WO2024056703A1 - Led driver for controlling a led fixture and a method of controlling a led fixture - Google Patents

Led driver for controlling a led fixture and a method of controlling a led fixture Download PDF

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Publication number
WO2024056703A1
WO2024056703A1 PCT/EP2023/075090 EP2023075090W WO2024056703A1 WO 2024056703 A1 WO2024056703 A1 WO 2024056703A1 EP 2023075090 W EP2023075090 W EP 2023075090W WO 2024056703 A1 WO2024056703 A1 WO 2024056703A1
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WO
WIPO (PCT)
Prior art keywords
bus voltage
led driver
pfc circuit
led
power
Prior art date
Application number
PCT/EP2023/075090
Other languages
French (fr)
Inventor
Franciscus Bernardus Marie Van Horck
Marc Saes
Original Assignee
Eldolab Holding B.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eldolab Holding B.V. filed Critical Eldolab Holding B.V.
Publication of WO2024056703A1 publication Critical patent/WO2024056703A1/en

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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]
    • H05B45/30—Driver circuits
    • H05B45/355—Power factor correction [PFC]; Reactive power compensation

Definitions

  • LED driver for controlling a LED fixture and a method of controlling a LED fixture
  • the technical field of the present invention relates to LED drivers operating in a standby mode.
  • an LED based product e.g. a LED fixture
  • the LED fixture in general comprises a plurality of LEDs, for example groups of LEDs which are arranged in a parallel connection. Based on the color characteristics of the plurality of LEDs applied, a desired color by the LED fixture can be generated.
  • the LED driver When the LED fixture is not outputting a color, the LED driver is typically operating in a standby mode. In the standby-mode the electric current flowing through the LEDs is interrupted but sufficient internal processes are kept running in the LED driver so that normal operation can be quickly resumed.
  • the LED driver should consume as little power as possible during standby mode.
  • Commonly used LED drivers have the disadvantage of having a relatively high power consumption when the LED driver is in the standby mode, or wherein a complex architecture and control algorithm is needed to reduce the standby power.
  • an LED driver configured to control a LED fixture comprising a plurality of LEDs, the LED driver comprising:
  • a power converter configured to convert an input power received from the external power supply at the input terminal to a load power at the output terminal for powering the LED fixture, the power converter comprising o a PFC circuit configured to convert the input power to a bus voltage provided to a DC voltage bus, o a converter arranged downstream the DC voltage bus configured to convert the bus voltage to the load power, • a control unit configured to control the power converter to provide the load power to the LED fixture, and wherein the control unit is configured to, when the LED driver is in a standby mode, o determine the bus voltage, o control the PFC circuit by
  • an LED driver is, in general applied for powering an LED fixture.
  • the LED fixture comprises a plurality of LEDs.
  • the plurality of LEDs may be grouped in LED groups.
  • the LED fixture is adapted to emit light with the desired colour, temperature and/or intensity.
  • the LED driver comprises an input terminal.
  • the input terminal is configured to be connected to an external power supply.
  • the external power supply is for example a mains power supply supplying an input voltage in the range of 120 V to 277 V at 60 Hz.
  • the input voltage is universal, for example in the residential areas the input voltage is the range of 100Vac to 277Vac.
  • LED drivers are used on 120Vac residential voltage levels and 277Vac industrial voltage levels.
  • the LED driver comprises an output terminal.
  • the output terminal is configured to be connected to the LED fixture.
  • the LED driver is configured to provide power from the external power supply to the LED fixture.
  • the LED driver further comprises a power converter.
  • the power converter is configured to convert an input power received from the external power supply at the input terminal to a load power at the output terminal for powering the LED fixture.
  • the load power is for example 100 W.
  • the power converter comprises a PFC circuit.
  • the PFC circuit has a power factor correction (PFC) property.
  • the PFC circuit is configured to convert the input voltage to a bus voltage provided to a DC voltage bus.
  • the PFC circuit is for example a PFC boost circuit configured to boost the input voltage to the bus voltage provided to the DC voltage bus. Boosting in this context means to increase the voltage. Therefore, the outputted bus voltage by the PFC boost circuit is always higher than the input voltage received from the external power supply.
  • the bus voltage in nominal conditions, i.e.
  • the power converter further comprises a converter arranged downstream the PFC circuit.
  • the converter is configured to convert the bus voltage to the load power for powering the LED fixture.
  • the LED driver further comprises a control unit.
  • the control unit is configured to control the power converter to provide the load power to the LED fixture.
  • the control unit is configured to, when the LED driver is in a standby mode, determine the bus voltage.
  • the load power is substantially zero. In the standby mode, the LED fixture is not emitting light.
  • the LED driver is consuming electrical power, e.g. due to switching losses by the PFC circuit, which is referred as standby power.
  • the standby power should be as low as possible.
  • the control unit When the LED driver is in the standby mode, the control unit is configured to control the PFC circuit by switching off the PFC circuit when the determined bus voltage is higher than or equal to a high bus voltage limit and switching on the PFC circuit when the determined bus voltage is lower than or equal to a low bus voltage limit.
  • the bus voltage decreases to a lower value.
  • the PFC circuit cannot be totally switched off. Otherwise, the bus voltage is too low and, therefore, the loss of the converter, e.g. a resonant DC-DC converter, would be increased too much, which leads to a higher power consumption of the LED driver.
  • the bus voltage is controlled with hysteresis control.
  • the PFC circuit is switched off such that the bus voltage decreases.
  • the PFC circuit is switched on again such that the bus voltage increases.
