Regulator control circuit

A regulator control circuit which is configured to control a switching regulator: a feedback comparator configured to compare a signal representative of a reference voltage with a signal representative of a voltage output of the switching regulator and to output a control signal for controlling the operation of the switching regulator dependent on the signals received by the feedback comparator; and a current feedback controller connected to the feedback comparator and configured to receive a signal representative of a current output by the switching regulator and determine whether the regulator control circuit adopts a first or second mode of operation based on the signal representative of a current output, such that, in the first mode of operation, the control signal is for controlling the switching regulator in accordance with a constant voltage control scheme and, in the second mode of operation, the control signal is for controlling the switching regulator in accordance with a constant current control scheme.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the national stage application of, and claims priority to, International Application No. PCT/GB2017/050739 filed Mar. 17, 2017, which was published as International Publication No. WO 2017/163026. International Application No. PCT/GB2017/050739 claims the benefit of United Kingdom Patent Application No. 1604753.2 filed Mar. 21, 2016.

DESCRIPTION OF INVENTION

Embodiments of the present invention relate to electrical supply control circuits for regulating a supply voltage to track a reference voltage. In particular, some embodiments relate to electrical supply control circuits for using in powering analogue circuits which may form part of a braking system of a vehicle.

Some vehicle electrical systems use analogue sensors and other devices which, for their correct operation, need to be powered by an electrical supply with a voltage which tracks a reference voltage used by an analogue-to-digital converter (ADC).

For vehicles, there is often a requirement for this electrical supply and the system implemented to track the reference voltage to be able to handle overloads—which may include a short circuit and/or connection to the main vehicle electrical supply (which may be as high as 42V).

Some previous systems use linear or switching tracking regulators; however, these systems commonly revert to a linear current limit dissipating several watts of power during overload situations, particularly when a large supply voltage range has to be accommodated.

Various other previous systems suffer from other problems, such as a lack of electrical supply in some fault situations or limited current characteristics.

Whilst described specifically in relation to a vehicle electrical supply system, and a braking system of a vehicle, it will be appreciated that some embodiments will be applicable to other electrical supply systems and/or to systems other than braking systems.

There is a need, therefore, to alleviate the problems with the prior art.

Accordingly, an aspect of the present invention provides a regulator control circuit which is configured to control a switching regulator: a feedback comparator configured to compare a signal representative of a reference voltage with a signal representative of a voltage output of the switching regulator and to output a control signal for controlling the operation of the switching regulator dependent on the signals received by the feedback comparator; and a current feedback controller connected to the feedback comparator and configured to receive a signal representative of a current output by the switching regulator and determine whether the regulator control circuit adopts a first or second mode of operation based on the signal representative of a current output, such that, in the first mode of operation, the control signal is for controlling the switching regulator in accordance with a constant voltage control scheme and, in the second mode of operation, the control signal is for controlling the switching regulator in accordance with a constant current control scheme.

The second mode may be adopted when the signal representative of the current output by the switching regulator exceeds a predetermined current.

The current feedback controller may be configured to modify the signal representative of the voltage output of the switching regulator in order to cause the adoption of the second mode.

The circuit may further include a first drive switch circuit which is configured to receive an output from the current feedback controller and selectively to control an input of the current feedback controller dependent on the output from the current feedback controller.

The circuit may further include a regulator drive circuit which is configured to receive the output from the feedback comparator and to control the operation of the switching regulator in accordance with the output from the feedback comparator.

The circuit may be further configured to clamp the output of the switching regulator to a clamp voltage and to modify the control signal to disable the switching regulator when the signal representative of the voltage output of the switching regulator and the signal representative of the reference voltage indicate that the voltage output is higher than the reference voltage.

The circuit may further include an output voltage transient protection circuit configured to protect the feedback comparator from high voltage transients in the output voltage.

