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AC regulator works on the principle of converting fixed AC voltage to a variable AC voltage operating at the same frequency. This principle is used in speed control of AC drives, pumps, illumination control, temperature control of ovens etc. The devices used for such a control are TRIACS, DIACS and THYRISTORS.

This trainer is intended to provide facility to change the phase angle ? of TRIAC GATE with reference to power line frequency. As a result of this the ON / OFF state of TRIAC is varied, thereby varying RMS value is changed. In this trainer it is possible to measure the phase difference between the input and the output signal. This trainer contains a TRIAC, DIAC necessary firing circuit, and power supply. Load circuit waveforms can be observed through the test points provided. You can connect the load like fan, lamp, pumps, etc. not exceeding max 1A at the load terminal. An isolated 12 AC reference supply is available, for comparing the phase difference at various points on the circuit board, using an external dual beam oscilloscope. In order to connect external loads like fan, lamp, pumps, etc, a separate power socket is available as part of TRIAC circuit. Using this AC loads upto 1 A can be connected. It is very important to note that, HIGH VOLTAGES EXIST on the circuit board, so sufficient and enough care must be taken while measuring the circuit under study.

The entire instrument is housed in an elegant FRP cabinet.

Specifications:

• Power : 230 V AC @ 50Hz
  
• TRIAC Load : AC load not exceeding 1 A.
  
• DIAC : 1 No.

An external dual beam oscilloscope is required for measuring and observing the waveforms.
NOTE: Enough care must be taken for isolating AC signals. Qualified staff must be present while conducting this experiment.

In this trainer two independent solid state relay modules. Are used for connecting AC loads. This relay consists of two TRIACS. The first TRIAC gets a control signal from a digital circuit. There is an opto-isolator between the control circuit and the first TRIAC. Depending on the status of the control signal, the first TRIAC is either activated or not. When activation signal is received by the first TRIAC, it sends gate pulse to second TRIAC. Thus enabling AC load to be activated. The solid state relay used in this trainer comes in the form of a packed module consisting of opto-isolator and TRAIC devices.

This module can at best be used in conjunction with a dedicated hardware or a Microprocessor or a Microcontroller or any other data acquisition system at the time of prototype development or just for experiment. Input signal level: TTL (0 to 5v DC). Output : 230V AC @ 3A.

Comparator and Zero Crossing Detectors (ZCD) is all too familiar circuit required in power electronics for control applications. This control can be to turn ON a Thyristor. For example, it is desired to set the output of a circuit TRUE (ON State) whenever a control signal is issued. This control signal is issued by setting either a variable DCvoltage or a variable amplitude pulse generator. This amplitude will be used as a signal to change the output state. This signal is called as ZCD. In any case the amplitude of control signal can not be greater than analog signal itself.

Suppose it is required to set the output to TRUE state whenever the control signal crosses say+10V, then the second input of the operational amplifier is used to set to trigger at +10V. In other words, this second signal becomes a control voltage required to perform ZCD.

This trainer consists of a monolithic FET input operational amplifier, which compares the actual signal, and ZCD operation is performed. In order to perform this experiment a ZCD with a two way switch is used. In one position an internal variable DC signal can be connected, in other position an external variable amplitude pulse generator can be connected. For Analog signal terminal an external function generator can be connected. You can observe input, ZCD and output waveforms on a CRO. This trainer requires an additional Lab power supply of 12V @ 500mA.

This trainer is intended to experiment and see how the current and voltage commutation circuit performs for different load conditions. This trainer has basic (a) Thyristorised power circuit with necessary commutation, (b) Chopper triggering circuit for SCR applications, and (c) a power supply for the triggering circuit only.

This requires an optional variable high voltage DC power supply. It must be in the range of 0 to 240V DC operating at 3A under peak load conditions. This will be used as power source for applying to different types of loads. These loads can be pure resistive or combination of R-L-C. All these are optional.

Using this trainer it is possible to observe load voltage, load current, commuting capacitor voltage, commuting capacitor current, for pure resistive loads using an Oscilloscope. For this you need suitable extra Voltmeter and Ammeter. The interconnections are established by using suitable patch cords. All the necessary circuit points are terminated on 4mm banana sockets for interconnections

Specifications:

• Thyristorised power circuit, operating at 230V @ 2A under peak load conditions
  
• Chopper Triggering circuit for exciting Thyristor power circuit operating at a frequency of 50 to 300 Hz.
  
