Electricity: power supply or regulation systems – In shunt with source or load – Using choke and switch across source
Reexamination Certificate
1999-11-22
2001-04-10
Sterrett, Jeffrey (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using choke and switch across source
C323S225000, C323S271000, C323S284000
Reexamination Certificate
active
06215286
ABSTRACT:
The invention relates to switching regulators, that is circuit arrangements for power supplies which step up or step down a DC voltage without using a transformer and which at their output supply a regulated voltage (so-called “regulated converters”). Furthermore, the invention relates to methods for operating such switching regulators.
Switching regulators can, for example, be used to obtain an optimum supply voltage for the circuit components in portable devices with a battery based power supply, such as a mobile telephone. If such devices are powered, for example, by a 3-cell Ni battery or by a Li+ battery, the battery can typically be discharged from a starting value of 5 volts to a voltage of 2.7 volts or even lower. The discharge curve of the battery will therefore, at a specific critical discharge point, go below the minimum supply voltage required by the circuit components of the device of, for example, 3.3 volts. In order to make optimum use of the battery capacity and, in particular, to use up the remaining capacity of the battery, switching regulators are used which supply the circuit components with a constant voltage slightly higher than the voltage required for the circuit components (of for example 3.4 V), so that at the beginning of the battery discharge curve, the battery voltage, which then will be in the range of for example 5 V, will be reduced by the switching regulator, and increased once the critical discharge point in the battery voltage is passed. But even before and after the critical discharge point, depending on the load situation, cases may present themselves when sometimes an increase and sometimes a reduction of the input voltage is required. By the use of the switching regulator it therefore becomes possible to increase the useful life of the battery and consequently the time of use of portable devices by a considerable amount. Since the battery voltage has to be both reduced and increased, step-up/step-down switching regulators are used in which the functions of step-up and step-down regulation are combined. Such a step-up/step-down switching regulator is, for example, described on pages 37 and 38 of the book “Schaltnetzteile” (Switching power supplies), second edition, by Udo Leonhard Thiel, and published by Franzis-Verlag, Poing in 1998, where it is represented in illustration 3.5.
The known switching regulator has, apart from the switching and regulating IC, an inductance, one of its terminals being connected to the input of the regulator via a first transistor switch and to ground via a first diode the cathode of which being connected to one of the terminals. The other terminal of the inductance is connected to the output of the switching regulator via a second diode whose anode is connected to the other terminal, and to ground via a second transistor switch. As is common practice with switching regulators, at the output of the regulator a capacitor is connected in parallel with the consumer, which temporarily takes over as a power supply when, because of the switching position, no current flows from the power source to the consumer. In the case of this regulator, the value of the output voltage is controlled by the ratio between the turn-on and off-times of the switches.
The switching regulator mentioned, however, suffers from the disadvantage that it comprises many components which cannot be integrated (diodes, inductance, capacitor), which represents a particular nuisance value when it is to be incorporated in a device where the smallest possible size is desirable for practical reasons, such as in the case of a mobile telephone where the dimensions of the device have a great influence on the purchase decision by the customer. It would certainly be possible to replace the diodes by integrated transistor circuits, but then it would be necessary in each clock cycle to switch four switches, since in the first part of the cycle the first switch and the second switch would have to be turned on, whereby the switches taking the place of the diodes would be turned off, and in the second part of the cycle the switches taking the place of the diodes would have to be turned on, whereby simultaneously the first switch and the second switch would have to be turned off. These frequent switching operations would cause high switching losses, which would reduce the efficiency of the switching regulator and therefore the time of effective use of the portable device.
The purpose of the present invention is to provide switching regulators which avoid the problems previously mentioned and which have a lower current consumption, thereby making them particularly suitable for applications in small portable devices, such as mobile telephones.
One solution according to the invention is realised in a switching regulator
with an inductance of which one terminal is connected to the input of the regulator by a first switch and to ground by a second switch, and whose other terminal is connected to the output of the regulator by a third switch, and to ground by a fourth switch, whereby all switches are capable of being controlled and where the regulator can be operated in step-down mode, where the third switch is constantly turned on and the fourth switch is constantly turned off, and the first and the second switches are periodically and alternatively switched on and off, as a function of the duty cycle determined by the on-time of the first switch, and in step-up mode in which the first switch is constantly on and the second switch is constantly off, and where the third and the fourth switch are periodically and alternatively switched on and off as a function of the duty cycle determined by the on-time of the fourth switch, and
a control circuit for the control of the switches, and
a pulse duration modulator for the modification of the corresponding duty cycle for the correction of the regulation deviation as a function of the regulation deviation of the output voltage of the regulator, and
comprising an element for monitoring the duty cycle and, when a duty cycle of 100% is approached in the step-down mode, switches to the step-up mode and when a duty cycle of 0% is approached in the step-up mode, switches to the step-down mode.
This switching regulator can also be realised in a particularly small size, since all the components of the switching regulator, with the exception of the inductance, can be made in the form of an integrated circuit.
Another solution to the problem according to the invention consists in a switching regulator
with a first inductance where one of its terminals is connected to the input of the regulator and where the other terminal is connected to one end of a first switch, as well as to ground by a second switch, and a second inductance where one of its terminals is connected to the other end of the first switch by means of a third switch, as well as to ground via a fourth switch, and whose other terminal forms the output of the regulator, whereby a capacitor is connected across the connecting point between the first and the third switch and ground, where all switches can be controlled and where the regulator is operated in a step-down mode, where the first switch is constantly turned on and the second switch is constantly turned off, and the third and the fourth switches are periodically and alternatively switched on and off, as a function of the duty cycle determined by the on-time of the third switch, and in step-up mode in which the third switch is constantly on and the fourth switch is constantly off, and where the first and the second switches are periodically and alternatively switched on and off as a function of the duty cycle determined by the on-time of the second switch, and
a control circuit for the control of the switches, and
a pulse duration modulator for the modification of the corresponding duty cycle for the correction of the regulation deviation as a function of the regulation deviation of the output voltage of the regulator, and
comprising an element for monitoring the duty cycle and, when a duty cycle of 100% is appro
Fattori Frank R.
Prexl Franz
Scoones Kevin
Kempler William B.
Sterrett Jeffrey
Telecky , Jr. Frederick J.
Texas Instruments Deutschland GmbH
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