Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2002-01-10
2004-04-06
Clinger, James (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S194000
Reexamination Certificate
active
06717374
ABSTRACT:
The invention relates to a microcontroller according to the preamble of patent claim
1
, a switched-mode power supply according to patent claim
10
, a ballast for at least one electric lamp according to the preamble of patent claim
11
, and a method of operating at least one electric lamp according to the preamble of patent claim
25
.
I. TECHNICAL FIELD
In particular, the invention relates to a microcontroller which is provided to drive the switching transistors of a switched-mode power supply, to be specific preferably of a switched-mode power supply for operating electric lamps. In the switched-mode power supplies normally used to operate electric lamps, there are normally inverters, in particular half-bridge, full-bridge and push-pull inverters, and also step-up converters and step-down converters. Modern electronic ballasts for operating electric lamps generally have an inverter to produce a high-frequency alternating current for lamp operation and often also have a step-up converter as a DC supply for the inverter. The switching transistors of the inverter and of the step-up converter are driven by means of driver circuits, which are constructed as integrated circuits designed using analog techniques. In addition, modern electronic ballasts for electric lamps also contain a microcontroller, which is generally used for communication with a control unit arranged outside the ballast and for evaluating the control commands from this control unit for lamp operation and also for monitoring the lamp operation.
II. PRIOR ART
The European publication EP 0 708 579 A1 discloses a circuit arrangement for operating a high-pressure discharge lamp using an inverter, whose switching transistors have pulse-width modulated control signals applied to them by means of a microcontroller and a downstream integrated driver circuit. The pulse-width modulated control signals are generated with the aid of the auto-reload timer implemented in the microcontroller. In principle, this is a counting mechanism which operates at the operating cycle frequency of the microcontroller. During the counting operation, the reaching of a reference value and the overflow of the counting mechanism are monitored. During the time period which is needed to reach the reference value, the output of the auto-reload timer is at the “high” logic level, and during the time period which the counting mechanism needs to count up from the reference value until the counter overflows, the output of the auto-reload timer is at the “low” logic level. In this way, with the aid of the microcontroller, pulse-width modulated control signals for the inverter are generated, in order to permit lamp operation with a frequency-modulated voltage in a small frequency range and with a comparatively low number of discrete frequencies.
However, in this way, using cost-effective microcontrollers, no finely graduated pulse-width modulation control nor any finely graduated frequency control of the inverter can be carried out, since the smallest possible, adjustable change in the pulse width or in the frequency of the control signal which can be generated by the counting mechanism explained above is limited by the operating cycle frequency of the microcontroller and by the memory size of the counting mechanism. In order, for example, to permit dimming operation of fluorescent lamps on an electronic ballast by means of frequency modulation of the lamp current, frequency changes in steps of approximately 50 Hz are required in the frequency range from about 30 kHz to 100 kHz. If this frequency modulation is to be generated with the aid of the auto-reload timer, a microcontroller with an operating cycle frequency of more than 100 MHz is needed for this purpose. However, for cost reasons, such microcontrollers cannot be used in electronic ballasts for lamp operation.
III. SUMMARY OF THE INVENTION
It is an object of the invention to provide a microcontroller with an improved device for pulse-width modulation control and/or frequency control of a switched-mode power supply.
A further object of the invention is to provide a switched-mode power supply provided with a microcontroller with improved driving of the switching means of the switched-mode power supply.
In addition, it is an object of the invention to provide a ballast equipped with an inverter for operating at least one electric lamp which, with the aid of a microcontroller, permits finely graduated frequency control and/or pulse-width modulation control of the switching means of the inverter.
Furthermore, it is an object of the invention to specify an improved method for generating frequency control signals and/or pulse-width modulation control signals for the switching means of an inverter of a ballast for operating electric lamps by means of a microcontroller.
The aforementioned objects of the invention are achieved by the features of the independent patent claims
1
,
10
,
11
and
25
, respectively. Advantageous refinements of the invention are described in the dependent patent claims.
The microcontroller according to the invention has at least one device for pulse-width modulation control and/or frequency control of a switched-mode power supply, this device having
a device for the alternate charging and discharging of a charge store that can be connected to the microcontroller or integrated into the microcontroller,
control means for the device for controlling the charging operations and/or the discharging operations, and
evaluation means which are used to evaluate the time periods required for recharging the charge store between different charge states and, on this basis, to generate a pulse-width modulation control signal and/or frequency control signal.
The device for the alternate charging and discharging of a charge store, and its control means, permit controlled charging operations and discharging operations to be carried out alternately with each other on a charge store and, with the aid of the evaluation means, the evaluation of the time periods which are needed for the partial charging and discharging of the charge store and on this basis the generation of a pulse-width modulation control signal and/or frequency control signal. Even if the microcontroller according to the invention has only a low operating cycle frequency, it can be used to implement finely graduated pulse-width modulation control and/or frequency control of a switched-mode power supply, since the device for the alternate charging and discharging of a charge store operates independently of the operating cycle frequency of the microcontroller.
The device for the alternate charging and discharging of a charge store advantageously comprises a controllable current source for applying an adjustable charging current to the charge store, and a controllable current sink for applying an adjustable discharging current to the charge store. As a result, the individual charging and discharging operations can be controlled independently of one another. In addition, the controllable current source and current sink can be produced in a known way by means of semiconductor technology and integrated into the microcontroller. In order to permit very fine graduation of the pulse-width modulation control signals and/or frequency control signals, the controllable current source and the controllable current sink are formed in such a way that their settings can be varied in relation to a reference current level, in each case with a resolution of at least 8 bits. The reference current level for the charging and the discharging current is in this case advantageously predefined with the aid of a nonreactive resistor. The control means provided for the device for the alternate charging and discharging of a charge store is advantageously at least one read/write memory. The content of the read/write memory can be updated continuously, for example under program control, and can be read in order to control the device for the alternate charging and discharging of a charge store. The control means advantageously comprise a switching means which
Clinger James
Patent-Treuhand-Gesellschaft fur elektrische Gluhlampen mbH
Tran Chuc
LandOfFree
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