Patent Grant
8203276
The present invention relates generally to the field of light dimming control. More particularly, the present invention relates to providing an improved phase controlled dimming LED (Light Emitting Diode) driver circuitry, system and a method thereof, which does not employ a processing unit (e.g., microcontroller) and enables “deep” light dimming, such as dimming down to 0.1% of the full light intensity.
Throughout this specification, the following definitions are employed:
AM: is an acronym for Amplitude Modulation, according to which the strength of the signal is varied in relation to the information being transferred.
TRIAC: is an acronym for TRIode for Alternating Current (AC) that is an electronic component/unit approximately equivalent to two silicon-controlled rectifiers joined in inverse parallel (paralleled but with the polarity reversed) and with their gates connected together.
PWM: is an acronym for Pulse Width Modulation of a signal, which involves the modulation of a signal duty cycle to either control the amount of power transferred to a load or to convey information over a communications channel.
THD: is an acronym for Total Harmonic Distortion. When the current drawn by a power line connected circuit is non-sinusoidal, a Fourier analysis of the resulting current waveform shows the presence of harmonics. The sum of these harmonics, expressed as a percentage of the current, is known as the total harmonic distortion or THD. Zero percent THD means a perfect sine wave. Most lighting prior art electronic equipment has less than 20% THD.
In recent years, the usage of LED illumination instead of other kinds of illumination (such as the fluorescent illumination, incandescent bulb illumination, and the like), has significantly increased due to the increasing luminosity of LED devices and due to their continuously decreasing costs. Although most people around the world still use fluorescent and incandescent bulb lighting, development of low-cost and efficient LED illuminating devices has recently accelerated rapidly.
Nowadays, various lighting devices include light dimmers, which enable adjusting the power delivered to the light sources, and thereby enable the control of the amount of light generated by these light sources. For this, the user interface of dimmers is usually equipped with an appropriate light adjustment mechanism (e.g., a slider). During such an adjustment, the light outputted from the light sources (e.g., LEDs) is gradually varied, enabling the user to adjust the desired level of illumination, which is the most appropriate for his needs, and to switch said light sources ON and OFF.
According to the prior art, conventional lighting devices are usually powered by an AC source (line voltage power, such as 120V RMS (Root Mean Square) at 60 Hz (Hertz) and 220V at 50 Hz); therefore, AC dimmers usually receive the AC line voltage at their input, and then output corresponding AC signals, having one or more variable parameters used to adjust an average voltage of these AC signals in response to a user's operation of the dimmer. Conventional AC dimmers are configured to control the power delivered to light sources in several different ways, such as increasing/decreasing voltage amplitude of the AC output signal and adjusting the duty cycle of the AC output signal (for example, by chopping-out portions of the AC voltage cycle). This technique is sometimes called phase/angle modulation, since it is based on the adjustable phase angle of the AC output signal. Usually, dimmers that implement such angle modulation use a TRIAC component/unit that is selectively operated to adjust the duty cycle of the AC signal outputted from the dimmer, and thereby to modulate the phase angle. Such dimmers are therefore called “TRIAC dimmers”.
Also, according to the prior art, the early technology in the field of LED illumination was based on providing a DC (Direct Current) power supply and then using a microprocessor to operate a PWM (Pulse Width Modulation) switch to control the brightness of the perceived light. On the other hand, in the fields of fluorescent and incandescent bulb lighting, the control of light has long been available by using phase control dimmers, such as the TRIAC dimmers. However, the use of TRIAC dimmers for other than incandescent lighting requires the overcoming of several problems, such as TRIAC instability.
The problems related to providing LED illumination have been recognized in the Prior Art, and various systems and methods have been developed to provide a solution.
U.S. Pat. No. 6,586,890 discloses a driver circuit that provides power to LEDs by using pulse width modulation (PWM). The driver circuit uses current feedback to adjust power to LED arrays and provides a full light and a dim mode.
U.S. Pat. No. 5,783,909 describes a method of controlling the light output from a LED by using PWM control of the LED current in response to signals provided from a light sensor, in order that the generated light will remain constant.
