Abstract:
A power supply circuit arrangement is provided that includes a switching regulator for generating a first regulated voltage, a controlled load element that is impinged upon by the first regulated voltage, and a first control element for controlling the load element. A method for generating a supply voltage is also provided. The switching regulator is adapted to generate a second, unregulated voltage that serves directly or indirectly as a supply voltage for the first control element. The circuit arrangement and method are used for example for a battery-based power supply of electric automotive components.

Description:
[0001]     This nonprovisional application is a continuation of International Application PCT/EP2004/009079, which was filed on Aug. 13, 2004, and which claims priority to German Patent Application No. DE 103 38 272.0, which was filed on Aug. 15, 2003, and which are all herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to a circuit arrangement for a power supply and to a method for generating a supply voltage.  
         [0004]     2. Description of the Background Art  
         [0005]     In battery-supplied systems, in cases in which considerable variations in a battery voltage occur, there is often the need to generate therefrom a stable system voltage or supply voltage. The battery voltage varies greatly particularly in vehicles and at times, for example, during a starter or starting procedure for the vehicle and thus may be lower than a desired supply voltage. Circuit arrangements for a battery-based power supply are customary for this purpose; these comprise one or more linear regulators, which, for example, in the case of sensors, analog circuit components, and microprocessors, generate a precise and stable supply voltage, which is substantially free of interfering residual or so-called “ripples.” Because linear regulators, due to their internal construction, require an input voltage that is higher than an output voltage, and their power dissipation depends on a voltage difference between the input and output voltage and an output load, switching regulators are inserted between the battery and the linear regulators. Switching regulators are suitable for low-dissipation generation of an output voltage, which may be considerably higher or lower than the input voltage. Their output voltage, however, typically has some residual ripple, so that it is often not directly suitable for generating a supply voltage for a circuit component sensitive to this.  
         [0006]     If the input voltage may be both higher and lower than the voltage to be generated from it, switching regulators are used, which can regulate in both the up and down direction. Examples of these are single-ended-primary-inductance-converters (SEPIC), flyback converters, and reverse converters.  
         [0007]     The output voltage of the switching regulator, which is used as the input voltage of the linear regulator(s), is adjusted to minimize dissipation in such a way that a voltage difference as low as possible becomes established between the input and output voltage of the linear regulator, for example, at about 1.5 V.  
         [0008]     A linear regulator normally comprises a controllable load element in the form of an NMOS transistor, which is supplied with the output voltage of the switching regulator, as an actuator and a control element for controlling the transistor. The transistor is looped into a load current path between the output of the switching regulator and the system(s) to be supplied. The overall size of the transistor depends greatly on its gate-source voltage. Conventionally, the control element is supplied with the voltage also applied at the transistor, as a result of which the gate-source voltage of the linear regulator is limited and a minimal overall size is established.  
         [0009]     The output voltage of the switching regulator can also be used to supply additional circuit components, which have a controllable load element, which is supplied with the output voltage. In this connection, this can be, for example, a motor regulator, which is operated with the output voltage via a load element in the form of a power transistor. Here as well, the minimum overall size of the power transistor again depends greatly on its gate-source voltage.  
       SUMMARY OF THE INVENTION  
       [0010]     It is therefore an object of the present invention to provide a circuit arrangement and a method, which can be realized at a relatively low cost and are capable of supplying a stable supply voltage at low dissipation, particularly also from a battery with appreciable battery voltage variations. It is desirable, furthermore, to minimize the overall size of the employed load elements.  
         [0011]     The circuit arrangement of the invention includes a switching regulator, which generates, in addition to a first regulated voltage, a second, unregulated voltage, which is used directly or indirectly as a supply voltage for the first control element. The first control element with this supply voltage independent of the first voltage can set a control voltage for the load element in such a way that an advantageous efficiency results and the overall size of the load element(s) is reduced.  
         [0012]     In a further embodiment of the circuit arrangement, the second voltage can be higher than the first voltage. This enables the control of the load element with control voltages, which are higher than the voltages applied at the load current path.  
         [0013]     In a further embodiment of the circuit arrangement, the controllable load element and the first control element can form a first linear voltage regulator to generate a third regulated voltage from the first voltage. This enables the generation of precise voltages with lower residual ripple with a simultaneously high efficiency.  
         [0014]     In a further embodiment of the circuit arrangement, the switching regulator comprises a second control element and the second voltage can serve directly or indirectly as its supply voltage. The second control element can be used, for example, for internal control of the switching regulator and can include one or more comparators, sawtooth generators, and operational amplifiers. The supplying by the second voltage facilitates a startup of the switching regulator at low input voltages.  
