Patent Application
20100060187
1. Field of the Invention
The present invention relates to light sources, and more specifically, to a hybrid light source having a high-efficiency lamp, a low-efficiency lamp, and drive circuits for controlling the amount of power delivered to each of the lamps.
2. Description of the Related Art
In order to reduce energy consumption, the use of high-efficiency light sources (e.g., high-efficacy light sources) is increasing, while the use of low-efficiency light sources (e.g., low-efficacy light sources) is decreasing. High-efficiency light sources may comprise high-efficacy lamps, for example, gas discharge lamps (such as compact fluorescent lamps), phosphor-based lamps, high-intensity discharge (HID) lamps, and light-emitting diode (LED) light sources. Low-efficiency light sources may comprise low-efficacy lamps, for example, black body radiators, such as incandescent lamps or halogen lamps. Both high efficiency and low-efficiency light sources can be dimmed, but the dimming characteristics of these two types of light sources typically differ. A low-efficiency light source can usually be dimmed to very low light output levels, typically below 1% of the maximum light output. However, a high-efficiency light source cannot be typically dimmed to very low output levels.
Further, high-efficiency and low-efficiency light sources typically provide different color rendering indexes and correlated color temperatures as the light sources are dimmed. A lower color temperature correlates to a color shift towards the red portion of the color spectrum which creates a warmer effect to the human eye.
“Color rendering” represents the ability of a light source to reveal the true color of an object. The color rendering index (CRI) is a scale used to evaluate the capability of a lamp to replicate colors accurately as compared to a black body radiator. The greater the CRI, the more closely a lamp source matches the capability of a black body radiator. Typically, low-efficiency light sources, such as incandescent lamps, have high quality color rendering, and thus, have a CRI of one hundred, whereas some high-efficiency light sources, such as fluorescent lamps, have a CRI of eighty as they do not provide as high quality color rendering as compared to low-efficiency light sources.
Generally, many people have grown accustomed to the dimming performance and operation of low-efficiency light sources. As more people begin using high-efficiency light sources—typically to save energy—they are somewhat dissatisfied with the overall performance of the high-efficiency light sources. Thus, it would be desirable to provide a light source that saves energy (like a fluorescent lamp), but provides a broad dimming range and pleasing light color across the dimming range (light an incandescent lamp).
According to a first embodiment of the present invention, a hybrid light source is characterized by a decreasing color temperature as a total light intensity of the hybrid light source is controlled near a low-end intensity. The hybrid light source is adapted to receive power from an AC power source and to produce a total light intensity, which is controlled throughout a dimming range from a low-end intensity and high-end intensity. The hybrid light source comprises a high-efficiency light source circuit having a high-efficiency lamp for producing a percentage of the total light intensity, and a low-efficiency light source circuit having a low-efficiency lamp for producing a percentage of the total light intensity. A control circuit is coupled to both the high-efficiency light source circuit and the low-efficiency light source circuit for individually controlling the amount of power delivered to each of the high-efficiency lamp and the low-efficiency lamp, such that the total light intensity of the hybrid light source ranges throughout the dimming range. The percentage of the total light intensity produced by the high-efficiency lamp is greater than the percentage of the total light intensity produced by the low-efficiency lamp when the total light intensity is near the high-end intensity. The percentage of the total light output produced by the high-efficiency lamp decreases and the percentage of the total light intensity produced by the low-efficiency lamp increases as the total light intensity is decreased below the high-end intensity. The control circuit turns off the high-efficiency lamp is turned off when the total light intensity is below a transition intensity, such that the low-efficiency lamp produces all of the total light intensity of the hybrid light source when the total light intensity is below the transition intensity.
In addition, a method of illuminating a light source to produce a total light intensity throughout a dimming range from a low-end intensity and high-end intensity is described herein. The method comprising the steps of: (1) illuminating a high-efficiency lamp to produce a percentage of the total light intensity; (2) illuminating a low-efficiency lamp to produce a percentage of the total light intensity; (3) enclosing the high-efficiency lamp and the low-efficiency lamp together in a housing; (4) individually controlling the amount of power delivered to each of the high-efficiency lamp and the low-efficiency lamp, such that the total light intensity of the hybrid light source ranges throughout the dimming range; (5) controlling the high-efficiency lamp and the low-efficiency lamp near the high-end intensity, such that first percentage of the total light intensity produced by the high-efficiency lamp is greater than the second percentage of the total light intensity produced by the low-efficiency lamp when the total light intensity; (6) decreasing the first percentage of the total light intensity produced by the high-efficiency lamp as the total light intensity decreases; (7) increasing the second percentage of the total light intensity produced by the low-efficiency lamp as the total light intensity decreases; (8) turning off the high-efficiency lamp when the total light intensity is below a transition intensity; and (9) controlling the low-efficiency lamp such that the low-efficiency lamp produces all of the total light intensity of the hybrid light source when the total light intensity is below the transition intensity.
