Switches Power semiconductor device

fig.2 : current/voltage/switching frequency domains of main power electronics switches.

the trade-offs between voltage, current, , frequency ratings exist switch. in fact, power semiconductor relies on pin diode structure in order sustain voltage; can seen in figure 2. power mosfet has advantages of majority carrier device, can achieve high operating frequency, cannot used high voltages; physical limit, no improvement expected in design of silicon mosfet concerning maximum voltage ratings. however, excellent performance in low voltage applications make device of choice (actually choice, currently) applications voltages below 200 v. placing several devices in parallel, possible increase current rating of switch. mosfet particularly suited configuration, because positive thermal coefficient of resistance tends result in balance of current between individual devices.

the igbt recent component, performance improves regularly technology evolves. has replaced bipolar transistor in power applications; power module available in several igbt devices connected in parallel, making attractive power levels several megawatts, pushes further limit @ thyristors , gtos become option. basically, igbt bipolar transistor driven power mosfet; has advantages of being minority carrier device (good performance in on-state, high voltage devices), high input impedance of mosfet (it can driven on or off low amount of power).

the major limitation of igbt low voltage applications high voltage drop exhibits in on-state (2-to-4 v). compared mosfet, operating frequency of igbt relatively low (usually not higher 50 khz), because of problem during turn-off known current-tail: slow decay of conduction current during turn-off results slow recombination of large number of carriers flood thick drift region of igbt during conduction. net result turn-off switching loss of igbt considerably higher turn-on loss. generally, in datasheets, turn-off energy mentioned measured parameter; number has multiplied switching frequency of intended application in order estimate turn-off loss.

at high power levels, thyristor-based device (e.g., scr, gto, mct, etc.) still choice. device can turned on pulse provided driving circuit, cannot turned off removing pulse. thyristor turns off no more current flows through it; happens automatically in alternating current system on each cycle, or requires circuit means divert current around device. both mcts , gtos have been developed overcome limitation, , used in power distribution applications.

a few applications of power semiconductors in switch mode include lamp dimmers, switch mode power supplies, induction cookers, automotive ignition systems, , ac , dc electric motor drives of sizes.