CN111225470A

CN111225470A - Light modulation device for LED lamp

Info

Publication number: CN111225470A
Application number: CN201811397686.7A
Authority: CN
Inventors: 熊坤
Original assignee: Ledvance GmbH
Current assignee: Ledvance GmbH
Priority date: 2018-11-22
Filing date: 2018-11-22
Publication date: 2020-06-02

Abstract

Dimming device (1) for an LED lamp or luminaire having one or more LEDs (2), comprising: a power stage (10) comprising: output ports (12, 13) configured to output power suitable for operating the LEDs (2); and a controller (11) comprising an input (CTRL) configured to receive a dimming control signal (Ds); wherein the controller (11) is configured to adjust the power at the output port (12, 13) based on the dimming control signal (Ds) such that the adjustment of the power is performed by analog dimming if the dimming control signal (Ds) indicates dimming in a first dimming range and by PWM dimming if the dimming control signal (Ds) indicates dimming in a second dimming range.

Description

Light modulation device for LED lamp

Technical Field

The invention relates to a dimming device for an LED lamp or luminaire with one or more LEDs. The dimming apparatus includes a power stage having an output port configured to output power suitable for operating the LED and a controller including an input configured to receive a dimming control signal.

Background

With the advent of LED lamps, efficient and long-life lighting devices can be used. The material of the LED lamp is safer than other conventional lighting devices such as fluorescent lamps, because, for example, mercury is not required. Furthermore, LED lamps have a longer service life and higher energy efficiency than halogen lamps or incandescent bulbs.

Like other light sources, the brightness of the LEDs can be adjusted by dimming. However, LED lamps and conventional lamps have different electrical and dimming characteristics. For example, an incandescent light bulb may be dimmed by simply reducing the input voltage. Since LED lamps almost always require electronics to properly power the light emitting semiconductors, the dimmer must be configured so that the electronics function as needed.

There are a number of ways to control the light intensity of an LED lamp.

A first conventional technique, known as analog or linear dimming, is based on a reduction of the current supplied to the LED. Due to the steep diode characteristics, the current needs to be controlled very precisely in order to obtain a constant brightness over time. Furthermore, the dimming range is typically limited to about 20% to 100%. Dimming, on the other hand, does not cause any flickering of the LEDs.

A second conventional technique, referred to as PWM dimming, is based on the adjustment of the duty cycle. In other words, the LEDs are alternately switched on and off. The frequency is usually set high enough that the individual pulses are not perceptible to the human eye. As long as the frequency is above the perception threshold of a single pulse, the eye integrates all pulses and forms a time average of the on and off states. A uniform brightness is perceived. In many applications it is recommended that the PWM frequency be about 500Hz or higher. However, increasing the PWM frequency negatively impacts the dynamic dimming range and accuracy. Furthermore, flicker can be perceived when shooting video, and stroboscopic effects cannot always be avoided, especially in the case of moving light sources. On the other hand, in addition to the above-described limitation on the high PWM frequency, the fine dimming can be performed substantially in the entire dimming range of 0% to 100%.

The above summary shows that: both approaches (analog dimming and PWM dimming) have their specific advantages and disadvantages.

Disclosure of Invention

It is an object of the present invention to provide an improved dimming device suitable for dimming LED lamps or luminaires.

This object is solved by a dimming device having the features as defined in claim 1. Preferred embodiments are defined in the dependent claims, the general description of the invention and the description of the specific embodiments and the drawings.

The dimming device according to the present invention is part of or adapted to be connected to an LED lamp or luminaire having one or more LEDs. The dimming device is preferably designed to generate and output a current and a voltage having a power factor suitable for driving the LED. Thus, the dimming device may comprise some or all of the electronics of a conventional LED driver. Alternatively, the dimming device may be designed to cooperate with the LED driver.

The dimming device according to the present invention has a power stage comprising an output port configured to output power suitable for operating the LED directly or via an LED driver. The dimming device also has a controller including an input configured to receive a dimming control signal. The controller is configured to adjust the power, e.g. the current and/or the voltage and/or the pulse frequency, at the output port based on the dimming control signal such that the adjustment of the power is achieved by analog dimming if the dimming control signal indicates dimming in a first dimming range, and by PWM dimming if the dimming control signal indicates dimming in a second dimming range.

