Inductively coupled ballast circuit

A ballast circuit is disclosed for inductively providing power to a load. The ballast circuit includes an oscillator, a driver, a switching circuit, a resonant tank circuit and a current sensing circuit. The current sensing circuit provides a current feedback signal to the oscillator that is representative of the current in the resonant tank circuit. The current feedback signal drives the frequency of the ballast circuit causing the ballast circuit to seek resonance. The ballast circuit preferably includes a current limit circuit that is inductively coupled to the resonant tank circuit. The current limit circuit disables the ballast circuit when the current in the ballast circuit exceeds a predetermined threshold or falls outside a predetermined range.

FIELD OF THE INVENTION

The present invention generally relates to ballasts and more particularly, to an inductively coupled ballast for non-contact power transfer to a secondary circuit or load.

BACKGROUND OF THE INVENTION

Ballasts are commonly used to supply power to a wide variety of electrically powered components. Often ballasts are connected directly to the component (or load), for example, by “permanent” connections, such as wires or soldered leads on a circuit board, or by “removable” connections, such as plugs or other connectors. Direct electrical connections present a number of problems. First, direct electrical connections make it difficult to install and remove the load from the ballast. With permanent connections, the electrical leads must be soldered or otherwise secured directly between the ballast and the load. If the ballast or the load is damaged, replacement is complicated by the permanent connections. Removable connections make separation of the ballast and the load easier, but still require some manual manipulation. Removable connectors are also subject to corrosion and may be inadvertently or unintentionally disconnected, for example, by vibrations. Second, in many environments, direct electrical connections must be insulated from the environment to prevent damage to the circuit. For example, in wet environments, exposed electrical connections are subject to a short circuit. Third, direct electrical connections provide a direct and essentially unimpeded path for electricity to flow between the ballast and the load. As a result, power surges and other potentially damaging abnormalities in one element can be directly transfer to the other, thereby permitting problems in one component to damage or even destroy the other.

To address these and other significant problems, there is an increasing trend to replace conventional direct electrical connections with inductive connections. Inductively coupled systems provide a number of significant advantages over direct connections. First, inductive couplings do not include permanent or removable physical connectors. Instead, the secondary coil of the load (or secondary circuit) simply needs to be placed in the close proximity to the primary coil of the ballast. This greatly simplifies installation and removal of the load. Second, the inductive coupling provide a significant level of isolation between the ballast and the load. This isolation can protect one component from power surges and other potentially damaging abnormalities in the other component.

Unfortunately, conventional inductively coupled ballasts suffer from a number of problems associated primarily with efficiency. To provide maximum efficiency, it is desirable for the circuit to operate at resonance. Conventional ballasts are designed to operate at resonance by carefully selecting the components of the ballast in view of the precise characteristics of the load. Any variation in the load can move the circuit dramatically out of resonance. Accordingly, conventional ballasts require very precise selection of the components of the ballast circuit and secondary circuit. In some applications, the impedance of the secondary circuit will vary over time, thereby changing the resonant frequency of the circuit. For example, in many conventional lighting applications, the impedance of the lamp will vary as the lamp is heated and will also vary over the life of the lamp. As a result of these changes, the efficiency of conventional, fixed-frequency ballasts will vary over time.

Conventional ballast control circuits employ bipolar transistors and saturating transformers to provide power. The ballast control circuits oscillate at frequencies related to the magnetic properties of the materials and winding arrangements of these transformers. Circuits with saturating transformer oscillators produce an output in the category of a square wave, require the transistors of the half bridge to hard-switch under load and require a separate inductor to limit the current through the load. Conventional circuits chop the available power supply voltage, developing voltage spikes at the corners of the square wave as a consequence of the current limiting inductor. Inductive couplings rely on electromagnetic induction to transfer power from a primary coil to a secondary coil. The amount of current induced in the secondary coil is a function of the changes in the magnetic field generated by the primary coil. Accordingly, the amount of current transferred through an inductive coupling is dependent, in part, on the waveform of the current driving the primary. A square waveform has relatively small regions of change and therefore provides relatively inefficient transfer of power.

These and other deficiencies in prior ballasts are addressed by the present invention.

SUMMARY OF THE INVENTION

The present invention discloses an inductively powered ballast circuit having a current sensing circuit that automatically adjusts the frequency of the ballast to maintain operation of the ballast at or near unity power factor.

In one embodiment, the inductively coupled ballast circuit is a self-oscillating half-bridge switching design that operates at high frequencies. In addition, the inductively coupled ballast circuit self-oscillates partly as a function of the current sensing circuit to maintain resonance, uses MOSFET transistors as switching elements, and is designed to accommodate an air-core transformer coupling arrangement.

One embodiment of the inductively coupled ballast circuit includes a control circuit, an oscillator, a driver, a half-bridge switching circuit, and a series resonant tank circuit. The secondary circuit preferably includes a secondary coil and a load. During operation, the control circuit provides electrical signals to the oscillator, which, in turn, provides electrical signals to direct the driver. The driver then causes the half-bridge switching circuit to become energized. The half-bridge switching circuit energizes the series resonant tank circuit, which includes a primary coil. Once the series resonant tank circuit, and consequently the primary coil, is energized, the secondary coil becomes inductively energized, thereby providing power to the load.

In one embodiment, the resonant frequency for the inductively coupled ballast circuit is about 100 kHz. In addition, the secondary circuit preferably resonates at about 100 kHz as well. The resonant frequency of operation can be adjusted up or down by the control unit to accommodate for convenient component selection. In addition, selection of the resonant frequency is a function of the component selection in the series resonant tank and the characteristics of the secondary circuit.

An interesting feature of the inductively coupled ballast circuit is the inductive coupling. The series resonant tank circuit includes an inductive coupler. In one embodiment, the inductive coupler is positioned adjacent the secondary coil with an air gap therebetween to form an air core transformer. When voltage is applied to the inductive coupler, magnetic flux in the air gap induces voltage in the secondary coil thereby energizing the secondary load.

Another interesting feature of the inductively coupled ballast circuit involves the air gap of one embodiment. The air gap is the distance between the inductive coupler and the secondary coil. The air gap may be selected to provide a current limiting function. In addition, the air gap provides a magnetic flux path for inducing sufficient voltage in the secondary coil to establish and maintain an operating point for the secondary load.

Yet another interesting feature involves the frequency of operation of the inductively coupled ballast circuit. Both the series resonant tank and the secondary load may be tuned by proper selection of components to operate at a similar resonant frequency. In addition, impedance matching between the series resonant tank and the secondary load may occur at the resonant frequency. Accordingly, power transfer from the inductive coupler to the secondary coil may be optimized at a resonant frequency to maximize power efficiency.

Still another interesting feature involves self-oscillation of the inductively coupled ballast circuit with the oscillator. The oscillator may include feedback control for monitoring the series resonance tank. The feedback control may allow the oscillator to adjust the frequency to minimize reflected impedance from the secondary circuit. Adjusting the frequency to maintain resonance minimizes the reflected impedance and maintains optimum power transfer as the impedance of the secondary circuit varies.

In another aspect, the present invention preferably includes a current limit circuit that monitors the ballast circuit and disables the ballast circuit if the current to the primary exceeds a desired threshold. The current limit circuit protects both the load and the ballast circuit from excessive current. The current limit circuit is preferably latched to keep the ballast circuit disabled until reset, for example, by a manual reset switch.

In an alternative embodiment, the current limit circuit may be configured to disengage the ballast circuit if the current falls outside of a desired operating range. This embodiment is particularly useful in application where the load may be damaged or function improperly when operating under low current.

