A complete guide to IGBT – composite semiconductor device of BJT and MOS

What is IGBT in simple words

IGBT, insulated gate bipolar transistor, is a composite fully controlled voltage-driven power semiconductor device composed of (BJT) bipolar transistor and insulated gate field effect transistor (MOS), which combines the advantages of high input impedance of (MOSFET) gold oxygen half-field transistor and low on-voltage drop of power transistor (GTR).

The main role of IGBT is to change high-voltage DC into AC and frequency conversion. (So it is used more in electric vehicles)

What is the main advantage and disadvantage of IGBT

IGBT has the input characteristics of BJT and the output characteristics of MOS tubes. However, the advantage of an insulated-gate bipolar transistor IGBT over a BJT or MOS transistor is that it provides a greater power gain than a standard bipolar transistor, as well as a higher operating voltage and lower MOSFET input loss.

Advantage

● The control circuit is simple, easy to install and use.

● It has good load characteristics, the control output voltage and current are stable and reliable, and the switching loss is small.

● Lower power loss than bipolar switch.

● Large current or voltage can be controlled by small control signals.

Disadvantage

● IGBT high-voltage transistors have high heat dissipation requirements, and large radiators and fans must be used.

● The operation delay is relatively large, which is greatly affected by temperature, resulting in increased switching loss.

● Because its switching speed is slow, it is generally used in low-frequency circuits.

What’s the structure of IGBT

The structure of IGBTs is mainly composed of three parts: metal oxide semiconductor oxide layer (MOS), bipolar transistor (BJT) and insulation layer.

Ⅰ. Metal oxide semiconductor oxide layer (MOS): It is the core of IGBT, which consists of a metal oxide semiconductor oxide oxide layer that can be controlled by a control circuit. It can control controllable parameters of the transistor, such as current and voltage.

Ⅱ. Bipolar transistor (BJT): It is the core of IGBT, which consists of two bipolar transistors, which can produce high power.

Ⅲ. Insulating layer: It is the basis of IGBT, which is composed of an insulating layer, which can protect IGBT components from erosion and damage by the external environment.

What’s the role of IGBT

① IGBT can be used as a switching element to control power, such as the input and output of power supply;

② IGBT can be used as an amplifier to amplify high-frequency signals;

③ IGBT can be used for constant voltage output, which can maintain the stability of the power supply;

④ IGBT can be used in field thyristor (FACTS) to adjust the frequency, voltage and power of the power system;

⑤ IGBT can be used in inverter circuits to provide reliable sinusoidal voltage and frequency;

⑥ IGBT can be used for power regulation, provide power regulation and monitoring system;

⑦ IGBT can be used for motor control, such as three-phase servo motor control system;

⑧ IGBT can be used in high-voltage electromagnetic converters for power conversion and regulation;

⑨ IGBT can be used in power converters for power conversion and regulation;

⑩ IGBT can be used for generator control, for generator automatic control system.

What is the working principle of IGBT

Ignoring the complex process of deriving semiconductor physics, here is how the simplified principle works.

IGBT has two types: N-channel type and P-channel type, and the circuit diagram symbols of the mainstream N-channel IGBT and its equivalent circuit are as follows:

So the whole process is simple:
When gate G is high, NMOS is on, so the CE of PNP is also on, and current flows through CE.
When gate G is low, NMOS is cut-off, so the CE of PNP is cut-off and no current flows through.

Unlike MOSFETs, IGBTs do not have parasitic reverse diodes inside, so in actual use (inductive loads) they need to be paired with appropriate fast recovery diodes.

Which of the parameter is used to control the IGBT

1. Voltage limit: The voltage range of IGBT is generally between 600V-6.5kV.

2. Power limit: The power range of IGBT is generally between 1W-15MW.

3. Leakage current: The leakage current of IGBT is much smaller than that of MOSFET, generally between 1mA-100mA.

4. Loss: The loss of IGBT is generally lower than that of MOSFET, which can reach between 1W and 15MW.

5. Thermal effect: The thermal effect of IGBT is smaller than that of MOSFET, which can reach between 20 °C and 150 °C.

6. Reaction time: The reaction time of IGBT is generally faster than that of MOSFET, which can reach between 1ns-50ns.

7. The collector-emitter rated voltage UCES is the maximum voltage that the IGBT can withstand between the collector and the emitter in the cut-off state, and the general UCES is less than or equal to the avalanche breakdown voltage of the device.

