Abstract:
The invention relates to a circuit for supplying a consumer ( 10 ) with electric energy provided by a battery ( 11 ). The battery voltage (Ub) is prevented from falling below a predetermined minimum voltage (Umin) by a regulator ( 18 ) which adjusts the battery voltage (Ub) to a predetermined minimum voltage (Umin) by influencing the average amount of energy which is provided to the consumer ( 10 ). Preferably, the inventive circuit is used in a motor vehicle.

Description:
FIELD OF THE INVENTION 
     The present invention is based on a circuit arrangement for supplying electrical energy to a load. 
     BACKGROUND INFORMATION 
     German Patent Application No. 39 36 638 describes a circuit arrangement that ensures the supply of energy to electrical loads in an electrical system of a motor vehicle. By deactivating individual loads in controlled fashion, the vehicle voltage is prevented from dropping below a predefined value. This action ensures that the energy content of the motor vehicle battery is at least sufficient for a starting operation. In order to prevent excessively frequent activation and deactivation of individual loads when a threshold battery voltage value is reached, it is necessary to provide a hysteresis which ensures that after being deactivated, a load is not reactivated again until the voltage has risen by an amount equal to the hysteresis. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a circuit arrangement for supplying electrical energy to a load that prevents the residual energy contained in a battery from dropping below a predefined quantity. 
     The circuit arrangement according to the present invention has the advantage that the energy stored in the battery can be made completely available for powering the loads until a predefined minimum battery voltage is reached. The fact that the circuit arrangement according to the present invention operates continuously prevents frequent complete activation and deactivation of the load. 
     The advantages are achieved by the fact that a controller is provided that regulates the battery voltage to the minimum battery voltage by delivering a manipulated variable, which defines the electrical power consumption of the load. A prerequisite is that the power of the load be controllable at least within predefined limits. If the circuit arrangement according to the present invention is arranged in a motor vehicle, such loads are, for example, a fan, an air conditioner, a refrigerator, a receiver of a remote control system or, for example, an alarm system. The minimum battery voltage that is to be defined is established in such a way that on the one hand the functionality of the load can still be maintained, and on the other hand a reserve still remains so that, for example in a motor vehicle, a starting operation can be performed. 
     A first advantageous embodiment provides for the power consumption of the load to be defined by a pulse-width modulation of the supply voltage of the load. The clock frequency is preferably defined in such a way that the load current flows as continuously as possible. 
     Another embodiment provides for the manipulated variable that defines the electrical power consumption of the load to be limited to a lower value. The limitation to a lower value can advisable in terms of the behavior of the load. Another considerable advantage is the fact that the voltage of the battery can largely be prevented from dropping below the predefined minimum battery voltage in the context of control fluctuations. 
     An advantageous embodiment provides for the minimum battery voltage to be influenced as a function of correction variables such as, for example, the battery temperature or the current flowing through the battery. 
     A preferred use of the circuit arrangement according to the present invention exists in a motor vehicle that has a vehicle electrical system with a battery. An air conditioner or at least one fan is provided, for example, as the load. A remote control system or an alarm system can also be provided as the load. These loads can be active while the vehicle is unoccupied, with no risk that the battery voltage will fall below the predefined minimum. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The FIGURE illustrates a block diagram of a circuit arrangement according to the present invention for supplying electrical energy, made available by a battery, to a load. 
    
    
     DETAILED DESCRIPTION 
     The FIGURE shows a load  10  that is to be supplied with electrical energy, which is made available by a battery  11 . Load  10  and battery  11  are connected to a circuit ground  12 . Load  10  can be connected via an output stage  13  to battery  11 . 
     The voltage at battery  11  is sensed by a voltage measuring device  14  and conveyed as battery voltage Ub to a summing point  15  that is contained in a control loop. Also conveyed to summing point  15  are a minimum battery voltage Umin that is made available by a minimum voltage setpoint generator  16 , and a correction voltage Ukorr that is made available by a battery parameter measuring device  17 . 
     Summing point  15  delivers a system deviation dU to a controller  18 , which generates a manipulated variable S that is conveyed to a manipulated variable converter  19 . Manipulated variable converter  19  has delivered to it a lower limit value Su that is made available by a limit value generator  20 , and delivers a limited manipulated variable Sb to output stage  13 . 