• Low voltage power supplies suitable for chopper circuit.
  
• All the above placed in an ergonomically designed cabinet.

Optional:

• Variable High voltage 0 to 240V DC @ 3A power supply Model PES-1
  
• Loading Rheostat 2A to act as pure resistive load
  
• Loading inductor (Air core type) @ 5A
  
• Loading Capacitor bank
  
• Suitable table top Voltmeter
  
• Suitable table top Ammeter

The rotational speed of a DC motor is directly proportional to the mean value of its supply voltage when operated under pulsed condition. If the motor is operating at a frequency 'f' and at an operating voltage of say +24V DC, then the pulse amplitude from the driver has to be 24V DC under all conditions at the given frequency. Under these conditions the speed is dependent on the duty cycle of the pulses from the driver. This type of circuit provides complete speed control from minimum to maximum speeds at reasonably high torque. The trainer makes use of a chopper circuit for speed control.

This trainer has all the facilities to vary the speed of the DC motor, observe wave forms at different test points in the circuit, namely at the output of oscillator, amplifier, driver, and at motor terminals. A recording of these observations in terms of amplitudes, pulse width, shape of pulses will provide a good understanding of how speed control can be achieved at different speeds.

This trainer is intended to demonstrate the speed control of a permanent magnet DC motor. This motor is mechanically coupled to a Tacho-Generator. Changing the voltage of armature from 0 to 24VDC controls the DC motor speed. As the voltage varies, the armature current increases and in turn the speed increases.

The change in armature voltage can be changed in this trainer

• Either by varying a potentiometer by DC voltage control or
  
• By pulse width modulated CHOPPER DRIVE, or
  
• It is possible to provide external pulses modulation from your circuitry also for exciting the motor. This external pulse modulation can be provided from any external controller like Microprocessor trainers Model MPT-85 or MPT-J-85 or MPT-86, Microcontroller trainer Model MCT-31, PLC trainer Model IM-29 or and Data Acquisition System Trainer Model DAS-1.

IGBT chopper driver circuit consists of a PWM waveform generator, and a hybrid driver circuit, with de-saturation detection. The pulse-input circuit is optically isolated from the driver circuit, The output circuit from this driver protects the IGBT module from dangerous transient voltages. The de-saturation trip time can be adjusted by a suitable capacitor in the driver stage.

NOTE: It is important to note that, dangerous voltage will exist when IGBTs are connected to this circuit. So all the precautions must be taken to avoid any fatalities while conducting the experiment.

Specifications:

• Pulse input : There is a built in PWM generator.
  
• PWM : Repetition rate is adjustable in the range of 100Hz to 1KHz and TTL
  
• Duty cycle : Duty cycle is adjustable in the range of 10% to 90%
  
• Opto-Isolator : 30kV/uSec.
  
• Electrical Isolation : Viso = 2500Vrms for one minute.
  
• Recommend for use with: Vces of 600V
  
• Facility to connect an external PWM also as input to the driver circuit
  
• Input to the driver : internally generated PWM or external PWM can be given as input to this driver and it is optically isolated.

Insulated Gate Bipolar Transistor (IGBT) is a switching transistor that is controlled by voltage applied to the gate terminal. Device operation and structure or similar to those of an insulated gate field effect transistor (IGFET) more commonly known as MOSFET. The principle difference between the two device types is that the IGBT uses conductivity modulation to reduce the ON state conduction losses.

The IGBT consists of IGBT power setup along with hybrid driver circuit having isolation between input and output with built-in Opto-coupler. A built-in de-saturation detector provides necessary short circuit protection. An LED will indicate the short circuit activation signal.

Using this trainer it is possible to study V-I characteristics of (a) VCE test, (b) Resistive load switching test, and (c) Half bridge switching test circuit. This unit has necessary gate drive circuits.

This requires external instruments as support equipment.
1. High voltage, high current DC source Model PES-1
2. 10 A DC current meter
3. Variable Resistive Load
4. Variable inductive Load

Specifications:
IGBT :

• Collector Emitter voltage :VCES = 600V
  
• DC Collector current : IC.nom = 50A
  
• Repetitive peak Collector current : ICRMvvvv = 100A
  
• Total power dissipation : PTOT = 280Watts
  
• Gate emitter peak voltage : VGES = 20V
  
• DC forward current : IF = 50A
  
• Collector Emitter saturation voltage : VCesat = 2.2V
  
• Gate threshold voltage : VGEth = 5.5 V
  
• Collector cutoff current : ICES = 1mA

This trainer must highlight the following features of an IGBT.