These and other features and advantages of the invention will become apparent upon consideration of the following detailed description of the presently preferred embodiments of the invention, viewed in conjunction with the appended drawings.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT OF THE INVENTION

The present invention is directed to an inductively coupled ballast circuit that is capable of providing power to a wide variety of electrically powered components in numerous applications. For purposes of disclosure, embodiments of the ballast circuit will be described in connection with a water treatment system, and more specifically in connection with the powering of an ultraviolet lamp in a water treatment system. Although described in connection with this particular application, the present invention is well-suited for use in providing power to other types of lamps, such as incandescent, fluorescent and halogen lamps used in numerous lighting applications, such as indoor and outdoor light fixtures, desk lamps, outdoor signage, decorative lighting, automotive lighting, underwater lighting, intrinsically safe lighting, and landscape lighting, to name only a few lighting configurations and applications. The present invention is also well suited for providing power to non-lighting components, such as integrated battery chargers in various electronic components, including cell phones, personal digital assistants and the like.

Referring toFIG. 1, the present invention, as used in the illustrated embodiment, discloses an electronic control system for a water treatment system10that generally uses carbon-based filters and ultraviolet light to purify water. In order to appreciate the present invention, it is helpful to have a general background of the mechanical aspects of water treatment system10for which this illustrated embodiment was intended. Water treatment system10includes a main housing12, a replaceable ultraviolet lamp assembly14and a filter assembly16. The ultraviolet lamp assembly14and the filter assembly16are removable and replaceable from the main housing12. The main housing12includes a bottom shroud18, a back shroud20, a front shroud22, a top shroud24and an inner sleeve shroud26. A lens28accommodates a display106(seeFIG. 3) so that information may be displayed about the status of the water treatment system10through the display106. To assemble the water treatment system10, the ultraviolet lamp assembly14is securely mounted to the main housing12and thereafter the filter assembly16is mounted over the ultraviolet lamp assembly14and to the main housing12.

As those skilled in the art would recognize, the replaceable ultraviolet lamp assembly14may be made in such a manner that the ultraviolet lamp assembly14may not be replaceable. In addition, those skilled in the art would recognize that the replaceable ultraviolet lamp assembly14may be interchanged with several different types of electromagnetic radiation emitting assemblies. As such, the present invention should not be construed to cover only systems that use ultraviolet lamp assemblies and those skilled in the art should recognize that the disclosure of the ultraviolet lamp assembly14represents only one embodiment of the present invention.

Referring toFIGS. 2A–C, the major mechanical components of the water treatment system10are shown in perspective view, as relevant to the present invention. As illustrated inFIG. 2A, the inner sleeve shroud26includes a plurality of inner sleeve covers30, an inlet valve assembly32and an outlet cup assembly34with an outlet cup36. A bottom shroud assembly38is further disclosed that includes the bottom shroud18along with an inlet assembly40and an outlet assembly42. An electronics assembly44fits securely in the bottom shroud18, the details of which will be set forth below in detail. These components are securely mounted to the bottom shroud18, the back shroud20, the front shroud22, the top shroud24, the inner sleeve shroud26and the lens28when the water treatment system10is fully assembled. A magnet holder46and a magnet48are also housed in the top shroud24in the illustrated embodiment.

Referring toFIG. 2B, the ultraviolet lamp assembly14generally includes a base subassembly50, a secondary coil52, a bottom support subassembly54, a top support assembly56, a pair of quartz sleeves58, an ultraviolet lamp60, an O-ring62and a pair of cooperating enclosure reflector subassemblies64. Generally speaking, the secondary coil52, the bottom support subassembly54and the enclosure reflector subassemblies64are connected with the base subassembly50. The enclosure reflector subassemblies64house the pair of quartz tubes58, the ultraviolet lamp60and the O-ring62. The top support assembly56fits securely over the top of the enclosure reflector assemblies64when the ultraviolet lamp assembly14is fully assembled.

As illustrated inFIG. 2C, the filter assembly16generally includes a base assembly66, a filter block assembly68, a filter housing70and an elastomeric filter-housing grip72. Generally speaking, the filter block assembly68fits over the base assembly66which, in turn, is encapsulated by the filter housing70. The filter housing grip72fits over the top of the filter housing70, thereby providing a better grip for removing the filter housing70. The filter assembly16filters a flow of water by directing the flow through the filter block assembly68before being directed to the ultraviolet lamp assembly14.

FIG. 3illustrates an electronic control system100for the water treatment system10generally described above. In the illustrated embodiment, the water treatment system10is controlled by a control unit102, which is preferably a microprocessor. As illustrated inFIG. 4, the control unit102is electrically connected with the inductively coupled ballast circuit103of the present invention. The ballast circuit103includes the ultraviolet lamp assembly14and electronic assembly44, which are inductively coupled as illustrated by the dotted line inFIG. 4. This control unit102is also electrically connected to the ultraviolet lamp assembly14through two-way wireless communication, as will be set forth in greater detail below. During operation, the control unit102is capable of generating a predetermined electric signal that is directed to the inductively coupled ballast circuit103, which instantaneously energizes the lamp assembly14which, in turn, provides high-intensity ultraviolet light that treats the flow of water.

In the illustrated embodiment, the control unit102is also electrically connected with a flow sensor circuit104, a display106, an ambient light sensor circuit108, a visible light sensor circuit110, a power detection circuit112, an ambient temperature sensor circuit114, an audio generation circuit116, a memory storage device118, a communications port120, a ballast feedback circuit122and a radio frequency identification system124. As further illustrated inFIG. 3, an ultraviolet light radio frequency identification transponder126is connected with the ultraviolet lamp assembly14and a filter radio frequency identification transponder128is connected with the filter assembly16. The ultraviolet radio frequency identification transponder126and the filter radio frequency identification transponder128communicate with the radio frequency identification system124using two-way wireless communication, as will be set forth in greater detail below.

Generally speaking, the flow sensor circuit104is used by the control unit102to determine when water or fluid is flowing and to keep track of the volume of water or fluid that is being processed by the water treatment system10. The display106is driven by the control unit102and is used to display information about the status of the water treatment system10. Several different types of displays are known in the art and may be used in the present invention; however, the preferred display is a vacuum florescent display. The ambient light sensor circuit108measures the amount of ambient light and, in turn, provides electrical signals to the control unit102so that it can adjust the intensity of the display106accordingly.

The visible light sensor circuit110provides the control unit102with electrical signals related to the intensity level of the light that is being emitted by the ultraviolet lamp assembly14. This is important because these signals allow the control unit102to increase or decrease the intensity of the electromagnetic radiation being emitted by the ultraviolet lamp assembly14. Those skilled in the art would recognize that the visible light sensor circuit110may be interchanged with various electromagnetic radiation sensor circuits that are capable of sensing the intensity of electromagnetic radiation that is emitted from various electromagnetic radiation emitting devices that may be used in the present invention.

The power detection circuit112provides the control unit102with electrical signals that indicate the presence or absence of power to the water treatment system10. Power is provided to the water treatment system10from an external power source, such as a conventional power outlet. Those skilled in the art would recognize that several circuits exist that monitor external power sources and provide corresponding electrical signals in response to losses of power.

The ambient temperature sensor circuit114measures the ambient temperature of the atmosphere so that the water treatment system10can maintain a temperature level above freezing or some other predetermined temperature setting. The control unit102can energize the ultraviolet lamp60to generate heat if necessary. The audio generation circuit116is used by the control unit102to generate audible enunciations. The audible enunciations typically occur during predetermined system states that are experienced by the water treatment system10. These predetermined system states are recognized by the control unit102which, in turn, activates the audio generation circuit116to create the audible enunciation.

As previously set forth, the memory storage device118is also electrically connected with the control unit102. The memory storage device118is used to store various data values related to the water treatment system10and its related components. In the illustrated embodiment, the memory storage device118is an EEPROM or some other equivalent storage device. Those skilled in the art would recognize that various memory storage devices are available that could be used in the present invention.

The communications port120is also electrically connected with the control unit102, which provides the water treatment system10with the ability to conduct bi-directional communication between the control unit102and a peripheral device, such as a personal computer or hand-held monitoring device. In the illustrated embodiment, the communications port120uses the RS-232 communication platform to communicate with the peripheral device. The communications port120may also be connected with the ultraviolet lamp assembly14and the filter assembly16to monitor and control various operational characteristics of these devices in other embodiments. However, in the illustrated embodiment, the radio frequency identification system124is used to report information to the control unit102about the ultraviolet lamp assembly14and the filter assembly16.

