Patent Description:
Some vehicle electrical systems (such as an antilock brake system for a trailer configured to be towed by a truck) require a defined current load in order to confirm the correct operation or connection of one or more parts of the electrical system. For example, some vehicle braking systems for vehicles comprising a truck and trailer combination require a current load to be applied to the truck ignition line in order to confirm the connection of a braking system of the trailer. This load may be required during the starting of the vehicle as well as for a period of operation of the vehicle (e.g. as the vehicle is travelling).

Accordingly, a resistor is commonly used to provide the current load. For example, a braking system of a trailer may include a resistor which draws current from the ignition line when the braking system of the trailer is connected to the truck.

Other instances in which this may occur includes parts of the vehicle electrical system which were originally designed for incandescent lamp. Many such systems require a relatively large current to be drawn by the incandescent lamp in order to indicate that a working incandescent lamp has been connected correctly. Subsequent retrofitting of LED lamps, however, mean that the same magnitude of current is no longer drawn and the vehicle electrical system may, therefore, cease the supply of electrical power to the lamp and/or issue an indication that the lamp is not functioning. This is conventionally resolved by providing a ballast resistor.

The resistors used in these examples draw current sufficient to satisfy the requirements of the vehicle electrical system but often perform no other useful function. A significant amount of power may be dissipated through the resistors.

Therefore, for the braking system example, a resistor value may be selected based on a cranking voltage of the vehicle (to ensure that the current load is sufficiently high even when the voltage on the ignition line is relatively low). However, the voltage on the ignition line will be much higher at other times (such as when a battery of the vehicle is being charged, e.g. using an alternator or other charging system). These periods of operation at a higher voltage may be much longer than the periods during which the ignition line is at a lower voltage. Therefore, the current drawn by the resistor may be higher than is necessary for a long period of time. For example, the current load required by the vehicle electrical system may be 80mA and the vehicle cranking voltage may be 16V. Therefore, a resistor of <NUM> Ohms would be needed (i.e. <NUM>/<NUM>). However, during charging, the ignition line voltage may be 32V. Thus, the power loss through the resistor would be 5W (i.e. <NUM><NUM>/<NUM>), which may be dissipated for substantially the entire time the vehicle is operating.

In both examples, the resistors dissipate the power as waste heat. Typically, the higher the current required, the lower the resistance required and the more power which must be dissipated, requiring a physically larger resistor. Therefore, not only is there an issue of inefficient use of electrical power but there is also an issue with housing/locating the resistors, removal of the heat generated, and, of course, the cost of the resistors.

<CIT> discloses a vehicle energy retrieving device which includes an input current detection circuit, a boost converter circuit, an output voltage detection circuit, a power source and a load end. The input current detection circuit controls input current and the boost converter circuit is electrically connected to the input current detection circuit in series and converts low voltage into high voltage. The output voltage detection circuit controls output voltage when the circuit is an open circuit. The vehicle energy retrieving device retrieves the surplus electric power and recharges the surplus electric power to the power source to improve the shortcomings of the conventional driving computer system so that when braking or driving, the driving computer system does not generate any false signals.

<CIT> discloses an electrical system for a tractor trailer combination.

There is a need, therefore, to alleviate the problems caused by vehicle electrical systems requiring a current load in these and similar circumstances.

Accordingly, an aspect of the present invention provides a trailer braking system current load circuit configured to provide a predetermined current load on a power line of an electrical supply system of a vehicle, the current load circuit comprising: a switching boost converter configured to be charged from the current load line and to discharge to a return line of the electrical supply system of the vehicle; and a current load control circuit configured to control the operation of the switching boost converter to maintain a current load on the current load line above a predetermined current during operation of the switching boost converter, such that a portion of the current drawn from the current load line is returned to the return line of the electrical supply system of the vehicle.

