2014-03-30 12-06 pm.pdf11.docxPower Ele.docx

2014-03-30 12-06 pm.pdf
1/1.docx
Power Electronics
Contents
1.0 Rectifier using Diodes 3
1.1 Rectifier with filter output current direct 7
1.2 Applications 8
2.0 Schmatic circuits 11
2.1 Rectifire circuit 11
2.2 Output waveforms 12
2.3 Controlled rectifier 13
3.0 References 18
Figure 1: simple half-wave rectifier circuit composed of a single
diode3
Figure 2: operation of a rectifier circuit for full-wave
alternating current composed of two silicon diodes.4
Figure 3: Schematic represent different forms of the same full-
wave bridge rectifier consists of four diodes.5
Figure 4: four-diode bridge rectifier6

Figure 5: linear direct current7
Figure 6: added to the filter resistance (R) or an inductance (L)8
Figure 7: 12 volt direct current (DC)9
Figure 8: current (DC) motor9
Rectifier using Diodes
The rectification of alternating current (AC) to convert it
into direct current (DC). This rectification is one of the oldest
technologies used in electronic circuits since early last century,
even before the existence of the solid state semiconductor
elements such as silicon diodes know today. Since the diodes
allow the passage of electric current in one direction and
prevent it in the opposite direction, have also been used for
many years in the detection of high-frequency signals, such as
broadcasters, to turn them into audible in radio receivers. At
present several types of special construction diodes can perform
functions other than simple correction or current detection when
installed in electronic circuits. Operation of a common half
wave rectifier diode To better understand how works
a semiconductor diode, remember that the first alternating
current (AC) flowing through the electrical circuit forming a
sinusoid, which has positive polarity half cycle while the other
half cycle has negative polarity. That is, when an alternating
current flows through a closed circuit constantly changes its
polarity many times as cycles per second or hertz frequency
have. In the case of alternating current that comes into our
homes can often be 50 or 60 cycles depending on the system
adopted by each country. In Europe the frequency adopted is 50
cycles and 60 cycles in most of Latin (See table of frequency of
the current country and the respective voltages).
Figure 1: simple half-wave rectifier circuit composed of a single
diode
In the animation above it can see that in the process of
rectifying the alternating current (AC) using a single diode, for
a first negative half cycle the electrons will flow through the
circuit through first diode and then the consumer or electric

charge, represented by a resistance (R) . At that moment, at the
ends of the resistance was able to detect a direct "pulsing" that
responds to the current half cycle. In the next half cycle (this
time positive), electrons change their direction of movement
and cannot pass nor resistance, nor the semiconductor diode,
because at that time the road will be blocked by the positive
terminal of the diode and no movement of current through the
circuit. Then and during the negative half cycle following again
the diode returns to allow the passage of electrons, to lock it
again to change the direction of current flow and so on while
you carry on giving power to the diode. therefore during each
negative half cycle of a source of alternating current
(AC) connected to a diode polarity registers fixed to the ends of
a load connected to the output circuit of the diode itself, while
during the following positive half cycle does not appear polarity
whatsoever due to blocking diode that provides the flow of
electrons in reverse itself. Thus, consumer via pulsed current
will flow, since in this case the diode acts as a rectifier for half-
wave alternating current. Operation of the full wave rectifier
diodes When an electric circuit or electronic requires a direct
current that non-pulsating, but much more linear than that
allowed a simple half-wave rectifier, it is possible to combine
from two to four rectifier diodes such that the resultant is a
direct current (DC) with less residual oscillations.
Figure 2: operation of a rectifier circuit for full-wave
alternating current composed of two silicon diodes.
The most usual for a rectifier bridge of "full-wave" structure is
composed of four diodes connected conveniently. However, in
some cases, a similar effect is obtained only by connecting two
diodes, using as a supply source of alternating current (AC) a
transformer with a center tap on the secondary winding. That
allows to feed equally diodes each with its symmetry in counter
phase which enables the
Winding midpoint is always the negative while the positive
changes at their ends each half cycle of alternating current

