Thyristor Semiconductor Products Page 80 Thyristor

2014 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 12/14/14 Teccor brand Thyristors AN1009 Introduction This application note presents design tips and facts on the following topics: AV , I RMS , and I PK Angles Relationship of I AV , I RMS , and I PK Since a single rectifier or SCR passes current in one direction only, it conducts for only half of each cycle of an AC sinewave. The average current (I AV ) then becomes half of the value determined for full-cycle conduction, and the RMS current (I RMS ) is equal to the square root of half the mean-square value for full-cycle conduction or half the peak current (I PK ). In terms of half-cycle sinewave conduction (as in a single-phase half-wave circuit), the relationships of the rectifier currents can be shown as follows: I PK AV AV I AV = (1/ ) I PK I PK RMS I RMS PK I AV = (2/ ) I RMS I RMS = ( /2) I AV AV When two identically rated SCRs are connected inverse parallel for full-wave operation, as shown in Figure AN1009.1, they can handle 1.41 times the RMS current rating of either single SCR. Therefore, the RMS value of two half sinewave current pulses in one cycle is 2 times the RMS value of one such pulse per cycle. Figure AN1009.1 SCR Anti-parallel Circuit dv/dt Definitions The rate-of-rise of voltage (dv/dt) of an exponential waveform is 63% of peak voltage (excluding any overshoots) divided by the time at 63% minus 10% peak voltage. (Figure AN1009.2) PK ] = (t 2 - t 1 ) Resistor Capacitor circuit t = RC = (t 2 - t 1 ) 3 - t 2 ) (Peak Value) 100% 0% 63% t 1 t 2 t 0 t 3 Percent of Voltage Time Numerical dv/dt 10% Figure AN1009.2 Exponential dv/dt Waveform The rate-of-rise of voltage (dv/dt) of a linear waveform is 80% of peak voltage (excluding any overshoots) divided by the time at 90% minus 10% peak voltage. (Figure AN1009.3) Linear dv/dt = 0.8 = [V PK ] = (t 2 - t 1 ) PK ] = (t 2 - t 1 ) 90% 0% 10% t 1 t 2 t 0 Percent of Voltage Time Figure AN1009.3 Linear dv/dt Waveform Miscellaneous Design Tips and Facts

Previous PageNext Page