PLC controller and discharge lighting ballast receiver with high noise immunity

This application is a Non-Provisional Utility application which claims the benefit of U.S. Provisional Application Ser. No. 61/034,004 filed Mar. 5, 2008, entitled “A Novel Low Cost PLC Controller and Discharge Lighting Ballast Receiver with High Noise Immunity” which is hereby incorporated by reference.

A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

The present invention relates generally to a power line communication system for transmitting a ballast dimming level to an electronic ballast.

More particularly, this invention pertains to a power line communication system that has improved noise immunity for transmitting the ballast dimming level to the electronic ballast.

Electronic ballasts are utilized to generate and control the amount of power consumed by gas discharge lamps. The ballast dimming level determines the power output of the electronic ballast and therefore the lighting intensity of the lamp. A ballast dimming level may be communicated to a power line receiver associated with the electronic ballast. The power line receiver receives a ballast control signal having dimming level information and generates a dimming level signal corresponding to the desired ballast dimming level. The dimming level signal then causes the electronic ballast to generate an AC lamp signal to the lamp in accordance with the desired dimming level. In this manner, a user can control the power consumed by the lamp.

Often, it is advantageous to communicate the lamp dimming level over the AC power signal that powers the electronic ballast. A power line controller may be utilized to insert information on the AC power signal to communicate the desired dimming level to the power line receiver. The power line controller generates the ballast control signal and inserts that ballast control signal on the AC power signal. The power line receiver then extracts this information from the AC power signal to generate the appropriate dimming level signal. Typically, the dimming level signal is transmitted to an inverter control circuit which controls the amount of power generated by the ballast to the lamp.

Several prior art solutions exist for transmitting information to the electronic ballast over AC power lines, including using power line modems, high frequency injection codes and line voltage modulation codes. Unfortunately, the equipment required to insert information into the AC power signal and then extract the information at the ballast is expensive. Furthermore, these systems are particularly sensitive to noise and require ballast control signals with high signal levels to communicate the desired ballast dimming level over the power line. This is particularly true if the system is communicating with several electronic ballasts at once.

What is needed, then, is a power line communication system that inserts information on the AC power signal that is more cost efficient and less sensitive to noise.

The present invention pertains to a power line communication system that communicates a ballast dimming level to an electronic ballast over an AC power line. The system has a power line controller and a power line receiver connected to the AC power line. The power line controller is operable to generate the ballast control signal and to insert that signal on the AC power signal being transmitted over the AC power line. The power line receiver receives the AC power signal and extracts the ballast control signal from the AC power signal to generate the dimming level signal corresponding with the desired ballast dimming level. The power line receiver may be integral to the electronic ballast or may be a separate apparatus that communicates with the electronic ballast.

A power line controller in accordance with this invention has a signal pattern circuit for producing a ballast control signal corresponding to a predetermined communication code for communicating dimming levels to electronic ballasts. This communication code is simply a method of representing dimming levels for an electronic ballast so that the power line receiver can translate this information into the appropriate dimming level signal. The desired ballast dimming level being communicated by the power line controller is embedded in the ballast control signal as a signal pattern that is associated with the desired ballast dimming level.

To insert the ballast control signal on the AC power signal, the power line controller has a transformer coupled to the signal pattern circuit. The secondary winding of this transformer is connected in series with the AC power line to insert the ballast control signal on the AC power signal.

This AC power signal is then transmitted to the electronic ballast. To extract the ballast control signal out of the AC power signal, the power line receiver has a resonant circuit connected in series with the AC power line. The resonant circuit should be tuned to transmit the ballast control signal and to filter out the AC power signal. A dimming level sensing circuit then senses the signal pattern on the ballast control signal and generates a dimming level signal corresponding to the desired ballast dimming level.

FIG. 1 is a block diagram of one embodiment of the power line communication system in accordance with this invention.

FIG. 1A is a frequency domain graph showing a frequency bandwidth of one embodiment of the ballast control signal, a frequency bandwidth of one embodiment of the AC power signal, and a bandwidth of transmission for one embodiment of the resonant circuit.

FIG. 2 is a circuit diagram of one embodiment of the power line controller of this invention.

FIG. 3 is an illustration of two graphs related to signals created by the power line controller shown in FIG. 2 . The top graph in FIG. 3 is a time domain illustration of the dimming level information signal generated by a switch pattern circuit of the power line controller. The bottom graph in FIG. 3 is a time domain illustration of an AC power signal for powering an electronic ballast after the power line controller has inserted a ballast control signal on the AC power signal.

FIG. 4 is a circuit diagram of one embodiment of the power line receiver coupled to an electronic ballast.

