AUTOMATIC DIMMING RANGE RECOGNITION METHOD

This invention relates generally to lamp dimming control, and more specifically to a method for automatic dimming range recognition.

Electronic ballasts for fluorescent lamps have become sophisticated and are widely used in a variety of applications. One application that has presented problems is dimmable electronic ballasts. Modern dimming switches, such as triac dimmers, generate a phase- controlled power with reduced on-time, i.e., the time in which the chopped phase-controlled power is non-zero. The line input power briefly crosses zero power between positive and negative, but the phase-controlled power holds the zero power longer to limit power to a load. Triac dimmers work well for resistive loads, such as incandescent lamps, but work poorly or not at all for non-linear loads, such as ballasts for fluorescent lamps. Non-linear loads can hum, buzz, run hot, or burn out. Dimmable electronic ballasts have been designed to work with triac dimmers, but such dimmable electronic ballasts are limited to use with a predetermined line input voltage, e.g., a dimmable electronic ballast for triac dimmers designed to operate at 120 Volts cannot be used with a 277 Volt line input voltage. The dimming control voltage signal is generated within the dimmable electronic ballast, so the voltage of the dimming control voltage signal is affected by the line input voltage to the dimmable electronic ballast. Attempting to use present dimmable electronic ballasts for triac dimmers at a voltage other than the predetermined line input voltage gives rise to problems with power factor, total harmonic distortion, and stability. Components that are sized for one line input voltage, such as capacitors and inductors, may be the wrong size for another line input voltage. The requirement that different dimmable electronic ballasts be used for different predetermined line input voltages causes additional expense in manufacturing and stocking different dimmable electronic ballasts for different line input voltages.

Dimmable electronic ballasts are also designed to work with triac dimmers having a particular dimmer range corresponding to a particular light output range, e.g., minimum dimmer output should correspond to minimum light output and maximum dimmer output

should correspond to maximum light output. Unfortunately, this is seldom the case. Triac dimmers between manufacturers and in different lots from a single manufacturer have different dimmer ranges. When the actual dimmer range is larger than the design dimmer range, there is a dead zone below the minimum light output and/or above the maximum light output so that the light output is insensitive to the dimmer adjustment. When the actual dimmer range is smaller than the design dimmer range, there is a light output loss above the minimum light output and/or below the maximum light output so that the light output fails to reach minimum light output at minimum dimmer output and/or fails to reach maximum light output at maximum dimmer output, respectively. The mismatch between dimmer range and light output range deduces the usefulness and desirability of the dimmable electronic ballasts.

It would be desirable to provide a method for automatic dimming range recognition that overcomes the above disadvantages.

One aspect of the invention provides an automatic dimming range recognition method for an electronic ballast including reading a control signal; determining whether the control signal is greater than control signal max; setting the control signal max to the control signal when the control signal is greater than the control signal max; determining whether the control signal is less than control signal min; setting the control signal min to the control signal when the control signal is less than control signal min; and calculating an output light level that corresponds to the control signal. Another aspect of the invention provides an automatic dimming range recognition method for an electronic ballast including providing an electronic ballast having a dimming range that extends between a first control signal limit and a second control signal limit; reading a control signal; determining whether the control signal is beyond the first control signal limit and outside the dimming range; and setting the first control signal limit to the control signal when the control signal is beyond the first control signal limit and outside the dimming range.

Another aspect of the invention provides an automatic dimming range recognition method for an electronic ballast including initializing range values for the electronic ballast at power on; automatically recognizing the range values while operating the electronic ballast;

adjusting range copy for the range values; and storing the range values for the electronic ballast at power down.

Another aspect of the invention provides a control circuit for an electronic ballast including an on-time converter, the on-time converter having a scaling circuit operably connected to receive a sensed phase-controlled power signal and generate a scaled power signal, and a comparator operably connected to compare the scaled power signal to a comparison voltage to generate an on-time signal; a line voltage detector, the line voltage detector generating a line voltage signal in response to the sensed phase-controlled power signal; and a microcontroller, the microcontroller being responsive to the on-time signal to generate a dimming control signal, and being responsive to the line voltage signal to generate a mains bias signal; wherein the mains bias signal biases the comparison voltage.

