Editing Power semiconductor device (section)

===Switches===

[[image:Switches domain.svg|thumb|350px|Fig.2 : Current/Voltage/switching frequency domains of the main power electronics switches.]]

The trade-offs between voltage, current, and frequency ratings also exist for a switch. In fact, any power semiconductor relies on a PIN diode structure in order to sustain voltage; this can be seen in figure 2. The [[power MOSFET]] has the advantages of a majority carrier device, so it can achieve a very high operating frequency, but it cannot be used with high voltages; as it is a physical limit, no improvement is expected in the design of a silicon [[MOSFET]] concerning its maximum voltage ratings. However, its excellent performance in low voltage applications make it the device of choice (actually the only choice, currently) for applications with voltages below 200&nbsp;V. By placing several devices in parallel, it is possible to increase the current rating of a switch. The MOSFET is particularly suited to this configuration, because its positive thermal coefficient of resistance tends to result in a balance of current between the individual devices.

The [[IGBT]] is a recent component, so its performance improves regularly as technology evolves. It has already completely replaced the [[bipolar transistor]] in power applications; a [[power module]] is available in which several IGBT devices are connected in parallel, making it attractive for power levels up to several megawatts, which pushes further the limit at which thyristors and [[Gate turn-off thyristor|GTOs]] become the only option. Basically, an IGBT is a bipolar transistor driven by a power MOSFET; it has the advantages of being a minority carrier device (good performance in the on-state, even for high voltage devices), with the high input impedance of a MOSFET (it can be driven on or off with a very low amount of power).

The major limitation of the IGBT for low voltage applications is the high voltage drop it exhibits in the on-state (2-to-4&nbsp;V). Compared to the MOSFET, the operating frequency of the IGBT is relatively low (usually not higher than 50&nbsp;kHz), mainly because of a problem during turn-off known as ''current-tail'': The slow decay of the conduction current during turn-off results from a slow recombination of a large number of carriers that flood the thick 'drift' region of the IGBT during conduction. The net result is that the turn-off {{ill|switching loss|de|Schaltverluste}} of an IGBT is considerably higher than its turn-on loss. Generally, in datasheets, turn-off energy is mentioned as a measured parameter; that number has to be multiplied with the switching frequency of the intended application in order to estimate the turn-off loss.

At very high power levels, a [[thyristor]]-based device (e.g., a [[Silicon-controlled rectifier|SCR]], a GTO, a [[MOS-controlled thyristor|MCT]], etc.) is still often used. This device can be turned on by a pulse provided by a driving circuit, but cannot be turned off by removing the pulse. A thyristor turns off as soon as no more current flows through it; this happens automatically in an [[alternating current]] system on each cycle, or requires a circuit with the means to divert current around the device. Both MCTs and GTOs have been developed to overcome this limitation, and are widely used in [[power distribution]] applications.

A few applications of power semiconductors in switch mode include lamp [[dimmer]]s, [[switch mode power supply|switch mode power supplies]], [[induction cooker]]s, automotive [[ignition system]]s, and AC and DC electric motor drives of all sizes.