IGBT关断过程的分析
IGBT工作原理
IGBT工作原理概述：IGBT（Insulated Gate Bipolar Transistor，绝缘栅双极晶体管）是一种高性能功率半导体器件，常用于控制和调节高电压和高电流的电力电子应用中。
本文将详细介绍IGBT的工作原理及其相关特性。
一、IGBT结构IGBT由三个主要部份组成：N型电流扩散层、P型基区和N型绝缘栅区。
它的结构类似于MOSFET和双极晶体管的结合体，具有MOSFET的高输入阻抗和双极晶体管的低导通压降特性。
二、IGBT工作原理1. 关断状态：当IGBT的栅极电压为0V时，处于关断状态。
此时，N型电流扩散层和N型绝缘栅区之间形成为了反向偏置的PN结，阻挠了电流的流动。
2. 开通状态：当给IGBT的栅极施加正向电压时，即使很小的电压也能引起电流的流动。
在开通状态下，栅极电压控制导通电流的大小。
3. IGBT的导通过程：当栅极电压高于临界电压时，电流开始从N型电流扩散层注入到P型基区，形成NPN型双极晶体管。
由于双极晶体管的放大作用，电流迅速增加。
同时，由于N型绝缘栅区的存在，栅极电压控制了电流的大小。
因此，IGBT具有较低的导通压降。
4. IGBT的关断过程：当栅极电压降低到临界电压以下时，电流开始减小。
在关断过程中，IGBT的关断速度取决于去除电荷的速度。
通常，通过施加负向电压或者短路栅极电压来加快关断速度。
三、IGBT的特性1. 高输入阻抗：由于IGBT的栅极绝缘层，其输入电流极小，因此具有高输入阻抗。
这使得IGBT可以被各种控制电路轻松驱动。
2. 低导通压降：IGBT的导通压降较低，这意味着在导通状态下能够减小功率损耗，提高效率。
3. 大功率承受能力：IGBT能够承受较高的电压和电流，适合于高功率应用，如变频器、电力传输、电动车等。
4. 快速开关速度：IGBT具有较快的开关速度，可以实现高频率的开关操作，适合于需要频繁开关的应用。
5. 温度依赖性：IGBT的导通压降和关断速度受温度影响较大。
igbt的工作原理
igbt的工作原理IGBT（Insulated Gate Bipolar Transistor）是一种广泛应用于电力电子领域的功率半导体器件，它结合了场效应晶体管（MOSFET）和双极型晶体管（BJT）的优点，具有高电压、高电流和高速开关特性。
IGBT的工作原理是指其在电路中的工作方式和特性，下面将详细介绍IGBT的工作原理。
当IGBT处于关断状态时，它的栅极和集电极之间的通道是关闭的，没有电流通过。
当施加正向电压到栅极时，栅极和发射极之间形成一个PN结，使得集电极和发射极之间的通道导通，电流开始流动。
IGBT的导通过程可以分为三个阶段，开启、饱和和关断。
首先是开启阶段，当正向电压施加到栅极时，栅极和发射极之间的PN结被击穿，形成导通通道。
此时，IGBT的电流开始增加，但电压降低。
接下来是饱和阶段，当电流继续增加时，IGBT的电压降低到一个稳定的值，此时IGBT处于饱和状态。
在饱和状态下，IGBT的电压降低到很小的值，电流可以自由地通过。
最后是关断阶段，当施加负向电压到栅极时，PN结被截断，IGBT的导通通道关闭，电流停止流动。
IGBT回到关断状态，等待下一次开启。
IGBT的工作原理可以用简单的模型来描述，当栅极电压施加时，形成PN结，使得集电极和发射极之间的通道导通，电流开始流动；当栅极电压去除时，PN结截断，导通通道关闭，电流停止流动。
这种工作原理使得IGBT在电力电子领域得到广泛应用，如变频空调、电动汽车、工业控制等领域。
总的来说，IGBT的工作原理是通过控制栅极电压来控制集电极和发射极之间的通道导通和截断，从而实现电流的控制和开关。
IGBT具有高电压、高电流和高速开关特性，是电力电子领域中不可或缺的器件之一。
希望通过本文的介绍，能够让大家对IGBT的工作原理有一个更加清晰的认识。
IGBT工作原理
IGBT工作原理IGBT（Insulated Gate Bipolar Transistor）是一种重要的功率半导体器件，广泛应用于高压、高频率和高电流的电力电子系统中。
本文将详细介绍IGBT的工作原理，包括结构、工作过程和特性。
一、结构IGBT由P型衬底、N+型外延区、N型沟道区、P型沟道区和N+型漏极组成。
其中，P型衬底和N+型外延区形成PN结，N型沟道区和P型沟道区形成PNP结，N+型漏极是电流输出端。
二、工作过程1. 关态：当控制端施加正向电压时，PN结正向偏置，PNP结反向偏置。
此时，P型沟道区的空穴和N型沟道区的电子被吸引到PNP结的N型区域，形成导电通道。
电流从漏极流向源极，IGBT处于导通状态。
2. 开态：当控制端施加负向电压时，PN结反向偏置，PNP结正向偏置。
此时，导电通道被截断，电流无法通过，IGBT处于截止状态。
3. 开关过程：IGBT从关态到开态的过程称为开启过程，从开态到关态的过程称为关断过程。
在开启过程中，控制端施加正向电压，PN结逐渐正向偏置，导电通道逐渐形成，电流逐渐增大。
在关断过程中，控制端施加负向电压，PN结逐渐反向偏置，导电通道逐渐截断，电流逐渐减小。
三、特性1. 高电压能力：IGBT具有较高的耐压能力，可以承受较高的电压。
这使得IGBT在高压应用中具有优势，如电力变换器、电力传输系统等。
2. 高频特性：IGBT具有较高的开关速度和频率响应，适合于高频率应用。
这使得IGBT在交流电动机驱动、变频器等领域得到广泛应用。
3. 低开启压降：IGBT的开启压降较小，能够减少功率损耗。
这使得IGBT在低功率应用中具有优势，如电源、逆变器等。
4. 温度特性：IGBT的工作温度范围较广，能够在较高的温度下正常工作。
这使得IGBT在高温环境下的电力电子系统中具有优势。
总结：IGBT是一种重要的功率半导体器件，具有高电压能力、高频特性、低开启压降和良好的温度特性。
它的工作原理基于PN结和PNP结的正向和反向偏置，通过控制端的电压来实现导通和截断。
IGBT模块三电平电路故障时关管顺序的讨论
IGBT模块三电平电路故障时关管顺序的讨论IGBT模块三电平电路故障时的关管顺序----传统办法在1字形二极管钳位三电平电路中，当发生短路故障或过流故障时，传统的关断IGBT的做法是，检测到故障的驱动器把故障信息传递给控制器，然后控制器先把外管关断，再关断内管。
这样的特定的关断顺序的原因是：1. 如果错误地先把内管关断，那么内管IGBT就会承担整个母线电压，这样内管会严重过压而马上损坏；2. 如果先关外管，外管的电压会被钳在半个母线电压上，不会出现过压，然后再关断内管，内管就安全了。
三电平电路故障时的传统关管顺序的时序关系：上图是一种三电平拓扑的传统故障管理的典型时序，当短路响应时间过了后，驱动器才能向控制器确认故障，而控制器确认故障则需要2us的时间。
也就是说，到控制器确认故障时，短路已经发生了10.5us了（8.5us短路响应时间+2us确认时间）。
这个时间还是理论上的最短时间，没有考虑控制器的计算时间及传输延时。
所以，三电平中的短路时间，一般都会略高于10us。
CONCEPT提出一种新的方法CONCEPT提出一种全新的思路：利用有源钳位功能提供的优势，忽略1字形三电平的关管顺序。
当IGBT检测到故障时，无论是内管还是外管，马上把对应的IGBT关掉，然后再向控制器报告；如果检测到故障的通道是内管，会马上给内管IGBT发关断指令，这样会导致内管IGBT过压，但实际上内管IGBT在这种情况下并不能被关断，因为有源钳位功能把内管电压钳住，而不会出现过压。
