Short circuit protection for power switch

Abstract

A control system for a power switch having a channel. The system includes short circuit protection circuitry configured to, when the control terminal of the power switch is at a second potential level, change the control terminal of the power switch from one potential level to another potential level in response to the overvoltage detection circuitry detecting an overvoltage on the power switch, therefore, the charge carrier concentration in the channel is increased.

Description

Technical Field

[0001] The present disclosure generally relates to semiconductor switches for switching power in applications including, for example, switch-mode power converters and inverters. Background Art

[0002] Electronic devices use electricity to operate. In many application environments, powering electronic devices requires switching relatively high voltages and / or currents. If a power switch is improperly designed and cannot withstand high voltages or carry high currents, the power switch may be damaged. In addition, even a properly designed power switch may be damaged under improper operating conditions (including short circuits, electrostatic discharge events, power surges, lightning strikes, etc.). Depending on the environment, a failure of a power switch can not only cause failure of the device including the power switch, but can also cause failure of other equipment.

[0003] The safe operating area (SOA) of a power switch is a definition of the current and voltage conditions within which the power switch can be expected to operate without self-damage or degradation. In practice, manufacturers and suppliers will present the safe operating area for different power switches in the datasheet for both forward bias (i.e., when the power switch is on) and reverse bias (i.e., when the power switch is off or turned off).

[0004] In addition to safety, it is also desirable to switch power efficiently. The two main sources of power loss in semiconductor switches are conduction losses and switching losses. Conduction losses occur when the power switch is conducting, and the conduction losses are due to the inherent forward voltage drop of the channel of the power switch. For example, the conduction losses can be reduced by reducing the duty cycle (i.e., the relative duration during which the power switch is conducting) and / or by reducing the forward voltage drop of the power switch channel. In general, the duty cycle is determined by the operating environment, and it is usually not practical to reduce the duty cycle in order to reduce conduction losses. For example, the forward voltage drop can be reduced by increasing the effective size of the channel (i.e., the size of a single channel or by conducting current via multiple channels in parallel) or by increasing the number of charge carriers in the channel. For example, the number of charge carriers can be increased by carefully designing the power switch and / or by biasing the control terminal of the switch to increase the number of mobile charge carriers in the channel in the on state.

[0005] For example, many modern enhancement mode IGBT power switches can be biased with a gate-to-emitter voltage of about +15 volts in the on-state. In many applications, this is sufficient to introduce enough carriers into the channel so that conduction losses are tolerable. However, in other applications (e.g., in applications with relatively low switching frequencies), conduction losses account for an unsatisfactory portion of the total losses. In these other applications, the gate-to-emitter voltage can be increased, for example to about +25 volts, so that more charge carriers are introduced into the channel.

[0006] Switching losses occur when the power switch switches from the off state to the on state, or vice versa. During switching, the voltage across the power switch and the current through the power switch both transition between their respective steady-state values ​​in the off state and the on state. During the transition, the product of this voltage and current is the power lost due to the switching. For example, switching losses can be reduced by reducing the switching frequency (i.e., how often the switch transitions are made) and / or by switching between the on state and the off state more quickly. In many cases, the switching frequency is determined by the operating environment, and reducing the switching frequency to reduce switching losses may not be practical. The duration of the switching can be reduced by moving charge carriers into and out of the channel of the switch more quickly, for example by carefully designing the power switch and / or by biasing the control terminals of the switch to increase the attractive / repulsive forces that move charge carriers into / out of the channel.

[0007] The desire to switch safely and efficiently is often conflicting, and design trade-offs must often be made. For example, in a short circuit condition, increasing the number of charge carriers in the channel makes it more likely that the current and voltage conditions in the power switch will exceed the safe operating area. There is inevitably a delay in detecting the short circuit and turning off the power switch after detection. During this delay, the current through the power switch can increase to a high level, so that the voltage on the power switch increases and the transistor saturates (for example, in the case of a MOSFET) or desaturates (for example, in the case of an IGBT). In the (de)saturation state, the current conducted by the power switch may become so high that the power switch is damaged or fails. To prevent this, the drive circuit system for the gate or other control terminal of the power switch typically includes a (de)saturation protection function. For example, the voltage on the power switch can be measured to detect (de)saturation.

[0008] To reduce the delay in responding to a short circuit condition, control and drive circuitry with (de)saturation protection is often coupled directly to the power switch. In some cases - especially in applications where the power switch is an IGBT - such drive circuitry may be implemented in an application specific integrated circuit (ASIC) designed to drive a power switch with certain characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic representation of various waveforms during response to detection of a short circuit during driving an IGBT power switch.

[0010] Figure 2 is a state diagram of the control and drive circuitry of the power switch during operation of the power switch and detection of a short circuit fault.

[0011] Figure 3 is a schematic representation of various waveforms during response to detection of a short circuit during driving an IGBT power switch.

[0012] Figure 4 is a schematic representation of circuitry involved in responding to the detection of a short circuit during driving an IGBT power switch.

[0013] Like reference symbols in the various drawings indicate like elements. DETAILED DESCRIPTION

[0014] For teaching purposes, the specific embodiments are described in terms of an insulated gate bipolar transistor (IGBT) power switch. However, the corresponding teachings can be applied to various enhancement or depletion mode devices (e.g., bipolar junction transistors (BJTs), metal oxide semiconductor field effect transistors (MOSFETs), high electron mobility transistors (HEMTs)) with electron or hole charge carriers. These devices can be implemented with silicon, silicon carbide, gallium nitride, or other semiconductor materials.

[0015] Figure 1 1 is a schematic representation of various waveforms 100, 105, 110, 112 during response to detection of a short circuit during driving an IGBT power switch. For example, the illustrated waveforms may occur when the IGBT power switch is biased with a gate-emitter voltage (e.g., a gate-emitter voltage of approximately +25 volts in modern IGBT devices) that is designed to introduce a relatively large number of charge carriers into the IGBT channel.