The dimming device synergistically combines the advantages of PWM dimming and analog dimming. The dimming device 1 achieves flicker-free dimming and particularly precise current control at the dimming level of the first dimming range, and good consistency at the dimming level of the second dimming range. Here, "uniformity" refers to the applicability of the dimming device to different LED lamps without strong differences in the light emission characteristics. The dimming device 1 can be implemented without significantly increasing the topology complexity, for example compared to a conventional PWM dimmer. Therefore, the light control device 1 is efficient, compact, and cost-effective.

Preferably, the first dimming range refers to a high dimming range including a dimming level equal to or greater than a dimming mode threshold, and the second dimming range refers to a low dimming range including a dimming level smaller than the dimming mode threshold. Here, the term "dimming level" denotes the brightness of the LED lamp or LED with respect to its maximum brightness. At low dimming levels, the light emission is low and flicker due to (high frequency) PWM control is acceptable. At higher dimming levels, the dimming arrangement according to the preferred embodiment switches to analog dimming, thereby achieving flicker free dimming. Thus, a particularly advantageous combination of PWM and analog dimming is achieved.

Preferably, the dimming mode threshold indicates a dimming level between 10% and 30%, for example 20%. The asymmetric selection of the dimming mode threshold allows PWM dimming to be performed only at very low dimming levels, maximizing the flicker free region. The asymmetric region provides an optimized combination of PWM dimming and analog dimming, since flicker becomes less recognizable at low light intensities.

Preferably, the dimming device further comprises a signal stage configured to generate the dimming control signal such that in the first dimming range the dimming control signal is an analog dimming signal, preferably a direct current signal, and in the second dimming range the dimming control signal is a PWM dimming signal. The generation and use of the analog dimming signal and the PWM dimming signal minimizes structural modifications to the power stage, particularly the controller. The power stage may be based on a conventional PWM dimmer with no or only small modifications, and the above technical effects and contributions may be achieved modularly by adding signal stages.

Preferably, the signal stage comprises an MCU having an analog MCU port and a PWM MCU port, wherein the MCU is configured such that if the MCU is instructed to perform dimming within a first dimming range, the MCU outputs an analog dimming signal as the PWM signal at the analog MCU port and no output at the PWM MCU port, and if the MCU is instructed to perform dimming within a second dimming range, the MCU outputs a PWM dimming signal as the PWM signal at the PWM MCU port and no output at the analog MCU port. The term "analog MCU port" means that its signal is used to indicate and trigger analog dimming, and not to refer to the waveform of the signal. Both the analog dimming signal and the PWM dimming signal preferably have PWM waveforms. An exemplary solution based on an MCU as defined above can be implemented by using standard components, thus achieving a particularly reliable and cost-effective solution.

Preferably, the signal stage further includes a diode, a resistor, and a capacitor, the diode, the resistor, and the capacitor being connected and configured such that if dimming is performed within the first dimming range, the PWM signal output at the analog MCU port is filtered and changed into a DC voltage, thereby generating the analog dimming signal. This preferred circuit requires only three additional components. The dimming device is therefore particularly efficient, compact and cost-effective.

Preferably, the power stage is connected to a DC power supply. To this end, the dimming device may further comprise an input port configured to connect the dimming device to an AC power source, and a rectifier circuit connected to the input port and configured to convert AC power provided by the input port into DC power to be supplied to the power stage. For example, the input port may be connected or connectable to a conventional network power supply.

Preferably, the controller is implemented by or comprises an integrated circuit. For example, the controller may be a combinational logic circuit, a Field Programmable Gate Array (FPGA), a processor capable of executing code, or another suitable component that provides the described functionality. Thus, the dimming device can be realized using standard components, thereby realizing a particularly reliable and cost-effective solution.

Preferably, the dimming means is implemented by or comprises a buck converter. High power factor can be achieved with a buck topology.

Drawings

Preferred embodiments of the present invention will be explained below with reference to the accompanying drawings.

Fig. 1 is a block diagram schematically illustrating a combination of an analog dimming signal and a PWM dimming signal for operating a controller of a dimming device.

Fig. 2 is a partial circuit diagram of an exemplary dimming device including a controller.

Fig. 3a to 3d are views showing waveforms of LED currents at different dimming levels, which are generated by the dimming device configured as shown in fig. 2.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Here, elements that are the same, similar or have the same or similar effect have the same reference numerals. The descriptions of these elements may be omitted to prevent redundant descriptions.

Fig. 1 is a block diagram schematically showing a combination of an analog dimming signal As and a PWM dimming signal Ps for operating a controller 11 of a dimming device 1 configured to dim one or more LEDs.

The controller 11 may be or include electronic circuitry, combinational logic circuitry, a Field Programmable Gate Array (FPGA), a processor capable of executing code, or another suitable component that provides the desired functionality described below. Preferably, the controller 11 is a commercially available IC (integrated circuit).