The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiment, 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.

FIG. 1 is a block diagram of a lighting system with a universal dimming electronic ballast made in accordance with the present invention;

FIG. 2 is a block diagram of a lighting system with a universal dimming electronic ballast made in accordance with the present invention;

FIG. 3 is a schematic diagram for the lighting system of FIG. 2 for a universal dimming electronic ballast made in accordance with the present invention;

FIG. 4 is a flow chart for automatic dimming range recognition for a universal dimming electronic ballast made in accordance with the present invention; and FIGS. 5-8 are flow charts for automatic dimming range recognition with range storage for a universal dimming electronic ballast made in accordance with the present invention. FIG. 1 is a block diagram of a lighting system with a universal dimming electronic ballast made in accordance with the present invention. The electronic ballast adapts to any

phase-controlled power provided by a dimmer to produce the lamp dimming desired. The waveform of the power to the lamp is unaffected by the line voltage. An on-time converter converts the phase-controlled power to a dimming control signal. A line voltage detector detects line voltage and adjusts boost circuit capacitance through a capacitance selection circuit. Those skilled in the art will appreciate that the phase-controlled power can be supplied by any phase-control device, such as a triac dimmer or the like.

Electronic ballast 24 receives phase -controlled power 20 from dimmer 18 at EMI filter 22 and provides lamp power 42 for a lamp 44 from resonant tank 40. The dimmer 18 receives mains power 16, such as 120 Volt or 277 Volt power line power, and controls the phase of the mains power 16 to reduce the power provided to the electronic ballast 24 and dim the lamp 44. The exemplary electronic ballast 24 includes the EMI filter 22 generating filtered mains power 26 operably connected to the dimmer 18 and a DC rectifier 28, which provides rectified power 30 to boost/power factor controller (PFC) 32. The boost/PFC 32 provides DC bus power 34 to switching circuit 36, which provides switched power 38 to resonant tank 40. The switching circuit 36 is responsive to switching control signal 46 from a switching controller 48. The resonant tank 40 provides lamp power 42 to the lamp 44.

The electronic ballast 24 can include a universal circuit 100 receiving a sensed phase- controlled power signal 52 from the filtered mains power 26 and generating a capacitance selector signal 64 and/or a dimming control signal 58. Those skilled in the art will appreciate that the sensed phase-controlled power signal provided to the universal circuit 100 can be sensed at other points besides the filtered mains power 26, such as being sensed from the rectified power 30, for example.

The universal circuit 100 can include a dimming circuit responsive to the sensed phase- controlled power signal 52 to generate the dimming control signal 58, which is provided to the switching controller 48. The dimming circuit senses the phase-controlled power, determines on-time for the sensed phase-controlled power, and controls lamp dimming in response to the on-time. As defined herein, on-time is the duration for which each positive or negative voltage pulse of the sensed phase-controlled power signal 52 is non-zero.

The universal circuit 100 can also include a capacitance selection circuit responsive to the sensed phase-controlled power signal 52 to generate a capacitance selector signal 64, which is provided to capacitance circuit 66. The capacitance circuit 66 is operably connected to adjust the capacitance to the boost/PFC 32. The capacitance selection circuit senses a phase-controlled power, determines line voltage for the sensed phase-controlled power, and adjusts boost/PFC capacitance in response to the line voltage.