FIG. 4A is a time domain illustration of the ballast control signal after it has been extracted from the AC power signal by the power line receiver shown in FIG. 4 .

Referring now to FIG. 1 , the power line communication system 10 communicates a desired ballast dimming level to one or more electronic ballasts 12 over AC power lines 14 A, 14 B. Power line controller 16 controls the electronic ballast 12 so that electronic ballast 12 dims a lamp 18 in accordance with a desired ballast dimming level.

To control the electronic ballast 12 , the power line controller 16 inserts a ballast control signal 20 on an AC power signal 22 transmitted over the AC power lines 14 A, 14 B. Power line receiver 24 receives the AC power signal 22 and extracts the ballast control signal 20 . Power line receiver 24 then generates a dimming level signal 28 corresponding to the desired ballast dimming level. This dimming level signal 28 may be received by an inverter control circuit 26 that controls the power output from the electronic ballast 12 . An inverter control circuit 26 may then adjust the operating frequency of an inverter circuit so that the electronic ballast 12 operates at the desired ballast dimming level.

The power line communication system 10 may operate by utilizing analog and digital communication codes for communicating dimming levels to electronic ballasts. These codes generally associate a particular signal pattern with a particular ballast dimming level. For example, if a digital communication code is used, the signal pattern will represent a series of “ones” and “zeros”. The power line receiver 24 may then translate the signal pattern into a digital word corresponding to a particular ballast dimming level to produce the appropriate dimming level signal 28 .

Referring now to FIGS. 1 and 1A , the ballast control signal 20 may be generated by the power line controller 16 to be within a particular frequency bandwidth 34 . The frequency bandwidth 34 of the ballast control signal 20 should be outside a frequency bandwidth 36 of the AC power signal 22 . Theoretically, the AC power signal 22 is represented as a Kronecker delta in the frequency domain and therefore has an infinitely thin frequency bandwidth 36 . In practice however, the frequency bandwidth 36 of the AC power signal 22 actually does have a measurable bandwidth. FIG. 1A illustrates that the center frequency 34 A of the ballast control signal 20 which is typically 15 kHz or higher. The power line receiver 24 may have a resonant circuit 38 with a response curve 38 A that has a bandwidth 40 outside the bandwidth 36 of the AC power signal 22 . The bandwidth 34 of the ballast control signal 20 however should be within the bandwidth 40 of the response curve 38 A of the resonant circuit 38 . This permits the power line receiver 24 to receive the ballast control signal 20 and to filter out the AC power signal 22 .

Bandwidth is generally defined as a range of frequencies in which the frequency signal components of a signal or the response curve of the circuit are above an amplitude threshold. The standard amplitude threshold for defining bandwidth is typically half of the maximum value of the signal or −3 decibels. However, the meaning of bandwidth for this application is not limited to half the maximum value or −3 decibel threshold. The bandwidth of interest should correspond to the particular application of the invention. For example, if the ballast control signal 20 is particularly flat in the frequency domain so to include a significant amount of signal components away from a center frequency, the bandwidth 34 of the ballast control signal 20 may be defined by a higher amplitude threshold to compensate for signal components which may be above or near to the −3 decibel threshold. Conversely, if the ballast control signal is particularly narrow, it may be advantageous to lower the amplitude threshold that defines the bandwidth 34 of the ballast control signal 20 which would require a less sensitive resonant circuit 38 .

Referring again to FIG. 1 and FIG. 1A , the resonant circuit 38 is connected in series with one of the AC power lines 14 A, 14 B. By connecting the resonant circuit 38 in series with one of the AC power lines 14 A, 14 B, the power line receiver 24 is able to detect ballast control signal 20 even if the ballast control signal 20 is very weak. The series connection of the resonant circuit 38 to one of the AC power lines 14 A, 14 B provides the power line receiver 24 with a detector with a high Q factor. This high Q factor allows the resonant circuit 38 to resonate with a high amplitude near the resonant frequency 38 B. Consequently, the resonant circuit 38 may be configured to have a resonant frequency 38 B as close as possible to the center frequency 34 A of the ballast control signal 20 . Theoretically, the resonant frequency 38 B is chosen to be equal to the center frequency 34 A of the ballast control signal 20 . This series-connected resonant circuit 38 provides for high noise immunity and permits the signal level of the ballast control signal 20 to be relatively low.

Referring now to FIG. 2 and FIG. 3 , the operation of one embodiment of the power line controller 16 is described. Power line controller 16 has a signal pattern circuit 43 that produces a dimming level information signal 42 with a signal pattern 44 that is utilized to communicate the desired ballast dimming level. As mentioned above, codes may be utilized to transmit information on the AC power signal 22 . The signal pattern 44 of the dimming level information signal 42 may be generated in accordance with one of these codes.