  • the PFC circuit is kept intermittent on and off in the standby mode, wherein the bus voltage is continuously maintained between the low bus voltage limit and the high bus voltage limit.
  • the power consumption of the LED driver in the standby mode is as low as possible due to the reduced switching loss of the PFC circuit without the risk that the power loss of the converter becomes too high.
  • the overall standby power loss is reduced.
  • the converter is a resonant converter.
  • the converter is a resonant DC-DC converter.
  • the DC-DC resonant converter comprises an isolation transformer having a primary circuit electrically separated from a secondary circuit.
  • the secondary circuit is magnetically coupled to the primary circuit.
  • DC power from the primary circuit is magnetically transferred to the secondary circuit.
  • the converter is for example a flyback converter equipped with an isolation transformer.
  • the external power supply is an AC power supply.
  • the AC power supply for example operates at 277 V, 60 Hz.
  • the LED driver further comprises a rectifier for rectifying the AC power supply.
  • the PFC circuit comprises the rectifier for rectifying the AC power supply. The rectifier converts the AC current to DC current.
  • the power converter comprises an electromagnetic interference filter (EMI) filter arranged downstream of the rectifier.
  • EMI electromagnetic interference filter
  • the EMI filter provides electromagnetic noise suppression for the LED driver.
  • the external power supply is a DC power supply.
  • the high bus voltage limit is between 400 V-500 V, preferably between 420 V-480 V, more preferably between 440 V-470 V.
  • the low bus voltage limit is between 200 V-380 V, preferably between 220 V-350 V, more preferably between 250 V-350 V.
  • the low bus voltage limit has to be set high enough such that the converter, when the LED driver is in the standby mode, has sufficient power to continue working. In case the bus voltage becomes too low, the converter could turn off which needs to be avoided in terms of energy efficiency. It requires more power to switch on again the converter compared to the situation wherein the converter operates continuously.
  • the high bus voltage limit and the low bus voltage limit define a bus voltage range.
  • the bus voltage range influence the off and on time during which the PFC circuit is switched off and on by the control unit. Within a given standby period, during which the LED driver is in the standby mode, and by setting a narrow bus voltage range, more cycles are needed to switch the PFC circuit. By having more switching cycles of the PFC circuit, the overall power loss would increase again. To have the most efficient control mechanism of the PFC circuit, an optimum regarding the bus voltage range has to be made by taking into account the number of switching cycles of the PFC circuit and the off time of the PFC circuit.
  • control unit is configured to receive a signal representative of the bus voltage, wherein the signal is generated by a measurement unit configured to measure the bus voltage.
  • the measurement unit performs current and/or voltage measurements, e.g. DC measurements, to derive the signal representative of the bus voltage.
  • the control unit receives the signal from the measurement unit, e.g. via a processing unit.
  • the measurement unit is for example integrated in the control unit. Based on the received signal, the control unit is able to determine the bus voltage.
  • the control unit directly determines the current and/or voltage, for example between the PFC circuit and the converter, instead of the measurement unit.
  • the PFC circuit comprises a switch.
  • the switch is for example a FET or a MOSFET.
  • the switching of the switch can e.g. be controlled by the control unit.
  • the PFC circuit is switched off when the switch is switched open.
  • the invention further pertains to a method of controlling a LED fixture comprising a plurality of LEDs by a LED driver, the LED driver comprising a power converter for powering the LED fixture and a control unit for controlling the power converter, the power converter comprising a PFC circuit configured to convert an input power to a bus voltage, the method comprising the steps of, when the LED driver is in a standby mode,
  • Fig. 1 Schematically illustrates an embodiment of an LED driver according to the invention
  • Fig. 2 Schematically illustrates an electrical implementation of the PFC circuit of the LED driver according to the invention
  • Fig. 3 Schematically illustrates an electrical implementation of the embodiment of an LED driver according to the invention
  • Fig. 4 Schematically illustrates an embodiment of a switching diagram of the PFC circuit.
  • FIG. 1 schematically illustrates an embodiment of an LED driver to control a LED fixture comprising a plurality of LEDs according to the invention.
  • the LED driver 1 according to the invention comprises an input terminal 2.
  • the input terminal 2 is connected to an external power supply 3.
  • the external power supply 3 is for example a mains power supply supplying an input voltage 3a in the range of 120 V to 277 V at 60 Hz 230 V at 50 Hz.
  • the input voltage 3a is universal, for example in the residential areas the input voltage is the range of 100 Vac to 277 Vac.
  • LED drivers are used on 120 Vac residential voltage levels and 277 Vac industrial voltage levels.
  • the LED driver 1 comprises an output terminal 4.
  • the output terminal 4 is connected to the LED fixture 5.
  • the LED driver 1 is configured to provide power, for example an output voltage or current 4a, from the external power supply 3 to the LED fixture 5.
  • the LED fixture 5 comprises a plurality of LEDs. The plurality of LEDs may be grouped in LED groups.
  • the LED fixture 5 is adapted to emit light with the desired colour, temperature and/or intensity.
  • the LED driver 1 further comprises a power converter 6.
  • the power converter 6 converts convert the input power 3a received from the external power supply 3 at the input terminal 2 to a load power 4a at the output terminal 4 for powering the LED fixture 5.
  • the load power 4a is for example 100 W.
  • the power converter 6 comprises a PFC circuit 7.
  • the PFC circuit 7 is a PFC boost circuit.
  • all types of converters having a PFC property are suitable for the implementation.
  • the PFC boost circuit 7 converts or boosts the input voltage to a bus voltage provided to a DC voltage bus 8.