The circuit may further comprise a fault detection circuit which is configured to determine whether a voltage on the return line is below a predetermined threshold voltage and to cease operation of the switching boost converter if the voltage on the return line is below the predetermined threshold voltage.

The current load control circuit may be coupled to a current sense element which is configured to provide the current load control circuit with an indication of the current through an inductor of the switching boost converter.

The circuit may further comprise a rectifier which is configured to rectify an output of the switching boost converter.

The rectifier may be a synchronous rectifier which is configured to operate synchronously with the switching boost converter and/or may be an AC coupled rectifier.

Another aspect provides an electrical supply system of a vehicle, including: a current load line; a return line; a trailer braking system switching boost converter configured to be charged from the current load line and to discharge to the return line; and a trailer braking system current load control circuit configured to control the operation of the switching boost converter to maintain a current load on the current load line above a predetermined current during operation of the switching boost converter, such that a portion of the current drawn from the current load line is returned to the return line of the electrical supply system of the vehicle.

The electrical supply system may further comprise a fault detection circuit which is configured to determine whether a voltage on the return line is below a predetermined threshold voltage and to cease operation of the switching boost converter if the voltage on the return line is below the predetermined threshold voltage.

The electrical supply system may further comprise a rectifier which is configured to rectify an output of the switching boost converter.

The electrical supply system may further comprise a control device which is configured to determine whether an element is connected or correctly connected to the electrical supply system based on the current load on the current load line.

Another aspect provides a vehicle including an electrical supply system as above, further comprising a braking system.

The trailer braking system switching boost converter and trailer braking system current load control circuit may form part of the braking system.

Embodiments of the present invention are described, by way of example only, with reference to the accompanying drawings, in which:.

In some embodiments, see <FIG> for example, the present invention includes a vehicle <NUM> to which a braking system <NUM> has been fitted. The vehicle <NUM> may include a truck <NUM> and trailer <NUM>, the trailer <NUM> being configured to be towed by the truck <NUM>. The braking system <NUM> may, therefore, include a portion which is part of the truck <NUM> and a portion which is part of the trailer <NUM>. Other configurations of braking system <NUM> and vehicle <NUM> may, however, be used in other embodiments.

The braking system <NUM>, with reference to <FIG>, includes a brake module <NUM> which is configured, on actuation, to apply a braking force to one or more ground engaging wheels of the vehicle <NUM> (e.g. of the truck <NUM> and/or trailer <NUM>) in order to slow the vehicle <NUM> and/or substantially prevent its movement. The braking system <NUM> may also include a braking system load recovery circuit <NUM>.

The vehicle <NUM> may, in some embodiments, include a lighting system <NUM> which may be part of the truck <NUM>, part of the trailer <NUM>, or part of both the truck <NUM> and the trailer <NUM> (see <FIG>, for example). The lighting system <NUM> may include, for example, one or more lamps <NUM> which are configured to light an area or volume around at least part of the vehicle <NUM> and/or to provide an indication of the operation or intended operation of the vehicle <NUM> (such as brake lights, turn signals, etc.). The lighting system <NUM> may also include a lighting system load recovery circuit <NUM>.

The vehicle <NUM> includes an electrical supply system <NUM>, see <FIG>, which is configured to provide electrical power to one or more units of the vehicle <NUM>, including the braking system <NUM> and the lighting system <NUM>, if provided.

The electrical supply system <NUM> may include a battery <NUM> and a generation system <NUM> (such as an electrical alternator or other generator) which is configured to generate electricity using mechanical power generated by an engine of the vehicle <NUM>, for example. The electrical supply system <NUM> may include an ignition or other current load line <NUM> which is configured, with a ground line, to supply electricity to the one or more units of the vehicle <NUM>. In this instance, the voltage of the electricity supplied through the electrical supply system <NUM> may be 12V, 24V, or 32V, for example. The battery <NUM> - if provided - may be configured to provide electrical power at any one of these voltages.