The current feedback controller may be further configured to determine whether the regulator control circuit adopts a fourth mode of operation in which hybrid pulse width and pulse frequency modulation is used to control the operation of the switching regulator.

Another aspect provides a sensor circuit including a regulator control circuit as above, the switching regulator, and at least one sensor connected to the output of the switching regulator.

The signal representative of the reference voltage may be a signal representative of a reference voltage of an analogue-to-digital converter which is configured to receive an output from the at least one sensor.

Another aspect may provide a braking system for a vehicle including a regulator control circuit as above or a sensor circuit as above.

Another aspect provides a vehicle including a braking system as above or a regulator control circuit as above or a sensor circuit as above.

In some embodiments, seeFIG. 1for example, the present invention includes a vehicle1to which a braking system2has been fitted. The vehicle1may include a truck11and trailer12, the trailer12being configured to be towed by the truck11. The braking system2may, therefore, include a portion which is part of the truck11and a portion which is part of the trailer12. Other configurations of the braking system2and vehicle1may, however, be used in other embodiments.

The braking system2, with reference toFIG. 2, includes a brake module21which is configured, on actuation, to apply a braking force to one or more ground engaging wheels of the vehicle1(e.g. of the truck11and/or trailer12) in order to slow the vehicle1and/or substantially prevent its movement. The braking system2may also include one or more analogue sensors22.

The or each analogue sensor22may be configured to measure a parameter associated with the operation of the vehicle1(which may include a parameter associated with the operation of the truck11, and/or of the trailer12, and/or of the braking system2[which may include the braking module21]). Examples of such analogue sensors22may include pressure sensors, position sensors, temperature sensors, and acceleration sensors. In some embodiments, the or each analogue sensor22may include a sensor which measures the speed of the vehicle1(which may be the speed of the truck11or trailer12) and/or may be configured to measure the speed of rotation of one or more ground engaging wheels of the vehicle1(which may include a ground engaging wheel of the truck11and/or the trailer12). The or each analogue sensor22may include a potentiometric sensor device.

The or each analogue sensor22may be used by other parts of the braking system2to determine one or more parameters regarding the operation of the vehicle1or braking system2, so that another aspect of the braking system2can be controlled based, at least in part, on the one or more parameters.

Accordingly, the braking system2may include a braking system controller23which is configured to receive the one or more parameters from the one or more analogue sensors22and to output a control signal to part of the braking system2(e.g. to the braking module21), the control signal being at least partly based on the one or more received parameters.

The braking system2may include an analogue-to-digital converter (ADC)24which is configured to receive an analogue signal representative of a parameter from an analogue sensor22of the one or more analogue sensors22. The ADC24may be configured to convert the received analogue signal into a digital signal which is then provided, by the ADC24, to the braking system controller23—which may be a digital controller (such as a microcontroller or microprocessor device).

In some embodiments, the braking system2includes a plurality of ADCs24, each associated with a different analogue sensor22. In some embodiments, a plurality of analogue sensors22are associated with the same ADC24and the braking system2includes a multiplexing device (not shown) which is configured to multiplex the analogue signals output by the plurality of analogue sensors22such that the ADC24operates on each analogue signal separately in turn.

The or each analogue sensor22may be configured to output an analogue signal in which the parameter being sensed is encoded in changes in the voltage of the analogue signal output by the analogue sensor22.

The or each analogue sensor22may, therefore, require an electrical supply, e.g. via an electrical supply system3, which has a predetermined relationship with a reference voltage associated with the ADC24—such that the ADC24correctly translates the or each received analogue signal into the appropriate digital signal for use by the braking system controller23. As will be understood, analogue sensors22are one example of a component which requires an electrical supply which has a predetermined relationship with a reference voltage (e.g. a reference voltage associated with the ADC24). Embodiments of the present invention are described, for ease of reference, in relation to one or more analogue sensors22but may equally be used with other examples of such components requiring this predetermined relationship.

