Abstract:
A regulating system comprises an input terminal for applying an input voltage, and an output terminal for providing an output voltage. A semiconductor element is connected between the input terminal and the output terminal and is operable to regulate the output voltage. A regulating signal generation circuit generates the regulating signal and comprises a current mirror arrangement including a first and second current mirror path, wherein a controlled current source is connected in series to the first current mirror path. The controlled current source induces a first current dependent on one of the output signals in the first current mirror path. A second current through the second current mirror path is dependent on the first current. A splitter circuit conducts the second current to the output terminal or to a reference potential, dependent on a load path voltage applied over the load path of the semiconductor element.

Description:
BACKGROUND 
   The invention relates to a regulating system. In particular, this invention relates to an electrical regulating system including a splitter circuit. 
   An example of a regulating system of this type designed as a voltage regulator is described in EP 0 990 199 B1 and is briefly explained based on  FIG. 1  to aid in understanding the following invention. 
   The voltage regulator includes an input terminal K 10  for application of an input voltage Vin 10  against a reference potential GND 10 , and an output terminal K 20  for providing a regulated output voltage Vout dependent on a reference voltage Vref in order to supply load Z 10 . 
   Functioning as the actuating element of the regulating system is a bipolar transistor Q 10 , the collector-emitter path of which is connected between the input and output terminals K 10 , K 20 . The regulating signal is the base current Ib 10  of the bipolar transistor, which current is provided by a current mirror arrangement which has a first and second current mirror path. 
   The first current mirror path includes a current mirror transistor Q 20 , connected as a diode, followed by a controlled current source in the form of a bipolar transistor Q 40 , which current source induces a current through a first current path which is dependent on reference signal Vref and on a voltage measurement signal, in turn dependent on the output voltage Vout, which signal is provided by a voltage divided R 10 , R 20 . For this purpose, the base of this bipolar transistor Q 40  is driven by a comparison signal which provides a comparator  10  from reference signal Vref and the voltage measurement signal. 
   The second current mirror path includes a second current mirror transistor Q 30 , the base of which is connected to the base of the first current mirror transistor Q 20 , and the collector-emitter path of which forms the second current mirror path. This second current mirror path is connected to output terminal K 20  through a diode. 
   In this regulating system, if the voltage Vec 10  over the load path of the regulating transistor Q 10  is below a predefined value Vth, produced by:
 
 Vth=Vbe   10 + Vcesat   30 + Vd   10   (1),
 
where Vbe 10  is the base emitter voltage of the regulating transistor Q 10 , Vcesat 30  is the saturation voltage of the second current mirror transistor Q 30 , and Vd 10  is the conducting-state voltage of diode D 1 , then diode D 1  is in the blocking state, and the regulating current Ib 10  of the regulating transistor is supplied exclusively by the current source transistor Q 40 , then the applicable equation is:
 
 Ic   40 = Ib   10 = I out/β 10   (2),
 
where Ic 40  is the load current of current source transistor Q 40 , Iout 10  is the load current flowing to the output terminal, and β 10  is the current gain of regulating transistor Q 10 .
 
   If the load path voltage Vec 10  of regulating transistor Q 10  exceeds the threshold value Vth according to (1), then diode D 10  is conductive so that both current mirror paths contribute to regulating current Ib 10 . Based on the current mirror relationship set via the emitter surfaces of the two current mirror transistors, the applicable equation for current Ic 40  through current mirror transistor Q 40  is:
 
 Ic   40 =1/( M+ 1)· Ib   10 = I out 10 /(β 10 ·( M+ 1))  (3).
 
   The analogous applicable equation for current Ic 30  along the second current mirror path, which based on the current mirror relationship is proportional to current Ic 40 , is:
 
 Ic   30 = M /( M+ 1)· Ib   10   (4)
 
   With diode D 10  conductive, regulating transistor Q 10  and second current mirror transistor Q 30  form a Darlington configuration, as a result of which the power loss for load path voltages Vec 10  greater than Vth is significantly reduced, since only a small component of the regulating current remains unutilized, whereas a larger component (for M&gt;1) is fed through diode D 10  to output terminal K 20 . 
   A problematic aspect here is that when diode D 10  is in the blocking state, the load current of current source transistor Q 40  must increase by the factor M+1 relative to the conducting state of the diode in order to provide the required base current needed to drive regulating transistor Q 10 —which is equivalent to saying that the driving voltage Vb 40  of this transistor, given by the equation
 
 Vb   40 = Vb   40 + Ic   40 · R   40   (5),
 
must also increase by the factor M+1. R 40  in (5) denotes the resistance value of the resistance following transistor Q 40 .
 
