Self-adaptive IGBT turn-off circuit based on PNP triode characteristics
By using an adaptive IGBT turn-off circuit based on the characteristics of a PNP transistor, the equivalent resistance value is adjusted by utilizing the inherent characteristics of the IGBT during turn-off. This solves the problems of voltage spike suppression and loss reduction during IGBT turn-off, thereby simplifying control and improving circuit reliability.
Patent Information
- Application Number
- CN202511810823.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-02
- Publication Date
- 2026-02-27
AI Technical Summary
During IGBT turn-off, it is difficult to balance electromagnetic interference and turn-off losses. Existing technologies cannot effectively suppress voltage spikes and reduce losses, and the control signal is susceptible to noise interference, making feedback control complex.
Design an adaptive IGBT turn-off circuit based on the characteristics of PNP transistors. Utilize the inherent characteristics of IGBTs during turn-off and adaptively adjust the equivalent resistance value through PNP transistors to balance voltage spike suppression and turn-off loss reduction, avoiding the need for additional switching and signal sampling feedback.
This technology effectively suppresses voltage spikes and reduces losses during IGBT turn-off, while simplifying the control circuit, reducing costs and control delays, and improving circuit reliability.
Smart Images
Figure CN121585151A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of power electronics and IGBT drive control technology, specifically to an adaptive IGBT turn-off circuit based on the characteristics of a PNP transistor. Background Technology
[0002] With the continuous development of power electronics technology, Insulated Gate Bipolar Transistors (IGBTs), as an important power switching device, have been widely used in various application fields. However, electromagnetic interference (EMI) is a common and serious problem in the operating environment of IGBTs. The current and voltage changes generated during IGBT switching can cause EMI, negatively impacting surrounding electronic equipment, communication systems, and measurement systems. Especially during the turn-off phase, there is a difficult trade-off between voltage spikes and turn-off losses: if fast turn-off is pursued to reduce losses, the collector current will drop too quickly, generating significant voltage spikes under the parasitic inductance of the power circuit, which may damage the IGBT and surrounding devices; if the focus is on suppressing voltage spikes, the turn-off speed needs to be slowed down, leading to increased turn-off losses and affecting system energy efficiency.
[0003] In existing technologies, voltage clamping devices such as Zener diodes or TVS diodes can be used to limit the maximum voltage through breakdown discharge; however, the energy surge at the moment of breakdown can reduce circuit reliability. Alternatively, the voltage can be controlled. V CE The / dt method utilizes an RC circuit to sample the rate of voltage change and adjust the drive voltage or current in real time. However, the sampled signal is susceptible to noise interference and requires extremely small feedback loop delay, making practical control difficult. Alternatively, a parallel absorption capacitor method can be used to increase the gate-collector capacitance ( C GC It slows down the voltage rise rate, but prolongs the IGBT turn-on process. It can only suppress spikes and cannot reduce turn-off losses. Summary of the Invention
[0004] To address the shortcomings of existing technical solutions, this invention is based on the concept of adaptive variable resistance switching. It utilizes the inherent characteristics of transistors and IGBTs during the turn-off process to achieve both voltage spike suppression and turn-off loss reduction during IGBT turn-off without the need to add a switch near the turn-off resistor or sample and feedback IGBT characteristic quantities.
[0005] To achieve the above objectives, this invention provides an adaptive IGBT turn-off circuit based on the characteristics of a PNP transistor, comprising: IGBT, wherein the IGBT has a gate, a collector, and an emitter; Power is turned off, wherein the power supply is a preset negative voltage power supply used to provide the drive voltage required for IGBT turn-off; Gate drive resistor R g The gate drive resistor R g One end is electrically connected to the gate of the IGBT; A PNP transistor, having a collector, a base, and an emitter; the PNP transistor is connected in series in the gate turn-off circuit of the IGBT, its collector is electrically connected to the output terminal of the turn-off power supply, and the emitter of the PNP transistor is connected to the gate drive resistor. R g The other end is electrically connected; base resistor R b The base resistor R b One end is electrically connected to the base of the PNP transistor Q1, and the base resistor R b The other end is connected to a preset negative voltage power supply. V BB Electrical connection; During the IGBT turn-off process, the PNP transistor can be based on the IGBT gate voltage. V ge The equivalent resistance value is adaptively adjusted to balance the suppression of voltage spikes during IGBT turn-off and the reduction of turn-off losses. The variation law of the equivalent resistance value is as follows: the t0~t1 and t1~t3 stages of IGBT turn-off are equivalent to small resistance to shorten the turn-off time; the t3~t4 stage of IGBT turn-off is equivalent to large resistance to suppress voltage spikes.
