Ballast having multiple circuit failure protection and method for ballast circuit protection

A ballast for a gas discharge lamp comprising a first circuit portion for providing power to a lighting load and a second circuit portion for processing data exchanged with a communication link, the first circuit portion receiving power from an AC main supply for conversion to a form suitable to supply power to the lamp, and the second circuit portion having a power supply supplied from the AC main supply, the power supply being coupled at the input of the AC main supply to the first circuit portion, further comprising a first protection circuit coupled in series with the AC main supply for protecting the first and second circuit portions in the event of an electrical circuit failure leading to an overcurrent condition, the power supply for the second circuit portion being coupled such that it is protected by the first protection circuit; further comprising a second protection circuit disposed in series with the first circuit portion and providing protection only in the event of electrical failure leading to an overcurrent condition in the first circuit portion; the second protection circuit adapted so that in the event of electrical failure in the first circuit portion, the second protection circuit will discontinue the supply of current to the first circuit portion, thereby preventing an overcurrent in the first protection circuit that would cause the first protection to interrupt current, and thereby allowing the first protection circuit to continue to supply electrical current to the second circuit portion.

BACKGROUND OF THE INVENTION

The present invention relates to power supplies, an in particular, to an intelligent ballast for powering a lighting load, for example a gas discharge lamp such as a fluorescent lamp. The present invention relates to ballasts of the type disclosed in the Assignee's U.S. patent application Ser. No. 10/824,248 filed Apr. 14, 2004 and entitled Multiple-Input Electronic Ballast With Processor, the entire disclosure of which is incorporated herein by reference.

In the ballast disclosed in the above-identified pending patent application, the ballast includes an input or front end power circuit section that includes an RF filter and rectifier and a valley fill circuit including an energy storage capacitor, for providing a DC bus voltage. The DC bus voltage is provided to a back end or output stage including an inverter and an output filter. In the back end, an inverter is driven to provide a high frequency AC output voltage that is filtered by an output filter and provided as the voltage supply to the lighting load.

The ballast includes a processing section including a microprocessor which receives inputs, from both internal sources within the ballast itself and from external sources. For example, the internal sources of inputs may include an input voltage from the AC main supply, an input voltage from the DC bus concerning the DC bus voltage, an input concerning the output lamp current, and an input from the output voltage to the lamp. In addition, external sources of inputs to the ballast may include an external photosensor, an infrared receiver, a phase-control dimmer, and an analog voltage source. Furthermore, the processor has a communication port that receives information via the DALI or other communications protocol. DALI stands for Digital Addressable Lighting Interface and is described in an International Electrotechnical Commission document IEC 60929. The DALI communication port, microprocessor, and sensor input circuitry are powered by a power supply which receives rectified AC voltage from the output of the rectifying circuit.

In the above-described ballast, a fuse is placed to protect the ballast in the event of ballast failure, for example a power circuit short. However, if the ballast fails, and the fuse blows, the entire ballast fails including the processing section. This presents a problem because in the processing section handles incoming information from attached sensors and communicates this information to the communication link via the communication port for use by other system components. If the ballast fails and the fuse blows as a result of a fault in the power circuit section, it is undesirable to have the processing circuit portion also be without power. If the processing section is without power, then the information from any connected sensors is no longer available to the rest of the system. Thus, a single ballast failure in the power circuit portion can have far reaching consequences to the system if the ballast that fails is one that has a sensor connected to it.

It is therefore desirable to provide a ballast circuit such that, if a failure occurs in the portion of the ballast that supplies lamp power, only the power circuit section will be without power when circuit power is interrupted and the remaining processing portion that processes inputs from the sensors connected to the ballast, continues to operate.

SUMMARY OF THE INVENTION

According to the invention, a ballast is provided comprising a first circuit portion for providing power to a lighting load, and a second circuit portion for processing data exchanged with a communication link, the first circuit portion receiving power from an AC main supply for conversion to a form suitable to supply power to the lighting load, and the second circuit portion having a power supply supplied from the AC main supply, the power supply being coupled at the input of the AC main supply to the first circuit portion, further comprising a first protection circuit coupled in series with the AC main supply for protecting the first and second circuit portions in the event of an electrical circuit failure leading to an overcurrent condition, the power supply for the second circuit portion being coupled such that it is protected by the first protection circuit; further comprising a second protection circuit disposed in series with the first circuit portion and providing circuit protection only in the event of electrical failure leading to an overcurrent condition in the first circuit portion; the second protection circuit being rated such that in the event of electrical failure in the first circuit portion, the second protection circuit will discontinue the supply of current to the first circuit portion thereby preventing an overcurrent in the first protection circuit that would cause the first protection circuit to interrupt current, and thereby allowing the first protection circuit to continue to supply electrical current to the second circuit portion.