   Frequently, however, this driving voltage is restricted by a protective circuit or by a supply voltage provided to driving circuit  10  with the risk that, given a small voltage drop, the regulator is not able to provide the full output current over the regulating transistor. Furthermore, problems due to a high substrate current may occur, if transistor Q 40  is operated in his saturation region for high currents Ic 40 . 
   The goal of the invention is to provide a regulating system of the type referred to at the outset which, even in the event of a small voltage drop over the semiconductor element connected between the input and output terminals is able to provide the required output voltage, and which has a reduced power loss in the event of larger voltage drops. 
   SUMMARY 
   The regulating system according to the invention includes an input terminal to apply an input voltage, an output terminal to provide an output voltage and output current, as well as a semiconductor element having a load path which is connected between the input terminal and the output terminal, and having a control input to which a regulating signal is applied. The regulating system also includes a regulating signal generation circuit to generate the regulating signal, wherein this regulating signal generation circuit has a current mirror arrangement with a first and second current mirror path, wherein a controlled current source is connected in series to the first current mirror path, which current source induces a first current in the first current mirror path dependent on one of the output signals, and wherein a second current is dependent through the second current mirror path on the first current. In addition, a splitter circuit or switch circuit is provided which, depending on a load path voltage applied through the load path of the semiconductor element through the second current mirror path, conducts the second current through the second current mirror path to the output terminal or to a reference potential. 
   In the regulating system, the regulating signal which is the base current of the bipolar transistor when a bipolar transistor is used, is always generated by two current mirror paths, the current being conducted through the second current mirror path to the output terminal when the voltage over the load path of the semiconductor element connected between the input and output terminals is above a threshold value. Given a voltage below this threshold value, the current is conducted through the second current mirror path to the reference potential. Since in this regulating system some of the regulating signal is always provided by the second current mirror path, interrupting the connection between the second current mirror path and the output terminal does not result—as is the case in prior-art regulating systems—in an increase in the current demand for the controlled current source in the first current path, which current source adjusts the regulating signal dependent on one of the output signals. 
   The regulating system may be employed as a voltage regulator in which the output signal fed back to the controlled current source is either the output voltage or a signal dependent on the output voltage. However, the regulating system may also be employed as a current regulator, in which case the signal fed back to the controlled current source is a signal dependent on the output current. The situation in both cases is that when the output signal, i.e., the output signal or the output voltage, rises above a certain reference value, the semiconductor connected between the input and output terminals is deactivated, whereas when the output signal falls below a certain threshold value it is activated again. 
   In one embodiment, the splitter circuit which conducts the current through the second current mirror branch either to the output terminal or to the reference terminal, depending on the load path voltage applied over the load path of the semiconductor element, includes at least one rectifier element, in particular, a diode, having a load path which is connected between the second current mirror branch of the current mirror arrangement and the output terminal. In addition, at least one switching device is present including a semiconductor element which is connected between the second current mirror path and the reference potential, and which is designed to conduct the current to the reference potential when the rectifier element is in the blocking state. 
   This at least one semiconductor switching element is preferably a transistor, the load path of which is connected between the second current mirror branch and the reference potential, and the driving terminal of which is coupled to the first current mirror branch. 
   In another embodiment, the switching device includes a first and second transistor in a Darlington circuit, the load paths of which are each connected between the second current mirror branch and the reference potential, wherein the driving terminal of the first transistor is coupled to the first current mirror branch, while the driving terminal of the second transistor is coupled to a load path terminal of the first current mirror transistor. 
   In another embodiment, the switching device has a current measurement arrangement to measure a current through the rectifier element and to provide a current measurement signal. This current measurement signal is fed to a driving circuit for the at least one semiconductor element of the switching device in order to drive this at least one semiconductor element in a current-dependent manner through the rectifier element. 
   In one embodiment, the regulating signal generation circuit includes a differential amplifier to which a signal dependent on the output signal and a reference signal are fed, and which supplies a differential signal. This differential signal is fed to the controlled current source as an adjusting signal. 
   The controlled current source is preferably a bipolar transistor, to the base of which this differential signal is fed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following discussion explains the invention in more detailed based on the figures. 
       FIG. 1  shows a regulating system according to the prior art. 
       FIG. 2  shows a first embodiment of a regulating system according to the invention. 
       FIG. 3  shows a second embodiment of a regulating system according to the invention. 
       FIG. 4  shows another embodiment of a regulating system according to the invention. 
   