[0006] Furthermore, the preset negative voltage power supply V BB The voltage value is -5V to -15V.
[0007] Furthermore, during the IGBT turn-off phase t0~t3, the PNP transistor is in the amplification region; during the later stage of the IGBT turn-off phase t3~t4, the emitter of the PNP transistor changes with the IGBT gate voltage. V ge The descent changes from positive to negative deflection, entering the cutoff region.
[0008] Furthermore, during the initial IGBT turn-off phase t0~t1, the gate drive resistor... R g Gate-emitter parasitic capacitance of IGBT C geProvides an initial discharge path, allowing the negative voltage of the power-off supply to pass through the gate drive resistor. R g Transmit to C ge ,trigger C ge Discharge.
[0009] Furthermore, the magnitude of the equivalent resistance of the PNP transistor is determined by the amplification factor of the PNP transistor and the base resistance. R b The amplification factor is determined by the resistance value of the IGBT; the amplification factor is proportional to the collector current of the PNP transistor, and the collector current varies with the gate voltage of the IGBT. V ge The decrease in the amplification factor leads to a decrease in the amplification factor and an increase in the equivalent resistance of the PNP transistor.
[0010] Furthermore, during the t0~t1 stage of IGBT turn-off, the equivalent small resistance of the PNP transistor, in conjunction with the gate drive resistor... R g This makes the gate voltage of the IGBT... V ge Rapidly drops to Miller plateau voltage V miller During the IGBT turn-off phases t1 to t3, the small equivalent resistance of the PNP transistor accelerates the IGBT collector-emitter voltage. V ce The rate of descent shortens the duration of the Miller platform.
[0011] Furthermore, during the IGBT turn-off phase t3~t4, the large equivalent resistance of the PNP transistor reduces the IGBT's collector current. I CE The rate of decrease, thereby suppressing the parasitic inductance of the power circuit. L s The resulting voltage overshoot.
[0012] Furthermore, the PNP transistor can be replaced with an NPN transistor, and at the same time V BB The voltage value is 10V.
[0013] Compared with existing technologies, the advantages of this invention are: it eliminates the concern that the control signal of ordinary variable resistor switches is susceptible to interference from power circuit noise, which can severely affect the normal operation of the drive circuit. Furthermore, it eliminates the need to design IGBT characteristic quantity sampling feedback circuits, utilizing the inherent characteristics of the IGBT during the switching process. V geThe voltage across the base-emitter junction of the transistor is changed by altering the voltage across the junction, thus achieving adaptive adjustment as the IGBT switches. Compared to the voltage modification method, this eliminates the need for a D / A chip, significantly reducing cost and circuit complexity. It also reduces control loop delay and eliminates issues affecting feedback control. Attached Figure Description
[0014] Figure 1 This is a schematic diagram of the topology of an adaptive IGBT turn-off circuit based on the characteristics of a PNP transistor. Figure 2 The IGBT turn-off waveform is shown in the figure; Figure 3 for t 0~ t A one-stage IGBT equivalent model; Figure 4 for t 1~ t 3-stage IGBT equivalent model; Figure 5 for t 3~ t 4-stage IGBT equivalent model; Figure 6 A schematic diagram of the gate turn-off circuit topology of a PNP transistor connected in series with an IGBT. Figure 7 This is a diagram showing the change in the equivalent resistance of the PNP transistor during the IGBT turn-off process. Detailed Implementation
[0015] To make the objectives, advantages, and features of the present invention more apparent, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be emphasized that the above drawings and the following description are merely exemplary and not intended to limit the scope of the present invention or its application.
