GB2428311A

GB2428311A - Electronic power switching unit

Info

Publication number: GB2428311A
Application number: GB0514391A
Authority: GB
Inventors: Frank Sheppard; John Sheppard; Tony Smith
Original assignee: A D DEVELOPMENTS Ltd
Current assignee: A D DEVELOPMENTS Ltd
Priority date: 2005-07-13
Filing date: 2005-07-13
Publication date: 2007-01-24
Anticipated expiration: 2025-07-13
Also published as: GB2428311B; GB0514391D0

Abstract

An electronic power control unit 1 has power input and power output terminals; a programmable control circuit 5 determining load current, load voltage and sensors 7, 8 for and temperature and acceleration of the unit. A switching circuit 3 is connected between the input and output terminals and the programmable control circuit is programmable to operate the switching circuit to disconnect the input terminal from the output terminal in response to predetermined signals or combinations of signals from the sensors. The control unit may include a microcontroller in which the programmable control circuit is incorporated. The current sensing means and the switching circuit may be incorporated in a single integrated circuit component. An additional input port 2 may be connected to the programmable controller to which an external sensor may be connected. The control unit may have a configuration port 25 connectable to an external device to enable programming of the reprogrammable control circuit. The unit may be used in vehicles.

Description

Electronic Power Control Unit

Introduction

The present invention relates to an electronic power control unit for connecting an external power supply to a load. The invention has been devised for the automotive industry but has many other potential applications.

Motor vehicles are currently equipped with numerous on-board electrical safety systems. For example, DE-A-10058898 discloses a system having a circuit breaker arranged between the battery and the starter as well as a pre-crash sensing arrangement arranged to disconnect the battery in response to a signal from the pre-crash sensing arrangement.

Known pre-crash sensing arrangements include complex mechanical accelerometers. More recently, solid state acceleration sensors have been available which are used to provide acceleration measurements for engine management systems.

It would be advantageous to provide a power control unit for a vehicle suitable for use as an add-on safety device to augment existing vehicle control systems.

The present invention provides an electronic power control unit having power input and power output terminals; a programmable control circuit; sensors for determining load current, voltage, temperature and acceleration, all providing input signals to the programmable control circuit; and a switching circuit connected between the input and output terminals; in which the programmable control circuit is programmable to operate the switching circuit to disconnect the input terminal from the output terminal in response to predetermined signals or combinations of signals from the sensors.

The programmable control circuit incorporated in the power control unit of the present invention enables the device to be configurable according to the specific requirements of its intended use. There are numerous possibilities for the configuration of the device. Typically these will involve the use of thresholds for the various signals from the sensors. For example, it would usually be a requirement that the power be disconnected if any one of the signals exceeds a predetermined threshold. Additionally, two or more of the signals exceeding predetermined lower thresholds might also trigger interruption of the power supply.

Preferably the control unit is a solid state device incorporated in a single housing. This makes it particularly suitable for installation in an existing vehicle or other situations. Thus, for example, the programmable control circuit would typically be provided by a microcontroller which might also incorporate the voltage sensor.

Switching circuits having in built current monitoring functions are readily available and may be used to advantage in the present invention.

To increase the flexibility of the power control unit, an additional input may be provided which is connectable to an external sensor.

For certain applications, it is advantageous to provide a configuration port connectable to an external device to enable re-programming of the programmable control circuit.

An embodiment of the invention will now be described with reference to the accompanying drawing which is a schematic diagram of the main functional elements of an electronic power control unit according to the present invention.

The preferred embodiment of the invention shown in Figure 1 is an intelligent power unit for controlling the flow of electrical power from an external DC (Direct Current) power source (such as an automobile battery) to one or more electrical loads.

In simple terms, the unit behaves as an electronic relay in that a low current signal derived from an external device is used to switch on and off a high current feed to the load(s).

However, in addition to its relay-like behaviour, the unit also features several protective functions that may be used to switch off (or switch on) the load power in response to a specific event, such as a change in acceleration of the unit, or a change in its ambient temperature. These protective functions are automatic in that they require no intervention or action on the part of the user.

The functional elements are discussed in more detail in the following description. Note that although the unit is primarily intended for the automotive market, it is not restricted to that market and may be used in any application requiring the control of electrical DC load power. Although a single-channel unit is described, the principles are equaliy applicable to a multi-channel unit. However, no more than two channels are presely envisaged.

Basic Functional Description

The main elements of the unit 1 are depicted in Fig. 1. Note that the unit 1 is entirely solid state', in that no mechanical parts are used to perform any of its various functions.

Input and Output Ports The main connections to the unit 1 are: the Power Input port (Pm); the Power Output port (Po); and the Switch Input port (Sm). The unit 1 also has two optional ports, namely: the External Sensor port (ES) for connection to an external sensor 2; and the Configuration port (C). There is also a negative return port, denoted -ye (OV), which simply provides a negative return for the unit's own power. The main and optional ports are described below.

