Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/10—Controlling the intensity of the light
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/37—Converter circuits
  • H05B45/3725—Switched mode power supply [SMPS]
  • H05B45/385—Switched mode power supply [SMPS] using flyback topology
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
  • Y02B20/30—Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Definitions

• the present invention relates generally to electronic systems and more specifically to systems and methods related to input voltage sensing for a switching power converter and a triac-based dimmer.
• Electronic lighting devices such as light-emitting-diodes (LEDs) and compact fluorescent lamps (CFLs) provide more energy efficient light relative to incandescent light bulbs. Accordingly, the more efficient electronic lighting devices are increasingly replacing
• Triac alternating current
• a triac-based dimmer sets a dimming level by phase cutting an alternating current (AC) input voltage at a particular phase angle to decrease the average amount of power delivered to a load, such as lamp.
• AC alternating current
• Incandescent bulbs naturally respond to the phase cut input voltage by reducing their light output.
• Many electronic lighting devices such as LEDs and CFLs, are constant current devices, meaning that the electronic lighting devices have a particular brightness for a particular current value.
• lighting systems that include electronic lighting devices often utilize a controller to convert the input voltage into a voltage and current useable by the electronic lighting devices.
• the controller To respond to the dimming level set by the phase angle of phase cut input voltage, the controller ideally correctly detects the phase angl e of the phase cut voltage and regulates a voltage and current for the electronic light devices commensurate with the dimming level.
• phase cut angle of the input voltage has proved challenging, especially when attempting to retain the energy efficiency of the electronic lighting devices.
• a triac-based dimmer connects and disconnects the input voltage to a load onetime each during a single half-cycle of the input voltage.
• a triac-based dimmer tends to improperly connect and disconnect the input voltage to the electronic lighting device multiple times during a single half cycle of the input voltage. This oscillation occurs because once a triac begins conducting, the triac wi ll continue to conduct until current flowing through the triac falls below a hold current value.
• Electronic lighting devices often draw only 10% of the current drawn by an incandescent light bulb while producing an equivalent amount of light.
• the electronic lighting device may draw less than the hold current causing the triac to prematurely connect and disconnect the input voltage to the load during a phase cut when the triac should remain nonconductive. Additionally, some circuits can cause the triac to prematurely disconnect after the phase cut of the input voltage.
• Improper functioning of the triac-based dimmer can cause difficulties in detecting the zero crossings of the input voltage. Improper or non-detection of the zero crossings of the input voltage can be disruptive to the proper operation of the controller in controlling the electronic lighting devices.
• a method includes probing an output of a triode for alternating current ("triac")-based. dimmer every Nth half cycle of an alternating current (AC) output voltage of the dimmer to allow a controller of a lighting system to sense the output voltage from a time when the triac connects an input voltage source to an output of the dimmer until an occurrence of a predetermined event.
• N is an integer greater than 1 .
• a controller to control a switching power converter of a lighting system.
• the controller is capable to generate a control signal to control probing an output of a triode for alternating current ("triac") based dimmer every Nth half cycle of an alternating current (AC) output voltage of the dimmer to allow the controller to sense the output voltage from a time when the triac connects an input voltage source to an output of the dimmer until an occurrence of a predetermined event, N is an integer greater than 1.
• the controller is further capable to sense the output voltage from the time when the triac connects an input vol tage source to an output of the dimmer until an occurrence of a predetermined event.
• a method in a further embodiment of the present invention, includes discharging parasitic capacitors in a power and lighting control system to allow sensing of a dimmer output voltage of a dimmer that tracks an input voltage to the dimmer. The method further includes sensing the dimmer output voltage
• an apparatus in another embodiment, includes a parasitic discharge circuit coupled to a dimmer in a power and lighting control system.
• the parasitic discharge circuit is capable to discharge parasitic capacitors in the power and lighting control system to al low sensing of a dimmer output voltage of the dimmer that tracks an input voltage to the dimmer.
• Figure 1 is a block diagram depicting a power and lighting control system.
• Figure 2 is a signal waveform diagram illustrating various exemplary phases of operation of lighting circuits.
• Figure 3 is a simplified schematic diagram of a po was and lighting control system
• Figures 4A-4B are block diagrams of zero-cross determining circui ts that may be used in circuits of the lighting circuits of Figures 1 and 3.
• Figure 5 is a signal waveform diagram illustrating signals within a lighting circuit.
• Figure 6A is power and lighting control system that includes a dimmer output voltage probing circuit.
• Figure 7 depicts a power and lighting control system that includes a parasitic discharge circuit.
• Figure 8 depicts exemplary current and voltage waveforms associated with an exemplary operation of the power and lighting control system of Figure 7.