     The circuit arrangement according to the present invention operates as follows: 
     Load  10 , which is supplied with electrical energy from battery  11 , is intended to be capable of operating as long as possible without creating the risk of a deep discharge of battery  11 . Battery  11  is arranged, for example, in a motor vehicle. When the engine is switched off, i.e. when the battery is not being recharged, provision must be made for there always to be enough energy remaining in battery  11  to start the engine. 
     Using the assumption that the average power consumption of load  10  is controllable at least within certain limits, the average power is defined in such a way that the battery voltage Ub is regulated to a predefined minimum battery voltage Umin. The control system thus attempts, while the battery is discharging and when the minimum battery voltage Umin is reached, to hold the battery voltage Ub for as long a period as possible at the value of the minimum battery voltage Umin, by lowering the average power of load  10 . 
     To perform the control action, the voltage present at battery  11  is sensed by voltage measuring device  14  and is conveyed, as the actual value of the battery voltage Ub, to summing point  15 , which is contained in a control loop. The setpoint of the control loop is made available by minimum voltage setpoint generator  16  as the minimum battery voltage Umin. Optionally, a correction is made which shifts the minimum battery voltage Umin at least slightly by way of the correction voltage Ukorr. The correction voltage Ukorr is made available by battery parameter measuring device  17 , which senses, for example, the temperature of battery  11  or, for example, the discharge current flowing through battery  11 . These parameters influence the energy that can be withdrawn from battery  11 , and are therefore advantageously utilized to correct the initially predefined minimum battery voltage Umin. The minimum battery voltage Umin must be established at a value at which a compromise is struck between the maximum possible operating time of load  10  and the remaining minimum energy quantity in battery  11 . 
     When the battery is completely charged, i.e. when the battery voltage Ub is much greater than the minimum battery voltage Umin, controller  18  defines the manipulated variable S at the maximum possible value, which is not modified further in manipulated value converter  19  and hence is conveyed unchanged to output stage  13  as the limited manipulated variable Sb. In this operating state, output stage  13  can be completely activated in order to supply load  10  with energy without limitation. 
     Controller  18  intervenes only when the system deviation dU has decreased to a value at which the battery voltage Ub approaches the battery voltage Umin. The manipulated variable S is then established, as a function of the algorithms defined in controller  18 , at a value that causes output stage  13  to reduce the average power conveyed to load  10 . Manipulated variable converter  19  can make the limited manipulated variable Sb available, for example, as a continuous signal that switches a transistor, contained in output stage  13 , on or off in continuous operation. Manipulated variable converter  19  preferably creates limited manipulated variable Sb from the manipulated variable S as a pulse-width modulated signal that switches output stage  13  either completely on or completely off at the defined clock cycle. 
     As soon as it is ascertained by way of the system deviation dU that the battery voltage has fallen below the predefined minimum voltage Umin, the manipulated variable S and thus the limited manipulated variable Sb are defined in such a way that output stage  13  is completely switched off. The linear or high-frequency operating mode prevents the battery voltage from oscillating. 
     One possibility for preventing the battery voltage Ub from falling below the predefined minimum battery voltage Umin is to limit the manipulated variable S to the predefined lower limit value Su that is made available by limit value generator  20 . The limited manipulated variable Sb that is made available by manipulated variable converter  19  therefore preferably exhibits a discontinuity point. 
     If the controller can no longer prevent the battery voltage from dropping even when the lower limit value Sn has been output, load  10  is completely deactivated. A complete deactivation of load  10  can also be provided for if a value of the limited manipulated variable Sb drops below a value that, for example, corresponds to 50% of the rated power of load  10 . 
     In the case where the circuit arrangement according to the present invention is used in a motor vehicle, an air conditioner or at least one fan as a component of the air conditioner is provided, for example, as load  10 . If interior temperatures are very high, the air conditioner or at least the fan can be activated, even if the motor vehicle is not running, without causing a risk of a deep discharge of battery  11 . In the case of a utilization in a motor vehicle, further loads  10  can be provided that are activated even when the vehicle is not running. Loads of this kind are, for example, a receiver of a remote control system or, for example, an alarm system.