FIG. 2, in which like elements share like reference numbers with FIG. 1, is a block diagram of a lighting system with a universal dimming electronic ballast made in accordance with the present invention. The electronic ballast adapts to any phase-controlled power provided by a dimmer to produce the lamp dimming desired. The waveform of the power to the lamp is unaffected by the line voltage. An on-time converter converts the phase-controlled power to an on-time, which is converted to a dimming control signal. A line voltage detector detects line voltage and adjusts boost circuit capacitance through a capacitance selection circuit and/or adjusts the power factor controller internal multiplier through a stability circuit to maintain electronic ballast operating stability. Those skilled in the art will appreciate that the phase-controlled power can be supplied by any phase-control device, such as a triac dimmer or the like.

Electronic ballast 24 receives phase -controlled power 20 from dimmer 18 at EMI filter 22 and provides lamp power 42 for a lamp 44 from resonant tank 40. The dimmer 18 receives mains power 16, such as 120 Volt or 277 Volt power line power, and changes the controls the phase of the mains power 16 to reduce the power provided to the electronic ballast 24 and dim the lamp 44. The exemplary electronic ballast 24 includes the EMI filter 22 generating filtered mains power 26 operably connected to the dimmer 18 and a DC rectifier 28, which provides rectified power 30 to boost/power factor controller (PFC) 32. The boost/PFC 32 provides DC bus power 34 to switching circuit 36, which provides switched power 38 to resonant tank 40. The switching circuit 36 is responsive to switching control signal 46 from a switching controller 48. The resonant tank 40 provides lamp power 42 to the lamp 44.

In this example, the electronic ballast 24 includes a universal circuit 100 with a dimming circuit, a capacitance selection circuit, and a stability circuit. The electronic ballast 24 can include a dimming circuit with an on-time converter 50 receiving a sensed phase-controlled power signal 52 and generating an on-time signal 54. A microcontroller 56, also known as an MCU, in the dimming circuit is responsive to the on-time signal 54 to generate a dimming control signal 58, which is provided to the switching controller 48. The dimming circuit senses the phase-controlled power, calculates on-time for the sensed phase-controlled power, and controls lamp dimming in response to the on-time. As defined herein, on-time is the duration for which each positive or negative voltage pulse of the sensed phase-controlled power signal 52 is non-zero. The microcontroller 56 receives DC power 70 from a DC power supply 72. The DC power supply 72 can be powered from any suitable location within the electronic ballast 24, such as the DC bus.

The electronic ballast 24 can include a capacitance selection circuit with a line voltage detector 60 receiving the sensed phase-controlled power signal 52 and generating a line voltage signal 62. The microcontroller 56 is responsive to the line voltage signal 62 to generate a capacitance selector signal 64, which is provided to capacitance circuit 66. The capacitance circuit 66 is operably connected to adjust the capacitance to the boost/PFC 32. The capacitance selection circuit implements a lamp control method that senses a phase-controlled power, determines line voltage for the sensed phase-controlled power, and adjusts boost/PFC capacitance in response to the line voltage.

The electronic ballast 24 can include a stability circuit with the line voltage detector 60 receiving the sensed phase-controlled power signal 52 and generating the line voltage signal 62. The microcontroller 56 is responsive to the line voltage signal 62 to generate an internal multiplier signal 68, which is provided to the boost/PFC 32. The stability circuit implements a lamp control method that senses a phase-controlled power, determines line voltage for the sensed phase-controlled power, and selects a boost/PFC internal multiplier in response to the line voltage.