• An electronic lighting system and method described herein control energy provided to an electronic lighting device, such as one or more light-emitting diodes (LEDs) and/or compact fluorescent lamps (CFLs), of the electronic lighting system.
• a triac-based dimmer phase cuts an input voltage provided to the electronic lighting system.
• a control ler of the electronic lighting system utilizes a probing circuit to overcome idiosyncrasies of the triac-based dimmer to prevent the dimmer from prematurely disconnected and, thus, allowing the controller to sense a dimmer output voltage.
• the controller rather than probing each cycle of the output voltage of the triac-based dimmer, the controller periodically or intermittently probes the output voltage of the triac-based dimmer.
• energy supplied to the electronic lighting devices is varied in accordance with a dimming value determined from a phase cut angle of an alternating current (AC) input voltage.
• a triac-based dimmer connects and disconnects (or vice versa) the AC input voltage to the electronic lighting system .
• the electronic lighting system efficiently senses the input voltage while still achieving an efficient dimming operation.
• the electronic lighting system includes a switching power converter, a controller to control the switching power converter, and a load that includes one or more electronic lighting devices.
• the switching power converter can be any type of switching power converter including a single stage switching power converter or a multi-stage switching power converter, such as a 2-stage switching power converter.
• the electronic lighting system senses the dimmer output voltage by probing a rectified output voltage of the dimmer periodically or intermittently.
• Probing an output of a mac -based dimmer even' Nth half cycle of an alternating current (AC) output voltage of the dimmer allows the controller of the lighting system to sense the output voltage from a time when the triac connects an input voltage source to the output of the dimmer unti l a time when the triac disconnects the input voltage source from the output of the dimmer.
• N is an integer greater than 1 , which reduces possible energy losses due to probing relative to probing each cycle of the dimmer output voltage. Additionally, N can vary over time or remain constant.
• probing the output voltage involves allowing the controller to sense an actual value of the dimmer output voltage.
• Periodic or intermittent probing of the dimmer output voltage allows the controller to, for example, correctly correct errors and reduce drift, or eliminate them, as, for example, a dimming value of the dimmer changes.
• the dimming value indicated by the phase angle of the phase cut dimmer output voltage is used by the controller to determine an amount of current to supply to the electronic lighting devices.
• Probing the output voltage of the dimmer allows the controller to determine one or more parameters of the lighting system. For example, in at least one embodiment, probing the dimmer output voltage allows the control ler to determine whether a dimmer is present and, if so, the type of dimmer, such as a leading edge or trailing edge type dimmer. In at least one embodiment, probing the dimmer output voltage also allows the dimmer to determine a frequency of the dimmer output voltage. In at least one embodiment, probing the dimmer output voltage also allows the control ler to determine zero crossings of the dimmer output voltage, in at least one embodiment, probing the dimmer output voltage results in the electronic lighting system drawing additional energy that is not needed for the electronic lighting devices.
• N is an integer.
• a 7 is an odd integer, which allows the controller to probe both positive and negative cycles of the dimmer output voltage and eliminate any direct current (DC) offset accumulation in, for example, circuits of the triac-based dimmer.
• N is greater than or equal to 9 and less than or equal to 51 , such as ⁇ Y equal 25 or 27. The greater the value of N, probing occurrences are less frequent and, thus, more efficient overal l.
• the sel ection of Nis a trade-off between energy efficiency and accurate knowledge .
• the controller probes the input voltage to the electronic lighting system by applying an impedance level to an output of the triac-based dimmer that ensures proper operation of timing circuits in the dimmer.
• the applied impedance level is less than or equal to a specified value to keep the triac of the triac- based dimmer connected until either a trailing edge phase cut by a trailmg-edge type dimmer or unti l a zero crossing at the end of a cycle of the input voltage for a leading edge type dimmer.
• the probing can extend across the balance of the half-cycle of the AC voltage source, or may be terminated as soon as sufficient information has been gathered to correctly predict the zero- crossing time.
• the switching power converter in lieu of probing, includes a parasitic discharge resistor that (i) discharges parasitic capacitances that can cause the triac-based dimmer to prematurely disconnect the input voltage from the switching power converter while (ii) preventing significant charging of a capacitor in parallel with the triac.
• the controller can sense the input voltage by sensing the voltage across the parasitic discharge resistor.
• the parasitic discharge resistor is used in conjunction with a single stage switching power converter. In at least one embodiment, the parasitic discharge resistor is used in conjunction with a multi-stage, such as a 2-stage, switching power converter.
