Patent Description:
In other examples, the half-bridge power stage topology is controlled by control circuitry. This control circuitry drives the gates of the power stage transistors to control the current flow through the various motor windings of the motors. While the power stage is constructed to handle the large currents required by the motors, the control circuitry is not.

The invention is defined by the independent claim. Preferred embodiments are recited by the dependent claims.

The invention is directed to a circuit for ground disconnection protection in for instance an electric motor, the circuit includes power metal oxide semiconductor field-effect transistors (MOSFETs) in a common-source arrangement coupled between a first ground and a second ground, configured to turn on during a ground disconnection event in an electric motor system, allowing a current to pass between the first ground and the second ground, the current bypassing a control circuit.

As described above, electric motor systems include both power circuitry and control circuitry used in the control of current to the several electrical coils found within an electric motor. In at least one example, the power circuitry includes high-power components designed to source and sink large currents through the electrical coils in a controlled manner in order to operate the electric motor as desired. The power circuitry is controlled by multiple signals provided by control circuitry. These signals are configured to turn on and off the high-power components within the power circuitry in a controlled fashion in order to operate the electric motor.

In other examples, the power circuitry is provided in close proximity to the electric motor, while the control circuitry is situated on a separate board or module and linked to the power circuitry via several electrical connections. In additional examples, the power circuitry and control circuitry have separate voltage sources and reference potentials (grounds). In at least one alternative, the power circuitry and control circuitry may be connected to the same voltage source, but have separate grounds which are coupled together through one or more of the electrical connections between the control circuitry and the power circuitry.

In normal operation, the grounds are linked together and remain at the same potential. However, when motors and their controllers are in actual use, it is possible for one of the grounds to be disconnected due to vibration or other forces. In such a ground disconnection event in one of the grounds, the electrical connections and the control circuitry may be subjected to the large currents from the power circuitry. For example, if the ground to the power circuitry becomes disconnected, the large currents flowing through the power circuitry attempt to flow through the control circuitry to the ground of the control circuitry. The control circuitry is not configured to handle these large currents, and is destroyed.

By providing ground disconnection protection circuitry between the two (or more) grounds, the control circuitry may be protected from these large currents. In an example, ground disconnection protection circuitry is configured to pass current between the two ground nodes when a voltage differential between the two ground nodes exceeds a threshold. In various examples the threshold is between Vdiode (about <NUM>. 7V) and about 4V. This voltage differential is termed the common mode range of the circuit. When the voltage differential exceeds the threshold (or common mode range of the circuit) ground disconnection protection circuits are activated to protect the control circuitry from large currents. Various ground disconnection protection circuits are described herein, some including extended common mode range.

Examples described herein provide wide common mode range while maintaining isolation of the control circuitry from the power circuitry. Motor current from the power stage must not bleed into the low power ground for reliability and electromagnetic interference (EMI) concerns. These examples also provide protection from ground disconnection during operation since damage to the control circuitry (or any other device) is not acceptable, especially in automotive and safety applications.

Previous solutions included a pair of back-to-back high-power diodes placed between the ground terminals on the printed circuit board (PCB). This pair of diodes provided a common mode range of Vdiode or about <NUM>. In order to extend the common mode range, additional high-power diodes were placed in series with each of the pair of back-to-back diodes with each additional pair of high-power diodes adding Vdiode or about <NUM>. 7V to the common mode range. Thus, placing four series high-power diodes in a back-to-back configuration (requiring a total of eight high-power diodes), a common mode range of approximately <NUM> X Vdiode or about <NUM>. 8V may be achieved. However, these high-power diodes are expensive and require large amounts of space on the PCB, resulting in a less than desirable solution.

Motor control systems are described herein, which can be employed to control direct current (DC) motors, among other elements. Depending on the type of motor and configuration, one or more motor windings might be provided within a motor. Motor windings are employed in motors to provide rotary or linear motion, and these windings may include wire coils, which are referred to herein as motor phases. Control systems control distribution of electrical current to and from motor windings. One example control circuit topology, a half-bridge power stage, includes control circuitry as well as power switching elements. These power switching elements can include metal oxide semiconductor field-effect transistor (MOSFETs), insulated-gate bipolar transistors (IGBTs), or thyristors, among other switching elements. Although the motor control circuitry described herein employs power MOSFETs, the described circuitry can be applied to control other types of switching elements.