The braking system <NUM> and/or the lighting system <NUM> are configured to be connected in electrical communication with the electrical supply system <NUM> such that electrical power from the electrical supply system <NUM> is provided to the braking system <NUM> and/or lighting system <NUM>. Accordingly, the ignition or other current load line <NUM> may be connected to the braking system <NUM> and/or the lighting system <NUM>.

The vehicle <NUM> may further include one or more control devices <NUM> which are each configured to control an aspect of the operation of the vehicle <NUM>. This may include, for example, determining whether the braking system <NUM> (or a part thereof) is correctly connected. Thus, a control device <NUM> of the one or more control devices <NUM> may be configured to determine whether a part of the braking system <NUM> associated with the trailer <NUM> is correctly connected to a part of the braking system <NUM> associated with the truck <NUM>. Similarly, the one or more control devices <NUM> may include a control device which is configured to determine whether a part of the lighting system <NUM> is correctly fitted and/or operating correctly. Thus, for example, the control device <NUM> may be configured to determine if a lamp <NUM> is fitted to the lighting system <NUM> and/or if the lamp <NUM> is operating correctly.

The or each control device <NUM> may use a current load to determine whether the braking system <NUM> (or a part thereof) is correctly connected and/or to determine if a lamp <NUM> is correctly fitted and/or functioning correctly.

The braking system load recovery circuit <NUM> and the lighting system load recovery circuit <NUM> may each be configured to provide the current load expected by the associated control device <NUM> such that the control device <NUM> can determine that the braking system <NUM> (or a part thereof) is correctly connected and/or if the lamp <NUM> is correctly fitted and/or functioning correctly.

The braking system load recovery circuit <NUM> and the lighting system load recovery circuit <NUM> may operate in a corresponding manner and embodiments will, therefore, be described with reference to a single load recovery circuit <NUM>/<NUM> which could be implemented as either of the braking system or lighting system load recovery circuit <NUM>. Of course, the same or a similar load recovery circuit <NUM>/<NUM> could be used in other situations in which a current load is required in part of a vehicle <NUM> in order to indicate the presence of a part of the vehicle <NUM>, the correct connection of that part, and/or the correct functioning of that part.

With reference to <FIG>, the load recovery circuit <NUM>/<NUM> is configured to receive electrical power from an ignition or other current load line <NUM>. A current load control circuit <NUM> is coupled in electrical communication with the ignition or other current load line <NUM> and is configured to determine, selectively, whether the electrical power is delivered to a switching boost converter <NUM> of the load recovery circuit <NUM>/<NUM>.

The switching boost converter <NUM> is configured to use the electrical power from the ignition or other current load line <NUM> in order to provide a return current to a battery return line <NUM>.

The current load control circuit <NUM> is further configured to ensure that the current drawn from the ignition or other current load line <NUM> exceeds a predetermined current load during operation of the switching boost converter <NUM>. The current load control circuit <NUM> may be further configured to control the operation of the switching boost converter <NUM> to moderate the current drawn from the ignition or other current load line <NUM> (i.e. the current load) is greater than the predetermined current load and may be configured to control the operation of the switching boost converter <NUM> to moderate the current drawn from the ignition or other current load line <NUM> below a further predetermined current load. In some embodiments, the current load control circuit <NUM> is configured to ensure that the current drawn from the ignition or other current load line <NUM> is substantially the predetermined current load during operation of the switching boost converter <NUM>. Accordingly, when the switching boost converter <NUM> is being discharged (i.e. an inductor <NUM> of the switching boost converter <NUM> is discharging), the current load control circuit <NUM> may couple a resistive load to the ignition or other current load line <NUM> to maintain the current load on the ignition or other current load line <NUM>. In some embodiments, the current drawn from the ignition or other current load line <NUM> may be substantially continuous but may include a degree of ripple. The current is, as will be understood, pulsed in the battery return line <NUM> during operation of embodiments.