According to another embodiment of the present invention, a dimmable hybrid lamp comprises a high-efficiency dimmable lamp, a low-efficiency dimmable lamp, and a common control means coupled to each of the dimmable lamps and operable to simultaneously dim the dimmable lamps from their respective minimum intensities to maximum intensities to control a total light intensity of the hybrid lamp from a low-end intensity to a high-end intensity across a dimming range. Only the low-efficiency lamp is turned on when the total light intensity is less than a transition intensity. The high-efficiency lamp is only turned on when the total light intensity is above the transition intensity, whereby the low-efficiency lamp turns on before the high-efficiency lamp turns on as the hybrid lamp is dimmed from the low-end intensity to the high-end intensity.
In addition, a lighting control system comprising a dimmable hybrid lamp and a dimmer switch coupled to the dimmable hybrid lamp is also described herein. The dimmable hybrid lamp includes a high-efficiency lamp and a dimmable ballast therefor, a low-efficiency lamp and a dimmable drive circuit therefor, and a common support for the high-efficiency lamp and the low-efficiency lamp. The high-efficiency lamp extends from the common support and spaced around a common central axis expending from the common support. The hybrid lamp comprises a tube having one end fixed to the common support and extending co-axially with the common axis to the low-efficiency lamp. The ballast and the drive circuit are supported within the common support. The hybrid lamp further includes a control circuit coupled to the dimmable ballast and the drive circuit for simultaneously adjusting the intensities of the high-efficiency and low-efficiency lamps between a low-end intensity and a high-end intensity across a dimming range of the hybrid lamp. The control circuit is responsive to the dimmer control to control the dimmable ballast for the high-efficiency lamp and the dimmable drive circuit for the low-efficiency lamp for simultaneously adjusting the intensities of the high-efficiency and low-efficiency lamps, respectively.
According to another embodiment of the present invention, a dimmable hybrid lamp comprises: (1) a high-efficiency lamp including at least first and second U-shaped gas filled tubes; (2) a low-efficiency lamp; (3) a common support for the high-efficiency lamp and the low-efficiency lamp having the first and second U-shaped gas-filled tubes of the high-efficiency lamp extending from the common support and spaced around a central axis extending from the common support; (4) a post having one end fixed to the common support and extending co-axially with the common axis to the low-efficiency lamp; (5) a dimmable ballast circuit for the high-efficiency lamp, the ballast circuit housed within the common support; (6) a dimmable drive circuit for the low-efficiency lamp, the drive circuit housed within the common support; and (7) a control circuit coupled to the ballast circuit and the drive circuit for simultaneously adjusting the intensities of the high-efficiency and low-efficiency lamps between a low-end intensity and a high-end intensity across a dimming range of the hybrid lamp.
Additionally, a process of dimming a hybrid lamp comprises the steps of: (1) positioning a low-efficiency lamp in close proximity to a high-efficiency lamp; (2) continuously dimming a high-efficiency gas discharge lamp from a first minimum intensity to a first maximum intensity; (3) dimming the low-efficiency lamp from a second minimum intensity to a second maximum intensity which is lower the first minimum intensity of the high-efficiency lamp; and (4) simultaneous controlling both of the lamps to control a light output of the hybrid lamp from a low-end intensity to a high-end intensity, such that the light output of the hybrid lamp has a red color shift as the hybrid lamp is dimmed toward the low-end intensity.
According to another aspect of the present invention, a hybrid light source comprises two input terminals adapted to be operatively coupled to the AC power source, a high-efficiency light source circuit having a high-efficiency lamp, and a low-efficiency light source circuit having a low-efficiency lamp, and is characterized by a low impedance throughout the length of each half-cycle of the AC power source. The high-efficiency and low-efficiency light source circuits draw current from the AC power source through the input terminals for powering the respective lamps. The hybrid light source comprises a control circuit coupled to both the high-efficiency light source circuit and the low-efficiency light source circuit for individually controlling the amount of power delivered to each of the high-efficiency lamp and the low-efficiency lamp, such that a total light output of the hybrid light source ranges throughout a dimming range from a minimum total intensity to a maximum total intensity, and the hybrid light source provides the low impedance throughout the length of each half-cycle of the AC power source.
In addition, a dimmable hybrid light source adapted to receive a phase-controlled voltage is described herein. The dimmable hybrid light source comprises two input terminals adapted to receive the phase-controlled voltage, a full-wave rectifier circuit coupled between the input terminals and generating a rectified voltage at output terminals, a high-efficiency light source circuit coupled to the output terminals of the rectifier circuit and having a high-efficiency lamp, a low-efficiency light source circuit coupled to the output terminals of the rectifier circuit and having a low-efficiency lamp, a zero-crossing detect circuit operatively coupled between the input terminals, and a control circuit coupled to both the high-efficiency light source circuit and the low-efficiency light source circuit for individually controlling the amount of power delivered to each of the high-efficiency lamp and the low-efficiency lamp in response to the zero-crossing detect circuit, such that a total light output of the hybrid light source ranges from a minimum total intensity to a maximum total intensity. The low-efficiency light source circuit comprises a semiconductor switch coupled in series electrical connection with the low-efficiency lamp, where the series combination of the semiconductor switch and the rectifier circuit is coupled between the output terminals of the rectifier circuit. The zero-crossing detect circuit detects when the magnitude of the phase-controlled voltage becomes greater than a predetermined zero-crossing threshold voltage each half-cycle of the phase-controlled voltage.