8. The gate-emitter rated voltage UGE is the maximum allowable voltage between the IGBT gate and the emitter, usually 20V. The voltage signal of the gate controls the turn-on and turn-off of the IGBT, and its voltage must not exceed the UGE.

9. The collector rated current IC is the maximum current that the IGBT is allowed to pass continuously in the saturated on state.

10. The collector-emitter saturation voltage UCE is the voltage drop between the collector and the emitter when the IGBT is saturated on. The smaller the value, the less power loss of the tube.

11. Switching frequency In the instruction manual of IGBT, the switching frequency is given in the turn-on time tON, the fall time t1 and the off-time tOFF, according to these parameters can be estimated the switching frequency of the IGBT, generally up to 30~40kHz. In frequency converters, most of the actual carrier frequencies used are below 15kHz.

What is IGBT and MOSFET difference

● Structure
The structural difference between IGBT and MOSFET is that the substrate of MOSFET is N-type or P-type, and the substrate of IGBT is P-type.
● Application
IGBTs are generally used in high-voltage power products, from 600V to several thousand volts, and MOSFET application circuits from tens of volts to about a thousand.
● Drive circuit
IGBT input capacitance is larger than MOS, so more voltage drive power is required, MOSFET is generally used in high-frequency and low-voltage applications, that is, power < 1000W and switching frequency > 100kHZ, while IGBT performs better in low-frequency and high-power occasions.

How to select IGBT

IGBT rated voltage selection

Three-phase 380V input voltage after rectification and filtering, the maximum value of DC bus voltage: under the condition of switching work, the rated voltage of IGBT is generally required to be higher than twice the DC bus voltage, according to the voltage level of IGBT specifications, select 1200V voltage level IGBT.

IGBT rated current selection

Taking 30kW inverter as an example, the load current is about 79A, due to the load electrical start or acceleration, the current is overloaded, generally required to withstand 1.5 times the overcurrent within 1 minute, the maximum load current is about 119A, it is recommended to choose 150A current level IGBT.

The selection of IGBT switching parameters

The switching frequency of the inverter is generally less than 10kHZ, and in the actual working process, the on-state loss of IGBT accounts for a relatively large proportion, it is recommended to choose low-on-state IGBT

Factors affecting the reliability of IGBT

1. Gate voltage.
IGBT work, must have forward gate voltage, commonly used gate drive voltage value is 15~187, the highest use to 20V, and shed voltage and gate resistance Rg has a lot to do with it, in the design of IGBT drive circuit, refer to the rated Rg value in the IGBT Datasheet, design suitable driving parameters, to ensure a reasonable forward gate voltage.

Because the working state of the IGBT has a lot to do with the forward shed voltage, the higher the forward gate voltage, the smaller the turn-on loss, and the smaller the forward voltage drop.

In the case of bridge circuits and high-power applications, in order to avoid interference, when the IGBT is turned off, the gate is added with a negative voltage, generally -5-15V, to ensure that the IGBT is turned off and avoid the influence of the Miller effect.

2. The Miller effect.
To reduce the effects of the Miller effect, improvements are applied in the IGBT gate drive circuit:

(1) Different gate resistances Rg, ON and Rg, off are used to turn on and off to ensure the effective opening and closing of IGBT;
(2) Add capacitor c between the gate and source to discharge energy to the voltage generated by the Miller effect;
(3) Add negative gate voltage when shutting down. In the actual design, the reasonable combination of the three is better for improving the Mille r effect.

What are the applications of IGBT

The main role of IGBT is high-voltage DC to AC, and frequency conversion.

1. Power conversion

IGBTs are widely used in power conversion equipment such as transformers, converters, reactors, capacitors, governors, converters, etc.

2. Power control

IGBT has a wide range of applications in power control fields such as generator control, high-voltage switch control, and adjustable proportional control.

3. Industrial control

IGBT has important applications in industrial automation control, robot control, industrial robots, servo control and other fields.

4. Electric vehicles

Due to their high efficiency, low loss and reliability, IGBTs have important applications in electric vehicle control, power conversion and charging systems.

5. Consumer electronics

IGBT has important applications in consumer electronic products such as televisions, computers, lighting, printers, desktops, copiers, and digital cameras.

Conclusion

So that’s about everything you need to know about integrated circuits and how they work. We at Qtech are always ready to give you solid advice about PCBs, PCBA, and ICs. Talk to us today and find out more on what we offer. With over a decade of experience in this field, you’re guaranteed quality always.