U.S. Pat. No. 6,788,011 presents systems and methods related to LED systems capable of generating light, such as for illumination or display purposes. The light-emitting LEDs may be controlled by a processor to alter the brightness and/or color of the generated light, e.g., by using pulse-width modulated signals. Thus, according to U.S. Pat. No. 6,788,011, the resulting illumination may be controlled by a computer program to provide complex, pre-designed patterns of light.
U.S. Pat. No. 7,038,399 relates to methods and apparatus for providing power to devices via an AC (Alternating Current) power source, and for facilitating the use of LED-based light sources on AC power circuits that provide signals other than standard line voltages. In one example, LED-based light sources may be coupled to AC power circuits that are controlled by conventional dimmers.
U.S. Pat. No. 6,744,223 discloses a multicolor lamp system that includes a dimming circuit and an illumination module electrically connected to the dimming circuit. The illumination module has a detection circuit for detecting the output of the dimming circuit. The detection circuit generates a detection signal corresponding to the output of the dimming circuit. A microcontroller is programmed to receive the detection signal and to supply a corresponding electrical signal to a plurality of LEDs.
U.S. Pat. No. 5,604,411 presents a dimming ballast for use with a phase control dimmer, including an EMI filter to avoid excessive voltage and peak currents in the filter due to resonance with the phase controlled AC waveform at low conduction angles, when the load presented by the lamp is low. The ballast includes circuitry to sense the rectified DC voltage and to discharge the filter capacitor when the rectified voltage is at or near zero, to thereby keep the EMI filter loaded and prevent misfiring of the phase control dimmer.
There is a continuous need in the art to enable the high quality dimming of light (e.g., generated by a LED load) by using a TRIAC dimmer that includes a TRIAC component/unit, substantially overcoming TRIAC component instability issues. Also, there is a need in the art to provide a phase controlled dimming LED driver, which eliminates the need to use a processing unit (e.g., a microprocessor, a microcontroller), and which pulse width modulates the output current provided to the LED load at a frequency unrelated to the power line frequency. In addition, there is a need to achieve “deep” dimming by using a TRIAC dimmer (e.g., dimming down to 0.1% of the full light brightness) and enabling keeping the TRIAC component of the TRIAC dimmer operating in a substantially stable manner. Further, there is a need to enable assembling LED drivers for color mixing, in which two or more separate LED drivers can be independently controlled by phase control dimmers (e.g., by TRIAC dimmers), so that any desired color light can be generated.
The present invention relates to providing an improved phase controlled dimming LED driver circuitry, system and a method thereof, which does not employ a processing unit (e.g., microcontroller) and enables “deep” light dimming, such as dimming down to 0.1% of the full light intensity.
A phase controlled dimming driver circuitry is configured to receive a regulated alternating current (AC) signal from a phase control dimmer and to enable dimming the intensity of light generated by a light source that is connected to said phase controlled dimming driver circuitry, comprising:
According to an embodiment of the present invention, the output stage further outputs a DC signal back to the flyback converter stage according to the magnitude of voltage on the constant voltage capacitor.
According to another embodiment of the present invention, the phase control dimmer is a TRIAC (TRIode for Alternating Current) dimmer.
According to still another embodiment of the present invention, the phase control dimmer comprises an adjusting means for controlling the required light dimming level of the light source.
According to still another embodiment of the present invention, the adjusting means is a slider.
According to a particular embodiment of the present invention, the input stage comprises one or more filters for receiving the regulated AC signal and filtering its noise.
According to another particular embodiment of the present invention, the input stage comprises one or more rectifiers for converting the regulated AC signal into the DC signal.
According to still another particular embodiment of the present invention, the input stage comprises a damper for damping down the ringing current within said input stage.
According to an embodiment of the present invention, the corresponding signal outputted from the output stage is chopped, according to the PWM signal.
According to a particular embodiment of the present invention, the light source is at least one light emitting diode (LED).
According to an embodiment of the present invention, the light generated by means of the light source is dimmed down to 0.1% of the full light source intensity.
According to still another embodiment of the present invention, the light source generates light of at least one color.
According to a further embodiment of the present invention, the phase controlled dimming driver circuitry further comprises a power factor correction (PFC) circuit.