frequency applied to the circuit. However, the output of the
rectifier circuit is obtained one direct current (DC) full wave.
However, most of the electrical or electronic circuits operating
with direct current (DC), use full-wave rectifiers consisting of
four diodes. Following are three outline shapes are illustrated in
a diagram the connection of the four diodes for full-wave
rectifier.
Figure 3: Schematic represent different forms of the same full-
wave bridge rectifier consists of four diodes.
A four-diode bridge rectifier works in the following way: as
shown in the part (A) for illustration, during the first negative
half cycle (-) of the power provided by the AC power supply
(AC) connected to bridge rectifier of electrons through the first
diode (1) , then the consumer (R) and then the diode (2)in order
to complete the flow of the current of electrons corresponding
to one half of the bridge rectifier circuit.
Figure 4: four-diode bridge rectifier
A four-diode bridge rectifier works in the following way: as
shown in the part (A) for illustration, during the first negative
half cycle (-) of the power provided by the AC power supply
(AC) connected to bridge rectifier of electrons through the first
diode (1) , then the consumer (R) and then the diode (2)in order
to complete the flow of the current of electrons corresponding
to one half of the bridge rectifier circuit.
For clarification, the arrival of the electrons on their way to the
connection point (a), cannot pass through the diode (4) because,
according to the placement of these cases within the circuit
block or impede the movement of electrons in that sense. Once
the electrons continue their journey, arriving at the connection
point (b), cannot pass through the diode (4), because the
electron current never flows toward his own encounter (similar
to what happens with the flow of water in a river), but always
moving toward the opposite pole of the power supply that
provides electricity, that is, the positive terminal of the

alternating current (AC) in this case. In Part (B) of the
illustration we see that the alternate current changes polarity
and hence the direction of flow of electrons. At this time,
electrons pass through the first diode (3), then pass through the
consumer (R) and finally, the diode (4) to return to the power
source and complete the circuit. Similar to what happened in the
previous cycle, now the diode (1) is responsible for block him
electrons so that they can direct towards the consumer (R) ,
while the diode (2) cannot pass through electrons, because they
cannot go at their own game, as in the previous half
cycle.Rectifier with filter output current direct
If want a rectifier device full wave give a possible as linear
direct current, we can place a filter composed of one or two
electrolytic capacitors polarized, such as (C 1 ) and (C 2 )
shown in the illustrations below, connected to the output circuit
of direct current (DC) and rectified.
Figure 5: linear direct current
Besides these capacitors should be added to the filter resistance
(R) or an inductance (L) connected between the two capacitors.
The filter function is to compensate for variations or residual
deformations that may be left remaining in the rectified current.
To do this during the negative half cycle and the capacitors are
charged during the positive half cycle next downloaded to fill
gaps without charge created between a ridge and the other
corresponding to the average rectified current waves.
Figure 6: added to the filter resistance (R) or an inductance (L)
However, some computers and electronic devices (especially the
sound, for example) require a direct current or rectified as pure
as linear as possible, so to get this result will need to place a
transistor below the filter, stabilizer function.Applications
Figure below show one full wave rectifier device used is shown
on a computer that operates on 12 volt direct current (DC),
connecting to a home making alternating current (AC) 220 volt.
On the left side of this device you can see a transformer

responsible for transforming or reduce the 220 volt input 12
volt output AC also. In the center it can see a bridge rectifier,
which converts the 12 volt alternating current (AC) into 12 volt
direct current (DC). To the right of the two electrolytic
capacitors and resistors which make filter function are
observed. The other strength is also visible, circuit is used to
reduce the voltage of the LED (at the bottom of photo)
employee as a witness or pilot light to indicate that the
computer is connected to AC power on your home network,
even when it is not in use.
Figure 7: 12 volt direct current (DC)
It is not always necessary to have a filter to use an alternating
current rectified. For example, in this photo it can see an only
made four separate diodes, which provide direct current (DC) to
a small bridge rectifier electric motor coupled to a fan
hairdryer. The black wires corresponding to the input
alternating current (AC) feeding the rectifier bridge. The
positive pole [with the sign (+) in red] and negative [with the
sign (-) in blue] indicate the output polarity of the direct current
and rectified by the bridge. In this case the positive and
negative terminals are connected directly to the input terminals
of the direct current (DC) motor, both located on the back
cover. As can be seen, in this case we have omitted the use of
filter as not being necessary for the engine to run.
Figure 8: current (DC) motor
Devices with different silicon diode bridges based rectifiers.
Alternately to make it directly. To the left is a laptop charger
that appears. Also allows us to continue working with it when
the batteries are always exhausted. They stay connected to the
network from the household AC outlet. In the center as shown
.Adapter used to energize a signal converter DTT (Digital
Television. On the right you can see a mobile phone charger.

