WO2005072026A1 - Electronic ballast with multi-slope current feedback - Google Patents

Electronic ballast with multi-slope current feedback Download PDF

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Publication number
WO2005072026A1
WO2005072026A1 PCT/IB2005/050224 IB2005050224W WO2005072026A1 WO 2005072026 A1 WO2005072026 A1 WO 2005072026A1 IB 2005050224 W IB2005050224 W IB 2005050224W WO 2005072026 A1 WO2005072026 A1 WO 2005072026A1
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WO
WIPO (PCT)
Prior art keywords
lamp current
current signal
circuit
sensed
response curve
Prior art date
Application number
PCT/IB2005/050224
Other languages
French (fr)
Inventor
William L. Keith
George L. Grouev
Kent E. Crouse
Original Assignee
Koninklijke Philips Electronics, N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics, N.V. filed Critical Koninklijke Philips Electronics, N.V.
Priority to JP2006550417A priority Critical patent/JP2007519201A/en
Priority to EP05702723A priority patent/EP1709843A1/en
Publication of WO2005072026A1 publication Critical patent/WO2005072026A1/en

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
    • H05B41/14—Circuit arrangements
    • H05B41/36—Controlling
    • H05B41/38—Controlling the intensity of light
    • H05B41/39—Controlling the intensity of light continuously
    • H05B41/392—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor
    • H05B41/3921—Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor with possibility of light intensity variations

