INTRODUCTION TO

INTRODUCTION TO OTHER
ELECTRONIC DEVICE

BY GROUP 5

TEAM MEMBERS

MUHAMMAD HARISH DANIAL
BIN SHAHRUL MAZNAN
(08DJK21F1059)

MUHAMMAD ALIFF SYAMIN
BIN MOHD ZAKI
(08DJK21F1061)

MUHAMMAD ASYRAF BIN MOHD
YUNUS

(08DJK21F1056)

ILUSTRATE THE PHYSICAL STRUCTURE
SCHEMATIC SYMBOLS OF THE
FOLLOWING COMPONENTS

SILICON CONTROLLED RECTIFIER

SCRs are unidirectional devices (i.e. can conduct current only in one direction) as opposed to
TRIACs, which are bidirectional (i.e. charge carriers can flow through them in either direction).
SCRs can be triggered normally only by a positive current going into the gate as opposed to
TRIACs, which can be triggered normally by either a positive or a negative current applied to its
gate electrode

TRIAC

Uses of Triac
1.They are used in control circuits.
2.It is used in High power lamp switching.
3.It is used in AC power control.

A Triac is defined as a three terminal AC switch which is different from the other silicon
controlled rectifiers in the sense that it can conduct in both the directions that is whether the
applied gate signal is positive or negative, it will conduct. Thus, this device can be used for AC
systems as a switch.

DIAC

The DIAC is an electronics component that is widely used to assist even triggering of a TRIAC when used
in AC switches and as a result they are often found in light dimmers such as those used in domestic
lighting. These electronic components are also widely used in starter circuits for fluorescent lamps.
Most DIACs have a three-layer structure with breakover voltage of approximately 30 V and an
on voltage of less than 3 V. Their behavior is analogous to the striking and extinction voltages of
a neon lamp.

UNI-JUNCTION TRANSISTOR (UJT)

A unijunction transistor (UJT) is a three-lead electronic semiconductor device with only one
junction that acts exclusively as an electrically controlled switch. The UJT is not used as a linear
amplifier. It is used in free-running oscillators, synchronized or triggered oscillators, and pulse
generation circuits at low to moderate frequencies (hundreds of kilohertz). It is widely used in the
triggering circuits for silicon controlled rectifiers.
The schematic diagram symbol for a unijunction transistor
represents the emitter lead with an arrow, showing the
direction of conventional current when the emitter-base
junction is conducting a current.

Explain and sketch the I-V characteristics of
the devices above.

TRIAC

FEATURES - FEATURES TRIAC
The triac is designed with two SCRs made in opposite directions to the
crystal. The operating characteristics of the triac on quadrants 1 and 3 are
similar but for current and voltage flow directions apply.

“how to convert digital to analog ”
The V-I characteristics of the triac on the first and third quadrants are essentially the same as the
SCR characteristics on the first quadrant. It can work with a gate control voltage of + Ve or –Ve but
in normal operation, the gate voltage is + Ve in the first quadrant and -Ve in the third quadrant.
The supply voltage of the triac to turn on depends on the gate current. This allows the use of a triac
to regulate AC power in loads from zero to full power in a smooth and constant manner without loss
of device control.

DIAC

The DIAC works like an open circuit until the transition is excessive. At that position, the
DIAC works until the current drops towards zero. Due to its abnormal construction, it does
not turn sharply to low voltage conditions at low current levels such as triacs or SCRs, upon
entering the transmission, the diac retains an almost constant -Ve resistance characteristic,
i.e., the voltage decreases with increasing current. This means that, unlike triacs and SCRs,
DIACs cannot be estimated to be able to maintain a low voltage drop until the current drops
below the resistance current level.

UNI JUNCTION TRANSISTOR

FEATURES - FEATURES (UJT)
Unijunction Transistor: Although a unijunction transistor is not a thyristor, this device can
trigger larger thyristors with a pulse at base B1. The unijunction transistor consists of an N-
type silicon bar that has a P-type connection in the center. See Figurebelow (a). The
connections at the ends of the bars are known as bases B1 and B2; the P-type midpoint is the
transmitter. With the transmitter decided, the total resistance of R BBO, a datasheet item, is
the sum of R B1 and R B2 as shown in Figurebelow (b). R BBO ranges from 4-12kΩ for different
device types. The intrinsic standoff ratio η is the ratio of R B1 to R BBO. It varies from 0.4 to
0.8 for different devices. The schematic symbol is Figurebelow (c)

BASIC CONSTRUCTION AND
APPLICATION

1.Silicon Controlled Rectifier(SCR)

CONSTRUCTION OF SCR
An SCR is constructed with the four layers that consist ofthe P-
type and the N-type semiconductor material.These are layered in
such a way that three junctions that are J1, J2, and J3. The three
terminals that are attached to it are known as anode,cathode, and
gate.

application of scr



Silicon control rectifier (SCR) is used in batterycharger. It is used to
Adjust light dimmer. It is used to control motors speed. The SCR is
used inpulse circuit. It is used for AC power control with solid relay.