The full-wave rectifiers have a wide use in different types of
devices such as adapters using different electronic equipment,
as well as battery chargers that use mobile phones, digital
cameras, mp3 players, computers laptops and many other more
appliances and electronic devices that operate with direct
current. Thus a bridge rectifier enables any device or equipment
direct current (DC) can connect to the network of alternating
current (AC) for domestic use thus being able, or otherwise
charge their batteries.
Schmatic circuitsRectifire circuit
The schematic figure above is using Pspice software.
· First circuit for single diode rectifier.
· Second circuit with adding inductive load “L” in series with
resistance.
· 3rd circuit with adding freewheeling diode in parallel with
load. Output waveforms
Yellow is output wave form and blue is AC input wave form
As noted from wave form waveforms when single diode rectifier
only in circuit with resistive load the output is normal as same
positive input wave form.
When adding inductive load “L” in series with resistance the
negative voltage is in appear due to coil discharge.
When adding freewheeling diode in parallel with load the
negative is removed by discharging in diode.

Controlled rectifier
Four circuits was drawn with Pspace as shown above. The
THYRISTOR and diode was used to build this circuits.
Both diode and SCR (Silicon Controlled Rectifier) are
semiconductor devices with P type and N type semiconductor
layers. They are used in many electronic switching applications.
Both devices have terminals called ‘anode’ and ‘cathode’ but
SCR has an additional terminal called ‘gate’. Both these devices
have application dependant advantages.
Diode is the simplest semiconductor device and it consists of
two semiconductor layers (one P-type and one N-type)
connected to each other. Therefore diode is a PN junction.
Diode has two terminals known as the anode (the P-type layer)
and cathode (the N-type layer).
Diode allows current flows through it only in one direction that
is anode to cathode. This direction of current is marked on its
symbol as an arrow head. Since diode restricts the current to
only one direction, it can be used as a rectifier. The full bridge
rectifier circuit which is made of four diodes can rectify an
alternative current (AC) to a direct current (DC).
The diode starts acting as a conductor when a small voltage is
applied in the direction of anode to cathode. This voltage drop
(known as the forward voltage drop) is always there when a
current flow happens. This voltage is usually about 0.7V for
normal silicon diodes.
SCR is a type of thyristor and widely used in current
rectification applications. SCR is made of four alternating
semiconductor layers (in the form of P-N-P-N) and therefore
consists of three PN junctions. In analysis, this is considered as
a tightly coupled pair of BJTs (one PNP and other in NPN
configuration). The outermost P and N type semiconductor
layers are called anode and cathode respectively. Electrode
connected to inner P type semiconductor layer is known as the
‘gate’.

In operation, SCR acts conducting when a pulse is provided to
the gate. It operates at in either ‘on’ or ‘off’ state. Once the
gate is triggered with the pulse, SCR goes to the ‘on’ state and
keep conducting until the forward current become less than a
threshold known as ‘holding current’.
SCR is a power device and most of the times it is used in
applications where high currents and voltages are involved. The
most used SCR application is controlling (rectifying) alternating
currents.
Figure above show out wave from 4 SCR with inductive load.
The out from as same when adding freewheeling diode
The out wave form when replace the two SCR in one above the
other in right side the output wave form have a noise as shown
in figure above.
When replace the two of SCR with two diode the output wave
from as the same connecting half wave rectifier.
References
Issa Batarseh, "Power Electronic Circuits" by John Wiley, 2003.
S.K. Mazumder, "High-Frequency Inverters: From Photovoltaic,
Wind, and Fuel-Cell based Renewable- and Alternative-Energy
DER/DG Systems to Battery based Energy-Storage
Applications", Book Chapter in Power Electronics handbook,
Editor M.H. Rashid, Academic Press, Burlington,
Massachusetts, 2010.
V. Gureich "Electronic Devices on Discrete Components for
Industrial and Power Engineering", 2008.