• a power and lighting system 100 includes AC line voltage source 6 provides an AC line voltage Vij ne to an electronic light source 10 through a triac-based dimmer 8,
• the line voltage Vu e is, for example, a nominally 60 Hz/1 10 V line voltage in the United States of America or a nominally 50 Hz/220 V line voltage in China and Europe.
• the dimmer 8 is actually designed for operation with incandescent bulbs having a power consumption of 40 W or greater.
• Electronic lighting system 10 controls electronic lighting device 13 to generate light.
• Electronic lighting device 13 is, for example, one or more LEDs and/or CFLs arranged in any desirable configuration.
• the two strings of series connected LEDs, LED A and LEDB, represents one embodiment of electronic lighting device 13.
• Electronic lighting device 13 generally consumes less power than an incandescent light bulb with equivalent light output.
• a 100W equivalent light output LED-based electronic lighting system 10 consumes 13W of power.
• the 13W LED- based el ectronic lighting system 10 consumes 13% of the energy consumed by a ! QOW incandescent light bulb.
• the electronic lighting system 10 and an incandescent light bulb operate from the same line voltage Vims, the input current I m drawn by the electronic lighting system 10 is much less than the input current drawn by an incandescent light bulb.
• the input current I m can fail below the hold current of the triac-based dimmer 8. Therefore, the triac T in triac-based dimmer 8 can fail to trigger properly due to the reduced current conducted through the triac T while the triac T conducts and connects the power line voltage source 6 to the electronic lighting system 10.
• the dimming value of triac-based dimmer 8 is determined from the width of the phase cut sine wave of rectified dimmer output vol tage V dim , and the electronic lighting system 10 utilizes the dimming value to control the magni tude of the current supplied electronic lighting device 13.
• the electronic lighting system 10 may not accurately determine the dimming value. Therefore, obtaining a correct dimming value is dependent on the timing circuit in triac-based dimmer 8 properly timing the position of the leading edge of the cut sine wave of rectified dimmer output voltage Vdi m at least unti l the time of an approximate next zero-crossing of AC line voltage V lme is correctly determined.
• a model equivalent circuit is shown that is useful for describing the operation of the triac T and timing circuits within an actual triac- based dimmer 8.
• the switch g illustrates operation of the triac T itself, which connects the AC voltage line source 6 and electronic lighting system 10 to conduct current i m and disconnects the AC voltage line source 6 and electronic lighting system 10 when the current IIMO, drops below a hold current value.
• EMI capacitor CE also often referred to as a "snubber” capacitor
• timing circuit formed by timing resistor RT and timing capacitor CT charge through the load presented by the electronic lighting system 10 at the output tenninal of triac-based dimmer 8 and the neutral tenninal of the voltage line source 6.
• switch g closes (i.e., the gate of the triac is triggered) and AC line voltage Vj jne is provided to the output of triac-based dimmer through an inductor LE, which is provided for EMI filtering and to reduce lamp buzz (acoustic noise in an incandescent filament).
• switch g remains closed (i.e., the triac continues to conduct) until the magnitude of current Ii n conducted through triac-based dimmer 8 falls below the hold current of the triac T, However, if an insufficiently low impedance load is connected to the o utp ut of the triac, th e stored energy from capacitor CE, which h as been dumped into inductor LE, will return to capacitor CE as the parallel combination of capacitor CE and inductor LE begins to oscillate. When the current through inductor LE falls below the hold current of the triac T, the triac will turn off.
• electronic lighting system 10 includes a dynamic impedance control circuit 16 that applies a damping impedance level sufficient to prevent the re-triggering of the triac in triac-based dimmer 8.
• a leading edge detector 18 detects a rise in rectified dimmer output voltage Vdi m caused by a turn-on event of triac-based dimmer 8 and asserts a control signal "triac on”.
• dynamic impedance control 16 applies a sufficiently low damping impedance level to prevent the re-triggering of the triac in triac-based dimmer 8 by damping the resonant circuit formed by capacitor CE and inductor LE.
• the impedance at the input of electronic lighting system 10 is maintained at or below the requisite damping impedance level until a predetermined time period has passed.
• the predetermined time period is determined for the range of triac-based dimmer 8 designs with which the electronic lighting system 10 operates and the circuit conditions present in electronic lighting system 10. In at least one embodiment, the predetermined time period is approximately 200 p.s in duration.
• the requisite damping impedance level also varies with the particular design of triac-based dimmer 8, but is generally between 100 ohms and Ik ohms.
• electronic lighting system 10 draws enough input current l- to maintain the triac-based dimmer 8 in a conducting state while energy needed to supply electronic lighting device 13 for the cycle of the dimmer output voltage Vdi m is being transferred.
