Patent Description:
Power transistor based switches are used in various applications to switch high currents or high voltages, for example to selectively couple a load to a power source like a supply voltage. Such switches may be provided with single power transistors, or as combinations of transistor and diode (for example an insulated gate bipolar transistor, IGBT, with anti-parallel freewheeling diode) or as combinations of several transistors, for example two power transistors in a half bridge configuration. Other combinations are also possible. Power transistors may be made up of a plurality of transistor cells coupled in series or in parallel to support high currents, for example several amperes, or high voltages.

In many applications, a short circuit protection for such power transistors is required. A short circuit may refer to a condition where the power transistors, in a switched on state, couples a very small load (e.g. only a few Ohms) to a power supply, for example a short circuit by a simple wire or other metal connection). In such a short circuit case, the current flowing through the power transistor can become very large, leading for example to heating or damaging of the power transistor. Furthermore, also other parts of an electronic circuit may be damaged by the high current.

For insulated gate bipolar transistors, a conventional approach for short circuit monitoring is referred to as desaturation (desat) detection. This, however, may be too slow in some cases, i.e. detection of the short circuit and subsequent switching off of the power transistor may take too long. Furthermore, this approach may limit performance of the power transistor and requires additional components outside a package of the power transistor like diodes, which require space and may lead to parasitic effects.

<CIT> and <CIT> disclose semiconductor devices which include an overcurrent limiting protection.

A switch module as defined in claim <NUM>, a driver circuit as defined in claim <NUM> and a method as defined in Claim <NUM> are provided. The dependent claims defined further embodiments as well as systems including a switch module and a driver circuit.

In the following, various embodiments will be described in detail referring to the attached drawings. These embodiments are to be understood as examples only and are not to be construed as limiting. For example, while embodiments may be described as comprising specific features (for example elements, components, devices, acts, events), in other embodiments some of these features may be omitted or may be replaced by alternative features. In addition to the features explicitly shown and described, additional features may be provided, for example features conventionally used in switch modules, driver circuits or systems and methods associated therewith.

Some embodiments relate to a switch module. A switch module is a device including one or more transistor switches. A switch module may be provided as a single package, with a single housing or integrated on a single chip. For example, one or more chips may be provided in a single package.

A transistor switch is a switch based on a transistor or several transistors. In some embodiments, the transistor may be a power transistor designed for switching high currents or voltages, for example currents of several amperes or voltages of several <NUM> V or even <NUM> V or above. However, in other embodiments the transistor switch may also be designed for lower voltages or currents, depending on the application. The term "switch" in transistor switch refers to the fact that the transistor switch is intended to be used as a switch in either an on state or an off state, for example in contrast to transistors used in a linear range.

Transistor switches, as mentioned already in the background may be made up of a plurality of transistor cells coupled in series or in parallel.

Transistor switches are described as comprising a control terminal, a first load terminal and a second load terminal. By applying a control signal to the control terminal, the transistor switch may be switched on or off. A transistor switch is switched on or in an on-state when it provides a low-ohmic connection between its first and second load terminal, and is switched off when it essentially provides an electric isolation (apart from very small leakage currents, which may occur in real implementations) between its first and second load terminals.

Various types of transistors may be used for transistor switches. Examples include field effect transistors (FETs) like metal oxide semiconductor field effect transistors (MOSFETs), bipolar junction transistors (BJTs) or insulated gate bipolar transistors (IGBTs). Transistors may be based on various semiconductor materials like Silicon (Si), Silicon Carbide (SiC) or III-V compounds like Gallium Arsenide. For example, a SiC MOSFET may be used in some embodiments.

In case of a field effect transistor, the control terminal is a gate terminal, the first load terminal is a source terminal and the second load terminal is a drain terminal. In case of a bipolar junction transistors, the control terminal is a base terminal, the first load terminal is an emitter terminal and the second load terminal is a collector terminal. In case of an insulated gate bipolar transistor, the control terminal is a gate terminal, the first load terminal is an emitter terminal and the second load terminal is a collector terminal.