Definitions

  • This invention relates to electronic ballasts for gas discharge lamps, and more particularly, to an electronic ballast with multi-slope current feedback for improved dimming control.
  • Gas discharge lamps such as fluorescent lamps, require a ballast to limit the current to the lamp.
  • Electronic ballasts have become increasingly popular due to their many advantages. Electronic ballasts provide greater efficiency — as much as 15% to 20% over magnetic ballast systems. Electronic ballasts produce less heat, reducing building cooling loads, and operate more quietly, without "hum.” In addition, electronic ballasts offer more design and control flexibility. Electronic ballasts must operate with different supply voltages, different types of lamps, and different numbers of lamps. Supply voltages vary around the world and may vary in a single location depending on the power grid.
  • An electronic ballast may operate with a single lamp, or two or more lamps.
  • the electronic ballast must operate reliably and efficiently under the various conditions.
  • One particular challenge is to provide lamp current control at the low current used by a dimmed lamp. Dimming ballasts must control the lamp current over a wide range, typically 5 to 280 mA from fully dimmed to fully lighted. The challenge is to provide fine control over the low end of the low lamp current range while providing control over the whole range. Because the perception of light differences is most pronounced at low light levels, irregularities, errors, or inconsistencies in light output in the low lamp current range are highly visible and annoying to the user.
  • Electronic ballasts presently use a current transformer to sense lamp current and provide the sensed current signal.
  • the microprocessor generates a desired current signal, which is compared to the sensed current signal to generate a current error signal. The current error signal is then used to adjust the electronic ballast operating point.
  • the microprocessor output is limited to the supply voltage, typically 5 Volts. This limits the options available to the designer. If the designer uses the full voltage range of the microprocessor to allow the current to be controlled over the entire dimming range, poor resolution results at low light levels. If the designer increases the resolution at the low light levels to improve visible dimming performance, it becomes impossible to reach full light output.
  • One approach that has been used to attempt to overcome this problem is to switch in or out current sense resistors to scale the sensed current signal. This approach is limited because the light output is discontinuous when switching from one current sense resistor to another, i.e., the light output jumps or drops when each new current sense resistor is switched into the circuit. Complex circuitry is required to smooth the discontinuous transition, due to the discreet values of the current sense resistors. The present arrangements either perform poorly or require the addition of complex, expensive circuits. It would be desirable to have an electronic ballast with multi-slope current feedback that would overcome the above disadvantages.
  • One aspect of the present invention provides an electronic ballast with multi-slope current feedback providing light output control over the whole light output range.
  • FIG. 1 is a block diagram of an electronic ballast with multi-slope current feedback made in accordance with the present invention
  • FIG. 1 is a block diagram of an electronic ballast with lamp type determination made in accordance with the present invention.
  • the electronic ballast 100 consists of AC/DC converter 122, half bridge 124, resonant tank circuit 126, microprocessor 128, regulating pulse width modulator (PWM) 130, high voltage (HV) driver 132, error circuit 134, and current response circuit 138.
  • PWM pulse width modulator
  • the AC/DC converter 122 receives the mains voltage 120 and the tank circuit 126 provides power to the lamp 136.
  • the mains voltage 120 is the AC line voltage supplied to the electronic ballast 100, such as 120V, 127V, 220V, 230V, or 277V.
  • the mains voltage 120 is received at the AC/DC converter 122.
  • the AC/DC converter 122 converts the AC mains voltage 120 to DC voltage 140, which is supplied to the half bridge 124.
  • the AC/DC converter 122 typically includes an EMI filter and a rectifier (not shown).
  • the AC/DC converter 122 can also include a boost circuit to increase the voltage of the DC voltage, such as from 180V to 470V.
  • the half bridge 124 converts the DC voltage 140 to a high frequency AC voltage 142.
  • the resonant tank circuit 126 supplies the AC voltage to the lamp 136.
  • the high frequency AC voltage typically has a frequency in the range of 25 to 60 kHz.
  • the microprocessor 128 controls the operation of the electronic ballast 100.
  • the microprocessor 128 stores and operates on programmed instructions, and senses parameters from throughout the electronic ballast 100 to determine the desired operating points. For example, the microprocessor 128 sets the AC voltage to different frequencies, depending on whether the lamp is in the preheat, strike, or run mode, or if no lamp is present.
  • the microprocessor 128 can control the power conversion and voltage output from the AC/DC converter 122.
  • the microprocessor 128 can also control the voltage and frequency of the AC voltage from the resonant tank circuit 126, by controlling the frequency and duty cycle of the half bridge 124 through the regulating PWM 130 and the HV driver 132.
  • the error circuit 134 compares sensed lamp current 144 and desired lamp current 146 and provides a lamp current error signal 148 to the regulating PWM 130 for adjustment of lamp current through the regulating PWM 130 and the HV driver 132.
  • the current response circuit 138 shown in FIG. 1, has a first responsiveness when the lamp current is at lower levels and a second responsiveness when the lamp current is at higher levels. The circuit responsiveness is the circuit output for a given circuit input.
  • the current response circuit 138 receives a high frequency (HF) sensed lamp current signal 144 and generates an adjusted lamp current signal 150, which is provided to the error circuit 134 and the microprocessor 128.
  • the error circuit 134 compares the adjusted lamp current signal 150 and a desired lamp current signal 146 from the microprocessor 128, and provides a lamp current error signal 148 to the regulating PWM 130 for adjustment of lamp current through the regulating PWM 130 and the HV driver 132.
  • the current response circuit 138 is more responsive when the HF sensed lamp current signal 144 is at the lower end of its operating range. This provides fine control when the electronic ballast is operating in the low lamp current range.
  • FIG. 4 is a detailed schematic diagram of the current response circuit.
  • DC power is supplied to the resonant half bridge across high voltage rail 200 and common rail 202 by the AC/DC converter (not shown).
  • Transistors Q2 and Q3 are connected in series between high voltage rail 200 and common rail 202 to form a half bridge circuit.
  • the HV driver U4 of FIG. 3 drives the transistors Q2 and Q3 so that they conduct alternately.
  • Inductor L5 and capacitor C33 form the resonant tank circuit and smooth the output at the junction between transistors Q2 and Q3 into a sinusoidal waveform.
  • the first filament 204 of the lamp 206 is connected across terminals Tl and T2 and the second filament 208 is connected across terminals T5 and T6.
  • one filament from the first lamp is connected across terminals Tl and T2 and the one filament from the second lamp is connected across terminals T5 and T6.
  • the other filaments, one from each lamp, are connected in series or parallel across terminals T3 and T4.
  • the microprocessor U2 is operable to receive inputs from inside and outside the electronic ballast, and to control ballast operation.