(i) Power Input port (P,) The positive terminal of the external DC power source is connected to P. This provides power for the unit 1 itself, and provides a high-current feed for the external load L via the unit's highside driver 3 to be described below. The external power source will typically be a vehicle's battery (or alternator), although the unit is not restricted to that kind of power source and could equally well derive its power from any suitable DC power source having the correct voltage rating. Inside the unit, the positive rail (denoted +Vs) is connected directly to the high-side driver 3, and also provides input power for a power supply circuit 4. The +V rail is continually monitored by a microcontroller 5.

(ii) Power Ouput port (P0) The Power Output port is connected directly to the external load and provides a switched power feed derived from the external power source via the unit's high-side driver 3. Although Fig.! shows a single load connected to P0, the unit 1 is not restricted to a single load and could be used to switch power to several loads, or even to power the entire electrical system on a vehicle, or any other electrical system having the appropriate DC voltage and power requirements. Note that the return path for the load current is via a common ground' (GND) path shared by the load and the power source.

In most automotive applications, the common ground will usually be the vehicle's chassis.

(iii) Switch Input port (Sv) Power to the load(s) is switched on and off under the control of a switch (or similar device) connected to the unit's Switch Input port (Sm). Although Fig.! depicts a switch contact 6 connected to S, the unit is not restricted to that kind of device and could equally well be controlled by any other suitable device such as a relay contact, a transistor, a digital signal derived from a computer, and so on.

(iv) External Sensor port (ES) The External Sensor port is an optional port in that it is not essential to the correct functioning of the unit 1, and is provided solely to enhance and expand the behaviour and applicability of the unit. Any one of a number of different external sensors 2 may be accommodated, such as temperature sensors, light sensors, pressure sensors, and so on. Alternatively, the external sensor could be replaced by a suitable voltage signal derived from an external electrical system.

(v) Configuration port (C) The Configuration port is an optional port in that it is not essential to the correct functioning of the unit 1. When provided, this port allows the user to reconfigure the behaviour of the unit in accordance with his or her specific needs. In this way, the configuration port provides enhanced flexibility in that the operation of the unit can be tailored to the user's needs at any suitable time after purchase. Typically, the configuration port will consist of two or more digital signal lines that will connect to an external computer or similar configuration device.

If the unit is not fitted with a configuration port, the behaviour of the unit will effectively be fixed' at the time of purchase. Thus, the user may request the manufacturer to configure the unit to his or her specific needs before it leaves the factory, or may elect simply to purchase a preconfigured unit from a range of specific options.

Main Functional Elements The unit's main functional elements are: the Power Supply Circuit 4; the Microcontroller 5; a High-Side Driver device 3; an Accelerometer 7; a Temperature Sensor 8. These components are described in more detail below.

(i) Power Supply Circuit All circuits within the unit derive their operating power from the external power source. The raw' DC voltage appearing at P is fed to an internal Power Supply circuit 4. Basically, this consists of a voltage regulator that processes the incoming voltage so as to provide a precisely controlled, stabilised DC voltage denoted V. This regulated voltage provides power for all the internal circuits.

For a typical automotive application, the voltage at P would normally be greater than V, requiring the regulator to step down' the incoming voltage.

However, there may be specialised applications in which the voltage at P could be smaller than V, requiring the regulator to step up' the incoming voltage. Thus, the type of regulator (step down or step up) will be chosen to suit the particular application.

(ii) Microcontroller The Microcontroller 5 is the unit's central processing unit, responsible for switching power to the load via the highside driver 3. The microcontroller's main tasks are: to determine the status of the switch contacts (or other device) at S; to interface with the internal sensors 7, 8 and external sensor 2 (if used); to monitor the magnitude of the power source voltage at P; to measure the load current by means of a feedback signal SENSE derived from the high-side driver 3; and to switch on or off the high-side driver 3, thus controlling the flow of power to the load.

The unit's operating parameters (the information used to determine how the unit controls the load power) are configured either by specific programming of the microcontroller 5 before the unit leaves the factory, or by means of digital signals sent to the microcontroller via the configuration port C at any time before or after the unit leaves the factory. Whichever method is used, the microcontroller stores the configuration data in electronic memory that resides inside the microcontroller itself, and/or by means of a memory device external to the microcontroller. The memory is non-volatile', in that the stored data and configuration information are not lost whenever the unit is powered down, but are retained for future use whenever power is re-applied to the unit.

(iii) High-Side Driver The unit employs a special-purpose semiconductor device 3 usually called a high-side driver' to control the load current. Also known as a solid state relay', a smart power switch' or a high-side power switch', the device incorporates a power MOSFET device together with protection and diagnostic functions integrated into a single package.