This reference voltage may be provided by a reference voltage output35of the electrical supply system3of the vehicle1or of the braking system2, for example. The reference voltage output35may be connected in electrical communication to a reference voltage regulator (not shown) which is configured to reduce or translate the reference voltage output35into the reference voltage (which may be a lower voltage than the voltage of the reference voltage output35). In some embodiments, the reference voltage regulator is part of the electrical supply system3and, in some embodiments, the reference voltage regulator is part of the braking system2.

The vehicle1includes an electrical supply system3, seeFIG. 2, which is configured to provide electrical power to one or more units of the vehicle1, including the braking system2and/or a lighting system4, if provided.

The electrical supply system3may include a battery31and a generation system32(such as an electrical alternator or other generator) which is configured to generate electricity using mechanical power generated by an engine of the vehicle1, for example. The electrical supply system3may include an ignition or other power line34which is configured, with a ground line, to supply electricity to the one or more units of the vehicle1. In this instance, the voltage of the electricity supplied through the electrical supply system3may be 12V, 24V, or 32V, for example. The battery31—if provided—may be configured to provide electrical power at any one of these voltages. As mentioned above, in some embodiments, the electrical supply system3is also configured to output a reference voltage output35.

In some embodiments, the reference voltage is at a level suitable for use by logic circuits (such as the ADC24, and/or the braking system controller23). In some embodiments, the reference voltage may be about 3V or 5V. The reference voltage is subject to variations during operation of the vehicle1—which may be due to other demands on the electrical supply system3of the vehicle1(e.g. during cranking) but could also be the result of faults or the result of connection of an electrical system of the truck11with an electrical system of the trailer12(or a part of the braking system2of the truck11with a part of the braking system2of the trailer12).

In embodiments of the invention, an electrical supply control system25is provided as part of the braking system2or otherwise (e.g. as part of the vehicle1more generally, which may include being part of the truck11and/or trailer12).

The electrical supply control system25is configured to be coupled in electrical communication with the ignition or other power line34and to the electrical power output over the ignition or other power line34to a sensor power output for use by the one or more analogue sensors22.

In some embodiments, the electrical supply control system25is configured to convert the voltage of power delivered over the ignition or other power line34to a sensor voltage, wherein the sensor voltage substantially tracks the reference voltage—i.e. a substantially constant voltage. In some embodiments, the electrical supply control system25is configured to provide the sensor power output at a substantially constant current.

In some embodiments, the electrical supply control system25, and/or the ADC24and/or the reference voltage output35may form part of the braking system controller23.

With reference to, for example,FIG. 3, some embodiments of the electrical supply control system25include a switching regulator251and a regulator control circuit252.

The switching regulator251is configured to receive electrical power from the electrical supply system3(e.g. via the ignition or other power line34) and to convert that electrical power into the sensor power output. The operation of the switching regulator251is controlled by the regulator control circuit252which is configured to provide two or more modes of operation.

In accordance with a first mode of operation of the regulator control circuit252, the switching regulator251is controlled to provide the sensor power output at the sensor voltage which tracks the reference voltage—i.e. a substantially constant voltage (albeit subject to some variations in practice).

In accordance with a second mode of operation of the regulator control circuit252, the switching regulator251is controlled to provide the sensor power output at a substantially constant current.

In accordance with an optional third mode of operation of the regulator control circuit252, the switching regulator251substantially prevents connection of the sensor power output to the ignition or other power line34(i.e. the switching regulator251may be substantially disabled). This mode of operation may be used, for example, if a fault occurs or is expected (e.g. a short circuit fault as described herein).

In some embodiments, the regulator control circuit252may be configured to control the operation of the switching regulator251to provide pulse frequency modulated control of the switching regulator251. In some embodiments, other forms or techniques of control are possible, such as pulse width modulated control. In some embodiments, the regulator control circuit252is configured to control the operation of the switching regulator251to provide a hybrid pulse width and pulse frequency modulated control of the switching regulator251—in such a hybrid, pulse width modulation may be used except when the load on the sensor power output is below a threshold when one or more pulses may be omitted (providing a degree of pulse frequency modulation). This may be viewed, in some embodiments, as a fourth mode of operation.