为了验证我们的这一创新性的提法，我们做了一系列验证实验。
三电平电路中有源钳位功能的有效性的研究以下测试将研究在错误的关断时序时，有源钳位功能如何保护三电平电路中的IGBT模块。
IGBT under test: F3L200R07PE4, 650V/200A, NPC1, 1字型三电平模块；IGBT driver: 2SC0108T2D0-12, CONCEPT，该驱动装备有源钳位功能；有源钳位门槛（TVS击穿的典型值）设为，479V(1mA,25℃)；以支持870V的最大直流母线电压Vdc（每个半直流母线电压均设为相同值以便于测量）。
IGBT工作原理
IGBT工作原理引言：IGBT（Insulated Gate Bipolar Transistor）是一种功率器件，广泛应用于电力电子领域。
本文将详细介绍IGBT的工作原理，包括结构、工作过程和特点等方面的内容。
一、结构IGBT由三个主要部份组成：N型沟道区、P型基区和N型漏极区。
其中，N 型沟道区和P型基区构成PN结，而P型基区和N型漏极区构成PNP结。
IGBT的结构类似于MOSFET和普通的MOS结构，但其特殊之处在于P型基区的存在。
二、工作过程1. 关态（开关态）：当IGBT的栅极电压为高电平时，栅极和N型沟道区之间形成正向偏置，使得PN结处于导通状态。
此时，电流可以从漏极流向源极，IGBT处于导通状态。
这个过程类似于MOSFET的导通过程。
2. 关断态：当IGBT的栅极电压为低电平时，栅极和N型沟道区之间形成反向偏置，使得PN结处于截止状态。
此时，电流无法从漏极流向源极，IGBT处于截止状态。
这个过程类似于MOSFET的截止过程。
3. 关断过程：当IGBT从导通状态切换到截止状态时，需要通过一定的关断过程来确保电流的截断。
这个过程中，栅极电压逐渐降低，直到PN结彻底截止。
三、特点1. 高压能力：IGBT具有较高的耐压能力，可以承受较高的电压。
这使得IGBT成为高压应用领域的理想选择，如电力电子转换器、电动汽车等。
2. 低导通压降：IGBT的导通压降较低，能够减小功率损耗，提高效率。
这使得IGBT在高频应用中具有优势，如变频器、电源等。
3. 高开关速度：IGBT具有较快的开关速度，能够实现快速的开关操作。
这使得IGBT在需要高频率开关的应用中表现出色，如逆变器、交流机电驱动器等。
4. 可靠性高：IGBT的结构设计和材料选择使其具有较高的可靠性和稳定性。
这使得IGBT 在各种恶劣环境下都能正常工作，如高温、高湿度等。
结论：IGBT作为一种重要的功率器件，具有高压能力、低导通压降、高开关速度和高可靠性等优点。
IGBT短路保护中的软关断技术分析
It is very common that an IGBT used for motor drive, UPS and some other industrial applications, be selected for 10 micro-second short-circuit withstand time (SCWT) if regular de-sat protection driver is used. But this driver generates high turn-off stress to the IGBT during inverter short circuit or the output becomes faulty. Under these abnor-mal conditions when the IGBT is turned-off abruptly, failures can occur if the IGBT is not selected properly. If the smart fault protection is not used, high turn-off loss will be generated and even short circuit current can ramp-up to a dangerous level destroying the IGBT. There are several ways to turn-off the IGBT once fault condition is detected. Some of these are as follows:Gate is discharged through high gate resistance. This discharge path is activated only during the above said abnormal conditions. This is not the best solution.Gate voltage is abruptly reduced to zero.Adding some source inductance which is common for both gate dis-charge path and load current.Gate de-bias occurs. But during normal condition switching loss is increased.Sense IGBT can also be used where fault current is sensed by pilot cell but the current sense accuracy of these pilot cells is not good which is further is affected by temperature.Gate voltage pattern analyzer for short-circuit protection in IGBT inverters [1]. These circuits are very sensitive to load changes and type of loads.Current sense resistor or Hall-effect devices are also used to detect fault through IGBT. But again these methods either generate power loss or are costly.But de-sat protection is the most commonly used for short-circuit and over current fault protection. De-sat detection truly provides the state of electrical over stress of IGBT under current fault condition when gate voltage is high. Reducing gate voltage in a controlled manner to just above gate threshold voltage is preferred and described in this article. This will