  • the power converter 6 further comprises a converter 9 arranged downstream the PFC boost circuit 7. The converter 9 converts the bus voltage to the load power 4a for powering the LED fixture 5.
  • the LED driver 1 further comprises a control unit 10.
  • the control unit 10 controls the power converter 6 to provide the load power 4a to the LED fixture 5.
  • the control unit 10 is configured to, when the LED driver 1 is in a standby mode, determine the bus voltage. When the LED driver 1 is in a standby mode the load power 4a is substantially zero. In the standby mode, the LED fixture 5 is not emitting light. During the standby mode, the LED driver 1 is consuming electrical power, e.g. due to switching losses by the PFC boost circuit 7, which is referred as standby power.
  • the standby power should be as low as possible.
  • the control unit 10 is configured to control the PFC boost circuit 7 by switching off the PFC boost circuit 7 when the determined bus voltage is higher than or equal to a high bus voltage limit and switching on the PFC boost circuit 7 when the determined bus voltage is lower than or equal to a low bus voltage limit.
  • the bus voltage decreases to a lower value.
  • the PFC boost circuit 7 cannot be totally switched off. Otherwise, the bus voltage is too low and, therefore, the loss of the converter 9, e.g. a resonant DC-DC converter, would be increased too much, which leads to a higher power consumption of the LED driver 1.
  • the bus voltage is controlled with hysteresis control.
  • the PFC boost circuit 7 is switched off such that the bus voltage decreases.
  • the PFC boost circuit 7 is switched on again such that the bus voltage increases.
  • the PFC boost circuit 7 is kept intermittent on and off in the standby mode, wherein the bus voltage is continuously maintained between the low bus voltage limit and the high bus voltage limit.
  • the power consumption of the LED driver 1 in the standby mode is as low as possible due to the reduced switching loss of the PFC boost circuit 7 without the risk that the power loss of the converter becomes too high.
  • the overall standby power loss is reduced.
  • Fig. 2 schematically illustrates an electrical implementation of the PFC circuit 7 of the LED driver according to the invention.
  • the circuitry of the PFC circuit 7 comprises EMI filter 21.
  • the external power supply 3 supplies an AC power to the EMI filter 21.
  • the EMI filter 21 mitigates electromagnetic interference.
  • the filtered AC power is provided to a rectifier 22.
  • the rectifier 22 rectifies the AC power to DC power.
  • the PFC circuit 7 converts the DC power into a bus voltage 8a.
  • the bus voltage 8a is subsequently supplied to the converter 9 converting the bus voltage 8a to the load power for powering the LED fixture 5.
  • the PFC circuit 7 further comprises a switch 23.
  • the switch 23 is a MOSFET.
  • the switching of the switch 23 can e.g. be controlled by the control unit (not shown in Fig. 2).
  • the switch 23 is switched with a high frequency, i.e. the switch 23 is intermittent open and closed.
  • the switch 23 is closed, energy is stored in the coil 24.
  • the switch 23 is open, the energy is transferred from the coil 24 to the capacitor 25 and the converter 9.
  • the switch 23 is continuously turned off, i.e. the switch 23 is open, the PFC circuit 7 is switched off.
  • FIG. 3 shows an electrical implementation of the embodiment of an LED driver according to the invention.
  • the features of the LED driver 1 corresponding with those of the LED driver shown in Fig. 1 are indicated with the same reference numerals in Fig. 3.
  • the LED driver 1 comprises a DC bus voltage sense unit 31, a hysteresis comparator 32 and some logic gates 33,34 in serial connection with the hysteresis comparator 32.
  • the DC bus voltage sense unit 31 is a voltage divider, wherein the voltage at an inverting terminal 35, i.e. the sensed DC bus voltage or V., of the hysteresis comparator 32 is represented as: wherein Vb is the DC bus voltage 8 and Re, R? are resistors.
  • the hysteresis comparator 32 compares one voltage level (V.) with another voltage level (V+) and produces an output voltage Ui based on this voltage comparison.
  • V+ and V. correspond to the voltages at a non-inverting terminal 36 and the inverting terminal 35 respectively.
  • the hysteresis comparator 32 uses a positive feedback for feeding back a part of the output voltage Ui to the non-inverting terminal 36 of the hysteresis comparator 32 via a voltage divider set up by the resistor Ri and R2.
  • a hysteresis is created having a high bus voltage limit and a low bus voltage limit.
  • OW are derived as: wherein V s is the supply voltage, e.g. 5 V, and V re f is a reference voltage.
  • the high bus voltage limit is between 400 V-500 V, preferably between 420 V-480 V, more preferably between 440 V-470 V.
  • the low bus voltage limit is between 200 V-380 V, preferably between 220 V-350 V, more preferably between 250 V-350 V.
  • the output voltage U1 When the sensed DC bus voltage V- is less than the input voltage V+ at the noninverting terminal 36, the output voltage U1 will be high, and thus approximately equal to the supply voltage V s . When the sensed DC bus voltage V. is higher than the input voltage V+ at the non-inverting terminal 36, the output voltage U1 will be low, and thus approximately equal to zero.
  • the hysteresis comparator is applied to control the switching of the PFC circuit 7.
  • the output voltage U1 is supplied to an inverting gate 33, wherein the inverting gate 33 outputs an inverted logic value (low or high): low when the output voltage U1 is high and high when the output voltage U1 is low.
  • the output of the inverting gate 33 is supplied to a first input terminal 34a of an AND gate 34.
  • a mode signal 37 representative of the operational mode of the LED driver 1 is supplied to a second input terminal 34b of the AND gate 34.