  • the microprocessor U2 determines the desired lamp operating frequency and sets the oscillator frequency of the regulating PWM U3, which drives the HV driver U4.
  • the HV driver U4 drives the transistors Q2 and Q3.
  • the microprocessor U2 can be an ST7LITE2 available from STMicroelectronics
  • the regulating PWM U3 can be an LM3524D available from National Semiconductor
  • the HV driver U4 can be an L6387 available from STMicroelectronics.
  • the current response circuit 240 senses high frequency (HF) lamp current at capacitor C37.
  • the current response circuit 240 provides an adjusted lamp current signal to the microprocessor U2 on line 210 and to the error op amp U6B of the error circuit through the resistor R64.
  • the microprocessor U2 generates a desired lamp current signal based on inputs and the desired operating condition and returns the desired lamp current signal to the error op amp U6B along line 212.
  • the error op amp U6B compares the adjusted lamp current signal and the desired lamp current signal to generate a lamp current error signal on line 214, which provides the lamp current error signal to the regulating PWM U3.
  • the regulating PWM U3 adjusts output pulse width, which adjusts the lamp current by the cycling of the transistors Q2 and Q3 with the HV driver U4.
  • the lamp current error signal When the sensed lamp current signal equals the desired lamp current signal at the error op amp U6B, the lamp current error signal will zero out and the electronic ballast will be in a steady state mode.
  • the electronic ballast operates in preheat, strike, and run modes.
  • the preheat mode provides a preheat sequence to the lamp filaments to induce thermionic emission and provide an electrical path through the lamp.
  • the strike mode applies a high voltage to ignite the lamp.
  • the run mode controls the current through the lamp after ignition.
  • the current response circuit 240 comprises slope altering circuit
  • the slope altering circuit 242 receives a high frequency (HF) lamp current signal from capacitor C37 and provides an altered lamp current signal to the half wave rectifier 244 at resistor R58.
  • the half wave rectifier 244 provides a rectified lamp current signal to the averaging circuit 246, which provides an adjusted lamp current signal to the microprocessor U2 on line 210 and to the error op amp U6B of the error circuit 248 at resistor R64.
  • the error op amp U6B compares the adjusted lamp current signal and the desired lamp current signal on line 212 from the microprocessor U2 and generates a lamp current error signal on line 214.
  • the slope altering circuit 242 consists of a parallel circuit of resistor R74 and diode D21 connected in series with parallel resistors R69 and R57 between the capacitor C37 and the common rail 202.
  • a diode D19 is connected between the capacitor C37 and the common rail 202.
  • the diode D19 is connected to provide the altered lamp current signal to the resistor R58.
  • the diode D19 is a Schottky diode.
  • the half wave rectifier 244 consists of current op amp U6A and high conductance ultra fast dual diode D18, with resistors R60 and R58 controlling gain.
  • the averaging circuit 246, which consists of the parallel circuit of resistor R62 and capacitor C38 in series with resistor R61, averages the rectified lamp current signal from the half wave rectifier 244.
  • the slope altering circuit 242 provides different altered lamp current signals depending on the portion of the lamp current cycle and the magnitude of the lamp current. During the positive portion of the current cycle, the altered lamp current signal is effectively zero. During the negative portion of the current cycle, the responsiveness of the lamp slope altering circuit 242 depends on the magnitude of the lamp current.
  • the slope altering circuit 242 senses lamp current at capacitor C37. During the positive portion of the current cycle, current flows from the capacitor C37 through the diode D19 to the common rail 202.
  • the altered lamp current signal to resistor R58 is approximately zero during the positive portion of the current cycle, because the forward voltage drop across the diode D19 is small. The small forward voltage drop across the diode D19 also minimizes power dissipation in the resistors R74, R69, and R57.
  • the diode D19 is off and current flows from the common rail 202 through the parallel resistors R69 and R57 to provide a negative voltage to the half wave rectifier 244 at resistor R58.
  • the negative voltage is a function of the lamp current.
  • the diode D21 operates below its threshold voltage and current from the parallel resistors R69 and R57 flows primarily through the resistor R74.
  • the diode D21 When the electronic ballast is operating the high lamp current range, the diode D21 operates above its threshold voltage and current from the parallel resistors R69 and R57 flows primarily through the diode D21. In one embodiment, threshold voltage for the diode D21 occurs when the lamp current is about 12 mA peak. The small forward voltage drop across the diode D21, such as 0.65 V, limits power dissipation in the resistor R74.
  • the slope altering circuit 242 provides a smooth, continuous transition between the low and the high lamp current ranges as the current flow from the parallel resistors R69 and R57 switches between the resistor R74 and the diode D21 with increasing lamp current.
  • the adjusted lamp current signal provided to the error circuit is plotted as a function of lamp current.
  • the continuous response curve 260 has a first response curve 262 in the low lamp current range and a second response curve 264 in the high lamp current range.
  • the slope of the first response curve 262 is typically greater than the slope of the second response curve 264 to provide a larger adjusted lamp current signal for the small lamp current in the low lamp current range.
  • the slope indicates the responsiveness of the circuit, i.e., the output for a given input.
  • a smooth continuous transition between the first response curve 262 and the second response curve 264 occurs at Point A.
  • Point B typically corresponds to full lamp output at 100% lamp current.
  • FIG. 5 is exemplary and variations can be employed to achieve particular results.
  • the first or second response curves can be a simple or complex curve, rather than linear.
  • the continuous response curve can consist of more individual curves than the first and second response curves.
  • FIG. 6 is a flow chart of a method of multi-slope current feedback for an electronic ballast made in accordance with the present invention.
  • the multi-slope continuous response curve is a dual slope curve.
  • a sensed lamp current signal is generated from high frequency (HF) lamp current at 270, an adjusted lamp current signal is generated from the sensed lamp current signal along a continuous response curve at 272, and the adjusted lamp current signal is compared to a desired lamp current signal to generate a lamp current error signal at 274.
  • the continuous response curve has a first response curve and a second response curve. The adjusted lamp current signal is generated along the first response curve when the sensed lamp current signal is in a low lamp current range and is generated along the second response curve when the sensed lamp current signal in a high lamp current range.
  • generating an adjusted lamp current signal from the sensed lamp current signal along a continuous response curve consists of generating an altered lamp current signal from the sensed lamp current signal, rectifying the altered lamp current signal to generate a rectified lamp current signal, and averaging the rectified lamp current signal to generate the adjusted lamp current signal.
  • the desired lamp current signal is generated from the adjusted lamp current signal, such as by providing the adjusted lamp current signal to a microprocessor and generating the desired lamp current signal in the microprocessor.