• the minimum current required to maintain the conducting state i.e. the hold current of the particular triac T, is generally between 25 rnA and 70 rnA.
• electronic lighting system 10 After energy is transferred, electronic lighting system 10 then enters a high impedance state, disabling switching power converter 12 so that a sudden change in impedance due to activation of switching power converter 12 does not trigger triac-based dimmer 8 by re-charging capacitor CT to the trigger threshold during any remaining portion of the half-cycle of AC line voltage Vune for which the corresponding triae output cycle has already been terminated.
• the impedance presented at the output of triac-based dimmer 8 should be low enough to avoid a voltage drop across the inputs of electronic lighting system 10 that would substantially affect the trigger point of the triac, e.g., the time at which switch g closes.
• electronic lighting system 10 includes a zero-cross prediction circuit 14 that predicts or detects a zero-cross time of AC line voltage Vu e by observing dimmer output voltage Vdim, and dynamic impedance control circuit 16 ensures that a sufficiently low impedance, referred to as the "glue” impedance herein, is presented at the input terminals of replacement lighting device from the zero-cross time until the turn-on event is detected by leading edge detection circuit 18, during a time referred to herein as the "glue interval”.
• dynamic impedance control circuit 16 ensures that the timing of the timing circuit in triac-based dimmer 8 is not disrupted by the absence of a passive low-impedance load such as an incandescent light bulb, at the output of the dimmer, while avoiding dissipating excess energy by applying the glue impedance only during the glue interval during which the triac in triac-based dimmer 8 is off.
• a passive low-impedance load such as an incandescent light bulb
• OUTPUT EMULATION filed August 17, 2010, inventor John L. Melanson (referred to herein as "Melanson J”);describes exemplary systems and methods for generating the glue impedance.
• the electronic lighting system 10 determines an accurate estimate or measurement of the zero-cross time of the dimmer output voltage V dim .
• the electronic lighting system 10 probes the output of the triac-based dimmer 8 to sense the line voltage V ne d uring all or part of a cycl e of the dimmer outp ut rectified dimmer output voltage V dim , i.e. during all or part of a half cycle of the line voltage Vun e .
• the electronic lighting system can derive information to properly operate the electronic lighting system 10.
• the probing impedance is applied so that the triac T in triac-based dimmer 8 remains conductive and that the timing circuit in triac-based dimmer 8 continues to operate accurately.
• the probing interval may extend ail the way to the zero-cross time, or may be terminated once sufficient information is derived to accomplish the purposes of the probing cycle.
• Exemplary purposes include accurately predicting a zero-cross time of the dimmer output voltage V d i m , the type of triac-based dimmer 8 (such as a trailing edge or leading edge type dimmer), the frequency of the line voltage Vn ae ,
• accurately predicting the next zero-cross of the line voltage Vjj lie generally occurs by extending the probing interval to at least after the peak of AC line voltage Vii ne , so that any ambiguity between different values of dimmer duty factor due to identical voltages at the leading edge can be resolved by knowing on which sid e of th e peak of AC line voltage V ne the leading ed ge of the o utp ut waveform of triac-based dimmer 8 occurs.
• a dimming value estimator 15 determines a dimming value for controlling the current supplied to electronic lighting device 13, by measuring the time interval between assertion of control signal triac on by leading edge detector 18 and the assertion of control signal zero by zero-cross detector, which is a direct measure of the duty factor of triac-based dimmer 8.
• Dynamic impedance control circuit 16 may be a controllable current sink, a resistor having a series-connected switching transistor, or other suitable circuit for shunting current across input terminals I N, or switching power converter 12 can be designed to provide a minimum conductance level during operation, and controlled such that the minimum conductance level is met during the probing intervals.
• the glue impedance used for proper timing is generally an impedance substantially equal to 100 ohms or less, which represents a conductance of less than or equal to 0.01 mhos.
• Such an impedance if present across the dimmer output terminals during the active phase of triac-based dimmer would require power transfer or dissipation on the order of that caused by a 100W light bulb, but since the glue impedance is applied while the triac is off, the power transfer is only that required to operate the timer circuit formed by capacitor CT and resistor RT.
• the energy drawn by the minimum conductance level applied during the damping period (the damping impedance) and the minimum current drawn by switching power convexter 12 during the active period still may be more energy than the energy to operate electronic lighting device 13.
• a half-cycle counter 17 within dynamic impedance control 16 is used to periodically allow switching power converter 12 to operate, so that operation of switching power converter 12 is coordinated with the turn-on time of the triac in triac-based dimmer 8, but so that active cycles of triac-based dimmer 8 can be skipped except when it is necessary to probe triac-based dimmer 8 to properly detect the zero-cross time of AC line voltage Viine and to operate switching power converter 12 to transfer sufficient energy to operate electronic lighting device 13.