  • the mode signal 37 is a standby signal when the LED driver is in the standby mode.
  • the output of the AND gate 34 is supplied to the switch 23.
  • the switch 23 is for example a FET or a MOSFET.
  • the switching of the switch 23 is controllable by the control unit 10 and the output of the AND gate 34. For example, by having a low logic value at the output of the AND gate 34, the switch 23 is switched open, i.e.
  • the LED driver 1 comprises a resonant DC-DC converter 9.
  • the resonant DC- DC converter 9 comprises an isolation transformer having a primary side 38 electrically separated from a secondary side 39.
  • the secondary side 39 is magnetically coupled to the primary side 38.
  • DC power from the primary side 38 is magnetically transferred to the secondary side 39.
  • a measurement circuit 40 is arranged at the secondary side 39 .
  • the measurement circuit 40 is configured to determine the operational mode of the LED driver 1, i.e. normal mode or standby mode.
  • the measurement circuit 40 comprises a measurement device 41 configured to measure a voltage at the secondary side 39. Based on the voltage, the measurement device 41 outputs the mode signal 37.
  • the measurement device 41 is an opto-coupler. In case the LED driver 1 is operating in standby mode, the opto-coupler 41 transmits a standby signal which is a high logic signal.
  • the PFC circuit 7 of Fig. 3 is for example switched according to the timing diagram as illustrated in Fig. 4.
  • the LED driver 1 is operating in normal mode.
  • the sensed DC bus voltage V. is higher than high bus voltage limit V up and the low bus voltage limit V
  • the opto-coupler 41 transmits a low logic for the mode signal 37 to the second input terminal 34b of the AND gate 34.
  • the AND gate 34 outputs a low logic value. In that case, the switch 23 is turned off and the PFC circuit 7 is operating normally (the PFC circuit is on).
  • the operating mode of the LED driver 1 shifts to the standby mode.
  • the opto-coupler transmits a high logic for the mode signal 37 to the second input terminal 34b of the AND gate 34. Because a high logic value is provided to the first input terminal 34a of the AND gate 34, the AND gate 34 outputs a high logic value causing the switch 23 to be turned on which turns the PFC circuit 7 off.
  • the DC bus voltage 8 decreases. Thereby, the voltage V. at the inverting terminal 35 of the hysteresis comparator 32 decreases as well, as visualised in Fig. 4.
  • V. becomes equal to the low bus voltage limit V
  • the output voltage Ui of the hysteresis comparator 32 changes to a high logic value and thus a low logic value is provided to the first input terminal 34a.
  • the output value of the AND gate 34 is inverted which causes the switch 23 to be turned off again in order to switch on the PFC circuit 7.
  • V. increases.
  • V. becomes equal to the high bus voltage limit V up .
  • the output voltage Ui of the comparator changes to a low logic value and thus a high logic value is provided to the first input terminal 34a.
  • the output value of the AND gate 34 is inverted again which causes the switch 23 to be switched on, wherein the PFC circuit 7 is turned off.
  • V. decreases till it reaches the low bus voltage limit V

Abstract

LED driver configured to control a LED fixture comprising a plurality of LEDs, a power converter configured to convert an input power to a load power, the power converter comprising a PFC circuit configured to convert the input power to a bus voltage provided to a DC voltage bus, a converter arranged downstream the DC voltage bus, a control unit configured to control the power converter, and wherein the control unit is configured to, when the LED driver is in a standby mode, determine the bus voltage, and to control the PFC circuit by switching off the PFC circuit when the determined bus voltage is higher than or equal to a high bus voltage limit, and switching on the PFC circuit when the determined bus voltage is lower than or equal to a low bus voltage limit.

Description

LED driver for controlling a LED fixture and a method of controlling a LED fixture
BACKGROUND
The technical field of the present invention relates to LED drivers operating in a standby mode.
In general, an LED based product, e.g. a LED fixture, is driven by an LED driver. The LED fixture in general comprises a plurality of LEDs, for example groups of LEDs which are arranged in a parallel connection. Based on the color characteristics of the plurality of LEDs applied, a desired color by the LED fixture can be generated.
When the LED fixture is not outputting a color, the LED driver is typically operating in a standby mode. In the standby-mode the electric current flowing through the LEDs is interrupted but sufficient internal processes are kept running in the LED driver so that normal operation can be quickly resumed.
The LED driver should consume as little power as possible during standby mode. Commonly used LED drivers have the disadvantage of having a relatively high power consumption when the LED driver is in the standby mode, or wherein a complex architecture and control algorithm is needed to reduce the standby power.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved LED driver and way of controlling the LED fixture, wherein the abovementioned issues are mitigated or wherein the invention at least provides an alternative.
According to the invention, there is provided an LED driver configured to control a LED fixture comprising a plurality of LEDs, the LED driver comprising:
• an input terminal configured to be connected to an external power supply,
• an output terminal configured to be connected to the LED fixture,
• a power converter configured to convert an input power received from the external power supply at the input terminal to a load power at the output terminal for powering the LED fixture, the power converter comprising o a PFC circuit configured to convert the input power to a bus voltage provided to a DC voltage bus, o a converter arranged downstream the DC voltage bus configured to convert the bus voltage to the load power, • a control unit configured to control the power converter to provide the load power to the LED fixture, and wherein the control unit is configured to, when the LED driver is in a standby mode, o determine the bus voltage, o control the PFC circuit by
■ switching off the PFC circuit when the determined bus voltage is higher than or equal to a high bus voltage limit,
■ switching on the PFC circuit when the determined bus voltage is lower than or equal to a low bus voltage limit.