The controller 11 includes an input or pin configured to receive a dimming control signal Ds indicative of a desired brightness of the LED to be dimmed. If dimming is based on PWM dimming only, the dimming control signal Ds may be the PWM dimming signal Ps. If the dimming is based on analog dimming only, the dimming control signal Ds may be the analog dimming signal As.

According to the embodiment shown in fig. 1, the dimming control signal Ds is a composite signal such that it depends on the dimming range. The dimming control signal Ds is the analog dimming signal As if dimming is performed within the first dimming range. The dimming control signal Ds is the PWM dimming signal Ps if dimming is performed within the second dimming range. Based on this situation distinction, the controller 11 is configured to perform analog dimming or PWM dimming.

Preferably, the first dimming range is a high dimming range, e.g. about 20% to 100%. Preferably, the second dimming range is a low dimming range, e.g. below 20%. The dimming level separating the high dimming range from the low dimming range may be denoted as "dimming mode threshold". Preferably, the dimming mode threshold indicates a dimming level between 10% and 30%, for example about 20%.

Fig. 2 is a partial circuit diagram of an exemplary dimming device 1 including a controller 11.

The dimming device 1 is configured to receive AC main power via a power line or an input port (not shown). For example, the power line may be part of or connected to a conventional network power supply. In this case, the dimming device 1 preferably comprises a rectifier circuit (not shown) configured to provide an unregulated DC voltage from the AC power. Alternatively, the dimming device 1 may be configured to receive DC power from a suitable electronic device.

The dimming device 1 comprises a power stage 10. The exemplary power stage 10 shown in fig. 2 includes an inductor L3, a controller 11, a diode D7, resistors R4, R6, R9, and capacitors C20, C24, connected as shown in fig. 2. Preferably, the power stage 10 utilizes a buck topology that can achieve a high power factor. The power stage 10 comprises

output ports

12, 13 for outputting a regulated power suitable for operating an LED lamp having one or more LEDs 2.

The controller 11 may include eight pins or input/output ports: SET, GND1, GND2, CTRL, SW1, SW2, N/C, VIN. The dimming control signal Ds is received via the CTRL pin and the output power, preferably the current and/or the voltage and/or the pulse frequency, at the

output ports

12, 13 is determined and adjusted based on the dimming control signal Ds.

The dimming device 1 further comprises a signal stage 20 configured to generate a dimming control signal Ds, e.g. based on a user input.

According to the embodiment shown in fig. 2, the signal stage 20 comprises an MCU (microcontroller) 21 comprising two MCU ports, hereinafter denoted analog MCU port 21a and PWM MCU port 21 b. The MCU21 is configured to generate and selectively output a PWM signal at the analog MCU port 21a or the PWM MCU port 21 b. If the MCU21 is instructed to perform dimming in a high dimming range, for example, 20% or more of the maximum brightness of the LED2, the MCU21 outputs a PWM signal at the analog MCU port 21a and no output at the PWM MCU21 b. If MCU21 is instructed to perform dimming in a low dimming range, e.g. below 20% of the maximum brightness of LED2, MCU21 outputs a PWM signal at PWM MCU port 21b and no output at analog MCU21 a port.

The PWM signal at the PWM MCU port 21b may be used directly as the dimming control signal Ds received by the CTRL pin of the controller 11. The PWM signal at the PWM MCU port 21b may be the PWM dimming signal Ps defined with respect to fig. 1.

Preferably the PWM signal at the analog MCU port 21a is converted to a DC voltage signal in order to trigger the controller 11 to perform analog dimming. For this purpose, the signal stage 20 may include a diode D1, a resistor R1, and a capacitor C1, which are connected as shown in fig. 2. Therefore, if dimming is performed in a high dimming range, the PWM signal output by the analog MCU port 21a is filtered by R1 and C1 and changed to a DC voltage, thereby implementing analog dimming.

Fig. 3a to 3d are views showing waveforms of LED currents at different dimming levels generated by the dimming device 1. Here, the dimming mode threshold is set to 20%.

Fig. 3a shows waveforms measured in a low dimming range (i.e., PWM scheme) with a dimming level of 18%. Fig. 3b shows the measured waveform in the low dimming range (i.e., PWM scheme) with a dimming level of 1%. Fig. 3c shows the measured waveform in the high dimming range (i.e. the analogue scheme) with a dimming level of 100%. Fig. 3d shows the measured waveform (i.e. the simulation scheme) in the high dimming range with a dimming level of 21%.