<FIG> shows a first example of motor control circuitry. <FIG> illustrates system <NUM> which provides power to one or more phase windings <NUM>-<NUM> (referred to as phases) of motor <NUM>. System <NUM> includes control circuitry <NUM>, power circuitry <NUM>, and motor <NUM>. Control circuitry <NUM> can communicate over link <NUM> with one or more external systems, such as to provide a programming interface for elements of system <NUM>. In operation, control circuitry <NUM> instructs power circuitry <NUM> over one or more links <NUM> to switch current for motor phase <NUM>. Power circuitry <NUM> thus provides electrical power over link <NUM> as sourced from VMOTOR to motor phase <NUM> as a portion of motor <NUM>. Further control circuitry and power circuitry can be included for additional phases <NUM>-<NUM> of motor <NUM>, or these phases might be controlled by elements of system <NUM>.

Power for control circuitry <NUM> is sourced from VSUPPLY. In the illustrated example, control circuitry <NUM> is of lower power compared to power circuitry <NUM>, and has a separate ground from the power circuitry <NUM>. These grounds are usually coupled together through one of links <NUM>. Control circuitry <NUM> includes one or more processing elements and control circuits to instruct power control circuitry <NUM> to selectively source or sink current from phase <NUM> over link <NUM>. Control circuitry <NUM> determines control voltages or control signals which couple to gate terminals of power transistor elements of power control circuitry <NUM>.

Control circuitry <NUM> can be implemented using various microprocessors, control logic, programmable logic devices, discrete logic devices, or other devices and elements. Control circuitry <NUM> can also include gate driver circuitry which drives the gate terminals of the power transistor elements. This driver circuitry can include power amplifiers, gate drive transformers, DC-DC converter elements, or other circuit components to provide sufficient voltages to control gate terminals of associated power transistor elements.

Power circuitry <NUM> includes power transistor elements that act as power switching elements with regard to a motor phase, such as phase <NUM>. Switching elements of power circuitry <NUM> are coupled between a voltage source, indicated in <FIG> as VMOTOR, and a reference potential (or ground). Although various transistor circuit topologies might be employed by power circuitry <NUM>, the examples herein include half-bridge topologies. Half-bridge power stage topologies can be used to control different motor types, such as DC motors. These half-bridge topologies can include H-bridge, triple half-bridge, and dual H-bridge types, among others. Usually, a half-bridge power stage includes two switching elements, such as power transistors, arranged to have a first (high-side) switching element and a second (low-side) switching element coupled at a common output node. This common output node is shown as link <NUM> in <FIG>, although various passive circuit elements might be positioned between the common output node and link <NUM>. The first switching element also couples to the voltage source, while the second switching element also couples to the reference potential.

In the examples herein, the switching elements includes power metal oxide semiconductor field-effect transistor (MOSFETs). Specifically, n-channel power MOSFETs are employed due to the lower on-resistance than p-channel power MOSFETS. Power MOSFETs includes gate terminals, drain terminals, and source terminals for connection to external components. Additionally, power MOSFETs include "body diode" components which result from the structural formation of semiconductor connections internal to each power MOSFET. These body diode components or elements might continue to conduct current after a corresponding power MOSFET has been switched into an 'off or inactive state. <FIG> shows operation of body diode components.

Half-bridge power stage topologies can employ first (high-side) and second (low-side) power MOSFET devices. A first power MOSFET is coupled at a drain terminal to the voltage source (VMOTOR), while a source terminal is coupled to the common output node of power circuitry <NUM>. A second power MOSFET is coupled at a source terminal to the reference potential (e.g. electrical ground), while a drain terminal is coupled to the common output node of power circuitry <NUM>. Gate terminals of the first MOSFET and second MOSFET are coupled via one or more links <NUM> to gate driver elements of control circuitry <NUM>. Various passive or active circuit components might be provided in power circuitry <NUM> to support operation of the power MOSFETs, such as resistors, capacitors, inductors, voltage limiters, diodes, logic gates, or other elements.

<FIG> shows a specific implementation of control circuitry <NUM> and power circuitry <NUM>. <FIG> includes power switching circuit <NUM> as an example of power circuitry <NUM>, and control circuitry <NUM> as an example of control circuitry <NUM>, although variations are possible. Circuit <NUM> includes two half-bridge topologies <NUM> and <NUM> each formed by two power MOSFET devices. Half-bridge <NUM> is formed by MOSFET devices <NUM> and <NUM> including their body diodes <NUM> and <NUM> respectively. Half-bridge <NUM> is formed by MOSFET devices <NUM> and <NUM> including their body diodes <NUM> and <NUM> respectively.

