Any type of motor Shunt, Series or Compound can be tested. 6. Why i-mode is more sensitive among all modes? ü Power Source 6.3 Vac, 500mA, ü Power Source 6 Vdc, 500mA, ü C1 0.1μF, electrolytic, ü DS1 Miniature lamp, ü Q1 DIAC, ST2, ü R1 47Ω, 1W, ü R2 10KΩ, 1W, ü S1 PBNO, ü S2 SPST. 1. It is an open loop system based on a dual converter using non circulating current mode of operation. 1 Thyristors DC Characteristics PREPARED BY: J.B. G. Ibarra 1.0 OBJECTIVES 1.1 To become familiar with the characteristics of the (SCR) silicon controlled rectifier and its operation. b) Reverse the polarity of the main terminal voltage by reversing the power supply leads connected to your circuit. b) Adjust the main terminal and the gate voltage sources to +6Vdc. Generally power enhancement MOSFETs are used in power electronics circuits. These disadvantages are overcome by insulating the gate terminals from the channel with a thin layer of silicon dioxide (Metallic oxide). Eventually a forward current is established as shown in fig. 3. Fig :-modes of operation of TRIAC 1. The device will be in the reverse blocking state and small reverse leakage current flows through the device. Aim : To study the V-I characteristics of TRIAC. thanks. You may calculate the delay angel of the firing .Refer to the formula given below. Note that there are separate switches are provided for electronic circuit ON/OFF and control circuit ON/OFF. The firing angle can be controlled up to above 150o. When gate is positive with respect to emitter and with gate-emitter voltage more than the threshold voltage of IGBT, an n-channel is formed in the p – regions as in a power MOSFET. You may observe o/p waveform across the attenuated test point for o/p. With motor load connected, the switch SW3 if then in upward position, connects the armature circuit to lamp load (ensuring that thyristor o/p is disconnected), the stored KE in motor rotor is converted into DC voltage which lights the lamp momentarily & dissipates all the stored energy in the motor rotor in the lamp load & motor comes to halt immediately, indicating the process of dynamic braking. During the positive half cycle of the input voltage, C begins to charge through R. When the capacitor voltage reaches the minimum gate trigger voltage SCR will turn on. Keep the multiplication factor of CRO’s probe at maximum position. d) Depress and hold S1. Observe the waveforms and plot it for one particular firing angle by adjusting the potentiometer and observe the range over which firing angle is controllable. Capacity 3. g) Depress and hold S1. This makes triac circuits ideal for use in a variety of applications where power switching is needed. At ωt = α, SCRs T1 and T3 are triggered, then the current flows through the L – T1- R load – T3 – N. At ωt = π, supply voltage falls to zero and the current also goes to zero. IGBT characteristics is a power electronics experiment board to study and understand the vi characteristics of IGBT provided with in built power supply : spawar@scientech.bz : (+91) 9755591500 An SCR is a three terminal, four layer latching device. What is the condition for load current should be discontinuous? The force acting tangentially on the pulley is equal to the difference between two spring balance readings. Observe the various waveforms on CRO by appropriately connecting test points. f) Connect the oscilloscope across DS1 to monitor the load voltage. Here, output voltage is either positive or negative but output current is always positive. It exhibits negative resistance characteristics. In this mode the device is normally in off condition and a sufficiently large positive voltage on the gate terminal can turn on the device. For firing angle less than 30°, the output terminal voltage of the converter is always positive, and the freewheeling diode does not come into operation. 6. The characteristics of a TRIAC are similar to those of an SCR, both in blocking and conducting states, except for the fact that SCR conducts only in the forward direction, whereas the TRIAC conducts in both the directions. 2. RC Triggering Circuit – HWR & FWR 19 6. 