Patent Application
20050099169
The invention relates to a regulating system according to the features listed in the preamble of claim 1.
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
The voltage regulator includes an input terminal K10 for application of an input voltage Vin10 against a reference potential GND10, and an output terminal K2 for providing a regulated output voltage Vout dependent on a reference voltage Vref in order to supply load Z10.
Functioning as the actuating element of the regulating system is a bipolar transistor Q10, the collector-emitter path of which is connected between the input and output terminals K1, K2. The regulating signal is the base current Ib10 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 Q20, connected as a diode, followed by a controlled current source in the form of a bipolar transistor Q40, 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 R10, R20. For this purpose, the base of this bipolar transistor Q40 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 Q30, the base of which is connected to the base of the first current mirror transistor Q20, and the collector-emitter path of which forms the second current mirror path. This second current mirror path is connected to output terminal K20 through a diode.
In this regulating system, if the voltage Vec10 over the load path of the regulating transistor Qlo is below a predefined value Vth, produced by:
Vth=Vbe10+Vcesat30+Vd10 (1),
where Vbe10 is the base emitter voltage of the regulating transistor Q10, Vcesat30 is the saturation voltage of the second current mirror transistor Q30, and Vd10 is the conducting-state voltage of diode D1, then diode D1 is in the blocking state, and the regulating current Ib10 of the regulating transistor is supplied exclusively by the current source transistor Q40, then the applicable equation is:
Ic40=Ib10=Iout/β10 (2),
where Ic40 is the load current of current source transistor Q40, Iout10 is the load current flowing to the output terminal, and β10 is the current gain of regulating transistor Q10.
If the load path voltage Vec10 of regulating transistor Q10 exceeds the threshold value Vth according to (1), then diode D10 is conductive so that both current mirror paths contribute to regulating current Ib10. Based on the current mirror relationship set via the emitter surfaces of the two current mirror transistors, the applicable equation for current Ic40 through current mirror transistor Q40 is:
Ic40=1/(M+1)·Ib10=Iout10/(β10·(M+1)) (3).
The analogous applicable equation for current Ic30 along the second current mirror path, which based on the current mirror relationship is proportional to current Ic40, is:
Ic30=M/(M+1)·Ib10 (4)
With diode D10 conductive, regulating transistor Q10 and second current mirror transistor Q30 form a Darlington configuration, as a result of which the power loss for load path voltages Vec10 greater than Vth is significantly reduced, since only a small component of the regulating current remains unutilized, whereas a larger component (for M>1) is fed through diode D10 to output terminal K20.
A problematic aspect here is that when diode D10 is in the blocking state, the load current of current source transistor Q40 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 Q10—which is equivalent to saying that the driving voltage Vb40 of this transistor, given by the equation
Vb40=Vb40+Ic40·R40 (5),
must also increase by the factor M+1. R40 in (5) denotes the resistance value of the resistance following transistor Q40.
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 Q40 is operated in his saturation region for high currents Ic40.
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.
This goal is achieved by the regulating system according to the features of claim 1. Advantageous embodiments of the invention are the subjects of the subclaims.
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.
The following discussion explains the invention in more detailed based on the figures.
Unless otherwise indicated, components with the same denotation are equivalent.
The regulating system includes an input terminal K1 to apply an input voltage Vin to reference potential GND, and an output terminal K2 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
The regulating system includes a regulating transistor Q1, 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 K1 and output terminal K2.
The regulating response of this system, i.e., the voltage drop Vec1 over the load path of regulating transistor Q1 to adjust output voltage Vout is provided by base current Ib1 of regulating transistor Q1.
The regulating signal Ib1 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 Q2 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 Q4 is connected in series to the first current mirror path, and a resistance R4 is connected following the current source. A first current I1 through the first current mirror path is depending on a first driving signal Vb4 from current source transistor Q4, 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 R1, R2 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 Vb4 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 Q3, the base of which is connected to the base of first current mirror transistor Q2, and the load path of which forms the second current mirror path. A second current 12 flows through the second current mirror path. In accordance with the current mirror relationship, this second current 12 is proportional to first current 11. In the embodiment shown, the area ratio between the emitter surface of first current mirror transistor Q2 and of second current mirror transistor Q3 is 1:M—so the applicable equation for second current I2 is:
I2=M·I1 (6)
In addition, the regulating system includes a splitter circuit or switch circuit (2a) which conducts the second current I2 of the second current mirror path to output terminal K2 depending on the load path voltage Vec1 of regulating transistor Q1, or to a reference potential, in this case the reference potential GND of the circuit.
In the embodiment of
This bias source Vx, shown schematically in
Diode D1 is conductive when load path voltage Vec1 of regulating transistor Q1 becomes greater than threshold voltage Vth, for which the applicable equation is:
Vth=Vbe1+Vcesat3+Vd1 (7)
where Vbe1 is the base-emitter voltage of regulating transistor Q1, Vecsat3 is the fabrication voltage of second current mirror transistor Q3, and Vd1 is the conducting-state voltage of diode D1. When diode D1 is conductive, regulating transistor Q1 and second current mirror transistor Q3, 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 I1 which does not contribute to output current Iout, while a larger component of regulating current Ib1 (for M>1) from regulating transistor Q1 is conducted to output K2 through the second current mirror path and diode D1.
Whenever load path voltage Vec1 falls below this threshold value Vth, then diode D1 is in the blocking state of diode D1, and second current 12 is conducted to reference potential GND through bipolar transistor Q5 of splitter circuit 20.
Independently of the switching state, one component of regulating current Ib1 is always formed by first current I1 in the first current mirror path, and a second, usually larger, component of regulating current Ib1 is formed by second current 12 in the second current mirror path in the regulating system shown. The applicable equation is always:
Ib1=I1+I2=(M+1)·I1 (8)
Because of splitter circuit 20, there is thus no increase in the current requirement of controlled current source Q4 when diode D1 is in the blocking state, and as a result, no abrupt rise in driving voltage Vb4 is required to drive transistor Q4, functioning in this example as the current source.
An additional bipolar transistor Q51 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 Q52 and resistance R5.
The regulating system shown in
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 Q1 is similarly deactivated, while transistor Q1 continues to be activated when output current Iout falls.
List of Reference Notations
| Number | Date | Country | Kind |
|---|---|---|---|
| 03 022 149.3 | Sep 2003 | EP | regional |