         [0015]     In a further embodiment of the circuit arrangement, the circuit arrangement comprises a second, linear voltage regulator, which generates a supply voltage for the first control element and/or a second control element from the second voltage. This enables on-demand generation of additional precise voltages for the internal supply. Because the power draw from the second voltage regulator is normally small, the dissipation due to said regulator remains low.  
         [0016]     In another further embodiment of the circuit arrangement, a first rectifier element, particularly a diode, is looped in the forward direction, as well as a reference potential of the switching regulator, and a smoothing capacitor in series between a junction point of an input inductor and a switch, the second voltage being available at the junction point of the first rectifier element and smoothing capacitor. The voltage at the junction point of the input inductor and the switch has periodic voltage spikes during operation, which correspond essentially to the sum of the input and output voltage of the switching regulator. The second voltage is obtained herefrom with the help of the first rectifier element and the smoothing capacitor and is higher than the input voltage or the output voltage of the switching regulator.  
         [0017]     In a further embodiment of the circuit arrangement, a second rectifier element, for example, a diode, is looped in the forward direction between an input terminal and a node of the switching regulator, to which the second voltage is available. The second rectifier element is used to start the switching regulator, when the input voltage is applied. A possibly not yet available or too low second voltage can then be replaced by the input voltage, which is put through the second rectifier element.  
         [0018]     Also, the load element can form an emitter follower or a source follower.  
         [0019]     Further, the switching regulator can be constructed as a SEPIC, flyback, or reverse converter. With the aid of converters of this type, output voltages can be generated, which depending on need are higher or lower than their input voltage.  
         [0020]     In the method of the invention a second, particularly unregulated voltage is generated by the switching regulator to supply the first control element.  
         [0021]     In a further embodiment of the method, the first and the second voltage can be generated in such a way that the second voltage is higher than the first voltage.  
         [0022]     In a further embodiment of the method, the controllable load element can be controlled by the first control unit in such a way that a third regulated voltage is generated from the first voltage.  
         [0023]     In a further embodiment of the method, a second control element, which controls the switching regulator internally, can be supplied directly or indirectly by the second voltage.  
         [0024]     In a further embodiment of the method, a supply voltage for the first control element and/or the second control element can be generated from the second voltage.  
         [0025]     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:  
         [0027]      FIG. 1  is a block diagram of a circuit arrangement for a power supply, according to an embodiment of the present invention;  
         [0028]      FIG. 2  is a block diagram of a circuit arrangement for a power supply with a SEPIC-type switching regulator; according to another embodiment of the present invention; and  
         [0029]      FIG. 3  is a block diagram of a circuit arrangement for a power supply with a flyback-type switching regulator, according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0030]      FIG. 1  shows a block diagram of a circuit arrangement for a power supply comprising a switching regulator SR, which generates a first regulated voltage UA 1  and a second unregulated voltage UA 2  from an input voltage UE, and a linear regulator LR. The linear regulator LR comprises a controllable load element LE, which is supplied with the first voltage UA 1  of the switching regulator SR, and a control element AE for controlling the load element LE. The control element AE controls the load element LE in such a way that a regulated voltage UALR, which has a low residual ripple and can be used to supply sensitive downstream circuit components (not shown), is generated from the first voltage UA 1  of the switching regulator SR. The second voltage UA 2  of the switching regulator SR is used to supply the control element AE.  
         [0031]     In the circuit arrangement shown in  FIG. 2 , the switching regulator SR of  FIG. 1  is constructed as a SEPIC-type converter. The switching regulator SR generates from an input voltage UESR, provided by a battery (not shown), a regulated output voltage UASR 1 , which can be selected to be higher or lower than the input voltage UESR. An input inductor L 1  and a switch in the form of a transistor T 1  are looped in series between an input terminal A 1  of the switching regulator SR and ground. The transistor T 1  is controlled by a control unit SE with a pulse width modulated signal.  
         [0032]     To generate the control signal, the control unit SE comprises an error amplifier in the form of an operational amplifier OP 1  and a sawtooth generator SG. A first reference voltage UR 1 , which is used as a setpoint value for the output voltage UASR 1  of the switching regulator SR, is applied at a first input of operational amplifier OP 1  and the output voltage UASR 1 , which is divided down suitably by a voltage divider, is applied at a second input of operational amplifier OP 1 . The pulse duty ratio of the pulse width modulated control signal of transistor T 1  is adjusted by the control unit SE in such a way that the desired value of the output voltage UASR 1  results. The switching regulator SR also includes capacitors C 1  and C 2 , an inductor L 2 , and a diode D 1  in the wiring typical for SEPIC-type converters.  