The switch module may include a single transistor switch, but may also include more than one transistor switch, for example two transistor switches in a half bridge or other configuration. In other embodiments, more than two transistor switches, for example four or six transistor switches, may be provided, which may be arranged in pairs to form half bridge configurations, for example for driving different phases of an electric motor. Different transistor switches in a switch module may be of the same type or of different types (for example only IGBTs, or a MOSFET together with an IGBT, etc.). In the following, for ease of explanations, switch modules with a single transistor switch will be discussed. However, it is to be understood that the techniques discussed herein are also applicable to switch modules including more than one transistor switches. In this sense, the reference to "a transistor switch" as used herein is to be construed as referring to one or more transistor switches.

A control signal for turning a transistor switch of a switch module on or off may be supplied by a driver circuit. Such a driver circuit may be provided separately to the switch module, for example on a separate chip, in a separate housing, integrated within another electronic circuit etc..

<FIG> illustrates a system according to an embodiment including a switch module <NUM> and a driver circuit <NUM>. Such a system may be referred to as an intelligent power module. Switch module <NUM> comprises a transistor switch <NUM>. Transistor switch <NUM> in the example of <FIG> is an insulated gate bipolar transistor (IGBT) with a freewheeling diode. As mentioned above, this is given only as an example, and other types of transistor switches and/or more than one transistor switch may be provided in a switch module <NUM>, for example a SiC-based MOSFET. A gate terminal of transistor switch <NUM> is coupled to an external gate terminal G of switch module <NUM>, a collector terminal of transistor switch <NUM> is coupled to an external collector terminal C of switch module <NUM> and an emitter terminal of transistor switch <NUM> is coupled to an external emitter terminal E and an external auxiliary emitter terminal E' of switch module <NUM>. External terminals G, C, E and E' are "external" terminals of switch module <NUM> in the sense that via these terminals switch module <NUM> may be coupled to other devices. Such external terminals may for example be realized as pins of a package.

In some embodiments, external terminals G, C, E and E' are the only external terminals of switch module <NUM>, or, more generally speaking, all external terminals of switch module <NUM> are coupled to the low terminals or control terminals of the transistor switch or transistor switches of switch module <NUM> (in this case to gate, collector and emitter terminals of transistor switch <NUM>). In some embodiments, in particular no separate terminals for supplying a short detection circuit <NUM> to be described later or additional terminals for outputting a signal indicating a short circuit are provided. In some embodiments, as in conventional switch modules additional measurement circuitry, for example a temperature measurement device like a temperature dependent resistor or thermistor, may be provided in switch module <NUM> and accessed via separate external terminals. Such separate external terminals, if provided, in some embodiments are independent from the terminals related to the components shown in <FIG> and in particular are not related to the short circuit detection described herein.

In operation, for example to supply a load selectively with power, external collector terminal C may be coupled to a supply voltage, and external emitter terminal E may be coupled to a load. A control signal CTRLCTRL is supplied to driver circuit <NUM>, which controls transistor switch <NUM> by applying a corresponding gate signal at external terminal G via a gate resistor RG, ext such that a corresponding gate emitter voltage (between terminals G and E') switches transistor switch <NUM> on or off, as demanded by control signal CTRL. Driver circuit <NUM> in the embodiment of <FIG> is supplied by positive supply voltages VCC1, VCC2.

Furthermore, switch module <NUM> comprises a short circuit detection circuit <NUM>. In the embodiment of <FIG>, short circuit detection circuit <NUM> receives an indication of a current through transistor switch <NUM> via a line <NUM>. An indication of the current refers to any signal indicative of the current through transistor switch <NUM>. Based on this indication of the current, also referred to as load current, short circuit detection circuit <NUM> detects whether a short circuit state is present at the load terminals of switch module <NUM>. Such a short circuit state for example would be present if collector terminal C is connected to a supply voltage, and then emitter terminal E is short-circuited to ground, i.e. connected to ground via a low ohmic connection like a wire or other comparatively low resistance. It should be noted that a short circuit state in this sense may still include some resistance, for example a resistance of a few Ohms. Generally, a short circuit state refers to a condition which could cause higher currents through transistor switch <NUM> than transistor switch <NUM> is designed for.