1/2.docxHalf and full wave rectifier
Contents
1.0 Introduction 3
1.1 Power diode 3
1.2 Thyristor drives (SCR Silicon Controlled Rectifier)4
1.3 Single-phase with a half-wave 5
2.0 Pspice simulation 12
2.1 Resistive load: 13
2.2 Controlled rectifier with RL load 13
2.3 Freewheeling 13
2.4 SCR-Electric operation 14
2.5 Full wave control rectified 15
2.5.1Output forms 16
2.6 Output form with freewheeling diode 17
2.6.1Half controlled rectified 19
3.0 References 21
Introduction
The electric energy is distributed in alternating current. The
need for a voltage requires a DC voltage conversion circuit.
If it is necessary a constant voltage of constant value is simply
a diode or, for greater efficiency, a configuration of said diodes
Graetz bridge. But if, as in the case of the drives, you need a
DC voltage which is possible to check the value, recourse must
be controlled diodes, the thyristor drives or SCR (Silicon
Controlled Rectifier).Power diode
The diode, illustrated in Figure 1, is a semiconductor
component, comprising a PN junction. In it, the current can
flow in only one direction, from the anode, A connected to the
area P, to the cathode, K connected to the zone E No 'A valve,
therefore, which leaves transit charges in one direction and
locks in the opposite direction. The diode conducts when the
voltage between the anode and cathode is positive, U AK > 0
(forward bias) does not conduct when it is negative (reverse

bias). In a real diode in conduction U AK is very low (about 1
V) and the current intensity assumes high value; reverse voltage
can be high and the diode is traversed by a small current
intensity. The transition from one state to another is not
instantaneous. Switching from a locked state to the conduction
occurs in a few microseconds. What diodes rapid in some tens
of nanoseconds.
The relationship between current and voltage is illustrated in
Fig. 1
Figure 1: relationship between current and voltage
Thyristor drives (SCR Silicon Controlled Rectifier)
It 'a device with four layers, then with three PN junctions, in
which the conduction between the anode A and cathode K,
connected to the outer layers, is controlled by a current pulse
supplied to a third electrode, said gate, connected to the layer P
internal, as illustrated in figure 2. If the voltage U AK is
negative (reverse bias), still lower than a maximum value U i,
max, the conduction is blocked: passes only a weak intensity
and a possible pulse on the gate has no effect. See also U AK is
positive (forward bias), and lower than a maximum value U d,
max similar to that which determines the download avalanche in
reverse bias,, there is no conduction. This, however, may be
triggered by a current pulse on the gate. Once the thyristor
drives entered into conduction remains in this state regardless
of the state of the gate, which loses control. The thyristor drives
returns blocking situation only when the intensity of current
between the anode and cathode, for any reason, it cancels. In
Figure 2 is shown the characteristic i, U AK.
Figure 2: current between the anode and cathode
When the thyristor drives is run there is a small voltage between
the anode and cathode of the order of volts. It therefore has a
power dissipation for which the thyristor drives requires a
system for removal of heat. The choice of thyristor drives must
take into account both the rms value of the current (I rms) that