According to an embodiment of the present invention, the control circuit is operable to turn off the high-efficiency lamp when the total light intensity is below a transition intensity, such that the low-efficiency lamp produces all of the total light intensity of the hybrid light source when the total light intensity is below the transition intensity. The control circuit is operable to control the amount of power delivered to the low-efficiency lamp to be greater than a minimum power level when the total light intensity is above the transition intensity. The control circuit controls the amount of power delivered to the low-efficiency lamp to the minimum power level when the total light intensity of the hybrid light source is at the maximum intensity. According to another embodiment of the present invention, the semiconductor switch is rendered conductive when the phase-controlled voltage across the hybrid light source is approximately zero volts.
A lighting control system receiving power from an AC power source is also described herein. The lighting control system comprises a hybrid light source comprising a high-efficiency light source circuit having a high-efficiency lamp and a low-efficiency light source circuit having a low-efficiency lamp. The hybrid light source is adapted to be coupled to the AC power source and to individually control the amount of power delivered to each of the high-efficiency lamp and the low-efficiency lamp. The lighting control system further comprises a dimmer switch comprising a bidirectional semiconductor switch adapted to be coupled in series electrical connection between the AC power source and the hybrid light source. The bidirectional semiconductor switch is operable to be rendered conductive for a conduction period each half-cycle of the AC power source, such that the hybrid light source is operable to control the amount of power delivered to each of the high-efficiency lamp and the low-efficiency lamp in response to the conduction period of the bidirectional semiconductor switch.
According to an embodiment of the present invention, the dimmer switch further comprises a power supply coupled in parallel electrical connection with the bidirectional semiconductor switch and operable to conduct a charging current through the hybrid light source when the bidirectional semiconductor switch is non-conductive. The low-efficiency light source circuit of the hybrid light source is operable to conduct the charging current when the bidirectional semiconductor switch is non-conductive. According to another embodiment of the present invention, the bidirectional semiconductor switch comprises a thyristor, and the low-efficiency light source circuit of the hybrid light source provides a path for enough current to flow from the AC power source through the hybrid light source, such that the magnitude of the current exceeds a rated holding current of the thyristor of the dimmer switch after the thyristor is rendered conductive. According to another embodiment of the present invention, the dimmer switch comprises a timing circuit coupled in parallel electrical connection with the bidirectional semiconductor switch and operable to conduct a timing current through the hybrid light source when the bidirectional semiconductor switch is non-conductive, wherein the low-efficiency light source circuit of the hybrid light source conducts the timing current when the bidirectional semiconductor switch is non-conductive.
Additionally, a method of illuminating a light source in response to a phase-controlled voltage from a dimmer switch is also described. The dimmer switch is coupled in series electrical connection with an AC power source and the light source and comprises a bidirectional semiconductor switch for generating the phase-controlled voltage and a power supply operable to conduct a charging current through from the AC power source through the light source when the bidirectional semiconductor switch is non-conductive. The method comprises the steps of: (1) enclosing the high-efficiency lamp and the low-efficiency lamp together in a translucent housing; (2) individually controlling the amount of power delivered to each of the high-efficiency lamp and the low-efficiency lamp in response to the phase-controlled voltage; and (3) conducting the charging current through the low-efficiency lamp when the bidirectional semiconductor switch is non-conductive.
According to yet another embodiment of the present invention, a method of illuminating a light source in response to a phase-controlled voltage from a dimmer switch having a thyristor for generating the phase-controlled voltage is presented. The dimmer switch is coupled in series electrical connection with between an AC power source and the light source and the thyristor is characterized by a rated latching current and a rated holding current. The method comprising the steps of: (1) enclosing the high-efficiency lamp and the low-efficiency lamp together in a translucent housing; (2) individually controlling the amount of power delivered to each of the high-efficiency lamp and the low-efficiency lamp in response to the phase-controlled voltage; and (3) conducting enough current from the AC power source and through bidirectional semiconductor switch of the dimmer and the low-efficiency lamp to exceed the rated latching current and the rated holding current of the thyristor of the dimmer switch.