In this example, both control circuitry <NUM> and power circuitry <NUM> are provided power from VSUPPLY <NUM>, but control circuitry <NUM> uses GND <NUM><NUM> (first ground) as a reference potential while power circuitry <NUM> uses GND <NUM><NUM> (second ground) as a reference potential. This configuration of separate grounds is usually due to instances where control circuitry <NUM> and power circuitry <NUM> are physically separate, such as on different circuit boards. However, note that GND <NUM><NUM> (first ground) and GND <NUM><NUM> (second ground) are electrically coupled through ESD Clamp <NUM>. In other versions, control circuitry <NUM> and power circuitry <NUM> are provided power from separate power sources. In the illustrated example, ESD Clamp <NUM> is configured to connect GND <NUM><NUM> (second ground) to GND <NUM><NUM> (first ground) whenever the voltage difference between the two reference potentials exceeds <NUM> volts. This voltage differential is referred to as common mode range.

MOSFET device <NUM> is the "high-side" (HS) device of half-bridge <NUM>, while MOSFET device <NUM> is the "low-side" (LS) device of half-bridge <NUM>. Each power MOSFET device also has a corresponding body diode <NUM> and <NUM>. First MOSFET device <NUM> is coupled at a drain terminal to a voltage source, referred to as VSUPPLY in <FIG>. MOSFET device <NUM> is coupled at a gate terminal to control system <NUM>. MOSFET device <NUM> is coupled at a source terminal to a drain terminal of MOSFET device <NUM>, which is also an output node <NUM> of circuit <NUM>. Output node <NUM> is coupled to a phase of a motor, shown as motor winding <NUM> in <FIG>. Second MOSFET device <NUM> is coupled at a gate terminal to control system <NUM>, and at a source terminal to a voltage reference (electrical ground) GND <NUM><NUM>.

MOSFET device <NUM> is the "high-side" (HS) device of half-bridge <NUM>, while MOSFET device <NUM> is the "low-side" (LS) device of half-bridge <NUM>. Each power MOSFET device also has a corresponding body diode <NUM> and <NUM>. MOSFET device <NUM> is coupled at a drain terminal to a voltage source, referred to as VSUPPLY in <FIG>. MOSFET device <NUM> is coupled at a gate terminal to control circuitry not illustrated here for simplicity. MOSFET device <NUM> is coupled at a source terminal to a drain terminal of MOSFET device <NUM>, which is also an output node <NUM> of circuit <NUM>. Output node <NUM> is coupled to a phase of a motor, shown as motor winding <NUM> in <FIG>. MOSFET device <NUM> is coupled at a gate terminal to control circuitry not illustrated here for simplicity, and at a source terminal to a voltage reference (electrical ground) GND <NUM><NUM>.

The gate terminal of MOSFET device <NUM> and a gate terminal of MOSFET device <NUM> are coupled over associated links <NUM> and <NUM> to gate driver circuits <NUM> and <NUM> respectively. The common or shared node <NUM> in the half-bridge arrangement, also includes an output node for the half-bridge. In operation, the half-bridge arrangement provides power to motor winding <NUM> in the form of electrical current. This electrical current has two polarities, namely a positive and negative polarity indicated. A positive current polarity is referred to in <FIG> as an outgoing current from half-bridge <NUM> to motor winding <NUM>, while a negative current polarity is referred to in <FIG> as an outgoing current from half-bridge <NUM> to motor winding <NUM>. Various switch states among MOSFET devices <NUM>, <NUM>, <NUM>, and <NUM> provide for sinking or sourcing the motor winding current and associated polarities. For example, when the first (high-side0 transistor <NUM> of half-bridge <NUM> is active, then current is supplied from VSUPPLY through MOSFET device <NUM> to motor winding <NUM>. Likewise, when the second (low-side) transistor <NUM> of half-bridge <NUM> is active, the current is drawn to ground through MOSFET device <NUM>.