In the embodiment depicted inFIG. 3, the radio frequency identification system124uses signals from the ultraviolet light radio frequency identification transponder126and the filter radio frequency identification transponder128to report various information to the control unit102. During operation, the ultraviolet light radio frequency identification transponder126and the filter radio frequency identification transponder128communicate with the radio frequency identification system124using wireless communication. Since the ultraviolet lamp assembly14and the filter assembly16are designed to be replaceable at the end of its useful life, each ultraviolet lamp assembly14and filter assembly16contains a transponder126,128that stores information specific to each device. Those skilled in the art would recognize that the ultraviolet light radio frequency transponder could be used in conjunction with other electromagnetic radiation emitting devices or assemblies. The radio frequency identification system124is set forth in greater detail below.

Referring toFIG. 4, in the illustrated embodiment of the invention, the ultraviolet lamp assembly14is energized by the inductively coupled ballast circuit103that is electrically connected with the control unit102. In the illustrated embodiment, the inductively coupled ballast circuit103is a self-oscillating, half-bridge switching design that operates at high frequencies. The inductively coupled ballast circuit103self-oscillates once resonance is achieved, uses MOSFET transistors as switching elements, and is designed to accommodate an air-core transformer coupling arrangement, which simplifies the design of the ultraviolet lamp assembly14. The ultraviolet lamp assembly14or other electromagnetic radiation emitting assemblies may be readily replaced because of the air-core transformer coupling arrangement created by the inductively coupled ballast circuit103.

As illustrated inFIG. 4, the inductively coupled ballast circuit103of the described embodiment generally includes a control circuit142, an oscillator144, a driver146, a half-bridge switching circuit148, and a series resonant tank circuit150. The ultraviolet lamp assembly14generally includes the secondary coil52(seeFIG. 2), a resonant lamp circuit152and the ultraviolet lamp60. The oscillator144is electrically connected with the control unit102, which energizes the oscillator144by providing electric signals to the control circuit142. During operation, the oscillator144provides electrical signals to direct the driver146, which then causes the half-bridge switching circuit148to become energized. The half-bridge switching circuit148energizes the series resonant tank circuit150that, in turn, inductively energizes the ultraviolet lamp60in the ultraviolet lamp assembly14.

As noted above and as further illustrated inFIG. 4, the ultraviolet lamp assembly14includes the secondary coil52, the resonant lamp circuit152and the ultraviolet lamp60while the electronic assembly44houses the control circuit142, the oscillator144, the driver146, the half-bridge switching circuit148and the series resonant tank circuit150. As previously set forth, once the series resonant tank circuit150is energized, the secondary coil52in the ultraviolet lamp assembly14becomes inductively energized as illustrated by the dotted line inFIG. 4. In the illustrated embodiment, the resonant frequency for the ballast circuit103is about 100 kHz. In addition, the ultraviolet lamp assembly14resonates at about 100 kHz as well. The frequency of operation may be varied to maintain resonance of the series resonant tank circuit150and the ultraviolet lamp assembly14as discussed in detail below. As known to those skilled in the art, the resonant frequency may be any desired frequency selected as a function of the component selection in the series resonant tank circuit150and the ultraviolet lamp assembly14.

Referring toFIG. 5, the control circuit142is electrically connected with the control unit102and the oscillator144. The control circuit142includes a plurality of resistors156,158,160,162,164,166, a plurality of capacitors168,170172, a diode174, a first operational amplifier176and a second operational amplifier178. As illustrated, resistor156is connected with a first direct current (“DC”) power source180, the output of the control unit102and resistor158. Resistor158is further connected with diode174, resistor160and capacitor168. The first DC power source180is connected with capacitor168, which is also connected with diode174. Diode174is further connected with a ground connection182, as those skilled in the art would recognize. Resistor160is connected with the negative input of operational amplifier176and the positive input of operational amplifier178to complete the current path from the control unit102to the operational amplifiers176,178.

Referring once again to the control circuit142depicted inFIG. 5, resistor162is connected with a second DC power source184and in series with resistors164and166. Resistor166is connected with the ground connection182and capacitor170, which is, in turn, connected with the first DC power source180and resistor164. The positive input of operational amplifier176is electrically connected between resistors162and164, which provides a DC reference voltage to operational amplifier176during operation. The negative input of operational amplifier178is electrically connected between resistors164and166, which provides a DC reference voltage to operational amplifier178during operation. The output of operational amplifiers176and178is connected with the oscillator144, as set forth in detail below.

During operation, the control circuit142turns the oscillator144on and off based on input from the control circuit102and the magnetic interlock sensor192, as described in more detail below. The control circuit142receives electrical signals from the control unit102and, in turn, acts as a window comparator that only switches the oscillator144on when the input voltage produced by the control unit102is within a certain voltage window. The preferred signal from the control unit102is an AC signal that, together with its duty cycle, allows the control unit102to turn the ultraviolet lamp60on and off through the remaining components of the inductively coupled ballast circuit103, as will be set forth below. The control circuit142also prevents false triggering and allows positive control if the control unit102fails.

As illustrated inFIG. 5, the first DC power source180and the second DC power source184provide power to the circuits depicted inFIG. 5. Those skilled in the art of electronics would recognize that DC power supply circuits are well known in the art and beyond the scope of the present invention. For the purposes of the present invention, it is important to note that such circuits exist and are capable of being designed to produce various DC voltage values from a given AC or DC power source. In the illustrated embodiment, a +14VDC and a+19VDC signal is used, as indicated throughout the figures. Those skilled in the art would recognize that the circuits disclosed inFIG. 5could be designed to operate on different DC voltage levels and that these values should not be construed as a limitation on the present invention. In another embodiment, 300VDC is used to supply power to the half-bridge switching circuit148to optimize power transfer.

In the embodiment depicted inFIG. 5, the output of the control circuit142is connected with an interlock circuit190to prevent the ultraviolet lamp60from becoming energized if the water treatment system10is not properly assembled. The interlock circuit190includes a magnetic interlock sensor192, a plurality of resistors193,194,196,198,200,202,204, a transistor206and a diode208. Referring toFIG. 1, in the illustrated embodiment, the magnetic interlock sensor192is positioned so that if the top shroud24is not securely positioned on the inner sleeve shroud26, the water treatment system10will not energize the ultraviolet lamp60. However, those skilled in the art would recognize that the magnetic interlock sensor192may be placed in other convenient places of the water treatment system10as well.

Referring toFIG. 5, the magnetic interlock circuit190operates by directing the output of the control circuit142to the ground connection182, through transistor206, if the magnetic interlock sensor192detects that the water treatment system10is not assembled properly, as set forth above. As those skilled in the art would recognize, if the water treatment system10is not assembled properly, the output of the magnetic interlock sensor192causes the current flowing through resistors194,196and198to energize the gate of transistor206, which thereby shorts the output signal of the control circuit142to the ground connection182. The magnetic interlock sensor192is powered by the second DC power source184through resistor193and is also connected with the ground connection182. In addition, the magnetic interlock sensor192sends a signal to the control unit102, through the combination of resistors200,202and204, diode208, first DC power source180and second DC power source184. This signal also allows the control unit102to determine when the water treatment assembly10is not assembled properly. To that end, the interlock circuit190provides two methods of ensuring that the ultraviolet lamp60is not energized if the water treatment system10is not assembled properly. The magnetic interlock is not necessary for the operation of the present invention.

Referring once again toFIG. 5, the oscillator144provides electrical signals that energize the driver146while the water treatment system10is treating a flow of water. The oscillator144begins operating immediately once an electrical signal is sent from the control unit102, through control circuit142, as set forth above. As readily apparent, the oscillator144may also be controlled by any other mechanism capable of activating and deactivating the oscillator144. The illustrated oscillator144comprises an operational amplifier210, a linear bias resistor212, a buffer circuit214, a buffer feedback protect circuit216and a current sensing circuit218. During operation, the operational amplifier210receives input signals from the control circuit142, the linear bias resistor212and the current sensing circuit218. The operational amplifier210is also connected with the second DC power source184and the ground connection182, which energizes the operational amplifier210.