The switching regulator251may, in some embodiments, include a power switch device2511which may be a transistor device and may be, for example, a PNP transistor device. The switching regulator251may further include an energy storage element2512such as an inductor. The switching regulator251may further include a diode2513.

In some embodiments, such as in the embodiment depicted inFIG. 4, the power switch device2511is connected in series with the energy storage element2512. The power switch device2511is further connected in series with the ignition or other power line34. Accordingly, the ignition or other power line34may be connected in selective electrical communication with the energy storage element2512. With the power switch device2511in an on-state, the ignition or other power line34may be connected in electrical communication with the energy storage element2512such that the energy storage element2512is charged. With the power switch device2511in an off-state, the ignition or other power line34may be disconnected from electrical communication with the energy storage element2512which may, as a result, discharge. The diode2513may be connected in electrical communication with both the power switch device2511and the energy storage element2512and may remain in electrical communication with the energy storage element2512irrespective of the on- or off-state of the power switch device2511. Accordingly, the diode2513may be oriented to allow the charging of the energy storage element2512with the power switch device2511in the on-state and to allow the discharging of the energy storage element2512with the power switch device2511in the off-state.

The energy storage element2512may be connected to a sensor voltage line26such that the discharging of the energy storage element2512is to the sensor voltage line26.

A capacitor2514of the switching regulator251may be connected between the sensor voltage line26and a ground connection or line36.

The actuation of the power switch device2511between the on- and off-states is controlled by the regulator control circuit252. In the case of the power switch device2511being a transistor device, therefore, the base of the power switch device2511is connected in electrical communication with the regulator control circuit252.

In the embodiment depicted inFIG. 4, for example, the power switch device2511is a PNP transistor device with its emitter connected in electrical communication with the ignition or other power line34and its collector connected in electrical communication with the energy storage element2512(and diode2513, which is also connected in electrical communication with the ground connection or line36). The base of the power switch device2511of the embodiment ofFIG. 4is, as discussed above, connected in electrical communication with the regulator control circuit252.

The regulator control circuit252is connected in electrical communication with the switching regulator251and, in some embodiments in particular, with the power switch device2511thereof.

The regulator control circuit252is also configured to receive a signal indicative of the voltage of the reference voltage output35and a signal representative of the electrical current provided by the switching regulator251to the sensor voltage line26(i.e. the current drawn through the sensor voltage line26, e.g. by the one or more analogue sensors22).

Accordingly, the regulator control circuit252may include a reference voltage input2521(which is configured to receive the signal indicative of the voltage of the reference voltage output35) and a current sense circuit2522which is configured to sense the current flowing from the switching regulator251to the sensor voltage line26.

The reference voltage input2521may include a connection to the reference voltage output35. This connection may be via one or more resistors and/or capacitors of the reference voltage input2521which serve to reduce and/or filter the voltage of the reference voltage output35prior to use in other parts of the regulator control circuit252.

In particular, the reference voltage input2521may include a potential divider circuit formed from a first resistor2521awhich is connected (or connectable) in electrical communication with the reference voltage output35at a first terminal of the first resistor2521a, a second terminal of the first resistor2521abeing connected in electrical communication with a first terminal of a second resistor2521bof the reference voltage input2521. A second terminal of the second resistor2521bmay be connected to the ground connection or line36. A capacitor2521cof the reference voltage input2521may be connected in parallel with the second resistor2521bto provide filtering which reduces the effects of transient (relatively high frequency) variations in the voltage of the reference voltage output35on other parts of the regulator control circuit252.