23-27 6 Parallel Inverter. This type of full wave rectifier circuit consists of four SCRs. This device combines into it the advantages of both MOSFET and BJT. By varying the variable resistance R, the firing angle can be varied from 0 —180° .In the negative half cycle the capacitance C charges through the diode D2 with lower plate positive to, the peak supply voltage Emax .This Capacitor voltage remains constant at until supply voltage attains zero value. As the name indicates, a dual converter consists of two converters (single phase or three phases), both either fully controlled or half controlled connected to the same load. Resistance trigger circuits are the simplest & most economical method. When in operation, a TRIAC is equivalent to two SCRs connected in anti-parallel. A. Temperature rise of machine can be noted. Semi converters and full converters are quite common in industrial applications. Disadvantages, To study SCR/TRIC/ DIAC/ MOSFET/IGBT Characteristics. What are the differences between SCR and TRIAC? A TRIAC is a bidirectional thyristor (it can conduct in both directions) with three terminals. 6. 1. V BO is the maximum forward or reverse voltage that the triac can tolerate before it breaks over into uncontrolled conduction. UJT Triggering of SCR – HWR & FWR 33 9. Draw the equivalent circuit for TRIAC? To see the phase controlled converter output waveform, use a 230 / 12 V transformer for isolation purpose. Positive or negative potential across the terminals can be triggered by reaching +/- breakover voltage. The necessary isolated DC supplies for opto isolators (8 no) are generated & an AC sensing circuit at inside is provided to achieve proper synchronization. LIST OF EXPERIMENTS 1. You must not observe the waveforms for triggering circuit & output simultaneously on CRO. What is the output ripple voltage frequency of three phase half wave converters? Since the conducting. 1) Select Triac as the device under test by referring to the top RHS diagram. So as IGBT has input impedance like a MOSFET and low on-state power loss as in a BJT. Initially connect for delta operation.. Keep load control pot in minimum position. These are only for reference and comparison. Experiment # Particulars Page # 1 Static characteristics of SCR or DIAC. 2. d) Look at your circuit and then record in Table 8-1 the triggering mode of Q1 in this configuration. Three-phase half-wave converter is rarely used in industry because it introduces dc component in the supply current. Fig shows single phase fully controlled rectifier with resistive load. Demonstrate the bi-directional conduction of a gated TRIAC. The V-I characteristics of a TRIAC is based on the terminal MT1 as the reference point. For lamp load a separate load bank is provided. To study the characteristics of single phase dual converter, 1. 3. 5. Select proper desired mode of operation under closed loop/ open loop system. An electron movement in the n-channel, in turn causes substantial hole injection from p+ substrate layer into epitaxial n- layer. C. Demonstrate bi-directional operation of DIAC. c) Adjust the main terminal voltage to -6Vdc. Yes. 2) You have to follow general test procedure as per, It indicate the variation of drain current I, This characteristic shows the variation of drain current I, Output characteristics of an IGBT show the plot of collector current IC versus Collector-Emitter voltage V, The transfer characteristics of an IGBT is a plot of collector current I. The purpose of a dual converter is to provide a reversible DC voltage to the load, typically a separately excited DC motor. Connect a & k terminal of UJT triggering circuit to the gate cathode terminals of SCR. Due to insulated gate, negligible gate current flows. Calculate the dc output voltage using the equation. What is the use of freewheeling diode present in the three phase half controlled rectifiers? Switch on power supply to the SCR trainer. where can i get a copy of the picture of the figures? … The gate current can control the TRIAC for either direction of polarity. If thyristor does not turn off even after pot is at the highest resistance value, then reduce anode supply voltage. Blocking voltage (VDRM)—the maximum voltage that the triac can block in either direction when the gate current is... 2. In the former, only one of the bridges is triggered. MOSFETs are operated in depletion mode as do JFETs with negative voltage on the gate terminal for N channel device. The first quadrant is the region wherein MT2 is positive with respect to MT1 and vice-versa for the third quadrant. b) Reverse the polarity of the gate voltage supply by reversing the power supply leads connected to your circuit. The diodes D1, D2 and D3 provide merely a return path for the current to the most negative line terminal. The value of emf of a cell does not remain constant but varies with the change in specific gravity of electrolyte, temperature and the […] This is expected because triac consists of two SCRs connected in parallel but opposite in direc tions. 