Abstract

An electronic ballast includes a multi-slope current feedback circuit comprising a current response circuit (138) responsive to lamp current and generating an adjusted lamp current signal (150), and an error circuit (134) receiving the adjusted lamp current signal (150) and a desired lamp current signal (146) to generate a lamp current error signal (148). The current response circuit (138) has a first responsiveness when the lamp current is in a low lamp current range and a second responsiveness when the lamp current is in a high lamp current range, the adjusted lamp current signal (150) being continuous between the low and the high lamp current range. The current response circuit (138) can comprises a slope altering circuit (242), a half wave rectifier (244), and an averaging circuit (246). A microprocessor can be responsive to the adjusted lamp current signal (150) and generate the desired lamp current signal (146).

Description

ELECTRONIC BALLAST WITH MULTI-SLOPE CURRENT FEEDBACK
This invention relates to electronic ballasts for gas discharge lamps, and more particularly, to an electronic ballast with multi-slope current feedback for improved dimming control. Gas discharge lamps, such as fluorescent lamps, require a ballast to limit the current to the lamp. Electronic ballasts have become increasingly popular due to their many advantages. Electronic ballasts provide greater efficiency — as much as 15% to 20% over magnetic ballast systems. Electronic ballasts produce less heat, reducing building cooling loads, and operate more quietly, without "hum." In addition, electronic ballasts offer more design and control flexibility. Electronic ballasts must operate with different supply voltages, different types of lamps, and different numbers of lamps. Supply voltages vary around the world and may vary in a single location depending on the power grid. Different types of lamps may have the same physical dimensions, so that different types of lamps can be used in a single fixture, yet be different electrically. An electronic ballast may operate with a single lamp, or two or more lamps. The electronic ballast must operate reliably and efficiently under the various conditions. One particular challenge is to provide lamp current control at the low current used by a dimmed lamp. Dimming ballasts must control the lamp current over a wide range, typically 5 to 280 mA from fully dimmed to fully lighted. The challenge is to provide fine control over the low end of the low lamp current range while providing control over the whole range. Because the perception of light differences is most pronounced at low light levels, irregularities, errors, or inconsistencies in light output in the low lamp current range are highly visible and annoying to the user. Electronic ballasts presently use a current transformer to sense lamp current and provide the sensed current signal. In one arrangement, the microprocessor generates a desired current signal, which is compared to the sensed current signal to generate a current error signal. The current error signal is then used to adjust the electronic ballast operating point. One problem with this arrangement is that the microprocessor output is limited to the supply voltage, typically 5 Volts. This limits the options available to the designer. If the designer uses the full voltage range of the microprocessor to allow the current to be controlled over the entire dimming range, poor resolution results at low light levels. If the designer increases the resolution at the low light levels to improve visible dimming performance, it becomes impossible to reach full light output. One approach that has been used to attempt to overcome this problem is to switch in or out current sense resistors to scale the sensed current signal. This approach is limited because the light output is discontinuous when switching from one current sense resistor to another, i.e., the light output jumps or drops when each new current sense resistor is switched into the circuit. Complex circuitry is required to smooth the discontinuous transition, due to the discreet values of the current sense resistors. The present arrangements either perform poorly or require the addition of complex, expensive circuits. It would be desirable to have an electronic ballast with multi-slope current feedback that would overcome the above disadvantages. One aspect of the present invention provides an electronic ballast with multi-slope current feedback providing light output control over the whole light output range. Another aspect of the present invention provides an electronic ballast with multi-slope current feedback providing smooth, continuous light output control. Another aspect of the present invention provides an electronic ballast with multi-slope current feedback using a simple, inexpensive circuit. The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention, rather than limiting the scope of the invention being defined by the appended claims and equivalents thereof. Various embodiment of the present invention are illustrated by the accompanying figures, wherein: FIG. 1 is a block diagram of an electronic ballast with multi-slope current feedback made in accordance with the present invention; FIGS. 2-4 are schematic diagrams of an electronic ballast with multi-slope current feedback made in accordance with the present invention; FIG. 5 is a graph showing a response curve for an electronic ballast with multi-slope current feedback made in accordance with the present invention; and FIG. 6 is a flow chart of a method of multi-slope current feedback for an electronic ballast made in accordance with the present invention. FIG. 1 is a block diagram of an electronic ballast with lamp type determination made in accordance with the present invention. The electronic ballast 100 consists of AC/DC converter 122, half bridge 124, resonant tank circuit 126, microprocessor 128, regulating pulse width modulator (PWM) 130, high voltage (HV) driver 132, error circuit 134, and current response circuit 138. The AC/DC converter 122 receives the mains voltage 120 and the tank circuit 126 provides power to the lamp 136. The mains voltage 120 is the AC line voltage supplied to the electronic ballast 100, such as 120V, 127V, 220V, 230V, or 277V. The mains voltage 120 is received at the AC/DC converter 122. The AC/DC converter 122 