THE DRIVE CIRCUIT OF THE IGBT

The drive circuit of the IGBT must have two functions: one is to achieve electrical isolation between the control circuit and the gate of the driven IGBT; the other is to provide a suitable gate drive pulse. There are many driving circuits for IGBTs, and the driving circuit for discrete components is simple and inexpensive. The dedicated integrated driving circuit has perfect protection functions and stable performance, but the price is slightly more expensive. 

EXB841 is a hybrid integrated circuit produced by Fujifilm of Japan. It can drive 600V IGBTs up to 400A and 1200V IGBTs up to 300A. The module has perfect functions, single power supply, positive and negative bias, overcurrent detection, protection, soft shutdown, etc. The main feature is a typical drive circuit. Powered by +20V DC power supply, it can generate +15V open-gate voltage and -5V off-gate voltage. Built-in TLP550 high-speed optocoupler isolation chip, drive circuit signal delay is less than 1us, internal over-current detection circuit and low-speed over-current cut-off Circuits have been widely used in China. Pay attention to the following aspects when using this module: the gate of the IGBT should be less than 1 m; the gate drive of the IGBT should be twisted pair; if a large voltage pulse is generated at the IGBT collector, the IGBT should be added. The tan-series resistor (RG); the 47uF capacitor is used to absorb voltage variations due to the power supply wiring impedance and is not a capacitor for the power supply filter. The following figure shows the drive and protection circuit consisting of EXB841:

 When the IGBT is working normally, the overcurrent signal indicating terminal of EXB841 is high level, 4N25 is not conducting, the trigger R pin is “0”, the Q pin is “1”, and the IGBT works normally. When the IGBT has an overcurrent signal, the EXB841 internal overcurrent detection circuit delays by a few microseconds to filter out the interference signal. The 5 pin becomes low level, 4N25 turns on, the flip-flop flips, and the Q pin is “0”. Turn off the IGBT drive signal for protection. In the work, the special integrated drive module EXB841 was applied, which driven the electromagnetic excitation coil of 2 kw inductive load-high frequency fatigue testing machine.

 The driving and protection of IGBTs were analyzed. Combined with practical applications, the following conclusions were drawn: 

1. The gate series resistance and the internal impedance of the drive circuit have a great influence on the turn-on process of the IGBT and the waveform of the drive pulse. The design should be considered together. 

2. Under large inductive loads, the switching time of the IGBT should not be too short to limit the peak voltage formed by di/dt to ensure the safety of the IGBT. 

3. Since IGBTs are mostly used in high voltage applications in power electronics, the drive circuit and control circuit should be strictly isolated at the potential, and the connection between the drive circuit and the IGBT should be as short as possible. 

4. The gate drive circuit of IGBT should be as simple and practical as possible. It is best to have its own protection function for IGBT and strong anti-interference ability. 

5. In practical applications, in order to achieve better results, methods such as soft turn-off and falling gate voltage are also required for overcurrent protection; clamp circuits are used to prevent surge voltages.

Source: https://www.slw-ele.com/drice-circuit-of-igbt.html

EQUESTRIAN STORY

In order to make the horses used in the chariots move accurately and accurately on the battlefield, the horses were often trained in various techniques and coordination, and later developed into equestrian competitions. Equestrian events require a rider and horse to match the horse’s skills, speed, endurance and ability to cross obstacles. Equestrian is not only a sport, but also a science. (Equestrian Helmet) 

ESTABLISH THE RIGHT EQUESTRIAN CONCEPT AND GET GREAT EQUESTRIAN ACHIEVEMENTS

DO YOUR DUTY AND BE GOOD

 In professional equestrian competitions, the rider will bring his own horse. If there is any problem with the horse, the athlete will lose the qualification to play. The 28th President of the United States, Woodrow Wilson, once said: “The sense of responsibility is directly proportional to the opportunity.” Equestrian athletes are also responsible for treating horses while being responsible for themselves. From the selection of horses, horse breeding, and horse training, one can see the attitude of a rider treating horses. The rider must not only learn to be self-disciplined, but also pay attention to the perfection and improvement of himself and the horse. Equestrian is a constantly improving and constantly surpassing sport that needs to advance and retreat with the horse. 

ESTABLISH THE RIGHT EQUESTRIAN CONCEPT AND GET GREAT EQUESTRIAN ACHIEVEMENTS

CAN BEND AND STRETCH, PERSEVERE

 Everyone on the road of life will be caught by the god of fate. When you are not willing to be a slave to fate and fail to hold the throat of fate, you must learn to be patient. Equestrianism brings us temporary setbacks and makes us better ourselves. Let the pain of failure fade in patience, let the tears of failure solidify in patience. Learn to fight hard in patience and learn to pursue in patience, rather than giving up in adversity. Yesterday I failed, today I work hard, tomorrow I will lead to the other side of success. (Helmet Wholesale) 