[0016] Specifically, waveform 100 refers to voltage V D The waveform 105 shows the actual (internal) gate-emitter voltage V GE As a function of time, waveform 110 shows the collector current I C is represented as a function of time, and waveform 112 represents the collector-emitter voltage V CE Expressed as a function of time. Reference voltage V DWaveform 100 represents the idealized voltage at the gate of the IGBT power switch, while the gate-emitter voltage V GE represents the actual voltage at the gate of the IGBT power switch. In real-world devices, the gate-emitter voltage V GE will be different from the reference voltage V D The exact nature of the difference will depend on the nature of the circuit system implementation. The collector current I in the form of waveform 110 C and the collector-emitter voltage V in the form of waveform 112 CE is the gate-emitter voltage V in the form of waveform 105 of the driving system GE Response.

[0017] The time scales of waveforms 100, 105, 110, 112 are the same, and for a typical IGBT power switch, the time span is typically between 2 and 10 microseconds. The voltage scales of waveforms 100, 105 are almost the same, and for a typical IGBT power switch, the voltage span is typically between -15 and 25 volts. For a typical IGBT power switch, the current scale of waveform 110 is typically between 2 and 30 kiloamperes. For a typical IGBT power switch, the voltage scale of waveform 112 is typically between 600 and 6500 volts.

[0018] At the beginning of the illustrated time span, the IGBT is in conduction. The reference voltage V represented by waveform 100 D and the gate-emitter voltage V represented by waveform 105 GE are substantially at their respective maximum levels 115, 120. For the illustrated time span, the gate and other capacitances (including gate-emitter capacitance, gate-collector capacitance, and parasitic capacitance) are substantially fully charged, and the reference voltage and actual gate voltage are substantially unchanged. In addition, the collector current I represented by waveform 110 is C is at level 125, and the collector-emitter voltage V CE At level 127. In general, the magnitude of the current at level 125 is primarily determined by system regulation. The magnitude of the voltage at level 127 is primarily determined by the device characteristics of the IGBT and the applied gate voltage and other parameters (e.g., temperature). In other words, the forward voltage drop of the IGBT is typically negligible compared to the voltage across the load. For the illustrated time span, the power demand of the load is constant and the collector current is stable over time.

[0019] Levels 115, 120 are selected so that the voltage drop across the IGBT channel in the on-state is relatively small. In any case, even if the IGBT is in the on-state, and if the reference voltage VD and the actual gate-emitter voltage V GE At levels lower than levels 115, 120, the voltage drop across the IGBT will remain negligible compared to the voltage drop across the load, and the IGBT control and drive circuitry drives the IGBT using a gate voltage that further reduces the forward voltage drop of the channel and reduces conduction losses.

[0020] At time T0, a short circuit condition occurs outside the power switch. The collector current I represented by waveform 110 C After a delay, in response to detecting a short circuit condition, the overcurrent protection function in the IGBT control and drive circuit system is triggered at time T1. Figure 1 In the example, the delay is the time difference between T0 and T1. The short circuit condition can be detected in a variety of different ways. For example, the rate of change of the voltage and / or collector current on the IGBT can be compared with corresponding thresholds to detect the short circuit condition.

[0021] Regardless of how the short-circuit condition is detected, the collector current I C The collector current I C rises to a level that will not allow the IGBT power switch to be turned off. In other words, at such a large collector current I C Directly turning off the IGBT power switch under such circumstances will damage the IGBT.

[0022] Therefore, rather than turning off the IGBT power switch directly, the IGBT control and drive circuitry initiates a two-stage process for turning off the IGBT. In the first stage, the IGBT control and drive circuitry does not attempt to drive the IGBT with a voltage that would switch the IGBT to the off state. Instead, the IGBT control and drive circuitry initially switches the IGBT off with a gate-to-emitter voltage V that is sufficient to reduce the number of charge carriers in the channel—and therefore their concentration. GE Level 135 is used to drive the IGBT. Generally speaking, the charge carrier concentration will be sufficient to maintain the IGBT in the on state. In other words, the IGBT control and drive circuit system will use the reference voltage V D By reducing the number of charge carriers in the channel, even a desaturated IGBT will have a lower collector current I C level, and the IGBT will not be damaged. In fact, many gate driver controllers for IGBT power switches already include a desaturation protection function that GE This function is sufficient to protect the IGBT power switch when the gate-emitter voltage V GEIn this case, the IGBT power switch can be switched to the off state in a safe manner.

[0023] In the illustrated context, voltage level 130 is lower than voltage level 115. For common IGBT devices, voltage level 130 may be, for example, between 12 and 17 volts, while voltage level 115 may be, for example, between 20 and 30 volts. However, in some cases, voltage level 130 may be, for example, between 5 and 12 volts, resulting in a reduced charge carrier concentration without keeping the power switch in a fully on state. In the illustrated embodiment, the idealized reference voltage V D The transitions between levels 115, 130 in waveform 100 are shown as idealized steps. In the real world, the actual gate-emitter voltage V GE In particular, due to gate and other capacitances, the actual gate-emitter voltage V represented by waveform 105 is GE The reference voltage V in waveform 100 is D Descending more slowly.

[0024] The IGBT control and drive circuit system will use the reference voltage V D Level 130 starts driving the IGBT power switch for some time, the collector current I C continues to increase, and the IGBT power switch will eventually desaturate. In the illustrated embodiment, the desaturation of the IGBT power switch occurs at T2, and the collector-emitter voltage V CE increases rapidly, as shown by waveform 112. In addition, in the illustrated embodiment, the collector current I C It reaches its maximum value near T2.