reduce fault current and after some finite time gate voltage is brought down to zero safely, turning-off the IGBT without stress.Gate Drive CircuitThe main function of any gate driver circuit is to convert a control sig-nal to a power signal that can efficiently controls the IGBT or MOS-FET turn-on and turn-off. If the IGBT or MOSFET requires short cir-cuit protection, the gate drive circuit must safely turn-off the switch during a shorted or abnormal overload condition. A more detailed list of the gate drive circuit requirements for an IGBT or MOSFET are as follows:A controlled turn-on and turn-off of the IGBT so as to optimize the conduction and switching losses.In some applications, electrical isolation between control circuit and power circuit is very important.In the case of a short circuit condition, the IGBT should be protected and turned-off safely with minimum power dissipation and stress. The gate drive circuit should be able to minimize short circuit current and short-circuit withstand time without device failure. If both of these parameters are minimized, the power dissipation under short circuit will reduce and the system reliability will increase.During a short circuit condition, the IGBT collector to emitter voltage can rise fast. The voltage across the gate to emitter should not beIGBT Behavior under Short Circuit and Fault ProtectionUsing Two-Step-Soft-Turn-Off Gate DriverIn inverter driven UPS or motor applications, the IGBT can be destroyed when it is turned-on into a faulted motor or an output short circuit or an input bus voltage shoot through. Under these conditions current through the IGBT increases rapidly until it saturates. After fault detection, depending on the point at which the fast turn-off pulse is applied, very different levels of hole current can flow under the n+ source region, making this an important factor in the successful containment of the fault current. We present experimental observations showing that IGBT failure under short-circuit conditions is dependent on where and how the turn-off pulse is applied. A two-step (two-level) turn-off gate driver circuit is introduced which safely turns-off even a high transconductance IGBT during short-circuit and abnormal over current faults. This turn-off process startsduring faulted condition only.By Sampat Shekhawat and Bob Brockway, Fairchild SemiconductorIGBT驱动的软关断技术分析35allowed to rise due to gate to collector displacement current flowinginto the gate to emitter capacitance, Cge. Current flowing into Cge will cause Vge to rise and further increase the short circuit current.One should make sure that this condition is avoided.Preferably a totem pole output stage with separate turn-on and turn-off resistance option. The gate discharging switch of the totem pole should be as close as possible to IGBT and minimize the loop induc-tance between this switch and IGBT gate & emitter terminals. Minimize the propagation delay time between input and output pulses of the gate driver.De-SaturationThe de-saturation detection technique for identifying a short circuit and fault condition in an IGBT is well known. Generally, a