BPE 22427 ● SCR Applications: choppers, voltage controllers, DC motor speed control, UPS, inverter ● Chopper: Circuit which is used to convert fixed dc voltage into variable dc voltage ● Chopper Applications: SMPS, battery charger, DC voltage boosting, electric cars ● Inverter Applications: UPS, conveyors, induction heating, aircraft power supply ● UPS Application: PLCs, medical equipment, computer, used in intensive care units ICU ● SMPS Advantages: lightweight and compact, smaller in size, wide output range ● IGBT Applications: UPS, SMPS, inverters, traction, AC and DC motor drives ● DIAC Application: used to trigger SCR, heat control ckt, light dimmer, fan speed ctrl ● TRIAC Applications: fan speed regulator, temperature controller, lamp dimmer ● PUT Applications: time delay ckt, logic circuit, SCR trigger circuit, sawtooth generator ● UJT Application: triggering device for SCR & TRIAC, timing ckt, sawtooth generator ● Polyphase Rectifiers Applications: radio transmitter, telephone exchange, traction ● Polyphase Rectifiers Advantages: large amount of power usually greater than 2 kW, it provides highest TUF (transform utilization factor) ● Triggering devices for SCR: UJT, PUT, SUS ● Triggering devices for TRIAC: DIAC and SBS ● Firing angle: angle of sine wave at which SCR is turned ON. This varies from 0 to 180° ● Revers Breakdown Voltage:(VBR) minimum value of reverse voltage from cathode to anode at which device breaks in avalanche region & starts conducting in reverse direction ● Use of free wheeling diode: to prevent reversal of load voltage and to prevent transfer of reactive power from load to supply and hence improve power factor of circuit ● LASCR Application: photoelectric control, used in HVDC high voltage dc transmission ● Commutation: The process to turn off conducting SCR is called commutation ● GTO Advantages: no commutation circuit required, reducing cost, size and weight of ckt, less turn off time and hence high frequency ● GTO Applications: inverter, UPS, dc motor drives ● Peak point voltage: maximum voltage developed across base and emitter of UJT Step Down Chopper: Step Up Chopper Draw ckt.diagram of 3φ half wave controlled rectifier with resistive load, also draw load voltage waveform for α= 0 ° & α= 60° light dimmer or fan speed control circuit usin DIAC & TRIAC. State relation between light intensity & firing angle. (just keep FAN in place of LAMP for fan speed control) Battery charger using SCR LASCR Class B Commutation ● Working of Class C Commutation: At first, when SCR1 is triggered load current IL starts flowing through (Vdc+, RL, SCR1, Vdc-). At the same time, capacitor ‘C’ will charge through Vdc+, R, C, SCR1, Vdc- When it is fully charged to Vs, charging current becomes zero. To turn off SCR1, SCR2 is triggered. When SCR2 is turned ON reverse voltage across ‘C’ is applied across SCR1, turning it OFF. Now capacitor will start charging through Vdc+, RL, C, SCR2, Vdc- Similarly, as SCR1 is turned ON the reverse voltage across ‘C’ is applied across SCR2, turning SCR2 OFF. SMPS Temperature controller using SCR HWCR with R-Load PUT as relaxation oscillator Parallel Inverter Effect of gate current on break over voltage of SCR