Govt. Exams
Entrance Exams
Modern VFDs support 0.1Hz to 500Hz+ output, enabling ultra-low speed precision applications and extended-speed motor operation.
MOSFETs have switching frequencies up to several MHz, while IGBTs typically reach 20-50kHz, thyristors <10kHz, and GTOs ~5kHz.
For a three-phase bridge rectifier: Vdc = (3√2/π) × Vline = 1.35 × 400 = 540V approximately.
Modern automotive DC-DC converters target 90-95% efficiency using advanced topologies, SiC MOSFETs, and optimized gate drives to minimize losses in 12V auxiliary systems.
Simultaneous conduction of upper switches creates a direct short across the DC link, causing massive current spike and potential device failure. This is prevented using dead-time insertion.
Snubber circuits limit the rate of change of voltage (dv/dt) across semiconductor switches during switching transients, preventing false triggering and overvoltage damage.
A freewheeling diode provides a discharge path for inductor current when the main switch opens, preventing voltage spikes and ensuring continuous current flow in inductive circuits.
Holding current is the minimum anode current required to keep the thyristor in ON state after the gate signal is removed. If anode current falls below Ih, the device turns OFF.
MOSFETs have switching frequencies up to several MHz, making them ideal for high-frequency applications. Thyristors are limited to lower frequencies (few kHz).
In an ideal chopper, theoretical efficiency is 100% as it transfers energy without dissipation. Practical efficiency is reduced by component losses
