The high power electronics are immensely robust and efficient. They are available as low quiescent current devices (SCRs, GTOs, GTAs) or high current devices (SCRs, GTOs, GTAs). Most devices are monolithic and made in advanced silicon processes. Power MOSFETs are also available in ever- shrinking size with enhanced IGBTs developed for niche applications where higher voltages are required. Many devices are capable of switching a large current of amperes or more with low switching losses to the circuit. However, a number of issues are still in focus such as maximum primary-to-primary turn-on voltage, the ability to switch in high frequency ranges and the efficiency in delivering power. For example, switching at higher frequencies results in higher switching losses. The output voltage may not be compatible with the voltage of the circuit to which it is connected.
The most common structure for the high power electronics is a switch first (SMPS-SFS) where a high capacity capacitor is charged by a certain current. When the switch is closed, capacitor discharges the energy into the load. The devices used in the circuit are either thyristors (operating in “pulse-width-modulation” – PWM) or gate-drive transistors (operating in “class-AB” or “class-G”). The gate-drive transistor has a much higher gate-to-drain voltage than the thyristor, resulting in a greater efficiency at higher currents. Although MOSFETs can switch at much higher frequency than bipolar devices, they have higher on and off-state resistance. The load between the gate and drain is connected through a FET. While the bipolar devices follow the classical gate-drive topology (PWM), the MOSFETs use some other drive scheme, such as the “source-follower” (SF, class-A) or “triode” (U, class-G) topology.
The switches have a number of options for protecting against short circuits and overloads. The switches can be engineered for different fault conditions by evaluating the maximum current to be handled and the voltage drop across the switch devices. d2c66b5586