Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
1999-04-01
2001-04-24
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S290000
Reexamination Certificate
active
06222356
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the electronics field. Specifically, the invention relates to a current-mode switching regulator for power supply, in particular for application in switched-mode power supplies.
Switched-mode power supplies are disclosed for example in Tietze and Schenk, “Electronic Circuits —Design and Application,” Springer-Verlag 1991, p. 502. Switched-mode power supplies of this type usually comprise a rectifier, a power switch provided for the purpose of pulse width modulation, a filter, and also a regulator for controlling the power switch. An input voltage—for example a rectified power supply system voltage—is converted into a pulsed DC voltage with a variable duty ratio by the power switch acting as pulse width modulator. In this case, the pulse frequency may be set to be variable or fixed.
The task of the regulator is to keep the voltage at the output of the filter constant over a wide output current range. In other words, the regulator has to process the voltage at the output of the filter and the current at the output of the filter as input variables and form from them a control signal for the power switch. In this case, the timing ratio of the switch is influenced by the control signal.
Essentially three different control strategies exist for the regulation of such switching regulators: voltage-mode regulation, feedforward regulation and current-mode regulation. These control strategies are described for example in R. E. Tarter, Solid-State Power Conversion Handbook, Wiley Interscience, New York, 1993.
Current-mode regulation thereby constitutes a particularly elegant and effective type of regulation which, moreover, requires only comparatively small compensation capacitances. It is thus ideal for use in integrated circuits.
Current-mode switching regulators have two control loops. The inner control loop thereby serves to regulate the load current, while the outer control loop serves, together with the inner control loop, to regulate the output voltage. When the switching transistor is switched on, the voltage across a measuring resistor caused by the current rising in ramped fashion through the inductor coil of the switching regulator likewise has a ramped profile. When a desired voltage predetermined by the outer control loop is reached, the switching transistor switches off.
In current-mode switching regulators, it has been necessary heretofore, as described above, for the load circuit to have a measuring resistor in order to detect the current at the inductor. For the current detection, this measuring resistor is typically designed with a low resistance and, on account of its losses, is not suitable for use in integrated circuits. Such measuring resistors have to be connected externally to the integrated circuits in a cost-intensive manner, which requires considerable outlay in the course of fabrication.
However, the provision of a, typically, external measuring resistor turns out not only to be disadvantageous for cost reasons, but also reduces the efficiency of the switching regulator. Since the measuring resistor typically has to be connected externally to the integrated circuit, it is sometimes necessary, apart from a greater space requirement on the circuit board, to provide an additional output terminal on the integrated circuit.
Finally, the voltage drop measured across the measuring resistor has, for each switching period, an initial voltage spike produced by charge reversal of parasitic capacitances when the power switch is switched on. These undesirable voltage spikes have to be blanked out by additional measures—such as e.g. so-called “leading edge current blanking”—which are complicated in terms of circuitry, since the voltage spikes would otherwise impermissibly corrupt the actual measured value.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a so-called current-mode switching regulator, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which is better suited to implementation in integrated circuitry.
The current-mode switching regulator includes a first regulating device for voltage regulation and a second regulating device for load current regulation. Each of the first and second devices has a first input, a second input, and an output. The first input of the first regulating device is connected to receive a reference signal and the second input of the first regulating device is connected to receive an output signal of the current-mode switching regulator, as a regulated variable. The output of the first regulating device is connected to the first input of the second regulating device. A power switch is connected to the second regulating device and is controlled by a control signal of the second regulating device. The power switch has a load path connected between a first supply potential and a second supply potential. A choke device or inductor is connected the load path of the power switch. An integrator is connected to the choke device and to the second regulating device. The integrator generates a regulating signal by integrating, with respect to time, an inductor voltage drop across the inductor device. The regulating signal mirrors a load current and is coupled, as regulated variable, into the second input of the second regulating device.
With the current-mode switching regulator according to the invention, it is possible to dispense with a measuring resistor for detecting the measurement voltage, as has been customary heretofore. The measurement voltage necessary for the regulation of the load current is in this case picked off at the inductor itself, which is necessary in any case for the functioning of the switching regulator. The relationship between current I and voltage U across an inductance I is utilized in this case, i.e.
U=L·dI/dt.
This inductor voltage U is subsequently fed to an integrator, e.g. a voltage-controlled current source with an integrating element connected downstream. In other words the voltage drop across the inductor is integrated over time. In this way, an additional measuring resistor typically of external design and having all the disadvantages described above is no longer necessary.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a current-mode switching regulator, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 4553082 (1985-11-01), Nesler
patent: 4959606 (1990-09-01), Forge
patent: 5367247 (1994-11-01), Blocher et al.
patent: 5627459 (1997-05-01), Itoyama et al.
Greenberg Laurence A.
Lerner Herbert L.
Riley Shawn
Siemens Aktiengesellschaft
Stemer Werner H.
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