converts the AC mains voltage 120 to DC voltage 140, which is supplied to the half bridge 124. The AC/DC converter 122 typically includes an EMI filter and a rectifier (not shown). The AC/DC converter 122 can also include a boost circuit to increase the voltage of the DC voltage, such as from 180V to 470V. The half bridge 124 converts the DC voltage 140 to a high frequency AC voltage 142. The resonant tank circuit 126 supplies the AC voltage to the lamp 136. The high frequency AC voltage typically has a frequency in the range of 25 to 60 kHz. The microprocessor 128 controls the operation of the electronic ballast 100. The microprocessor 128 stores and operates on programmed instructions, and senses parameters from throughout the electronic ballast 100 to determine the desired operating points. For example, the microprocessor 128 sets the AC voltage to different frequencies, depending on whether the lamp is in the preheat, strike, or run mode, or if no lamp is present. The microprocessor 128 can control the power conversion and voltage output from the AC/DC converter 122. The microprocessor 128 can also control the voltage and frequency of the AC voltage from the resonant tank circuit 126, by controlling the frequency and duty cycle of the half bridge 124 through the regulating PWM 130 and the HV driver 132. The error circuit 134 compares sensed lamp current 144 and desired lamp current 146 and provides a lamp current error signal 148 to the regulating PWM 130 for adjustment of lamp current through the regulating PWM 130 and the HV driver 132. The current response circuit 138, shown in FIG. 1, has a first responsiveness when the lamp current is at lower levels and a second responsiveness when the lamp current is at higher levels. The circuit responsiveness is the circuit output for a given circuit input. The current response circuit 138 receives a high frequency (HF) sensed lamp current signal 144 and generates an adjusted lamp current signal 150, which is provided to the error circuit 134 and the microprocessor 128. The error circuit 134 compares the adjusted lamp current signal 150 and a desired lamp current signal 146 from the microprocessor 128, and provides a lamp current error signal 148 to the regulating PWM 130 for adjustment of lamp current through the regulating PWM 130 and the HV driver 132. The current response circuit 138 is more responsive when the HF sensed lamp current signal 144 is at the lower end of its operating range. This provides fine control when the electronic ballast is operating in the low lamp current range. FIGS. 2-4 are schematic diagrams of an electronic ballast with multi-slope current feedback made in accordance with the present invention. FIG. 4 is a detailed schematic diagram of the current response circuit. Referring to FIG. 2, DC power is supplied to the resonant half bridge across high voltage rail 200 and common rail 202 by the AC/DC converter (not shown). Transistors Q2 and Q3 are connected in series between high voltage rail 200 and common rail 202 to form a half bridge circuit. The HV driver U4 of FIG. 3 drives the transistors Q2 and Q3 so that they conduct alternately. Inductor L5 and capacitor C33 form the resonant tank circuit and smooth the output at the junction between transistors Q2 and Q3 into a sinusoidal waveform. For use with a single lamp, the first filament 204 of the lamp 206 is connected across terminals Tl and T2 and the second filament 208 is connected across terminals T5 and T6. When two lamps are used with the electronic ballast, one filament from the first lamp is connected across terminals Tl and T2 and the one filament from the second lamp is connected across terminals T5 and T6. The other filaments, one from each lamp, are connected in series or parallel across terminals T3 and T4. Referring to FIG. 3, the microprocessor U2 is operable to receive inputs from inside and outside the electronic ballast, and to control ballast operation. The microprocessor U2 determines the desired lamp operating frequency and sets the oscillator frequency of the regulating PWM U3, which drives the HV driver U4. The HV driver U4 drives the transistors Q2 and Q3. In one embodiment, the microprocessor U2 can be an ST7LITE2 available from STMicroelectronics, the regulating PWM U3 can be an LM3524D available from National Semiconductor, and the HV driver U4 can be an L6387 available from STMicroelectronics. Those skilled in the art will appreciate that particular components and circuits other than the exemplary components and circuits described herein can be selected to achieve the desired result. Referring to FIG. 2, the current response circuit 240 senses high frequency (HF) lamp current at capacitor C37. The current response circuit 240 provides an adjusted lamp current signal to the microprocessor U2 on line 210 and to the error op amp U6B of the error circuit through the resistor R64. The microprocessor U2 generates a desired lamp current signal based on inputs and the desired operating condition and returns the desired lamp current signal to the error op amp U6B along line 212. The error op amp U6B compares the adjusted lamp current signal and the desired lamp current signal to generate a lamp current error signal on line 214, which provides the lamp current error signal to the regulating PWM U3. In response to the lamp current error signal, the regulating PWM U3 adjusts output pulse width, which adjusts the lamp current by the cycling of the transistors Q2 and Q3 with the HV driver U4. When the sensed lamp current signal equals the desired lamp current signal at the error op amp U6B, the lamp current error signal will zero out and the electronic ballast will be in a steady state mode. The electronic ballast operates in preheat, strike, and run modes. The preheat mode provides a preheat sequence to the lamp filaments to induce thermionic emission and provide an electrical path through the lamp. The strike mode applies a high voltage to ignite the lamp. The run mode controls the current through the lamp after ignition. Referring to FIG. 4, the current response circuit 240 comprises slope altering circuit