As illustrated inFIG. 5, the illustrated buffer circuit214comprises a first transistor220, a second transistor222and a pair of resistors224,226. The output of operational amplifier210is connected with the gates of transistors220,222, thereby controlling operation of transistors220,222. The second DC power source184is connected with resistor224, which is also connected with collector of transistor220. The emitter of transistor220is connected with resistor226, the emitter of transistor222and the input of the driver146. The collector of transistor222is connected with ground connection182. During operation, the buffer circuit214buffers the output signal from the operational amplifier210and prevents load changes from pulling the frequency of oscillation. In addition, the buffer circuit214increases the effective gain of the inductively coupled ballast circuit103, which helps ensure a quick start of the oscillator144.

The buffer feedback protect circuit216comprises a pair of diodes228,230that are electrically connected with the output of the buffer circuit214by resistor226. As illustrated inFIG. 5, the second DC power source184is connected with the cathode of diode228. The anode of diode228and the cathode of diode220are connected with resistor226and the linear bias resistor212. The linear bias resistor212provides bias feedback signals to the negative input of operational amplifier210. In addition, the anode of diode230is connected with ground connection182, which completes the buffer feedback protect circuit216. The buffer feedback circuit216protects the buffer circuit214from drain to gate Miller-effect feedback during operation of the water treatment system10.

As illustrated inFIG. 5, the current sensing circuit218includes a first multi-winding transformer232, a plurality of resistors234,236,238, a pair of diodes240,242, and a capacitor244. The transformer232preferably includes a primary having two windings that are connected in parallel between the output of the half-bridge switching circuit148and the input of the series resonant tank circuit150as illustrated inFIG. 5. The transformer232preferably includes a primary with two windings connected in parallel rather than a single winding to reduce the total reactance on the primary side of the transformer, thereby reducing the reactive impact of the transformer232on the tank circuit150. In other applications, the primary side of the transformer may be divided into a different number of windings. For example, the transformer232may include only a single winding where reduction of the reactive impact of the transformer is not important or may include three or more windings where even further reduction of the reactive impact of the transformer232is desired.

The first lead of the secondary coil of transformer232is electrically connected with resistors234,236,238, the diodes240,242and the positive input of the operational amplifier210. The second lead of the secondary coil of the transformer232is connected with resistor238, the cathode of diode242, the anode of diode240and capacitor244. As such, resistor238and diodes242,244are connected in parallel with the secondary winding of transformer232, as illustrated inFIG. 5. Capacitor244is also electrically connected with the negative input of operational amplifier210. In addition, resistor234is connected with the second DC power source184and resistor236is connected with the ground connection182. Resistors234,236and238protect the operational amplifier210from current overload and diodes240,242clip the feedback signal that is sent to the input of the operational amplifier210.

During operation, the oscillator144receives signals from the control circuit142that charge capacitor244, which, in turn, sends an electrical signal to the negative input of the operational amplifier210. The output of the operational amplifier210is electrically connected to the driver146through the buffer circuit214. As described in more detail below, the driver146energizes the half-bridge switching circuit148, which in turn provides power to the tank circuit150ultimately powering inductive coupler270. As illustrated inFIG. 5, the transformer232is connected in the current path between the half-bridge switching circuit148and the tank circuit150. The transformer232sends electrical signals back through resistors234,236and238, which limit the current, to the inputs of the operational amplifier210to provide a current sensing feedback. As described in more detail below, the current sensing feedback provided by transformer232allows the oscillator144to self-resonate despite changes in the load. The inductively coupled ballast circuit103remains oscillating until the control unit102shuts the water treatment system10down or transistor206of the interlock circuit190pulls the input to the oscillator144low.

More specifically, the current sensing circuit218provides feedback to the operational amplifier210that controls the timing of the oscillator144so that the oscillator144does not impair the tank circuit's150inherent tendency to oscillate at resonant frequency. In general, the current in the series resonant tank circuit150flows through the primary coils of transformer232, thereby inducing a voltage in the secondary coil of transformer232. The AC signal generated by the transformer232is superimposed upon a DC reference voltage set by resistors234and236. The operational amplifier210is preferably a conventional difference operational amplifier providing an output based, in part, on the difference between the amplitude of the signal on the positive lead and the amplitude of the signal of the negative. Accordingly, the output of the operational amplifier210oscillates above and below the reference voltage in accordance with the oscillating signal of the current feedback circuit. The operational amplifier210is preferably alternately driven between saturation and cutoff, thereby providing a quasi-square wave output. When the output of the operational amplifier210exceeds the reference signal, transistor220is driven to “on,” while transistor222is driven to “off,” thereby charging capacitor248and discharging capacitor250. When the output of the operational amplifier210falls below the reference signal, transistor222is driven to “on” while transistor220is driven to “off,” thereby discharging capacitor248and charging capacitor250. This alternating charging/discharging of capacitors248and250results in an alternating signal being applied to the primary coil of the driver146, as described in more detail below. The frequency shifting (or resonance seeking) operation of the circuit is described in more detail with reference toFIG. 15. In this illustration, the current in the inductive coupler270is represented by waveform600, the voltage in the current transformer232is represented by waveform602and the current feedback signal is represented by waveform604(shown without clipping of diodes240and242). As noted above, the operational amplifier210is alternately driven between saturation and cutoff with a transition period interposed between the saturation and cutoff portions of the waveform. The length of the transition period is dictated by the slope of the current feedback signal. The timing of the operational amplifier210is dependent on the length of the transition period. By varying the length of the transition period, the timing of the transitions in the operational amplifier210output signal is controlled. This shift in timing is perpetuated through the driver146and half-bridge switching circuit148having the affect of varying the frequency and also possibly the amplitude of the signal in the tank circuit150. The altered signal in the tank circuit150is reflected into the current feedback signal by the current transformer232to perpetuate the frequency shift. When the load on the secondary coil52increases, a corresponding increase occurs in the amplitude of the current in the tank circuit150. This increased signal is represented by waveform606inFIG. 15. The increased signal in the tank circuit150results in a corresponding increase in the voltage in the current transformer232. The increased voltage in the current transformer232is represented by waveform608. The increased voltage in the current transformer232finally results in an increase in the amplitude of the current feedback signal, represented by waveform610(shown without clipping of diodes240and242). The increased current feedback signal has a greater slope at the zero crossings and therefore causes the operational amplifier210to transition from one state to the other sooner in time. This in turn causes the transistors220and222to switch sooner in time and the AC signal applied to the driver146to alternate sooner in time. Ultimately, there is a corresponding shift in the timing of the signals applied to the tank circuit150by the half-bridge switching circuit148. The shift in timing of the signals applied by the half-bridge switching circuit148has the effect of increasing the frequency and possibly the amplitude of the inherent oscillating signal in the tank circuit150, thereby shifting, or “truncating,” the timing of the signal in the tank circuit150. The truncated signal in the tank circuit150is reflected into the current sensing circuit218. This varies the current feedback signal applied to the operational amplifier210, thereby perpetuating the frequency shift and effecting an increase in the frequency of the oscillator. In this way the oscillator144and driver146permit the tank circuit150to shift its frequency to remain at resonance despite a change in load. When the load on the secondary coil52decreases, the frequency of the oscillator144decreases in a manner essentially opposite that described above in connection with an increase in frequency. In summary, the decreased load results in decreased current in the tank circuit150. This results, in turn, in a decrease in the voltage induced in the current transformer232and a decrease in the amplitude of the current feedback signal. The decreased current feedback signal has a decreased slope, and accordingly causes the operational amplifier210to complete the transition between saturation and cutoff later in time. The transistors220and222also transition later in time, thereby shifting the timing of the driver146and the timing of the switching circuit148. The net effect of the shift in the timing of the switching circuit148is to shift, or “extend”, the frequency and possibly vary the amplitude of the signal in the tank circuit150. The extended signal is reflected into the current sensing circuit218where it is returned to the operational amplifier210to perpetuate the decrease in frequency of the oscillator144. Optimal performance is achieved when the half-bridge switching circuit148alternates at the zero crossings of the current signal in the tank circuit150. This provides optimal timing of the energy supplied by the switching circuit148to the tank circuit150. In some applications, it may be necessary or desirable to shift the phase of the current feedback signal to provide the desired timing. For example, in some applications, the parasitic effect of the various circuit components may result in a shift in the phase of the current feedback signal. In such applications, the current sensing circuit can be provided with components, such as an RC circuit, to shift the signal back into alignment so that the switching circuit148alternates at the zero crossings.FIG. 17illustrates a portion of an alternative current sensing circuit218′, which includes an RC circuit configured to shift the phase of the current feedback signal 120 degrees. In this embodiment, the current sensing circuit218′ is essentially identical to the current sensing circuit218of the above described embodiment, except that it includes two capacitors800,802and two resistors804,806that are connected along the leads extending back to the operation amplifier210.FIG. 17further illustrates that the secondary of the current transformer232can be connected to ground182to provide a zero reference, if desired. If the current transformer232is connected to ground182, resistor238is eliminated.