• the glue impedance is still applied from the predicted zero-cross time until the turn-on time of triac-based dimmer 8 so that the internal circuits of triac-based dimmer will continue to operate properly during the idle time.
• Dynamic impedance control circuit 16 generates a control signal run, which permits switching power converter 12 to start energy transfer if energy transfer is needed . Dynamic impedance control circuit 16 also generates a control signal probe, which requires switching power converter 12 to present the minimum conductance level at the output of triac-based dimmer 8 so that a probing cycle is provided to acc urately time the duty factor of triac-based dimmer 8.
• control signal probe is asserted at intervals of odd half-cycles of AC line voltage Vu lls , so that switching power converter 12 will draw most of the energy from triac-based dimmer 8 during half-cycles of alternating polarity, any remaining requirements for transfer during subsequent assertions of control signal ran should have a net zero effect, since any consistent operating pattern in the subsequent intervals of
• control signal run will also be applied to half-cycles of opposite polarity, in at least one embodiment, electronic lighting system 10 is designed so that switching power converter 12 operates when control signal run is asserted.
• the control signal r n merely permits switching power converter 12 to operate if needed to replenish energy storage within switching power converter.
• dynamic impedance control 16 may activate additional loading to provide the damping and/or probing impedance, or switching power converter 12 can be designed to present a conductance no less than the conductance provided by the maximum damping impedance level.
• switching power converter 12 can have a non-uniform energy transfer characteristic so that more current is drawn during the damping time period than is drawn during the active time period.
• control signal run is provided to switching power converter 12 to indicate to switching power converter 12 both when switching power converter 12 is permitted to start an energy transfer cycle, and how long the cycle may potentially extend, i.e., the maximum duration of the active cycle is the duration of the high-state pulse of control signal run.
• Control signal run is asserted at time ton along with control signal probe, to cause switching power converter 12 to present the minimum conductance at the output of triac-based dimmer so that the duty factor of triac-based dimmer can be probed.
• the input of electronic lighting system 10 enters a high-impedance state during idle time interval tidle and the triac in triac-based dimmer circuit 8 turns off. Then, once zero-crossing prediction circuit 14 indicates, by asserting control signal zero, that a zero-crossing of AC line voltage Vij ne is occurring, dynamic impedance control 16 asserts the glue impedance at the output of tri ac-based dimmer 8, so that the timer circuit in triac-based dimmer 8 formed by capacitor CT and resistor RT will charge properly and generate the next leading edge of dimmer output voltage Vdim at the proper time ton2.
• control signal probe is not asserted, and so energy transfer is only performed as needed at each assertion of control signal run until time ton 10, at which control signal probe is again asserted on the ninth half-cycle of AC line voltage Vii ise after the previous assertion of control signal probe.
• Zero-cross prediction circuit 14 uses either analog techniques, such as multiple threshold comparators to trigger waveshape generators, e.g., a parabolic waveform generator that provides a close approximation to a sinusoidal waveshape, or digital techniques such as using an analog-to-digital converter (ADC) with a processing block that can extrapolate the zero crossing location from the shape of the cut sine waveform of dimmer output voltage Vdi m .
• ADC analog-to-digital converter
• ADC analog-to-digital converter
• a phase lock loop can alternatively be used to predict the zero-crossing location by performing phase comparisons with the rectified dimmer output voltage Vdim and a reference timer clock output.
• PLL phase lock loop
• Using a PLL also can provide a consistent time base for operation of half- cycle counter 17 and a measure of the frequency of AC line voltage Vjj lie -
• FIG. 3 a lighting circuit 30 is shown.
• the circuit of Figure 3 is provided to illustrate details of a two-stage switching power converter that may be used to implement switching power converter 12 of Figure 1.
• the output of a dimmer is provided to a bridge rectifier 41 that generates a rectified dimmer output voltage Vdim.
• A. capacitor CRECT provides filtering of higher frequency switching components generated by a buck input stage implemented by inductor LL switching transistor NL diode Dl and capacitor CLINK.
• a resistor R l provides for current-sensing of the primary current provided through transistor N2.
• An integrated circuit 40 provides control of transistor Nl from a first stage controller 44 A and further controls a flyback converter stage from a second stage controller 44 B that switches transistor N2 to provide current through a transformer Tl in response to feedback provided from current sensing circuit 46.
