The "magic" that allows these converters to work so precisely is Pulse Width Modulation. By turning a switch on and off thousands of times per second and varying the "on-time" (duty cycle), we can control the average output voltage. For example, if a switch is on 50% of the time, the average output voltage will be half of the input. This high-speed toggling is what makes modern power supplies so small and efficient compared to the heavy transformers of the past. Why Power Electronics 1 Matters
AC to AC (Cycloconverters): These are used to change the frequency or magnitude of an AC signal, often used in heavy industrial motor drives to control the speed of large machinery. Pulse Width Modulation (PWM)
| Device | Symbol | Controlled by | Best for | Limitations | | :--- | :--- | :--- | :--- | :--- | | | | Uncontrolled (voltage polarity) | Rectification | Cannot be turned off actively. | | BJT (Bipolar Junction Transistor) | | Current | Low-frequency apps ( <10 kHz) | Low current gain, thermal runaway. | | MOSFET (Metal Oxide Semiconductor FET) | | Voltage (Gate) | High-frequency (100 kHz – MHz), low to medium power | High conduction loss at high voltage. | | IGBT (Insulated Gate Bipolar Transistor) | | Voltage (Gate) | High voltage, high power (EVs, trains, welders) | Slower than MOSFET (20-50 kHz). |