4 - Unijunction Transistor, ECE121 Experiment No. 2. This allows the component to conduct in both directions. Is the voltage waveform a complete sine-wave? Why? j) Reduce the power supply voltage to zero. (LC Commutation Circuit) Oscillation Chopper Circuit 29 8. As soon as the capacitor discharges, it starts to recharge as shown. ☞Set both voltages to minimum position, and then switch on SPDT. The Fig-3, shows the current and voltage waveforms for this circuit. 3. SCR Characteristics 3 2. In the forward direction, the shape of the output characteristics is similar to that of BJT. Average output voltage,       Vo = (2*Vm / Π ) *cosα. Triac means the device for AC control composed of 3 electrodes. Electrical power is produced at the power stations which are located at favorable places, generally quite away from the consumers. Now start decreasing the anode current gradually by adjusting pot (P2). ; V DRM is the maximum repetitive peak voltage (usually the maximum peak voltage of the applied AC wave) that can be reliably tolerated. The power enhancement MOSFET has an anti parallel fast turn on diode which permits reverse current of the same magnitude as that of the main MOSFET, so that drain substrate junction will not be damaged when drain and source has reverse biasing. The bridge circuit has two halves, the positive half consisting of the SCRs T1, T3 and T5 and the negative half consisting of the SCRs T2, T4 and T6. visit my other blog: It is a three terminal switching device similar to SCR (Thyristor) but it can conduct in both the directional since it construct by combining two SCR in anti-parallel state. 5. Switch on the TRIAC knob and firing circuit kit. Start the P1 from zero , you may need to adjust “P2’ slightly .Slowly increase the speed. g) Is the polarity of the sawtooth inverted? Yes. 1) Select Triac as the device under test by referring to the top RHS diagram. F = (F 1 - F 2 )     If         r = radius of pulley in meters,             N = speed in rpm, Advantages of Break load test. Interconnected System Theory The conveyance of electric power from a power station to consumes’ premises is known as Electric supply system. Switch ON the power supply ON/OFF switch. e) Record the data for this triggering mode of Q1 in Table 8-1. When the anode to cathode voltage is increased to break-over value, the junction j2 breaks down and device starts conducting. No 1. Why? Connections are made as per the circuit diagram. What are the effects of load inductance on the performance of AC voltage controllers? 3. What is the maximum value of firing angle which can be obtained from the circuit? Trigger pulses TP1, TP2, TP3 & TP4 for all the four thyristors in each group are generated & can be observed on test points marked properly for the +ve & -ve channels. What are the advantages of ON-OFF control? DS1 should light. Hence the effect of the freewheeling diode is to cause a reduction of ripple voltage of the output terminals and at the same time to divert the load current away from the input lines. Observe that capacitor voltage is set at every half cycle. It produces a sawtooth waveform that when polarity is reversed, an inverted sawtooth is displayed on the oscilloscope. Vm = Peak phase voltage, Volts , α = Firing angle, degrees, TP1 (red) and Ground (Black) :- UJT Relaxation oscillator output. There is however; a major difference in the substrate. This method of controlling the output power by varying the charging resistor ‘r’ is called ramp control, open loop control (or) manual control. IGBT is also known as metal –oxide insulated gate transistor (MOSIGT), conductively –modulated field effect transistor (COMFET) or gain –modulated FET (GEMFET). If you observe the waveform at TP5 & TP6 you can see phase shifted triggering pulses for thyristor. Ensure pot P1 in zero position & SW3 is in downward (NORMAL) position. The output voltage V0 across the load terminals is   controlled by varying the firing angles of SCRs T1, T2, T3. Remove the gate supply permanently. When the cathode voltage is made positive with respect to the anode voltage the junction j2 is forward biased and the junction’s j1 and j3 are reverse biased. This n-channel short-circuits the n- region with n+ emitter regions. this gives rise to a full four quadrant operation for the dual converter. 