[0025] As discussed above, if the IGBT control and drive circuitry continues to drive the IGBT directly into the off state, the increased collector current I C Will rise to a level where damage to the IGBT may occur. Instead of doing this, the IGBT control and drive circuit system drives the IGBT power switch with a voltage level sufficient to reduce the number of charge carriers in the channel and can maintain the IGBT in the on state. Over time (here, the time between T2 and T3), the collector current will drop to a level where the IGBT power switch is driven off. At time T3, the IGBT is desaturated, but can be safely driven to the off state.

[0026] In addition, the gate-emitter voltage V GEThe time at which the level 135 is approximately reached is not necessarily the same as the time at which the IGBT power switch can be safely driven into the off state. In other words, in other embodiments, the gate-emitter voltage V GE The level 135 will be approached before or after time T3.

[0027] As for the collector current I C , even in the IGBT control and drive circuit system instructions will be at T1 with the reference voltage V D After driving the IGBT at level 130, it will also initially continue to increase rapidly. The collector-emitter voltage V CE will increase as the IGBT desaturates. However, at a certain point, the collector current I C will reach a peak value and - as the gate-emitter voltage V GE and the number of charge carriers in the channel decreases - the collector current I C will also begin to decrease. The collector-emitter voltage V CE Usually the collector current I C It reaches its peak shortly after reaching its peak and then starts to decline. At T3, the collector-emitter voltage V CE will reach a level where the IGBT can be safely driven into the off state. In response, at T3, the IGBT control and drive circuit system uses the reference voltage V D Level 145 drives the IGBT, the reference voltage V D Level 145 is low enough to switch the IGBT to the off state. In the illustrated waveform 100, level 145 is negative. For example, level 145 may be between -3 and -20 volts.

[0028] Collector current I C It falls relatively quickly during this transition and will drop to approximately zero when the IGBT reaches the off state. The collector-emitter voltage V CE During this transition, V increases and - as shown - may exceed the level 155 of the switched voltage. Nevertheless, this exceeding is still within the safe operating area of ​​the IGBT power switch. Ultimately, the collector-emitter voltage V CE Will stabilize at the switched voltage level 155.

[0029] Figure 22 is a state diagram 200 of the control and drive circuit system of a power switch. For didactic purposes, state diagram 200 omits many aspects of the operation of the control and drive circuit system. For example, when the switch is transitioning to the off state (e.g., during transitions 229, 213 in state diagram 200), the active clamping function will generally continue to operate. As another example, a multi-step drive may be used to transition the switch to the on state (e.g., during transition 229 in state diagram 200). As yet another example, state diagram 200 omits device startup entirely. As yet another example, the illustrated states may not be exclusive, or may include more than one state. For example, there may be multiple reduced gate voltage states in which the control and drive circuit system drives the IGBT power switch with different reduced reference gate voltages. As yet another example, there may be multiple active clamping states in which the gate-emitter voltage V GE Furthermore, there may be additional transitions between such "enhanced" and "reduced" clamping states. Therefore, state diagram 200 is to be construed as illustrating only a portion of the operation of the control and drive circuitry.

[0030] State diagram 200 includes a switch on state 205 , a reduced gate voltage state 210 , an active clamp state 215 , a switch off state / fault condition 220 , and a switch off state / no fault condition 225 .

[0031] During normal operation, the power switch will transition between the switch-on state 205 and the switch-off state / no-fault condition 225 along transition 229, depending on the operating environment of the power switch. The switch-off state / no-fault state 225 initiates one or more reflexive transitions 227, which indicate continuous monitoring of one or more conditions, which indicate that the IGBT power switch will be transitioned into the switch-on state 205. The switch-on state 205 initiates one or more reflexive transitions 228, which indicate continuous monitoring of one or more conditions, which indicate that the IGBT power switch will be transitioned into the switch-off state / no-fault state 225. The conditions are varied and may include, for example, a feedback signal reaching a certain level, a request signal from other circuit systems, a start command, or a restart command. For convenience, despite these multiple possibilities, only a single reflexive transition 227, 228 is illustrated for each state 205, 225.

[0032] Turning to short circuit detection and protection, the switch on state 205 initiates a reflexive transition 207 and a state transition 209. The reflexive transition 207 indicates continued monitoring to detect a short circuit condition external to the IGBT power switch. As discussed above, such a short circuit can be detected, for example, based on a relatively high rate of change of the collector current on the IGBT power switch. Short circuit detection monitoring can include comparing a parameter to a threshold level indicative of a short circuit. State transition 209 is triggered by the detection of a short circuit and transitions the control and drive circuit system to a reduced gate voltage state 210. In the reduced gate voltage state 210, the control and drive circuit system drives the IGBT power switch with a reduced reference gate voltage. In the Figure 1 In the context of the waveforms shown in , state transition 209 corresponds to the reference voltage V occurring at T1 D transformation.

[0033] The reduced gate voltage state 210 initiates a reflexive transition 212 and two state transitions 213, 214. The reflexive transition 212 indicates that the voltage V on the IGBT power switch is CE This monitoring can include the voltage V CE The voltage V that indicates the threshold level of harmful overvoltage on the IGBT power switch and the voltage V that indicates that the IGBT power switch can be turned off without exiting the safe operating area CE As discussed further below, V CE Monitoring can be accomplished using active or passive components. For example, control and drive circuitry can detect when V crosses a threshold. CE The response of can be triggered, for example, by a comparator or by a passive component such as a diode. State transition 213 is caused by the voltage V on the IGBT power switch. CE Indicates the IGBT power switch desaturation trigger and transitions the control and drive circuit system to state 220, in which the IGBT power switch is driven off. Figure 1 In the context of the waveforms shown in FIG. 2 , state transition 213 corresponds to the reference voltage V occurring at T3. D In other embodiments, the collector current I C , to detect when the IGBT power switch transitions to the off state.