The switching boost converter <NUM> may be connected in electrical communication with a rectifier circuit <NUM> which may be configured to ensure that the output voltage of the switching boost converter <NUM> with respect to the ground line is the correct polarity to charge a battery <NUM> connected to the battery return line <NUM> - i.e. a positive voltage with respect to the ground line.

The rectifier circuit <NUM> may, accordingly, also form part of the load recovery circuit <NUM>/<NUM>.

The load recovery circuit <NUM>/<NUM> may further include a fault detection circuit <NUM> which is configured to detect a fault situation and to terminate operation of the switching boost converter <NUM> in the event of a detected fault situation. In particular, the fault detection circuit <NUM> may be configured to detect a low voltage on the battery return line <NUM> (with respect to the ground line) which may indicate, for example, that the battery <NUM> has become disconnected, discharged or is faulty. In such a fault situation, operation of the switching boost converter <NUM> is ceased with the aim of reducing the risk of the load recovery circuit <NUM>/<NUM> becoming the main source of electrical power for one or more other parts of the vehicle <NUM>.

Thus, in operation, the current load control circuit <NUM> operates to maintain a current load which is greater than or equal to the predetermined current load, whilst operating the switching boost converter <NUM> to return a part of the electrical power drawn from the ignition or other current load line to a battery return line <NUM> to which the battery <NUM> may be connected. As such, compared to many prior systems, this arrangement may result in less wasted power, for example. The efficiency of the operation of some embodiments may be over <NUM>% in some instances, so instead of 5W dissipated by some conventional systems the power dissipated may be as low as about <NUM>.

Accordingly, reference is now made to the example embodiment in <FIG> with this figure used to describe the operation of the depicted embodiment but also other embodiments of the invention.

In this example embodiment, the current load control circuit <NUM> includes a current sense element <NUM> which may be configured to sense the current draw by the switching boost converter <NUM> (e.g. in the charging of an inductor <NUM> thereof). The current sense element <NUM> may be coupled to a control switch device <NUM> of the current load control circuit <NUM> which is configured to be actuated between an on and an off state. When in the on-state, the control switch device <NUM> is configured to couple the ignition or other current load line <NUM> in electrical communication with the switching boost converter <NUM> and, in particular, with a drive circuit <NUM> of the switching boost converter <NUM>. When in the off-state, the control switch device <NUM> is configured to disconnect the ignition or other current load line <NUM> from the switching boost converter <NUM> and, in particular, from the drive circuit <NUM> of the switching boost converter <NUM>.

In some embodiments, the current sense element <NUM> is a relatively low value resistor (e.g. <NUM> or <NUM> Ohms) and the control switch device <NUM> is a transistor device which may be a PNP transistor. The current sense element <NUM> may, therefore, be connected between the base of the control switch device <NUM> and the ignition or other current load line <NUM>. The emitter of the control switch device <NUM> may be connected to the ignition or other current load line <NUM> and the collector of the control switch device <NUM> may be connected to the ground line via one or more resistors. The one or more resistors may include a first resistor <NUM> and a second resistor <NUM>, such that the switching boost converter <NUM> (e.g. the drive circuit <NUM> of the switching boost converter <NUM>) is connected in electrical communication between the first and second resistors <NUM>,<NUM> - which may, as will be understood, form part of a level translator.

The base of the control switch device <NUM> may be further connected to the switching boost converter <NUM> and, in particular, to the inductor <NUM> of the switching boost converter <NUM>.

When the inductor <NUM> of the switching boost converter <NUM> is uncharged or below an energy threshold, as determined by the current sense element <NUM>, the control switch device <NUM> is in its off-state. In other words, as the current through the current sense element <NUM> is less than a threshold current (set by the resistance of the current sense element), the control switch device <NUM> is in its off-state. As the level of energy stored in the inductor <NUM> rises, the current through the current sense element <NUM> will increase until the threshold current is exceeded. This will cause the control switch device <NUM> to adopt its on-state.