FIG. 3 is a schematic diagram for the lighting system of FIG. 2 for a universal dimming electronic ballast made in accordance with the present invention. The universal circuit 100 includes dimming, capacitance selection, and stability circuits. The dimming circuit converts the sensed phase-controlled power signal to a dimming control signal, the capacitance selection circuit detects the line voltage and switches capacitance at the boost/PFC, and the stability circuit detects the line voltage and provides that information to the boost/PFC. DC power supply 72 receives DC bus power 380 and powers the microcontroller circuit, capacitance selection circuit, stability circuit, and other components as desired. The DC power supply 72 includes 15V power supply 382 and 5 V power supply 384. The dimming circuit includes the on-time converter 50 and the microcontroller 56. The on-time converter 50 receives the sensed phase-controlled power signal 52 and generates the on-time signal 54. The microcontroller 56 receives the on-time signal 54 and generates dimming control signal 58. The on-time converter 50 includes scaling circuit 402 and comparator 404. The scaling circuit 402 scales and smoothes the sensed phase-controlled power signal 52 to generate a scaled power signal 403, which is compared to a comparison voltage 405 at the comparator 404 to generate the on-time signal 54. The mains bias signal 69 biases the comparison voltage 405 and indicates whether the mains power is low voltage or high voltage. In one embodiment, the mains bias signal 69 is a low level when the mains power is a low voltage, such as 120 Volts, and a high level when the mains power is a high voltage, such as 277 Volts. The mains bias signal 69 increases the comparison voltage when the mains power is a high voltage to balance the sensed phase-controlled power signal 52 and assure accurate measurement of the on-time pulse. The processing of the on-time signal 54 to generate the switching control signal 46 from the dimming control signal 58 is discussed above. The capacitance selection circuit includes the line voltage detector 60, microcontroller 56, and capacitance circuit 66. The line voltage detector 60 detects the voltage of the main power feeding the dimmer 18. In this example, the line voltage detector 60 is a line peak detector which provides a line voltage signal 62 proportional to the peak voltage of the sensed phase-controlled power signal 52. The microcontroller 56 detects the level of the line voltage

signal 62 and determines whether the main power is high voltage, such as 277 Volts, or a lower voltage, such as 120 Volts. In this example, the microcontroller 56 generates an inverted capacitance selector signal 406, which is inverted at inverter 408 to generate the capacitance selector signal 64. When the main power is high voltage, the microcontroller 56 sets the inverted capacitance selector signal 406 to a first level and when the main power is not high voltage, the microcontroller 56 sets the inverted capacitance selector signal 406 to a second level. When the main power is high voltage as indicated by the capacitance selector signal 64, transistor Q3 in the capacitance circuit 66 is off and no extra capacitance is added to the boost/PFC. When the main power is not high voltage as indicated by the capacitance selector signal 64, transistor Q3 in the capacitance circuit 66 is on and extra capacitor C4A is added to the boost/PFC. Decreasing capacitance increases stability at the higher main power voltage. Using different capacitance values also improves power factor and total harmonic distortion at the different main power voltages.

The stability circuit includes the line voltage detector 60 and microcontroller 56. As discussed above for the capacitance selection circuit, the line voltage detector 60 receives the sensed phase-controlled power signal 52 and generates the line voltage signal 62 at the microcontroller 56. The microcontroller 56 detects the level of the line voltage signal 62 and determines whether the main power is high voltage, such as 277 Volts, or a lower voltage, such as 120 Volts. When the main power is high voltage, the microcontroller 56 sets the internal multiplier signal 68 to a first level and when the main power is not high voltage, the microcontroller 56 sets the internal multiplier signal 68 to a second level. The internal multiplier signal 68 is provided to the boost/PFC, such as the MULTIN pin of a PFC integrated circuit in the boost/PFC. When the main power is high voltage as indicated by the internal multiplier signal 68, the MULTIN pin of a PFC integrated circuit is held at a first level. When the main power is not high voltage as indicated by the internal multiplier signal 68, the MULTIN pin of a PFC integrated circuit is held at a second level. For example, in one embodiment the first level is low and the second level is high. Those skilled in the art will appreciate that the effect of feeding a small current to the MULTIN pin voltage to increase

stability of the PFC integrated circuit depends on the particular electronic ballast design, so that whether the MULTIN pin is held high or low for high voltage depends on the particular electronic ballast design.