   Unless otherwise indicated, components with the same denotation are equivalent. 
   DESCRIPTION 
     FIG. 2  shows a first embodiment of a regulating system according to the invention in the form of a voltage regulator. 
   The regulating system includes an input terminal K 1  to apply an input voltage Vin to reference potential GND, and an output terminal K 2  to provide both an output voltage Vout to reference potential GND and an output voltage Iout. A load Z supplied by this output voltage Vout and this output current Iout is shown by a broken line in  FIG. 2 . 
   The regulating system includes a regulating transistor Q 1 , which in this embodiment is in the form of a pnp bipolar transistor, the load path or collector-emitter path of which is connected between input terminal K 1  and output terminal K 2 . 
   The regulating response of this system, i.e., the voltage drop Vec 1  over the load path of regulating transistor Q 1  to adjust output voltage Vout is provided by base current Ib 1  of regulating transistor Q 1 . 
   The regulating signal Ib 1  is provided by a current mirror arrangement which has a first current mirror path and a second current mirror path. The first current mirror path includes a first current mirror transistor Q 2  interconnected as a diode, and a bias source Vx, the function of which will be explained below. A controlled current source in the form of a transistor Q 4  is connected in series to the first current mirror path, and a resistance R 4  is connected following the current source. A first current I 1  through the first current mirror path is depending on a first driving signal Vb 4  from current source transistor Q 4 , this driving signal being generated by a regulator  1  from a reference signal Vref and a signal Vm fed back from the output. A voltage divider R 1 , R 2  is connected in parallel to the output terminals of the regulating system to generate feedback signal Vm dependent on output voltage Vout. 
   Regulator  1  has, for example, a proportional regulating response, and in the simplest case is in the form of a differential amplifier which provides driving signal Vb 4  which is proportional to the difference between reference signal Vref and feedback signal Vm, this feedback signal Vm in the example shown being proportional to output voltage Vout. In order to reduce control deviations, regulator  1  may, of course, also have a proportional-integral response (PI regulator) or an integral response (I regulator). 
   The current mirror arrangement includes a second current mirror transistor Q 3 , the base of which is connected to the base of first current mirror transistor Q 2 , and the load path of which forms the second current mirror path. A second current I 2  flows through the second current mirror path. In accordance with the current mirror relationship, this second current I 2  is proportional to first current I 1 . In the embodiment shown, the area ratio between the emitter surface of first current mirror transistor Q 2  and of second current mirror transistor Q 3  is 1:M—so the applicable equation for  second current I 2  is:
 
 I   2 = M·I   1   (6)
 
   In addition, the regulating system includes a splitter circuit or switch circuit ( 20 ) which conducts the second current I 2  of the second current mirror path to output terminal K 2  depending on the load path voltage Vec 1  of regulating transistor Q 1 , or to a reference potential, in this case the reference potential GND of the circuit. 
   In the embodiment of  FIG. 2 , this splitter circuit  20  includes a diode D 1  connected between the second current mirror path, i.e. the load path of second current mirror transistor Q 3 , and output terminal K 2 . In addition, splitter circuit  20  includes a semiconductor element in the form of pnp bipolar transistor Q 5 , the load path of which is connected between the second current mirror path and reference potential GND. The base terminal of this transistor Q 5  is connected to the collector terminal of first current mirror transistor Q 2  through bias source Vx. This bias source Vx serves to bias transistor Q 5  which functions as a semiconductor switch, this bias Vx being chosen such that transistor Q 5  takes over none of, or only a very small fraction of, second current I 2  when diode D 2  is conductive. 
   This bias source Vx, shown schematically in  FIG. 2  as a voltage source, may be implemented, for example, as a diode (see  FIG. 3 ), or also as an ohmic resistance. 
   Diode D 1  is conductive when load path voltage Vec 1  of regulating transistor Q 1  becomes greater than threshold voltage Vth, for which the applicable equation is:
 
 Vth=Vbe   1 + Vcesat   3 + Vd   1   (7)
 
where Vbe 1  is the base-emitter voltage of regulating transistor Q 1 , Vecsat 3  is the fabrication voltage of second current mirror transistor Q 3 , and Vd 1  is the conducting-state voltage of diode D 1 . When diode D 1  is conductive, regulating transistor Q 1  and second current mirror transistor Q 3 , also in the form of a pnp bipolar transistor, form a Darlington configuration. The power loss of the regulating system in this operating state here is determined essentially by current I 1  which does not contribute to output current Iout, while a larger component of regulating current Ib 1  (for M&gt;1) from regulating transistor Q 1  is conducted to output K 2  through the second current mirror path and diode D 1 .
 