With the control switch device <NUM> in its on-state, the switching boost converter <NUM> will discharge the inductor <NUM> to the return line <NUM> - as described below.

The switching boost converter <NUM> may include the drive circuit <NUM> which is configured to drive the operation of a main switch device <NUM> of the switching boost converter <NUM> - the main switch device <NUM> controlling whether the inductor <NUM> is charged or discharged. As will be appreciated, the inductor <NUM> in the switching boost converter <NUM> is an example of an energy storage element configured to be charged and discharged during operation of the switching boost converter <NUM>.

The current drive circuit <NUM> may include a drive switch device <NUM> which is configured to control the operation of the main switch device <NUM> of the switching boost converter <NUM>. Accordingly, the drive switch device <NUM> may include a transistor device. The drive switch device <NUM> may be connected to the ignition or other current load line via at least part of the fault detection circuit <NUM>.

In some embodiments, the drive switch device <NUM> is a transistor device which may be an NPN transistor. The emitter of the drive switch device <NUM> may be connected in electrical communication with the ground line, and the collector of the drive switch device <NUM> may be connected in electrical communication with the fault detection circuit <NUM>, which may be via a resistor <NUM>. The base of the drive switch device <NUM> may be coupled in electrical communication with the current load control circuit <NUM> such that the current load control circuit <NUM> is configured to control its operation. The connection of the base of the drive switch device <NUM> may be to the potential divider formed by the first and second resistors <NUM>,<NUM> of the current load control circuit <NUM>, for example.

Accordingly, as will be understood, the actuation of the drive switch device <NUM> between an on and an off state is controlled by the current load control circuit <NUM>.

A coupling capacitor <NUM> of the drive circuit <NUM> may couple the base of the drive switch device <NUM> to the collector of the main switch device <NUM> - see below. The coupling capacitor <NUM>, if included, provides positive feedback which speeds up the switching of the main switch device <NUM> and which may improve efficiency.

The main switch device <NUM> is configured to be actuated by on and off states by the drive switch device <NUM>. With the drive switch device <NUM> in its on-state (determined by the control switch device <NUM> being in its on-state), the main switch device <NUM> is configured to be in its off-state. With the drive switch device <NUM> in its off-state (determined by the control switch device <NUM> being in its off-state), the main switch device <NUM> is configured to be in its on-state.

When in the on-state, the main switch device <NUM> is configured to cause the charging of the inductor <NUM> of the switching boost converter <NUM> and, when in the off-state, the main switch device <NUM> is configured to cause the discharging of the inductor <NUM> of the switching boost converter <NUM>.

The main switch device <NUM> may be a transistor device and may be an NPN transistor. The emitter of the main switch device <NUM> may be connected in electrical communication with the ground line, the base may be connected in electrical communication with the collector of the drive switch device <NUM>, and the collector may be connected in electrical communication with the inductor <NUM>.

The switching boost converter <NUM> may include a diode <NUM> (see <FIG>) which is also connected in electrical communication with the inductor <NUM>, and the main switch device <NUM> (e.g. with the collector thereof). The diode <NUM> may also be connected in electrical communication with the battery return line <NUM>.

In some embodiments, a rectifier circuit <NUM> is provided instead of or in addition to the diode <NUM> (see <FIG>). The rectifier circuit <NUM> may be configured to operate synchronously with the switching boost converter <NUM>. In some embodiments, the rectifier circuit <NUM> is an AC coupled synchronous rectifier.