In accordance with the present invention, an LED driver is, in general applied for powering an LED fixture. The LED fixture comprises a plurality of LEDs. The plurality of LEDs may be grouped in LED groups. The LED fixture is adapted to emit light with the desired colour, temperature and/or intensity.
The LED driver comprises an input terminal. The input terminal is configured to be connected to an external power supply. The external power supply is for example a mains power supply supplying an input voltage in the range of 120 V to 277 V at 60 Hz. Preferably, the input voltage is universal, for example in the residential areas the input voltage is the range of 100Vac to 277Vac. For example, in the United States LED drivers are used on 120Vac residential voltage levels and 277Vac industrial voltage levels.
The LED driver comprises an output terminal. The output terminal is configured to be connected to the LED fixture. The LED driver is configured to provide power from the external power supply to the LED fixture.
The LED driver further comprises a power converter. The power converter is configured to convert an input power received from the external power supply at the input terminal to a load power at the output terminal for powering the LED fixture. The load power is for example 100 W. The power converter comprises a PFC circuit. The PFC circuit has a power factor correction (PFC) property. The PFC circuit is configured to convert the input voltage to a bus voltage provided to a DC voltage bus. The PFC circuit is for example a PFC boost circuit configured to boost the input voltage to the bus voltage provided to the DC voltage bus. Boosting in this context means to increase the voltage. Therefore, the outputted bus voltage by the PFC boost circuit is always higher than the input voltage received from the external power supply. The bus voltage in nominal conditions, i.e. the LED fixture is emitting light, is for example 450 V. The power converter further comprises a converter arranged downstream the PFC circuit. The converter is configured to convert the bus voltage to the load power for powering the LED fixture. The LED driver further comprises a control unit. The control unit is configured to control the power converter to provide the load power to the LED fixture. The control unit is configured to, when the LED driver is in a standby mode, determine the bus voltage. When the LED driver is in a standby mode the load power is substantially zero. In the standby mode, the LED fixture is not emitting light. During the standby mode, the LED driver is consuming electrical power, e.g. due to switching losses by the PFC circuit, which is referred as standby power. The standby power should be as low as possible.
When the LED driver is in the standby mode, the control unit is configured to control the PFC circuit by switching off the PFC circuit when the determined bus voltage is higher than or equal to a high bus voltage limit and switching on the PFC circuit when the determined bus voltage is lower than or equal to a low bus voltage limit. By switching off the PFC circuit, the bus voltage decreases to a lower value. However, it should be noted that the PFC circuit cannot be totally switched off. Otherwise, the bus voltage is too low and, therefore, the loss of the converter, e.g. a resonant DC-DC converter, would be increased too much, which leads to a higher power consumption of the LED driver.
In order to obtain an optimal power consumption of the LED driver when in the standby mode, the bus voltage is controlled with hysteresis control. When the bus voltage, determined by the control unit, is higher than or equal to the high bus voltage limit, the PFC circuit is switched off such that the bus voltage decreases. When the bus voltage becomes lower or equal to the low bus voltage limit, the PFC circuit is switched on again such that the bus voltage increases. The PFC circuit is kept intermittent on and off in the standby mode, wherein the bus voltage is continuously maintained between the low bus voltage limit and the high bus voltage limit.
By using this approach, the power consumption of the LED driver in the standby mode is as low as possible due to the reduced switching loss of the PFC circuit without the risk that the power loss of the converter becomes too high. By obtaining an optimal trade-off between both power losses, the overall standby power loss is reduced.
In an embodiment, the converter is a resonant converter. For example, the converter is a resonant DC-DC converter. The DC-DC resonant converter comprises an isolation transformer having a primary circuit electrically separated from a secondary circuit. The secondary circuit is magnetically coupled to the primary circuit. DC power from the primary circuit is magnetically transferred to the secondary circuit. Alternatively, the converter is for example a flyback converter equipped with an isolation transformer.
It is further acknowledged that other types of converters such as boost, buck-boost, Cuk, SEPIC or other, either synchronous or non-synchronous may advantageously be applied in combination with the present invention. In an embodiment, the external power supply is an AC power supply. The AC power supply for example operates at 277 V, 60 Hz. The LED driver further comprises a rectifier for rectifying the AC power supply. For example, the PFC circuit comprises the rectifier for rectifying the AC power supply. The rectifier converts the AC current to DC current.
Additionally, the power converter comprises an electromagnetic interference filter (EMI) filter arranged downstream of the rectifier. The EMI filter provides electromagnetic noise suppression for the LED driver.
Alternatively, the external power supply is a DC power supply.
In an embodiment, the high bus voltage limit is between 400 V-500 V, preferably between 420 V-480 V, more preferably between 440 V-470 V.
In an embodiment, the low bus voltage limit is between 200 V-380 V, preferably between 220 V-350 V, more preferably between 250 V-350 V. The low bus voltage limit has to be set high enough such that the converter, when the LED driver is in the standby mode, has sufficient power to continue working. In case the bus voltage becomes too low, the converter could turn off which needs to be avoided in terms of energy efficiency. It requires more power to switch on again the converter compared to the situation wherein the converter operates continuously.
The high bus voltage limit and the low bus voltage limit define a bus voltage range. The bus voltage range influence the off and on time during which the PFC circuit is switched off and on by the control unit. Within a given standby period, during which the LED driver is in the standby mode, and by setting a narrow bus voltage range, more cycles are needed to switch the PFC circuit. By having more switching cycles of the PFC circuit, the overall power loss would increase again. To have the most efficient control mechanism of the PFC circuit, an optimum regarding the bus voltage range has to be made by taking into account the number of switching cycles of the PFC circuit and the off time of the PFC circuit.