ESTABLISH THE RIGHT EQUESTRIAN CONCEPT AND GET GREAT EQUESTRIAN ACHIEVEMENTS

FEARLESS, BRAVE

 Going forward is a kind of spirit, a kind of power. In a professional competition, the psychological quality of a rider is also very important. You can’t panic for any reason, and you can’t escape because of any excuses. Under the dual pressures of the tough system and the wonderful performance of the opponents, what the rider can do is to convince himself not to be afraid and to courageously complete all the challenges. Successful equestrian athletes need to have the courage to go forward and the heroic feelings of whoever they are on the court! (Equestrian Helmet) 

ESTABLISH THE RIGHT EQUESTRIAN CONCEPT AND GET GREAT EQUESTRIAN ACHIEVEMENTS

NO END TO THE ROAD, NO END TO LEARNING

 Learning is a never-ending process, a process that continues and never stops. Don’t think of training as a task, but as a progressive opportunity to seize this opportunity. If you don’t understand it, ask for more equestrian knowledge and lay a solid foundation for the future.

 Establish the right equestrian concept and get great equestrian achievementsEquestrian is not just a sport, it also contains many correct values. The great equestrian achievements are a tough voyage. The tides and tides will never be smooth sailing. Only those who are brave enough to persevere can reach the other side of success. (Helmet Manufacturer)

Source: https://www.oemhelmet.com/equestrian-story.html

HOW DOES THE IGBT WORK AND APPLICATION

First, what is IGBT?

IGBT (Insulated Gate Bipolar Transistor), insulated gate bipolar transistor, is a composite fully controlled voltage-driven power semiconductor device composed of BJT (bipolar transistor) and MOS (insulated gate field effect transistor), and has MOSFET The advantages of both the high input impedance and the low turn-on voltage drop of the GTR. The GTR saturation voltage is reduced, the current carrying density is large, but the driving current is large; the MOSFET driving power is small, the switching speed is fast, but the conduction voltage drop is large, and the current carrying density is small. The IGBT combines the advantages of the above two devices, with low driving power and reduced saturation voltage. It is very suitable for converter systems with DC voltages of 600V and above, such as AC motors, inverters, switching power supplies, lighting circuits, traction drives, etc.


 
Generally speaking, IGBT is a kind of high-power power electronic device. It is a non-on-off switch. IGBT does not have the function of amplifying voltage. It can be regarded as a wire when it is turned on and an open circuit when it is disconnected. The three characteristics are high voltage, high current and high speed.

 
Second, IGBT module

 
IGBT is the abbreviation of Insulated Gate Bipolar Transistor. IGBT is a kind of device composed of MOSFET and bipolar transistor. Its input is extremely MOSFET, and the output is extremely PNP transistor. It combines these two kinds. The advantages of the device not only have the advantages of small driving power and fast switching speed of the MOSFET device, but also have the advantages of low saturation voltage and large capacity of the bipolar device. The frequency characteristics are between the MOSFET and the power transistor, and can work normally. In the frequency range of 10 kHz, it has been widely used in modern power electronics technology, and it has occupied a dominant position in high-frequency large and medium power applications.
 
 
The equivalent circuit of the IGBT is shown in Figure 1. It can be seen from Fig. 1 that if a positive driving voltage is applied between the gate and the emitter of the IGBT, the MOSFET is turned on, so that the collector and the base of the PNP transistor are in a low-resistance state, so that the transistor is turned on; When the voltage between the gate and the emitter is 0V, the MOS is turned off, and the supply of the base current of the PNP transistor is cut off, so that the transistor is turned off. The IGBT is also a voltage-controlled device like the MOSFET. A DC voltage of more than ten V is applied between its gate and emitter, and only the leakage current in the uA stage flows, and substantially no power is consumed.
 

 
1, the choice of IGBT module

 
The voltage specification of the IGBT module is closely related to the input power of the device used, that is, the voltage of the test power supply. Their relationship is shown in the table below. In use, when the collector current of the IGBT module increases, the resulting rated loss also becomes large. At the same time, the switching loss increases, which increases the heat of the original. Therefore, the rated current should be greater than the load current when the IGBT module is selected. Especially when used as a high-frequency switch, the heating loss is aggravated due to the increase of the switching loss, and should be used when it is selected.
 

 

2, the precautions in use

 
Since the IGBT module is a MOSFET structure, the gate of the IGBT is electrically isolated from the emitter through an oxide film. Since the oxide film is very thin, its breakdown voltage generally reaches 20 to 30V. Therefore, gate breakdown due to static electricity is one of the common causes of IGBT failure. Therefore, pay attention to the following points during use:
 
 
When using the module, try not to touch the drive terminal part by hand. When it is necessary to touch the module terminal, first discharge the static electricity on the human body or clothing with a large resistance grounding, and then touch.
 
When connecting the module drive terminals with conductive materials, do not connect the modules until the wiring is not connected;
 
In applications, although it is ensured that the gate drive voltage does not exceed the maximum rated voltage of the gate, the parasitic inductance of the gate wiring and the capacitive coupling between the gate and the collector also generate an oscillating voltage that damages the oxide layer. To this end, twisted pairs are often used to transmit drive signals to reduce parasitic inductance. The oscillating voltage can also be suppressed by connecting a small resistor in series with the gate wiring.
 