• measurement of switching losses (IGBT and diode)
  
• measurement of on-state losses(IGBT and diode)
  
• overall loss evaluation
  
• short circuit test
  
• evaluation of the driver circuit under different boundary conditions
  
• comparison of the IGBT behavior under different conditions (voltage, driving, temperature, freewheeling diode)

NOTE: it is important to note that, dangerous voltage will exist when IGBTs are connected to this circuit. So all the precautions must be taken to avoid any fatalities while conducting the experiment.

This is a general-purpose power circuit development panel. This consists of six numbers of thyristors and three numbers of power diodes. Using these devices, one can assemble any combination of SCR power circuits. This unit requires an external SCR trigger circuit with proper conditioning for gate firing. This unit has three fuse holders. The AC power required for enabling the power devices must be routed through fuses as a protective measure for the circuit board components.

NOTE: The circuit developer must take adequate precautions while handling this board, as high voltages do exist when high voltage AC power is connected to this device circuit panel. For safety of the operator, it is necessary to have an external circuit breaker as part of AC power inlet connections.

Specifications:

• Thyristors used : 6 Nos.
  
• Power diodes : 3 Nos.
  
• Fuse protection : on 3 lines
  
• Terminals : 4mm colored terminals for each device
  
• Patch cords : 4mm banana patch cords required.

Thyristor:
The Thyristor used works on CLIP ASSEMBLY technology with
a) An average ON-State current of 10A @ 180? conduction angle.
b) Critical rate of rise of on-state current 50 A/ ?sec.
c) Peak gate current with 4A.
d) Average gate power dissipation 1 Watt.
e) Maximum peak reverse gate voltage 5 V.
f) Threshold voltage 0.77V.
g) Average gate power dissipation 1Watt.
h) Snubber circuit is connected across each thyristor.

Diode: 16Amps with PIV of

NOTE: Suitable External SCR trigger circuit required as per your circuit design. Alternately SCR TRIGGER APPLICATIONS TRAINER Model PE-14 can be used.

Sampling is a technique to capture a dynamic signal on the FLY. For example a variable frequency similar to voice signal can neither be reproduced nor it's amplitude be constant. Every time a voice command is issued it will be different. Therefore to capture such a signal, sampling technique is used. The fineness depends on how many times such a signal is captured and stored in a second. This is typically called as sampling rate. It is also necessary to HOLD the sampled signal to initiate a conversion process. When sampling and HOLD operations are performed together, there exists a finite phase difference and Lag due to the HOLD capacitor. As a result of this the result may be somewhat different than the actual signal itself. However the held signal will be nearly equal to the original signal, not the same signal. Hence study of SAMPLE and HOLD signal block in a larger circuit becomes necessary.

The SAMPLE and HOLD circuit trainer helps in understanding the rudiments of teaching SAMPLE and HOLD method by experimentation. This trainer requires an additional Lab power supply of 12V @ 500mA, a signal source similar to function generator and a pulse generator, a DMM.

A circuit breaker by the very name it suggests that, it is a mechanism, by which the power circuit must be disabled / disconnected if the output exceeds beyond a set current range. This facilitates the saving of men and material from any possible destruction. In this trainer, the circuit breaker is essentially monitors the load current. The sensing circuit determines the maximum load current CUTOFF point, beyond which the circuit should not function. In order to demonstrate this principle, an SCR based SSR is used in this trainer. This trainer comes with load current limiting circuit.

This trainer consists of DC power source at 12VDC @ 1A as supply to the load circuit. Suitable current limiting circuit measures the load current. An Ammeter measures the load current. It is possible to preset the load current in the range of 100mA to 800mA at load circuit side. An SCR based switch is used to cutoff the load supply to the loading circuit, when the load current exceeds beyond set current limits. An external loading rheostat NOT more than 1A is required to load the circuit.

Specifications:

• Load current limiting : between 100mA to 800mA
  
• Analog Current meter : 1A DC FSD monitors load current.
  
• Current limit : By preset potentiometer.

