cathode, the junction J1 and J3 are forward biased. The junction J2 is reverse biased and only the small leakage current flows from positive to negative. The thyristor is then said to be in forward blocking or off-state condition and the leakage current is known as off-state current ID. If the anode-to-cathode voltage VAK is increased to a sufficiently large value. The reverse biased junction J2 will break. This is known as avalanche breakdown and the corresponding voltage is called forward breakdown voltage VBO. Since the other junctions J1 and J3 are already forward biased. There will be free movement of carriers across all three junctions, resulting, in a large forward anode current. The device will be in a conducting state or on state. The voltage drop would be due to the ohmic drop in the four layers and it is small typically 1V. In the on state, the anode current is limited by an external impedance or a resistance R L shown in figure. The anode current must be more then a value known as latching current I L . In order to maintain the requires amount of carrier flow across the junction. Otherwise, the device will revert to the blocking condition as the anode to cathode the voltage is reduced.
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VI CHARACTERISTICS OF SCR
PEC16M1B
Elementary circuit for obtaining VI Characteristics of SCR
4.2
SCR CHARACTERISTICS
Latching current IL is the minimum anode current required to maintain the thyristor in the onstate immediately after the thyristor has been turned on and the gate signal has been removed. The VI characteristics of thyristor is shown below.
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VI CHARACTERISTICS OF SCR
PEC16M1B
Once a thyristor conducts, it behaves like a conducting diode and there is no control over a device. The device will continue to conduct. Because there is no depletion layer on the junction J2 due to free movements of carriers. However, if the forward anode current is reduced below a level known as holding current IH , a depletion region will develop around junction J2 due to the reduced number of carriers and the thyristor will be in the blocking state. The holding current is in the order of milliamperes and is less than the latching current IL. That is I L >IH. Holding current is the minimum anode current to maintain the thyristor in on-state. When the cathode voltage is positive with respect t o the anode, the junction J2 is forward biased, but junction J1 and J3 are reverse biased. The thyristor will be in reverse blocking state and a reverse leakage current known as reverse current IR , would flow through the device. A thyristor can be turned ON by increasing the forward volt age V AK beyond VBO , but such a turn on could be destructive. In practice the forward voltage is maintained below VBO and the thyristor is turned on by applying a positive voltage between gate and cathode. Once a thyristor is turned on by a gating signal and its anode current is greater than the holding current the device. Continues to conduct due to positive feedback, even if the gating signal is removed. A thyristor is a latching device.
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VI CHARACTERISTICS OF SCR 4.3
PEC16M1B
DEVICE TESTING PROCEDURE
SCR
1. Set the multimeter to diode mode of operation. 2. Connect multimeter voltage terminal to gate terminal of SCR. 3. Connect multimeter common terminal to cathode terminal of SCR. 4. Multimeter will show the low resistance value (typical 40 to 120S). 5. Remaining any of two combination will show the very much high value resistance (or) open.
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VI CHARACTERISTICS OF SCR 4.4
PEC16M1B
PRECAUTIONS
Before doing the installation check out the below mentioned apparatus. #
VI characteristics of SCR trainer module (PEC16M1B).
Do’s
i.
Ensure the fuses are in good condition.
ii. Switch ON the power. iii. Ensure the input supply 230V AC, 50Hz signal. iv. Whenever doing the connections make sure that all switches are in OFF condition. v. Make the connections as per the connection procedure. vi. Switch ON the power and SPDT switches. vii. Do the experiment as per the experimental procedure. Dont's
i. Do not short connectors P1 and P2. ii. Do not short connectors P14 and P15. 4.5
SERVICE TIPS
*
Check for 18V AC signal at VDC1,else replace 230V/18V transformer (or) rectifier.
*
Check for 24V AC signal at VDC2,else replace 230V/24V transformer (or) rectifier.
*
Check for voltage variation up to 24V (VDC2) else replace POT3 (or) Regulator.
*
Check for the fine and coarse adjustment of the gate voltage (VDC1) else replace POT2 and POT1 respectively.(or) Regulator
*
Check for the SCR device by following the device testing procedure else replace SCR device. If it fails, replace the SCR device.
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