According to an embodiment of the present invention, a phase controlled dimming driver circuitry is configured to receive a DC signal converted from a regulated AC signal, provided from a phase control dimmer, and to enable dimming intensity of light generated by a light source that is connected to said phase controlled dimming driver circuitry, comprising:
According to another embodiment of the present invention, a phase controlled dimming driver circuitry is configured to enable dimming intensity of light generated by a light source, said phase controlled dimming driver circuitry being connected to a phase control dimmer that provides to it a regulated AC signal, wherein said phase controlled dimming driver circuitry does not include a microprocessor and pulse width modulates its output current, provided to said light source, at a frequency unrelated to the AC signal frequency.
According to still another embodiment of the present invention, a phase controlled dimming driver circuitry is configured to enable dimming intensity of light generated by a light source, said phase controlled dimming driver circuitry being connected to a phase control dimmer that outputs to it a regulated AC signal, wherein said phase controlled dimming driver circuitry does not include a microprocessor and applies amplitude modulation (AM) and pulse width modulation substantially simultaneously to the output current provided to said light source.
According to still another embodiment of the present invention, a phase controlled dimming driver circuitry is configured to enable dimming intensity of light generated by a light source and being connected to a TRIAC (TRIode for Alternating Current) dimmer that outputs a regulated AC signal, wherein said phase controlled dimming driver circuitry comprises a power dissipating load that is gradually activated, as the output current of said phase controlled dimming driver circuitry is reduced, for enabling a substantially stable operation of a TRIAC unit provided within said TRIAC dimmer.
According to a further embodiment of the present invention, a phase controlled dimming driver circuitry is configured to enable dimming intensity of light generated by a light source and being connected to a TRIAC (TRIode for Alternating Current) dimmer that provides a regulated AC signal, wherein as the voltage provided from said TRIAC dimmer is reduced, the output current of said light source becomes substantially constant, and the light generated by said light source dims substantially linearly until a predefined level.
A system is configured to control dimming of the light source intensity, said system comprising:
According to an embodiment of the present invention, the phase controlled dimming driver circuitry further decodes control data from the regulated AC signal received from the phase control dimmer.
According to an embodiment of the present invention, the system is a multicolor light generating system.
According to another embodiment of the present invention, a system is configured to control dimming of the light source intensity, said system comprising:
According to still another embodiment of the present invention, a system configured to control dimming of the light source intensity, said system comprising:
According to still another embodiment of the present invention, a system is configured to control dimming of the light source intensity, said system comprising:
According to a further embodiment of the present invention, a system comprises at least two phase controlled dimming drivers configured to enable dimming light intensity of at least one light source, each of said at least two phase controlled dimming drivers being connected to a corresponding phase control dimmer that independently controls it and outputs to it a regulated AC signal for enabling color mixing of light to be generated by said at least one light source, thereby generating multicolor light.
In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.
In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, systems, procedures, components, units, circuits and the like have not been described in detail so as not to obscure the present invention.
Hereinafter, whenever the term “LED” is mentioned, it should be understood that it refers to any type of a light illumination source, such as a LED-based source, an incandescent source (a filament lamp, a halogen lamp, etc.), a high-intensity discharge source (sodium vapor, mercury vapor, a metal halide lamp and the like), a fluorescent source, a phosphorescent source, laser, an electroluminescent source, a pyro-luminescent source, a cathode-luminescent source using electronic satiation, a galvano-luminescent source, a crystallo-luminescent source, a kine-luminescent source, a candle-luminescent source (a gas mantle, a carbon arc radiation source, and the like), a radio-luminescent source, a luminescent polymer, a thermo-luminescent source, a tribo-luminescent source, a sono-luminescent source, an organic LED-based source and any other type of a light illumination source.
According to an embodiment of the present invention, TRIAC dimmer 105 enables a user of system 100 to regulate the light illumination. When the TRIAC dimmer is controlled up and down by a user (e.g., by using a conventional adjusting means, such as a slider provided on said TRIAC dimmer 105), then illumination of LEDs provided within LED load 115 becomes brighter and dimmer, respectively. Phase controlled dimming LED driver 110 receives a power input from TRIAC dimmer 105, which in turn is fed by an AC power line. It should be noted that LED driver 110, for example, can receive voltages from 120 to 6 Volts RMS, in the example of 120V system 100.