Short circuit detection circuit <NUM> may for example detect a short circuit state by comparing the indication by the current received to a threshold value, and if the comparison shows that the current exceeds the threshold, this corresponds to a short circuit detection. In other embodiments, a short circuit state may be detected if the indication indicates a fast rising current. When a short circuit is detected, short circuit detection circuit <NUM> electrically couples a line <NUM> connected to the gate terminal of transistor switch <NUM> to a line <NUM> coupled to the emitter terminal of switch device <NUM>. This electric coupling causes a gate emitter voltage to drop, which switches switch <NUM> off. Such an electric coupling between lines <NUM>, <NUM> may essentially short-circuit in lines <NUM>, <NUM> or may couple lines <NUM>, <NUM> with a resistor sufficiently low-ohmic to allow the drop of the gate emitter voltage.

In the embodiment of <FIG>, short circuit detection circuit <NUM> does not receive a separate supply voltage, which would for example have to be supplied via additional external terminals of switch module <NUM>, but is supplied by the gate emitter voltage via lines <NUM>, <NUM>. In this respect, it should be noted that when the gate emitter voltage is low, transistor switch <NUM> is off, such that no short circuit monitoring is required (as transistor switch <NUM> is switched off anyway). On the other hand, to switch transistor switch <NUM> on, a sufficiently high gate emitter voltage has to be supplied, which then is able to also supply short circuit detection circuit <NUM>.

<FIG> shows a system according to a further embodiment, which is a variation of the system of <FIG>. Apart from the differences described in the following, the above explanations for <FIG> also apply to <FIG>, and corresponding elements bear the same reference numerals and will not be described again.

Switch module <NUM> of <FIG> comprises an external auxiliary collector terminal C' coupled to the collector terminal of switch transistor <NUM>. Driver circuit <NUM> is coupled to external auxiliary collector terminal C' via a resistor RDESAT and a Diode DDESAT. A capacitor CDESAT is coupled as shown between Resistor RDESAT and external auxiliary emitter terminal E'. As will be explained further below, this in some embodiments allows a conventional desaturation based short circuit detection by driver circuit <NUM>.

An example implementation of short circuit detection circuit <NUM> is illustrated in <FIG>. Other implementations are also possible.

In the example of <FIG>, short circuit detection circuit <NUM> includes a diode <NUM> coupled to line <NUM> which prevents reverse currents. Line <NUM> is coupled to a voltage supply <NUM> which provides a voltage to a detector/driver circuit <NUM>, when the gate emitter voltage between lines <NUM> and <NUM> is large enough, for example at least in the range of a threshold voltage necessary for switching transistor switch <NUM> on. A buffer capacitor <NUM> is coupled between voltage supply <NUM> and detector/driver circuit <NUM>.

Detector/driver circuit <NUM> receives the indication of the current from line <NUM> to detect the short circuit state. In some implementations, detector/driver circuit <NUM> may include a comparator to compare the indication of the current to a threshold value, and if the threshold value is exceeded, a short circuit is detected. Additionally or alternatively, detector/driver circuit <NUM> may include a differentiator in combination with a comparator, to detect fast increases of the current, in a range typical for a short circuit. When a short circuit is detected, detector/driver circuit controls a transistor <NUM> to be switched on, which couples lines <NUM>, <NUM> and therefore, gate and emitter terminals of transistor switch <NUM>, via a resistor <NUM>. Resistor <NUM> may for example have a resistance value such that the gate emitter voltage drops in case of a short circuit and transistor switch <NUM> is switched off. For example, the resistance value may be selected depending on gate resistor RG, ext, an on-resistance Rds, on of transistor <NUM> and an internal resistance of driver <NUM> such that when transistor <NUM> is switched on, the gate-emitter voltage of transistor switch <NUM> is lower than the threshold voltage of transistor switch <NUM>, but high enough for voltage supply <NUM> to still receive sufficient voltage to maintain operation of short circuit detection circuit <NUM>.

Furthermore, as will be explained later, driver circuit <NUM> in some embodiments may include an additional short circuit detection. In this case, short circuit detection <NUM> enables a short reaction time for short circuit detection, for example below <NUM>, to switch off transistor switch <NUM> quickly. After some more time, for example <NUM>, the short circuit driver circuit <NUM> "takes over". However, as a short circuit detection and handling is already provided within switch module <NUM>, in other embodiments driver circuit <NUM> need not include a short circuit detection.

Next, possible implementations for obtaining an indication of a current on line <NUM> will be explained with reference to <FIG>.

