EC-12.5 Rectifiers, DC-DC Converters and Inverters
You can analyse a rectifier with its filter, derive the output of the three basic switching converters from the duty ratio, explain how an inverter synthesises an alternating output, and say where each of them is used.
Before:EC-2. Electromagnetics and Transmission LinesEC-6. Semiconductor Devices and Device Models
This is the topic that connects a wall socket to every device a reader owns, and it is the one that makes the earlier device material pay. The three switching converters in particular are worth learning as one idea with three arrangements, because that is how they are actually derived and it makes the fourth and fifth arrangements readable without being taught.
Work through these
Rectifiers, and the filter that follows
A bridge of four diodes turns alternating into pulsating direct voltage, and a capacitor smooths it. The ripple, the peak current in the diodes and the poor power factor all follow from the size of that capacitor.
NPTEL: Power Electronics (IIT Bombay) · CourseControlled rectification, and delaying the turn-on
Replacing diodes with thyristors and delaying their firing reduces the average output. It was the standard method of control for decades and it distorts the supply current, which is why it is now regulated.
NPTEL: Power Electronics (IIT Bombay) · CourseThe step-down converter, and the duty ratio
A switch, a diode, an inductor and a capacitor produce an output that is the input times the fraction of time the switch is on. Everything else in switching supplies is a variation on that arrangement.
NPTEL: Power Electronics (IIT Bombay) · CourseStep-up and inverting arrangements
Moving the same four parts into different positions gives an output above the input, or one of the opposite polarity. Deriving each from the inductor's volt-second balance is quicker than memorising three formulas.
NPTEL: Power Electronics (IIT Bombay) · CourseContinuous and discontinuous conduction
If the inductor current falls to zero each cycle, the output no longer depends only on the duty ratio but on the load as well. Knowing which mode a converter is in explains otherwise puzzling behaviour.
NPTEL: Power Electronics (IIT Bombay) · CourseThe inverter, and making a sinusoid out of switching
Switching a direct supply between two polarities gives a square wave, and varying the width of each pulse across the cycle shapes the average into a sinusoid. A filter then removes what is left.
NPTEL: Power Electronics (IIT Bombay) · Course
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