Republic of the Philippines
Polytechnic University of the Philippines
Office of the Vice President for Academic Affairs
College of Engineering
ELECTRONICS ENGINEERING (ECE) DEPARTMENT
ECEN 3364-INDUSTRIAL ELECTRONICS AND PLC APPLICATIONS
Group Members
Group No.: 2
Belinario, John Orville T.
Delos Reyes, Arvin Godfrey
Duran, Reineir
Mampusti, Jayron
Rivera, Shawn Ivan
BEN B. ANDRES, DEM, PECE
Professor
________________________________
________________________________
Rating
EXPERIMENT NO. 3
TRIAC
I.
OBJECTIVES
1. To become familiar with the structure, operation, characteristics parameters and
applications of TRIAC.
2. To demonstrate how AC current to a load can be controlled by a TRIAC.
II.
DISCUSSION
The TRIAC is basically a three-layer PN device with added N regions. It can be
triggered into conduction in either direction, making it a bilateral switching device having the
official name of “bi-directional triode thyristor”.3
Structure, Equivalent Circuit and Schematic symbol of TRIAC
Figure 2.1
a) Structure
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Terminal 1
Gate (G)
Terminal 2
b) Equivalent Transistor Circuit
c) Schematic Symbol
Operation of a TRIAC
The TRIAC conducts when the voltage across its main terminals (T 1 and T2) exceeds
the break over points or if it is triggered by a positive or negative voltage pulse applied to
the gate lead.
Figure 2.2 Four Modes of Triggering TRIAC
a) Positive Terminal V with Positive Gate V b) Positive Terminal V with Negative Gate V
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c) Negative Terminal V with Positive Gate V d) Negative Terminal V with Negative Gate V
Current-Voltage Characteristics of a TRIAC
Figure 2.3
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AC Control Using a TRIAC
Figure 2.4 AC Triggering of a TRIAC
0o
90o
180o
270o
360o
current through the load
TRIAC
on
TRIAC
off
TRIAC
on
a) Resistive Triggering Time= 0o to 90o and 180o to 270o
0o
90o
180o
270o
360o
current through the load
TRIAC
off
TRIAC
on
TRIAC
on
b) RC Triggering Time= entire cycle
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TRIAC Definitions
+V
Table 2.1
Forward voltage or positive alternation applied to main terminals of device
-V
Reverse voltage or positive alternation applied to main terminals of device
+VBO
Forward breakover voltage
-VBO
Reverse breakover voltage
VT1
Voltage from terminal 1 to ground
VT2
Voltage from terminal 2 to ground
+I
Forward current when the TRAIC is on
-I
Reverse current when the thyristor is off
III.MATERIALS NEEDED:
1
1
1
2
24-V rms transformer or ac source
Oscilloscope (use only one channel)
2N5752 TRIAC or equivalent
1N5231 zener diodes or equivalent (Z1 and Z2)
2
1
1
1
100-ohm resistors at 0.5W (Rl and RA)
10k-ohm potentiometer (RG)
5.0 uF capacitor at 50 WV dc (CG)
Breadboard for constructing circuit
IV.PROCEDURES:
Part 1.
The first part of this experiment uses only a variable resistor to vary the
trigger time from 0o to 90o and 180o to 270o. An oscilloscope is used to view the voltage
waveforms across the TRIAC and RL.
1. Construct a circuit shown in the Figure 2.4a.
2. Place the oscilloscope across the TRIAC.
3. Vary RG back and forth and view the voltage waveform across the TRIAC.
4. Adjust RG so that the TRIAC triggers about halfway between 0 o and 90o and 180o
and 270o.voltage).
5. Place the oscilloscope across RL.
6. Draw the voltage waveform across RL in the space provided, making sure to align
it with the proper degrees for one cycle. (Indicate peak-to-peak voltage).
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Waveform across TRIAC
Waveform across RL
75% 10k ohm potentiometer
Peak to peak voltage = 47.262V
75% 10k ohm potentiometer
Peak to peak voltage = 2.786 V
Part 2.