• Second stage controller provides information about energy requirements to dynamic impedance control circuit 16, which provides control indication to first stage controller 44 A to dynamically control the impedance presented at the input terminal that receives the output of bridge rectifier 41 , thereby controlling the impedance presented to the output of triac-controller dimmer 8.
• Zero-cross predictor 14, leading edge detector 18 and dimming value estimator 15 operate as described above with reference to Figure 1.
• Electronic lighting device 13 may be supplied through a secondary switching circuit 48 that alternates application of the secondary current between LED strings, which may be of different color in order to provide a color profile that varies with the dimming value dim or under other control input.
• First stage controller 44 A is activated by control signal run and control signal probe as described above.
• a zero-cross detection circuit 14 A as may be employed in the above-described embodiments of the electronic lighting system 10 ( Figure 1) and lighting circuit 30 ( Figure 3).
• a hysteresis comparator Kl detects when rectified dimmer output voltage Vdim exceeds threshold voltage Vth, and one-shots 54A and 54B generate pulses that are combined by logical-OR gate OR 1 to provide a pulse at each zero-crossing of AC line voltage Viine.
• An averaging circuit 56 such as a digital processing block or PLL, is included to reconstruct the input AC line voltage Vii ne phase from the rectified dimmer output voltage VDIM, which may be accomplished as described in Melanson I and King I.
• the output of zero- cross prediction circuit 14A is a pulse that is asserted at the end of each half-cycle of AC line voltage V " ii ne , and indicates to one of the above-described circuits, when to apply the glue impedance or current level at the output of triac-based dimmer circuit 8.
• An ADC 50 provides input to parabolic approximation logic 52 that generates control signal zero according to the predicted location of the zero-crossings of AC line voltage Vi; ne .
• ADC 50 may be replaced by a pair of comparators, and parabolic approximation logic 52 may be replaced by an analog circuit that performs piecewise approxim ation to approximate the waveshape of AC line voltage Vii owned e from the cut sine wave shape of rectified dimmer output voltage V dim .
• Melanson I and King I describe exempl ary embodiments of the parabolic approximation logic 52,
• exemplary signals associated with the electronic lighting system 10 ( Figure 1) and the lighting circuit 30 ( Figure 3) are shown in a signal waveform diagram.
• a leading edge of rectified dimmer output voltage V d im indicates a triac turn- on event and for time period tactive, energy is drawn from the output terminals of triac-based dimmer 8 of Figure 1.
• Current waveform linl corresponds to an input current drawn by electronic lighting system 10 of Figure 1 , having a substantially constant value during the interval between times tl and t2. Transitions in current waveform linl cannot be too abrupt, or oscillation of EMI inductor LE and EMI capacitor CE can result, causing the triac to turn off at the wrong time.
• Voltage waveform Vlink corresponds to the output of first stage controller 44A in the circuit depicted in Figure 3.
• link voltage Vlink has fallen below link threshold voltage Vlmin and at time t4, the next odd-numbered half-cycle after the previous probing period begins, so first stage controller 44A is again activated to charge link capacitor CLINK.
• Half- cycles prior to a particular numbered half-cycle of alternate polarity, during which control signal probe is asserted, can be enabled for operation of first stage controller 44 A mitigate as shown by the dashed lines in control signal run.
• FIG. 6A depicts a power and lighting control system 600, which represents one embodiment of the power and lighting control system 100 of Figure 1.
• the power and lighting control system 600 includes electronic lighting system 602, which represents one embodiment of electronic lighting system 100.
• the electronic lighting system 602 includes a controller 604 that controls the operation of the single-stage, flyback-type switching power converter 606 and, thereby, controls the light output of electronic lighting device (ELD) 13.
• ELD electronic lighting device
• the controller senses the dimmer output voltage V d i m via the sense signal VSENSE-
• the sense signal VSENSE can be a current or voltage and can be an approximately exact or a scaled version of the dimmer output voltage d i m .
• the electronic lighting system 602 is contained within a housing of a lamp.
• the electronic lighting system 602 includes a probing circuit 608 to probe the dimmer output voltage Vdim-
• the probing circuit 608 provides the dimmer output voltage Vdj m every Nth half cycle of the dimmer output voltage Vdim to allow the controller 604to sense the dimmer output voltage Vdim from a time when the triac of the triac-based dimmer 8 connects the input voltage source 610 to the output of the dimmer 8 until a time when the triac disconnects the input voltage source 610 from the output of the dimmer 8.
• N is an integer greater than 1.
• N is an integer greater than 1 indicates that the probing circuit 608 does not probe the dimmer output voltage Vdim during every cycle of the dimmer output voltage Vdim-
• probing circuit 608 draws additional power from the input voltage source 610, Thus, using the probing circuit 608 decreases the efficiency of the electronic lighting system 602.