[0034] State transition 214 is determined by the voltage V on the IGBT power switch. CEThe active clamping state 214 transitions the control and drive circuitry to the active clamping state 215. Generally, active clamping is configured to slow the transition of the IGBT power switch into the off state by slowing the depletion of charge carriers in the channel during the transition. Active clamping can be implemented in a number of different ways, but the different approaches generally slow the discharge of the gate of the IGBT power switch. This transition is described below. Figure 3 is exemplified in .

[0035] Active clamp state 215 initiates reflexive transition 217 and state transition 219. Reflexive transition 217 indicates that the voltage V CE This monitoring can include the voltage V CE With the indicated voltage V CE The voltage V on the IGBT power switch is compared to a threshold level which has dropped to a level within the safe operating region of the IGBT power switch. State transition 219 is determined by the voltage V on the IGBT power switch. CE The threshold level has dropped to trigger and return the control and drive circuitry to the reduced gate voltage state 210.

[0036] In some embodiments, the functionality for triggering active clamping of the IGBT control and drive circuitry will be active in both the switch on state 205 and the active clamping state 215. Thus, the same functionality already present in the IGBT control and drive circuitry can be used in both states 205, 215. In some embodiments, the gate-emitter voltage V in the active clamping state 215 is GE Same as in the switch on state 205. However, this is not necessarily the case, and the gate-emitter voltage V of the IGBT control and drive circuitry used to drive the power switch GE The magnitude does not need to be the same as the gate-emitter voltage V in the switch on state 205. GE For example, in some embodiments, the gate-emitter voltage V in the active clamp state 215 is GE can be slightly lower than the gate-emitter voltage V in the switch on state 205 GE In view of this potential difference, the switch-on state 205 and the active clamping state 215 are illustrated separately. Furthermore, it is noted that the active clamping function of the IGBT control and drive circuitry will be effective in both the switch-on state 205 and the active clamping state 215.

[0037] The switch disconnect state / fault condition 220 initiates a reflexive transition 222 and a state transition 224. The reflexive transition 222 indicates continuous monitoring for a reset of the fault condition. In the fault condition, the IGBT control and drive circuit system is unable to drive the IGBT power switch into the on state. The reset may be initiated, for example, by a human operator, a delay circuit, or other circuit system indicating that the IGBT power switch is again allowed to be driven into the on state. State transition 224 is triggered by such an indication and transitions the IGBT control and drive circuit system to the switch disconnect state / no fault condition 225.

[0038] Figure 3 3 is a schematic representation of various waveforms 300, 305, 310, 315 during response to detection of a short circuit during driving an IGBT power switch. In particular, waveform 300 converts a reference voltage V D As a function of time, waveform 305 shows the gate-emitter voltage V GE As a function of time, waveform 310 shows the collector current I C is shown as a function of time, and waveform 315 represents the collector-emitter voltage V CE is expressed as a function of time. The range is similar to Figure 1 in the range.

[0039] At the beginning of the illustrated time span, the IGBT is in conduction. The reference voltage V represented by waveform 300 D and the gate-emitter voltage V represented by waveform 305 GE are substantially at their respective maximum levels 320, 325. In addition, the collector current I represented by the waveform 310 C is at level 330, and the collector-emitter voltage V CE At level 335. In general, levels 320, 325 are selected to make the voltage drop across the IGBT relatively small and to reduce conduction losses.

[0040] At time T0, a short circuit condition occurs external to the power switch. The collector current represented by waveform 310 begins to increase rapidly. The overcurrent protection function in the IGBT controller is triggered in response to detecting the short circuit condition. As previously described, after detecting the short circuit condition, the overcurrent protection function in the IGBT controller initiates the process for shutting down the IGBT at time T1. The duration of the delay (i.e., the time between T0 and T1) is the time required to initiate the short circuit protection. Again, the IGBT control and drive circuit system does not initially drive the IGBT with a voltage that switches the IGBT to the off state. Instead, the IGBT control and drive circuit system initially uses a reference voltage V D The IGBT is driven by the reference voltage V DWhen driving the IGBT at level 320, the reference voltage V D Level 340 reduces the charge carrier concentration. Generally speaking, even this lower charge carrier concentration may be sufficient to maintain the IGBT in the on state. Similar to Figure 1 In FIG. 3 , for a common IGBT, voltage level 320 may be, for example, between 20 and 30 volts, and voltage level 340 may be, for example, between 7 and 17 volts.

[0041] The IGBT controller and associated circuitry detects the collector-emitter voltage V CE , and by increasing the gate-emitter voltage V represented by waveform 305 at time T3 GE The increase can be achieved using an active clamping function. For example, as shown below Figure 4 As illustrated in , any clamping of the gate can be removed, and the active clamping function can increase the voltage applied to the gate. In the illustrated embodiment, the gate-emitter voltage V GE At time T3, the gate-emitter voltage V increases to the same level as the on state 320 in a step-like transition over the illustrated time range. This is not necessarily the case. For example, in other embodiments, the gate-emitter voltage V GE can be increased to a level between levels 340 and 320. As another example, in some embodiments, the gate-emitter voltage V GE The increase can be more gradual, for example, with a collector-emitter voltage V CE Customize or adjust the rate of change.

[0042] Regardless of the gate-emitter voltage V GE The details of how additional charge carriers are introduced into the channel of the IGBT power switch and the collector current I C In other words, the collector-emitter voltage V CE The increase in the level of the switched voltage by 360° is proportional to the stray inductance of the commutation loop and the rate of change of the current through the IGBT power switch. By introducing additional charge carriers into the channel of the IGBT power switch, the collector current I C and the collector-emitter voltage V CE However, due to the collector-emitter voltage V CE At a lower and therefore safer level, there is no danger of the IGBT exiting the safe operating area.