de-satura-tion condition is said to exist if the voltage across the IGBT collector to emitter terminals rises above 5-8 volts while the gate to emitter voltage is high. This condition indicates that the current through the IGBT has exceeded the normal operating level. The gate drive circuit should be designed so that it reacts promptly to the short circuit and safely turns-off the IGBT within SCWT rating of the IGBT. However, in recent years, IGBTs have been designed with lower conduction and switching losses but this generally reduces SCWT. IGBT technology utilizes shallow junctions to decrease switching and conduction loss-es. However these new technologies have increased the transcon-ductance (gm) of the IGBT. Since the magnitude of the IGBT short circuit current is directly proportional to gm, during a short-circuit con-dition, a higher collector current results. The large collector current and high bus voltage place the IGBT in a state of high instantaneous power dissipation that can only be sustained for a few microseconds.The gate drive circuit must respond very quickly and efficiently to the fault current to protect the IGBT. Due to the two-step turn-off, the IGBT with even 4 microseconds short circuit withstand time can safe-ly be turned-off and protected. The IGBT, used in conjunction with the two-step turn-off gate drive, safely turns off low impedance over-cur-rent faults and shorted bus conditions where single-step gate drivers fail. The Industry standard (10 µs) SCWT is no longer required when the IGBT is used with this gate driver.IGBT Behavior during short circuit and over currentThe peak current during a short circuit is limited by the gm of the IGBT. Moreover, the rate of rise of the current is limited by the turn-on characteristics of the IGBT in combination with common emitter inductance. If IGBT collector current does not saturate and reach a state of equilibrium and bus voltage has not raised high enough attempting to turn off the IGBT during can lead to IGBT latch-up [2].In case of fault conditions very different hole current flow under n+source regions. These different hole current conditions and patterns of hole current under n+ source generate different electrical stress. In case if the gate voltage is brought down abruptly to zero before device voltage reaches clamp, the IGBT can latch-up and fail. Flow of electron through the channel is cutoff once the gate is turned off.Holes continue to inject from emitter of p-n-p structure which isknown as IGBT collector. This process stops when electrons in IGBT N-base are depleted. At this point IGBT current is almost all hole cur-rent. The amount of holes is very high here and if IGBT does not reach clamp voltage IGBT can latch-up and fail. However if enough time is allowed to complete this process and plasma of electrons in IGBT N-base is reduced or depleted so that base current reaches zero. At this point the carriers from emitter of IGBT p-n-p transistor are no longer injected and IGBT current is almost all hole current.IGBT voltage rises at a rate so that edge of the depletion spread cansweep out enough