For example, the embodiment of the power line controller 16 illustrated in FIG. 2 has a signal pattern circuit 43 that generates the dimming level information signal 42 in accordance with a digital high frequency injection scheme. The signal pattern 44 of the digital high frequency injection scheme is a series of high frequency pulses 44 A that represent a series of bits. To illustrate, the presence of a high frequency pulse 44 A during a particular time interval 45 of the dimming level information signal 42 may represent a “one” while the absence of a high frequency pulse 44 A during a particular time interval may represent a “zero”. This series of bits represents the desired ballast dimming level.

To generate the series of high frequency pulses 44 A, the switch pattern circuit 43 has a high frequency signal production circuit 46 that generates a high frequency signal 47 . The frequency of the high frequency signal 47 should be higher than the frequency of the AC power signal 22 . In the illustrated embodiment, the AC power signal 22 operates at 50 Hz to 60 Hz while the frequency of the high frequency signal 47 is greater than 154 kHz.

A primary winding 50 of transformer TX_ 1 is coupled to the signal pattern circuit 43 . Output terminals 54 A, 54 B of the power line controller 16 should be configured to connect the secondary winding 54 in series with AC power line 14 B. High frequency pulses 44 A are created by opening and closing the switch 48 which is coupled to the high frequency signal production circuit 46 and the transformer TX_ 1 . Transformer, TX_ 1 , may isolate switch pattern circuit 43 from the AC power signal 22 to protect the circuit. Switch 48 couples the high frequency signal 47 to the transformer TX_ 1 when the switch 48 is closed and suspends the transmission of the high frequency signal 47 to the transformer TX_ 1 when the switch 48 is open. By timing the opening and closing of switch 48 , the signal pattern 44 of the dimming level information signal 42 represents the desired ballast dimming level through the series of high frequency pulses 44 A.

The ballast control signal 20 is inserted on the AC power signal 22 and is associated with the dimming level information signal 42 . The ballast control signal 20 may be the dimming level information signal 42 . The power line receivers and AC power systems may be designed to be robust enough to receive and process a dimming ballast control signal 20 as simply the dimming level information signal 42 itself. However, dimming level information signal 42 may have characteristics that are disadvantageous for transmission over the AC power lines 14 A, 14 B. If so, certain components may be included so that the power line controller 16 inserts a suitable ballast control signal 20 on the AC power signal 22 .

For example, a DC filter 54 may be coupled between the signal pattern circuit 43 and the transformer TX_ 1 to filter out DC signal components from the dimming level information signal 42 . This prevents DC signal components from being transmitted over the AC power lines 14 A, 14 B. Transformer TX_ 1 may also affect the characteristics of the dimming level information signal 42 , such as the voltage and current amplitudes of the ballast control signal 20 . The power line controller 16 may also have additional equipment for manipulating the timing, frequency characteristics, or shape of the signal pattern 44 on the ballast control signal 20 in accordance with the particular characteristics required by the power line receiver. A high frequency filter C 2 may be connected between the AC power lines 14 A, 14 B to prevent high frequency components in the ballast control signal 20 from being reflected on the AC power lines, 14 A, 14 B.

Secondary winding 54 of transformer TX_ 1 may connect in series with AC power line 14 B to insert the ballast control signal 20 on the AC power signal 22 . However, power line controller 16 may connect to either AC power line 14 A, 14 B to insert the ballast control signal 20 on the AC power signal 22 . The series connection of secondary winding 24 allows the power line controller 16 to insert what may be a relatively weak ballast control signal 20 on AC power signal 22 .

In the illustrated embodiment, switch control circuit 56 in the signal pattern circuit 43 opens and closes the switch 48 to generate the signal pattern 44 . This switch control circuit 56 receives a dimming level input signal 58 to determine the desired ballast dimming ballast level which is to be communicated over the AC power lines 14 A, 14 B. Dimming level input signal 58 may be a digital signal that represents the desired dimming level or may be an analog signal such as a DC signal whose DC level represents the desired dimming level.

In either case, switch control circuit 56 translates this information into the appropriate signal pattern 44 , for transmitting the desired ballast dimming level and opens and closes the switch 48 accordingly. Switch control circuit 56 may thus store or receive information about dimming level codes to produce the appropriate dimming level information signal 42 . In addition, if the dimming level input signal 58 is a digital signal then the switch control circuit 56 may simply cause the switch 48 to open and close and create a signal pattern 44 of ones and zeros in accordance with the “ones” and “zeros” of the digital signal.