242, half wave rectifier 244, and averaging circuit 246. The slope altering circuit 242 receives a high frequency (HF) lamp current signal from capacitor C37 and provides an altered lamp current signal to the half wave rectifier 244 at resistor R58. The half wave rectifier 244 provides a rectified lamp current signal to the averaging circuit 246, which provides an adjusted lamp current signal to the microprocessor U2 on line 210 and to the error op amp U6B of the error circuit 248 at resistor R64. The error op amp U6B compares the adjusted lamp current signal and the desired lamp current signal on line 212 from the microprocessor U2 and generates a lamp current error signal on line 214. The slope altering circuit 242 consists of a parallel circuit of resistor R74 and diode D21 connected in series with parallel resistors R69 and R57 between the capacitor C37 and the common rail 202. A diode D19 is connected between the capacitor C37 and the common rail 202. The diode D19 is connected to provide the altered lamp current signal to the resistor R58. In one embodiment, the diode D19 is a Schottky diode. The half wave rectifier 244 consists of current op amp U6A and high conductance ultra fast dual diode D18, with resistors R60 and R58 controlling gain. The averaging circuit 246, which consists of the parallel circuit of resistor R62 and capacitor C38 in series with resistor R61, averages the rectified lamp current signal from the half wave rectifier 244. In operation, the slope altering circuit 242 provides different altered lamp current signals depending on the portion of the lamp current cycle and the magnitude of the lamp current. During the positive portion of the current cycle, the altered lamp current signal is effectively zero. During the negative portion of the current cycle, the responsiveness of the lamp slope altering circuit 242 depends on the magnitude of the lamp current. The slope altering circuit 242 senses lamp current at capacitor C37. During the positive portion of the current cycle, current flows from the capacitor C37 through the diode D19 to the common rail 202. The altered lamp current signal to resistor R58 is approximately zero during the positive portion of the current cycle, because the forward voltage drop across the diode D19 is small. The small forward voltage drop across the diode D19 also minimizes power dissipation in the resistors R74, R69, and R57. During the negative portion of the current cycle, the diode D19 is off and current flows from the common rail 202 through the parallel resistors R69 and R57 to provide a negative voltage to the half wave rectifier 244 at resistor R58. The negative voltage is a function of the lamp current. When the electronic ballast is operating in the low lamp current range, the diode D21 operates below its threshold voltage and current from the parallel resistors R69 and R57 flows primarily through the resistor R74. This provides a large enough altered lamp current signal to regulate lamp current at very low dimming levels. When the electronic ballast is operating the high lamp current range, the diode D21 operates above its threshold voltage and current from the parallel resistors R69 and R57 flows primarily through the diode D21. In one embodiment, threshold voltage for the diode D21 occurs when the lamp current is about 12 mA peak. The small forward voltage drop across the diode D21, such as 0.65 V, limits power dissipation in the resistor R74. The slope altering circuit 242 provides a smooth, continuous transition between the low and the high lamp current ranges as the current flow from the parallel resistors R69 and R57 switches between the resistor R74 and the diode D21 with increasing lamp current. FIG. 5 is a graph showing a response curve for an electronic ballast with multi-slope current feedback made in accordance with the present invention. The adjusted lamp current signal provided to the error circuit is plotted as a function of lamp current. The continuous response curve 260 has a first response curve 262 in the low lamp current range and a second response curve 264 in the high lamp current range. The slope of the first response curve 262 is typically greater than the slope of the second response curve 264 to provide a larger adjusted lamp current signal for the small lamp current in the low lamp current range. The slope indicates the responsiveness of the circuit, i.e., the output for a given input. A smooth continuous transition between the first response curve 262 and the second response curve 264 occurs at Point A. Point B typically corresponds to full lamp output at 100% lamp current. Those skilled in the art will appreciate that the continuous response curve of FIG. 5 is exemplary and variations can be employed to achieve particular results. In one embodiment, the first or second response curves can be a simple or complex curve, rather than linear. In another embodiment, the continuous response curve can consist of more individual curves than the first and second response curves. FIG. 6 is a flow chart of a method of multi-slope current feedback for an electronic ballast made in accordance with the present invention. In this example, the multi-slope continuous response curve is a dual slope curve. A sensed lamp current signal is generated from high frequency (HF) lamp current at 270, an adjusted lamp current signal is generated from the sensed lamp current signal along a continuous response curve at 272, and the adjusted lamp current signal is compared to a desired lamp current signal to generate a lamp current error signal at 274. The continuous response curve has a first response curve and a second response curve. The adjusted lamp current signal is generated along the first response curve when the sensed lamp current signal is in a low lamp current range and is generated along the second response curve when the sensed lamp current signal in a high lamp current range. In one embodiment, generating an adjusted lamp current signal from the sensed lamp current signal along a continuous response curve consists of generating an altered lamp current signal from the sensed lamp current signal, rectifying the altered lamp current signal to generate a rectified lamp current signal, and averaging the rectified lamp current signal to generate the adjusted lamp current signal. In another embodiment, the desired lamp current signal is generated from the adjusted lamp current signal, such as by providing the adjusted lamp current signal to a microprocessor and generating the desired lamp current signal in the microprocessor. While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.