• the probing circuit 608 reduces energy losses by approximately 1 N relative to probing each cycle of the dimmer output voltage Vdim-
• probing the dimmer output voltage V d im can increase the accuracy of the sensed voltage V SE SE .
• the value of N represents a potential trade-off between efficiency and accuracy.
• N is greater than or equal to 9 and less than or equal to 51, such as N equal 25 or 27.
• N varies over time so that the probing circuit 608 intermittently probes the dimmer output voltage Vdim-
• N is constant so that the probing circuit 608 periodically probes the dimmer output voltage Vdim- N can be an even integer, an odd integer, or can vary between even and odd over time. Utilizing an odd value for N can eliminate any DC offset accumulation in, for example, circuits of the triac-based dimmer 8.
• the input voltage source 610 is any AC voltage source that can provide sufficient energy to the electronic lighting system 602. In at least one embodiment, the input voltage source is the line voltage source 8.
• probing the dimmer output voltage Vdim allows the controller 602 to derive information regarding characteristics of the power and lighting system 600. For example, in at least one embodiment, probing the dimmer output voltage Vdim allows the controller 602 to (i) detect and/or estimate zero crossings of the dimmer output voltage Vdim, (ii) detect the frequency of the dimmer output voltage Vdim, and/or (iii) detecting a dimmer type, such as a leading edge or trailing edge type dimmer.
• Figures 6B and 6C depict exemplary embodiments of the probing circuit 608.
• the particular make-up and configuration of the probing circuit 608 is a matter of design choice.
• the purpose of the probing circuit 608 is to allow the dimmer output voltage Vdj m to track a rectified version of the input voltage V I until an occurrence of a predetermined event.
• Probing circuit 612 represents one
• probing circuit 608 To initiate a probing interval (also referred to as a probing event) with probing circuit 612, controller 602 generates and asserts a pulse of the probe signal PROBE, switch 614 conducts, which introduces a resistance of resistors Rl and R2 across the output of the dimmer 8 and the neutral terminal 614 of input voltage source 610.
• switch 614 is an n-channel field effect transistor (FET). The resistance value of resistors Rl and R2 is sufficient to draw sufficient current through the triac of the dimmer 8 to prevent the triac from disconnecting prior to reaching an occurrence of a predetermined event.
• the event can be, for example, a particuiar value, such as a predetermined voltage level of the dimmer output voltage V dim or completion of a particular function, such as obtaining sufficient information from the dimmer output voltage Vdim to derive the desired information regarding the characteristics of the power and lighting system 600.
• a particuiar value such as a predetermined voltage level of the dimmer output voltage V dim or completion of a particular function, such as obtaining sufficient information from the dimmer output voltage Vdim to derive the desired information regarding the characteristics of the power and lighting system 600.
• predetermined voltage level is an approximately zero voltage of the dimmer output voltage Vdim.
• FIG. 6C depicts probing circuit 615, which represents another embodiment of the probing circuit 608.
• Probing circuit 615 includes a constant current source 617, which is controlled by the control signal PROBE.
• the control signal PROBE activates the constant current source 615 so that the probing circuit 613 presents a low impedance to the output of the dimmer 8.
• the constant current source 617 draws sufficient current through the triac of the dimmer 8 to prevent the triac from disconnecting prior to reaching an occurrence of the previously described predetermined event.
• the controller 604 controls the duty cycle of control signal CSj in accordance with the dimming level indicated by the phase angle of the dimmer output voltage ' 3 ⁇ 4 ⁇ .
• the phase angle of the dimmer output voltage Vdim s representative of the duty cycle of the triac of triac-based dimmer 8 and vice versa.
• the input current I in flows through diode 616 as long as the dimmer output voltage Vdim s greater than the capacitor voltage Vc across capacitor 617 plus the intrinsic forward bias voltage of diode 616,
• control signal CSj causes switch 618 to conduct, the primary current i PRIMARY energizes the primary-side coil 620 of transformer 622.
• Switch 618 can be any type of switch and is, in at least one embodiment, a FET.
• controller 602 When controller 602 generates the control signal CSi to cause the switch 61 8 to stop conducting, the primary-side voltage Vp reverses polarity, i.e. "flys back", and the dot configuration of the transformer 622 produces a secondary- side voltage Vs across the secondary- side coil 623 that forward biases the diode 624.
• the forward biased diode 624 allows the secondary-side current ⁇ S E CON D A RY to charge capacitor 626.