Note: An external loading rheostat NOT more than 1A is required

The purpose of this instrument is to demonstrate an application of a ring counter which drives an opto-isolated SCR. SCR in turn will s witch ON a 230V AC activated device as and when a trigger pulse from these counter is applied to the gate of this SCR through an opto-isolator module. A Lamp load is used to demonstrate this principle. This can be used as either a Straight Binary counter or DECIMAL counter.

This is a 4 bit presettable CMOS ring counter. This counter has UP Count facility, by switch selection. DOWN Count facility by switch selection. Preset a count in the range of 0000 to 1001 in case of DECIMAL count or from 0000 to 1111 in case of BINARY count. This is achieved by setting the 4bit PRESET state switches to either at 0 or at 1 state.

Using the above counter any mode of operation can be set. A logic-1 output of this counter is used as gate trigger required for the SCR to go into active state. This in turn will act as a solid switch.

A 230V AC operated Lamp load is used to display the state of the counter. In addition 4 bit LEDs will also display the status of this counter.

This is an SCR trigger circuits trainer. This consists of ready-made circuits on board. The circuits included on this trainer are for
(a) AC regulators scheme,
(b) Digital firing circuit scheme, and
(c) Op-Amp firing circuit schemes.

This can be used as a ready-made firing circuit for SCR applications. This can be used in conjunction with Power device module Model PE-27. This trainer has all the necessary power supplies for on board electronics.

Cycloconverters find extensive use in high power systems like locomotive drives, cement and sugar mills etc. Cycloconverters works on the principle of converting single fixed frequency AC signal to Variable frequency AC signal. This is achieved by using a center tap transformer. Four different SCRs used. Appropriate snubber circuits protect these SCRs. Volt meter and Current meters for the measurement of voltage and current within the circuit.

PHASE CONTROL CIRCUITS

Why phase control?
Power systems using Thristors often exert control of load power by control of the time of firing during the AC cycle. This implies delaying conduction of the thyristor so that only a selectable portion of the AC cycle is available for the load. The non-sinusoidal voltage and current wave applied to the load has operational, measurement, analytic, and harmonic interference not encountered with straight DC or with AC sine-wave power. However, such phase-control circuits are relatively simple, efficient, and very convenient. Efficiency is high because turn on is extremely fast, and turn off is reasonably fast. Also conductive losses tend to be low because of the volt or so dropped across these devices. A good thing about using thyristor for phase controlled power is the self commutating feature, wherein turn off automatically obtains when the current wave goes through zero. The phase control can be achieved either on a full or half wave basis. A single SCR yields a half wave circuit, whereas TRIACS enable full wave operation from a single wave operation from a single device. Several relationships pertaining to phae controlled proper are often overlooked or become the sources of confusion. Best thing is to experiment and see your self what is right or for that matter why is it right.

AC regulator works on the principle of converting fixed AC voltage to a variable AC voltage operating at the same frequency. This principle is used in speed control of AC drives, pumps, illumination control, temperature control of ovens etc. The devices used for such a control are THYRISTORS. This trainer contains a THYRISTOR, necessary firing circuit, and power supply, test points for observing waveforms.

Thyristors find extensive applications in power electronic circuits such as DC motor drives, large power application drive circuits etc. This trainer provides an opportunity to study, how a single phase Half / Fully controlled bridge circuit works.

This trainer has four thyristors connected in a bridge configuration. Necessary firing circuit is provided for control. It is possible to connect a resistive load to the output terminals to observe waveforms on CRO and record. A voltmeter and an Ammeter are used to measure the line and load characteristics.

This electrical setup is used in POWER ELECTROINCS LAB to study the No load characteristics of a DC SHUNT motor. A shunt motor is connected in the same way as a shunt generator. The field windings are connected in parallel (shunt) with the armature windings. Once you adjust the speed of a dc shunt motor, the speed remains relatively constant even under changing load conditions. One reason for this is that the field flux remains constant.

The DC shunt motor has two windings, namely Armature winding and Field winding. In order to activate the motor, both Field and armature windings have to be given sufficient power to enable them to start under controlled condition. Since the consumption of current by the armature is large compared to field current, when the motor is at rest, it is necessary to excite the armature gradually to enable the motor to start properly. It means, the field winding must provide the starting current, and eventually the current flowing through the field winding can be minimized, once the rated speed is achieved. Hence this leads to a conclusion that the armature current has to be provided in a controlled atmosphere starting from rest to rated speed. This needs further discussion for considering load conditions. There are several methods adopted for this purpose.