The reference voltage input2521is connected in electrical communication with a feedback comparator2523of the regulator control circuit252and may be configured, in such embodiments, to receive the signal indicative of the voltage of the reference voltage output35(e.g. via the reference voltage input2521and the potential divider of the reference voltage input2521if provided).

The feedback comparator2523may be further configured to receive selectively a signal representative of a voltage of the sensor voltage line26.

The feedback comparator2523is configured, in the first mode of operation, to compare the signal indicative of the voltage of the reference voltage output35with the signal indicative of the voltage of the sensor voltage line26and to output a command signal which is configured to control the operation of the switching regulator251and, in particular embodiments, the power switch device2511of the switching regulator251. The control of the operation of the switching regulator251may, in this first mode of operation, be to maintain a substantially constant voltage at the power switch device2511, wherein substantial variations in the reference voltage are mirrored in the sensor voltage.

The feedback comparator2523may, therefore, include a comparator device2523a, an input of which is configured to be connected in electrical communication with the reference voltage input2521(e.g. with the output of the potential divider thereof, if provided). The comparator device2523amay have a second input which is configured to receive the signal indicative of the voltage of the sensor voltage line26(i.e. the sensor voltage).

The comparator device2523amay be powered by the reference voltage output35in some embodiments—a filter capacitor2523bmay be used to reduce the effects of transient variations of the reference voltage output35on the operation of the comparator device2523aand may, therefore, be connected in parallel with the power supply to the comparator device2523a. A resistor2523cmay also be connected between an output of the comparator device2523aand the reference voltage output35.

In some embodiments, such as depicted inFIG. 4, the signal representative of the voltage in the reference voltage output35is connected in electrical communication with a non-inverting input of the comparator device2523aand the signal representative of the sensor voltage is connected in electrical communication with the inverting input of the comparator device2523a.

The signal representative of the sensor voltage may be produced by coupling of an input of the feedback comparator2523(e.g. one of the inputs of the comparator device2523asuch as the non-inverting input thereof) to the sensor voltage line26. This coupling may be via one or more other components to modify the sensor voltage prior to provision to the feedback comparator2523. For example, the coupling may be via one or more resistors and/or capacitors. In some embodiments, the coupling is via a potential divider to reduce the sensor voltage for provision to the feedback comparator2523. In some embodiments, the coupling may additionally or alternatively be via one or more filtering circuits to improve the stability of the operation of the feedback comparator2523and/or other components which control the voltage of the sensor voltage line26. For example, in the depicted embodiment, the sensor voltage line26is coupled to a voltage feedback circuit2524of the regulator control circuit252which provides feedforward compensation.

The voltage feedback circuit2524may, therefore, be configured to modify the sensor voltage (as mentioned above) for provision to the feedback comparator2523.

In the depicted embodiment ofFIG. 4, the voltage feedback circuit2524includes one or more resistors and/or capacitors arranged in a network. For example, the voltage feedback circuit2524may include a first and second resistor2524a,2524bwhich are connected in series between the sensor voltage line26and the ground connection or line36. A further resistor2524dmay be connected in electrical communication with a terminal of the first resistor2524awhich is also connected to the second resistor2524b. A capacitor2524cmay be connected between the other terminal of the further resistor2524dand a terminal of a resistor2522aof the current sense circuit2522which is also connected to the energy storage device2512. The further resistor2524dand the capacitor2524cmay be connected to an input to the feedback comparator2523.

An input to the feedback comparator2523is, therefore, connected to the sensor voltage line26in some embodiments via the voltage feedback circuit2524. That input to the feedback comparator2523may also be connected to the ignition or other power line34via a first drive switch circuit2525of the regulator control circuit252.

The first drive switch circuit2525is configured to connect, selectively, the ignition or other power line34with the input to the feedback comparator2523. The first drive switch circuit2525may, therefore, include a switch device2525awhich is actuated between an on-state in which the ignition or other power line34is connected in electrical communication with the input to the feedback comparator2523and an off-state in which the ignition or other power line34is disconnected from electrical communication with the input to the feedback comparator2523.