 
In addition, when an open circuit is applied between the gate and the emitter, if a voltage is applied between the collector and the emitter, the gate potential increases due to the leakage current of the collector due to the change of the collector potential, and the collector Then there is a current flowing. At this time, if there is a high voltage between the collector and the emitter, there is a possibility that the IGBT generates heat and is damaged.
 
 
In the case of using an IGBT, when the gate circuit is abnormal or the gate circuit is damaged (the gate is in an open state), if a voltage is applied to the main circuit, the IGBT is damaged. To prevent such a fault, it should be in the gate. A 10KΩ resistor is connected in series between the pole and the emitter.
 
 
When installing or replacing an IGBT module, the contact surface condition and tightening degree of the IGBT module and the heat sink should be taken seriously. In order to reduce the contact thermal resistance, it is best to apply thermal grease between the heat sink and the IGBT module. Generally, a heat dissipation fan is installed at the bottom of the heat sink. When the heat dissipation fan is damaged, the heat dissipation of the heat dissipation fin may cause the IGBT module to generate heat and malfunction. Therefore, the cooling fan should be inspected regularly. Generally, a temperature sensor is installed on the heat sink near the IGBT module. When the temperature is too high, the IGBT module will be alarmed or stopped.


 

Third, IGBT drive circuit

The function of the IGBT drive circuit is mainly to amplify the power of the pulse output of the single chip to achieve the purpose of driving the IGBT power device. The drive circuit plays a vital role in ensuring reliable, stable and safe operation of the IGBT device.
 
 
The equivalent circuit of the IGBT and the conformity are shown in Figure 1. The IGBT is controlled by the gate positive and negative voltage. When a positive gate voltage is applied, the tube conducts; when a negative gate voltage is applied, the tube is turned off.
 
The IGBT has a volt-ampere characteristic similar to that of a bipolar power transistor, and as the control voltage UGE increases, the characteristic curve shifts upward. The IGBT in the switching power supply changes its UGE level to alternate between saturation and cutoff.
 
 
(1) Provide appropriate forward and reverse voltages to enable the IGBT to be turned on and off reliably. When the positive bias voltage increases, the IGBT on-state voltage drop and turn-on loss decrease, but if the UGE is too large, the IC will increase with the increase of UGE when the load is short-circuited, which is unfavorable for safety. It is better to use UGEν15V in use. The negative bias voltage can prevent the IGBT from being mis-conducted due to excessive surge current during shutdown. Generally, UGE=-5V is preferred.
 
 
(2) The switching time of the IGBT should be considered comprehensively. Fast turn-on and turn-off helps increase operating frequency and reduce switching losses. However, under large inductive loads, the turn-on frequency of the IGBT should not be too large, because high-speed breaking and turn-off will generate high peak voltage and may cause breakdown of the IGBT itself or other components.
 
 
(3) After the IGBT is turned on, the drive circuit should provide sufficient voltage and current amplitude to prevent the IGBT from being damaged due to normal saturation and overload.
 
 
(4) The resistor RG in the IGBT drive circuit has a large influence on the working performance, and the RG is large, which is beneficial to suppress the current rising rate and the voltage rising rate of the IGBT, but increases the switching time and switching loss of the IGBT; Will cause the current rise rate to increase, causing the IGBT to be mis-conducted or damaged. The specific data of RG is related to the structure of the driving circuit and the capacity of the IGBT, generally in the range of several ohms to tens of ohms, and the IGBT value of the small-capacity IGBT is large.
 
 
(5) The drive circuit should have strong anti-interference ability and protection function for IG2BT. The control, drive and protection circuits of the IGBT should be matched with its high-speed switching characteristics. In addition, G-E can not be opened without proper anti-static measures.
 
Fourth, the structure of the IGBT
The IGBT is a three-terminal device that has a gate G, a collector c, and an emitter E. The structure of the IGBT, simplified equivalent circuit and electrical graphic symbols are shown in the figure.
 
 
The figure shows a schematic cross-sectional view of the internal structure of an N-channel IGBT (N-IGBT) combined with an N-channel VDMOS FFT and a GTR. The IGBT has one more P+ implant region than the VDMOSFET, forming a large-area PN junction J1. Since the IGBT is turned on, the P+ implant region emits a minority to the N-base region, so that the drift region conductivity is modulated, and the IGBT can have a strong current-passing capability. The N+ layer between the P+ implant region and the N-drift region is called a buffer. The presence or absence of a buffer determines the IGBT's different characteristics. IGBTs with N* buffers are called asymmetric IGBTs, also known as punch-through IGBTs. It has the advantages of small forward voltage drop, short dog break time, and small tail current when shutting down, but its reverse blocking ability is relatively weak. An IGBT without an N-buffer is called a symmetrical IGBT, also called a non-punch-through IGBT. It has strong forward and reverse blocking capability, but its other characteristics are not as good as asymmetric IGBTs.
 
 
The simplified equivalent circuit shown in Figure 2-42 (b) shows that the IGBT is a Darlington structure composed of GTR and MOSFET. Part of the structure is MOSFET drive, and the other part is thick base PNP transistor.