<FIG> shows a case where a sense transistor is used to sense the current. As indicated by a second emitter <NUM>, a small proportion of the active area of transistor switch <NUM> is provided as separate emitter terminal (or source terminal in the case of field effect transistors) such that via line <NUM> a current proportional to the current between external collector terminal C and external emitter terminal E, but much smaller, is provided. Any conventional implementations of such sense transistors may be used. The current thus provided on line <NUM> may then be measured by detector/driver circuit <NUM>, for example as a voltage drop over a measurement resistor.

<FIG> shows a contactless measurement device <NUM> for measuring the current. Such contactless measurement devices may for example measure the current based on a magnetic field generated by the current. In this case, the measurement device may include a Hall sensor, a magnetoresistive sensor or any other kind of magnetic field sensor. A signal representing the magnetic field thus sensed, which may be proportional to the current, is provided on line <NUM> and then evaluated in detector/driver circuit <NUM>.

In <FIG>, a measurement resistor <NUM> is coupled in series to the transistor of transistor switch <NUM>, and a voltage job over resistor <NUM> is provided on line <NUM> as indication of the current. This approach is for example applicable to low power application.

As <FIG> show, various approaches for obtaining the indication of the current may be used.

Next, operation of driver circuit <NUM> according to some embodiments will be discussed in more detail. Examples for a driver circuit <NUM> including various features which may be used independently, but also in combination, are shown in <FIG> and <FIG>.

During normal operation (when no short circuit is present) driver circuit <NUM> may operate as and be implemented as a conventional driver circuit for driving transistor switches. For example, in some implementation, driver circuit <NUM> may include a push-pull-driver including transistors T1, T2 and a controller <NUM> driving transistors T1, T2 based on control signal CTRL to output a signal to gate terminal G.

Additionally, in embodiments driver circuit <NUM> provides short circuit detection. In some implementations, a conventional driver circuit using short circuit detection based on desaturation, as mentioned above, may be used. In the examples of <FIG> and <FIG>, such a desaturation based detection is performed using a current source <NUM> providing a current IDESAT and a comparator <NUM> receiving, at one input, the current IDESAT combined with a signal from auxiliary emitter terminal C' of switch device <NUM> via diode DDESAT and resistor RDESAT as shown in <FIG>, and, at another input, a reference voltage VREF_DESAT. Essentially, in this case a short circuit is detected based on a temporary voltage rise between the external auxiliary collector terminal C' and the external auxiliary emitter terminal E'. Based on an output of comparator <NUM>, controller <NUM> detects a short circuit and switches off transistor switch <NUM> in response to the detection of a short circuit. For this measurements, as in conventional desaturation measurements, as mentioned initially, the additional circuit elements of <FIG>, i.e. diode DDESAT, resistor RDESAT and capacitor CDESAT are required. While short circuit detection by desaturation measurement is, as mentioned, slow, inter alia due to the charging of capacitor CDESAT, compared to the fast short circuit detection and switching off of transistor switch <NUM> provided by short circuit detection circuit <NUM>, this slower short circuit detection by driver <NUM> in some embodiments essentially does not negatively impact the performance of the system of <FIG> in case of short circuits.

In other cases, instead of a conventional driver circuit <NUM>, a driver circuit <NUM> according to an embodiment is provided, which again contains a conventional driver like a push-pull driver with transistors T1, T2 for driving transistor switch <NUM> in normal operation. However, unlike conventional driver circuits, such a driver circuit uses signals at gate terminal G and/or auxiliary emitter terminal E' for short circuit detection. In one implementation shown in <FIG>, controller <NUM> of driver circuit <NUM> monitors the current flowing from driver circuit <NUM> to external gate terminal G of switch module <NUM> using a current meter <NUM>. When short circuit detection circuit <NUM> provides the electrical connection between lines <NUM> and <NUM> in case of a short circuit, an increased current flows from gate terminal G to emitter terminal E or auxiliary emitter terminal E'. This increased current flow to gate terminal G is provided by driver circuit <NUM> and may be measured by driver circuit <NUM>. Any conventional current measurement techniques, for example contactless methods as described with reference to <FIG> or a shunt resistor as described with reference to <FIG>, are also a sense transistor, depending on the design of driver circuit <NUM>, may be used as current meter <NUM>. The current detection may be made at the corresponding terminal of driver circuit <NUM> or at internal circuit components, for example driver components, of driver circuit <NUM>. The thus sensed current may be compared to a threshold, for example by a comparator, and when the current exceeds the threshold, a short circuit is detected and the control signal to gate terminal G is set to switch transistor switch <NUM> off.