In an embodiment, the control unit is configured to receive a signal representative of the bus voltage, wherein the signal is generated by a measurement unit configured to measure the bus voltage. As an example, the measurement unit performs current and/or voltage measurements, e.g. DC measurements, to derive the signal representative of the bus voltage. The control unit receives the signal from the measurement unit, e.g. via a processing unit. The measurement unit is for example integrated in the control unit. Based on the received signal, the control unit is able to determine the bus voltage.
Alternatively, the control unit directly determines the current and/or voltage, for example between the PFC circuit and the converter, instead of the measurement unit. In an embodiment, the PFC circuit comprises a switch. The switch is for example a FET or a MOSFET. The switching of the switch can e.g. be controlled by the control unit. For example, the PFC circuit is switched off when the switch is switched open.
According to a further aspect of the invention, the invention further pertains to a method of controlling a LED fixture comprising a plurality of LEDs by a LED driver, the LED driver comprising a power converter for powering the LED fixture and a control unit for controlling the power converter, the power converter comprising a PFC circuit configured to convert an input power to a bus voltage, the method comprising the steps of, when the LED driver is in a standby mode,
- determining the bus voltage,
- controlling the PFC circuit by o switching off the PFC circuit when the determined bus voltage is higher than or equal to a high bus voltage limit, o switching on the PFC circuit when the determined bus voltage is lower than or equal to a low bus voltage limit.
The invention will be described in more detail below with reference to the figures, in which in a non-limiting manner exemplary embodiments of the invention will be shown. The same reference numerals in different figures indicate the same characteristics in different figures.
In the figures:
Fig. 1 : Schematically illustrates an embodiment of an LED driver according to the invention;
Fig. 2: Schematically illustrates an electrical implementation of the PFC circuit of the LED driver according to the invention;
Fig. 3: Schematically illustrates an electrical implementation of the embodiment of an LED driver according to the invention;
Fig. 4: Schematically illustrates an embodiment of a switching diagram of the PFC circuit.
Figure 1 schematically illustrates an embodiment of an LED driver to control a LED fixture comprising a plurality of LEDs according to the invention. The LED driver 1 according to the invention comprises an input terminal 2. The input terminal 2 is connected to an external power supply 3. The external power supply 3 is for example a mains power supply supplying an input voltage 3a in the range of 120 V to 277 V at 60 Hz 230 V at 50 Hz. Preferably, the input voltage 3a is universal, for example in the residential areas the input voltage is the range of 100 Vac to 277 Vac. For example, in the United States LED drivers are used on 120 Vac residential voltage levels and 277 Vac industrial voltage levels.
The LED driver 1 comprises an output terminal 4. The output terminal 4 is connected to the LED fixture 5. The LED driver 1 is configured to provide power, for example an output voltage or current 4a, from the external power supply 3 to the LED fixture 5. The LED fixture 5 comprises a plurality of LEDs. The plurality of LEDs may be grouped in LED groups. The LED fixture 5 is adapted to emit light with the desired colour, temperature and/or intensity.
The LED driver 1 further comprises a power converter 6. The power converter 6 converts convert the input power 3a received from the external power supply 3 at the input terminal 2 to a load power 4a at the output terminal 4 for powering the LED fixture 5. The load power 4a is for example 100 W. The power converter 6 comprises a PFC circuit 7. In this case, the PFC circuit 7 is a PFC boost circuit. However, all types of converters having a PFC property are suitable for the implementation.
The PFC boost circuit 7 converts or boosts the input voltage to a bus voltage provided to a DC voltage bus 8. The bus voltage in nominal conditions, i.e. the LED fixture 5 is emitting light, is for example 450 V. The power converter 6 further comprises a converter 9 arranged downstream the PFC boost circuit 7. The converter 9 converts the bus voltage to the load power 4a for powering the LED fixture 5.
The LED driver 1 further comprises a control unit 10. The control unit 10 controls the power converter 6 to provide the load power 4a to the LED fixture 5. The control unit 10 is configured to, when the LED driver 1 is in a standby mode, determine the bus voltage. When the LED driver 1 is in a standby mode the load power 4a is substantially zero. In the standby mode, the LED fixture 5 is not emitting light. During the standby mode, the LED driver 1 is consuming electrical power, e.g. due to switching losses by the PFC boost circuit 7, which is referred as standby power. The standby power should be as low as possible.
When the LED driver 1 is in the standby mode, the control unit 10 is configured to control the PFC boost circuit 7 by switching off the PFC boost circuit 7 when the determined bus voltage is higher than or equal to a high bus voltage limit and switching on the PFC boost circuit 7 when the determined bus voltage is lower than or equal to a low bus voltage limit. By switching off the PFC boost circuit 7, the bus voltage decreases to a lower value. However, it should be noted that the PFC boost circuit 7 cannot be totally switched off. Otherwise, the bus voltage is too low and, therefore, the loss of the converter 9, e.g. a resonant DC-DC converter, would be increased too much, which leads to a higher power consumption of the LED driver 1.
In order to obtain an optimal power consumption of the LED driver when in the standby mode, the bus voltage is controlled with hysteresis control. When the bus voltage, determined by the control unit 10, is higher than or equal to the high bus voltage limit, the PFC boost circuit 7 is switched off such that the bus voltage decreases. When the bus voltage becomes lower or equal to the low bus voltage limit, the PFC boost circuit 7 is switched on again such that the bus voltage increases. The PFC boost circuit 7 is kept intermittent on and off in the standby mode, wherein the bus voltage is continuously maintained between the low bus voltage limit and the high bus voltage limit.