The switch device2525aof the first drive switch circuit2525may be a transistor device and may, in the depicted embodiment ofFIG. 4, be a PNP transistor device. An emitter of the switch device2525amay be connected in electrical communication with the ignition or other power line34and a collector may be connected in electrical communication, via a resistor2525bof the first drive switch circuit2525, to the input of the feedback comparator2523.

As will be appreciated, therefore, the first drive switch device2525ais configured, selectively, to connect a signal representative of the voltage of the ignition or other power line34(or another relatively high voltage line in some embodiments) to the feedback comparator2523at the input thereof which is otherwise configured to receive the signal indicative of the sensor voltage. In other words, the first drive switch device2525ais configured to provide a current to the feedback comparator2523(i.e. to the comparator device2523athereof) which makes the comparator device2523aoutput low.

Actuation of the first drive switch circuit2525may be controlled in some embodiments by a current feedback controller2526of the regulator control circuit252. The current feedback controller2526is configured to control the operation of the first drive switch circuit2525between its on- and off-states dependent on a signal representative of the current flowing from the switching regulator251to the sensor voltage line26(i.e. the sensor current).

If the signal indicative of the sensor current is higher than a predetermined level, then the current feedback controller2526causes a change in the operation of the regulator control circuit252to the second mode of operation by taking over the provision of the input to the feedback controller2526(or otherwise influencing that input).

The predetermined level may be a predetermined operating current level for the switching regulator251for example.

The current feedback controller2526may include a switch device2526awhich may be a transistor device and may be an NPN transistor device (such as in the depicted embodiment ofFIG. 4). An output of the current feedback controller2526may be connected in electrical communication with the first drive switch circuit2525to control its operation between the on- and off-states—as described above.

Accordingly, in some embodiments (e.g. as depicted inFIG. 4), the current feedback controller2526includes the switch device2526ain the form of an NPN transistor device. The base and emitter of the switch device2526are connected in electrical communication with the current sense circuit2522and may be coupled by a capacitor2526bof the current feedback controller2526.

A resistor2526cmay be provided in series between the base of the switch device2526and the current sense circuit2522.

The collector of the switch device2526aof the current feedback controller2526may be connected to the ignition or other power line34via one or more resistors. In the depicted example, two such resistors are provided2526d,2526ewith the first drive switch circuit2525(e.g. the base of the switch device2525aof the first drive switch circuit2525) connected between the two resistors2526d,2526e—which, therefore, form a potential divider.

The switch device2526aof the current feedback controller2526has an on- and off-state (and, therefore, the current feedback controller2526also has an on- and off-state). As will be appreciated, with the current feedback controller2526in its on-state, the first drive switch circuit2525(i.e. the switch device2525athereof) is also in its on-state. Similarly, with the current feedback controller2526in its off-state, the first drive switch circuit2525(i.e. the switch device2525athereof) is also in its off-state.

Accordingly, therefore, as will be understood, the switch device2526of the current feedback controller2526and the switch device2525aof the first drive switch circuit2525act as level translators in accordance with embodiments—such that the operation of some embodiments is maintained over a wide range of voltages on the ignition or other power line34and output by the current sense circuit2522.

The current sense circuit2522is configured to output a signal indicative of the sensor current (i.e. the current downstream of the switching regulator251), this may include current drawn by the one or more sensor22and/or any current due to the sensor voltage line26being short circuited to ground. The current sense circuit2522may, therefore, comprise a resistor2522aof known resistance (and, in this example, a relatively low resistance such as 7.5 Ohms). The resistor2522aof the current sense circuit2522and the capacitor2514form a filter which reduces ripple voltages in the sensor voltage line26.

The current feedback controller2526may be connected in parallel with the current sense circuit2522. As such, in the depicted embodiment ofFIG. 4, the base and emitter of the switch device2526aof the current feedback controller2526may be connected to respective opposing terminals of the resistor2522aof the current sense circuit2522.