In contrast, if the power line receiver is not equipped to translate the digital format of the dimming level input signal 58 , the switch control circuit 56 may translate the dimming level input signal into the appropriate digital format for the desired ballast dimming level and generate a signal pattern 44 in accordance with this format.

If the dimming level input signal 58 is an analog signal, then the switch control circuit 56 may associate the signal level of the dimming level input signal 58 with the desired ballasts dimming level and open and close the switch 48 accordingly. Once the ballast control signal 20 has been inserted on the AC power signal 22 , the AC power signal 22 is transmitted over the AC power lines 14 A, 14 B to power one or more electronic ballasts 12 . The illustrated embodiment generates a ballast control signal 20 having the series of high frequency pulses 44 A in the dimming level information signal 42 . The AC power signal 22 is shown in the bottom graph in FIG. 1A after having been inserted with ballast control signal 20 . High frequency pulses 44 A have been inserted on the AC power signal 22 for communication to a power line receiver.

Referring now to FIG. 1A , FIG. 4 , and FIG. 4A , the operation of one embodiment of the power line receiver 24 that receives AC power signal 22 with ballast control signal 20 is shown and described. The power line receiver 24 shown in FIG. 4 is integrated into the electronic ballast 80 . Input terminals TAR, TBR are configured so that when the power line receiver 24 is connected to AC power line 14 B, resonant circuit 38 is connected in series with the AC power line 14 B. Resonant circuit 38 of the power line receiver 24 is shown as a parallel resonant circuit having capacitor C_r and the primary winding 60 of transformer TX_r. This resonant circuit 38 should be connected to the AC power line 14 B in front of the electromagnetic interference filter 63 in the electronic ballast 80 to avoid distortion of the ballast control signal 20 . Transformer TX_r thus acts to isolate the power line receiver 24 from the power line 14 B and also is part of a resonant circuit 38 for receiving the ballast control signal 20 .

As explained above, the resonant circuit 38 may have a bandwidth 40 for transmitting the ballast control signal 20 and filtering out the AC power signal 22 . Consequently, components C_r and primary winding 60 of the resonant circuit 38 are tuned to give resonant circuit 38 the appropriate bandwidth 40 for receiving this ballast control signal 20 . In this manner, resonant circuit 38 extracts the ballast control signal 20 from the AC power signal 22 and transmits the ballast control signal 20 to secondary winding 64 of transformer TX_r which is connected to a dimming level sensing circuit 66 . As illustrated in FIG. 2 , the bandwidth 34 of the ballast control signal 20 is within the bandwidth 40 for the response curve 38 A of the resonant circuit 38 .

The dimming level sensing circuit 66 senses the signal pattern 68 on the ballast control signal 20 and generates a dimming level signal 72 corresponding to the desired ballast dimming level. In the illustrated embodiment, signal pattern 68 is formatted according to a high frequency digital communication code. Each “one” or “zero” is represented by the presence or absence of a high frequency pulse 68 A during a time interval 68 B of the ballast control signal 20 . Dimming level sensing circuit 66 receives the ballast control signal 20 at signal pattern decoder circuit 70 which is operable to convert the signal pattern 68 into a digital signal 74 representing the desired ballast dimming level. Signal pattern decoder circuit 70 is thus equipped with an analog-to-digital converter capable of sensing a high frequency pulse 68 A and creating a digital signal 74 in accordance with the transmitted signal pattern 68 of the ballast control signal 20 . Dimming signal production circuit 76 receives digital signal 74 and is operable to generate the dimming level signal 72 corresponding to the desired ballast dimming level based on the digital signal 74 .

Dimming level signal 72 may then be transmitted to an inverter control circuit 76 that controls the switch frequency of an inverter 78 of the electronic ballast 80 . In this embodiment, dimming level signal 72 is a DC signal having a signal level corresponding to the desired ballast dimming level. Inverter control circuit 76 utilizes the dimming level signal 72 as a reference signal and compares the reference signal with a signal from the inverter 78 or lamp. Switch frequency of the inverter 78 is adjusted to produce an AC lamp signal 82 in accordance with this comparison. The power consumed by lamp 84 is thus adjusted in accordance with the dimming level signal 72 . Dimming signal production circuit 76 may thus be configured with an digital to analog converter that receives the digital signal 74 and converts that digital signal 74 into the dimming level signal 72 .

Thus, although there have been described particular embodiments of the present invention of a new and useful A LOW COST PLC CONTROLLER AND DISCHARGE LIGHTING BALLAST RECEIVER WITH HIGH NOISE IMMUNITY, it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.