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]
  • H05B45/40—Details of LED load circuits
  • H05B45/44—Details of LED load circuits with an active control inside an LED matrix
  • H05B45/48—Details of LED load circuits with an active control inside an LED matrix having LEDs organised in strings and incorporating parallel shunting devices

Definitions

• This relates in general to lighting systems, and in particular to a switched lighting system and method of operation.
• Efficient (high lumens per watt) lighting systems may be powered directly by alternating current (AC) power mains (such as 120V RM S, 60HZ, or 230V RM S, 50 Hz). Examples include household and commercial indoor lighting, outdoor street lights, traffic lights, and signage. Light-emitting diodes (LEDs) are one example technology for efficient light emitters.
• AC alternating current
• LEDs Light-emitting diodes
• FIG. 1A shows an example of a conventional lighting system 100, in which LEDs 102 are connected in series and driven directly by a rectified AC supply voltage V R AC-
• the system 100 may also include a current limiter or current regulator 104.
• FIG. IB shows example timing for the lighting system 100, in which V T is a threshold at which V R AC exceeds the forward-biased voltage of the entire series of LEDs 102 plus the voltage drop across the current limiter 104.
• V R AC starts increasing from zero.
• V R AC exceeds the threshold V T , and the LEDs 102 emit light.
• V R AC falls below the threshold V T , and the LEDs 102 stop emitting light. Accordingly, the LEDs 102 are on during only the time period from ti until t 2 (shaded portion 106). In that manner, light is emitted for only a fraction of the time, and the light flickers at twice the frequency of the AC power mains. If the peak of V R AC drops too far (such as during a "brown-out" or responsive to a dimming switch), then the lighting system 100 may fail to turn on.
• FIG. 2 shows an example of an alternative conventional lighting system 200, in which current for LEDs is provided by electronic drivers.
• a rectified AC supply voltage V R AC provides power to driver/bypass circuits (204, 206, 208, 210) connected in series, and to a current limiter or current regulator 202.
• Each driver/bypass circuit (204, 206, 208, 210) drives a respective LED (212, 214, 216, 218).
• Each driver/bypass circuit (204, 206, 208, 210) includes a respective bypass switch that can bypass current around its LED.
• driver/bypass circuit 204 When the supply voltage (V R AC) exceeds a voltage sufficient to power LED 212 (and the current limiter or current regulator 202, and accounting for the series voltage drops of the bypass switches), driver/bypass circuit 204 turns on, opens its bypass switch, and drives its LED 212. As the supply voltage (V R AC) continues to increase, the driver/bypass circuits (206, 208, 210) sequentially turn on (and open their respective bypass switches) until all LEDs are being driven. When the supply voltage (V R AC) decreases, the driver/bypass circuits (204, 206, 208, 210) sequentially turn off (and close their respective bypass switches). Accordingly, LEDs start turning on at a relatively low voltage. As the supply voltage (V R AC) increases, more LEDs are driven, and the overall intensity increases. As the supply voltage (V R AC) decreases, fewer LEDs are driven, and the overall intensity decreases.
• a lighting system includes a switch that is configured so that: when the switch is in a first state, current from a supply flows to a light emitter; and when the switch is in a second state, current from the supply flows through the switch bypassing the light emitter.
• a capacitor connected in parallel with the light emitter provides current to the light emitter, sufficient to cause the light emitter to emit light when the switch is in the second state.
• FIG. 1 A is a block diagram schematic of an example of a conventional lighting system.
• FIG. IB is a timing diagram of example timing for the lighting system of FIG. 1A.
• FIG. 2 is a block diagram schematic of an example of an alternative conventional lighting system.
• FIG. 3 is a block diagram schematic of an example embodiment of an improved lighting system.
• FIGS. 4A - 4D are timing diagrams of example timing for the lighting system of FIG. 3.
• FIG. 5 is a block diagram schematic of a switch controller for the lighting system of FIG. 3.
• FIG. 6 is a flowchart of an operation of the example embodiment.