Other features, objects and advantages of the present invention will become apparent from the detailed description that follows:

DETAILED DESCRIPTION OF THE INVENTION

With reference now to the drawings,FIG. 1is a block diagram of a first embodiment of a ballast according to the present invention. As described above, the ballast includes a power circuit section8having a front end or input section10, a DC bus16having a bus capacitor17coupled thereacross, and a back end or output section20that supplies a lamp load22with power. The front end10includes an RF filter and rectifier12and a boost converter14and the back end includes an inverter and an output filter. Note that the boost converter can be any type of active or passive power factor correcting circuit. The ballast also includes a processing section24including a microprocessor26, sensor input circuitry28that receives inputs from external sensors such as occupancy sensors, photosensors, and infrared sensors, as well as other inputs from the power circuit section8of the ballast itself to monitor and control the operation of the ballast. The microprocessor26is also connected to a communication port30for exchanging data with a communication link (not shown). The microprocessor26receives information via a communication port30from other ballasts or other devices, such as a central controller (not shown). The microprocessor26also transmits information, such as the sensor input information from the sensor input circuitry, over the link to other ballasts and the central controller. The communication port30may operate according to the DALI standard or any other suitable communications protocol.

The processing section24is powered by a power supply32that draws current from the AC main supply through the RF filter and rectifier12. Because the power supply32takes advantage of the rectifier in the front end10, the power supply does not need an internal rectifier.

A first protection circuit comprising a main fuse1is provided at the AC input of the ballast and all current supplied to the ballast flows through this fuse.

According to the invention, a second protection circuit is provided. In particular, a second fuse2is provided in addition to the main fuse1provided on the AC line. Second fuse2is disposed in series with the power circuit section8and, in particular, is located between the RF filter and rectifier12and the boost converter14.

In the illustrated embodiment, the main fuse1on the AC line is preferably a slow acting fuse and is preferably rated such that it is of a larger current rating than the second fuse2. The second fuse2is preferably a fast acting fuse and rated at a smaller current rating than the main fuse1. In the illustrated embodiment, the main fuse is a three amp, slow acting fuse and the second fuse is a two amp, fast acting fuse. Although fuses are shown, other circuit protection elements can be used such as circuit breakers.

This arrangement has the following desirable effects. Should a failure occur in the boost converter14or the back end20of the powertrain section8of the ballast, the fast acting second fuse2will blow rapidly, without blowing the first main fuse1. Once the second fuse2blows, the second fuse2will discontinue the supply of current to the boost converter14and the back end20, so as to prevent an overcurrent in the first fuse1that would cause the first fuse1to interrupt current. Thus, the first fuse1will remain conducting and power will be provided to the processing portion of the ballast, enabling the sensor inputs to be provided over the communication link by the microprocessor communications port30. The components used in the RF filter and rectifier12are generally more robust than the components of the boost converter14and back end20, which comprise semiconductor switches that tend to fail due to shorts and electrolytic capacitors that tend to dry up as they age. Thus, the power supply32can use the rectified voltage at the output of the RF filter and rectifier12and does not need an internal rectifier.

As shown, the second fuse2may be provided between the RF filter and rectifier12and boost converter14. However, the second fuse2can also be provided before the RF filter and rectifier12but after the junction of the AC main supply with the power supply32as shown inFIG. 2. By placing the fuse2ahead of the front end10, should the RF filter and rectifier12fail, or should there be a fault anywhere else in the powertrain section8of the ballast, the fuse2will blow prior to the first fuse1blowing, thereby continuing to provide power to the processing section24.

Although the invention shows the main fuse1having a larger current rating than the second fuse2, that is, in the illustrated embodiments,3amp for the main fuse1and2amp for the second fuse2, it is also possible that the main fuse1can have the same rating as the second fuse2but simply be a slow acting fuse whereas the second fuse2is a fast acting fuse. Thus, the second fuse2will still blow more quickly than the main fuse1in the event of a power circuit portion failure in the ballast. Once the second fuse2blows, the overcurrent condition will be discontinued and thus the main fuse1will continue to provide power to the processing section24of the ballast and thereby operation of the sensors, microprocessor, and communication port will continue, thus allowing sensor data from sensors attached to the failing ballast to continue to be exchanged with the network.

Should a failure occur in the processing section24leading to an overcurrent condition, the first fuse1is designed to blow to discontinue power to the entire ballast.

FIG. 3andFIG. 4show block diagrams of a third and a fourth embodiment of the protected ballast, respectively.

Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. Therefore, the present invention should be limited not by the specific disclosure herein, but only by the appended claims.