Additionally or alternatively, as shown in <FIG>, the short circuit may be detected by controller <NUM> monitoring the voltage between gate terminal G and auxiliary emitter terminal E' using a voltage meter <NUM>. When short circuit detection circuit <NUM> detects a short circuit and provides the electrical connection between lines <NUM> and <NUM>, due to this connection there is a dip, i.e. at an at least temporary decrease, in the voltage between gate terminal G and emitter terminal E'. This voltage dip may be detected by driver circuit <NUM>, for example by continuously measuring the voltage. For measuring the voltage, as voltage meter <NUM> for example an analog to digital converter may be used, and the measured voltage may then be evaluated digitally.

It should be noted that by these approaches (measuring current to gate terminal G or detecting a voltage dip between gate terminal G and auxiliary emitter terminal E'), no additional communication of the short circuit state from short circuit detection circuit <NUM> to driver circuit <NUM> is needed, but the short circuit is detected by driver circuit <NUM> based on the behavior of signals resulting from short circuit detection circuit <NUM> providing the electrical connection between line <NUM>, <NUM>. Therefore, no additional signal and no additional external terminals for signaling are required. Additional signal in this case refers to a signal which is provided for signaling the short circuit in addition to the behavior of signals at terminals G or E' which follows from the electrical connection between G and E via lines <NUM> and <NUM> provided by short circuit detection circuit <NUM> in response to detecting the short circuit.

It should be noted that the various possibilities for short circuit detection in driver circuit <NUM> may be used singly or in combination. For example, driver circuit <NUM> of <FIG> implements both desaturation based short circuit detection and gate current based short circuit detection, and driver circuit <NUM> of <FIG> implements both desaturation based short circuit detection and gate-emitter voltage based short circuit detection. In other embodiments, the desaturation based short circuit detection (i.e. components <NUM>, <NUM> and terminal C') in <FIG> and <FIG> may be omitted, and a corresponding driver circuit may then be used e.g. in the system of <FIG>. Other combinations are also possible.

<FIG> is a flow chart illustrating a method according to some embodiments. The method of <FIG> may be implemented in the systems, switch modules and driver circuits discussed above, and in order to avoid repetitions will be described with respect to the previous explanations. However, the method of <FIG> may also be implemented in other systems, switch modules and driver circuits than the ones explained above.

At <NUM>, the method comprises driving a switch module, i.e. driving one or more transistors switches of a switch module to switch them on and off. At <NUM>, the method comprises detecting a short circuit by the switch module. In other words, the short circuit is detected within the switch module and not by an external entity like a driver circuit. As an example, the short circuit may be detected by short circuit detection circuit <NUM> described previously.

At <NUM>, in response to detecting the short circuit, the method includes electrically coupling a control terminal of a transistor switch of the switch module to a first load terminal of the transistor switch, in the example of <FIG> by electrically coupling lines <NUM> and <NUM>. This turns off the transistor switch at least temporarily.

At <NUM>, the method comprises detecting the short circuit also by a driver circuit, for example driver circuit <NUM> as discussed previously. In response to detecting the short circuit, the driver circuit controls switches of the switch modules, i.e. controls one or more transistor switches of the switch module to be switched off.

Claim 1:
A switch module (<NUM>), comprising:
a transistor switch (<NUM>) including a control terminal, a first load terminal and a second load terminal,
a short circuit detection circuit (<NUM>) configured to detect a short circuit state between the first load terminal and the second load terminal and to switch the transistor switch (<NUM>) off by switching on a transistor (<NUM>) to electrically couple the control terminal to the first load terminal in response to detecting the short circuit state,
wherein the short circuit detection circuit (<NUM>) is configured to be supplied with power by a voltage applied between the control terminal and the first load terminal when the voltage applied between the control terminal and the first load terminal is high enough to switch the transistor switch (<NUM>) on,
wherein the short circuit detection circuit (<NUM>) is configured to measure a current through the transistor switch (<NUM>) between the first and second load terminals and to detect the short circuit state if the current exceeds a predefined threshold.