• FIG. 3 shows an example embodiment of an improved lighting system 300.
• light emitters (306, 308, 310, 314, 316, 320) are divided into three segments (SEGMENT 1, SEGMENT2, SEGMENT3), and the segments are connected in series. The number of segments and the number of light emitters per segment may vary.
• FIG. 3 shows one simplified example.
• the light emitters (306, 308, 310, 314, 316, 320) are LEDs, but the lighting system 300 is likewise applicable to other efficient low-voltage light emitters.
• the lighting system 300 is driven by a rectified AC supply voltage V R AC-
• the lighting system 300 includes a current regulator 302.
• Each segment includes a respective electronic bypass switch (SW1, SW2, SW3), a respective isolation diode (304, 312, 318) connected in series with the segment's light emitter(s), and a respective capacitor (CI, C2, C3) connected in parallel with the segment's light emitter(s).
• Each electronic bypass switch (SW1, SW2, SW3) has associated switch control circuitry, as shown in FIG. 5.
• the capacitors may fully charge over a few half-cycles of V R AC- After the capacitors (CI, C2, C3) are charged, they supply current in the steady-state to the light emitters (306, 308, 310, 314, 316, 320) when the bypass switches (SW1, SW2, SW3) are closed, so that the light emitters emit light continuously.
• the isolation diodes (304, 312, 318) prevent the capacitors from discharging through the bypass switches (SW1, SW2, SW3).
• bypass switch SW2 opens: (a) light emitters 314 and 316 receive current through bypass switch SW1 and isolation diode 312; (b) light emitters 314 and 316 emit light; and (c) capacitor C2 charges.
• bypass switch SW2 opens, the voltage at the anode of isolation diode 312 in SEGMENT2 is near V R AC, and the voltage at the anode of isolation diode 318 in SEGMENT3 then drops by the voltage across SEGMENT2.
• the voltage at the anode of isolation diode 318 may then drop below the first threshold.
• bypass switch SW3 will close again. If bypass switch SW3 closes again, then it will open again when the voltage at the anode of isolation diode 318 again increases above the first threshold.
• bypass switch SW1 opens, so current flows to light emitters 306, 308, and 310 and to capacitor CI . Light emitters 306, 308, and 310 then emit light, and capacitor CI charges.
• bypass switch SWl opens, the voltage at the anode of isolation diode 304 is at V R AC, and the voltage at the anode of isolation diode 312 in SEGMENT2 drops by the voltage across SEGMENT 1.
• Bypass switches SW2 and SW3 may then close again. If bypass switch S W3 closes again, then it will open again when the voltage at the anode of isolation diode 318 again increases above the first threshold. If bypass switch S W2 closes again, then it will open again when the voltage at the anode of isolation diode 312 again increases above the second threshold.
• bypass switch SW3 When the bypass switch SW3 opens, current from V R AC flows to the light emitter 320 and to capacitor C3. When the bypass switch SW3 closes again, current flows from V R AC through the bypass switch SW3, bypassing the light emitter 320 and the capacitor C3. When the bypass switch SW3 closes, current from capacitor C3 flows through the light emitter 320 until the bypass switch SW3 opens again. Depending on the size of capacitor C3, it may fully charge over multiple half-cycles of V R AC- After capacitor C3 is fully charged, light emitter 320 emits light continuously, receiving current from V R AC or capacitor C3, depending on the state of bypass switch SW3.
• the lighting system 300 emits light continuously and with almost constant intensity. Only a relatively small amount of intensity variation results from reducing voltage on the capacitors (CI, C2, C3) as they discharge. If the peak voltage of V R AC falls below the third threshold but is above the second threshold (such as during a brown-out or as a result of a dimmer switch), then the light emitters in SEGMENT2 and SEGMENT3 will continue to emit light. If the peak voltage of V R AC falls below the second threshold but is above the first threshold, then the light emitters in SEGMENT3 will continue to emit light.