Claims

1. A method for multi-slope current feedback for an electronic ballast comprising: generating a sensed lamp current signal from high frequency (HF) lamp current 270; generating an adjusted lamp current signal from the sensed lamp current signal along a continuous response curve 272, the continuous response curve having a first response curve and a second response curve, the adjusted lamp current signal being generated along the first response curve when the sensed lamp current signal is in a first range and being generated along the second response curve when the sensed lamp current signal is in a second range; and comparing the adjusted lamp current signal to a desired lamp current signal to generate a lamp current error signal 274.
2. The method of claim 1 wherein generating an adjusted lamp current signal from the sensed lamp current signal along a continuous response curve 272 comprises: generating an altered lamp current signal from the sensed lamp current signal; rectifying the altered lamp current signal to generate a rectified lamp current signal; and averaging the rectified lamp current signal to generate the adjusted lamp current signal.
3. The method of claim 2 wherein the sensed lamp current signal has a positive cycle portion and a negative cycle portion, and generating an altered lamp current signal from the sensed lamp current signal comprises: zeroing the altered lamp current signal for the positive cycle portion; transforming the sensed lamp current to the altered lamp current signal at a first responsiveness for the negative cycle portion when the sensed lamp current signal is below a threshold; and transforming the sensed lamp current to the altered lamp current signal at a second responsiveness for the negative cycle portion when the sensed lamp current signal is above the threshold.
4. The method of claim 1 further comprising generating the desired lamp current signal from the adjusted lamp current signal.
5. The method of claim 4 wherein generating the desired lamp current signal from the adjusted lamp current signal comprises providing the adjusted lamp current signal to a microprocessor and generating the desired lamp current signal in the microprocessor.
6. The method of claim 1 wherein the first response curve has a greater slope than the second response curve.
7. The method of claim 1 wherein the first response curve is selected from the group consisting of lines, simple curves, and complex curves.
8. The method of claim 1 wherein the second response curve is selected from the group consisting of lines, simple curves, and complex curves.
9. A system for multi-slope current feedback for an electronic ballast comprising: means for generating a sensed lamp current signal from high frequency (HF) lamp current; means for generating an adjusted lamp current signal from the sensed lamp current signal along a continuous response curve, the continuous response curve having a first response curve and a second response curve, the adjusted lamp current signal being generated along the first response curve when the sensed lamp current signal is in a first range and being generated along the second response curve when the sensed lamp current signal is in a second range; and means for comparing the adjusted lamp current signal to a desired lamp current signal to generate a lamp current error signal.
10. The system of claim 9 wherein the means for generating an adjusted lamp current signal from the sensed lamp current signal along a continuous response curve comprises: means for generating an altered lamp current signal from the sensed lamp current signal; means for rectifying the altered lamp current signal to generate a rectified lamp current signal; and means for averaging the rectified lamp current signal to generate the adjusted lamp current signal.
11. The system of claim 10 wherein the sensed lamp current signal has a positive cycle portion and a negative cycle portion, and the means for generating an altered lamp current signal from the sensed lamp current signal comprises: means for zeroing the altered lamp current signal for the positive cycle portion; means for transforming the sensed lamp current to the altered lamp current signal at a first responsiveness for the negative cycle portion when the sensed lamp current signal is below a threshold; and means for transforming the sensed lamp current to the altered lamp current signal at a second responsiveness for the negative cycle portion when the sensed lamp current signal is above the threshold.
12. The system of claim 9 further comprising means for generating the desired lamp current signal from the adjusted lamp current signal.
13. The system of claim 9 wherein the first response curve has a greater slope than the second response curve.
14. A multi-slope current feedback circuit for an electronic ballast providing lamp current at a ballast output, the circuit comprising: a current response circuit 138 responsive to the lamp current and generating an adjusted lamp current signal 150; and an error circuit 134 receiving the adjusted lamp current signal 150 and a desired lamp current signal 146, the error circuit 134 generating a lamp current error signal 148; wherein current response circuit 138 has a first responsiveness when the lamp current is in a first range and a second responsiveness when the lamp current is in a second range, the adjusted lamp current signal 150 being continuous between the first range and the second range.
15. The circuit of claim 14 wherein the current response circuit 138 comprises: a slope altering circuit 242 responsive to the lamp current and generating an altered lamp current signal; a half wave rectifier 244 responsive to the altered lamp current signal and generating a rectified lamp current signal; and an averaging circuit 246 responsive to the rectified lamp current signal and generating the adjusted lamp current signal.
16. The circuit of claim 15 wherein the slope altering circuit 242 comprises: a parallel circuit of a first resistor R74 and a first diode D21; a series circuit of the parallel circuit and a second resistor R69, R57 operably connected between the ballast output and a common rail 202; a second diode D19 operably connected between the ballast output and the common rail 202; and an output for the altered lamp current signal operably connected between ballast output and the second diode D19.
17. The circuit of claim 16 wherein the second diode D19 is a Schottky diode.
18. The circuit of claim 16 wherein the first diode D21 operates below a threshold voltage in the first range.
19. The circuit of claim 14 further comprising a microprocessor, the microprocessor being responsive to the adjusted lamp current signal 150 and generating the desired lamp current signal 146.
20. The circuit of claim 14 wherein the first responsiveness is greater than the second responsiveness.
PCT/IB2005/050224 2004-01-20 2005-01-19 Electronic ballast with multi-slope current feedback WO2005072026A1 (en)