FIG. 4 is a flow chart for an automatic dimming range recognition method for a universal dimming electronic ballast made in accordance with the present invention. In this example, the automatic dimming range recognition method is implemented on a universal dimming electronic ballast employing a microcontroller 56 as described for FIGS. 2 & 3 above. The microcontroller 56 stores a lighting function, such as a table or equations, that provides a dimming control signal 58 as an output light level in response to a sensed phase - controlled power signal 52 as a current control signal. In one embodiment, the lighting function is a logarithmic function that allows for the perception of light levels by human observers. The microcontroller 56 can also store a control signal min stored and a control signal max stored, which are stored when the electronic ballast is powered down and retrieved when the electronic ballast is powered up; a control signal min default and a control signal max default, which are the highest minimum and lowest maximum expected, respectively, for any phase-controlled dimmer that is expected to provide phase-controlled power to the electronic ballast; and/or a control signal min allowed and a control signal max allowed, which are the lowest minimum and highest maximum allowed, respectively, for the electronic ballast.

The automatic dimming range recognition method 800 includes reading a control signal 802, such as a sensed phase-controlled power signal. The control signal is compared to a control signal max to determine whether the control signal is greater than the control signal max 804. When the control signal is greater than the control signal max, the control signal max is set to the control signal 806, and the method 800 continues with calculating the output light level 812. When the control signal is not greater than the control signal max, the method 800 continues with comparing the control signal to a control signal min to determine whether the control signal is less than the control signal min 808. When the control signal is less than the control signal min, the control signal min is set to the control signal 810, and the method 800 continues with calculating the output light level 812. When the control signal is not less

than the control signal min, the control signal is between the existing values of the control signal min and the control signal max, and the method 800 continues with calculating the output light level 812. Once the output light level has been calculated, the method 800 continues with reading the next control signal 802. Those skilled in the art will appreciate that the control signal min and control signal max defining the range value on starting the method 800 can be an allowed value, such as the control signal min allowed and the control signal max allowed; an expected value, such as the control signal min default and the control signal max default; or a learned value, such as the control signal min stored and the control signal max stored. The control signal min allowed and the control signal max allowed are the limiting values allowed for operation of the electronic ballast and define an allowed range. The control signal min default and the control signal max default are the values expected for any dimmer to be used with the electronic ballast and define an expected range, and lie within the allowed range formed by the control signal min allowed and the control signal max allowed. The control signal min stored and the control signal max stored are values based on operation of the electronic ballast when the control signal min and the control signal max are stored in the microcontroller in non- volatile memory, and lie between the allowed range and the expected range, i.e., the control signal min stored is less than or equal to the control signal min default and greater than or equal to the control signal min allowed, and the control signal max stored is greater than or equal to the control signal max default and less than or equal to the control signal max allowed.

The calculating the output light level 812 includes determining an output light level step. When the lighting function is a table providing a number of output light level steps as a function of a number of control signal steps, the output light level step can be determined by interpolating between the control signal min and the control signal max for the present control signal. The determination can be expressed algebraically as:

_{n 4. l T} ' _u i , _{r i π} Control Signal - Control Signal Min

Output Light Level [steps] = * Resolution[steps]

Control Signal Max - Control Signal Min

where the Resolution[steps] is the number of divisions of the control signal and Output Light Level[steps] is the particular step for the present Control Signal. The Output Light Level[steps] corresponds to an output light level that can be used to set the dimming control signal. The resolution can be determined by the memory space available in the microcontroller, such as 256, 512, 1024, etc. corresponding to 8, 9, 10, etc. bits, respectively.

The method 800 can run continuously when the electronic ballast is energized. In one embodiment, the control signal min and the control signal max are each set to predetermined values stored in the microcontroller when the electronic ballast is first energized. The control signal min and the control signal max are then adjusted as required by the method 800 as the user changes the control signal. In another embodiment, the control signal min and the control signal max from each time the electronic ballast is energized are each stored in the microcontroller in non-volatile memory, such as an EEPROM, so that the electronic ballast learns the values for the particular dimmer to which it is connected and keeps them when the electronic ballast is de-energized.