• FIGS. 4A-4D are timing diagrams of example timing, example segment voltages, and example thresholds for the lighting system 300 of FIG. 3.
• the voltage across SEGMENT3 when bypass switch SW3 is open is assumed to be 20V
• the voltage across SEGMENT2 when bypass switch SW2 is open is assumed to be 40V
• the voltage across SEGMENT 1 when bypass switch SWl is open is assumed to be 80V.
• the headroom required for the current regulator 302 and switches is assumed to be 5V
• the first threshold V T i is assumed to be 25V
• the second threshold V T2 is assumed to be 45V
• the third threshold V T3 is assumed to be 85V.
• FIGS. 4A-4D respectively show V R AC, the voltage across SEGMENT 1, the voltage across SEGMENT2, and the voltage across SEGMENT3.
• V R AC starts increasing from zero.
• V R AC exceeds the first threshold V TI (25V), and bypass switch SW3 opens.
• V R AC exceeds the second threshold V T2 (45V), and bypass switch SW2 opens.
• the controller for bypass switch SW3 again senses 25V relative to ground, and bypass switch SW3 opens again.
• V R AC exceeds the third threshold V T3 (85V), and bypass switch SW1 opens.
• bypass switch SW1 When bypass switch SW1 opens at time t4, the voltage across SEGMENT2 and SEGMENT3 drops by the voltage across SEGMENT 1 (80V), and bypass switches SW1 and SW2 close.
• V R AC exceeds 105V
• the controller for bypass switch SW3 again senses 25V relative to ground, and bypass switch SW3 opens again.
• V R AC exceeds 125V (notably, peak voltage for a 120V RM S mains is -170V)
• the controller for bypass switch SW2 again senses 45V relative to ground, and bypass switch SW2 opens again.
• bypass switch SW2 opens at time t 6 , the voltage across SEGMENT3 drops by the voltage across SEGMENT2 (40V), and bypass switch SW3 closes again.
• VRAC exceeds 145V
• the controller for bypass switch SW3 again senses 25V relative to ground, and bypass switch SW3 opens again.
• V R AC falls below 145V, and the switching sequence described above progresses in the reverse order.
• segment voltages and thresholds Many alternative choices exist for segment voltages and thresholds. The above assumed thresholds and segment voltages were chosen to improve efficiency. However, each switch transition from open-to-close or close-to-open generates a transient current on the AC mains. Alternatively, the segment voltages and thresholds may be chosen to reduce the number of switch transitions to reduce transient currents on the AC mains. Also, the thresholds may be adjusted to change the order in which segments turn on and off. The following example is for a lighting system with minimal current transients, which adjusts the order in which segments turn on and off. Assume a lighting system as in FIG. 3, but with four segments, with SEGMENT 1 closest to the AC mains, and SEGMENT4 closest to ground.
• V R AC is 230V RM
• SEGMENT4 has a segment voltage of 40V, and the remaining three segments have segment voltages of 80V.
• the threshold for SEGMENT4 is 48V
• the threshold for SEGMENT 1 is 88V
• the threshold for SEGMENT2 is 172V
• the threshold for SEGMENT3 is 256V.
• the order of the thresholds is different than the order of the segments.
• Table 2 lists the states of the four bypass switches (SW1, SW2, SW3, SW4) as a function of V R AC for these assumed values. For these assumed values, only bypass switch SW4 switches ON and OFF multiple times as V R AC increases from zero to a peak voltage. The remaining switches only switch once, which reduces the transient currents on the AC mains.
• the voltage across the current regulator 302 ranges from ⁇ 5V to ⁇ 25V.
• V R AC is slightly below 65V
• a 40V drop exists across SEGMENT2
• the voltage across the current regulator 302 is ⁇ 25V.
• bypass switch SW3 opens, and a 20V drop exists across SEGMENT3 in addition to the 40V drop across SEGMENT2, so the voltage across the current regulator 302 drops to ⁇ 5V.
• the voltage across the current regulator ranges from ⁇ 8V to -48 V for most of the range of V R AC.
