Characteristics of DIAC
AIM:
To study the characteristics of DIAC in forward and reverse bias.
APPARATUS REQUIRED:
| S.No | Components | Specification | quantity |
| 1 | DIAC | | 1 |
| 2 | Resistor | 1kohm | 1 |
| 3 | Ammeter | (0-30)mA | 2 |
| 4 | Voltmeter | (0-30)V | 1 |
| 5 | Bread Board | | 1 |
| 6 | Regulated Power Supply | 0-30V | 1 |
THEORY:
Diacs are three-layer bilateral trigger diodes. Like PIN diodes, diacs are breakdown devices. However, unlike PIN diodes, diacs are triggered from a blocking-to-conduction state in either polarity of applied voltage. Consequently, there are no band encirclings around the device body to indicate the cathode end, because the orientation of the device is irrelevant. For example, if the rated breakover voltage (the breakdown voltage, or avalanche point) for a specific diac is 30 volts, it will present an extremely high resistance until the voltage drop across it equals about 30 volts. At that point, it will become highly conductive; and it will remain in this state until the voltage across it reaches a minimum level. At that point, it becomes highly resistive again. It will react this way regardless of the voltage polarity; hence, it is bilateral in operation.
Diacs are most commonly used in high-power control circuitry to provide the turn-on pulses for silicon controlled rectifiers (SCRs) and triacs. Diacs were designed to be a solid-state replacement for neon tubes.
PROCEDURE:
1. Connect the circuit as per the circuit diagram.
2. Vary the input voltage in steps.
3. Note down the Voltage across and Current through the device using the Voltmeter and Ammeter.
4. Plot the graph and study the Characteristics.
RESULT:
Thus the characteristics of DIAC is studied and the graph were plotted.
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Characteristics of TRIAC
AIM:
To study the characteristics of TRIAC in forward and reverse bias.
APPARATUS REQUIRED:
| S.No | Components | Specification | Quantity |
| 1 | TRIAC | | 1 |
| 2 | Resistor | 1kohm | 1 |
| 3 | Ammeter | (0-30)mA | 2 |
| 4 | Voltmeter | (0-30)V | 1 |
| 5 | Bread Board | | 1 |
| 6 | Regulated Power Supply | 0-30V | 1 |
THEORY:
Triacs are devices similar to SCRs they act as electrically controlled switches but unlike SCRs, they are designed to pass current in both directions, therefore making them suitable for ac applications. Triacs come with three leads, a gate lead and two conducting leads called MT1 and MT2. When no current/voltage is applied to the gate, the triac remains off. However, if a specific trigger voltage is applied to the gate, the device turns on. To turn the triac off, the gate current/voltage is removed.
Triacs are used in ac motor control circuits, light-dimming circuits, phase-control circuits, and other ac power-switching circuits. They are often used as substitutes for mechanical relays.
PROCEDURE:
1. Connect the circuit as per the circuit diagram.
2. Keep IG=0.Varying the voltage across MT1 and MT2.
3. Note down the current through MT1 to MT2.
4. Repeat the same procedure for different IG value.
RESULT:
Thus the characteristics of TRIAC is studied and the graph were plotted.
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CHARACTERISTICS OF UJT
AIM:
To study the characteristics of UJT.
APPARATUS REQUIRED:
| S.No | Components | Specification | Quantity |
| 1 | UJT | | 1 |
| 2 | Resistor | 1kohm | 1 |
| 3 | Ammeter | (0-30)mA | 2 |
| 4 | Voltmeter | (0-30)V | 1 |
| 5 | Bread Board | | 1 |
| 6 | Regulated Power Supply | 0-30V | 1 |
THEORY:
Unijunction transistors (UJTs) are three-lead devices that act exclusively as electrically controlled switches (they are not used as amplifier controls). The basic operation of a UJT is relatively simple. When no potential difference exists between its emitter and either of its base leads (B1 or B2), only a very small current flows from B2 to B1. However, if a sufficiently large positive trigger voltage relative to its base leads is applied to the emitter, a larger current flows from the emitter and combines with the small B2-to-B1 current, thus giving rise to a larger B1 output current. Unlike the other transistors where the control leads (e.g., emitter, gate) provided little or no additional current—the UJT is just the opposite; its emitter current is the primary source of additional current.
PROCEDURE:
1. Connect the circuit as per the circuit diagram.
2. Keep VB1B2=0.Vary VEB1 in steps and note down IE value.
3. Repeat the same procedure for different value of VB1B2.
4. Plot the graph.
RESULT:
Thus the characteristics of UJT is studied and the graph were plotted.
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