[0043] At time T4, the collector-emitter voltage V represented by waveform 315 is CEThe IGBT controller and associated circuitry can monitor the collector-emitter voltage V CE , and in response to the drop, the gate voltage can be lowered again to a voltage level that reduces the charge carrier concentration in the channel and causes the forward voltage drop of the channel to be higher than that with the gate-emitter voltage V GE Voltage drop when driven horizontally at 325.

[0044] IGBT controllers and associated circuitry can sense the collector-emitter voltage V in several different ways. CE For example, in some embodiments, a transient voltage suppressor in an active clamping circuit system coupled to the collector of an IGBT power switch can passively monitor the collector-emitter voltage V CE If the collector-emitter voltage V CE If the collector-emitter voltage V rises above the breakdown voltage of the transient voltage suppressor diode associated with the IGBT power switch, the active clamping circuitry can use the current drawn from the collector to increase the gate bias, and additional charge carriers can be introduced into the channel of the IGBT power switch. CE When it falls below the threshold, the feedback from the collector of the IGBT power switch stops and the gate voltage is reduced. Other approaches are also possible.

[0045] In the illustrated embodiment, the IGBT control and drive circuitry operates at the same reference voltage V as during the time span between T1 and T3. D Level 340 drives the IGBT. However, this is not necessarily the case, and other reference voltages V below or above level 320 may be used. D The gate-emitter voltage V represented by waveform 305 is GE The reference voltage V shown in waveform 300 is D Descending more slowly.

[0046] In some cases, desaturation of the IGBT power switch will be detected and the collector current I C A level will be reached where it is safe to drive the IGBT into the off state. In some embodiments, this is a steady-state desaturation condition. In response, the IGBT control and drive circuitry switches the IGBT to the off state with a (typically negative) gate-emitter voltage V that is low enough to switch the IGBT to the off state. GE The level 375 drives the IGBT.

[0047] However, in the illustrated embodiment, the collector current I CBefore reaching this level, the collector-emitter voltage V shown in waveform 315 CE The IGBT controller and associated circuitry detects the collector-emitter voltage V CE and at time T5, by allowing the reference voltage V represented by waveform 300 to D is increased in response. Again, an approximately step-like transition to level 320 is shown, but this is not required. Additional charge carriers are introduced into the channel of the IGBT, and the collector current I C The rate of decrease of is reduced. In addition, the collector-emitter voltage V represented by waveform 315 CE Start to descend.

[0048] At time T6, the collector-emitter voltage V represented by waveform 315 is CE has fallen again to a point where it is unlikely that the IGBT will exit the safe operating area. The IGBT control and drive circuitry can monitor the collector-emitter voltage V CE , and in response to the drop, the gate-emitter voltage V GE to a voltage level that reduces the charge carrier concentration in the channel and causes a higher forward voltage drop in the channel than when driven with level 325. The gate-emitter voltage V represented in waveform 305 GE will also be reduced.

[0049] As mentioned before, the expected gate-emitter voltage V GE is close to level 355. In addition, during a longer period (here, between T6 and T7), the collector current I C A level will be reached at which the IGBT can be safely driven into the off state. In some cases, this level is a steady-state level determined by the applied gate voltage, the level of the voltage being switched 360, temperature, and other factors. In any case, the desaturation protection circuitry can detect the desaturation of the IGBT power switch, and at T7, in response, the IGBT control and drive circuitry will switch the IGBT to the off state with a (typically negative) gate-emitter voltage V GE Level 365 to drive the IGBT.

[0050] Again, the gate-emitter voltage V represented by waveform 305 GE The reference voltage V in waveform 300 is D Falls more slowly. Collector current I CIt falls relatively quickly during this transition and will fall to approximately zero when the IGBT reaches the off state. C The rapid change of collector-emitter voltage V CE may momentarily exceed the level of the switched voltage by 360. Ultimately, the collector-emitter voltage V CE Will stabilize at the level 360 of the switched voltage.

[0051] Figure 4 is a schematic representation of circuitry 400 that is involved in responding to the detection of a short circuit during driving of an IGBT power switch. Circuitry 400 includes the IGBT power switch 405 itself, as well as drive circuitry 410 , IGBT controller 415 , and short circuit detection and protection circuitry 420 .

[0052] The IGBT power switch 405 is illustrated as an n-channel device and includes a collector coupled to a node 407, an auxiliary emitter coupled to an internal parasitic inductance 425 (i.e., a bond wire between the auxiliary emitter and the main emitter), and a main emitter node 409. Typically, the IGBT power switch 405 will be able to withstand relatively high voltages, such as voltages between 600 and 6500 volts. The IGBT power switch 405 can be part of any of a number of different devices in different operating environments. For example, the IGBT power switch 405 will typically be part of a half-bridge topology, such as part of a phase leg in an inverter, part of a motor drive, or part of a switch-mode power converter.

[0053] The driver circuitry 410 is coupled to the gate of the IGBT power switch 405. In the illustrated embodiment, the driver circuitry includes a pull-up transistor 430, a pull-down transistor 435, and an associated resistor that acts as a gate resistor for the IGBT power switch 405. Other embodiments are possible, including, for example, using additional voltage levels, transistors, and a single gate resistor. For example, in some embodiments, two or more pull-up transistors may be provided to bias the gate of the IGBT power switch 405 to different levels (e.g., levels 320, 340, etc.). Figure 3 )). In response to the on signal, the pull-down transistor 435 is turned off and the pull-up transistor 430 is switched into conduction and forms a conductive path between the supply voltage 412 and the gate of the IGBT power switch 405. In the illustrated embodiment, the supply voltage 412 has a fixed level relative to the auxiliary emitter node 411. The level of the supply voltage 412 is selected to make the voltage drop across the IGBT power switch 405 relatively small. Figure 1 and Figure 3 In this case, the supply voltage 412 is at levels 115 and 320.