[0016] The basic principle of this IGBT turn-off circuit is to utilize the characteristics of the PNP transistor itself and the changes in key state quantities during the IGBT turn-off process to achieve adaptive dynamic changes in the equivalent resistance of the PNP transistor during the turn-off process, thereby achieving the goal of both suppressing voltage spikes and reducing turn-off losses during the IGBT turn-off process.
[0017] First, we analyze the IGBT turn-off process. An IGBT is a voltage-type semiconductor transistor, controlled by a voltage signal to turn on and off. A positive drive voltage turns it on, and a negative drive voltage turns it off. The simplest IGBT driver is to amplify the PWM signal and connect it to the IGBT's gate, allowing the IGBT to operate. Using this simplest IGBT driver circuit, the IGBT turn-off waveform is as follows: Figure 2 As shown, the IGBT turn-off process consists of four parts, which will be analyzed one by one.
[0018] t 0~ t Phase 1, t At time 0, driving voltage V drive When the voltage changes from positive to negative, the gate capacitance... C ge Discharge begins, gate voltage V ge It started to decline, but at this point the IGBT was still in the saturation region. I CE The decline has not yet begun; the equivalent model for this stage is as follows: Figure 3 As shown. Due to C gc The current on it is very small, so the driving current is all C ge The discharge current, therefore V ge The expression is: ; t 1 to t 3 stages t At moment 1, V ge Reduce to a value to ensure IGBT current and inductor current I CE Equal, then enter the Miller plateau phase, because V CE At lower levels, Miller capacitance C gc The value is relatively high, so V CE The ascent speed is relatively slow. t 2 o'clock, due to V CE As the current rises, holes in the IGBT drift region begin to flow, forming a sweep-out current, thus reducing the MOSFET current. V ge It has become smaller, but not significantly so yet, therefore it will remain so. t 2 to t The three stages are viewed as... t 1 to t The same as Phase 2, V ge constant. t 1 to t 3-stage equivalent model such as Figure 4 because C ge There is no current, so V CEThe rate of ascent is: ;
[0019] along with V CE The increase, C gc It will decrease, eventually tending towards a fixed value, so V CE The rate of increase will continue to increase until it reaches a fixed value.
[0020] t 3 to t The equivalent model of the four stages is as follows: Figure 5 As shown, t At 3 o'clock, V CE When the bus voltage is reached, the anti-parallel diode of the upper transistor conducts. I CE The descent begins, the rate of descent... V ge It is related to the rate of descent. Therefore I CE The rate of descent is: ;
[0021] During this stage, due to the parasitic inductance of the power circuit L s The existence of this will produce V CE Overshoot, the specific reason is I CE Rapid descent, in L s An induced voltage is generated on the bus, which, when superimposed on the bus voltage, causes a voltage overshoot. ;
[0022] Therefore, the magnitude of voltage overshoot and I CE The rate of voltage drop is related to the voltage descent rate; to control voltage overshoot, it is necessary to control... I CE The descent rate, the novel multi-stage driving method, is achieved by controlling d during shutdown. I CE / dt is used to control voltage overshoot.
[0023] t 4 o'clock later, t At time 4, V ge Descending to V ge(th) However, at this time the current I CEIt hasn't dropped to 0 yet because some voids in the drift region haven't been squeezed out. I CE It is still slowly descending until these holes disappear. I CE Once the value drops to 0, the entire shutdown process ends.
[0024] The multi-stage driving method involves segmenting the IGBT turn-off process and using different control methods for different stages. This minimizes the turn-off delay and losses caused by control, resulting in shorter turn-off time and lower turn-off losses while achieving the same control objectives.
[0025] t 0 to t In stage 1, it can be derived from formula (1) that... V ge Drop to Miller voltage V miller Time required for: ;
[0026] From formula (5), we can see that, V ge Drop to Miller voltage V miller Required time Δ t 0 and gate drive resistance R g and IGBT gate-emitter capacitance C ge The size is directly proportional to the value, where C ge Since the inherent characteristics of IGBTs cannot be changed, the only way to shorten the IGBT turn-off time is to reduce the gate drive resistance. R g The value of .