<FIG> illustrates the control circuitry <NUM> and power circuitry <NUM> from <FIG> in the case where a disconnection <NUM> from GND <NUM><NUM> has occurred. In this example, node <NUM> is now disconnected from GND <NUM><NUM> while motor winding <NUM> is still being driven by half-bridges <NUM> and <NUM>. A large current, illustrated by dashed line <NUM> now has no direct path to electrical ground. This causes the current <NUM> to flow through control circuitry <NUM>. When the voltage differential between node <NUM> and GND <NUM><NUM> exceeds <NUM> volts, ESD Clamp <NUM> attempts to route the current from node <NUM> to GND <NUM><NUM>. However, since control circuitry <NUM> is a low-power device, it is not capable of handling the amount of current required by power circuitry <NUM>, and ESD Clamp <NUM> is destroyed, possibly along with other circuitry within control circuitry <NUM>.

<FIG> illustrates the control circuitry <NUM> and power circuitry <NUM> from <FIG> along with non-claimed ground disconnection protection circuitry configured to protect control circuitry <NUM>. In this example, ground disconnection protection circuitry including back-to-back power diodes <NUM> and <NUM> have been added between GND <NUM><NUM> and GND <NUM><NUM> (before disconnection <NUM> occurs). In this example, a cathode terminal of power diode <NUM> and an anode terminal of power diode <NUM> are coupled to GND <NUM><NUM> (before disconnection <NUM> occurs), while an anode terminal of power diode <NUM> and a cathode terminal of power diode <NUM> are coupled to GND <NUM><NUM>.

In operation, this example provides a common mode range of Vdiode or about <NUM> volts. After disconnection <NUM> occurs, when the voltage differential between GND <NUM> and node <NUM> exceeds <NUM> volts, either power diode <NUM> or power diode <NUM> will turn on (depending on the polarity of the voltage differential) and sink current from node <NUM> to GND <NUM><NUM>. This current path is illustrated in <FIG> as dashed line <NUM>.

<FIG> illustrates the control circuitry <NUM> and power circuitry <NUM> from <FIG> along with non-claimed ground disconnection protection circuitry configured to protect control circuitry <NUM>. In this example, ground disconnection protection circuitry including power MOSFETs <NUM> and <NUM> are provided in a common-source arrangement between GND <NUM><NUM> and GND <NUM><NUM> (before disconnection <NUM> occurs). In this example, a source terminal of power MOSFET <NUM> is coupled with a source terminal of power MOSFET <NUM> at node <NUM>. A drain terminal of power MOSFET <NUM> is coupled with GND <NUM><NUM>, while a drain terminal of power MOSFET <NUM> is coupled with GND <NUM><NUM> (before disconnect <NUM> occurs). A gate terminal of power MOSFET <NUM> is coupled with a gate terminal of power MOSFET <NUM> at node <NUM>. Power MOSFETs <NUM> and <NUM> each include body diodes <NUM> and <NUM> respectively.

In this example, the ground disconnection protection circuitry further includes two low-power diodes <NUM> and <NUM> and a gate low-power resistor <NUM> to provide gate biasing to the pair of power MOSFETs. A cathode terminal of diode <NUM> is coupled with the gate terminal (node <NUM>) of power MOSFET <NUM>, while an anode terminal of diode <NUM> is coupled with GND <NUM><NUM> (first ground). A cathode terminal of diode <NUM> is coupled with the gate terminal (node <NUM>) of power MOSFET <NUM>, while an anode terminal of diode <NUM> is coupled with GND <NUM><NUM> (second ground), (before disconnection <NUM> occurs.

Diodes <NUM> and <NUM> effectively provide a logical OR function between GND <NUM><NUM> and GND <NUM><NUM> (or node <NUM> after disconnection <NUM> occurs). After disconnection <NUM> occurs, when the voltage differential between either node <NUM> or GND <NUM><NUM> and node <NUM> exceeds <NUM> volts, power MOSFETs <NUM> and <NUM> will turn on and sink current from node <NUM> to GND <NUM><NUM>. This provides a baseline common mode range of <NUM>*Vdiode + Vt of the power MOSFETs, roughly a little over <NUM> volts. Resistor <NUM> is coupled between nodes <NUM> and <NUM> in order to provide a low-current leakage path between the two nodes and acts to keep power MOSFETs <NUM> and <NUM> in an off state during normal operation. In an example, resistor <NUM> is a low-power resistor with a resistance of at least <NUM>,<NUM> ohms.

Compared to the circuit illustrated in <FIG>, the baseline common mode range is improved, and this circuit allows for the extension of the common mode range by the addition of low cost, low-power components instead of costly high-power components. Examples of the extension of common mode range are shown in <FIG>.