[0054] In response to the disconnect signal, the pull-up transistor 430 is turned off and the pull-down transistor 435 is switched into conduction and forms a conductive path between the supply voltage 414 and the gate of the IGBT power switch 405. In the illustrated embodiment, the voltage provided by the supply voltage 414 has a negative level relative to the auxiliary emitter node 411. Figure 1 and Figure 3 In the case of , the supply voltage 414 is at the levels 145, 150 and at the levels 375, 365. Furthermore, the IGBT controller 415 is configured to ensure that the transistors 430, 435 are not switched into conduction at the same time.

[0055] The IGBT controller 415 is a controller configured to control the switching of the IGBT power switch 405. The IGBT controller 415 includes a V CE Sense terminal 440 and participate in active clamping function 445. V CE The sensing terminal 440 is coupled to the IGBT power switch 405 to sense the collector-emitter voltage V CE .

[0056] The active clamping function 445 is configured to slow down the transition of the IGBT power switch 405 into the off state in the event of a collector-emitter overvoltage and to suppress transient voltages that would be generated due to rapid changes in the collector current. In the illustrated embodiment, the active clamping function 445 includes a DC path for charging the gate of the IGBT power switch 405 using the voltage on the collector of the IGBT power switch 405, and functions internal to the IGBT controller 415. The illustrated embodiment of the DC path includes a Zener diode 450 (or similar device) and a diode 455 for charging the gate of the IGBT power switch 405 using the voltage on the collector of the IGBT power switch 405, and functions internal to the IGBT controller 415. For example, in some embodiments, the active clamping function 445 may include circuitry to reduce the current flowing through the pull-down transistor 435 in response to detecting a collector overpotential. By reducing this current, the gate of IGBT power switch 405 can be charged faster via Zener diode 450 (or similar device) and diode 455 .

[0057] Furthermore, in the illustrated embodiment, active clamping function 445 includes an output terminal 460 coupled to control switches in short circuit detection and protection circuitry 420. During active clamping, clamping circuitry 475 will be disabled and the gate voltage will be allowed to increase.

[0058] The embodiment of the short circuit detection and protection circuit system 420 shown schematically includes a comparator 470, a clamp circuit system 475, and a switch 480. The comparator 470 is coupled to compare the voltage across the inductor 425 with a reference voltage V R The voltage across the inductor 425 indicates the collector current I C In real-world implementations, detection of a short circuit condition will typically involve other components and functions. For example, blanking circuitry will be used to eliminate the collector current I during the on period. C high rate of change.

[0059] Additionally, for didactic purposes, the battery is shown as providing a reference voltage V relative to reference voltage 409. R This is not necessarily the case, and generally, the reference voltage V R In some embodiments, the reference voltage V R It may be set by a user, for example, based on a safe operating area or other characteristics of the IGBT power switch 405 and / or an operating environment of the IGBT power switch 405 .

[0060] The clamping circuit system 475 is configured to reversibly clamp the gate voltage of the IGBT power switch 405 to a maximum value. For example, the clamping circuit system 475 can clamp the voltage applied to the gate of the IGBT power switch 405 at levels 130, 340 ( Figure 1 , Figure 3 ). Clamping circuitry 475 thus forms a dynamic voltage suppressor and, in the illustrated embodiment, includes a Zener diode (or similar device) and a transistor switch. In the illustrated embodiment, the maximum value of the gate voltage of the IGBT power switch 405 will be set by the breakdown voltage of the Zener diode (or similar device) and the voltage drop across the transistor switch. The transistor switch can be switched to conduct and not conduct to reversibly clamp and unclamp the gate voltage.

[0061] Switch 480 may be switched by IGBT controller 415 to allow or prevent comparator 470 from clamping the gate voltage of IGBT power switch 405 using clamp circuitry 475 .

[0062] In operation, the IGBT controller 415 can control the transistors 430, 435 so that the IGBT power switch 405 is in an on state. The short circuit detection and protection circuit system 420 can be configured to detect the short circuit by setting the collector current I C The rate of change of the threshold reference voltage V R Comparison is performed to detect a short circuit. In the event of a short circuit being detected, the comparator 470 may output a signal that:

[0063] - turning off the pull-up transistor 430, and

[0064] - Bias clamp circuitry 475 to clamp the gate voltage of the IGBT power switch 405 .

[0065] In state diagram 200( Figure 2 ), this corresponds to state transition 209. If clamping continues, the actual gate-emitter voltage V GE The voltage level 412 will eventually drop to the clamping level (i.e., below the voltage level supplied by the power supply voltage 412), and the number of charge carriers present in the channel of the IGBT power switch 405 will decrease. In the event that the IGBT power switch 405 reaches the desaturation level, it can be safely driven into the off state, and the IGBT controller 415 can control the transistors 430, 435 to transition the IGBT power switch 405 into the off state. In the state diagram 200 ( Figure 2 ), this corresponds to state transition 213.

[0066] In some cases, even though the gate voltage is clamped, the IGBT controller 415 will CE Sense terminal 440 detects overvoltage. In these cases, active clamp function 445 outputs a signal through terminal 460 that opens switch 480 and prevents comparator 470 from clamping the gate voltage of IGBT power switch 405. In the absence of clamping, the gate of IGBT power switch 405 would rise due to the charge provided by active clamp function 445 (e.g., via Zener diode 450 (or similar device) and resistor 455). In state diagram 200 ( Figure 2 ), this corresponds to state transition 214.

[0067] After desaturation is detected and the collector current I C Having now dropped to a level where it is safe to drive the IGBT power switch 405 into the off state, the IGBT controller 415 can control transistors 430, 435 to transition the IGBT power switch 405 into the off state, corresponding to state transition 213. In the event of an overvoltage reappearing on the IGBT power switch 405, the active clamping function 445 will resume active clamping, corresponding to state transition 214.