Referring once again toFIG. 5, the output of the oscillator144is electrically connected with the driver146. In the illustrated embodiment, the driver146is a multi-winding transformer that provides power to the half-bridge switching circuit148. Transformer246is the preferred driver146in the illustrated embodiment because the phasing arrangement of the transformer246insures that the half-bridge switching circuit148will be alternately driven, which avoids cross conduction. A double arrangement of capacitors248,250is electrically connected with the primary winding of transformer246, thereby preventing DC current saturation in the transformer246. Capacitor246is also connected with the ground connection182and capacitor250is also connected with the second DC power source184.

The transformer246includes two secondary coils that are electrically connected to opposite legs of the half-bridge switching circuit148so that the half-bridge switching circuit148receives energy from transformer246. The half-bridge switching circuit148, which is also illustrated inFIG. 5, is electrically arranged as a MOSFET totem pole half-bridge switching circuit252that is driven by both secondary coils of transformer246. The MOSFET totem pole half-bridge switching circuit252includes a first MOSFET transistor254and a second MOSFET transistor256that provide advantages over conventional bipolar transistor switching circuits. Energy is transferred from the driver146to the MOSFET transistors254,256through a plurality of resistors258,260,262,264. The MOSFET transistors254,256are designed to soft-switch at zero current and exhibit only conduction losses during operation. The output generated by MOSFET transistors254,256is more in the form of a sine wave that has fewer harmonics than that generated by traditional bipolar transistors. Using MOSFET transistors254,256also provides advantages by reducing radio frequency interference that is generated by the MOSFET transistors254,256while switching during operation.

In the half-bridge switching circuit148depicted inFIG. 5, the first secondary coil of transformer246is connected with resistor258and resistor260. The second secondary coil of transformer246is connected with resistor262and resistor264. Resistor260is connected with the gate of MOSFET transistor254and resistor264is connected with the gate of MOSFET transistor256. As illustrated, the first secondary coil of transformer246and resistor258are connected with the source of MOSFET transistor254. The second secondary coil of transformer246and resistor264are connected with the gate of MOSFET transistor256. The drain of MOSFET transistor254is connected with the second DC power source184and the source of MOSFET transistor254is connected with the drain of MOSFET transistor256. The source of MOSFET transistor256and resistor262are connected with the ground connection182.

A further benefit of the driver146is that multi-winding transformer246is a very convenient way to apply gate drive voltage to the MOSFET transistors254,256that exceeds the second DC power source184. The MOSFET transistors254,256provide further advantages because they have diodes inherent in their design that protect the MOSFET totem pole half-bridge switching circuit252from load transients. In addition, over-voltages reflected from the series resonant tank circuit150, by changes in load, are returned to supply rails by the inherent diodes within MOSFET transistors254,256.

Referring toFIG. 5, the output of the half-bridge switching circuit148is connected with the input of the series resonant tank circuit150, which, in turn, inductively energizes the secondary coil52of the ultraviolet lamp assembly14(FIG. 4). As set forth above, in the illustrated embodiment of the invention, the current sensing circuit218of the oscillator144is connected with the output of the half-bridge switching circuit148and the input of the series resonant tank circuit150to provide current sense feedback to operational amplifier210of the oscillator144during operation. The primary coil of the transformer232is connected in series between the output of the half-bridge switching circuit148and the input of the series resonant tank circuit150as illustrated inFIG. 5.

Referring toFIG. 5, the series resonant tank circuit150comprises an inductive coupler270, the parallel combination of a pair of tank capacitors271,272, a pair of diodes274,276and a capacitor278. The inductive coupler270is connected to the primary coil of transformer232and tank capacitors271,272. Tank capacitor271is also connected with the second DC power source184and tank capacitor272is also connected with the ground connection182. In addition, tank capacitor271and the second DC power source184are connected with the anode of diode274. The cathode of diode274and capacitor278are both connected with the second DC power source184. Capacitor278is connected with the anode of diode276and the ground connection182. Tank capacitor272is also connected the cathode of diode276.

The series resonant tank circuit150sees all of the stray inductances of the component combination of the inductively coupled ballast circuit103. This is relevant because the stray inductance, which is the combined inductance seen by the series resonant tank circuit150, will limit the power transfer to the load (the ultraviolet light assembly14) if its precludes the system from operating outside of resonance. The inductance of the secondary coil52and the resonant lamp circuit152are also reflected impedance values that help determine and limit the power that is delivered to the secondary coil52of the ultraviolet lamp assembly14. In general, brute force oscillator/transformer combinations have power transfer limits because of stray and reflected inductance. In other words, the inductance of transformers and capacitors appears in series with the load thereby limiting power transfer capability.

In the illustrated embodiment, the frequency of operation for the series resonant tank circuit150is set near 100 KHz, which is determined by the inductance of the inductive coupler270and the parallel capacitance value of tank capacitors271,272, which are 0.1 uF capacitors in the illustrated embodiment. Tank capacitors271,272must have low dissipation factors and be able to handle high levels of current, which is about 14 amps at start up. This resonant frequency may be adjusted up or down and has been selected only for convenient component selections. As noted above, the ballast circuit103seeks resonance through a feedback signal from the current sensing circuit218. The current feedback signal is proportional to the current in the resonant tank circuit150. The range of frequencies through which the ballast circuit103can search for resonance are readily varied by adjusting the values of the tank capacitors271,272. For example, by increasing the value of the tank capacitors271,272, the range can generally be decreased.

The inductive coupler270of the illustrated embodiment includes 10 turns of wire to generate the power required to inductively energize the secondary coil52in the ultraviolet lamp assembly14. The inductive coupler270is preferably positioned in the outlet cup36(seeFIG. 2A) of the water treatment system10and wire is wrapped around the outlet cup36in a diameter of about 3.5 inches. In the illustrated embodiment, litz wire is used for the inductive coupler270because litz wire is especially efficient in both performance and operating temperature, due to a skin effect caused by operating at 100 kHz. As set forth above, the inductive coupler270inductively energizes the secondary coil52of the ultraviolet lamp assembly unit14during operation.

Referring toFIG. 2A, the secondary coil52of the ultraviolet lamp assembly unit14is positioned in the outlet cup36and the inner sleeve shroud26when the water treatment system10is assembled. In the illustrated embodiment, the secondary coil52has 55 turns of small diameter wire that is wrapped around the secondary coil52in a diameter of about two inches. It is important to note that the coupling between the outlet cup36and the base subassembly50, which houses the secondary coil52, is designed to be very tolerant of gaps and misalignment. In fact, gaps are used to adjust the coupling coefficient, thereby adjusting the operating point of the ultraviolet lamp60.

