Patent Application
20110199024
1. Field of the Invention
The present invention relates to electronic ballasts for fluorescent lamps, and more particularly to ballast controllers capable of providing brightness levels overview and brightness setting of a fluorescent lamp.
2. Description of the Related Art
In supplying power to light emitting devices such as fluorescent lamps or cold cathode fluorescent lamps or compact fluorescent lamps, electronic ballasts are widely adopted to keep the lamp current stable.
To offer dimming function for electronic ballasts, some prior art ballast controllers have implemented a DIM input pin for receiving a DIM control voltage to provide a dimming control means. The DIM control voltage is generally generated by an additional dial switch (wall dimmer) or a remote control means, and users have to operate the additional dial switch or the remote control means other than an existing lamp rocker switch to trigger the electronic ballast to adjust the luminance of the lamp.
Through the setting of the DIM control voltage, a luminance of the fluorescent lamp corresponding to the setting of the DIM input is generated.
However, since the setting of the DIM control voltage in the prior art has to be done by manipulating an additional dial switch or a remote control means other than an existing lamp switch, users have to pay more cost for the additional dial switch or remote control means. Besides, the additional dial switch may have to be mounted on the wall wherein the wiring between the dial switch and the ballast is bothersome. As to the remote control means, the communication between the transmitter and the receiver needs power, and if the remote control means runs out of battery, then there is no way to dim the lamp unless the battery is replaced.
Therefore, there is a need to provide a solution capable of reducing the cost and eliminating the requirement of an additional dial switch or remote control means in implementing a ballast application with dimming function.
Seeing this bottleneck, the present invention proposes a novel topology of a single chip ballast controller capable of providing brightness levels overview and brightness setting of a fluorescent lamp by switching a corresponding lamp switch, without the need of any additional dial switch or remote control means.
One objective of the present invention is to provide a ballast controller capable of providing brightness levels overview and brightness setting of a fluorescent lamp by sensing the switching of a power line, without the need of any additional dial switch or remote control means.
Another objective of the present invention is to provide a ballast controller with brightness adjusting function which is controlled by the switching of a corresponding lamp switch.
Still another objective of the present invention is to provide a single chip ballast controller with concise architecture, which can control the luminance of the lamp by regulating the lamp current according to a settled level of a time-varying reference voltage determined by the switching of a corresponding lamp switch.
To achieve the foregoing objectives, the present invention provides a single chip ballast controller, capable of providing brightness levels overview and brightness setting of a fluorescent lamp during power-on period, comprising: a switching detection circuit, used to generate a set signal, which changes from an inactive state to an active state when a supply voltage falls below a threshold voltage; a time-varying reference voltage generator, used to generate a time-varying reference voltage varying gradually between a first level and a second level during a power-on period, wherein the time-varying reference voltage can be fixed at a level between the first level and the second level by the active state of the set signal during the power-on period; and a gating signal generator, used to generate a high side driving signal and a low side driving signal according to an error voltage between the time-varying reference voltage and a current sensing voltage in a way that the high level durations of the high side driving signal and the low side driving signal vary in the same direction as the amplitude of the error voltage, wherein the current sensing voltage is proportional to a lamp current flowing through the fluorescent lamp.
To make it easier for our examiner to understand the objective of the invention, its structure, innovative features, and performance, we use a preferred embodiment together with the accompanying drawings for the detailed description of the invention.
a shows a time-varying reference voltage waveform during the power-on period.
b shows a time-varying reference voltage waveform with a setting during the power-on period.
The present invention will be described in more detail hereinafter with reference to the accompanying drawings that show the preferred embodiment of the invention.
Please refer to
The ballast controller 100 is used to generate a pair of non-overlapping driving signals composed of a high side driving signal VGH and a low side driving signal VGL according to an error voltage between a time-varying reference voltage and a current sensing voltage VCS (non-negative), wherein the current sensing voltage VCS is generated according to a lamp current ILAMP. The high level durations of the high side driving signal VGH and the low side driving signal VGL, non-overlapping with each other, are controlled by the error voltage in a way that the high level durations of the high side driving signal VGH and the low side driving signal VGL vary in the same direction as the error voltage, so when the error voltage increases—it means the lamp current ILAMP is below an expected value—the high level durations of the high side driving signal VGH and the low side driving signal VGL will be prolonged to have more energy delivered to the lamp circuit 105 to increase the lamp current ILAMP. For a given level of the time-varying reference voltage, the error voltage will be settled to a corresponding value in a finite period, and the also settled high level durations of the pair of non-overlapping driving signals will then result a corresponding brightness level of the fluorescent lamp.
The time-varying reference voltage generated inside the ballast controller 100 is varying gradually between a first level and a second level during a power-on period, and will be fixed at a level between the first level and second level when a switching of a power line VBUS causes a supply voltage VCC to fall below a threshold voltage. After the level of the time-varying reference voltage fixed, it can be further increased by switching the power line VBUS a first number of times (for example one time) in an adjustment period, or decreased by switching the power line VBUS a second number of times (for example two times) in the adjustment period, so users can adjust the time-varying reference voltage up or down to a satisfied level within a plurality of the adjustment periods.