The method 800 can be illustrated by an example of the operation. In this example, the resolution is 256 steps, the control signal min is 25, and the control signal max is 75. Assuming the control signal on energizing the electronic ballast is read as 50 at 802, the control signal is less than the control signal max of 75 at 804 and greater than the control signal min of 25 at 808, so the output light level step is determined at 812 as:

Output Light Level [steps] = ⁵ ° ^{~ 25} * 256 = 128

The output light level step corresponds to an output light level in the middle of the output light level range that can be used to set the dimming control signal. Next, assume the dimmer is adjusted upwards and the control signal is read as 100 at

802. The control signal is greater than the control signal max of 75 at 804, so the control

signal max is set to 100 at 806. When the control signal is next set to 50 as read at 802, the output light level step is determined at 812 as:

Output Light Level [steps] = ^' - * 256 = 85

100 - 25

Therefore, a control signal of 50 now results in an output light level step of 85, which is lower that the initial output light level step for a control signal of 50. The output light level step corresponds to an output light level that can be used to set the dimming control signal.

Next, assume the dimmer is adjusted downwards and the control signal is read as 20 at 802. The control signal is less than the control signal min of 25 at 808, so the control signal min is set to 20 at 810. When the control signal is next set to 50 as read at 802, the output light level step is determined at 812 as:

Output Light Level [steps] = ^' - * 256 = 96

100 - 20

Therefore, a control signal of 50 now results in an output light level step of 96, which is lower that the initial output light level step for a control signal of 50 but higher than the output light level step after adjustment of the control signal max. The output light level step corresponds to an output light level that can be used to set the dimming control signal. The control signal min and the control signal max now match the range of the control signal from the phase-controlled dimmer associated with the electronic ballast.

Those skilled in the art will appreciate that the automatic dimming range recognition method can be used to adjust either the control signal max or the control signal min without adjusting both. The method of adjusting one includes providing an electronic ballast having a dimming range that extends between a first control signal limit and a second control signal limit; reading a control signal; determining whether the control signal is beyond the first control

signal limit and outside the dimming range; and setting the first control signal limit to the control signal when the control signal is beyond the first control signal limit and outside the dimming range. The method can continue and adjust the other limit by determining whether the control signal is beyond the second control signal limit and outside the dimming range; and setting the second control signal limit to the control signal when the control signal is beyond the second control signal limit and outside the dimming range. The method can include calculating an output light level when the control signal is within the dimming range.

The control signal min and the control signal max from each time the electronic ballast is energized can be stored as control signal min stored and the control signal max stored in the microcontroller in non- volatile memory, such as an EEPROM, so that the electronic ballast learns the values for the particular dimmer to which it is connected and keeps them when the electronic ballast is de-energized. When the control signal min and the control signal max are stored, the lamp connected to the electronic ballast provides the same light output for a given dimmer switch position each time the electronic ballast is energized. When the control signal min and the control signal max are stored, replacement of the dimmer switch with another dimmer switch can require reset of the control signal min and the control signal max to the default values. The replacement dimmer switch is unlikely to have the same dimmer range as the dimmer switch being replaced. When the replacement dimmer switch has a larger range, the electronic ballast can adjust for the range using the automatic dimming range recognition method 800. When the replacement dimmer switch has a smaller range, the electronic ballast can be reset to adjust for the range.

The electronic ballast can be reset by providing a reset signal to the electronic ballast to direct the microcontroller to reset the control signal min to a control signal min default and the control signal max to a control signal max default. In one embodiment, the reset signal is a control sequence signal including turning the dimmer on and off and/or moving the dimmer between maximum and minimum in a predetermined time, such as turning the dimmer on and off a certain number of times with a certain speed, moving the dimmer between maximum and minimum a certain number of times with a certain speed, combinations thereof, or the like. In

one example, a human operator manually enters the control sequence signal by manipulating the dimmer. In another example, the replacement dimmer has the control sequence signal stored in non- volatile memory of an automatic reset dimmer and the control sequence signal is transmitted to the electronic ballast automatically when the replacement dimmer is installed. In another embodiment, the reset signal is a no-dimmer signal, i.e., the mains voltage applied to the electronic ballast without the dimmer installed. The electronic ballast detects the regular AC voltage rather than the chopped voltage which is present when the dimmer is installed.

