Today we would like to introduce VBSEMI's new product IGBT, also known as insulated gate bipolar transistor.
The most common electronic components in practical electronic applications are bipolar junction transistors, BJTs and MOS transistors.
And IGBT (Insulated Gate Bipolar Transistor) you can think of it as a fusion of BJT and MOS transistor because IGBT has the input characteristics of BJT and the output characteristics of MOS transistors.
Compared to them, VBSEMI's IGBTs have a higher power gain, higher operating voltage, higher short-circuit current level, smaller chip size, and lower heat capacity and short-circuit withstand time.
In view of the above advantages of IGBTs, in this article, we will discuss the problem of short-circuit protection of IGBTs from VBSEMI in industrial motor drive applications.
First, let's look at the short-circuit tolerance of IGBTs
In the beginning, IGBT people thought that short-circuit capability was based on the length of short-circuit tolerance. However, in many cases, the short-circuit tolerance cannot be used to characterize the actual short-circuit capability. In fact, short-circuit endurance is actually a thermal failure, and it is a failure when the heat distribution of the chip is relatively uniform, and its short-circuit endurance time is related to its transconductance or gain.
In general, higher gain results in higher short-circuit currents within the IGBT, so IGBTs with lower gain have lower short-circuit levels. However, higher gains also result in lower on-state conduction losses.
This is where the trade-offs come in.
With the development of technology, IGBTs gradually increase the short-circuit current level and reduce the advantages of short-circuit withstand time. This makes it smaller in chip size and shrinks the size of the module.
IGBT overcurrent protection
In the case of IGBTs, they are not fail-safe elements, so in the event of a fault, it can directly lead to DC bus capacitance** and cause the entire drive to fail. Therefore, for overcurrent protection, it is necessary to achieve it by means of current measurement or saturation detection.
For example, when performing current measurements, measurement devices such as shunt resistors need to be incorporated into the inverter and phase output to cope with straight barrel faults and motor winding faults. The fast-actuating jump circuit in the controller or gate driver must shut down the IGBT in time to prevent the short-circuit withstand time from being exceeded.
The collector-emitter voltage of the IGBT is very low (1 V to 4 V typical) during normal operation. However, if a short circuit event occurs, the IGBT collector current rises to a level that drives the IGBT out of the saturation zone and into the linear operating area. This results in a rapid increase in collector-emitter voltage.
In the above case, the normal voltage level indicates that there is a short circuit, and usually during desaturation, the gate-emitter voltage will be too low, and the IGBT will not fully drive the value saturation region, so it should be carefully detected to prevent false triggering. A current source charge capacitor or RC filter is also often added to create a brief time constant in the sensing mechanism.
Under normal operation, it is recommended that the gate driver be designed to shut down the IGBT as quickly as possible in order to minimize switching losses. This can be achieved with lower driver impedance and gate drive resistance. If the same gate shutdown rate is applied to the overcurrent condition, the collector-emitter DI dt will be much larger because the current will vary greatly over a shorter period of time.
Therefore, in order to reduce the level of DI dt and other potentially damaging overvoltages, it is important to provide a high-impedance shutdown path when turning down the IGBT.
Then, in addition to the above detection methods, it is also very important to select IGBT. In most IGBY specifications, the short-circuit current index is generally specified, and we should pay attention to the following parameters:
1.VCC voltage, that is, the VCE voltage in the short-circuit test, or the bus capacitance voltage in the short-circuit test;
2.VGE voltage, i.e., driving voltage;
3.RG drive resistor.
4.The test temperature is usually 25, but there are also 120 or 150
5.Some datasheets also have a maximum number of repetitions for the short circuit test.
The IGBTs of VBSEMI have the following advantages:
1.It has higher voltage and current handling capabilities.
2.It has a very high input impedance.
3.Very high currents can be switched using very low voltages.
4.Voltage control device, i.e. it has no input current and low input loss.
5.The gate drive circuit is simple and inexpensive, reducing the gate drive requirements.
6.It can be easily turned on by applying a positive voltage and can be easily turned off by applying a zero or negative voltage.
7.It has low on-resistance and high current density, allowing it to have a smaller chip size.
8.It has higher power gain and higher switching speed than BJT and MOS tubes.
9.High current levels can be switched using a low control voltage.
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