  

Fifth, the working principle of IBGT

Simply put, the IGBT is equivalent to a thick base PNP transistor driven by a MOSFET. Its simplified equivalent circuit is shown in Figure 2-42(b). The RN in the figure is the modulation resistor in the base of the PNP transistor. It is clear from the equivalent circuit that the IGBT is a Darlington-structured composite device composed of a transistor and a MOSFET. The transistor in the figure is a PNP transistor, and the MOSFET is an N-channel field effect transistor. Therefore, the IGBT of this structure is called an N-channel IIGBT, and its symbol is an N-IGBT. Similarly there is a P-channel IGBT, ie a P-IGBT.
 
 
 
The electrical graphic symbol of the IGBT is shown in Figure 2-42(c). The IGBT is a field-controlled device whose turn-on and turn-off are determined by the gate-emitter voltage UGE. When the gate-emitter voltage UCE is positive and greater than the turn-on voltage UCE(th), a channel is formed in the MOSFET and is PNP. The transistor provides a base current to turn on the IGBT. At this time, N-holes (minor carriers) are injected from the P+ region to conduct conductance modulation on the N-region, and the resistance RN of the N-region is reduced to make the resistance high. The pressed IGBT also has a small on-state voltage drop. When no signal is applied between the gate emitters and a reverse voltage is applied, the channel in the MOSFET disappears, the base current of the PNP transistor is cut off, and the IGBT is turned off. It can be seen that the driving principle of the IGBT is basically the same as that of the MOSFET.
 
 
1 When UCE is negative: J3 junction is in reverse bias state, and the device is in reverse blocking state.
 
2 When uCE is positive: UC< UTH, the channel cannot be formed, the device is in a forward blocking state; UG>UTH, N-channel is formed under the insulating gate, and conductance is generated in the N-region due to carrier interaction Modulation to make the device forward.
 
 
 
1) Conduction
 
The structure of the IGBT silicon wafer is very similar to that of the power MOSFET. The main difference is that JGBT adds a P+ substrate and an N+ buffer layer (NPT-non-punch-IGBT technology does not add this part), one of the MOSFETs drives two bipolar devices. (There are two polar devices). The application of the substrate creates a J, junction between the P and N+ regions of the tube. When the positive gate bias causes the P-base region to be inverted below the gate, an N-channel is formed, simultaneously with a flow of electrons, and a current is generated in full accordance with the power MOSFET. If the voltage generated by this electron current is in the range of 0.7V, then J1 will be in forward bias, some holes will be injected into the N-region, and the resistivity between N- and N+ will be adjusted, which reduces the power conductivity. The total loss is passed and a second charge flow is initiated. The end result is two temporary current topologies in the semiconductor hierarchy: one electron current (MOSFET current) and one hole current (bipolar). When UCE is greater than the turn-on voltage UCE(th), a channel is formed in the MOSFET to provide a base current to the transistor and the IGBT is turned on.
 
 
 
2) Conduction pressure drop
 
The conductance modulation effect reduces the resistance RN and the on-state voltage drop is small. The so-called on-state voltage drop refers to the tube voltage drop UDS of the IGBT entering the conduction state, and this voltage decreases as the UCS rises.
 
 
 
3) Shutdown
 
When a negative bias is applied to the gate or the gate voltage is below the threshold, the channel is disabled and no holes are injected into the N-region. In any case, if the current of the MOSFET drops rapidly during the switching phase, the collector current gradually decreases. This is because after the start of commutation, there are still a small number of carriers (less than) in the N layer. This reduction in residual current value (wake) depends entirely on the density of the charge at turn-off, which in turn is related to several factors, such as the amount and topology of the dopant, the layer thickness and the temperature. The attenuation of the minority carriers causes the collector current to have a characteristic wake waveform. The collector current will cause increased power consumption and cross-conduction problems, especially on devices that use freewheeling diodes.
 
In view of the fact that the wake is related to the reorganization of the minority, the current value of the wake should be closely related to the chip's Tc, IC: and uCE, and is closely related to the hole mobility. Therefore, depending on the temperature reached, it is feasible to reduce the undesirable effects of this current on the design of the terminal device. When a back pressure or no signal is applied between the gate and the emitter, the channel in the MOSFET disappears, the base current of the transistor is cut off, and the IGBT is turned off.
 
 
 
4) Reverse blocking
 
When a reverse voltage is applied to the collector, J is subjected to reverse bias control and the depletion layer is extended to the N-region. This mechanism is important because it can't achieve an effective blocking ability because it reduces the thickness of this layer too much. In addition, if the size of this area is excessively increased, the pressure drop is continuously increased.
 
 
 
5) Positive blocking
 
When the gate and emitter are shorted and a positive voltage is applied to the collector terminal, J, the junction is controlled by the reverse voltage. At this time, the externally applied voltage is still received by the depletion layer of the N-drift zone.
 
 
6) Latch
 
ICBT has a parasitic PNPN thyristor between the collector and the emitter. Under special conditions, this parasitic device will turn on. This phenomenon causes an increase in the amount of current between the collector and the emitter, a decrease in the controllability of the equivalent MOSFET, and usually causes a breakdown of the device. The thyristor conduction phenomenon is called an IGBT latch. Specifically, the causes of such defects vary, but are closely related to the state of the device.
 