As will be understood, therefore, the regulator control circuit252operates in a first mode of operation with the feedback comparator2523controlling the operation of the switching regulator251on the basis of the signal representative of the sensor voltage. However, when the sensor current exceeds the predetermined level, the current feedback controller2526operates to cause the feedback comparator2523to control the operation of the switching regulator251on the basis of the signal representative of the sensor current.

In embodiments including the third mode of operation, the third mode of operation may be triggered by the voltage of the sensor voltage line26being higher than a predetermined voltage indicative of a fault—such as a short circuit fault (e.g. shorted to a connection with a higher voltage, such as a power supply of the vehicle1). This predetermined voltage may be a voltage which is predetermined and substantially fixed or may be a voltage which varies in accordance with variations in the reference voltage35.

In particular, in some embodiments, the current feedback controller2526may operate, when the current exceeds the predetermined level, to actuate the first drive switch circuit2525to control the operation of the feedback comparator2523to turn the switching regulator251into its off-state until the current falls below the predetermined level again, at which point the state of the switching regulator251is determined by the voltage of the sensor voltage line26again. Such embodiments may be used to prevent or substantially reduce the risk of the switching regulator251being kept in its on state for a long period of time if the desired voltage at the sensor voltage line26cannot be achieved. In other words, constant current control takes over from constant voltage control in such scenarios.

Accordingly, in the first mode of operation, constant voltage control is used and, in the second mode of operation, constant current control is used.

The feedback controller2526may be configured to control the operation of the switching regulator251via a regulator drive circuit2527of the regulator control circuit252. The regulator drive circuit2527is configured to receive the output from the feedback controller2526and to output a signal to control the switching regulator251in accordance with the output of the feedback comparator2523.

The regulator drive circuit2527may, therefore, include a switch device2527awhich may be a transistor device and may be an NPN transistor device. The switch device2517ais connected between the ground connection or line36and a control input of the switching regulator251(e.g. a base of the power switch device2511). The switch device2527aof the regulator drive circuit2527is configured to connect the control input to the switching regulator251into and out of electrical communication with the ground connection or line36selectively based on the output of the feedback comparator2523. The regulator drive circuit2527may further include a pull-up resistor2527bwhich is connected in electrical communication between the ignition or other power line34and the control input of the switching regulator251. A further resistor2527cmay be provided in series between the control input and the switch device2527a. Accordingly, in the depicted example ofFIG. 4, the emitter of the switch device2527aof the regulator drive circuit2527is connected in electrical communication with the ground connection or line36, the collector is connected to the control input and the base is connected to the output of the feedback comparator2523.

In some embodiments, a short circuit handling circuit2528is provided as part of the regulator control circuit252(the short circuit handling circuit2528may be configured in some embodiments to handle other faults or events too). The short circuit handling circuit2528may include a first diode2528awhich is coupled between the output of the reference voltage input2521(between the reference voltage input2521and the feedback comparator2523) and the reference voltage output35. The short circuit handling circuit2528may include a second diode2528bwhich is coupled between the output of the voltage feedback circuit2524(between the voltage feedback circuit2524and the feedback comparator2523) and the reference voltage output35. In other words, both inputs of the feedback comparator2523may include respective diodes2528a,2528bwhich are connected in electrical communication between those inputs and the reference voltage output35. The diodes2528a,2528bmay be oriented to allow the flow of current from the inputs of the feedback comparator2523to the reference voltage output35.

Accordingly, if the voltage of the sensor voltage line26exceeds the reference voltage output35(i.e. an over-voltage fault), then the second diode2528bserves to clamp the sensor voltage line26voltage to just above the reference voltage output35(i.e. a clamp voltage). This will, in turn, cause the comparator device2523aoutput to be low which will turn the switch device2527aof the regulator drive circuit2527to its off-state, which disables the switching regulator251(i.e. keeps the power switch device2511in its off-state). This is the third mode of operation discussed herein.