The speed control is achieved by varying the firing angle of the thyristor, which is controlling the armature winding. In this experimental setup, the DC Motor is mechanically coupled to a Tachogenerator, to provide necessary feedback for the measurement of speed as set by the speed control potentiometer. This feedback signal is further processed through conditioning circuits and a suitable signal is provided to the triggering controller. The trigger circuit is further processed through pulse transformer, before applying as Gate signal to the Thyristors.

This trainer has necessary power supplies, signal conditioners, feedback circuits, pulse triggering circuits, power driver, Ramp generator for smooth starting of drive, necessary current amplifiers and current limiting circuit, SCR firing controller, suitable pulse transformer for isolation and Opto-Isolator circuits.

The scope of this trainer is limited to the extent of observing various waveforms at different points along the whole circuit flow, till the DC motor using an external 15MhZ oscilloscope.

Specifications:
There are two options of Motors are available. You must choose the correct option before placing your purchase order. The options are

Option ?1, BENN make DC Motor with the following specifications will be supplied
HP =1; RPM = 1500; Excitation voltage: 180V DC, Current handling: 5.1A;Class: B

Option ?2, the DC Motor with the following specifications will be supplied.
HP =0.25;RPM = 1500;Excitation voltage: 220V DC, Current handling: 1A;Class: B

The following are common specifications for the rest of the equipment:
? Tachogenerator : It provides 33V DC / 1000 RPM
? Speed : 1500RPM
? Input voltage to the system : 220 V AC / Single phase
? Speed Indicator : An external Digital meter is supplied to indicate RPM
? Speed variation : 0 to 1500 RPM continuously variable.

The Thyristor used works on CLIP ASSEMBLY technology with
a) An average ON-State current of 10A @ 180? conduction angle.
b) Critical rate of rise of on-state current 50 A/ ?sec.
c) Peak gate current with 4A.
d) Average gate power dissipation 1 Watt.
e) Maximum peak reverse gate voltage 5 V.
f) Threshold voltage 0.77V.
g) Average gate power dissipation 1Watt.

The following test points are available for observations using an Oscilloscope.
? Tachogenerator feedback voltage.
? Signal and summing amplifier.
? Signal conditioner output before the UJT firing circuit
? Relaxation oscillator output
? Pulse transformer output
? Anode and Cathode points of Thyristors for ARMATURE control
? Anode and Cathode points of FIELD windings

Using the above trainer, the user can experiment and study
1. Plot the graph of Speed Vs Armature/ Field voltages.
2. Speed Vs No load characteristics.

This is a table type model. However the motor assembly, need to be mechanically fastened to the table top with Nut and Screw arrangement for stability of operation at high speeds.The entire system is supplied with functional block diagrams printed on the front panel for easy identification of various blocks of the controller. Various test points are provided on the front panel for observations of signals at various points of the circuit. An external 15MhZ, dual beam Oscilloscope is required to observe the waveforms.

This trainer is intended to study the speed control of DC Motor using Thyristor Triggering. Using this trainer, it is possible study and observes waveforms at different points of circuit, during study. Additional equipment like a Dual Beam

Oscilloscope of 15MHz is required for observation of waveforms. This trainer consists of the following facilities.

a. Speed adjustment potentiometer,
b. Signal conditioning circuit,
c. Pulse triggering circuit,
d. Pulse transformer kit,
e. Power driver circuit using thyristors, a PMDC Motor,
f. Built-in Digital RPM indicator, and
g. Necessary power supplies.

Specifications:
? PMDC motor operating at 40V DC mounted on a stand and securely fastened.
? Maximum SPEED of the motor is 1440 RPM.
? Built-in Digital RPM indicator to observer the motor speed.
? Built in power supplies.

The test points include observation of the following:
a) Adjustable speed control voltage in the range of 0 to 5V DC.
b) Waveforms to observe RAMP generator
c) Trigger waveform produced by the triggering circuit
d) Transformed pulse output
e) GATE triggering of G1 and G2,
f) Anode and Cathode points of SCRs.