According to another aspect of the present invention, a hybrid light source adapted to receive power from an AC power source has a monotonically decreasing power consumption as the total light intensity decreases from a maximum total intensity to a minimum total intensity. The hybrid light source comprises two input terminals adapted to be operatively coupled to the AC power source, a high-efficiency light source circuit having a high-efficiency lamp, a low-efficiency light source circuit having a low-efficiency lamp, and a control circuit coupled to both the high-efficiency light source circuit and the low-efficiency light source circuit. The high-efficiency and low-efficiency light source circuits draw current from the AC power source through the input terminals for powering the respective lamps. The control circuit individually controls the amount of power delivered to each of the high-efficiency lamp and the low-efficiency lamp, such that a total light output of the hybrid light source ranges from a minimum total intensity to a maximum total intensity and the hybrid light source has a monotonically decreasing power consumption as the total light intensity decreases from the maximum total intensity to the minimum total intensity.
Other features and advantages of the present invention will become apparent from the following description of the invention that refers to the accompanying drawings.
The foregoing summary, as well as the following detailed description of the preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purposes of illustrating the invention, there is shown in the drawings an embodiment that is presently preferred, in which like numerals represent similar parts throughout the several views of the drawings, it being understood, however, that the invention is not limited to the specific methods and instrumentalities disclosed.
The dimmer switch 104 typically includes a bidirectional semiconductor switch 105B, such as, for example, a thyristor (such as a triac) or two field-effect transistors (FETs) coupled in anti-series connection, for providing a phase-controlled voltage VPC (i.e., a dimmed-hot voltage) to the hybrid light source 100. Using a standard forward phase-control dimming technique, a control circuit 105C renders the bidirectional semiconductor switch 105B conductive at a specific time each half-cycle of the AC power source, such that the bidirectional semiconductor switch remains conductive for a conduction period TCON during each half-cycle (as shown in
The high-efficiency lamp (i.e., the fluorescent lamp 106) has a greater efficacy than the low-efficiency lamp (i.e., the halogen lamp 108). For example, the fluorescent lamp 106 may be typically characterized by an efficacy greater than approximately 60 lm/W, while the halogen lamp 108 may be typically characterized by an efficacy less than approximately 30 lm/W. The present invention is not limited to high-efficiency and low-efficiency lamps having the efficacies stated above, since improvements in technology in the future could provide high-efficiency and low-efficiency lamps having higher efficacies.
The hybrid light source 100 further comprises a screw-in Edison base 110 for connection to a standard Edison socket, such that the hybrid light source may be coupled to the AC power source 102. The screw-in base 110 has two input terminals 110A, 110B (
The fluorescent lamp 106 and halogen lamp 108 may be surrounded by a housing comprising a glass light diffuser 114 and a fluorescent lamp reflector 115. Alternatively, the light diffuser 114 could be made of plastic or any suitable type of transparent, translucent, partially-transparent, or partially-translucent material, or no light diffuser could be provided. The fluorescent lamp reflector 115 directs the light emitted by the fluorescent lamp 106 away from the hybrid light source 100. The housing may be implemented as a single part with the light diffuser 114 and the light reflector 115.
As shown in
The hybrid light source 100 provides an improved color rendering index and correlated color temperature across the dimming range of the hybrid light source (particularly, near a low-end lighting intensity LLE) as compared to a stand-alone compact fluorescent lamp.
The hybrid light source 100 is further operable to control the fluorescent lamp 106 and the halogen lamp 108 to provide high-efficiency operation near the high-end intensity LHE.
Since the fluorescent lamp 106 cannot be dimmed to very low intensities without the use of more expensive and complex circuits, the fluorescent lamp 106 is controlled to be off at a transition intensity LTRAN, e.g., approximately 8% (as shown in
A control circuit 160 simultaneously controls the operation of the high-efficiency light source circuit 140 and the low-efficiency light source circuit 150 to thus control the amount of power delivered to each of the fluorescent lamp 106 and the halogen lamp 108. The control circuit 160 may comprise a microcontroller or any other suitable processing device, such as, for example, a programmable logic device (PLD), a microprocessor, or an application specific integrated circuit (ASIC). A power supply 162 generates a first direct-current (DC) supply voltage VCC1 (e.g., 5 VDC) referenced to a circuit common for powering the control circuit 160, and a second DC supply voltage VCC2 referenced to a rectifier DC common connection, which has a magnitude greater than the first DC supply voltage VCC1 (e.g., approximately 15 VDC) and is used by the low-efficiency light source circuit 150 (and other circuitry of the hybrid light source 100) as will be described in greater detail below.
