Coded data generation or conversion – Analog to or from digital conversion – Differential encoder and/or decoder
Reexamination Certificate
2003-02-28
2004-06-22
JeanPierre, Peguy (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Differential encoder and/or decoder
C341S155000, C341S144000
Reexamination Certificate
active
06753798
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a filter configuration, in particular, to a filter configuration that is suitable for filtering an output voltage signal of a power factor controller, a method for filtering an analog filter input signal, and a power factor controller.
FIG. 1
shows an exemplary embodiment of a power factor controller according to the prior art. Such a power factor controller has the task of forming a uniform output voltage Uout from an alternating input voltage Uin, in which case the intention is for the output voltage Uout to be kept at least approximately constant both in the event of changes in a load that can be connected to output terminals AK
1
, AK
2
and for AC voltages having different peak values or root-mean-square values. To convert the input voltage Uin into the output voltage Uout, use is made of a step-up switching regulator (boost converter) that is connected downstream of a bridge rectifier and has a series circuit including an inductor L and a switch T in parallel with the bridge rectifier BR and a series circuit including a diode D and a capacitor C in parallel with the switch, it being possible to tap off the output voltage Uout at the capacitor C. With switch T closed, the inductor takes up energy and outputs it through the diode D to the capacitor when switch T has, subsequently, been opened.
The switch T, which is a power transistor, in particular, is driven in clocked fashion by a pulse width modulator PWM, the output voltage Uout or the power consumption of the power factor controller being dependent on the frequency with which the switch is closed and on the switch-on duration for which the switch remains closed.
The power factor controller has both a current regulating circuit for regulating the current consumption from the mains and a voltage regulating circuit for regulating the output voltage Uout. The task of the current regulating circuit is to regulate the current I
L
through the coil such that the average value of the coil current is proportional to the input voltage Uin, or the magnitude of the input voltage Uin, for the comparison of an instantaneous value of the input voltage Uin and of the coil current I
L
, the pulse width modulator PWM is fed, from a measuring configuration MA
1
through a multiplier, an input voltage signal that is dependent on the input voltage Uin, and a voltage Ui that is present across a current sensing resistor Rs, as current signal.
The task of the voltage regulating circuit is to keep the output voltage Uout constant in the event of fluctuations in a load connected to the output terminals AKI
1
, AK
2
or in the event of a variable input voltage Uin. To that end, a second voltage signal, which is dependent on the output voltage and is formed by a second measuring configuration MA
2
, is compared with a reference value Vref. The information regarding the deviation of the second voltage signal Vs
2
from the reference value is fed to the pulse width modulator PWM by multiplication of the differential signal by the first voltage signal Vs
1
. The amplitude of the voltage signal Vs fed to the pulse width modulator PWM is, thus, raised or lowered depending on the output voltage Uout.
The signal Vs
1
fed to the multiplier MUL for multiplication by the first voltage signal, preferably, changes very slowly in comparison with the period duration of the input voltage. To prevent hum signals that are superposed on the output voltage signal Vs
2
from distorting the sinusoidal waveform of the voltage signal Vs, and from thus disturbing the regulation of the output voltage, a low-pass filter is provided in the voltage regulating loop. The low-pass filter is formed by two capacitors Cf
1
, Cf
2
and a resistor, which are connected up to an operational amplifier OP
1
that forms the difference between the reference signal Vref and the second voltage signal.
The capacitors and the resistor have to be embodied as external components, that is to say, they cannot be integrated in an integrated circuit, which is how the pulse width modulator PWM is usually embodied. This need for external components increases the costs of the drive circuit of the switch.
The paper: “Easy Power Factor Corrector Using a DSP” by Yves De Mari et al., Power Conversion, June 1999 Proceedings, pages 585 to 592, discloses using a digital signal processor (DSP) for filtering a signal dependent on the output voltage in a power factor controller. Such a procedure is expedient if a DSP is present, there is still free computational capacity in the DSP, and there is no need for mains isolation between the DSP and a power section of the power factor controller. Otherwise, the use of a DSP that is used only for filtering the voltage signal is too cost-intensive for most applications.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a filter configuration, a method for filtering an analog filter input signal, and a power factor controller that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that can be realized cost-effectively and without external components and that can be accommodated, in particular, as a constituent part of an integrated circuit in a drive circuit of a power transistor.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a filter configuration for filtering an analog signal, including an analog-to-digital converter unit having an input for receiving an analog filter input signal having a magnitude and an output supplying a pulse signal having a sequence of pulses, a number of the pulses per unit time being dependent on the magnitude of the filter input signal, a counter configuration being connected to the output of the analog-to-digital converter unit and receiving the pulse signal from the analog-to-digital converter unit, the counter configuration having at least one counter supplying a counter reading having a value, and a digital-to-analog converter unit connected to the counter configuration, the counter configuration supplying to the digital-to-analog converter unit in each case once during an evaluation interval the counter reading and forming an analog filter output signal having an amplitude dependent upon the value of the counter reading.
Accordingly, the filter configuration has an analog-to-digital converter unit having an input, to which an analog filter input signal is fed, and having an output, at which a pulse signal is available. In such a case, the pulse signal has a sequence of pulses, the analog-to-digital converter unit being configured such that the number of pulses of the pulse signal per unit time is dependent on the magnitude of the filter input signal. Connected downstream of the analog-to-digital converter unit is a counter configuration, to which the pulse signal is fed and that has at least one counter whose counter reading changes depending on the pulses of the pulse signal. The counter is configured such that, in each case at the end of a periodically recurring sampling interval, the counter reading of the at least one counter is acquired and is available as counter output signal. Connected downstream of the counter configuration is a digital-to-analog converter unit, to which the counter output signal is fed and that provides an analog filter output signal dependent on the value of the counter reading.
Such a filter according to the present invention can be used as a filter in a feedback path of a power factor controller, but it can also be used for filtering arbitrary output signals with long time constants from sensors. In particular, the power factor controller can include input terminals for applying an input voltage, output terminals for providing an output voltage, an inductor having an energy uptake, the inductor connected to at least one of the input terminals, at least one switch connected to the inductor and controlling the energy uptake of the inductor, a drive circuit connected to the
Greenberg Laurence A.
Infineon - Technologies AG
Jean-Pierre Peguy
Locher Ralph E.
Stemer Werner H.
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