Switching powerĪ reduction in on-state voltage can cost the IGBT to experience slower switching speed at turn-off. There are, however, two limitations: the transit time of electrons across the drift region and the time required to charge/discharge the input gate and “Miller” capacitances.
The absence of minority carrier transports allow MOSFETs to switch at higher frequencies. As a result, an additional diode (often referred to as a “freewheeling” diode) gets placed parallel with the IGBT to conduct the current in an opposite direction. Unfortunately, it also blocks reverse current flow. This increase in conductivity within the n-layer helps reduce the total on-state voltage of the IGBT. In this extra layer, holes are injected into the highly-resistive n-layer, creating a carrier overflow. When it comes to electron current flow, an important difference is the addition of a p-substrate layer beneath the n-substrate layer in the IGBT. The structures of both transistors are very similar. They’re also used to generate large power pulses in areas like particle and plasma physics, and have established a role in modern appliances like electric cars, trains, variable-speed refrigerators, air conditioners, and more. This unique capability is why IGBTs are often used with amplifiers to synthesize complex waveforms with pulse width modulation and low-pass filters. In fact, its pulse repetition frequency actually gets into the ultrasonic range. The IGBT is specially designed to turn on and off rapidly. It does this by using an isolated gate field effect transistor for the control input, and a bipolar power transistor as a switch. The IGBT combines the simple gate-drive characteristics found in the MOSFET with the high-current and low-saturation-voltage capability of a bipolar transistor. Its gate/control signal takes place between the gate and emitter, and its switch terminals are the drain and emitter. The IGBT is also a three terminal (gate, collector, and emitter) full-controlled switch. Due to its efficiency, power MOSFETs are used in power supplies, dc/dc converters, and low-voltage motor controllers. Its voltage rating is a direct function of the doping and thickness of the N-epitaxial layer, and its current rating is related to the channel’s width (the wider the channel, the higher the current). This is because most power MOSFETs structures are vertical (not planar). What’s more, it can sustain a high blocking voltage and maintain a high current. When compared to the IGBT, a power MOSFET has the advantages of higher commutation speed and greater efficiency during operation at low voltages. They’re only used in “on” or “off” states, which has resulted in their being the most widely used low-voltage switch. It’s specially designed to handle significant power levels. There are many different types of MOSFETs, but the one most comparable to the IGBT is the power MOSFET. Also, because MOSFETs can operate at high frequencies, they can perform fast switching applications with little turn-off losses. On-state losses are lower because the transistor’s on-state-resistance, theoretically speaking, has no limit. This means there’s little-to-no chance of thermal runaway. In order to function properly, MOSFETs have to maintain a positive temperature coefficient. This allows for less power consumption, and makes the transistor a great choice for use as an electronic switch or common-source amplifier. The gate itself is made of metal, separated from the source and drain using a metal oxide. The gate/control signal occurs between the gate and source, and its switch terminals are the drain and source. The MOSFET is a three-terminal (gate, drain, and source) fully-controlled switch. So, rather than say that one is outright better than the other, here’s a basic overview on the differences between both transistors. It varies from application to application, and a wide range of factors, such as speed, size, and cost, all play a role in determining the right choice. Which is better MOSFET or IGBT? While everyone has an opinion on which device works best in an SMPS application, the truth is this: there’s no universal standard to determine which device offers better performance in a specific type of circuit. High-voltage, high-current and low switching frequencies, on the other hand, favor IGBTs.
Historically speaking, low-voltage, low-current and high switching frequencies favor MOSFETs. Two of the more popular versions are the metal-oxide semiconductor field effect transistor (MOSFET) and the insulated-gate bipolar transistor (IGBT). There are many types of switch-mode power supply (SMPS) transistors to choose from today. When it comes to SMPS applications, both transistors have their advantages, but which one’s right for you?
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