One of the IGBT Application: gold melting furnace

Source  :  https://www.slw-ele.com/how-does-the-igbt-work-and-application.html

IGBT MODULE INVERTER CIRCUIT DIAGRAM

Igbt module inverter circuit diagram design (1)

The essence of solar photovoltaic power generation is that under the illumination of sunlight, the solar array (ie, the PV module square array) converts the solar energy into electrical energy, and the output direct current is converted into the alternating current that the user can use after passing through the inverter. The conventional photovoltaic power generation system is an inverter circuit composed of a power FET MOSFET. However, as the voltage increases, the on-resistance of the MOSFET increases. In some high-voltage and large-capacity systems, the MOSFET may increase the switching loss due to its on-state resistance. In practical projects, IGBT inverters have gradually replaced power FET MOSFETs because IGBTs have large on-state currents, high forward-reverse configuration voltages, and voltage control to turn them on or off. The IGBT is more advantageous in the system of medium and high voltage capacity. Therefore, the use of IGBT to form a switching device for the key circuit of solar photovoltaic power generation helps to reduce the unnecessary loss of the entire system and achieve the best working condition. In practical projects, IGBT inverters have gradually replaced power FET MOSFETs.

How IGBT inverter works

The inverter is a key component in the solar photovoltaic system because it is the necessary process to convert the direct current into the alternating current that the user can use, and is the only way to connect the solar energy and the user. Therefore, to study the process of solar photovoltaic power generation, it is necessary to focus on the inverter circuit. As shown in Fig. 2(a), it is a relatively simple push-pull inverter circuit composed of a power FET MOSFET. The neutral tap of the transformer is connected to the positive pole of the power supply, and one end of the MOSFET is connected to the negative pole of the power supply. The alternating operation of tubes Q1 and Q2 finally outputs AC power, but the disadvantage of this circuit is that the ability to carry inductive loads is poor, and the efficiency of the transformer is also low, so there are some conditional restrictions on application. A full-bridge inverter circuit composed of an insulated gate bipolar transistor IGBT is shown in Fig. 2(b). The phase between Q1 and Q2 is 180° out of phase, and the value of the output AC voltage varies with the output of Q1 and Q2. Q3 and Q4 are simultaneously turned on to form a freewheeling circuit, so the waveform of the output voltage is not affected by the inductive load, so the shortcomings of the push-pull inverter circuit composed of the MOSFET are overcome, so the full bridge inverter composed of the IGBT is used. The application of the circuit is more extensive.

The insulated gate bipolar transistor IGBT is equivalent to adding a P+ region under the drain of the MOSFET. Compared with the MOSFET, there is one more PN junction. When a negative voltage is applied between the collector and the emitter of the IGBT, the PN junction In the reverse bias state, no current flows between the collector and the emitter, so the IGBT has higher voltage resistance than the MOSFET. Also due to the existence of the P+ region, the IGBT is in a low-resistance state when turned on, so the current capacity of the IGBT is larger relative to the MOSFET.

IGBT inverter circuit design

The pre-stage DC-DC converter part of the inverter circuit adopts the PIC16F873 single-chip microcomputer as the control core, and the DC-AC part of the latter stage adopts the high-performance DSP chip TMS320F240 as the full-bridge inverter circuit of the control core. In order to improve the efficiency of the solar photovoltaic inverter, it can be done by reducing the inverter loss, in which the drive loss and switching loss are the key targets. The key to reducing the drive loss depends on the gate characteristics of the power switch IGBT. The key to reducing the switching loss depends on the control mode of the power switch IGBT. Therefore, the following solutions are proposed for the characteristics of drive loss and switching loss.

1, the drive circuit

The driving circuit converts the signal output by the main control circuit into a driving signal required by the inverter circuit, that is, it is a bridge between the main controller and the inverter, so the design of the driving circuit performance is crucial of. The EXB841 integrated circuit is used to form the gate drive circuit of the IGBT. As shown in Figure 3, the EXB841 has a fast response speed, which can reduce the drive loss by controlling the resistance of its gate and improve its working efficiency. The EXB841 has an overcurrent protection circuit inside, which reduces the design of the external circuit and makes the circuit design simpler and more convenient. Compared with the typical EXB841 application circuit, a resistor Rg is connected in series with the gate of the IGBT. This is to reduce the oscillation before and after the control pulse. The selection of the appropriate Rg resistance has a significant impact on the IGBT drive. . Based on the EXB841 typical application circuit, this circuit optimizes the series resistor on the IGBT gate so that its resistance changes as needed during the turn-on and turn-off of the IGBT.

The specific implementation is as follows: Rg2 and VD1 are connected in series and then connected in parallel with Rg1. When the IGBT is turned on, the positive voltage is output from the 3rd leg of the EXB841 in the driving circuit, VD1 is turned on, and Rg1 and Rg2 work together because the total resistance after paralleling is less than The sub-resistance of a branch, so the value of the total resistance Rg connected in series on the gate is smaller than the values ​​of Rg1 and Rg2, so that the switching time and switching loss decrease as the total resistance decreases, thereby reducing the drive. loss. When the IGBT is turned off, the 5 pin of the EXB841 inside the driving circuit is turned on, the 3 pin is not turned on, and the emitter of the IGBT provides a negative voltage, so that the VD1 in series with Rg2 is turned off, Rg1 works, and Rg2 does not work. The value of the total resistance Rg on the gate is the resistance of Rg1, so that when the IGBT is turned off, the resistance between the gates is not too small, which leads to mis-conduction of the device, thereby improving the working efficiency.