The exemplary waveforms of fig. 3a to 3d reveal the advantage that the dimming device 1 synergistically combines PWM dimming and analog dimming. The dimming device 1 achieves flicker-free dimming at high dimming levels and particularly accurate current control, as well as good uniformity at low dimming levels. Here, "uniformity" refers to the applicability of the dimming device 1 to different lamps without strong differences in light emission characteristics. At low dimming levels, the light emission is low and flicker due to PWM control (preferably high frequency) is acceptable. At higher dimming levels, the dimming device 1 switches to analog dimming, thereby achieving flicker-free dimming. The dimming device 1 can be implemented without significantly increasing the topology complexity compared to e.g. a conventional PWM dimmer. The exemplary circuit shown in fig. 1 requires only three additional components, D1, C1, and R1. Therefore, the light control device 1 is efficient, compact, and cost-effective.

The present invention is not limited by the description based on the embodiments. Rather, the invention encompasses any novel feature and any combination of features, including in particular any combination of features in the patent claims, even if this feature or combination is not explicitly specified in the patent claims or exemplary embodiments.

List of reference numerals

1 light modulation device

2 LED

10 power stage

11 controller

12 output port

13 output port

20 signal stage

21 MCU

21a analog MCU port

21b PWM MCU port

Ds dimming control signal

As analog dimming signal

Ps PWM dimming signal

L3 inductor

D1, D7 diode

R1, R4, R6 and R9 resistors

C1, C20, C24 capacitor

Claims

1. Dimming device (1) for an LED lamp or luminaire having one or more LEDs (2), comprising:

a power stage (10) comprising: output ports (12, 13) configured to output power suitable for operating the LEDs (2); and a controller (11) comprising an input (CTRL) configured to receive a dimming control signal (Ds); wherein the content of the first and second substances,

the controller (11) is configured to adjust the power at the output port (12, 13) based on the dimming control signal (Ds) such that if the dimming control signal (Ds) indicates dimming in a first dimming range, the adjustment of the power is performed by analog dimming, and if the dimming control signal (Ds) indicates dimming in a second dimming range, the adjustment of the power is performed by PWM dimming.

2. The dimming device (1) according to claim 1, wherein the first dimming range refers to a high dimming range comprising a dimming level equal to or greater than a dimming mode threshold, and the second dimming range refers to a low dimming range comprising a dimming level smaller than the dimming mode threshold.

3. The dimming device (1) according to claim 2, wherein the dimming mode threshold indicates a dimming level between 10% and 30%, preferably 20%.

4. The dimming arrangement (1) according to claim 1, further comprising a signal stage (20), the signal stage (20) being configured to generate a dimming control signal (Ds) such that in the first dimming range the dimming control signal (Ds) is an analog dimming signal (As), preferably a direct current signal, and in the second dimming range the dimming control signal (Ds) is a PWM dimming signal (Ps).

5. The dimming device (1) according to claim 4, wherein the signal stage (20) comprises an MCU (21) with an analog MCU port (21a) and a PWM MCU port (21b), wherein

The MCU (21) is configured such that if the MCU (21) is instructed to perform dimming within the first dimming range, the MCU (21) outputs the analog dimming signal (As) As a PWM signal at the analog MCU port (21a) and no output at the PWM MCU port (21b), and if the MCU (21) is instructed to perform dimming within the second dimming range, the MCU (21) outputs a PWM dimming signal (Ps) As a PWM signal at the PWM MCU port (21b) and no output at the analog MCU port (21 a).

6. The dimming device (1) of claim 5, wherein the signal stage (20) further comprises a diode (D1), a resistor (R1) and a capacitor (C1), the diode (D1), the resistor (R1) and the capacitor (C1) being connected and configured such that if dimming is performed within the first dimming range, the PWM signal output by the MCU (21) at the analog MCU port (21a) is filtered and changed to a DC voltage, thereby generating the analog dimming signal (As).

7. The dimming device (1) according to claim 1, wherein the power stage (10) is connected to a direct current power supply.

8. The dimming device (1) according to claim 7, further comprising an input port configured to connect the dimming device (1) to an alternating current power source and a rectifier circuit connected to the input port and configured to convert alternating current power provided by the input port into direct current power to be supplied to the power stage (10).

9. The dimming device (1) according to claim 1, wherein the controller (1) is realized by or comprises an integrated circuit.

10. The dimming device (1) according to claim 1, wherein the power stage (11) is realized by or comprises a buck converter.