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JP2006550417A JP2007519201A (en) 2004-01-20 2005-01-19 Electronic ballast with multi-slope current feedback
EP05702723A EP1709843A1 (en) 2004-01-20 2005-01-19 Electronic ballast with multi-slope current feedback

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US53780104P 2004-01-20 2004-01-20
US60/537,801 2004-01-20

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB611333A (en) * 1945-05-02 1948-10-28 Standard Telephones Cables Ltd Vacuum tube voltmeter
US4574271A (en) * 1981-11-09 1986-03-04 Takeda Riken Co., Ltd. Multi-slope analog-to-digital converter
EP0490329A1 (en) * 1990-12-07 1992-06-17 Tridonic Bauelemente GmbH System for controlling the light intensity and the behaviour of gas discharge lamps
US5198816A (en) * 1991-08-30 1993-03-30 Eg&G, Inc. General purpose system for digitizing an analog signal
US6337544B1 (en) * 1999-12-14 2002-01-08 Philips Electronics North America Corporation Digital lamp signal processor
US20020067303A1 (en) * 2000-02-11 2002-06-06 Hyundai Electronics Industries, Ltd. Image sensor with programmable multi-slope ADC
WO2003047320A1 (en) * 2001-11-29 2003-06-05 Koninklijke Philips Electronics N.V. Device and method for operating a discharge lamp

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB611333A (en) * 1945-05-02 1948-10-28 Standard Telephones Cables Ltd Vacuum tube voltmeter
US4574271A (en) * 1981-11-09 1986-03-04 Takeda Riken Co., Ltd. Multi-slope analog-to-digital converter
EP0490329A1 (en) * 1990-12-07 1992-06-17 Tridonic Bauelemente GmbH System for controlling the light intensity and the behaviour of gas discharge lamps
US5198816A (en) * 1991-08-30 1993-03-30 Eg&G, Inc. General purpose system for digitizing an analog signal
US6337544B1 (en) * 1999-12-14 2002-01-08 Philips Electronics North America Corporation Digital lamp signal processor
US20020067303A1 (en) * 2000-02-11 2002-06-06 Hyundai Electronics Industries, Ltd. Image sensor with programmable multi-slope ADC
WO2003047320A1 (en) * 2001-11-29 2003-06-05 Koninklijke Philips Electronics N.V. Device and method for operating a discharge lamp

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JP2007519201A (en) 2007-07-12
EP1709843A1 (en) 2006-10-11
CN1910966A (en) 2007-02-07

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