• the voltage across the current regulator varies from ⁇ 8V to ⁇ 52V when V R AC is in the range of 128V to 172V, and the voltage across the current regulator varies from ⁇ 12V to -48 V when V R AC is the range of 172V to 208V. Accordingly, selecting segment voltages and thresholds to reduce transient currents on the AC mains results in a slightly higher average voltage across the current regulator, resulting in a slightly reduced efficiency (slightly more heat loss occurs in the current regulator).
• FIG. 5 shows an example embodiment of switch control circuitry 500 for one of the electronic bypass switches (SW1, SW2, SW3) of FIG. 3. Specifically, FIG. 5 shows switch control circuitry for bypass switch SW2 in SEGMENT2.
• the switch control circuitry 500 in FIG. 5 is simplified.
• the switch control circuitry 500 is driven by the voltage across capacitor C2 (Vi N - Vs).
• a voltage regulator 502 provides a constant voltage Vcc for the electronics.
• bypass switch SW2 is implemented as a MOS transistor Q2.
• Transistor Q2 is driven by a latch 506.
• the latch 506 is SET dominant (so that, if both SET and RESET are high, then the latch 506 is SET).
• the SET input of the latch 506 is driven by an amplifier 504.
• a current source ii is connected between the input of the amplifier 504 and Vs.
• a resistor Rl is connected between the input of the amplifier 504 and ground.
• the RESET input of the latch 506 is driven by an amplifier 508.
• the resistor Rl is also connected to the negative input of the amplifier 508, and a second resistor R2 is connected between the negative input of the amplifier 508 and Vm.
• a voltage source Vi is connected to the positive input of the amplifier 508.
• the voltage of V R AC at which the RESET amplifier 508 changes states is slightly below the voltage at which the SET amplifier 504 changes states. This provides hysteresis to prevent the transistor Q2 from being affected by noise on V R AC or ground.
• V R AC As V R AC increases from zero, V IN and Vs increase, and the SET amplifier 504 drives the SET input of the latch 506. As V R AC increases above a RESET threshold, the RESET input of the latch 506 is also driven. Then, when the current through Ri exceeds the current source ii, the SET amplifier 504 ceases driving the SET input of the latch 506, so the latch 506 is RESET when the SET input is no longer driven. As V R AC decreases from the peak voltage, the SET input of the latch 506 is again driven at the higher threshold of amplifier 504. Accordingly, the voltage at which the transistor Q2 switches from ON-to-OFF as V R AC is rising is lower than the voltage at which Q2 switches from OFF-to-ON as V R AC is falling.
• FIG. 6 is a flowchart 600 of an operation of the example embodiment.
• a switch control circuit senses a voltage at the switch control circuit.
• the switch control circuit opens a switch, allowing current to flow to a light emitter and to a capacitor.
• the switch control circuit closes the switch, bypassing the light emitter and the capacitor.
• the capacitor provides current to the light emitter when the switch is closed.
• the system of FIGS. 3 and 5 emits light continuously and with almost constant intensity.
• the system does not require any power source other than the AC mains.
• the only active circuitry in the current path through the light emitters is a current regulator.
• the system self-senses when to bypass AC mains current around light emitters and when to allow AC mains current to flow through light emitters.
• No communications connections, other than local voltage sense connections, are required for the switch controllers.
• the system can be adjusted to improve efficiency by reducing the average voltage drop across the current regulator. Alternatively, the system can be adjusted to reduce current transients on the AC mains.

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• Circuit Arrangement For Electric Light Sources In General (AREA)

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• 2013
  • 2013-12-09 US US14/100,382 patent/US9332605B2/en active Active
• 2014
  • 2014-06-09 CN CN201480032489.9A patent/CN105284187B/zh active Active
  • 2014-06-09 JP JP2016518064A patent/JP6340419B2/ja active Active
  • 2014-06-09 WO PCT/US2014/041587 patent/WO2014197906A1/en not_active Ceased

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