The permeance of the air gap between the inductive coupler270and the secondary coil52may be adjusted by changing the distance between the inductive coupler270and the secondary coil52, as known in the art. As is apparent, the air gap within the air core transformer formed with the inductive coupler270and the secondary coil52may be selectively adjusted to limit power transfer from the inductive coupler270to the secondary coil52. In addition, selective adjustment of the air gap may adjust the control response of the oscillator144. Accordingly, selection of the permeance of the air gap balances overcurrent protection of the inductively coupled ballast circuit103with the bandwidth and responsiveness of the oscillator144when the secondary coil52is inductively energized.

As known in the art, inductive energization of the secondary coil52occurs when the inductive coupler270induces a magnetic flux in the air gap between the secondary coil52and the inductive coupler270. In the illustrated embodiments, the magnetic flux is an alternating flux with a frequency that is preferably controlled by the oscillator144in an effort to maintain resonance.

During operation, the oscillator144may control the frequency at close to the resonant frequency of the series resonant tank circuit150and the ultraviolet lamp assembly unit14. As previously discussed, the current sensing circuit218monitors the reflected impedance in the series resonance tank circuit150to allow the inductively coupled ballast circuit103to self-oscillate to a frequency which optimizes power transfer efficiency. If, for example, the impedance reflected by the ultraviolet light assembly14to the series resonant tank circuit150shifts slightly, the current sensing circuit218may adjust the frequency to correct for the shift in power transfer efficiency.

In the case where the impedance shifts significantly lower, such as, for example, when the ultraviolet lamp60fails in a shorted condition, the increase in current is limited by the air gap. As known in the art, the air gap functions to limit the amount of impedance that may be reflected. In addition, the impedance that is reflected may result in an impedance mismatch causing the reflection of power back to the series resonant tank circuit150. As is readily apparent, the reflection of power to the series resonance tank circuit150may further limit power transfer to the secondary coil52. Based on the combination of the air gap and the resonant frequency control, the inductively coupled ballast circuit103may be optimized for efficient operation while maintaining desirable levels of overcurrent protection.

The configuration of the air core transformer provides for simple and efficient replacement of the ultraviolet light assembly14. In addition, the present invention provides further advantages by providing a coupling that does not require special contacts for the ultraviolet lamp assembly14because of the inductively coupled ballast circuit103. Further, the configuration eliminates the need for conductors or other similar power transfer mechanism that may compromise waterproofing, corrode and/or otherwise malfunction.

As readily apparent to those skilled in the art, the inductively coupled ballast circuit103set forth above may be readily incorporated into other lighting systems or other systems requiring the transmission of electric power, and provides advantages over prior art ballast circuits because it drives lamps and other loads without requiring a physical connection and because it seeks resonance with the secondary. The inductively coupled ballast circuit103is also capable of instantaneously energizing several different styles of lamps, bulbs and other loads.

Referring once again toFIG. 5, the ballast feedback circuit122is electrically connected with the inductive coupler270of the series resonant tank circuit150and the control unit102. The ballast feedback circuit122provides feedback to the control unit102while the inductively coupled ballast circuit103is driving the ultraviolet lamp60. This allows the control unit102to monitor the energy being provided by the inductive coupler270to the secondary coil52of the ultraviolet lamp assembly14. This provides the control unit102with the ability to determine if the ultraviolet lamp60is on or off and also, in other embodiments, the amount of current and voltage being applied to the ultraviolet lamp60.

As depicted inFIG. 5, the ballast feedback circuit122includes an operational amplifier280, a pair of resistors282,284, a pair of diodes286,288and a capacitor290. The signal from the series resonant tank circuit150is directed to the anode of diode286. The cathode of diode286is connected with capacitor290and resistor282. In addition, resistor282is connected with the anode of diode288, resistor284and the positive input of operational amplifier280. Resistor284is also connected with the positive input of operational amplifier280and the first DC power source180. Capacitor290is also connected with the first DC power source180, while the cathode of diode288is connected with the second DC power source184. The negative input of operational amplifier280is connected directly with the output of operational amplifier280. The output of operational amplifier280is connected with the control unit102, thereby providing the feedback signal from operational amplifier280to the control unit102.

Referring toFIG. 6, the ultraviolet lamp assembly14of one embodiment includes the ultraviolet lamp60, the resonant lamp circuit152and the secondary coil52. The ultraviolet lamp60of the illustrated embodiment comprises a pair of bulbs300,302and a pair of filaments304,306. The bulbs300,302are held together with an upper connection bracket308and a lower connection bracket310. The secondary coil52is connected with the resonant lamp circuit152, which, in turn, is connected with the filaments304,306of the ultraviolet lamp60. The resonant lamp circuit152comprises a capacitor312that is electrically connected in series with the bulbs300,302and a starter circuit314as illustrated.

Although an ultraviolet lamp assembly14is set forth in the illustrated embodiment of the present invention, as previously set forth, those skilled in the art would recognize that present invention is well-suited for use with other electromagnetic radiation emitting assemblies or light sources. For example, the ultraviolet lamp assembly14may use a pulsed white light lamp or a dielectric barrier discharge lamp to deactivate microorganisms in the flow of water. Those skilled in the art would recognize that the inductively coupled ballast circuit103may be used to drive not only various types of electromagnetic radiation emitting devices, but also other loads that might benefit from the wireless power supply or resonance-seeking characteristic of the present invention. As such, the present invention should not be limited to water treatment systems or lamps assemblies, but instead should be broadly interpreted to encompass a wide variety of power supply applications.

As illustrated inFIG. 7, the starter circuit314comprises a bridge rectifier circuit320, a silicon-controlled rectifier322, a series arrangement of diodes324,326,328,330, a triac332, a plurality of transistors334,336, a plurality of resistors338,340,342,344,346and a plurality of capacitors348,350. As those skilled in the art would recognize, the triac332may be any equivalent device, such as a FET transistor or a silicon controlled rectifier. In addition, those skilled in the art would recognize that the bridge rectifier circuit320comprises a plurality of diodes352,354,356,358that are connected with the filaments304,306of the ultraviolet lamp60.

Referring toFIG. 7, the bridge rectifier circuit320is connected with silicon-controlled rectifier322, resistor338and the ground connection182. Silicon-controlled rectifier322is also connected with the series arrangement of diodes324,326,328,330and the triac332, which are both also connected with the ground connector182. Resistor338is connected with triac332, resistor340and resistor342. Resistor340is connected with the collector of transistor334, the base of transistor336, capacitor348and resistor344. Capacitor348and resistor344are further connected with the ground connection182. Resistor342is connected with the emitter of transistor336and capacitor350, which is also connected with the ground connection182. The gate of triac332is connected with the emitter of transistor334. The collector of transistor336is connected with the base of transistor334and resistor346. Resistor346is connected with the ground connection182to complete the starter circuit314.

Referring back toFIG. 6, during operation, capacitor312limits the current supplied to the ultraviolet lamp60from the secondary coil52by changing the reflected impedance of the ultraviolet lamp60through the inductive coupler270(seeFIG. 5) of the series resonant tank circuit150. As is apparent, by selecting the value of capacitor312in view of the impedance of the ultraviolet lamp60and the secondary coil52, the ultraviolet lamp assembly14may be impedance matched with the power source (the series tank circuit150). In addition, the ultraviolet lamp assembly14may be tuned to resonate at a frequency similar to the resonant frequency of the series resonant tank circuit150, thereby optimizing coupling and minimizing reflected power.