carriers to maintain inductive current. If enough time is allowed to stabilize the bus voltage while the channel current is flowing, the IGBT N-base is depleted and because of this current flow is more uniformly distributed. The displacement current becomes very small since dv/dt reduces and latch-up is avoided. If enoughtime is not allowed for the IGBT to reach clamp voltage and gate volt-age is removed abruptly, IGBT voltage will rise with high dv/dt and current in IGBT is non-uniformly distributed, high displacement cur-rent generated by high dv/dt can latch-up IGBT. Non-uniform gate ESR combined with Miller capacitance result in non-uniform turn-off of IGBT active area. This results into high localized hole current den-sity flowing laterally in P-base of parasitic n-p-n bipolar resulting in latch-up of parasitic thyristor. Because of these reasons one has to wait untill IGBT reaches clamp voltage collector current saturates. So it is safer to choose IGBT with 10 microseconds SCWT for motor drive and UPS inverter applications if a regular gate driver is used.Two step soft turn-off gate driveIt is clear that if the collector to emitter voltage rises to the DC Bus slowly and high transconductance increases short circuit current, reg-ular driver does not protect an IGBT with a low short circuit withstand time (<5us). However the longer SCWT comes at the cost of higher switching and conduction losses. The rate of rise of the collector to emitter voltage is dependent upon the operating conditions and can take several microseconds to rise to bus voltage. However, the gate drive must respond quickly to initiate turn off to protect a low SCWT IGBT. The only solution is to lower the gate voltage to just above threshold voltage of the IGBT. The IGBT reaches clamp voltage faster and reduces IGBT current during fault.The schematic of two step gate driver is shown in Figure 1. The gate driver output will produce a positive signal with respect to the IGBT emitter terminal when the control signal goes high. As the control sig-nal goes high, transistor Q1 turns on, Q2 turns off, and the LED of optocoupler U1 turns on. This forces the output voltage of the opto-coupler to the low state. When the optocoupler output goes low, both transistors Q3 and Q4 turn off, turning on the Darlington combination of transistors Q5 and Q7. This will connect the Von supply to the gate of the IGBT through the gate turn-on resistor initiating the IGBT turn-on process.During the time that transistor Q4 is off, the output stage PNP tran-sistor Q6 remains off. Once the IGBT is turned on, the inverting inputFigure 1: Two-step gate drive circuitof comparator U3 will be clamped to one diode drop (forward voltage drop of de-saturation diode DC) plus the IGBT Vcesat voltage. For the gate driver to operate properly, the inverting voltage node must be at a lower voltage level than the non-inverting voltage node. The non-inverting input voltage is set by zener diode Z2. When the con-trol signal goes low, the LED of U1 turns off, and the optocoupler out-put voltage Von goes high with respect to negative terminal of VccG.This turns