[0027] t 1 to t Stage 3, this stage is the Miller plateau period, as can be seen from formula (2), V CE The descent rate and gate drive resistance R g and IGBT gate-collector capacitance C gc The magnitudes are inversely proportional. C gc Since the inherent characteristics of IGBTs cannot be changed, the only way to shorten the Miller plateau time during IGBT turn-on is to reduce the gate drive resistance. R g The value of .
[0028] t 3 to t In stage 4, through analysis of the mechanism of IGBT turn-off voltage spike generation, it can be seen that the control... V CE The key to overshoot is control. I CE The rate of ascent. From formula (4), we can see that... I CE The rise rate and the transconductance of IGBT g m IGBT gate-emitter capacitance C ge and gate drive resistor R g The size is related to, among which g m and C ge These are all inherent characteristics of the IGBT itself and cannot be changed. To suppress the IGBT turn-off voltage spikes, the only solution is to increase the gate drive resistance. R g The value of .
[0029] The analysis of different needs in the three time periods above shows that, in order to achieve the goal of balancing voltage spike suppression and turn-off losses during IGBT turn-off, it is necessary to... t 0 to t Phase 1 and t 1 to t The third stage uses a smaller gate drive resistor to shorten the IGBT turn-on time. t 3 to t The fourth stage uses a larger driving resistor to suppress turn-off voltage spikes.
[0030] Utilizing the IGBT gate voltage during IGBT turn-off V ge The characteristic that the transistor's base current changes during the IGBT turn-off process, combined with the fact that the base current is related to the base voltage, base resistance, and emitter voltage, allows a PNP transistor to be connected in series with the IGBT's gate turn-off circuit, such as... Figure 6 As shown.
[0031] The transistor's collector is always reverse-biased, while the emitter is forward-biased, placing the transistor in its amplification region. This is due to the parasitic capacitance of the IGBT. C ge When the transistor is discharged to the point where the emitter is reverse-biased, the transistor enters the cutoff region. The magnitude of the base current of the transistor is related to the base voltage, base resistance, and emitter voltage. At this time, the emitter of the transistor is connected to the gate of the IGBT. ;
[0032] The change in the equivalent resistance of the PNP transistor during IGBT turn-off is as follows: Figure 7 As shown t 0 to t In stage 1, the turn-off voltage is applied to the IGBT parasitic capacitance through a resistor. C ge As can be seen from the capacitor discharge current characteristic curve, the gate current initially... I g The current rises rapidly to its peak value. At this point, the collector current of the transistor is very large, and the transistor's amplification factor is very large. As shown in formula (6), the equivalent resistance of the transistor is very small at this time, making... t 0 to t Phase 1 V ge The IGBTs descend to the Miller platform at a faster rate to shorten the IGBT turn-off time.
[0033] t 1 to t 3 stages t IGBT gate voltage at time 1 V ge Drop to Miller plateau voltage, t After time 1, the IGBT gate voltage V ge Keeping the platform voltage constant, the IGBT gate current also remains constant. Due to the transistor's inherent characteristics, the transistor's amplification factor also remains constant, ultimately resulting in the transistor's equivalent resistance becoming a smaller Miller resistance. (It is known that...) V CE The descent rate and gate drive resistance R g The magnitude is inversely proportional to the value; therefore, using a smaller resistor accelerates the process. V CE The purpose is to shorten the duration of the Miller platform by reducing its descent.
[0034] t 3 to t The IGBT has four stages, and due to the transistor's inherent characteristics, the amplification factor is directly proportional to the collector current. As the turn-off voltage discharges the gate-emitter junction capacitance of the IGBT, V ge The continuous decrease in current leads to a reduction in the base current of the transistor, which in turn reduces the collector current, resulting in a decrease in the amplification factor. Therefore, the equivalent resistance of the transistor increases linearly.
[0035] The above embodiments have provided a detailed description of the technical solution of the present invention. Obviously, the present invention is not limited to the described embodiments. Based on the embodiments of the present invention, those skilled in the art can make various modifications, but any modifications that are equivalent to or similar to the present invention fall within the scope of protection of the present invention.