Accordingly, in some embodiments, the rectifier circuit <NUM> is configured to be actuated to an on-state (in which a current is permitted to pass to the battery return line <NUM>) by an output of the main switch device <NUM>. As such, the rectifier circuit <NUM> may include an active switch device <NUM> which is coupled to the main switch device <NUM> and configured to be actuated in accordance therewith. This coupling may be via a capacitor <NUM>. The active switch device <NUM> may be a transistor device and may be an NPN transistor. Accordingly the base of the active switch device <NUM> may be coupled in electrical communication with the collector of the main switch device <NUM>, e.g. via the capacitor <NUM>. The base and the emitter of the active switch device <NUM> may be coupled in electrical communication via a resistor <NUM>, for example. The emitter of the active switch device <NUM> may be further connected in electrical communication with the battery return line <NUM> and the collector of the active switch device <NUM> may be connected in electrical communication with the inductor <NUM> such that, when the active switch device <NUM> is in its on-state current is allowed to pass from the inductor <NUM>, through the rectifier circuit <NUM>, and to the battery return line <NUM>.

The diode <NUM> also, as will be understood, serves as a rectification circuit. Therefore, may be referred to herein as an alternative to the rectifier circuit <NUM> and references to the rectifier circuit <NUM> may be references to a rectifier circuit of which the rectifier circuit <NUM> in <FIG> is one example and the diode <NUM> of <FIG> is another.

When the main switch device <NUM> is in its on-state, the active switch device <NUM> may be in its off-state (such that the inductor <NUM> does not discharge through the diode <NUM>/rectifier circuit <NUM>) and with the main switch device <NUM> in its off-state, current may pass through the diode <NUM> or the active switch device <NUM> may be in its on-state and current may pass therethrough to the return line <NUM>.

As will be appreciated, with the control switch device <NUM> is in its off-state, the drive switch device <NUM> is in its off-state (as a result of the second resistor <NUM>). The main switching device <NUM> is consequently in its on-state by virtue of the current through the fault detection circuit <NUM> (e.g. through a shutdown switch device <NUM>, see below) and the resistor <NUM>.

The current through the inductor <NUM> rises and, when the current through the current sense element <NUM> increases to exceed the threshold current, this will cause the control switch device <NUM> to adopt its on-state.

With the control switch device <NUM> in its on-state, the drive switch device <NUM> will be actuated to its on-state which, in turn, causes the main switch device <NUM> to actuate to its off-state.

The energy in the inductor <NUM> will dissipate by delivering current to the rectifier circuit <NUM> and/or the diode <NUM>. The current through the rectifier circuit <NUM> and/or diode <NUM> will, therefore, rise as the energy stored in the inductor <NUM> decays. Accordingly, the inductor <NUM> returns current to the return line <NUM> (e.g. through the rectifier circuit <NUM> and/or diode <NUM>).

As a result of the operation of some embodiments, the current drawn from the current load line <NUM> is substantially continuous but the current returned to the battery return line <NUM> is intermittent (but at a higher voltage).

The fault detection circuit <NUM> is configured to compare a voltage on the battery return line <NUM> with a further voltage (which may be a predetermined voltage and/or which may be dependent on the voltage of the ignition or other current load line <NUM>). If the voltage on the battery return line <NUM> is sufficiently low, then the fault detection circuit <NUM> is configured to cease the operation of the main switch device <NUM>. This may be achieved, for example, by altering the operation of the drive circuit <NUM> (e.g. the drive switch device <NUM>). In particular, the fault detection circuit <NUM> may be configured to disconnect the collector of the drive switch device <NUM> from the ignition or other current load line <NUM> on detection of a fault.

The fault detection circuit <NUM> may include a shutdown switch device <NUM> which is configured to cause the operation of the main switch device <NUM> to cease and may include a drive shutdown switch device <NUM> which is configured to drive the operation of the shutdown switch device <NUM>. The shutdown and drive shutdown switch devices <NUM>,<NUM> may include transistor devices and may both be PNP transistors.