Thyristor:
The Thyristor used works on CLIP ASSEMBLY technology with
a) An average ON-State current of 10A @ 180? conduction angle.
b) Critical rate of rise of on-state current 50 A/ ?sec.
c) Peak gate current with 4A.
d) Average gate power dissipation 1 Watt.
e) Maximum peak reverse gate voltage 5 V.
f) Threshold voltage 0.77V.
g) Average gate power dissipation 1Watt.

Uni-Junction Transistor (UJT) specifications:
(Maximum ratings):
a) Base 1 ? Emitter voltage 30V,
b) Base 2 ? Emitter voltage 30V,
c) RMS Emitter current 50mA,
d) Emitter peak current 2A,
e) Total Power dissipation 300Mw

This trainer is intended to study the characteristics of SCR, TRIAC, DIAC and MOSFET devices. In order to facilitate the experimental procedure, necessary support peripheral components like lamp load is provided on the system for interconnections. In order the observe various waveforms of the devices on oscilloscope, an external 12 AC reference is available on board. This trainer has all the necessary components like potentiometers, switches, Transformer, lamp load etc is provided. These are required to conduct all the experiment of the devices.

Note: (a) An external current meter in the range of 25mA AC to 2A is required to measure respective currents, (b) a dual beam oscilloscope, and (c) a high impedance volt meter are essential requirements.

Specifications:

Thyristor : 1 No
The Thyristor used works on CLIP ASSEMBLY technology with
a) An average ON-State current of 10A @ 180? conduction angle.
b) Critical rate of rise of on-state current 50 A/ ?sec.
c) Peak gate current with 4A.
d) Average gate power dissipation 1 Watt.
e) Maximum peak reverse gate voltage 5 V.
f) Threshold voltage 0.77V.
g) Average gate power dissipation 1Watt.

• MOSFET : 1 No
  
• DIAC : 1 No
  
• TRAIC : 1 No
  
• Lamp load : 230 AC @ 100Watts and 12 DC @ 100mA lamp ? 1 each
  
• Potentiometers : Wire wound ? 3 Nos.
  
• Transformer : 12 AC @ 100mA for waveform synchronization.
  
• Resistor, capacitor, diode of assorted values
  
• Power :230 V AC @ 50 Hz

The entire instrument is housed in an elegant FRP cabinet.

Current Transformers are devices, which convert high power signals to lower, more manageable signals. This transformer encircles the wire carrying the signal and via induction transmits a proportional signal through two leads attached to the secondary side. It is also intended to perform roles for safety protection and current limiting.

They can also cause circuit events to occur when the monitored current reaches a specified level.This is done by constructing the secondary coil consisting of many turns of wire, around the primary coil, which contains only a few turns of wire. In this manner, measurements of high values of current can be obtained. A burden resistor connected across the secondary produces an output voltage proportional to the resistor value, based on the amount of current flowing through it. When choosing the burden resistor, the engineer can create any output voltage per amp, as long as it doesn't saturate the core.

This trainer is intended to study how the current transformer functions. With this it is possible to make measurements on the secondary by properly connecting the Burden resistor at the secondary. In order to accomplish this task the trainer is provided with a current transformer with maximum primary current of 1A and secondary current of 200mA for 1A input. Two independent current meters monitor both primary and secondary currents. In order to facilitate the loading of primary, a lamp load consisting of 300W is available. An external Variac ( Dimmer-stat) of at least 3A, is required to vary the input current.

At the end of the experiment, a graph depicting the primary Vs secondary current is drawn. Transformer losses are not considered at this stage.

Specifications:

• Primary current : 1A Max.
  
• Secondary current : 200mA proportional to the primary current
  
• Lamp load : 300W built-in
  
• Meters : 1A in primary side and 250mA at secondary
  
• Burden resistor : 5 Ohms
  
• Optional : Variac operating in the range of 0 to 240V AC @ 3A current rating.
  
• Enclosure : Instrument is housed in an ergonomically designed cabinet.

This trainer is intended to study and experiment with the most popular Linear Voltage regulator IC-723. This is by far the most popular component used in all most all the power supplies. This is because, it has the ability to vary the output voltage linearly upto the desired level. While doing so, it acts as a controller, for increasing the current handling capabilities when associated with series pass transistors.

This trainer has built in power transformer, power diodes, capacitor, load resistors, series pass transistor, current limiting component, etc. You need an extra external current and voltmeters to observe and record the readings for further analysis.