The state of the high-side driver is determined by the on/off signal output by the microcontroller 5. With the signal in the off' state, the driver behaves like an open switch and no current flows to the load. With the signal in the on' state, the driver behaves like a closed switch with very low internal resistance such that current flows to the load with minimal power dissipation in the driver device itself. Note that although Fig.! depicts a single high-side driver 3, the unit may incorporate two or more devices connected in parallel in order to minimise internal power losses, and/or to maximise the current that can be switched to the load. In this case, the drivers would effectively function as one large driver device in that they would all be switched on and off together.

In addition to power switching and protection functions, several highside drivers also provide a sense current' function, whereby the device outputs a low-level current (SENSE) that is directly proportional to the load current conducted by the internal power MOSFET. This function is utilised by the unit to measure the load current.

Alternatively, if the driver's sense current function is unsuitable for a particular application, an alternative way of measuring the load current will be employed. In either case, a signal proportional to the load current will be fed back to the microcontroller and monitored continually in real time.

(iv) Accelerometer The Accelerometer 7 is a sensor fixed inside the unit that is responsible for measuring its acceleration. Essentially, the accelerometer generates an electrical signal proportional to the unit's rate of change in velocity. This signal is monitored by the microcontroller and used to determine whether the high-side driver 3 should be switched on or off. Depending on the particular type of device fitted, the accelerometer 7 may also be used to detect and measure the unit's position relative to the horizontal plane. In this way, the device can provide a signal that is proportional to the unit's angle of'tilt'.

(v) Temperature Sensor The Temperature Sensor 8 effectively functions as a thermometer that monitors the unit's ambient temperature. The electrical signal output by the sensor is measured by the microcontroller 5 which may use the information to affect the state of the high-side driver 3. This allows the unit to respond to changes in temperature in order to switch on or off the load power whenever the temperature crosses a particular threshold.

Operation The unit's operational behaviour is determined by specific control algorithms programmed into the microcontroller 5. These algorithms effectively determine the appropriate status of the on/off signal fed to the high-side driver 3 according to the state of the switch (or other device) at S, and by monitoring the magnitude of the signals generated by: the load current sense function; the accelerometer 7; the temperature sensor 8; and any external sensor 2 that may be connected. Additionally, the magnitude of +V may also be used to influence the state of the high-side driver 3. The behaviour of the control algorithms is influenced directly by the configuration parameters stored in the unit's non-volatile memory.

The way in which each of the individual elements affects the unit's operation is described below.

(i) Input Switch The switch 6 contacts connected to the Switch Input port (SN) are used to switch on the high-side driver 3 and thus switch power to the load. Depending upon the unit's configuration, the contacts may be connected either to the battery's positive terminal (high-side switching) or to the negative terminal (low-side switching), and the load may be energised either when the contacts close (for normally open' contacts), or when they open (for normally closed' contacts).

The input device need not be a switch, but could be a relay contact, a thermostatic element, an optoisolator output, a transistor, a digital signal, or any other device that provides a switching signal of the correct polarity and magnitude.

Note that a switch or other device need not be connected to S in order to switch power to the load. If required, the unit can be made to energise the load at the instant the power source is connected to the Power Input port (Pm). This may be achieved either by hard wiring' the S port directly to the battery's positive or negative terminal, or by configuring the unit to activate the high-side switch as soon as power is applied to P. (ii) Load Current Monitoring The microcontroller 5 measures the load current (determined either by the high- side driver's current sense function, or by some other method) and compares it with a pre-configured limit, or threshold'; should the load current cross the threshold, the microcontroller 5 turns off the high- side driver 3. In this way, the unit 1 may be configured to disconnect a power source whenever the load current exceeds a particular value. The threshold may be pre-set before the unit leaves the factory, or may be configured by the user via the configuration port C. By disconnecting the power source when the load current crosses the threshold, the unit 1 behaves as an electronic fuse' or, more correctly, as a programmable circuit breaker. The unit 1 may be configured to re-try' the load a certain number of times at specific intervals in order to determine whether the overcurrent' condition has cleared.

This is achieved by turning on the high-side driver 3 for a brief period, during which the resulting load current is monitored. If, during such a re-try, the load current has fallen back to a level within its normal range, the high-side driver 3 is turned on continually thereby resuming normal operation. On the other hand, if the overcurrent condition persists, the driver is turned off and remains off until such time as the fault has been cleared and the unit has been reset' either by cycling the input power or by turning the input device off and then on again.

The ability to measure the load current accurately and to take appropriate action should it exceed a particular value is one of the unit's key protective functions.