The first diode2528amay be configured to protect the comparator device2523a—e.g. from high voltage transients (i.e. over-voltage transients) in the ignition or other power line34—and is an example of an output voltage transient protection circuit.

Looking at the operation of the depicted embodiment in a short circuit condition in more detail, as the sensor current (i.e. the current drawn by the sensor voltage line26) increases, the switching regulator251will be operated to increase the duty cycle of the power switch device2511so that more current is passed through to the sensor voltage line26.

This increase in the sensor current will, of course, cause an increase in the current sensed by the current sense circuit2522(e.g. the voltage across the resistor2522athereof). As the voltage output by the current sense circuit2522reaches the base-emitter threshold of the switch device2526a(i.e. a threshold voltage provided by a threshold sensor current), then the switch device2526awill change to its on-state which will also change the switch device2525ato change to its on-state. With the switch device2525ain its on-state, a current will pass through the switch device2525aand will forward bias the diode2528bwhich will cause the output from the comparator device2523ato be low. This turns the switch device2527ato its off-state which turns the power switch device to its off-state. This rise of the sensor current will, therefore, cease, and the sensor current will decay as the energy storage element2512discharges.

Once the sensor current has decayed sufficiently to turn the switch device2526ato its off-state, then the sequence will repeat. The switching frequency in this mode of operation is dependent on the energy storage device2512and the current sense circuit2522.

In addition, in embodiments which include this short circuit handling capability, a hysteresis circuit may be provided as part of the feedback comparator2325or otherwise. This hysteresis circuit may include one or more resistors and/or capacitors. For example, in the depicted embodiment ofFIG. 4, a capacitor2323eand series resistor2523dmay be connected in electrical communication with the output of the comparator device2523aand the inverting input thereof. As will be appreciated, the hysteresis circuit defines an upper bound and a lower bound.

In embodiments which include the fourth mode of operation (the hybrid pulse width and frequency modulation), when the sensor current is low, the voltage across the capacitor2514will increase to the upper bound of the comparator hysteresis threshold but may take longer than the pulse width modulation cycle to decay to the lower bound of the comparator hysteresis threshold. Accordingly, a modulation pulse which would have otherwise occurred may be skipped, which will reduce switching losses, and results in a lower switching frequency.

Embodiments of the present invention, therefore, provide a system by which multiple modes of operation can be achieved dependent on the sensor current. Embodiments of the present invention may also provide handling of fault currents and/or an output over-voltage. The transition between at least the first two modes of operation may, in some embodiments, be relatively smooth and the same may be true of the other modes of operation described herein.

Some embodiments also seek to reduce the issues caused by short circuits of the sensor voltage line26to the battery31or to the ground connection or line36.

Some embodiments also seek to provide a relatively low power dissipation over a relatively wide range of voltages on the ignition or other power line34.

Some embodiments further seek to provide a very low quiescent current when there is no load on the sensor voltage line36.

Although embodiments have been described in relation to the provision of power for use by one or more analogue sensors22, it will be appreciated that embodiments could be used in relation to the provision of power to other circuit elements which require a power supply with a voltage which tracks a reference voltage. Some such embodiments may be particularly useful in relation to vehicles1and vehicle sensors (which may output analogue signals but which may still require a power supply with a voltage which tracks a reference voltage).

As will be appreciated, the regulator control circuit252of some embodiments may form part of a sensor circuit, which may include the switching regulator151and one or more sensors which are each configured to receive electrical power via the switching regulator.

As will be appreciated, embodiments of the present invention seek to provide a tracking regulator control circuit which may, in some embodiments, tolerate one or more of current overloads, over-voltages applied to the regulated output without causing excessive power dissipation, or imposing current overloads or over-voltages on the power supply or voltage reference.