the peak value and the value of the blocking voltage. The
thyristor drives despite the disadvantage of not being able to
interrupt a current triggered, has a wider field of use as regards
the values of voltage and current with respect to the transistor
and, for equal performance, is more economical. In addition,
when using it as a rectifier, the disadvantage of not being able
to be turned off is irrelevant because there is no need for
this. Single-phase with a half-wave
The transistor can also perform the function of switch as the
thyristor drives. In addition the transistor has the advantage of
being able to interrupt the current at any time. This possibility
has not, however, of no importance in rectifying circuits
(different story for the inverter: Converts DC->
AC). Furthermore, the thyristor drives cover a wider range of
values of voltage and current and, at the same performance, are
cheaper. Remember however briefly the operation of the BJT
(Bipolar Junction Transistor)
It 'a component with three-layer NPN or PNP, then with two
PN junctions. The two electrodes are called extreme emitter and
collector, the intermediate base. Conventional current flows
from the collector to the emitter in NPN and PNP emitter to the
collector. The transistor used as a switch and static 'which
switching NPN faster than the PNP. The collector emitter
voltage U CE is positive and also the current I C (from collector
to emitter). In addition to the normal conduction losses
(U CE. I C). Figure 3 in addition to the circuit symbol and the
construction scheme, are shown the characteristics of the
manifold, namely the link between the current and the voltage U
IC CE. The value of I c depends on the value of the base
current. If I b = 0, the transistor as a switch is open, when I b >
0, the transistor can be operated so that the U EC is very low, so
it behaves like a closed switch. The product U CE *
The C corresponds to the loss during the run. To these must be
added the losses that occur during the switching between the
conduction state and that of the block. The latter are the more
significant the higher the switching frequency.

Figure 3: Single-phase with a half-wave
The principle for converting an alternating current into a
constant is to use a valve that lets pass the current in only one
of the two senses. Is obtained at the output a unidirectional
current with fluctuations around the mean value, more or less
marked depending on the nature of the load.
The average value is constant if the valve is not actuated
(simple diode), adjustable if it is controlled (thyristor)
Figure 4: principle of the half-wave controlled rectifier
In Figure 4 is illustrated the principle of the rectifier controlled
to a half-wave. The load between P and N is a pure resistance
for which the shape of the current is identical to that of the
voltage. For the II PDK one has u AK = u-u R with u R =
R. the ; u AK is positive for all the positive half wave and
negative for all the negative one because of a resistance current
and voltage are in phase. A pulse on the gate of the thyristor
drives when u AK > 0, it brings in conduction and the waveform
of the voltage on the resistance u R, marked in bold, is identical
to that of the current. Assuming ideal diode during conduction
did u AK = 0.
It has, as we see, the exploitation of a single half cycle, for
which in practice it can use the configuration Graetz Bridge or
double half-wave, shown in Figure 5.
Figure 5: Graetz Bridge or double half-wave
The four thyristor drives form the sides of a quadrilateral fed
between the vertices A and B from the alternating voltage. For
simplicity, it think of a purely resistive load applied between
the points P and N. When u AB is positive d 1 and 2 are biased,
and a pulse on their gate sends them to run while d 3 and 4,
reverse biased, do not lead. The voltage between P and N
coincides with u AB. When u AB is negative (u BA positive)
are d 3 and 4 to be biased so that a pulse on their gate sends

them to run while d 1 and 2 are reverse biased and do not
conduct. The voltage between P and N now coincides with the
u BA: P is therefore always positive with respect to N and the
voltage on the load is unidirectional, with the average value,
U DC, adjustable by varying the instant in which it gives the
impulse conduction defined by the angle.
Denoting by U the rms value of the voltage (also called rms
value), U M the peak value, U DC the actual mean value,
UD0 the average maximum value possible, when you get the
urge to turn on the thyristor drives is given at the beginning of
the period, then for = 0, we have the relationships shown in
the figure:
· U M = 1.41 * U
· U D0 = 0.637 U * M * U = 0.9
· U DC = 0.5 * UD0 * (1 + cos o)
Figure 6 shows the waveforms of voltages and currents when
the load is ohm-inductive load, such as the winding of a
motor. And 'considered the case of a half-wave rectifier, but the
considerations are also valid for the bridge rectifier.
Figure 6: voltages and currents when the load is ohm-inductive
load
Figure 7 shows the graphs of the current and voltage of a circuit
ohm-inductive insertion of a sinusoidal emf u when it is half of
the maximum value (phase angle = 30 °). It should be noted that
the current in transient that follows is the sum of the steady
state component of the p and a damped transient the t: i = i p +
i t. The voltage uR = R * i and u is the voltage on the
inductor L = L * di / dt = uu R. At time of insertion, having to
be i = 0 is the t -i = p . We observe that the current starts at zero
and is reset when the hatched area on the right equals that of the
left. The two areas represent the increase and the decrease of
the magnetic flux due to the current that grows at first and then
falls, bringing the energy stored in the magnetic field to a
maximum, requesting the power generator, and then returning it
fully. The two areas are given by the difference uu R u = L ,