   Whenever load path voltage Vec 1  falls below this threshold value Vth, then diode D 1  is in the blocking state of diode D 1 , and second current I 2  is conducted to reference potential GND through bipolar transistor Q 5  of splitter circuit  20 . 
   Independently of the switching state, one component of regulating current Ib 1  is always formed by first current I 1  in the first current mirror path, and a second, usually larger, component of regulating current Ib 1  is formed by second current I 2  in the second current mirror path in the regulating system shown. The applicable equation is always:
 
 Ib   1 = I   1 + I   2 =( M+ 1)· I   1   (8)
 
   Because of splitter circuit  20 , there is thus no increase in the current requirement of controlled current source Q 4  when diode D 1  is in the blocking state, and as a result, no abrupt rise in driving voltage Vb 4  is required to drive transistor Q 4 , functioning in this example as the current source. 
     FIG. 3  shows the regulating system of  FIG. 2  with a modified splitter circuit  20 . In place of the single transistor Q 5 , this splitter circuit  20  includes two transistors Q 51 , Q 52  connected in a Darlington configuration, in which the load path is connected in series to a resistance R 5  between the second current mirror path and reference potential GND. The base of this bipolar transistor is coupled to the first current mirror path, wherein in  FIG. 3  a diode D 2  is employed as the bias source which is connected between the collector terminal of first current mirror transistor Q 4  and the collector terminal of current source transistor Q 4 , the base terminal of bipolar transistor Q 52  being connected to the junction of diode D 2  and the collector terminal of current source transistor Q 4 . Diode D 2  ensures that the base potential of bipolar transistor Q 52  always remains below the value of the emitter potential of this transistor by an amount equal to the conducting-state voltage of diode D 2 , with the result that transistor Q 52  is biased. If diode D 1  is conductive, this bias is insufficient, however, to take over an essential fraction of second current I 2 . 
   An additional bipolar transistor Q 51  is connected between the second current mirror path and reference potential GND, which transistor is in the form of a npn bipolar transistor, the base of which is connected to a junction of the load path of transistor Q 52  and resistance R 5 . 
     FIG. 4  shows another embodiment of a splitter circuit  20 . This splitter circuit includes a current measurement arrangement  25  which measures the current through diode D 1 , and which supplies a current measurement signal to a driving circuit  26  which serves to drive a switch  27  connected between the second current mirror path and the reference potential. If diode D 1  is conductive in response to load path voltage Vec 10  from regulating transistor Q 1  that is above threshold voltage Vth, and if a current through diode D 1  thus exceeds a predefined threshold value, then switch  27  is in the blocking state as controlled by driving circuit  26 . If diode D 1  is in the blocking state, and if the current through this diode thus falls below the predefined threshold value, then switch  27  is conductive, being controlled by driving circuit  26 , so as to take over the second current I 2  through the second current mirror path. 
   The regulating system shown in  FIGS. 2 through 4  is in the form of a voltage regulator arrangement. Here a voltage signal Vm dependent on output voltage Vout is fed back to regulator  1  which provides a regulating current Ib 1  for regulating transistor Q 1  through controlled current source Q 4  in connection with the current mirror. When output voltage Vout rises here, and when feedback signal Vm rises as a result above reference value Vref, transistor Q 1  is deactivated. Conversely, the transistor is activated when the output voltage Vout falls. 
   The regulating system shown may, of course, also be employed as a current regulating system wherein in place of signal Vm dependent on output voltage Vout, a signal dependent on output current Iout is fed back to regulator  1 . In this case, when output current Iout rises, regulating transistor Q 1  is similarly deactivated, while transistor Q 1  continues to be activated when output current Iout falls. 
   LIST OF REFERENCE NOTATIONS 
   
       
       D 1  diode 
       D 2  diode 
       GND 10  reference potential 
       I 1  first current 
       I 2  second current 
       IB 1  regulating signal, regulating current 
       Ib 10  base current 
       IC 30  collector current 
       IC 40  collector current 
       Iout output current 
       Iout 10  output current 
       K 1  input terminal 
       K 10  input terminal 
       K 2  output terminal 
       K 20  output terminal 
       Q 1  regulating transistor 
       Q 10  regulating transistor, pnp bipolar transistor 
       Q 2 , Q 3  current mirror transistors 
       Q 20 , Q 30  current mirror transistors 
       Q 4  current source, npn bipolar transistor 
       Q 40  current source, npn bipolar transistor 
       Q 5  npn bipolar transistor 
       Q 51  npn bipolar transistor 
       Q 52  pnp bipolar transistor 
       R 1 , R 2  resistances 
       R 10 , R 20  resistances 
       R 40  resistance 
       R 5  resistance 
       S 25  current measurement signal 
       S 26  driving signal 
       VB 40  driving voltage 
       VBE 40  base-emitter voltage 
       Vec 10  load path voltage 
       Vin input voltage 
       Vin 10  input voltage 
       Vm feedback voltage 
       VM 10  feedback signal 
       Vout output voltage 
       Vout 10  output voltage 
       Vref reference signal 
       Vref reference voltage 
       Vx bias source 
       Z 10  load 
         1  regulator 
         10  regulator 
         25  current measurement arrangement 
         26  driving circuit 
         27  switch