[0068] The transition between the gate voltage of the clamped IGBT power switch 405 and the gate voltage increased due to active clamping can continue until the collector current I C drops to a level where it is safe to drive the IGBT power switch 405 into the off state, corresponding to state transition 213 .

[0069] A number of implementations have been described. However, it will be appreciated that various modifications may be made. Accordingly, other implementations are within the scope of the following claims.

[0070] In addition, the present invention can also be implemented through one or more of the following embodiments.

[0071] Embodiment 1. A control system for a power switch having a channel, the system comprising: a short-circuit detection circuit system configured to detect an external short circuit; an overvoltage detection circuit system configured to detect an overvoltage on the power switch; and a short-circuit protection circuit system configured to: when the power switch is in a first on-state, in response to the short-circuit detection circuit system detecting an external short circuit, change the control terminal of the power switch from a first potential level providing a charge carrier concentration in the channel of the power switch to a second potential level, wherein the second potential level reduces the charge carrier concentration in the channel; and when the control terminal of the power switch is at the second potential level, in response to the overvoltage detection circuit system detecting an overvoltage on the power switch, change the control terminal of the power switch from the second potential level to a third potential level, wherein the third potential level increases the charge carrier concentration in the channel.

[0072] Embodiment 2. A control system according to embodiment 1, wherein the short circuit detection circuit system is configured to detect an external short circuit condition based on a time rate of change of current in the power switch.

[0073] Embodiment 3. A control system according to embodiment 1 or 2, wherein the short circuit protection circuit system includes an active clamping circuit system, and the active clamping circuit system is configured to: slow down the transition of the power switch to the off state in response to detecting an overvoltage.

[0074] Embodiment 4. The control system of Embodiment 3, wherein the active clamp circuitry is configured to charge a control terminal of the power switch using a voltage switched by the power switch.

[0075] Embodiment 5. A control system according to any one of Embodiments 1 to 4, wherein the short-circuit protection circuit system includes a switchable clamp, and the switchable clamp is configured to clamp the control terminal of the power switch at the second potential level.

[0076] Embodiment 6. A control system according to embodiment 5, wherein the short-circuit protection circuit system includes an active clamping circuit system, and the active clamping circuit system is configured to slow down the transition of the power switch, wherein the short-circuit protection circuit system is configured to terminate or reduce the clamping of the control terminal of the power switch to slow down the transition.

[0077] Embodiment 7. A control system according to any one of embodiments 1 to 6, wherein the short-circuit protection circuit system is configured to: clamp the control terminal of the power switch in response to the short-circuit detection circuit system detecting the external short circuit.

[0078] Embodiment 8. A control system according to embodiment 7, wherein the short-circuit protection circuit system includes an active clamping circuit, and the active clamping circuit system is configured to slow down the transition of the power switch, wherein the short-circuit protection circuit system is configured to terminate or reduce the clamping of the control terminal of the power switch to slow down the transition.

[0079] Embodiment 9. A control system according to any one of Embodiments 1 to 8, wherein the third potential level is the first potential level.

[0080] Embodiment 10. A control system according to any one of embodiments 1 to 9, wherein: the power switch is an IGBT power switch; the voltage level of the first potential level is between 20 and 30 volts; and the voltage level of the second potential level is between 7 and 17 volts.

[0081] Embodiment 11. A control system according to any one of Embodiments 1 to 10, wherein when the control terminal is at the second potential level, the power switch remains in the second on-state.

[0082] Embodiment 12. A control system according to any one of embodiments 1 to 11, wherein the short-circuit protection circuit system is further configured to: in response to detecting desaturation of the power switch, change the control terminal of the power switch circuit to a fourth potential level, wherein the fourth potential level reduces the charge carrier concentration in the channel and switches the power switch to an off state.

[0083] Embodiment 13. A method for controlling a power switch, the method comprising: biasing the power switch in an on state to provide a first carrier concentration in a channel of the power switch; while biasing the power switch to provide the first carrier concentration, detecting an external short circuit, the external short circuit increasing a current flowing through the power switch; in response to detecting the external short circuit, biasing the power switch to provide a second carrier concentration in the channel of the power switch, wherein the second carrier concentration is less than the first carrier concentration; while biasing the power switch to provide the second carrier concentration, detecting an overvoltage on the power switch; in response to detecting the overvoltage, biasing the power switch to provide a third carrier concentration in the channel of the power switch, wherein the third carrier concentration is greater than the second carrier concentration.

[0084] Embodiment 14. The method according to Embodiment 13 further includes: detecting that the voltage on the power switch has dropped to a threshold level during the period when the power switch is biased to provide the third carrier concentration; and biasing the power switch to provide a fourth carrier concentration in the channel of the power switch, wherein the fourth carrier concentration is less than the third carrier concentration.

[0085] Embodiment 15. The method according to embodiment 14 also includes: repeatedly biasing the power switch to: first, provide a higher carrier concentration in response to detecting an overvoltage, and then, provide a lower carrier concentration in response to detecting that the voltage on the power switch has dropped to the threshold level.

[0086] Embodiment 16. A method according to any one of Embodiments 13 to 15, wherein the potential level for providing the first carrier concentration and the potential level for providing the third carrier concentration are the same, and the potential level for providing the second carrier concentration and the potential level for providing the fourth carrier concentration are the same.

[0087] Embodiment 17. A method according to any one of Embodiments 13 to 16, wherein detecting the external short circuit includes detecting that a time rate of change of the current flowing through the power switch exceeds a threshold.

[0088] Embodiment 18. A method according to any one of Embodiments 13 to 17, wherein: biasing the power switch to provide the second carrier concentration includes clamping the control terminal of the power switch to a voltage level; and biasing the power switch to provide the third carrier concentration includes unclamping the control terminal of the power switch from the voltage level.

[0089] Embodiment 19. A method according to any one of Embodiments 13 to 18, wherein biasing the power switch to provide the third carrier concentration includes biasing a control terminal of the power switch using a voltage switched by the power switch.