Potential transformer (PT) is intended to measure high voltages in a circuit as a function of step-down voltage. While the PT provides a good isolation from the power circuit to measuring circuit, it is also used for safe instrumentation and control purposes. A potential transformer is an accurate transformer.

This trainer has a potential transformer with 0.003mV / V input. Using this transformation, it would be possible to measure a secondary voltage in the range of 0 to 0.69V FSD. In order to accomplish the measurements, this trainer has two suitable voltmeters one for primary and secondary voltages. The scope of experiment restricts to measurement of turns ratio and a graph between primary voltage Vs secondary voltage. Power factor measurements are not within the scope of supply.

Specifications:

• Potential transformer scope : with 0.003mV / V input
  
• Maximum input : 230 V AC, single phase.
  
• Meters : 230 V AC analog type and 1V FSD digital
  
• VARIC : Continuously variable in the range of 0 to 230VAC@ 3A
  

A switching power supply is a device transforming the voltage from one level to another. A switching-mode power supply (SMPS) is a power supply that provides the power supply function through low loss components such as capacitors, inductors, and transformers and the use of switches that are in one of two states, on or off. The advantage is that the switch dissipates very little power in either of these two states and power conversion can be accomplished with minimal power loss, which equates to high efficiency. Usually a switching-mode power supply is circuit that operates in a closed loop system to regulate the power supply output.

The switching mode power supply contains a transformer/coil and to make this as small as possible, the internal switching frequency has to be quite high, something typically in the range between 20KHz and 1MHz. This also makes the device noiseless to human ears. The oscillator noise is often conducted onto the input and output lines with a frequency that varies with the load.

This trainer consists of fundamental blocks like multivibrator, pulse width modulator, control voltage feedback, MOSFET power devices etc. This operates at 60KHZ. This trainer essentially demonstrates how SMPS works. The scope of this trainer provides necessary test points for observation of the above referred signals for study.

Specifications:

? Operates on principle of PWM
? Duty cycle: 85%
? Output: 5V @ 1A
? Input: Unregulated at 10V
? Oscillator : 60KHz
? Voltage feedback circuit to determine PWM duty cycle.

This trainer is intended to study the different type of triggering circuits for the SCR applications. The types of trigger are Synchronized firing angle that can be controlled from 0 to 1800, Phase shift triggering in the range of 0 to 1800 and UJT Triggering. In order to provide necessary gate signals to the thyristor, a built-in power transformer with buffer circuit is provided. For the purpose of experimentation, necessary components like resistors, potentiometers, diodes, capacitors are available onboard. The circuits are to be inter-connected using patch cords to study the experiments.

This trainer has necessary power supplies, 12V AC transformer for waveform comparison on one channel of oscilloscope. An external dual beam oscilloscope is required to observe the control signals.

Specifications:
Uni-Junction Transistor ? 1 No
Thyristor : 1 No
The Thyristor used works on CLIP ASSEMBLY technology with
a) An average ON-State current of 10A @ 180? conduction angle.
b) Critical rate of rise of on-state current 50 A/ ?sec.
c) Peak gate current with 4A.
d) Average gate power dissipation 1 Watt.
e) Maximum peak reverse gate voltage 5 V.
f) Threshold voltage 0.77V.
g) Average gate power dissipation 1Watt
h) Pulse transformer with two outputs
i) Potentiometer: Two numbers of suitable potentiometers
j) Buffer transistor: 1 No
k) 12 AC transformer for waveform comparison.
l) All assembled in an elegant FRP cabinet.

A Zero Crossing Detector (ZCD) is one, which transforms the synchronizing signal into a square wave signal. By the very name it suggests that some thing should happen if it crosses 0V or if it crosses any preset voltage levels.

One of the following can be obtained.
(a) The output should be ON when the incoming signal is positive going and should and the output should be 0V, for the negative going signal. All signals commensurate w.r.t.DC.
(b) Alternately output should be 0V when the incoming signal is positive going and the output should be ON, for the negative going signal.

This can be accomplished by using diodes in the respective paths. One of the above refered signals are used to activate another output device. It could be a hardware, or a control circuit etc.

In this trainer the process of ZCD is experimented. In order to understand better, the experimenter has a variable reference signal to observe how the ZCD output behaves. The instrument is provided with necessary circuits to accomplish this task.