• capacitor 626 is large enough so that the secondary-side current ⁇ SECOND A RY provided to the electronic lighting device 13 is approximately constant, which produces an approximately constant light brightness and, in at least some embodiments, the color. Adjusting the duty cycle of the control signal CSi in accordance with the dimming level allows the controller 602 to control the value of the secondary-side current IS E CON D A RY and, thus, control the brightness and, in at least some embodiments, the color of the light produced by the electronic lighting device 13.
• Figure 7 depicts a power and light control system 700 that includes a parasitic discharge circuit 704.
• Figure 8 depicts exemplar ⁇ ' current and voltage waveforms 800 present during an exemplary operation of the power and light control system 700.
• the line current I LI E in Figure 8 is depicted as an absolute value, which is representative of the input current I in .
• the line current ILINE rises and charges the parasitic capacitor C P A R A .
• the input current ⁇ 1 ⁇ also charges the parasitic capacitor CPA R A D C-
• the voltage across the snubber capacitor CE is approximately 0V while the triac T conducts.
• Resistor RAC and inductor L A C represent the respective intrinsic resistance and inductance of the conductors.
• the line current ILINE decreases as the dimmer output voltage Vdim increases.
• the capacitor voltage Vc lus the intrinsic forward bias voltage of the diode 616 exceeds the dimmer output voltage V dj . n , and the diode 616 becomes reverse biased, i.e. non-conductive.
• the voltage Vc across capacitor 617 slowly decays until the triac T begins conducting again at time t 3 .
• the impedances of the power and light control system 700 to the left of the diode 616 are too large to allow the line current i L iNE to remain above the hold current value HC.
• the parasitic capacitors would remain charged after time tj during a cycle of the dimmer output voltage V d j m and hold dimmer output voltage Vdim at approximately the value of the dimmer output voltage Vdi m at time ti,
• the capacitance of the snubber capacitor CE is much larger than the capacitance of the parasitic capacitors CPARA AC and CPARA_DC-
• the capacitance of the snubber capacitor is 100 times greater than the capacitance of each of the parasitic capacitors CPARA AC a d C P A E A D C, e.g. approximately 100 nF to approximately 1 nF.
• the time constant of the combination of the snubber capacitor CE and the voltage exposing resistor V E is sufficiently large so that the time constant of the dimmer 8 is approximately unchanged and the voltage across the snubber capacitor CE remains
• the parasitic discharge circuit 704 discharges the parasitic capacitors C P A R A AC and C P A R A . D C so that the dimmer output voltage Vdim faithfully tracks the input voltage Vj N even after the triac T stops conducting.
• the parasitic discharge circuit 704 discharges the parasitic capacitors CPARA AC and CPARA DC without significantly affecting a time constant associated with the snubber capactor CE.
• the parasitic discharge circuit avoids affecting a time constant associated with the snubber capacitor CE by limiting the input current ⁇ 1 ⁇ and, thus, not allowing significant amounts of charge to reach the snubber capacitor CE while the triac T is nonconductive.
• the voltage VCE across the snubber capacitor remains at approximately 0V. Since the voltage VCE across the snubber capacitor is approximately 0V, the dimmer output voltage Vdim is approximately equal to a rectified version of the input voltage ⁇ ⁇ .
• the voltage exposing resistor R VE of exemplary parasitic discharge circuit 706 represents one embodiment of the parasitic discharge circuit 704.
• the voltage exposing resistor RV E has a sufficiently low resistance relative to the capacitance of the parasitic capacitors CPA R A AC and C P A R A D C to provide a discharge path and a time constant so that the voltage across the parasitic capacitors C P A R A AC and CPARA .
• D C follows the input voltage VI while the triac T is nonconductive.
• the voltage across the voltage exposing resistor RVE follows the input voltage VIN while the triac T is nonconductive.
• the controller 702 is able to essentially sense the actual dimmer output voltage V d i m .
• the resistance value of the resistor R VE is set to achieve the result of exposing the dimmer output voltage V djm to the controller 702 without significantly changing the time constant of the dimmer 8.
• the resistance of the voltage exposing resistor R YE is, for example, lOOMohms.
• the controller 702 does not utilize a probing circuit, and the remainder of the power and lighting system 700 and the controller 702 otherwise function as previously described.
• a probing circuit probes a dimmer output voltage every N cycles of the dimmer output voltage to allow the electronic lighting system to efficiently sense the dimmer output voltage for all or part of a non-zero portion of a cycle of the dimmer output voltage.
• a voltage exposing resistor RV E exposes the dimmer output voltage to a controller during each entire cycle of the dimmer output voltage.

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  • 2012-06-29 CN CN201280027673.5A patent/CN103582995B/zh not_active Expired - Fee Related
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