2. triac

CONTRUCTION OF TRIAC
TRAIC is a four-layer device that is made from acombination of two
antiparallel SCRs having three terminals Gate, MT1 and MT2. Both
main terminals (MT1and MT2) electrodes are connected with both P
and Nregions of both SCRs. So that it can conduct current inboth
directions.

APPLICATION OF TRIAC

 The Triac is most commonly used semiconductor devicefor switching and power
control of AC systems as thetriac can be switched “ON” by either a positive ornegative
Gate pulse, regardless of the polarity of the ACsupply at that time.
It finds applications in switching, phase control, chopperdesigns, brilliance control
in lamps, speed control in fans,motors,and etc

3.DIAC

CONTRUCTION OF DIAC
DIAC can be constructed in 3-layer and 5-layersymmetrical structure. The 3-layer
structure is mostly usedwhich is made by either sandwiching N or P between
itsalternating layers forming PNP or NPN structure. Thebreak over voltage of such DIAC
lies around 30 volts.

APPLICATION OF DIAC

The main application of a DIAC is its use in a TRIAC triggering circuit. The DIAC
is connectedto the gate terminal of the TRIAC. When the voltage across the
gate decreases below apredetermined value, the gate voltage will bezero and
hence the TRIAC will be turned off.

UNI JUCTION TRANSISTOR(UJT)

CONSRUCTION OF UJT
The UJT consists of an n-type silicon semiconductor barwith an electrical on each end. The terminals of
theseconnections are called Base terminals (B1 and B2). Nearto base B2, a pn-junction is formed between a p-
typeemitter and the n-type silicon bar.

APPLICATION OF UNI JUCTION TRANSISTOR(UJT)

The most common application of a unijunctiontransistor is as a triggering device for SCR's
andTriacs but other UJT applications includesawtoothed generators, simple oscillators,
phasecontrol, and timing circuits. The simplest of all UJT circuits is the Relaxation Oscillator
producing non-sinusoidal waveforms.

Equivalent Circuit of UTJ and its
operation

Equivalent Circuit of a UJT

OPERATION OF A UJT

Imagine that the emitter supply voltage is turned down to zero. Then the intrinsic
stand-off voltage reverse-biases the emitter diode, as mentioned above. If VB is
the barrier voltage of the emitter diode, then the total reverse bias voltage is VA +
VB = Ƞ VBB + VB. For silicon VB = 0.7 V.

Now let the emitter supply voltage VE be slowly increased. When VEbecomes equal to Ƞ VBB, IEo will
be reduced to zero. With equal voltage levels on each side of the diode, neither reverse nor forward
current will flow. When emitter supply voltage is further increased, the diode becomes forward-biased
as soon as it exceeds the total reverse bias voltage (Ƞ VBB + VB). This value of emitter voltage VE is
called the peakpoint voltage and is denoted by VP. When VE = VP, emitter current IE starts to flow
through RB1 to ground, that is B1.

This is the minimum current that is required to trigger the UJT. This is called the
peak-point emitter current and denoted by IP. Ip is inversely proportional to
the interbase voltage, VBB. Now when the emitter diode starts conducting,
charge carriers are injected into the RB region of the bar. Since the
resistance of a semiconductor material depends upon doping, the
resistance of region RB decreases rapidly due to additional charge carriers
(holes). With this decrease in resistance, the voltage drop across RB also
decrease, cause the emitter diode to be more heavily forward biased. This,
in turn, results in larger forward current, and consequently more charge
carriers are injected causing still further reduction in the resistance of the RB
region. Thus the emitter current goes on increasing until it is limited by the
emitter power supply. Since VA decreases with the increase in emitter
current, the UJT is said to have negative resistance characteristic. It is seen
that the base-2 (B2) is used only for applying external voltage VBB across it.
Terminals E and B1 are the active terminals. UJT is usually triggered into
conduction by applying a suitable positive pulse to the emitter. It can be
turned off by applying a negative trigger pulse.

HOW CAN SCR BE TURNED ON

When S1 is opened no current flows at the RL (lamp) load as shown in Figure 1.2 (a) and (b)
the SCR will only live when a pulse of positive current is applied at its gate terminal and at
the same time the anode terminal is more positive than cathode. This trigger will cause a
forward current to flow from the anode to the cathode. At this time the anode-cathode
terminals are in a short-circuit state. This forward bias current will continue to flow even if
the trigger voltage at the gate is stopped as long as the anode-cathode terminals are in the
forward bias state. When switch S1 is closed then the gate terminal will receive the trigger
current and trigger the SCR. This trigger causes current to flow from the anode to the
cathode of the SCR and the lamp will illuminate. When switch S1 is opened current is still
flowing to the load or the lamp is still on

HOW CAN SCR BE TURN
OFF

How SCR can be turned off
To turn off the SCR, there are three methods that can be done, namely, by bypassing the
anode-cathode terminal, disconnecting the current supply to the anode or reversing the
voltage supply source so that reverse current flows from the cathode to the anode.

Simple Lamp Circuit using a TRIAC

THANK TOU !