🔍 Key Concepts

• Look closely at the symbols used in the bridge rectifier section versus the controlled inverter bridge section. • Recall the difference between an uncontrolled rectifier (using diodes) and a controlled rectifier (using thyristors/SCRs). • Remember that modern variable frequency drives (VFDs) often use IGBTs (a type of transistor) on the inverter (output) side for switching.

💭 Think About

• In figure A, what semiconductor symbol is shown in the bridge rectifier block? Is it a diode, a transistor, or a thyristor? • In the controlled inverter bridge block, what device is explicitly labeled, and is that device a transistor or a thyristor? • Which part of the circuit actually needs rapid high‑frequency switching to create variable‑frequency AC for the motor?

✅ Before You Answer

• Verify whether the rectifier symbol has any gate/control connection (which would indicate a controlled device like a thyristor) or if it is just a simple diode bridge. • Confirm that the inverter section is labeled with IGBT, and recall whether an IGBT is classified as a transistor or a thyristor. • Eliminate any choice that claims a device type or control method that does not match the symbols and labels shown in the illustration.