The control circuit 160 is operable to determine the target total lighting intensity LTARGET for the hybrid light source 100 in response to a zero-crossing detect circuit 164. The zero-crossing detect circuit 164 provides a zero-crossing control signal VZC, representative of the zero-crossings of the phase-controlled voltage VPC, to the control circuit 160. A zero-crossing is defined as the time at which the phase-controlled voltage VPC changes from having a magnitude of substantially zero volts to having a magnitude greater than a predetermined zero-crossing threshold VTH-ZC (and vice versa) each half-cycle. Specifically, the zero-crossing detect circuit 164 compares the magnitude of the rectified voltage to the predetermined zero-crossing threshold VTH-ZC (e.g., approximately 20 V), and drives the zero-crossing control signal VZC high (i.e., to a logic high level, such as, approximately the DC supply voltage VCC1) when the magnitude of the rectified voltage VRECT is greater than the predetermined zero-crossing threshold VTH-ZC. Further, the zero-crossing detect circuit 164 drives the zero-crossing control signal VZC low (i.e., to a logic low level, such as, approximately circuit common) when the magnitude of the rectified voltage VRECT is less than the predetermined zero-crossing threshold VTH-ZC. The control circuit 160 determines the length of the conduction period TCON of the phase-controlled voltage VPC in response to the zero-crossing control signal VZC, and then determines the target lighting intensities for both the fluorescent lamp 106 and the halogen lamp 108 to produce the target total lighting intensity LTOTAL of the hybrid light source 100 in response to the conduction period TCON of the phase-controlled voltage VPC.
The low-efficiency light source circuit 150 comprises a halogen lamp drive circuit 152, which receives the rectified voltage VRECT and controls the amount of power delivered to the halogen lamp 108. The low-efficiency light source circuit 150 is coupled between the rectified voltage VRECT and the rectifier common connection (i.e., across the output of the front end circuit 130). The control circuit 160 is operable to control the intensity of the halogen lamp 108 to the target halogen lighting intensity corresponding to the present value of the target total lighting intensity LTOTAL of the hybrid light source 100, e.g., to the target halogen lighting intensity as shown in
The high-efficiency light source circuit 140 comprises a fluorescent drive circuit (e.g., a dimmable ballast circuit 142) for receiving the rectified voltage VRECT and for driving the fluorescent lamp 106. Specifically, the rectified voltage VRECT is coupled to a bus capacitor CBUS through a diode D144 for producing a substantially DC bus voltage VBUS across the bus capacitor CBUS. The negative terminal of the bus capacitor CBUS is coupled to the rectifier DC common. The ballast circuit 142 includes a power converter, e.g., an inverter circuit 145, for converting the DC bus voltage VBUS to a high-frequency square-wave voltage VSQ. The high-frequency square-wave voltage VSQ is characterized by an operating frequency fOP (and an operating period TOP=1/fOP). The ballast circuit 142 further comprises an output circuit, e.g., a “symmetric” resonant tank circuit 146, for filtering the square-wave voltage VSQ to produce a substantially sinusoidal high-frequency AC voltage VSIN, which is coupled to the electrodes of the fluorescent lamp 106. The inverter circuit 145 is coupled to the negative input of the DC bus capacitor CBUS via a sense resistor RSENSE. A sense voltage VSENSE (which is referenced to a circuit common connection as shown in
The high-efficiency lamp source circuit 140 further comprises a measurement circuit 148, which includes a lamp voltage measurement circuit 148A and a lamp current measurement circuit 148B. The lamp voltage measurement circuit 148A provides a lamp voltage control signal VLAMP
The control circuit 160 is operable to control the inverter circuit 145 of the ballast circuit 140 to control the intensity of the fluorescent lamp 106 to the target fluorescent lighting intensity corresponding to the present value of the target total lighting intensity LTOTAL of the hybrid light source 100, e.g., to the target fluorescent lighting intensity as shown in
The inverter circuit 145 further comprises first and second semiconductor switches, e.g., field-effect transistors (FETs) Q220, Q230, which are coupled between the terminal ends of the primary winding of the main transformer 210 and circuit common. The FETs Q220, Q230 have control inputs (i.e., gates), which are coupled to first and second gate drive circuits 222, 232, respectively, for rendering the FETs conductive and non-conductive. The gate drive circuits 222, 232 receive first and second FET drive signals VDRV
The push/pull converter of the ballast circuit 140 exhibits a partially self-oscillating behavior since the gate drive circuits 222, 232 are operable to control the operation of the FETs Q220, Q230 in response to control signals received from both the control circuit 160 and the main transformer 210. Specifically, the gate drive circuits 222, 232 are operable to turn on (i.e., render conductive) the FETs Q220, Q230 in response to the control signals from the drive windings 224, 234 of the main transformer 210, and to turn off (i.e., render non-conductive) the FETs in response to the control signals (i.e., the first and second FET drive signals VDRV
When the first FET Q220 is conductive, the terminal end of the primary winding connected to the first FET Q220 is electrically coupled to circuit common. Accordingly, the DC bus voltage VBUS is provided across one-half of the primary winding of the main transformer 210, such that the high-frequency square-wave voltage VSQ at the output of the inverter circuit 145 (i.e., across the primary winding of the main transformer 210) has a magnitude of approximately twice the bus voltage (i.e., 2·VBUS) with a positive voltage potential present from node B to node A as shown on
As shown in
The high-frequency square-wave voltage VSQ is provided to the resonant tank circuit 146, which draws a tank current ITANK from the inverter circuit 145. The resonant tank circuit 146 includes a “split” resonant inductor 240, which has first and second windings that are magnetically coupled together. The first winding is directly electrically coupled to node A at the output of the inverter circuit 145, while the second winding is directly electrically coupled to node B at the output of the inverter circuit. A “split” resonant capacitor (i.e., the series combination of two capacitors C250A, C250B) is coupled between the first and second windings of the split resonant inductor 240. The junction of the two capacitors C250A, 250B is coupled to the bus voltage VBUS, i.e., to the junction of the diode D144, the bus capacitor CBUS, and the center tap of the transformer 210. The split resonant inductor 240 and the capacitors C250A, C250B operate to filter the high-frequency square-wave voltage VSQ to produce the substantially sinusoidal voltage VSIN (between node X and node Y) for driving the fluorescent lamp 106. The sinusoidal voltage VSIN is coupled to the fluorescent lamp 106 through a DC-blocking capacitor C255, which prevents any DC lamp characteristics from adversely affecting the inverter.