2, soft switching DC-DC converter circuit

For switching losses, soft switching technology is used. Soft switching technology is relative to hard switching. The traditional switching method is called hard switching. The so-called soft switching technology is that the semiconductor switch has a short time when it is turned on or off, so that the current flowing through the switch is added or added. The voltage of the switch is small, almost zero, which reduces switching losses. The essence is to reduce the volume and weight of the transformer and the filter by increasing the switching frequency, thereby greatly increasing the power density of the converter, reducing the audio noise of the switching power supply, thereby reducing the switching loss. When the IGBT power switch is turned on, the voltage applied to both ends is zero, which is called zero voltage switch. When the IGBT is turned off, the current flowing through it is zero, which is called zero current switch. Since the IGBT has a certain switching loss, the phase-shifted full-bridge zero-voltage zero-current PWM soft-switching converter (shown in Figure 4) is used. The structure is simple and there is no lossy component, which reduces the influence of the IGBT tail current, thereby reducing the switch. Loss increases the efficiency of the inverter.

Q1～Q4 are 4 IGBT power switch tubes, where Q1 and Q3 are super forearms, Q2 and Q4 are lagging arms, Q1 and Q3 lead one phase of Q2 and Q4, when Q1 and Q4 are turned off, and Q2 and Q3 are turned on. The voltage across the UAB is equal to the voltage across V1, and the capacitor C1 is charged by the supply voltage V1. When Q3 is turned on to off, capacitor C3 is charged, and inductor L1 releases energy, causing capacitor C1 to resonate and discharge until the voltage on capacitor C1 is zero, so that Q1 has a zero-voltage conduction condition. The zero voltage conduction principle of the forearm Q3. When Q1 and Q4 are turned on and Q2 and Q3 are turned off, the voltage across AB is equal to the voltage across V1, and capacitor C3 is in the charging state. When Q1 and Q4 are continuously turned on, inductor L2 and capacitor C8 resonate. Therefore, the capacitor C8 is charged. When Q1 is turned on to off, capacitor C1 is charged, so that C3 starts to discharge, the voltage across AB decreases, so that C8 is resonantly discharged, C8 continues to discharge, and finally diode D7 continues to flow, and the driving pulse of Q4 continues to drop until Zero, and finally completed the zero current shutdown of Q4. Similarly, the zero current turn-off principle of the lag arm Q2 can be known.

Therefore, it can be said that the super-arms Q1 and Q3 complete the zero voltage conduction and turn-off through the parallel capacitors C1 and C3, respectively, thereby reducing the switching loss; the lag arms Q2 and Q4 discharge the C8 through the auxiliary circuit, so that the transformer flows through The primary current is reduced to zero to complete zero current turn-on and turn-off.

The general circuit waveform close to the square wave part indicates that its output contains more harmonic components, which will cause unnecessary additional loss of the system. Figure 5 is an improved circuit using IGBT, the waveform is very close to sine wave, ideal sine wave The total harmonic distortion is zero, but it is difficult to achieve such a level in real life, so it basically meets the requirements. At the same time, since the PIC16F873 single-chip microcomputer has a multi-channel PWM generator and has a better output sine wave, it is verified. The feasibility of the design has achieved the desired results.

Through the comparison and analysis of the device, the improvement and optimization of the circuit, the integrated circuit EXB841 itself contains an overcurrent protection circuit, which solves the requirements of the IGBT on the driver circuit part, and reduces the design of the external circuit, so that the whole The design process is simple and convenient. The soft switching technology solves the problem of excessive current flowing through the IGBT during turn-on and turn-off, and the drive loss and switching loss of the whole system are greatly reduced. The output waveform is a relatively stable sine wave, thereby improving the overall system. Work efficiency.

The following figure shows the internal structure of the M57962L driver. The optocoupler is used for electrical isolation. The optocoupler is fast. It is suitable for high-frequency switching operation. The primary side of the optocoupler has series current limiting resistor (about 185 Ω), which can be 5 V. The voltage is applied directly to the input side. It uses a dual power supply structure, integrated with 2 500 V high isolation voltage optocoupler and overcurrent protection circuit, overcurrent protection output signal terminal and TTL level compatible input interface, drive electrical signal delay up to 1.5 Us.

Igbt module inverter circuit diagram Daquan (six igbt module inverter circuit design schematic diagram detailed)

When the M57962L is used alone to drive the IGBT. There are three points that should be considered. First of all. The maximum current rate of change of the driver should be set within the limits of the minimum RG resistance, because for many IGBTs, when RG is used too large, td(on) (on-delay time) is increased, td(off) (cut-off delay time), tr (rise time) and switching loss, this loss should be avoided as much as possible in high frequency applications (over 5 kHz). Also. The loss of the drive itself must also be considered.

