This section provides overview, applications, and principles of isolated gate drivers. Also, please take a look at the list of 6 isolated gate driver manufacturers and their company rankings.
An isolated gate driver is a circuit used to drive and control the gate terminals of a voltage-driven type of MOSFET or IGBT.
Currently, the most general-purpose isolated gate driver is a circuit that drives and controls the gate of a MOSFET, but there are analog circuit technologies that use resistors, diodes, bipolar and other transistors. Recently, isolated gate driver peripheral circuit components themselves have also evolved.
Although there are many types and combinations of them, learning gate voltage drive control circuits using MOSFETs is the most practical.
Isolated gate drivers are used to drive power transistors with a simple drive circuit consisting only of MOSFETs and gate resistors.
The advantage of isolated gate drivers are the small number of components. The disadvantage is that switching speed and loss vary greatly depending on the resistance value, and it is difficult to set an appropriate resistance value. As a circuit that improves this problem of adjusting the resistance value, it is also used in circuits where the gate of a MOSFET is turned on and off separately driven by a diode.
The voltage for the diode remains, so it cannot be completely zero, but a circuit called a push-pull, in which the Pch and Nch of the MOSFET are connected up and down, solves this problem. This is currently the most common use of isolated gate drivers.
Isolated gate drivers consists of a push-pull circuit of transistors.
A push-pull circuit is a circuit that performs switching or amplification by using two transistors to operate alternately. There are two types of push-pull circuits: "emitter follower type" and "emitter grounded type," but the latter is basically used in most cases.
The isolated gate drivers consists of a circuit that acts as a middleman between the power element, which is the powerhouse that does the heavy lifting at the transistor site, and the microcontroller, which is the brain that commands the control policy and plays the role of president.
Power MOSFETs and IGBTs are examples of power elements that can carry large currents. The voltages and currents that directly drive these devices are in most cases insufficient for the currents and voltages that a normal microcontroller can output.
Therefore, isolated gate drivers are needed between the power devices and the microcontroller to drive them.
Ultra-high-speed isolated gate drivers are isolated gate drivers that specialize in high-speed switching. The ultrahigh-speed category is generally defined as a device with a switching speed of several tens of ps (pico-seconds) or less.
Pico is 10 to the minus 12th power, so switching speed is less than one trillionth of a second. This evolution can be said to have occurred due to recent technological innovations in semiconductor devices.
The following ultra-fast device isolated gate drivers are in practical use.
The first is a transistor using silicon, the most commonly used semiconductor. The bipolar type is fast, capable of switching in tens of picoseconds, while the MOS type has delayed operation but is suitable for high-density circuit integration.
The second type is the compound semiconductor type transistor. These include the MESFET, a Schottky gate type field-effect transistor, the HBT, a hetero-bipolar transistor, and the HEMT, a high-mobility field-effect transistor. The semiconductor used is a gallium arsenide compound. This device is capable of switching operations of a few picoseconds, making it the fastest semiconductor available today for ultrahigh speeds.
The third, although still in the research stage, is the Josephson device, which utilizes the tunneling effect between two types of superconductors; it has half the switching speed of the second device and uses metallic materials such as niobium. However, it requires cryogenic temperatures for operation, and there are still challenges to be overcome before it can be put into practical use.
SiC isolated gate drivers are semiconductor devices that have been attracting attention in the recent power electronics world because of their superior breakdown voltage performance and improved switching speed. The isolated gate drivers are composed of a semiconductor called silicon carbide (commonly known as SiC), the use of which has become a trend in the industry.
In particular, MOSFETs using SiC have contributed to a significant improvement in switching performance, which has been an issue in high-power inverters, and have improved heat dissipation while achieving high breakdown field strength and carrier drift speed.
However, SiC has the challenge of resolving voltage differences in various SiC composition configurations.
Currently, the main devices that we want to operate with isolated gate drivers are voltage-driven devices called MOSFETs and IGBTs. Although isolated gate drivers do not require a constant flow of current, they do require a short pulse current during switching operations, so the rated current and voltage values as power devices must be carefully considered.
In particular, in the case of IGBTs, compared to MOSFETs, their characteristics are best demonstrated at high voltages of several 10 V. Therefore, it is safer to select bias characteristics for the isolated gate drivers that match the voltage range and application as much as possible.
IGBTs are characterized by their tendency to operate at high voltages and to break down instantly when their maximum ratings are exceeded. For this reason, IGBT modules, which combine IGBTs with isolated gate drivers ICs and protection circuits, are easier to use than IGBTs alone (discrete), and are now widely accepted in the market.
Future trends in isolated gate drivers technology development will include not only more compact, high-performance, and easy-to-use products, but also application-specific ICs such as Class-D amplifiers and motor drive ICs. These isolated gate drivers will be differentiated from the isolated gate drivers for SiC semiconductors and GaN devices mentioned earlier.
*Including some distributors, etc.
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