FIGS. 5-8 are flow charts for automatic dimming range recognition with range storage for a universal dimming electronic ballast made in accordance with the present invention. The automatic dimming range recognition method 800 as described for FIG. 4 can be included in the automatic dimming range recognition with range storage method 500 of FIG. 5. The method 500 includes starting the method 500 at 502, initializing range values for the electronic ballast at power on 600, automatically recognizing the range values while operating the electronic ballast by applying the automatic dimming range recognition method 800, adjusting range copy for the range values 700, storing the range values at power down 900, and ending the method at 504. In one embodiment, the range values are a minimum value and a maximum value for the control signal range. Depending on the operating history of the electronic ballast, the range values can be a control signal min allowed and/or a control signal max allowed; a control signal min default and/or a control signal max default; or a control signal min stored and/or the control signal max stored. Those skilled in the art will appreciate that in another embodiment the range values can be defined by one of the minimum value and the maximum value for the control signal range and the control signal range span. The method 500 is particularly useful when the control signal range has been expanded by the automatic dimming range recognition method 800 and the dimmer position is between control signal min and control signal max when the electronic ballast is powered down, i.e., the dimmer position is not at control signal min or control signal max. The method 500 is also self-healing so that errors in the variables are corrected as the electronic ballast is powered on and powered down over a number of cycles.

FIG. 6 is a flow chart for initializing range values for the electronic ballast at power on 600. The initializing method 600 sets the control signal range to the allowed control signal range when the stored values of the control signal limits are at or outside the allowed control signal range. Starting the initializing 602, the stored values of the control signal limits from the non-volatile memory are entered into the control signal limits, which are the working variables for the range values, and the control signal limit copies 604. The control signal min and the control signal min copy are set to the control signal min stored. The control signal max and the control signal max copy are set to the control signal max stored. When the electronic ballast is powered on for the first time, the control signal min stored and the control signal max stored can be the control signal min default and the control signal max default.

The values of the control signal limit copies are checked relative to the control signal limit allowed values. The control signal limits and control signal limit copies are set to the control signal limit allowed when the control signal limit copies are outside the allowed control signal range. When the control signal max copy is greater than or equal to the control signal max allowed 606, the control signal max and the control signal max copy are set equal to the control signal max allowed 608 and the method continues at 610. When the control signal min copy is less than or equal to the control signal min allowed 610, the control signal min and the control signal min copy are set equal to the control signal min allowed 612 and the method continues at 614. The control signal limit and the control signal limit copy are equal throughout the initializing method 600 and so can be used interchangeably.

The initializing method 600 can continue with an optional validity checking of the range values, such as the control signal limit and/or the control signal limit copies. In one example, it is determined whether the control signal min copy is greater than the control signal max copy 614. When the control signal min copy is greater than the control signal max copy, indicating the values are not valid, the control signal min and the control signal min copy are set equal to the control signal min default and the control signal max and the control signal max copy are set equal to the control signal max default 616. In another example, the optional checking is a comparison of the control signal limit copies to expected values for the control signal limits,