If the loss of the drive itself is too large, it will cause the drive to overheat and cause damage. Finally, when the M57962L is used to drive large-capacity IGBTs, its slow turn-off will increase losses. The cause of this phenomenon is that the current flowing to the gate of the M57962L through the Gres (reverse transfer capacitor) of the IGBT cannot be absorbed by the driver. Its impedance is not low enough, this slow turn-off time will become slower and requires a larger snubber capacitor to apply the driver circuit of the M57962L design as shown below.

Circuit Description: Power supply decoupling capacitors C2 ~ C7 use aluminum electrolytic capacitors, the capacity is 100 uF / 50 V, R1 resistance value is 1 kΩ, R2 resistance value is 1.5kΩ, R3 is 5.1 kΩ, power supply uses positive and negative l5 V power supply module Connected to the 4th and 6th pins of the M57962L respectively, the logic control signal IN is input to the driver M57962L via the l3 pin. The bidirectional voltage regulator Z1 is selected to be 9.1 V, Z2 is 18V, and Z3 is 30 V. The gate and emitter of the IGBT are prevented from breakdown and the drive circuit is damaged. The diode adopts the fast recovery FR107 tube.

The IR2110  drives the IGBT circuit as shown. The circuit adopts the bootstrap driving mode, VD1 is the bootstrap diode, and C1 is the bootstrap capacitor. When the power is turned on, Cy is charged by VDt when VT2 is turned on. This circuit is suitable for driving smaller capacity IGBTs. For the IR2110, there is a protection function to turn off the driver when the supply voltage is low. The bootstrap drive mode dominates the turn-on voltage of the VT2, so a lower voltage protection is a necessary condition. If the IGBT is driven when the driving voltage is low, the IGBT is thermally damaged. VD1 selects ERA38-06, ERB38-06 and other diodes with high speed and withstand voltage greater than 600V.

An insulated gate bipolar transistor (IGBT) is a device in which a MOSFET is combined with a bipolar transistor. The utility model has the advantages that the power MOSFET is easy to drive, the control is simple, the switching frequency is high, and the power transistor has low on-voltage, large on-state current and small loss.

The main circuit of the full-bridge inverter consists of main components such as power switch IGBT and intermediate frequency transformer. As shown in Figure 1, the fast recovery diodes VD1~VD4 are connected in parallel with lGBT1~IGBT4 in reverse, and the reverse current generated by the load is applied to protect the IGBT. . IGBT1 and IGBT4 are a group, IGBT2 and IGBT3 are a group, each group of IGBTs is turned on and off at the same time. When the excitation pulse signal drives IGBT1, IGBT4 and IGBT2, IGBT3 in turn, the inverter main circuit converts DC high voltage to 20 kHz. The AC voltage is sent to the intermediate frequency transformer and output by the step-down rectification filter.

One of the major drawbacks of full-bridge inverters is the problem of biasing the IF transformer. Under normal operating conditions, the power switching device has the same conduction pulse width in the first half of the working period and the second half of the working cycle, and the saturation voltage drop is equal, and the front and rear half cycles alternately. There is no remanence in the transformer core. However, if the IGBT drive circuit output pulse width is asymmetrical or other reasons, the positive and negative half-cycle imbalance will occur. At this time, the magnetic core in the transformer will accumulate residual magnetism in a certain half-cycle, and a "unidirectional bias" phenomenon occurs. With a few pulses, the unidirectional flux of the transformer can be saturated, the transformer loses its function, and it is equivalent to a short circuit. This is extremely dangerous for IGBTs and can cause an explosion.

Another disadvantage of bridge circuits is that they are prone to shoot-through. The straight-through phenomenon means that the IGBTs of the same bridge overlap in the conduction period of the front and rear half cycles, and the main circuit board path, the huge addition current instantaneously passes through the IGBT.

In view of the above two shortcomings, from the perspective of driving, the designed driving circuit must satisfy the four-way driving waveform completely symmetrical, strictly limit the maximum working pulse width, and ensure that the dead time is sufficient.

For a full-bridge inverter with hard-switching trigger mode, the four-way drive circuit is identical, but the circuits must be isolated from each other on the circuit to prevent interference or false triggering. The four-way drive signals are divided into two groups according to the trigger phase. in contrast. Figure 3 shows a gate drive circuit. The rectifier bridges B1 and B2 and the electrolytic capacitors C1 and C2 form a rectification and filtering circuit to provide +25V and -15V DC drive voltages for the drive circuit. The function of the optocoupler 6N137 is to achieve isolation between the control circuit and the main circuit and to transmit the PWM signal. The resistor R1 and the Zener diode VS1 form a PWM sampling signal, and the resistor R2 limits the optocoupler input current. Resistors R3 and R4 and voltage regulators VS3 and VS4 form a 5.5V optocoupler level limiting circuit, respectively, which provide driving levels for the optocoupler and MOSFET Q3. Q3 operates under the optocoupler control state. The MOSFETs Q1 and Q2 form a push-pull amplifier circuit, and the amplified output signal is input to the IGBT gate to provide a gate drive signal. When the control signal is input, the optocoupler U is turned on, Q3 is turned off, and Q2 is turned on to output the +15V driving voltage. When the control signal is zero, the optocoupler U is turned off, Q3 and Q1 are turned on, and the output voltage is -15V. When the IGBT is turned off, the gate is provided with a negative bias to improve the anti-interference ability of the lGBT. The voltage regulators VS3 to VS6 limit the input voltage of Q2 and Q1 to -10V and +15V respectively, preventing Q1 and Q2 from entering deep saturation and affecting the response speed of the MOS tube. The resistors R6 and R7 and the capacitor C0 are Q1 and Q2 to form a bias network. The capacitor C0 is for accelerating the rising current of the drain current of the Q2 tube when it is turned on, providing an overshoot current to the gate, and accelerating the gate conduction.