The start-up resistor 101, coupled to the rectifying and filtering circuit 103, is used to provide a start-up current path for building the supply voltage VCC from a main input voltage VBUS.
The driving stage 102, powered by the power line VBUS, is used to generate a square signal VSQR at an output end with a high level and a low level according to the high side driving signal VGH and the low side driving signal VGL. The high level of the square signal VSQR is provided by connecting the output end through a first switch—turned on in the high level duration of the high side driving signal VGH—to the main input voltage VBUS, and the low level of the square signal VSQR is provided by connecting the output end through a second switch—turned on in the high level duration of the low side driving signal VGL—to a reference ground. The first switch preferably comprises a high side NMOS transistor and the second switch preferably comprises a low side NMOS transistor.
The rectifying and filtering circuit 103 is used to provide the supply voltage VCC. In the start-up period, the supply voltage VCC is charged up by the main input voltage VBUS via the start-up resistor 101 to enable the ballast controller with step-dimming function 100 to generate the high side driving signal VGH and the low side driving signal VGL, and thereby the square signal VSQR of the driving stage 102. The rectifying and filtering circuit 103 then rectifies and filters the square signal VSQR to generate the supply voltage VCC.
The LC resonant circuit 104 acts as a band-pass filter to process the square signal VSQR to generate the lamp current ILAMP having a resonant waveform.
The lamp circuit 105 comprises a fluorescent lamp of which the luminance varies in the same direction as the root-mean-squared value of the lamp current ILAMP.
The current sensing resistor 106 is used to carry the positive portions of the lamp current ILAMP, by the unilateral switching of the diode 107, to provide the current sensing voltage VCS, and the diode 108 is used to clamp the anode voltage of the diode 107 at around −0.7V when the lamp current ILAMP is in negative half cycles.
As the time-varying reference voltage varies gradually between the first level and second level, the high side driving signal VGH and the low side driving signal VGL will cause the average of the current sensing voltage VCS to approach the time-varying reference voltage, thereby providing a brightness levels overview of the fluorescent lamp, and users can choose a preferred brightness level during the overview by switching the power line VBUS. Besides, the ballast controller 100 can be a single chip or it can be integrated with the driving stage 102 into a single chip.
Please refer to
The switching detection circuit 201 preferably comprises a comparator. The comparator is used to generate a set signal VSET, wherein the set signal VSET changes from an inactive state to an active state when the supply voltage VCC falls below a threshold voltage.
The time-varying reference voltage generator 202, for example but not limited to waveform generator, is used to generate a time-varying reference voltage Vref varying gradually between a first level and a second level during the power-on period. Please refer to
The combiner 203 is used to subtract the time-varying reference voltage Vref with the current sensing voltage VCS to generate an error voltage Verror. The amplitude of the error voltage Verror varies in the same direction as the brightness of the fluorescent lamp because the amplitude of the current sensing voltage VCS is proportional to that of the lamp current ILAMP, and the larger the amplitude of the lamp current is, the brighter the fluorescent lamp will be.
The gating signal generator 204 is used to generate the high side driving signal VGH and the low side driving signal VGL according to the error voltage Verror in a way that the high level durations of the high side driving signal VGH and the low side driving signal VGL vary in the same direction as the amplitude of the error voltage Verror.
A preferred embodiment of the gating signal generator 204 is disclosed in
The amplifier 401 amplifies the error voltage Verror (for example but not limited to 0˜10 mVP-P) with a gain (for example but not limited to 100V/V) to generate a control voltage VCONTROL (for example but not limited to 0˜1VP-P).
The combiner 402 is used to add the control voltage VCONTROL with a DC voltage VDC to generate a high threshold voltage VTHH, wherein the DC voltage VDC, for example but not limited to 3.8V, is used to define a minimum brightness level.
The oscillator 403, preferably but not limited to an astable type, is used to generate an oscillating signal OSC according to the high threshold voltage VTHH and a low threshold voltage VTHL. The frequency of the oscillating signal OSC varies in the opposite direction as the high threshold voltage VTHH, i.e., as the level of the high threshold voltage VTHH goes up/down, the frequency of the oscillating signal OSC will become lower/higher.
The frequency divider 404 is used to divide the frequency of the oscillating signal OSC to generate a pair of complementary clock signals CLK and CLKB.
The dead time insertion and level shifting circuit 405 is used to insert a dead time between the pair of complementary clock signals CLK and CLKB and up shift the pair of complementary clock signals CLK and CLKB to generate the high side driving signal VGH and the low side driving signal VGL.
Through the implementation of the present invention, a single-chip ballast controller capable of providing brightness levels overview and brightness setting of a fluorescent lamp during power-on period by sensing the switching of a lamp switch and sensing the lamp current is presented. The topology of the present invention is much more concise than prior art circuits, so the present invention does conquer the disadvantages of prior art circuits.
While the invention has been described by way of examples and in terms of preferred embodiments, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.
In summation of the above description, the present invention herein enhances the performance than the conventional structure and further complies with the patent application requirements and is submitted to the Patent and Trademark Office for review and granting of the commensurate patent rights.