on transistors Q3 and Q4. When Q3 turns on, capacitor C5discharges through R24 allowing the output of the comparator U3 to remain high. Once transistor Q4 is on, the output stage Darlington combination turns off, and the PNP transistor Q6 turns on. Now, the gate of the IGBT will discharge through R21, R22 and transistor Q6,initiating the IGBT turn-off. During normal operation (no short-circuit or overload condition) comparator U3 remains off without effecting the gate driver circuit.However, the de-saturation circuit activates when a fault occurs at the inverter output, or the complimentary IGBT turns on due to noise.When the IGBT is turned-on into the low impedance load, it draws a large current, which causes the collector to emitter voltage of the IGBT to rise towards the bus voltage. As the IGBT collector to emit-ter voltage rises, the voltage across capacitor C5 will begin to charge towards VccG.When the voltage across C5 rises above Z2 zener voltage, the com-parator U3 turns-on. When U3 turns on, the base voltage of Darling-ton transistor Q5 lowers to approximately 8 volts with some quick slope. R14, R15, R27, C6 and D2 set this voltage and slope. The applied gate voltage of the IGBT is reduced from approximately 13volts to about 8 volts, significantly decreasing the saturation current of the IGBT. As soon as the gate bias reduces, electron current (MOSFET current) reduces. As electron current reduces, base cur-rent of the IGBT structure PNP transistor reduces. Hence, the satura-tion current of the IGBT reduces.When IGBT is turned-on into an inductive short-circuit or it is under shoot through condition current ramps quickly. The voltage across the device increases and current through the IGBT saturates if the gate voltage is kept on. Now if the gate voltage is brought to zero after IGBT current saturates and drain voltage rises to clamp voltage the IGBT will turn-off safely.The Ic U4 & U5 decide the time duration of first step level voltage and after this time the comparator U2 turns on and transistor Q5 &Q7 turn-off and Q6 turns-on turning-off IGBT safely. During first step time, the collector to emitter voltage across the IGBT rises faster than it would by holding the gate at 15 volts. As previously mentioned, the faster collector to emitter voltage rise is beneficial for the IGBT to safely turn-off the IGBT under a shorted load.Figure 2 and Figure 3 depicts the Fairchild 1200V Trench IGBT turn-ing on into a resistive load and after 1 micro-second the resistor is shorted. In ‘case 1’IGBT is protected within 2.6 micro-seconds. The zener Z2 decides when to start first step. The second step voltage level is decided by D1 and Vbe of gate turn-on transistor as shown in figure 2. When the zener Z2 value is 8.2V, that allows IGBT peak cur-rent to rise up to about 300A but still it turns-off IGBT safely asshown figure 2 ‘case 1’. But in figure 3 ‘case 2’when this zener value is reduced to 5.6 volts the short circuit current only rises up to about 190A. By selecting this zener properly depending on type of IGBT technology one can reduce this short circuit peak current and increase system