Electricity: power supply or regulation systems – For reactive power control – Using converter
Reexamination Certificate
2003-06-09
2004-06-01
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
For reactive power control
Using converter
C323S222000, C323S285000, C323S288000
Reexamination Certificate
active
06744241
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a method for driving a switch in a switch-mode converter and also relates to a drive circuit for a switch in a switch-mode converter. The method includes: producing a threshold signal, producing a ramp signal synchronized with a clock signal such that the slope of the ramp signal is dependent on the output voltage of the converter, and comparing the threshold signal with the ramp signal and driving the switch as a function of the result of the comparison.
A method such as this and an apparatus such as this are known from U.S. Pat. No. 6,307,361. In the known method and the known apparatus, a signal that is dependent on an input current to a switch-mode converter is compared with a pulsed ramp signal or a sawtooth waveform signal. The pulsed ramp signal or the sawtooth waveform signal has a slope that is dependent on the output voltage of the switch-mode converter. A switch, which controls the power consumption of the switch-mode converter is in this case pulsed, and is driven as a function of a comparison of the threshold signal with the ramp signal. The switch is switched on when the ramp signal reaches the value of the threshold signal and is switched off when the ramp signal is reset. When the input voltage of the switch-mode converter rises during this process, then the period for which it is switched on decreases, in order to keep the power consumption constant. When the output voltage falls because of an increase in the power consumption of any load that is connected to the switch-mode converter, then the period for which it is switched on increases, in order to increase the power consumption, and thus to readjust the output voltage.
In the case of the known method and the known apparatus, the input current and hence the threshold signal are inversely proportional to the square of the input voltage. The input voltage is normally a sinusoidal voltage or a voltage with a sinusoidal magnitude, at a frequency that is considerably lower than the clock frequency of the switch. If the root mean square value of the input voltage varies between 90 V and 270 V (=3·90 V), as is the case for switch-mode converters in so-called wide area network sections, then, because of the input voltage, this results in a dynamic range for the threshold value of 1:3
2
, or 1:9. Furthermore, if the output voltage is constant, the input current is proportional to the power emitted to the load. If, by way of example, this power consumption varies by a factor of 1:20, then these fluctuations result in the threshold value having a dynamic range of 1:20. In other words: when the input voltage is at its maximum root mean square value and the power consumption of the load is at its minimum, which is then the minimum threshold value x
min
, then the maximum threshold value which occurs with the input voltage with the lowest root mean square value and with the maximum load power consumption is x
max
=180·x
min
.
The circuit configuration for producing the ramp signal must in this case be designed such that it produces a ramp signal which has just as wide a dynamic range, in order on the one hand to reach the threshold value in each clock period, and hence to switch on the switch. Furthermore, the comparator must be designed to produce an exact comparison result over this dynamic range.
The switch-mode converter taught in U.S. Pat. No. 6,307,361 is in the form of a boost converter, whose power consumption increases as the period for which the switch is switched on in each clock period increases.
A method for driving a switch in a switch-mode converter in the form of a boost converter is known from Sam Ben-Yaakov, Ilya Zeltser: “PWM Converters with Resistive Input”, IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 45, NO. 3, June 1998, in which the input current on the network side is filtered and is multiplied by a controlled variable that is dependent on the output voltage. The multiplication signal that is formed is compared with a ramp signal or sawtooth waveform signal, in order to define periods during which the switch in the switch-mode converter is switched off, on the basis of the comparison result. In this method, when the input voltages have a high root mean square value and the loads are low, the controlled variable that is dependent on the output voltage would have to be very large, so that a multiplier with a very wide linearity range is required, and this can be produced only with a high degree of circuitry complexity.
A method is likewise known from Hwang, Chee, Ki: “New Universal Control Methods for Power Factor Correction and DC to DC Converter Applications”, IEEE, 1997, in which a threshold signal which is dependent on an input current to a switch-mode converter is compared with a ramp signal whose amplitude and slope are variable. The switch in the switch-mode converter is driven as a function of a comparison of the threshold signal with the ramp signal. In this method as well, the amplitude of the variable ramp signal would need to have a very wide dynamic range in order to reach the threshold signal, and hence to switch on the switch, once in each clock period. Furthermore, there are stringent requirements for the accuracy of the comparison configuration that compares these two signals, namely the threshold signal and the ramp signal, which have a wide dynamic range.
A method for driving a switch in a switch-mode converter is known from Published German Patent Application DE 10 725 842 A1, in which the instantaneous value of the output voltage is multiplied by a controlled variable that is dependent on the output voltage. A difference signal between the multiplication signal and a signal that is dependent on the input current is supplied to a pulse width modulator in order to produce drive signals for the switch. An exponential transfer function is in this case applied to the control signal before it is supplied to the multiplier.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and a drive circuit for driving a switch in a switch-mode converter, which overcome the above-mentioned disadvantages of the prior art apparatus and methods of the general type in which a threshold signal is compared to a ramp signal that is dependent on an output voltage of the switch-mode converter, and in which the switch in the switch-mode converter is driven as a function of the result of the comparison.
In particular, an object of the invention is to provide a method and a drive circuit of the type mentioned above that can be used in switch-mode converters having a predetermined dynamic range for the input voltage and having a predetermined dynamic range for the power consumption of the load.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for driving a switch in a switch-mode converter having input terminals for supplying an input voltage and output terminals for providing an output voltage. The method includes the following steps: producing a threshold signal dependent on a quotient of a first signal dependent on an input current to the switch-mode converter and a second signal dependent on the output voltage; producing a ramp signal synchronously in time with a clock signal, the ramp signal having a slope dependent on the output voltage; and obtaining a comparison result by comparing the threshold signal with the ramp signal and driving the switch as a function of the comparison result.
Using a threshold signal that is dependent on the quotient of a signal, which is dependent on the input current, and a signal, which is dependent on the output voltage, reduces the dynamic range of the threshold signal. This results in the ramp signal likewise having a narrower dynamic range, thus also reducing the requirements for a comparator circuit that carries out a comparison between the threshold signal and the ramp signal.
One embodiment of the method provides for a control signal that is dependent on the output volta
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Riley Shawn
Stemer Werner H.
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