[0090] Embodiment 20. A method according to any one of Embodiments 13 to 19, wherein: the power switch is an IGBT power switch; the first carrier concentration is provided by a gate-emitter voltage between 20 and 30 volts; and the second carrier concentration is provided by a gate-emitter voltage between 7 and 17 volts.

[0091] Embodiment 21. The method of any one of Embodiments 13 to 20, wherein the switch remains in an on state at the second carrier concentration and the third carrier concentration.

[0092] Embodiment 22. The method according to any one of Embodiments 13 to 21 further includes: detecting desaturation of the power switch; and in response to detecting desaturation of the power switch, biasing the power switch to an off state.

Claims

1. A control system for a power switch having a channel, the system comprising: a short circuit detection circuit system configured to detect an external short circuit; an overvoltage detection circuit system configured to detect an overvoltage on the power switch; as well as The short circuit protection circuit system is configured as follows: in response to the short circuit detection circuitry detecting an external short circuit when the power switch is in a first on-state, changing a control terminal of the power switch from a first potential level providing a charge carrier concentration in a channel of the power switch to a second potential level, wherein the second potential level reduces the charge carrier concentration in the channel; as well as When the control terminal of the power switch is at the second potential level, in response to the overvoltage detection circuit system detecting an overvoltage on the power switch, the control terminal of the power switch is changed from the second potential level to a third potential level, and the third potential level increases the charge carrier concentration in the channel. 2 . The control system of claim 1 , wherein the short circuit detection circuitry is configured to detect an external short circuit condition based on a time rate of change of current in the power switch.

3. The control system of claim 1, wherein the short circuit protection circuitry includes active clamp circuitry configured to slow down a transition of the power switch to an off state in response to detecting an overvoltage. 4 . The control system of claim 3 , wherein the active clamp circuitry is configured to charge a control terminal of the power switch using a voltage switched by the power switch. 5 . The control system of claim 1 , wherein the short circuit protection circuitry comprises a switchable clamp configured to clamp a control terminal of the power switch at the second potential level.

6. The control system of claim 5, wherein the short circuit protection circuit system includes an active clamp circuit system configured to slow down the transition of the power switch, wherein the short circuit protection circuit system is configured to terminate or reduce the clamping of the control terminal of the power switch to slow down the transition.

7. The control system of claim 1, wherein the short circuit protection circuitry is configured to clamp a control terminal of the power switch in response to the short circuit detection circuitry detecting the external short circuit.

8. The control system of claim 7, wherein the short circuit protection circuit system includes an active clamp circuit system configured to slow down the transition of the power switch, wherein the short circuit protection circuit system is configured to terminate or reduce the clamping of the control terminal of the power switch to slow down the transition.

9. The control system of claim 1, wherein the third potential level is the first potential level.

10. The control system of claim 1, wherein: The power switch is an IGBT power switch; The voltage level of the first potential level is between 20 and 30 volts; and The voltage level of the second potential level is between 7 and 17 volts.

11. The control system of claim 1, wherein when the control terminal is at the second potential level, the power switch remains in a second conductive state.

12. The control system of claim 1 , wherein the short circuit protection circuit system is further configured to, in response to detecting desaturation of the power switch, change a control terminal of the power switch circuit to a fourth potential level, wherein the fourth potential level reduces a charge carrier concentration in the channel and switches the power switch to an off state.

13. A method for controlling a power switch, the method comprising: biasing the power switch in an on state to provide a first carrier concentration in a channel of the power switch; detecting an external short circuit while biasing the power switch to provide the first carrier concentration, the external short circuit increasing a current flowing through the power switch; In response to detecting the external short, biasing the power switch to provide a second carrier concentration in a channel of the power switch, wherein the second carrier concentration is less than the first carrier concentration; detecting an overvoltage on the power switch during biasing the power switch to provide the second carrier concentration; In response to detecting the overvoltage, the power switch is biased to provide a third carrier concentration in a channel of the power switch, wherein the third carrier concentration is greater than the second carrier concentration.

14. The method according to claim 13, further comprising: detecting that a voltage across the power switch has dropped to a threshold level during biasing the power switch to provide the third carrier concentration; as well as The power switch is biased to provide a fourth carrier concentration in a channel of the power switch, wherein the fourth carrier concentration is less than the third carrier concentration.

15. The method according to claim 14, further comprising: The power switch is repeatedly biased to first provide a higher carrier concentration in response to detecting an overvoltage, and then provide a lower carrier concentration in response to detecting that the voltage across the power switch has dropped to the threshold level.

16. The method of claim 14, wherein a potential level providing the first carrier concentration and a potential level providing the third carrier concentration are the same, and a potential level providing the second carrier concentration and a potential level providing the fourth carrier concentration are the same. 17 . The method of claim 14 , wherein detecting the external short circuit comprises detecting a time rate of change of current flowing through the power switch exceeding a threshold value.

18. The method of claim 14, wherein: Biasing the power switch to provide the second carrier concentration includes clamping a control terminal of the power switch to a voltage level; and Biasing the power switch to provide the third carrier concentration includes de-clamping a control terminal of the power switch from the voltage level.

19. The method of claim 14, wherein biasing the power switch to provide the third carrier concentration comprises biasing a control terminal of the power switch using a voltage switched by the power switch.

20. The method of claim 14, wherein: The power switch is an IGBT power switch; The first carrier concentration is provided by a gate-emitter voltage between 20 and 30 volts; and The second carrier concentration is provided by a gate-emitter voltage between 7 and 17 volts.

21. The method of claim 13, wherein the switch remains in an on state at the second carrier concentration and the third carrier concentration.

22. The method of claim 13, further comprising: detecting desaturation of the power switch; as well as In response to detecting desaturation of the power switch, the power switch is biased into an off state.

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