The starter circuit314is designed to short filaments304,306during start-up, thereby causing maximum preheat of the bulbs300,302. This allows the ultraviolet lamp60to strike maximum dispersion of the mercury in bulbs300,302, thereby causing maximum intensity and delivering the highest dose of ultraviolet light to the water as it passes through the ultraviolet lamp assembly14. In other words, the starter circuit314is designed so that the ultraviolet lamp60instantly turns on at maximum intensity. The placement of mercury in bulbs300,302is important for maximum output. When the mercury condenses within the plasma path, the mercury is dispensed more evenly throughout bulbs300,302. The faster dispersion also allows quicker peak intensity, thereby providing the ability to give the flow of water a faster, more intense dose of ultraviolet light at start-up. As is apparent, the shorting of the starter circuit314allows maximum power transfer while maintaining optimum power transfer efficiency since impedance matching remains in place. It is further apparent from the foregoing discussion that the air gap functions to provide current limiting during startup while still providing sufficient power transfer to the secondary coil to almost instantly start the ultraviolet light60at maximum intensity.

Referring toFIG. 2B, the O-ring62acts as a heat sink and is purposefully placed between the path of water, which flows through the pair of quartz tubes58, and the ultraviolet lamp60plasma path to allow the mercury to condense within the plasma path for improved instant ultraviolet light output. Referring again toFIG. 6, as the ultraviolet lamp60is energized, the full-circuit voltage potential is applied across capacitor312, filaments304,306and the starter circuit314. Because of the low impedance value of the filaments304,306and the starter circuit314, which acts as a short at start-up, the current is high for maximum preheat of the ultraviolet lamp60. This causes the preheat of the ultraviolet lamp60to disperse some initial mercury at start-up. When the starter circuit314heats up, the starter circuit314RC time constant releases the shorting device, which is the triac332(FIG. 7) in one embodiment, thereby providing full voltage across the filaments304,306. In other embodiments, the shorting device may be other mechanisms such as, for example, electromagnetically controlled reed switches, an optically controlled triac and/or any other device capable of moving between a contacting and non-contacting state. In addition, the shorting device may be controlled by an external control mechanism such as, for example, electromagnet control signals, radio frequency control signals, optical control signals or any other mechanism capable of communicating some form of signal to the shorting device absent conductors therebetween. The starter circuit314allows a better start than a thermister because thermisters consume more energy after opening and do not open as quickly. In addition, as is apparent, operation of the starter circuit314occurs in a stand-alone fashion without external control wires or other features that may compromise water tightness and/or replacement ability of the ultraviolet light assembly14.

Referring toFIG. 8, one radio frequency identification system124is illustrated electrically connected with the control unit102. The radio frequency identification system124uses a base station to communicate with the ultraviolet light radio frequency identification transponder126and the filter radio frequency identification transponder128. The radio frequency identification system124allows contactless reading and writing of data, which is transmitted bidirectionally between the base station360and the transponders126,128. In one embodiment, the radio frequency identification system124is manufactured by TEMIC Semiconductors under model number TR5551A-PP.

The radio identification system124is used by the control unit102to keep track of information specific to each ultraviolet lamp assembly14and filter assembly16. As previously set forth, the ultraviolet lamp assembly14and the filter assembly16are both designed to be readily replaceable. Since the ultraviolet light radio frequency identification transponder126and the filter radio frequency transponder128are located in the ultraviolet lamp assembly14or the filter assembly16, these devices are never separated, which allows the control unit102to read and write information to and from the transponders126,128through the base station360.

Referring once again toFIG. 8, the ultraviolet light radio frequency identification transponder126includes a transponder antenna362and a read/write IDIC® (e5551) chip364. The read/write IDIC® (e5551) chip further includes an EEPROM device366that physically stores the relevant information for each respective ultraviolet lamp assembly14in memory locations. In the illustrated embodiment, the information consists of an ultraviolet lamp serial number, ultraviolet lamp start limit, ultraviolet lamp on-time limit, ultraviolet lamp install time limit, ultraviolet lamp cycle on-time, cycle mode low temperature, minimum ultraviolet lamp on-time, ultraviolet lamp high-mode time and ultraviolet lamp preheat time. In addition, the EEPROM device366in the ultraviolet light radio frequency identification transponder126allows the control unit102to keep track of ultraviolet lamp install time, ultraviolet lamp powered time, ultraviolet lamp starts and total ultraviolet lamp cold starts.

The ultraviolet lamp serial number is unique to each ultraviolet lamp assembly14and allows the control unit102of the water treatment system10to keep track of which ultraviolet lamp assemblies14have been installed in the water treatment system10. The ultraviolet lamp start limit relates to the maximum allowed number of ultraviolet lamp starts and the ultraviolet lamp on-time limit relates to the maximum allowed installation time for the ultraviolet lamp60. The ultraviolet lamp install time limit relates to the maximum allowable installation time for the ultraviolet lamp assembly14and the ultraviolet lamp cycle on-time relates to the minimum amount of time the ultraviolet lamp60needs to be energized in low-temperature mode. The cycle mode low-temperature information relates to the temperature value to which the water treatment system10switches to low-temperature mode and the minimum ultraviolet lamp on-time relates to the minimum amount of time the ultraviolet lamp60must remain energized. The ultraviolet lamp high-mode time information relates to the amount of time the ultraviolet lamp60operates in high mode and the ultraviolet lamp preheat time relates to the amount of time the ultraviolet lamp60needs to be preheated.

As previously set forth, the EEPROM device366in the ultraviolet light radio frequency identification transponder126is also capable of keeping track of the ultraviolet lamp install time. This information tracks the number of hours that the current ultraviolet lamp60has been plugged into the water treatment system10. In one embodiment, for every minute the ultraviolet lamp60is plugged into the water treatment system10, one minute is added to the total. The EEPROM device366also keeps track of the ultraviolet lamp powered time and the total ultraviolet lamp powered time. The ultraviolet lamp powered time and the total ultraviolet lamp powered time keeps track of the amount of time the ultraviolet lamp60has been on so that the control unit102can determine if a new ultraviolet lamp assembly14needs installed. The ultraviolet lamp starts memory location stores the number of times the ultraviolet lamp60has been started, so that the control unit102can use this information to determine the end of life of the ultraviolet lamp60. The total ultraviolet lamp cold-starts memory location tracks the number of times the ultraviolet lamp60has been started when the ambient temperature sensor114indicates that the temperature is below a predetermined threshold value.

Referring once again toFIG. 8, the filter radio frequency identification transponder128includes a transponder antenna368and a read/write IDIC® (e5551) chip370. The read/write IDIC® (e5551) chip370further includes an EEPROM device372that physically stores the relevant information for each respective filter assembly16in memory locations. In the described embodiment, the relevant information consists of a filter assembly serial number, a filter assembly volume limit, a filter assembly install time limit, and a plugged filter assembly threshold percent.

The filter assembly serial number is used for unique identification of different filter assemblies16so that the control unit102can monitor which filter assemblies16have been installed in the water treatment system10. The filter assembly volume limit is associated with the volume of water the filter assembly is designed to filter before reaching the end of its useful life. The filter assembly install time limit is used by the control unit102to compute the remaining life of the filter assembly16based on a predetermined allowable wet time. The plugged filter assembly threshold percent contains the maximum allowable percentage of flow reduction for the filter assembly16before it needs replaced. This maintains the percent of degradation of the filter assembly16before a plugged filter assembly16error is initiated by the control unit102.

The radio frequency identification system124includes the base station360, a coil380, a plurality of diodes382,384,386,388,390,392,394, a plurality of resistors396,398,400,402,404,406,408,410,412,414,416,418,420and a plurality of capacitors422,424,426,428,430,432,434,436that are electrically connected as illustrated inFIG. 8. Those skilled in the art would recognize that the connection of the aforementioned components is well known to those skilled in the art. The radio frequency identification system124has been installed in the water treatment system10using specifications set forth for the TK5551A-PP, which, as previously set forth, is manufactured by TEMIC Semiconductors. For the purpose of the present invention, it is important to note that the base station360uses the coil380for bidirectional communication with the ultraviolet light radio frequency identification transponder126and the filter radio frequency identification transponder128.

The control unit102is electrically connected with the base station360so that the control unit102can communicate with the base station360. As such, the control unit102is capable of reading and writing information to and from the ultraviolet light radio frequency identification transponder126and the filter radio frequency identification transponder128through the base station360by using the coil380. The radio frequency identification system124is connected with the first DC power source180and the second DC power source184as illustrated inFIG. 8, which provides the radio frequency identification system124with energy to function during operation.

