10ECL78_PE Lab Manual_Updated_16-07-14.pdf - CONTENTS EXPT NO NAME OF THE EXPERIMENT PAGE NO 01 Static characteristics of SCR 3 02 Static

10ECL78_PE Lab Manual_Updated_16-07-14.pdf - CONTENTS EXPT...

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C ONTENTS E XPT . N O . NAME OF THE EXPERIMENT P AGE N O . 01 Static characteristics of SCR 3 02 Static characteristics of MOSFET and IGBT 6 03 Controlled HWR and FWR using RC triggering circuit 11 04 SCR turn off using LC circuit and auxiliary commutation 14 05 UJT firing circuit for HWR and FWR circuits 18 06 Generation of firing signals for thyristors / trials using digital circuits/microprocessor 24 07 AC voltage controller using TRIAC / DIAC combination 30 08 Single phase fully controlled bridge converter with R and R-L loads 32 09 Voltage(impulse) commutated chopper both constant frequency and variable frequency operations 37 10 Speed control of a separately excited dc motor 41 11 Speed control of Universal motor 46 12 Speed control of Stepper motor 49 13 Parallel / Series Inverter 52 14 Static characteristics of DIAC 56 VIVA QUESTIONS 58
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Power Electronics Laboratory Manual 10ECL78 Page 2 Ex.No:01 STATIC CHARACTERISTICS OF SCR AIM: To find the characteristics of SCR and to find the forward resistance, holding. Current and latching current APPARATUS Sl. No. Components Details Specification Qty 1. SCR 2P4M 1 No. 2. Ammeter 250 A, 10 mA. 2 Nos. 3. Dual Regulated power supply 30V/2A 1No. 4. Resistance 1k /10w 1No. 5. Resistance 5k /10w 1No. 6. Diode BY127 1No. 7. Multimeter, Connecting Board THEORY Silicon controlled rectifier (SCR) also called, as thyristor is one of the most widely used semi-controlled switching devices in power electronics. It has a p-n-p-n structure and three terminals anode (A), cathode (K) and gate (G). SCR can be turned on by injecting a current into the gate only when its anode is positive with respect to cathode i.e. when it is forward biased. Then current flows through it in the direction anode to cathode, It does not conduct when reverse biased even if gate current is injected. Therefore, SCR is a current controlled Uni.-directional switch. With iG = 0, when the device is forward biased, a very small forward leakage current of few A flows as long as VAK < VBO. When VAK becomes equal to VBO, the device turns on causing a sudden drop in VAK. This turns on damages the device. Then iA abruptly increases to a value limited by any impedance connected in series with the device. The device remains in on state if IL IA where IL is called the latching current. A conducting SCR can be brought to off state by first reducing the anode current below IH where IH is called holding current and then by applying reverse voltage across the device for duration not less than the turn off time specified by the manufacturer. With forward bias, when a gate current is injected, the device turns on at a lower forward voltage than VBO. This is the normal way of turning on the device. The forward voltage at which the device turns on reduces with increase in gate current. After turn on, the gate has no control over the device. Therefore SCR is called semi-controlled switch. This is the Main disadvantage of the device when compared to fully controlled switches like IGBT or MOSFET.
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