Power semiconductors are chips that switch and convert electric power. They decide how much current goes from a battery to a motor, from the mains into a phone charger, or from solar panels into the grid. A power chip does not calculate anything. It is a switch that turns a large current on and off very fast, under the control of a microcontroller.
Why switch so fast? Say a motor needs half the battery's power. Instead of wasting the other half as heat, the power switch turns fully on and fully off thousands of times a second, and stays on for half of each cycle. The motor receives the average power, half of the full amount. By changing the share of time the switch stays on, the controller sets the power. The same trick, with the switches turned on and off in a pattern, turns direct current (DC), which goes one way only, into alternating current (AC), which reverses direction 50 times a second in India.
There are several kinds. A MOSFET is a fast power transistor used at lower voltages: in phone chargers, laptops, home inverters and two-wheelers. A transistor is a microscopic electrical switch, and a power transistor is a large one built to carry many amperes. An IGBT handles higher voltages and currents, in trains, factory motor drives and many electric cars. Two newer materials are replacing silicon in some uses. Silicon carbide (SiC) wastes less power at high voltages, so it is used in electric-car motor drives and fast chargers. Gallium nitride (GaN) switches even faster, which lets a laptop charger be much smaller.
Here is a typical case: a home inverter in Patna during an evening power cut. The inverter's battery supplies 12 volts DC. The fans, lights and TV need 230 volts AC. The inverter's microcontroller switches a set of MOSFETs thousands of times a second, in a pattern that rises and falls 50 times a second. A transformer then raises the voltage from 12 volts to 230 volts. With 400 watts of fans and lights running, the battery supplies about 40 amperes. The MOSFETs waste part of that power as heat, so they are bolted to an aluminium heat sink. Each percentage point of efficiency matters here: it decides how many hours the battery lasts before the power returns.
The same chips sit in many other places. In an electric car or scooter, they carry the battery pack's power to the motor, and an EV charger uses them to charge the battery. On a roof, a microinverter under each solar panel uses them to turn the panel's DC into AC for the house. In a data centre, they convert power for every rack, and a loss of a few per cent across thousands of servers adds up to megawatts; see data centre power and cooling. In a car, they also power the automotive processors.
Like other machine chips, a power chip is chosen once for a product and then made for many years, which is called a design win. Power chips are tested for heat and for surges of current, because a failed switch can stop a motor or start a fire. Their makers design them in Bengaluru and elsewhere.