then the area under the curve u L .
Figure 7: current and voltage of a circuit ohm-inductive
insertion of a sinusoidal emf
As long as you do not give the pulse on the gate, the thyristor
drives does not conduct, u R and u L , then also u RL = u R +
u L , are null and u AK = uu RL coincides with u . Impulse
with u AK > 0 , develops a current (positive A to K), and then
become non-zero and positive voltages u R and u L . The
current increases, reaches the positive maximum, and then
begins to decrease. The magnetic flux and the magnetic energy
evolve in the same way. In the first stage, therefore, the
inductance stores energy which then returns in full in the
second phase, thus the increase of flow of the first stage is
identical to the decrease of the second, as already put the rest in
evidence in Figure 7. When the magnetic energy
decreases, u L becomes negative. When also u becomes
negative the current is not anything yet, then the magnetic
energy stored has not yet been returned in full. The current still
flowing in the direction indicated as positive continuing to
decrease. As the current cancels cancels u R , and at that
moment u L = u . Magnetic energy has been completely
restored. The thyristor drives at this point no longer leads, the
voltage u L vanishes and is reverse biased thyristor
drives: u AK = u <0.
The instant in which the thyristor drives had begun to conduct
up to that in which the conduction ceases, the bipole RL is
applied the voltage u . As the current cancels cancels the
voltage on the load RL. There is therefore a fraction of a period
in which the voltage across the load is negative while the
current is still positive. And 'the interval between the instant
when u becomes negative and the instant in which u L becomes
equal to u, while u AK is nothing, that is the instant in
which the , then u R vanish. In this part of the year returns
energy to the load to the generator.
The average value of the voltage applied to the load, which is

given by the algebraic sum of the areas subtended by the curve
u RL divided by the period, decreases compared to the case of R
pure.
If an emf E acts in series with the circuit element RL, as in the
case of the winding armature of a DC motor to speed,
everything happens as described in the previous case, with the
values of u R and u L reduced because instead of u must
consider the difference Eu . Figure 8 shows the waveforms.
It should be noted in this regard that the impulse conduction
should be given when the difference is positive Eu, because in
this case is that the thyristor drives is biased. As the speed of
the engine grows narrows the interval of
conduction The maximum speed is when E is equal
to the average maximum value U C U * = 0.637 M. At the rate
which corresponds to the E, the angle for the pulse conduction
is between 39.5 and 140.5 degrees.
The fig. 8 assumes a constant E which corresponds to a constant
speed of the motor. There is in this respect be noted that this is
the AND of the engine is not actually constant is not constant
because the speed of the motor. When the thyristor drives goes
to run the engine speeds up, then increases its kinetic energy
while the magnetic energy at first increases and then decreases
by the same amount. As the current cancels the motor
decelerates at the expense of its kinetic energy. The speed then
oscillates around a mean value, and with it the BEMF E.
The oscillation has an excursion greater the greater is the load
resistance; equal resistant torque the oscillation depends on the
inertia (moment of inertia) of the engine system-load and
increases as it is smaller.

