Question 3-23C1

Connecting two SCRs in parallel with reverse polarity, also known as an anti-parallel or inverse parallel configuration, allows for full-wave AC power control. In this setup, one SCR conducts during the positive half-cycle of the AC waveform, while the other conducts during the negative half-cycle. This effectively distributes the instantaneous power dissipation across the two devices over a complete AC cycle, enabling safer handling of the total load. Connecting SCRs in series (A) primarily increases the total voltage rating, not the current or power handling for a single half-cycle, and can lead to triggering issues. Connecting them in parallel with the same polarity (B) is generally unsafe for current sharing. Due to slight differences in their forward voltage drop, one SCR would conduct more current than the other, leading to uneven heating, thermal runaway, and eventual failure of the device carrying the heavier load. A combination series and parallel configuration (D) would not resolve these fundamental issues of current sharing or AC power distribution.