In the second part of this experiment, a capacitor is added to the original circuit to
extend the trigger time for nearly the entire cycle. The zenerdiodes simulate a DIAC, which
makes the trigger more symmetrical.
7. Modify the circuit shown in Figure 2.4b by adding the capacitor.
8. Place the oscilloscope across the TRIAC.
9. Vary RG back and forth and view the voltage waveform across the TRIAC.
10. Adjust RG so that the TRIAC triggers past 90o and 270o.
11. Draw the voltage waveform across the TRIAC in the space provided, making
sure to align it with the proper degrees.
12. Place the oscilloscope across RL.
Waveforms across TRIAC
Vp = 25.790V at 75% 10k ohm
potentiometer
Peak to peak voltage = 51.58V
Waveform across RL
75% 10k ohm potentiometer
Peak to peak voltage = 6.3V
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V. OBSERVATION:
The place which firing signal was sent will determine how much signal will only
pass. By varying the time between zero cross and firing pulse we can control the power. By
adding capacitor it helps more to control the power for the load.
VI.CONCLUSION:
o By applying a firing pulse on the gate of the TRIAC we can control the power on
both positive and negative side of the wave.
o By adding capacitor it is used as trigger voltage, which has its phase varies by
changing the variable resistor.
VII.QUESTIONS:
1.
a.)
b.)
c.)
d.)
A TRIAC can be triggered into conduction when the voltage on:
Its T2 terminal is positive and the gate is positive.
Its T2 terminal is positive and the gate is negative.
Its T2 terminal is negative and the gate is positive.
All of the above
2. The device that has a low-voltage drop across its main terminal in either direction when
conducting is a:
a.) SCR
c.) DIAC
b.) TRIAC
d.) none of the above
3. The combination of DIAC and TRIAC forms a:
a.) QUADRAC
c.) Thyristor
b.) VARIAC
d.) LASCR
4. The approximate trigger times for a TRIAC circuit without a capacitor are:
a.) 0o to 45o and 180o to 270o
c.) 0o to 90o and 180o to 270o
b.) 0o to 90o and 270oto 360o
d.) 0o to 180o and 180o to 360o
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5. The approximate trigger times for a TRIAC circuit with a capacitor can be:
a.) 0o to 90o and 180o to 270o
c.) 0o to 180o
o
o
o
o
b.) 0 to 90 and 270 to 360
d.) nearly the entire cycle
6. The turning off a thyristor is known as:
a.) Gating
b.) Commutating
c.) Forward biasing
d.) Interrupting
7. Suppose a TRIAC is used to control the speed of a motor. Also assume that the motor is
highly inductive and causes loss of commutation. What is the likely result?
a.) The TRIAC will short and be ruined.
c.) Power control will be lost.
b.) The TRIAC will open and be ruined.
d.) The motor will lost.
8. The TRIAC is primarily:
a.) An RF device.
b.) An AC power control device.
c.) A dc power control device.
d.) A bidirectional diode.
9. The best device to use as a light dimmer in an ac circuit is the:
a.) Bipolar transistor.
c.) TRIAC
b.) SCR.
d.) Rheostat.
10. Which of the following statements is incorrect?
a.) The gate lead of a TRIAC is used to turn the device on and off.
b.) A TRIAC can be tested with an ohmmeter.
c.) The TRIAC is similar to two SCRs connected in inverse parallel with the gates tied
together.
d.) A TRIAC can be triggered on the positive and negative alternations of a sine wave.
VIII. TRIAC CIRCUITS AND APPLICATIONS
1. CIRCUIT
OPERATION/APPLICATION
TRIAC Switching Circuit
- Can be used for switching of and of of
lights such as traffic lights
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2. CIRCUIT
OPERATION/APPLICATION
Modified TRIAC Switching Circuit
-Can be used for speed control such as
using electric fans.
3. CIRCUIT
OPERATION/APPLICATION
TRIAC Phase control
-Used to control the speed of the motor
such as generator applications etc.
4. CIRCUIT
OPERATION/APPLICATION
Lamp Dimmer Circuit
-Primary used for dimming lights.
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