Pspice simulation
In the following figure schematic of diode rectifier was drawing
in Pspice three in 3 cases as shown.
Figure 8: diode rectifier
The first case using diode with resistive load only.
In practice, the half wave rectifier is used most often in low
power applications because the average current in the supply
will not be zero, and nonzero average current may cause
problems in transformer performance. The output as shown in
right figures of resistive load as shown above.Resistive load:
· The objective is to create a load voltage that has a nonzero dc
component
· The diode is a basic electronic switch that allows current in
one direction onlyControlled rectifier with RL load
With a RL load it was observed that the average output voltage
reduces. This disadvantage can be overcome by connecting a
diode across the load as shown in figure. The diode is called as
a Free Wheeling Diode (FWD).Freewheeling
When the circuit is first energized, the load current is zero and
cannot change instantaneously. The current reaches periodic
steady state after a few periods (depending on the L/R time
constant), which means that the current at the end of a period is
the same as the current at the beginning of the period,
SCR-Electric operation
Applying the anode of 'SCR a negative voltage relative to the

cathode, you get no electrical conduction, as occurs in a
common semiconductor diode. The SCR can thus be likened to
an open switch.
Reversing the polarity of the voltage, the SCR remains stuck in
contrast to what happens in a normal diode, in which it would
conduct electricity, but the block remains until it receives a
positive pulse on the gate respect to the cathode, of amplitude
such as to put the controlled diode in full conduction. And this
switching occurs in a very short time, of the order of 0.5 us. As
you can immediately deduce, this time is much shorter than that
required by similar electromechanical systems. Once triggered,
the SCR remains conductive without need of any control voltage
on the gate. Preserving this condition even when the gate pulses
are applied to the new command. To de-energize the SCR, that
is, to return to its interdiction, there are two systems: one can
reduce to zero the voltage between the anode and the cathode,
or you can become negative to the anode relative to the
cathode. In this case the alternating voltage proves very useful,
because it passes through zero when reverses its polarity at each
half cycle.
In Figure below is presented the example of a SCR as a function
of electronic switch in a power supply circuit of a light bulb
filament into alternating current. Let's see now the theoretical
behavior.
Figure 9: Circuit theoretical application of a diode SCR switch
function, closed or open, the ignition of the lamp LP.
In the absence of signal on the gate, the SCR behaves like an
open switch, which does not conduct current and the lamp LP
remains off.
But when applying a voltage pulse to each half cycle of the
alternating voltage, the switch is closed and the lamp LP
lights. Not, however, in the fall of its brightness, because the
SCR behaves like a normal diode in series to the circuit, which
rectifies the alternating voltage. In practice, the ignition of the
lamp is reduced to 50%. In Figure below is shown the new

condition of the electrical circuit of Figure 5, in which I SCR
turns into a rectifier diode of the alternating voltage.
Figure 10: SCR diode, connected in series with a conductor path
by alternating current, it behaves as a rectifying element,
leaving the way open to the passage of only the positive half-
waves.Full wave control rectified
Figure 11: full wave full control rectifier
Output forms
The output forms in yellow color and input in blue color as
shown below
Figure 12: full control rectifier
Figure 13: wave form with SCR gate pluses (green)Output form
with freewheeling diode
Figure 14: full wave controlled rectifier with RL load and
Freewheeling diode
Half controlled rectified
Figure below show the circuit on Pspice using two SCR and 2
Diode
Figure 15: Half controlled rectified
The outputs form as in figure shown below
The green color is SCR gate pluses and yellow color is output
wave and blue is input voltage

Figure 16:The green color is SCR gate pluses and yellow color
is output wave and blue is input voltage
Figure 17: The green color is SCR gate pluses and yellow color
is output wave and blue is input voltage
References
· Kharagpur. "Power Semiconductor Devices" Retrieved 25
March 2012.
· Muhammad H. Rashid,POWER ELECTRONICS HANDBOOK
DEVICES, CIRCUITS, AND APPLICATIONS Third Edition
· Mohan, N. (2003). Power Electronics Converters Applications
and Design. Michigan: John Wiley and Sons.
· Lipo; Kim, Sul. "AC/AC Power Conversion Based on Matric
Converter Topology with Unidirectional Switches". IEEE
Transactions on Industry Applications

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