Accordingly, the emitter of the shutdown switch device <NUM> may be connected in electrical communication with the ignition or other current load line <NUM>, the collector of the shutdown switch device <NUM> may be connected in electrical communication with the main switch device <NUM> (e.g. the base thereof and may be via the resistor <NUM>) and the drive circuit <NUM> (e.g. with the drive switch device <NUM> and maybe with the collector thereof, and maybe via the resistor <NUM>). The base of the shutdown switch device <NUM> may be connected in electrical communication with the drive shutdown switch device <NUM> (e.g. in particular, with the collector thereof). The collector of the drive shutdown switch device <NUM> may be further connected in electrical communication with the ground line (e.g. via a resistor <NUM>), and the emitter may be connected in electrical communication with the ignition or other current load line <NUM>. The base of the drive shutdown switch device <NUM> may be connected in electrical communication with a reference voltage and the battery return line <NUM>. The reference voltage may be provided by the ignition or other current load line <NUM>. If the battery return line voltage is sufficiently high, then the drive shutdown switch device <NUM> controls the shutdown switch device <NUM> to maintain the operation of the main switch device <NUM> and, hence, the switching boost converter <NUM>. If, however, the battery return line voltage drops sufficiently, then the drive shutdown switch device <NUM> controls the shutdown switch device <NUM> to cease the operation of the main switch device <NUM> and, hence, the switching boost converter <NUM>. Accordingly, the base of the drive shutdown switch device <NUM> may be connected in electrical communication with the battery return line <NUM>, via a first resistor <NUM> to the ignition or other current load line <NUM>, and via a second resistor <NUM> to the ground line.

A protective diode <NUM> and return line resistor <NUM> may be provided in series on the battery return line <NUM> between the rectifier circuit <NUM> connection to the battery return line <NUM> and rest of the fault detection circuit <NUM>. If the battery return line <NUM> voltage is sufficiently high for the drive shutdown switch device <NUM> to control the shutdown switch device <NUM> to maintain the operation of the main switch device <NUM> and, hence, the switching boost converter <NUM>, then the protective diode <NUM> will not conduct.

In some embodiments, the fault detection circuit <NUM> may be configured to turn off the shutdown switch device <NUM>, if the current load line <NUM> voltage exceeds a voltage threshold (this may occur, for example, as a result of load dump transients). In some embodiments, the voltage threshold may be defined by a plurality of resistors - such as the first resistor <NUM> and the second resistor <NUM> - which may form a potential divider.

Accordingly, if the voltage of current load line <NUM> exceeds the threshold voltage then the drive shutdown switch device <NUM> controls the shutdown switch device <NUM> to cease the operation of the main switch device <NUM> and, hence, the switching boost converter <NUM>.

As will be appreciated, in accordance with some embodiments, the current load is provided on the ignition or other current load line <NUM> and yet a portion of the current is returned to the battery return line <NUM> - to recharge the battery <NUM>. Accordingly, some embodiments provide more energy efficient mechanisms for providing the current load than some prior systems. In addition, some embodiments eliminate or substantially reduce the need to provide large ballast resistors in order to achieve the required current load. Furthermore, some embodiments, provide the current load over a relatively wide range of voltages on the current load line <NUM> and/or return line <NUM>, such that the current load is provided during the voltages on the ignition or other current load line <NUM> which are likely to be encountered during cranking of the vehicle <NUM> and also during normal operation of the vehicle <NUM> - that current load being the predetermined current load and substantially the same over this range of voltages.

The fault detection circuit <NUM> which may be included in some embodiments, helps to ensure that the load recovery circuit <NUM>/<NUM> is not used to power unintended parts of the vehicle <NUM> which may draw an excessive current from the load recovery circuit <NUM>/<NUM> if the battery <NUM> is not present or is overly discharged and/or to disable the load recovery circuit <NUM>/<NUM> if the current load line <NUM> and/or return line <NUM> voltage exceeds a respective threshold.

