Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-05-02
2001-09-25
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
Reexamination Certificate
active
06294905
ABSTRACT:
TECHNICAL FIELD
The invention relates to an electric circuit for controlling a load in accordance with a target or desired signal.
BACKGROUND OF THE INVENTION
The term “load” is to be understood in the present context in the broadest possible scope. Primarily, it is an electric load, for example an electric motor, a coil, a resistor or the like, and such electric components then may have the “load” proper coupled thereto, for example in the form of an electromagnetic valve, an electric heating or a part to be moved mechanically by an electric motor.
For illustrating the invention in representative manner, an inductive load in the form of an electromagnetic driver device for a braking valve of a brake system is to be considered specifically in the following. Such an electromagnetic driver device is concerned with controlling/adjusting the pressure of brake fluid. The pressure is adjusted by the electromagnetic valve as a function of the current flowing through the coil of the electromagnet. The control signal for such a control/closed-loop control is usually supplied to an electronic switch in the form of a PWM adjusting or control signal (PWM=Pulse Width Modulation), with this PWM control signal opening and closing the electronic switch with a specific pulse duty factor or duty cycle (ratio of pulse duration to pulse interval) so that the current flow through the electronic switch connected in series with the load determines the current flow through the load.
As with other usual closed-loop control circuits, the circuit according to the invention also employs an arrangement in which a first signal source issuing the desired signal as well as a second signal source issuing an actual signal are connected, via a control signal generating circuit, to a controller, for example the control terminal of an electronic switch (for example a MOSFET).
There are numerous possible designs for the control signal generating circuit. Decisive for the output signal of the control signal generating circuit is the deviation between actual signal and desired signal. With slight control deviation, i.e., a little difference between the actual signal and the desired signal, the control signal is of such a nature that only a relatively minor change in the quantity to be controlled or adjusted in the load is still taking place towards the desired signal. With a large control deviation, the control signal is “larger”, i.e., there is a faster change of the actual signal for approximation to the desired signal.
In order to accelerate the approximation of the desired signal and the actual signal in case of large control deviations, the control signal is provided with a differential component. The control signal is thus amplified overproportionally in case of large control deviation in order to obtain an as fast as possible approximation of the actual value to the desired value.
The prior art reveals a large variety of measures for obtaining in addition to proportional control also differential and/or integral control, either alternatively or in addition thereto.
In the past few years an increasing number of digital circuits has been employed for controlling/adjusting electric loads. For producing a PWM control signal, a digital control circuit employs, for example, an up/down counter whose continuously changing count is compared to a digital periodical ramp signal. Depending on the ratio of the numerical values compared with each other, the level of the PWM control signal obtained therefrom is either high or low. The up/down counter is clocked by a constant clock signal, with the counting direction being set in accordance with the ratio between desired signal and actual signal.
SUMMARY OF THE INVENTION
It is conceivable now not to compare the count directly to the ramp signal, but to first convert the count of the counter in accordance with a predetermined function in order to thus obtain a proportional, integral or differential behavior.
The disclosed embodiments of the invention are directed to an electric circuit for controlling a load in accordance with a desired signal, in which relatively rapid approximation of the actual signal in the load to the desired signal is achieved with relatively simple means, with the speed of approximation between the actual signal and the desired signal increasing as the deviation increases.
The disclosed embodiments of the invention provide an electric circuit for controlling a load in accordance with an actual signal, said circuit comprising:
a first signal source issuing the desired signal;
a second signal source issuing an actual signal representative of the current state of the load;
a controller coupled to the load and having a control terminal, and
a control signal generating circuit which at an input thereof receives a deviation signal representative of the difference between desired signal and actual signal, which generates a control signal in accordance with the deviation signal and which feeds the control signal via an output to the control terminal of the controller,
the control signal generating circuit including a counter operated in accordance with the deviation signal so as to generate the control signal, and a count clock input of the counter being connected to the output of a voltage-controlled oscillator receiving the deviation signal at the input thereof.
Instead of operating the counter with a clock signal of fixed frequency or with a clock signal of a frequency derived from a fixed frequency, the counter is operated according to one embodiment or the invention with the clock signal derived from the output of a voltage-controlled oscillator.
Voltage-controlled oscillators are known in the prior art in various designs. Usually, the oscillation frequency at the output of the voltage-controlled oscillator (VCO) is dependent on the voltage difference at the input terminal pair thereof. If the voltage difference is large, the output frequency is relatively high, and with low voltage difference the output frequency is relatively low.
The present invention makes use of this special feature of a voltage-controlled oscillator in conjunction with a control or adjusting means. When the deviation between the desired signal and the actual signal is high, the voltage controlled oscillator delivers a signal of relatively high frequency at its output. The counter is operated in correspondingly rapid manner, and as a consequence thereof the control signal supplied to the control terminal of the controller is shaped such that rapid approximation of the actual signal to the desired signal takes place.
A preferred embodiment of the invention expediently employs a comparator circuit comparing the desired signal to the actual signal and forming the deviation signal at the output thereof. Instead of a separate comparator circuit, it is also possible to apply the actual signal and the desired signal directly to the two inputs of the voltage-controlled oscillator. The deviation signal then is the voltage difference between the desired signal and the actual signal.
An essential component of the circuit according to one embodiment of the invention is the voltage-controlled oscillator in conjunction with a counter. The manner in which the control signal is formed on the basis of the count is dependent upon the particular application. For example, an analog control signal is fed to the control terminal (base, gate) of a transistor. This analog control signal could be obtained by digital-to-analog conversion from the count of the counter, with the counter then being expediently designed as an up/down counter (forward-backward counter). Depending on the sign of the differential signal obtained from subtraction of the actual signal from the desired signal, the counter count is either increased or decreased, with the speed of counting, according to the invention, being dependent upon the frequency of the clock signal at the output of the voltage-controlled oscillator.
According to another embodiment of the invention, it is provided that the control signal is a PWM control si
Galanthay Theodore E.
Riley Shawn
Seed IP Law Group PLLC
STMicroelectronics GmbH
Tarleton E. Russell
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