The IGBT gate withstand voltage is generally around ±20V, so the gate is voltage-protected at the output of the driver circuit, the parallel resistor Rge and the reverse series limiting regulator.

The gate series resistance Rg has a great influence on the IGBT turn-on process. Rg is small to speed up the turn-off speed and reduce the turn-off loss, but too small will cause the di/dt to be too large, resulting in a large collector voltage spike. According to the specific requirements of this design, Rg selects 4.7Ω.

The parasitic inductance of the gate wiring and the parasitic capacitance between the gate and the emitter will generate an oscillating voltage, so the gate lead should be transmitted by twisted pair and driven as short as possible, preferably not exceeding 0.5 m. Reduce the wiring inductance.

Source: https://www.slw-ele.com/igbt-module-inverter-circuit-diagram.html

IGBT BASIC KNOWLEDGE

1. Overall Arrangement
We will take the Infineon FF600R17ME4 IGBT module to explain. First look at its pin definition and internal layout.

Note: The internal arrangement of the brown module is actually the corresponding model produced by Fuji, because its package and pin definition are exactly the same. There is no big difference in its internal layout.

A. The module is internally filled with a certain amount of transparent silica gel to increase the insulation performance and can be used as a buffer for vibration.

B. There is also a parallel connection inside the module, and three IGBTs and three diodes are connected in parallel inside the module.

C. The chips and chips are isolated and they are connected by bond wires.

The structure of the IGBT includes a frame and a cover plate, a chip, a bonding wire, a substrate, a substrate, and the like. The main components are briefly introduced below.

2. Plastic frame
Remarks: The frame mentioned in this article includes the cover plate, the same.

The environment in which the frame works may be at -55-150 degrees Celsius and is operated in a high temperature, high voltage environment. This requires the framework to have the following performance:

A, dimensional stability

B, high mechanical strength

C, good insulation performance (CTI requirements above 400)

D, high temperature resistance (high temperature of 250 degrees Celsius when soldering IGBT pins)

E, Good fire resistance (UL94-V0 level)

F, RoHS compliant, can not contain harmful substances such as halogen and arsenic oxide

In the long-term practice, the following plastics meet the application requirements of IGBT modules: PPS, PBT, PA, PET, etc.

3. Substrate
Basic knowledge of IGBT modules (2) Module structure
4. Substrate
The substrate is usually made of copper, has a thickness of 3-8 mm, and has a nickel plating layer of 3-10 mm.

Not all modules have a substrate, usually only medium and high power substrates, and some low power modules have no substrate.

5. Bond wire
The material of the bonding wire can be gold wire, copper wire or aluminum wire, but the current process is mainly aluminum. The bond wires are connected to other components by ultrasonic welding.

It should be noted that the number of bond wires is determined by the current through which it needs to flow, but at the same time it is affected by the resistance and thermal resistance. Since the bonding wire is welded to the DCB or the frame at one end and one end, the heat dissipation condition is good, so the temperature is the highest among them, but since the bonding wire is in the silica gel, the silica gel determines the temperature that the bonding wire can reach. online.

DCB to DCB are usually connected by bond wires, but there are other methods.

Basic knowledge of IGBT modules (2) Module structure
6. External circuit connection
There are many ways to connect external circuits, such as soldering, nut connection, spring (reed) connection, connector, crimping, etc. The failure rate of different connection methods is as follows.

6.1 bolted connection

6.2 Welding connection

6.3 plugin connection

6.4 Crimp connection

6.5 spring and reed connection

The spring and reed connection are used more in the SEMIKRON module, mainly in the control part of the module. The SEMIKRON MiniSKiiP is connected by a spring piece; the SEMiX module uses a spring connection, a reed and a spring structure.

Spring contact connections have more advantages than solder and plug connections when board assembly

– Better use of board area and easier wiring because there is no need to punch holes.

– Simpler and easier to automate assembly, because there are no components that are inserted into the weld hole on a large scale and below a certain error requirement. – Assembly of (heavy) power semiconductors after assembly of the board and preliminary review of the heat sink.

– Higher temperature adaptability because the contact points are free to slide

– Higher impact and vibration resistance (no solder joint fatigue)

– Quasi-sealed contact, corrosion resistant

– No electronic migration

Source: https://www.slw-ele.com/igbt-basic-knowledge.html