<FIG> illustrate examples of ground disconnection protection circuitry for motor power control systems adapted for extended common mode range. The examples shown in <FIG> are not claimed. <FIG> illustrates the ground disconnection protection circuitry from <FIG> including power diodes <NUM> and <NUM> between GND <NUM> and GND <NUM><NUM> (before disconnection <NUM> occurs).

<FIG> illustrates the ground disconnection protection circuitry from <FIG> as modified to provide an extended common mode range of about <NUM> volts. In this example, in order to reach a common mode range of <NUM> volts, diode <NUM> has been replaced by <NUM> high-power diodes <NUM> coupled in series, and diode <NUM> has been replaced by <NUM> high-power diodes <NUM> also coupled in series, for a total of <NUM> high-power diodes. While the example solution works, high-power diodes are expensive, and require large amounts of space on the PCB.

In contrast, <FIG> illustrates the ground disconnection protection circuitry from <FIG> including power MOSFETs <NUM> and <NUM> in a common-source arrangement between GND <NUM><NUM> and GND <NUM><NUM> (before disconnection <NUM> occurs). As described above, this configuration has a common mode power range of roughly a little over <NUM> volts.

<FIG> illustrates the ground disconnection protection circuitry from <FIG> as modified to provide an extended common mode range of about <NUM> volts. In this example, in order to reach a common mode range of <NUM> volts, low-power diode <NUM> has been replaced by a pair of series diodes <NUM> including low-power diodes <NUM> and <NUM>, and low-power diode <NUM> has been replaced by a pair of series diodes <NUM> including low-power diodes <NUM> and <NUM>. Each pair of series diodes includes a first diode coupled at an anode terminal to a cathode terminal of a second diode. This configuration increases the common mode range by Vdiode or about <NUM> volts, to a total of roughly <NUM> volts.

In this example, the first pair of series diodes is coupled at a cathode terminal to a gate terminal of the first power MOSFET and a gate terminal of the second power MOSFET, and coupled at an anode terminal to the drain terminal of the first power MOSFET. The second pair of series diodes is coupled at a cathode terminal to the gate terminal of the second power MOSFET and the gate terminal of the first power MOSFET and coupled at an anode terminal to the drain terminal of the second power MOSFET.

In this example, the first pair of series diodes includes a first diode coupled at an anode terminal to a cathode terminal of a second diode. The cathode terminal of the first pair of series diodes is a cathode terminal of the first diode, and the anode terminal of the first pair of series diodes is an anode terminal of the second diode.

The second pair of series diodes comprises a third diode coupled at an anode terminal to a cathode terminal of a fourth diode. The cathode terminal of the second pair of series diodes is a cathode terminal of the third diode, and the anode terminal of the second pair of series diodes is an anode terminal of the fourth diode.

In an optional example, resistor dividers may be used to control the gate terminals of the power MOSFETs, however, this is not as efficient as adding additional low-power diodes to the circuit.

In contrast to the circuits illustrated in <FIG>, the circuits of <FIG> provide for the extension of the common mode range simply by the additions of low-power diodes in series. These low-power diodes are much smaller and less expensive than the high-power diodes required by the circuits of <FIG>. In various other examples, the ground disconnection protection circuitry illustrated in <FIG> includes three or more series diodes in order to increase the common mode range of the circuit as desired.

Claim 1:
A circuit for ground disconnection protection, comprising:
a first power metal oxide semiconductor field-effect transistor (MOSFET) (<NUM>) having a first drain terminal coupled to a first ground (<NUM>), a first source terminal, and a first gate terminal;
a second power MOSFET (<NUM>) having a second drain terminal coupled to a second ground (<NUM>), a second source terminal coupled to the first source terminal, and a second gate terminal coupled to the first gate terminal;
a first diode (<NUM>) having a first cathode coupled to the first gate terminal, and having a first anode;
a second diode (<NUM>) having a second cathode coupled to the first anode, and a second anode coupled to the first drain terminal;
a third diode (<NUM>) having a third cathode coupled to the second gate terminal, and having a third anode; a fourth diode (<NUM>) having a fourth cathode coupled to the third anode, and a fourth anode coupled to the second drain terminal; and
a resistor (<NUM>) coupled at a first terminal to the gate terminals of the first and second power MOSFETs (<NUM>, <NUM>), and coupled at a second terminal to the source terminals of the first and second power MOSFETs (<NUM>, <NUM>).