An alternative embodiment is depicted in <FIG>. This embodiment is similar to the embodiment of <FIG> and like parts have been provided with like reference numerals. However, in accordance with this embodiment, and some other embodiments, the current load control circuit <NUM> takes a different form. In particular, the first resistor <NUM> is not used but a resistor 532d is provided instead to provide a tail current. The control switch device <NUM> is supplemented with a further control switch device 532a. Again the further control switch device 532a may be a transistor device and may be a PNP transistor device. The emitters of the control switch device <NUM> and further control switch device 532a may be connected together in electrical communication and coupled via the resistor 532d to the ignition or other current load line <NUM>. The base of the further control switch device 532a may be coupled in electrical communication with the ground line and, via a first resistor 532c (to provide a bias and base current for the further control switch device 532a). The base of the further control switch device 532a may be further coupled in electrical communication via a Zener diode 532b to the ignition or other current load line <NUM>. Accordingly, in some embodiments, a bandgap diode (e.g. the Zener diode 532b) is provided to achieve a regulated current drawn from the ignition or other current load line <NUM>. In addition, in this and some other embodiments, the coupling capacitor <NUM> of the drive circuit <NUM> of the switching boost converter <NUM> (see above) may be provided. This coupling capacitor <NUM> may be provided to seek to improve switching efficiency, for example.

The embodiments of <FIG>, <FIG> and <FIG>, and some other embodiments, provide a regulated current load control circuit <NUM>. In some embodiments, the regulated current load control circuit <NUM> of <FIG> is more tolerant to variations in the voltage of the ignition or other current load line <NUM> and/or temperature variations than the embodiments of <FIG> and <FIG>.

<FIG> shows the provision of both the diode <NUM> and the rectifier circuit <NUM>. As discussed above, in some variations only one of the diode <NUM> and rectifier circuit <NUM> may be provided.

As explained above, the load recovery circuit <NUM>/<NUM> may be used as a braking system load recovery circuit <NUM> or a lighting system load recovery circuit <NUM>.

A vehicle <NUM> may include one or more such load recovery circuits <NUM>/<NUM>. In some embodiments, the truck <NUM> may include one or more such load recovery circuits <NUM>/<NUM>. In addition or alternatively, the trailer <NUM> may include one or more such load recovery circuits <NUM>/<NUM>.

Embodiments of the invention have been described with reference to lighting and braking systems. However, it will be appreciated that embodiments may be used in relation to other elements and systems which are configured to be connected to the electrical supply system of a vehicle.

In some embodiments, the current drawn from the ignition or other current load line <NUM> is less than 100mA. In some embodiments, the current drawn from the ignition or other current load line <NUM> is about 80mA. The load recovery circuit <NUM>/<NUM> of some embodiments may be configured to return a substantial part of this current to the return battery line <NUM> (for example, about <NUM>%-<NUM>% of the load current from the current load line <NUM> may be returned in some embodiments). In some other embodiments, e.g. for lighting applications, the current from the current load line <NUM> could be higher with, in some embodiments, a similar proportion returned.

As will be appreciated, therefore, the operation of the current load circuit <NUM>/<NUM> of embodiments provides a regulated current load which may use pulse width modulation to maintain a substantially constant current load via an inductor <NUM> which is used to provide a return current.

Claim 1:
A trailer braking system current load circuit (<NUM>,<NUM>) configured to provide a predetermined current load on a current load line (<NUM>) of an electrical supply system of a vehicle (<NUM>), the current load circuit (<NUM>,<NUM>) comprising:
a switching boost converter (<NUM>) configured to be charged from the current load line (<NUM>) and to discharge to a return line (<NUM>) of the electrical supply system of the vehicle (<NUM>); and
a current load control circuit (<NUM>) configured to control the operation of the switching boost converter (<NUM>) to maintain a current load on the current load line (<NUM>) above a predetermined current during operation of the switching boost converter (<NUM>), such that a portion of the current drawn from the current load line (<NUM>) is returned to the return line (<NUM>) of the electrical supply system of the vehicle (<NUM>).