[0036] The contents not described in detail in this specification are existing technologies known to those skilled in the art.
Claims
1. An adaptive IGBT turn-off circuit based on the characteristics of a PNP transistor, characterized in that, include: IGBT, wherein the IGBT has a gate, a collector, and an emitter; Power is turned off, wherein the power supply is a preset negative voltage power supply used to provide the drive voltage required for IGBT turn-off; Gate drive resistor R g The gate drive resistor R g One end is electrically connected to the gate of the IGBT; A PNP transistor, having a collector, a base, and an emitter; the PNP transistor is connected in series in the gate turn-off circuit of the IGBT, its collector is electrically connected to the output terminal of the turn-off power supply, and the emitter of the PNP transistor is connected to the gate drive resistor. R g The other end is electrically connected; base resistor R b The base resistor R b One end is electrically connected to the base of the PNP transistor Q1, and the base resistor R b The other end is connected to a preset negative voltage power supply. V BB Electrical connection; During the IGBT turn-off process, the PNP transistor can be based on the IGBT gate voltage. V ge The equivalent resistance value is adaptively adjusted according to the change, so as to balance the suppression of voltage spikes when the IGBT is turned off and the reduction of turn-off loss. The variation pattern of the equivalent resistance value is as follows: the t0~t1 and t1~t3 stages of IGBT turn-off are equivalent to small resistance to shorten the turn-off time; the t3~t4 stages of IGBT turn-off are equivalent to large resistance to suppress voltage spikes.
2. The adaptive IGBT turn-off circuit based on PNP transistor characteristics according to claim 1, characterized in that, The preset negative voltage power supply V BB The voltage value is -5V to -15V.
3. The adaptive IGBT turn-off circuit based on PNP transistor characteristics according to claim 1, characterized in that, During the IGBT turn-off phase t0~t3, the PNP transistor is in the amplification region; during the later stage of the IGBT turn-off phase t3~t4, the emitter of the PNP transistor changes with the IGBT gate voltage. V ge The descent changes from positive to negative deflection, entering the cutoff region.
4. The adaptive IGBT turn-off circuit based on PNP transistor characteristics according to claim 1, characterized in that, During the initial IGBT turn-off phase t0~t1, the gate drive resistor R g Gate-emitter parasitic capacitance of IGBT C ge Provides an initial discharge path, allowing the negative voltage of the power-off supply to pass through the gate drive resistor. R g Transmit to C ge ,trigger C ge Discharge.
5. The adaptive IGBT turn-off circuit based on PNP transistor characteristics according to claim 1, characterized in that, The magnitude of the equivalent resistance of the PNP transistor is determined by the amplification factor of the PNP transistor and the base resistance. R b The amplification factor is determined by the resistance value of the IGBT; the amplification factor is proportional to the collector current of the PNP transistor, and the collector current varies with the gate voltage of the IGBT. V ge The decrease in the amplification factor leads to a decrease in the amplification factor and an increase in the equivalent resistance of the PNP transistor.
6. The adaptive IGBT turn-off circuit based on PNP transistor characteristics according to claim 1, characterized in that, During the t0~t1 phase when the IGBT is turned off, the equivalent small resistance of the PNP transistor, in conjunction with the gate drive resistor... R g This makes the gate voltage of the IGBT... V ge Rapidly drops to Miller plateau voltage V miller During the IGBT turn-off phases t1 to t3, the small equivalent resistance of the PNP transistor accelerates the IGBT collector-emitter voltage. V ce The rate of descent shortens the duration of the Miller platform.
7. The adaptive IGBT turn-off circuit based on PNP transistor characteristics according to claim 1, characterized in that, During the t3~t4 stage when the IGBT is turned off, the equivalent large resistance of the PNP transistor reduces the collector current of the IGBT body. I CE The rate of decrease, thereby suppressing the parasitic inductance of the power circuit. L s The resulting voltage overshoot.
8. The adaptive IGBT turn-off circuit based on PNP transistor characteristics according to claim 1, characterized in that, The PNP transistor can be replaced with an NPN transistor, and at the same time V BB The voltage value is 10V.