(iii) Impact and Tilt Sensing Depending on the type of device fitted, the internal accelerometer 7 provides a measure either of the unit's acceleration, or of its angle of tilt relative to the horizontal plane. By configuring the unit to disconnect the power source when the accelerometer 7 output signal crosses a pre-set threshold, the load may be de-energised (or energised) either when the acceleration reaches a critical level (for example, upon impact in the event of the vehicle crashing), or when the angle of tilt has exceeded a safe level (as occurs when a vehicle rolls', or topples over).

Typically, the unit 1 will be configured to de-energise the load in the event of a crash or roll, such that the vehicle's electrical systems may be shut down to prevent the risk of fire or other danger. However, by appropriate configuration, the unit may be programmed to energise the load in the event of a crash or roll in order to activate one or more of the vehicle's safety functions, such as protective air-bags, fire extinguishers, andsoon.

Like the circuit breaker function described above, the ability to shut down the vehicle's electrical systems or to activate safety functions automatically in the event of a crash is one of the unit's most important protective functions.

(iv) Temperature Sensing The unit's internal thermometer 8 allows it to detect extremes of temperature and to take appropriate action. As determined by the configuration parameters, the unit may be programmed to energise or de-energise the load should the ambient temperature cross a pre-set threshold.

The unit 1 may be configured to respond to excessively low or excessively high temperatures. For example, the unit could be programmed to turn on a heating device whenever the ambient temperature dropped below a given level. Conversely, the unit could be configured to activate a cooling fan should the ambient temperature exceed a safe' level.

Alternatively, the unit could be programmed to de-energise an electrical system whenever the temperature exceeded a pre-set threshold in order to minimise the possibility of fire or other damage.

Like the load current sensing and accelerometer functions described above, the temperature sensing thresholds could be pre-set before the unit leaves the factory, or could be configured at any suitable time by means of the configuration port.

(v) External Sensor The unit may be configured to respond to an external sensor 2 connected to the optional External Sensor port ES. The output signal generated by the sensor 2 is continually monitored by the microcontroller 5. When the signal crosses a pre-set threshold determined by the configuration parameters, the microcontroller changes the state of the on/off signal fed to the high-side driver, thereby energising or deenergising the load.

The unit can accommodate any kind of sensor that generates the correct type of output signal. Typically, the signal will be in the form of a variable voltage, although other signal types (such as variable frequency digital signals, variable duty-cycle digital signals, current signals, and so on) may be accommodated.

(vi) Voltage Level Sensing The magnitude of the supply voltage (+V5) may be used to change the state of the high-side driver 3. The microcontroller 5 continually monitors the magnitude of +V and compares it to a pre-set threshold determined by the configuration parameters.

Should the voltage level cross the threshold, the microcontroller 5 changes the state of the on/off signal in order to energise or deenergise the load, as required.

Both undervoltage' and overvoltage' conditions may be dealt with. By detecting when the voltage level falls below the pre-set threshold, the unit can be made to de-energise a load that could otherwise malfunction due to insufficient supply voltage. Conversely, by detecting when the voltage level exceeds a pre-set threshold, the unit can be made to deenergise a load that would otherwise be damaged by excessively high voltage levels.

In order to avoid the effects of transient fluctuations of the supply voltage, the unit may be configured to wait until the end of a variable, pre-set delay' period before changing the state of the high-side driver 3. If the supply voltage has not returned to a level within its normal range at the end of the delay period, the change in voltage is considered to be permanent and the load is energised or de-energised as required.

Conversely, if the supply voltage has returned to normal levels by the end of the delay, the variation is treated as a transient event and the state of the load is not changed.

Imposing the delay period ensures that the unit does not respond to the transient effects of noise' and other short-term supply variations which are not uncommon in automotive and similar applications.

Claims

Claims: 1. An electronic power control unit having power input and power

output terminals; a programmable control circuit; sensors for determining load current, voltage, temperature and acceleration, all providing input signals to the programmable control circuit; and a switching circuit connected between the input and output terminals; in which the programmable control circuit is programmable to operate the switching circuit to disconnect the input terminal from the output terminal in response to predetermined signals or combinations of signals from the sensors.
2. A control unit is claimed in claim 1 including a microcontroller in which the programmable control circuit is incorporated.
3. A control unit as claimed in claim 2 in which the voltage sensor is incorporated in the microcontroller.
4. A control unit as claimed in claim 1, 2 or 3 in which current sensing means and the switching circuit are incorporated in a single integrated circuit component.
5. A control unit as claimed in any preceding claim having an additional input port connected to the programmable controller to which an external sensor may be connected.
6. A control unit as claimed in any preceding claim having a configuration port connectable to an external device to enable reprogrammable of the programming control circuit.
7. A control unit as claimed in any preceding claim in which all of the components are solid state devices.
8. A control unit as claimed in any preceding claim in which all of the components are contained in a single housing.
9. A control unit substantially as hereinbefore described with reference to the accompanying drawings.