         [0033]     To generate a second unregulated output voltage UASR 2 , the switching regulator SR comprises a rectifier element in the form of another diode D 2  and a smoothing capacitor C 3 , which is looped in series between a junction point N 1  of input inductor L 1  and the first transistor T 1  and ground, the second output voltage UASR 2  being available at junction point N 2  of diode D 2  and smoothing capacitor C 3 . The voltage at junction point N 1  of input inductor L 1  and transistor T 1  has periodic voltage spikes during operation, which correspond essentially to the sum of the input voltage UESR and the output voltage UASR 1  of the switching regulator SR. The second output voltage UASR 2  of the switching regulator SR is obtained herefrom with the help of diode D 2  and smoothing capacitor C 3  and is higher than the input voltage UESR and the output voltage UASR 1  of the switching regulator.  
         [0034]     Another rectifier element in the form of another diode D 3  is looped in the forward direction between input terminal A 1  of the switching regulator SR and node N 2 . It is used to start the switching regulator, when the input voltage is applied. A possibly not yet available or too low second output voltage UASR 2  can then be replaced by the input voltage, which is put through diode D 3 . Diode D 3  is optional and can be omitted depending on the specification to be met.  
         [0035]     From the second output voltage UASR 2  of the switching regulator SR, with use of a linear voltage regulator LR 1 , a precise, low-residual-ripple supply voltage for the control element SE and for a control element of another linear voltage regulator LR 2  is generated, which in this example is formed by an operational amplifier OP 2 . If lower requirements are imposed on the quality of this supply voltage, voltage regulator LR 1  can be omitted and the second supply voltage UASR 2  can serve directly as the supply voltage for the control element SE and operational amplifier OP 2 . Instead of the linear regulator LR 1 , a simpler stabilization circuit can also be used.  
         [0036]     The linear regulator LR 2  is used to generate a system voltage UALR 2  and comprises a controllable load element in the form of an NMOS transistor T 2 , which is supplied at its drain connection with the output voltage UASR 1  of the switching regulator SR, and the operational amplifier OP 2  whose output voltage is used to control transistor T 2 . Transistor T 2  forms a load current path between the output voltage UASR 1  of the switching regulator SR and the output voltage UALR 2  of the linear regulator LR 2 . A reference voltage UR 2 , which is used for adjusting the output voltage UALR 2 , is applied at a first input of operational amplifier OP 2 . The output voltage UALR 2 , tapped off by a measuring resistor RM and divided down as needed, is back coupled at a second input. Because operational amplifier OP 2  is supplied with the output voltage of voltage regulator LR 1 , which is higher than the output voltage UASR 1  of the switching regulator applied at the drain connection of transistor T 2 , it is also capable of providing control voltages, which are higher than the output voltage UASR 1 . The maximum gate-source voltage UGS of transistor T 2  can be 5 V, for example, depending on the employed technology. Consequently, transistor T 2  can be dimensioned accordingly small. Overall, chip area can be saved by this, which reduces manufacturing costs.  
         [0037]      FIG. 3  shows a circuit variant, in which the switching regulator SR is constructed as a so-called flyback converter. Because the function of the shown circuit agrees substantially with the circuit shown in  FIG. 2 , only the differences will be discussed below.  
         [0038]     The input voltage UESR, which is converted to a suitable value within the control unit SE, is used directly as the supply voltage of the control unit SE in this exemplary embodiment. Linear regulator LR 1  of  FIG. 2  is omitted and the second voltage UASR 2  of the switching regulator SR, available at the node N 2 , is used directly to supply operational amplifier OP 2  of the linear voltage regulator LR 2 . Diode D 3  shown in  FIG. 2  has been omitted. The second voltage UASR 2  is tapped by diode D 2  and capacitor C 3  at a primary winding of a transformer formed by inductors L 1  and L 2 .  
         [0039]     In the shown embodiments, the second output voltage UA 2  or UASR 2  of the switching regulator SR is used to supply the control element AE or operational amplifier OP 2  of the linear voltage regulator LR or LR 2 . Because of the voltage UA 2  or UASR 2 , which is higher than the first output voltage UA 1  or UASR 1  of the switching regulator, it is possible to dimension the load element LE or the transistor T 2  smaller.  
         [0040]     The invention is not limited to the shown exemplary embodiments, however. Thus, the linear voltage regulator LR 2  can be replaced, for example, by a regulator or a drive component for an electric motor, in which a power transistor is controlled as the load element in a similar way by a suitable control element.  
         [0041]     The switching regulator can also be designed in general as a reverse converter. The second voltage here is basically tapped as shown with the use of a rectifier element and a capacitor connected to ground as a function of the employed converter type either at a node between the switching element and an inductor or a primary winding of a transformer.  
         [0042]     The invention makes possible an economically realizable circuit arrangement for a power supply, for example, for vehicles, because the employed load elements due to their improved control can be dimensioned smaller and the operational reliability is assured over a broad input voltage range.  
         [0043]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.