By using this approach, the power consumption of the LED driver 1 in the standby mode is as low as possible due to the reduced switching loss of the PFC boost circuit 7 without the risk that the power loss of the converter becomes too high. By obtaining an optimal trade-off between both power losses, the overall standby power loss is reduced.
Fig. 2 schematically illustrates an electrical implementation of the PFC circuit 7 of the LED driver according to the invention. The circuitry of the PFC circuit 7 comprises EMI filter 21. In the embodiment as shown, the external power supply 3 supplies an AC power to the EMI filter 21. The EMI filter 21 mitigates electromagnetic interference. The filtered AC power is provided to a rectifier 22. The rectifier 22 rectifies the AC power to DC power. The PFC circuit 7 converts the DC power into a bus voltage 8a. The bus voltage 8a is subsequently supplied to the converter 9 converting the bus voltage 8a to the load power for powering the LED fixture 5.
The PFC circuit 7 further comprises a switch 23. The switch 23 is a MOSFET. The switching of the switch 23 can e.g. be controlled by the control unit (not shown in Fig. 2). When the PFC circuit 7 is operational (the PFC circuit 7 is "on”) the switch 23 is switched with a high frequency, i.e. the switch 23 is intermittent open and closed. When the switch 23 is closed, energy is stored in the coil 24. When the switch 23 is open, the energy is transferred from the coil 24 to the capacitor 25 and the converter 9. When the switch 23 is continuously turned off, i.e. the switch 23 is open, the PFC circuit 7 is switched off.
Figure 3 shows an electrical implementation of the embodiment of an LED driver according to the invention. The features of the LED driver 1 corresponding with those of the LED driver shown in Fig. 1 are indicated with the same reference numerals in Fig. 3.
The LED driver 1 comprises a DC bus voltage sense unit 31, a hysteresis comparator 32 and some logic gates 33,34 in serial connection with the hysteresis comparator 32. The DC bus voltage sense unit 31 is a voltage divider, wherein the voltage at an inverting terminal 35, i.e. the sensed DC bus voltage or V., of the hysteresis comparator 32 is represented as:
Figure imgf000009_0001
wherein Vb is the DC bus voltage 8 and Re, R? are resistors.
The hysteresis comparator 32 compares one voltage level (V.) with another voltage level (V+) and produces an output voltage Ui based on this voltage comparison. V+ and V. correspond to the voltages at a non-inverting terminal 36 and the inverting terminal 35 respectively. The hysteresis comparator 32 uses a positive feedback for feeding back a part of the output voltage Ui to the non-inverting terminal 36 of the hysteresis comparator 32 via a voltage divider set up by the resistor Ri and R2. By using the positive feedback loop a hysteresis is created having a high bus voltage limit and a low bus voltage limit. The high bus voltage limit Vup and the low bus voltage limit V|OW are derived as:
Figure imgf000010_0001
wherein Vs is the supply voltage, e.g. 5 V, and Vref is a reference voltage.
The high bus voltage limit is between 400 V-500 V, preferably between 420 V-480 V, more preferably between 440 V-470 V. The low bus voltage limit is between 200 V-380 V, preferably between 220 V-350 V, more preferably between 250 V-350 V.
When the sensed DC bus voltage V- is less than the input voltage V+ at the noninverting terminal 36, the output voltage U1 will be high, and thus approximately equal to the supply voltage Vs. When the sensed DC bus voltage V. is higher than the input voltage V+ at the non-inverting terminal 36, the output voltage U1 will be low, and thus approximately equal to zero.
The hysteresis comparator is applied to control the switching of the PFC circuit 7. The output voltage U1 is supplied to an inverting gate 33, wherein the inverting gate 33 outputs an inverted logic value (low or high): low when the output voltage U1 is high and high when the output voltage U1 is low. The output of the inverting gate 33 is supplied to a first input terminal 34a of an AND gate 34. A mode signal 37 representative of the operational mode of the LED driver 1 is supplied to a second input terminal 34b of the AND gate 34. The mode signal 37 is a standby signal when the LED driver is in the standby mode. The output of the AND gate 34 is supplied to the switch 23. The switch 23 is for example a FET or a MOSFET. The switching of the switch 23 is controllable by the control unit 10 and the output of the AND gate 34. For example, by having a low logic value at the output of the AND gate 34, the switch 23 is switched open, i.e. the switch 23 is off.
In Fig. 3 the LED driver 1 comprises a resonant DC-DC converter 9. The resonant DC- DC converter 9 comprises an isolation transformer having a primary side 38 electrically separated from a secondary side 39. The secondary side 39 is magnetically coupled to the primary side 38. DC power from the primary side 38 is magnetically transferred to the secondary side 39. At the secondary side 39 a measurement circuit 40 is arranged. The measurement circuit 40 is configured to determine the operational mode of the LED driver 1, i.e. normal mode or standby mode. The measurement circuit 40 comprises a measurement device 41 configured to measure a voltage at the secondary side 39. Based on the voltage, the measurement device 41 outputs the mode signal 37. The measurement device 41 is an opto-coupler. In case the LED driver 1 is operating in standby mode, the opto-coupler 41 transmits a standby signal which is a high logic signal.