such as a fraction or multiple of the control signal limit default values. In another example, the optional checking is a data check of the control signal limit copies, such as a check sum of the control signal limit copies. An output max/min flag is reset to off limit and a rate change flag is reset to unchanged 617, and the initializing method 600 ends at 618. The automatic dimming range recognition with range storage method 500 can continue with the automatic dimming range recognition method 800 as described for FIG. 4. The method 500 automatically recognizes the appropriate range values for the dimmer switch while operating the electronic ballast, expanding the electronic ballast control signal range when the dimmer is moved beyond the present control signal min and/or control signal max. FIG. 7 is a flow chart for adjusting range copy for the range values 700 so that the range values are available for storage when the electronic ballast is turned off. The control signal limit copies are set to the range values for the expanded signal control range when the range is expanded. Flags are set to indicate the expansion and/or the output light level at the output light level limit. After the automatic dimming range recognition method 800, the automatic dimming range recognition with range storage method 500 can continue with adjusting the range copy 700. The adjusting range copy 700 starts at 702. When it is determined that the control signal max is greater than the control signal max copy 704 or that the control signal min is less than the control signal min copy 710, the control signal max copy is set to the control signal max and the control signal min copy is set to the control signal min 706. The range change flag is set to changed 708, indicating that the control signal range of the electronic ballast changed during initializing the electronic ballast range after power on 600 or normal operation with the automatic dimming range recognition method 800.

Referring to FIG. 7, the adjusting range copy for the range values 700 continues with determining whether the output light level is at the maximum or minimum. The output light level varies over a light output range as predetermined for a particular electronic ballast design, such as from 0 to 255. When it is determined that the output light level is at the output light level maximum 712 or that the output light level is at the output light level minimum 718, the output max/min flag is set to limit 714. When it is determined that the output light level is not

at the output light level maximum 712 or that the output light level is not at the output light level minimum 718, the output max/min flag is set to off limit 720. The adjusting method 700 ends at 716. The automatic dimming range recognition with range storage method 500 can continue with storing the range values at power down 900. FIG. 8 is a flow chart for storing the range values at power down 900 so that the values are available for use when the electronic ballast is next turned on. The control signal limits stored in non- volatile memory are set to the control signal limit default values when the output light level is at an output light level limit and are set to the expanded range values when the control signal range has expanded. The storing the range values at power down 900 starts at 902. When it is determined that the output max/min flag is set to limit 904, indicating that the output light level is at the maximum or minimum, the control signal limits, control signal limit stored values are set to the default values 906. The control signal min stored is set to the control signal min default and the control signal max stored is set to the control signal max default 906. In another optional embodiment that can be useful when the electronic ballast is subject to a brownout or power interruption and is not powering down, the working variables stored in volatile RAM memory can be set as well. The control signal limit copies and control signal limit stored values are set to the default values 907. The control signal min and control signal min copy are set to the control signal min default 907. The control signal max and control signal max copy are set to the control signal max default 907. The output max/min flag is reset to off limit and the rate change flag is reset to unchanged 908, and the storing method 900 ends at 910. When it is determined that the output max/min flag is not set to limit 904 and the rate change flag is set to changed 912, the control signal min stored is set to the control signal min copy and control signal max stored is set to the control signal max copy 914. The output max/min flag is reset to off limit and the rate change flag is reset to unchanged 908, and the storing method 900 ends at 910. When it is determined that the output max/min flag is not set to limit 904 and the rate change flag is not set to changed 912, the control signal min stored and control signal max stored remain the same. The output max/min flag and the rate change flag need not be reset. The storing method 900 ends at 910.

The automatic dimming range recognition with range storage method 500 of FIG. 5 does not require a reset of the electronic ballast for the replacement of the dimmer switch with another dimmer switch, unless the replacement dimmer switch has a smaller control signal range that the other dimmer switch. When the replacement dimmer switch has a smaller range, the electronic ballast can be reset to adjust for the range by providing a reset signal to the electronic ballast to direct the microcontroller to reset. The reset signal can be a control sequence signal or a no -dimmer signal that resets the control signal min to a control signal min default and the control signal max to a control signal max default.

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 scope of the invention. For example, the electronic ballast control signal ranges can be stored as an endpoint, such as the control signal max or min, with a span for the range, rather than the control signal max and min as described above. Those skilled in the art will appreciate that the embodiments described are exemplary and that alternative circuits can be used as desired for particular applications. 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.