reliability.SummaryA new two-step gate drive circuit has been proposed which protects the IGBT during short circuit and over load fault. The gate-drive safe-ly turns-off the IGBT in two steps. The IGBT stress during short cir-cuit or fault current conditions is minimized. The new gate drive cir-cuit can safely shut-off IGBTs with SCWT as low as 3?sec. The Fairchild trench IGBT can be turned-off safely in less than 3 micro-seconds.REFERENCES[1] Jun-Bae Lee, Dac-Woong Chung and Bum-Seok Suh, “Gate Volt-age Pattern Analyzer for Short-Circuit Protection in IGBT Inverters”APEC, 2007.[2] A. Bhalla, S. Shekhawat, J. Gladish, J. Yedinak, G. Dolny, “ IGBT Behavior During Short circuit and Fault Current Protection”ISPSD’98, pp. 245-248, June 3-6,1998.[3] B. Jayant Baliga, “Modern Power Devices” John Wiley & Sons”Figure 2: Trench IGBT (FGA25N120ANTD) into short circuit ‘case 1’Figure 3: Trench IGBT (FGA25N120ANTD) into short circuit ‘case 2’。
开关磁阻电机功率变换器IGBT关断电压尖峰的分析与抑制
Ｉ Ｇ Ｂ Ｔ的尖 峰电压 主要 发生 在 Ｉ Ｇ Ｂ Ｔ关 断的时候 ， 对关 收稿 日期 ： ２ ０ １ ３ — ０ ５ — １ ０
１功率变换器 关断尖峰 电压的分析
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Ｒ ｅ ｓ ｅ ａ ｒ ｃ ｈ＆ Ｄ ｅ ｓ ｉ ｇ ｎ研 究 与 设 计 鬻 溅 溺 粼 鞭
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开关磁阻电机功率变换器 Ｉ Ｇ Ｂ Ｔ 关断电压尖峰 的分析 与抑制
丁 小刚 ， 程 晶 晶
（ 中国矿业大学信电学院， 江苏 徐 州 ２ ２ １ ０ ０ ８ ）
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IGBT工作原理
IGBT工作原理概述：IGBT（Insulated Gate Bipolar Transistor）是一种高压、高功率开关器件，广泛应用于工业电力电子领域。
它结合了MOSFET的高输入阻抗和BJT的低导通压降，具有低开关损耗和高开关速度的优点。
本文将详细介绍IGBT的工作原理。
1. IGBT结构：IGBT由P型衬底、N型衬底和P型上层构成。
其中，N型衬底被分为N+区和N-区，P型上层被分为P+区和P-区。
N+区和P+区分别作为漏极和源极，N-区和P-区形成P-N结，是IGBT的主导电流区域。
2. IGBT工作原理：当IGBT的栅极施加正向电压时，栅极结与源极结之间形成正向偏置，使N-区的空间电荷区域扩展，导致P-N结区域的电导增加。
此时，IGBT处于导通状态，漏极和源极之间形成低阻抗通路，电流可以流过。
3. IGBT关断过程：当IGBT的栅极施加负向电压时，栅极结与源极结之间形成反向偏置，使N-区的空间电荷区域收缩，导致P-N结区域的电导减小。
此时，IGBT处于关断状态，漏极和源极之间形成高阻抗断路。
为了加速IGBT的关断过程，通常会在栅极上施加负向脉冲。
4. IGBT的三个工作区域：IGBT的工作可以分为三个区域：饱和区、过渡区和截止区。
- 饱和区：当栅极电压高于临界电压时，IGBT处于饱和区。
此时，漏极和源极之间的电阻很低，电流可以自由流动。
- 过渡区：当栅极电压在临界电压附近时，IGBT处于过渡区。
此时，漏极和源极之间的电阻会逐渐增加，电流流动受到一定限制。
- 截止区：当栅极电压低于临界电压时，IGBT处于截止区。
此时，漏极和源极之间的电阻非常高，电流无法流动。
5. IGBT的优点：- 低导通压降：IGBT的导通压降比MOSFET低，可以减小功率损耗。
- 高开关速度：IGBT的开关速度比BJT快，可以提高系统响应速度。
- 高输入阻抗：IGBT的输入阻抗比MOSFET高，可以减小驱动功耗。
- 高耐压能力：IGBT可以承受较高的电压，适合于高压应用场景。
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IGBT关断过程的分析
IGBT关断过程的分析上一篇，我们写了基于感性负载下，IGBT的开通过程，今天，我们就IGBT的关断过程进行一个叙述。
对于IGBT关断的可以基于很对方面进行分析，而今天我们从电压电流对IGBT的关断过程进行分析。
1前言
绝缘栅双极型晶体管(IGBT) 是双极型晶体管(BJT) 和场效应晶体管(MOSFET) 的复合器件,IGBT将BJT的电导调制效应引入到VDMOS 的高阻漂移区, 大大改善了器件的导通特性, 同时还具有MOSFET栅极输入阻抗高、开关速度快的特点。
很多情况，由于对IGBT 关断机理认识不清, 对关断时间随电压和电流的变化规律认识不清, 导致无法解释在使用过程中出现的电流拖尾长、死区时间长等现象, 不能充分发挥IGBT 的性能; 导致IGBT 因使用不当, 烧毁。
今天我们就IGBT关断时的电流和电压进行简单的叙述。
02关断机理
IGBT 结构等同于n 沟道MOSFET与pnp晶体管构成的达林顿结构, MOSFET 的漏极与pnp晶体管的基极相连。
等效电路和基本结构图如下：
IGBT的关断波形如下图所示，大致分为三个阶段：①关断延迟时间td(off)；②关断过程中电压上升到10%到电流下降到90%时间Δt；③关断下降时间tf。
IGBT关断时间表达式为：
toff=td(off)+Δt +tf
ICE=IMOS+IC(BJT)=Ids+Ice
BJT 是一种电流控制型器件, 发射极e和集电极c传导的工作电流受基极b引入的较小电流的控制, 如等效电路所示, BJT受MOSFET漏极电流控制. 在IGBT关断td(off)和Δt 程中, MOSFET 的门极电压Vgs减小至Miller平台电压Vmr, 漏源电压Vds增大至Vds(max), 而漏源电流Ids保持不变. 由于Ib=Ids, BJT的集射极电流Ice受Ib控制, 所以,在IGBT关断td(off)和Δt过程中, Ice电流仍然保持不变, 如上图所示. 由上式ICE等式可知, IGBT的。