The symmetric (or split) topology of the resonant tank circuit 146 minimizes the RFI noise produced at the electrodes of the fluorescent lamp 106. The first and second windings of the split resonant inductor 240 are each characterized by parasitic capacitances coupled between the leads of the windings. These parasitic capacitances form capacitive dividers with the capacitors C250A, C250B, such that the RFI noise generated by the high-frequency square-wave voltage VSQ of the inverter circuit 145 is attenuated at the output of the resonant tank circuit 146, thereby improving the RFI performance of the hybrid light source 100.
The first and second windings of the split resonant inductor 240 are also magnetically coupled to two filament windings 242, which are electrically coupled to the filaments of the fluorescent lamp 106. Before the fluorescent lamp 106 is turned on, the filaments of the fluorescent lamp must be heated in order to extend the life of the lamp. Specifically, during a preheat mode before striking the fluorescent lamp 106, the operating frequency fOP of the inverter circuit 145 is controlled to a preheat frequency fPRE, such that the magnitude of the voltage generated across the first and second windings of the split resonant inductor 240 is substantially greater than the magnitude of the voltage produced across the capacitors C250A, C250B. Accordingly, at this time, the filament windings 242 provide filament voltages to the filaments of the fluorescent lamp 106 for heating the filaments. After the filaments are heated appropriately, the operating frequency fOP of the inverter circuit 145 is controlled such that the magnitude of the voltage across the capacitors C250A, C250B increases until the fluorescent lamp 106 strikes and the lamp current ILAMP begins to flow through the lamp.
The measurement circuit 148 is electrically coupled to a first auxiliary winding 260 (which is magnetically coupled to the primary winding of the main transformer 210) and to a second auxiliary winding 262 (which is magnetically coupled to the first and second windings of the split resonant inductor 240). The voltage generated across the first auxiliary winding 260 is representative of the magnitude of the high-frequency square-wave voltage VSQ of the inverter circuit 145, while the voltage generated across the second auxiliary winding 262 is representative of the magnitude of the voltage across the first and second windings of the split resonant inductor 240. Since the magnitude of the lamp voltage VLAMP is approximately equal to the sum of the high-frequency square-wave voltage VSQ and the voltage across the first and second windings of the split resonant inductor 240, the measurement circuit 148 is operable to generate the lamp voltage control signal VLAMP
The high-frequency sinusoidal voltage VSIN generated by the resonant tank circuit 146 is coupled to the electrodes of the fluorescent lamp 106 via a current transformer 270. Specifically, the current transformer 270 has two primary windings which are coupled in series with each of the electrodes of the fluorescent lamp 106. The current transformer 270 also has two secondary windings 270A, 270B that are magnetically coupled to the two primary windings, and electrically coupled to the measurement circuit 148. The measurement circuit 148 is operable to generate the lamp current ILAMP control signal in response to the currents generated through the secondary windings 270A, 270B of the current transformer 270.