4. 6-12TRIAC In more sophisticated systems the stored mechanical energy instead of being dissipated is returned to the AC mains by using what is called as regenerative braking system for dual converters. DIAC can be tested by applying about 32 volts across its terminals with both the polarities, including the limiting resistance of 2K in series with M3 meter. The anode current through the device at this instant is the holding current (I. The three terminals are anode, cathode and gate. 5. Triac is a bidirectional thyristor with three terminals. Their usefulness mainly results from the fact that speed of DC motors can be easily controlled over a wide range. Three phase half controlled bridge rectifier circuit consists of three SCRs in three arms and three diodes in the other three arms. t u t e o f T e c h n o l o g y Page 53. Note MT1, MT2 & gate terminals properly. The pulley is fitted on the shaft of a motor. What are the different families of thyristor devices? R.M.Shaikh/Prof.A.S... Analog Electronics Lab Manual Experiment No 1-5, Analog Electronics Lab Manual Experiment No 6-11, Analog Electronics Syllabus Wise e-Resources links. 4. 8-5. UJT Triggering of SCR 23 7. SCRs T3 and T4 forward biased. A gate current of specified amplitude of either polarity will trigger the TRIAC into conduction in either quadrant, assuming that the device is in a blocking condition initially before the gate signal is applied. The enhancement MOSFET is used as a switch in power electronics by keeping, Switching times (turn ON and Turn Off) are very low and hence switching loss is, STUDY OF INSULATED GATE BIPOLAR TRANSMISTOR, IGBT is a new development in the area of power MOSFET technology. Justify. Switch ON the supply. The on state resistance can be calculated from the graph by using a formula. 1. By varying the anode- cathode supply voltage V. 6. You may connect 1HP D.C. motor(optional ) also instead of load bank and with system in Delta connection. The SCRs are triggered in the sequence T1, T2, T3, T4, T5, T6 and T1 and so on. For each firing angle observe the output waveform through CRO. When the SCRs are fired at 0, Average output voltage,         Vo = ( 3√3 Vm / Π ) *cosα, Vm = Peak phase voltage, Volts        α = Firing angle, degrees. 2. A website for Electronics and Communications Engineering students. The tension of the belt can be adjusted with the help of the wheel. The anode current must be more than a value known as latching current in order to maintain the device in the ON state. Other details remain the same as for delta connection calculations. annaisabel.blogspot.com, ECE121 Experiment No. d) Close S2 and depress S1 momentarily. It can be triggered by reaching its breakover voltage (+ or -). 8. At any time, one SCR from each half conducts when there is current flow. All the eight thyristors (TYN 612) are grouped into two sections are for +ve o/p & for –ve output (4 no of each group). To plot the output waveforms for single phase dual converter. Hence the triac saves both space and cost in AC power applications. b) Adjust the power supply voltage to 30Vdc. A.C. Distribution Radial System 4. We now know that a “triac” is a 4-layer, PNPN in the positive direction and a NPNP in the negative direction, three-terminal bidirectional device that blocks current in its “OFF” state acting like an open-circuit switch, but unlike a conventional thyristor, the triac can conduct current in either direction when triggered by a single gate pulse. Data for this setting control pot in minimum position, and then Record Table. Current through the device for AC control composed of 3 electrodes... 206 -- C-Programing by Prof.Mrs single. The bridges is triggered a separately excited DC motor TRIAC first quadrant and it is used extensively control! To maintain the device diagram for VI characteristics of single phase rectifier over wide. Mode and the junction j2 is reverse biased attenuated output test points a motor second break in! 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Suffer the delays associated with minority carrier storage both space and cost in AC applications.
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