The PFC circuit 7 of Fig. 3 is for example switched according to the timing diagram as illustrated in Fig. 4. Between time to and ti the LED driver 1 is operating in normal mode. In normal mode, the sensed DC bus voltage V. is higher than high bus voltage limit Vup and the low bus voltage limit V|OW. Referring to Fig. 3, in case the LED driver 1 is operating in normal mode, a high logic value is provided to the first input terminal 34a. Further, the opto-coupler 41 transmits a low logic for the mode signal 37 to the second input terminal 34b of the AND gate 34. However, irrespective of the logic value at the first input terminal 34a of the AND gate 34, the AND gate 34 outputs a low logic value. In that case, the switch 23 is turned off and the PFC circuit 7 is operating normally (the PFC circuit is on).
At time ti , the operating mode of the LED driver 1 shifts to the standby mode. The opto-coupler transmits a high logic for the mode signal 37 to the second input terminal 34b of the AND gate 34. Because a high logic value is provided to the first input terminal 34a of the AND gate 34, the AND gate 34 outputs a high logic value causing the switch 23 to be turned on which turns the PFC circuit 7 off. When the PFC circuit 7 is switched off, the DC bus voltage 8 decreases. Thereby, the voltage V. at the inverting terminal 35 of the hysteresis comparator 32 decreases as well, as visualised in Fig. 4.
At time t2, V. becomes equal to the low bus voltage limit V|OW. As a result, the output voltage Ui of the hysteresis comparator 32 changes to a high logic value and thus a low logic value is provided to the first input terminal 34a. Thereby, the output value of the AND gate 34 is inverted which causes the switch 23 to be turned off again in order to switch on the PFC circuit 7. When the PFC circuit 7 is turned on at time t2, V. increases.
At time fe, V. becomes equal to the high bus voltage limit Vup. As a result, the output voltage Ui of the comparator changes to a low logic value and thus a high logic value is provided to the first input terminal 34a. Thereby, the output value of the AND gate 34 is inverted again which causes the switch 23 to be switched on, wherein the PFC circuit 7 is turned off. When the PFC circuit 7 is off at time fe, V. decreases till it reaches the low bus voltage limit V|OW at time t4. The above process between the time period t2-t4 repeats during the standby mode.
When the LED driver goes back into the normal operating mode at time ts, the PFC circuit 7 is kept ON. The DC bus voltage 8 increases again to the DC bus voltage in normal mode.

Claims

CLAIMS LED driver (1) configured to control a LED fixture (5) comprising a plurality of
LEDs, the LED driver comprising:
- an input terminal (2) configured to be connected to an external power supply (3),
- an output terminal (4) configured to be connected to the LED fixture,
- a power converter (6) configured to convert an input power (3a) received from the external power supply at the input terminal to a load power (4a) at the output terminal for powering the LED fixture, the power converter comprising o a PFC circuit (7) configured to convert the input power to a bus voltage (8a) provided to a DC voltage bus (8), o a converter (9) arranged downstream the DC voltage bus configured to convert the bus voltage to the load power,
- a control unit (10) configured to control the power converter to provide the load power to the LED fixture, and wherein the control unit is configured to, when the LED driver is in a standby mode, o determine the bus voltage, o control the PFC circuit by
- switching off the PFC circuit when the determined bus voltage is higher than or equal to a high bus voltage limit,
- switching on the PFC circuit when the determined bus voltage is lower than or equal to a low bus voltage limit. LED driver according to claim 1 , wherein the converter is a resonant converter. LED driver according to any of the preceding claims, wherein the external power supply is an AC power supply. LED driver according to claim 3, wherein the PFC circuit comprises a rectifier (22) for rectifying the AC power supply. LED driver according to any of the preceding claims, wherein the high bus voltage limit is between 400 V-500 V, preferably between 420 V-480 V, more preferably between 440 V-470 V. LED driver according to any of the preceding claims, wherein the low bus voltage limit is between 200 V-380 V, preferably between 220 V-350 V, more preferably between 250 V-350 V. LED driver according to any of the preceding claims, wherein the control unit is configured to receive a signal representative of the bus voltage, wherein the signal is generated by a measurement unit configured to measure the bus voltage. LED driver according to claim 7, wherein the control unit comprises the measurement unit. LED driver according to any of the preceding claims, wherein the PFC circuit comprises a switch (23). LED driver according to claim 9, wherein the control unit is configured to control the switch to switch the PFC circuit on or off. LED driver according to any of the preceding claims, wherein the PFC circuit is a PFC boost circuit. Method of controlling a LED fixture (5) comprising a plurality of LEDs by a LED driver (1), the LED driver comprising a power converter (6) for powering the LED fixture and a control unit (10) for controlling the power converter, the power converter comprising a PFC circuit (7) configured to convert an input power (3a) to a bus voltage (8a), the method comprising the steps of, when the LED driver is in a standby mode,
• determining the bus voltage,
• controlling the PFC circuit by o switching off the PFC circuit when the determined bus voltage is higher than or equal to a high bus voltage limit, o switching on the PFC circuit when the determined bus voltage is lower than or equal to a low bus voltage limit.
PCT/EP2023/075090 2022-09-16 2023-09-13 Led driver for controlling a led fixture and a method of controlling a led fixture WO2024056703A1 (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102014221511A1 (en) * 2014-10-23 2016-04-28 Tridonic Gmbh & Co Kg PFC circuit with voltage-dependent signal feed
US20160141964A1 (en) * 2014-11-17 2016-05-19 Infineon Technologies Austria Ag System and Method for a Switched-Mode Power Supply

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102014221511A1 (en) * 2014-10-23 2016-04-28 Tridonic Gmbh & Co Kg PFC circuit with voltage-dependent signal feed
US20160141964A1 (en) * 2014-11-17 2016-05-19 Infineon Technologies Austria Ag System and Method for a Switched-Mode Power Supply

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