As previously mentioned, the first and second FETs Q220, Q230 are rendered conductive in response to the control signals provided from the first and second drive windings 224, 234 of the main transformer 210, respectively. The first and second gate drive circuits 222, 232 are operable to render the FETs Q220, Q230 non-conductive in response to the first and second FET drive signals VDRV
When the second FET Q230 is conductive, the tank current ITANK flows through a first half of the primary winding of the main transformer 210 to the resonant tank circuit 146 (i.e., from the bus capacitor CBUS to node A as shown in
When the first FET Q220 is conductive, the magnitude of the high-frequency square wave voltage VSQ is approximately twice the bus voltage VBUS as measured from node B to node A. As previously mentioned, the tank current ITANK flows through the second half of the primary winding of the main transformer 210, and the current IINV1 flows through the first half of the primary winding. The sense voltage VSENSE is generated across the sense resistor RSENSE and is representative of the magnitude of the inverter current IINV. Note that the sense voltage VSENSE is a negative voltage when the inverter current IINV flows through the sense resistor RSENSE in the direction of the inverter current IINV shown in
To turn off the first FET Q220, the control circuit 160 drives the first FET drive signal VDRV
The control circuit 160 drives the second FET drive signal VDRV
Specifically, the second FET Q230 is rendered conductive in response to the control signal provided from the second drive winding 234 of the main transformer 210 after the first and second FET drive signals VDRV
Since the square-wave voltage VSQ has a positive voltage potential from node A to node B, the body diode of the second FET Q230 eventually becomes non-conductive. The current IINV2 flows through the second half of the primary winding and through the drain-source connection of the second FET Q230. Accordingly, the polarity of the sense voltage VSENSE changes from positive to negative as shown in
During startup of the ballast 100, the control circuit 160 is operable to enable a current path to conduct a startup current ISTRT through the resistors R336, R337 of the second gate drive circuit 232. In response to the startup current ISTRT, the second FET Q230 is rendered conductive and the inverter current IINV1 begins to flow. The second gate drive circuit 232 comprises a PNP bipolar junction transistor Q340, which is operable to conduct the startup current ISTRT from the unregulated supply voltage VUNREG through a resistor R342 (e.g., having a resistance of 100Ω). The base of the transistor Q340 is coupled to the unregulated supply voltage VUNREG through a resistor R344 (e.g., having a resistance of 330Ω).
The control circuit 160 generates a FET enable control signal VDRV
Another NPN transistor Q352 is coupled to the base of the transistor Q346 for preventing the transistor Q346 from being rendered conductive when the first FET Q220 is conductive. The base of the transistor Q352 is coupled to the junction of the resistors R325, R326 and the transistor Q323 of the first gate drive circuit 222 through a resistor R354 (e.g., having a resistance of 10 kΩ). Accordingly, if the first drive winding 224 is conducting current through the diodes D324 to render the first FET Q220 conductive, the transistor Q340 is prevented from conducting the startup current ISTRT.
The halogen lamp drive circuit 152 receives a halogen lamp drive level control signal VDRV
The halogen lamp drive circuit 152 controls the amount of power delivered to the halogen lamp 108 using a semiconductor switch (e.g., a FET Q410), which is coupled in series electrical connection with the halogen lamp. A push-pull drive circuit (which includes an NPN bipolar junction transistor Q412 and a PNP bipolar junction transistor Q414) provides a gate voltage VGT to the gate of the FET Q410 via a resistor R416 (e.g., having a resistance of 10Ω). The FET Q410 is rendered conductive when the magnitude of the gate voltage VGT exceeds the specified gate voltage threshold of the FET. A zener diode Z418 is coupled between the base of the transistor 414 and the rectifier common connection and has a break-over voltage of, for example, 15V.
The halogen lamp drive circuit 152 comprises a comparator U420 that controls when the FET Q410 is rendered conductive. The output of the comparator U420 is coupled to the junction of the bases of the transistors Q412, Q414 of the push-pull drive circuit and is pulled up to the second DC supply voltage VCC2 via a resistor R422 (e.g., having a resistance of 4.7 kΩ). A halogen timing voltage VTIME
The halogen target threshold voltage VTRGT
When the halogen lamp drive level control signal VDRV
The halogen timing voltage VTIME
The halogen frequency control signal VFREQ
The base of the transistor Q442 is coupled to the collector of the transistor Q444 via a diode D454 and a resistor R456 (e.g., having a resistances of 33 kΩ). A diode D458 is coupled between the collector of the transistor Q442 and the collector of the transistor Q444. When the halogen frequency control signal VFREQ
The comparator U420 causes the push-pull drive circuit to generate the gate voltage VGT at the constant halogen lamp drive circuit operating frequency fHAL (defined by the halogen frequency control signal VFREQ
The low-efficiency light source circuit 150 is operable to provide a path for the charging current ICHRG of the power supply 105D of the dimmer switch 104 when the semiconductor switch 105B is non-conductive, and thus the zero-crossing control signal VZC is low. The zero-crossing control signal VZC is also provided to the halogen lamp drive circuit 150. Specifically, the zero-crossing control signal VZC is coupled to the base of an NPN bipolar junction transistor Q464 via a resistor R466 (e.g., having a resistance of 33 kΩ). The transistor Q464 is coupled in parallel with the transistor Q444, which is responsive to the halogen frequency control signal VFREQ
As previously mentioned, the bidirectional semiconductor 105B of the dimmer switch 104 may be a thyristor, such as, a triac or two silicon-controlled rectifier (SCRs) in anti-parallel connection. Thyristors are typically characterized by a rated latching current and a rated holding current. The current conducted through the main terminals of the thyristor must exceed the latching current for the thyristor to become fully conductive. The current conducted through the main terminals of the thyristor must remain above the holding current for the thyristor to remain in full conduction.