Those skilled in the art would recognize that other identification systems could be used with the present invention, such as contact-type identification systems. However, the illustrated embodiment of the invention uses a radio frequency identification system124because of the inherent benefits such a system provides.

Referring toFIG. 9, the flow sensor circuit104is connected with the control unit102to provide electrical signals to the control unit102indicating that water is flowing through the water treatment system10. The flow sensor circuit104includes a flow sensor440, a plurality of capacitors442,444and a resistor446. The flow sensor is manufactured by Allegro under model number 3134. Capacitor442is connected with the flow sensor440, the first DC power source180and the second DC power source184. The output of the flow sensor440is connected with the parallel combination of resistor446and capacitor444, before being connected with the control unit102. Resistor446and capacitor444are also connected with the second DC power source184. During operation, the flow sensor440delivers electrical signals to the control unit102, which indicates that water is flowing in the water treatment system10, thereby causing the control unit102to instantaneously energize the ultraviolet lamp60. Those skilled in the art would recognize that several variations exist on the disclosed flow sensor circuit104and that the disclosed flow sensor circuit104is provided by way of example only and should be not construed as a limitation of the present invention.

Referring toFIG. 10, the ambient light sensor circuit108comprises a photosensitive diode450, an operational amplifier452, a plurality of resistors454,456,458,460, a diode462and a capacitor464electrically connected as illustrated. For purposes of the present invention, it is sufficient to note that the photosensitive diode450provides electrical signals to the negative input of the operational amplifier452, which, in turn, conditions the signal for the control unit102. The ambient light sensor circuit108is powered by the first DC power source180and the second DC power source184.10. Those skilled in the art would recognize that several variations exist on the design of ambient light sensor circuits108and that the illustrated embodiment should not be construed as a limitation on the present invention.

Referring toFIG. 11, as previously set forth, the visible light sensor circuit110is connected with the control unit102to provide electrical signals to the control unit102corresponding to the intensity of the ultraviolet lamp60during operation. In one embodiment, the visible light sensor circuit110comprises a photosensitive resistor470, an operational amplifier472, a diode474, a plurality of resistors476,478,480,482,484,486and a capacitor488electrically connected as depicted inFIG. 11. In addition, the visible light sensor circuit110is powered by the first DC power source180and the second DC power source184. Those skilled in the art would recognize that the visible light sensor circuit110takes the electrical signal generated by the photosensitive resistor470and amplifies it with the operational amplifier472, before being directed to the control unit102. Further, those skilled in the art would recognize that the design of visible light sensor circuits110can vary and that the disclosed ultraviolet light sensor circuit110is by way of example only and should not be construed as a limitation of the present invention.

Referring toFIG. 12, as previously set forth, one ambient temperature sensor circuit114is connected with the control unit102to provide the control unit102with electrical signals that change with corresponding changes in the ambient temperature. The ambient temperature sensor circuit114comprises a thermistor490, an operational amplifier492, a plurality of resistors494,496,498and a capacitor500that are electrically connected as illustrated inFIG. 12. During operation, the voltage drop across thermistor490changes as the ambient temperature changes, thereby causing the electrical signal that is sent from the output of the operational amplifier492to the control unit102to either increase or decrease. Those skilled in the art would recognize that the design of ambient temperature sensor circuits114can vary. One ambient temperature sensor circuit114illustrated inFIG. 12is by way of example only and should not be construed as a limitation of the present invention.

Referring toFIG. 13, as previously set forth, one audio generation circuit116is connected with the control unit102for generating audible enunciations in response to predetermined system states. One audio generation circuit116comprises a piezoelectric element510, a plurality of transistors512,514,516, a plurality of resistors518,520,522,524,526,528,530,532,534, a plurality of capacitors536,538and a diode540, which are electrically connected as depicted inFIG. 13. As readily apparent to those skilled in the art, the control unit102is capable of energizing the piezoelectric element510, thereby causing the piezoelectric element510to generate audible tones through vibrations. Those skilled in the art would recognize that several devices and circuits exist that are capable of generating audible tones. The presently disclosed audio generation circuit116is by way of example only and likewise should not be construed as a limitation of the present invention.

Referring toFIG. 14, as previously set forth, the communications port120is connected with the control unit102. The communications port120is used by the control unit102to communicate bidirectionally with a peripheral device (not shown), such as a personal computer or a hand-held device. In one embodiment, the communications port120comprises a plurality of zenar diodes550,552,554and a plurality of resistors556,558,560,562,562,566,568,570, which are electrically connected as illustrated inFIG. 14. The first DC power source180and the second DC power source184provide power to the communications port120. The communications port120is designed to use the RS-232 communications standard, as well known in the art. A port connector572is provided so that the peripheral device can be connected with the communications port120. Those skilled in the art would recognize that different types of communication ports may be used and are beyond the scope of the present invention. To that end, one communications port120disclosed herein is by way of example only and should not be construed as a limitation of the present invention.

In one embodiment, the ballast circuit103also includes a current limit circuit700designed to monitor the current produce by the circuit, and shut the circuit down when it falls outside of desired parameters. The current limit circuit700can be configured to disable the ballast circuit103when a current threshold is exceeded (i.e. an upper limit) or when the current falls outside of a range (i.e. both upper and lower limits). Upper and lower limits are particularly useful in applications where low current and unstable operation can damage the load, for example, in lighting applications where a dimming function is achieved by increasing the air gap between the primary coil and the secondary coil.

One embodiment of the current limit circuit700is shown inFIG. 16. The current limit circuit700includes a current sensing transformer702that produces current proportional to the flow of current to the primary coil270. The current transformer702is preferably created by forming a coil of wire around the core of the current sensing transformer232of the current sensing circuit218. The current from the current transformer702develops a voltage across resistor704. Another resistor706is tied to the input voltage of ballast circuit. The relationship to the input voltage causes the level to shift as the input voltage shifts. This permits the current transformer702to track the real performance even as input voltage shifts. Resistor708allows a voltage bias from ground that helps to raise the variable current transformer voltage to a level detectable by the operational amplifier710. Resistors712is connected between voltage source184and the positive input of operational amplifier710. Resistor714is connected between ground connection182and the positive input of operational amplifier710. Resistors712and714establish a limit or threshold to set the operating and non-operating modes. Resistor716is connected between the current transformer70and the negative input lead of operational amplifier710to prevent the operational amplifier710from drawing too much current from the current transformer102. The output of the operational amplifier702is connected to integrated circuit720, which is preferably a conventional latch or flip-flop, such as IC 14044. When the output from the operational amplifier702is driven high, the latch is triggered, thereby latching the disable signal. The integrated circuit720preferably maintains the ballast circuit103in the disabled condition until the manual reset switch722is pressed or otherwise actuated. Alternatively, the reset switch722can be replaced by a timer circuit (not shown) that resets the current limit circuit700after a defined period of time. The current limit circuit700may also include a test circuit724that permits testing of the operation of the current limit circuit700. The test circuit724is connected to power source184and includes resistor726and switch728. When switch728is depressed or otherwise actuated, current in excess of the threshold is applied to the operational amplifier710. If operating properly, this current will cause the current limit circuit700to disable the ballast circuit103.

As an alternative, the current from the current transformer702can be monitored by a microprocessor that is programmed to disable the ballast circuit when the current exceeds the desired threshold or falls outside of the desired range. In some applications, however, the microprocessor may not provide sufficient speed to provide acceptable response times. Accordingly, the hardware embodiment described may be preferable in some application.

While the invention has been described in its currently best known modes of operation and embodiments, other modes and embodiments of the invention will be apparent to those skilled in the art and are contemplated. In addition, although one embodiment of the present invention is directed to a water treatment system10, those skilled in the art would recognize that the present invention may be readily incorporated in several different types of fluid treatment systems.