The control circuit 160 of the hybrid light source 100 controls the low-efficiency light source circuit 150, such that the low-efficiency light source circuit provides a path for enough current to flow to exceed the required latching current and holding current of the semiconductor switch 105B. To accomplish this feature, the control circuit 160 does not completely turn off the halogen lamp 108 at any points of the dimming range, specifically, at the high-end intensity LHE, where the fluorescent lamp 106 provides the majority of the total light intensity LTOTAL of the hybrid light source 100. At the high-end intensity LHE, the control circuit 160 controls the halogen target threshold voltage VTRGT
Accordingly, the hybrid light source 100 (specifically, the low-efficiency light source circuit 150) is characterized by a low impedance between the input terminals 110A, 110B during the length of the each half-cycle of the AC power source 102. Specifically, the impedance between the input terminals 110A, 110B (i.e., the impedance of the low-efficiency light source circuit 150) has an average magnitude that is substantially low, such that the current drawn through the impedance is not large enough to visually illuminate the halogen lamp 108 (when the semiconductor switch 105B of the dimmer switch 104 in non-conductive), but is great enough to exceed the rated latching current or the rated holding current of the thyristor in the dimmer switch 104, or to allow the timing current ITIM or the charging current ICHRG of the dimmer switch to flow. For example, the hybrid light source 100 may provide an impedance having an average magnitude of approximately 1.44 kΩ or less in series with the AC power source 102 and the dimmer switch 104 during the length of each half-cycle, such that the hybrid light source 100 appears like a 10-Watt incandescent lamp to the dimmer switch 104. Alternatively, the hybrid light source 100 may provide an impedance having an average magnitude of approximately 360Ω or less in series with the AC power source 102 and the dimmer switch 104 during the length of each half-cycle, such that the hybrid light source 100 appears like a 40-Watt incandescent lamp to the dimmer switch 104.
In
The target light intensity procedure 500 begins at step 510 in response to a rising edge of the zero-crossing control signal VZC, which signals that the phase-controlled voltage VPC has risen above the zero-crossing threshold VTH-ZC of the zero-crossing detect circuit 162. The present value of the timer is immediately stored in a register A at step 512. The control circuit 160 waits for a falling edge of the zero-crossing signal VZC at step 514 or for a timeout to expire at step 515. For example, the timeout may be the length of a half-cycle, i.e., approximately 8.33 msec if the AC power source operates at 60 Hz. If the timeout expires at step 515 before the control circuit 160 detects a rising edge of the zero-crossing signal VZC at step 514, the target light intensity procedure 500 simply exits. When a rising edge of the zero-crossing control signal VZC is detected at step 514 before the timeout expires at step 515, the control circuit 160 stores the present value of the timer in a register B at step 516. At step 518, the control circuit 160 determines the length of the conduction interval TCON by subtracting the timer value stored in register A from the timer value stored in register B.
Next, the control circuit 160 ensures that the measured conduction interval TCON is within predetermined limits. Specifically, if the conduction interval TCON is greater than a maximum conduction interval TMAX at step 520, the control circuit 160 sets the conduction interval TCON equal to the maximum conduction interval TMAX at step 522. If the conduction interval TCON is less than a minimum conduction interval TMIN at step 524, the control circuit 160 sets the conduction interval TCON equal to the minimum conduction interval TMIN at step 526.
At step 528, the control circuit 160 calculates a continuous average TAVG in response to the measured conduction interval TCON. For example, the control circuit 160 may calculate an N:1 continuous average TAVG using the following equation:
T
AVG=(N·TAVG+TCON)/(N+1). (Equation 1)
For example, N may equal 31, such that N+1 equals 32, which allows for easy processing of the division calculation by the control circuit 160. At step 530, the control circuit 160 determines the target total light intensity LTOTAL in response to the continuous average TAVG calculated at step 528, for example, by using a lookup table.
Next, the control circuit 160 appropriately controls the high-efficiency light source circuit 140 and the low-efficiency light source circuit 150 to produce the desired total light intensity LTOTAL of the hybrid light source 100 (i.e., as defined by the plot shown in
Referring to
If the target total light intensity LTOTAL is not greater than the transition intensity LTRAN plus the hysteresis offset LHYS at step 536, but is less than the transition intensity LTRAN minus the hysteresis offset LHYS at step 546, the control circuit 160 turns of the fluorescent lamp 106 and only controls the target halogen intensity of the halogen lamp 108. Specifically, if the fluorescent lamp 106 is on at step 548, the control circuit 160 turns the fluorescent lamp 106 off at step 550. The control circuit 160 generates the halogen lamp drive level control signal VDRV
If the target total light intensity LTOTAL is not greater than the transition intensity LTRAN plus the hysteresis offset LHYS at step 536, but is not less than the transition intensity LTRAN minus the hysteresis offset LHYS at step 546, the control circuit 160 is in the hysteresis range. Therefore, if the fluorescent lamp 106 is not on at step 554, the control circuit 160 simply generates the halogen lamp drive level control signal VDRV
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. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.