According to an embodiment of the present invention, TRIAC dimmer 105 comprises a TRIAC component (unit) that operates in a substantially stable manner. The TRIAC unit is a latching unit, which is either ON or OFF. It is triggered ON at a point in time, which is an adjustable interval after the AC power line voltage zero crossing. When it turns ON, the voltage which is applied to dimming LED driver 110 can vary, for example, from a zero value to 100V [Volts] in a microsecond. Inside the TRIAC dimmer 105 can be provided a relatively small inductor (not shown) that is intended to prevent the current from rising unduly fast. This may be required because an input stage 120 (
According to an embodiment of the present invention, phase controlled LED driver 110 does not contain a microprocessor and pulse width modulates the current outputted to LED load 115 at a frequency unrelated to the AC power line frequency. According to another embodiment of the present invention, phase controlled LED driver 110 applies both amplitude modulation and pulse width modulation substantially simultaneously to the current outputted to LED load 115, enabling “deep” light dimming, where the light generated by means of LED load 115 can be dimmed, for example, down to 0.1% of the full light brightness.
According to a further embodiment of the present invention, the “deep” dimming is achieved by gradually phasing in a power dissipating load (resistor R53 (FIG. 2D)), as the LED load 115 output current is being reduced and phased back by means of a PWM signal, for the purpose of providing a sufficient load to the TRIAC component located within TRIAC dimmer 105 to keep said TRIAC component operating in a substantially stable manner and enabling continuous “deep” dimming.
According to still a further embodiment of the present invention, an assemblage of two or more dimming LED drivers 110 can be constructed for enabling color light mixing, wherein said dimming LED drivers 110 are being independently controlled by means of one or more phase control dimmers (such as TRIAC dimmer 105), so that any desired color (multicolor) light can be generated. For this, LED load 115 can be provided in groups of red LEDs, blue LEDs and green LEDs. If all groups of LEDs are switched ON to a suitable degree (all twelve LEDs are ON), then the produced light color is white. Thus, the light color can be adjusted by modulating the light output of the different groups of LEDs: for example, by partially turning OFF a blue group of LEDs. When said blue group of LEDs is turned OFF, then the intensity of the blue light is reduced, resulting in producing a different light color.
According to an embodiment of the present invention, Input Stage 120 comprises Filters 121 for receiving an AC input signal and preventing noise generated in the driver module from escaping onto the AC power line; Rectifiers 122 for converting (rectifying) the received AC signal into a DC (Direct Current) signal; and Damper 123 for damping down the ringing current, which flows between inductors L2 and L3 and capacitors C23, C1 and C4 (
According to an embodiment of the present invention, Phase Decode and PWM Generation Stage 125 comprises Phase Decoder 126 and Pulse Width Modulator 127 for generating a PWM signal and providing it into Output stage 135 for regulating brightness dimming of LEDs within LED load 115. The input into Phase Decode and PWM Generation Stage 125 is a rectified DC voltage signal outputted from Input stage 120. In addition, Phase Decode and PWM Generation Stage 125 receives auxiliary 15V power voltage from Flyback converter stage 130. The output of Phase Decode and PWM Generation Stage 125 goes through optocoupler U2 (
Flyback converter stage 130 comprises Flyback converter 131 that receives a rectified DC voltage signal from Input stage 120. It should be noted that Flyback converter 131 can draw power from the AC power line with better than 20% THD (Total Harmonic Distortion), when substantially no phase control is applied to LED driver 110. It should be noted that when TRIAC phase control is applied, then the THD of the AC line current can be, for example, 60% or more. Further, it should be noted that regardless of the level of the phase control, according to which the TRIAC component (provided within TRIAC dimmer 105 (
Output stage 135 is a constant current stage that receives a PWM signal from Phase Decode and PWM Generation Stage 125, said PWM signal coming out of optocoupler U2. Output stage 135 gets an information input from the magnitude of the voltage on constant voltage capacitor C12, when said voltage is less than 59V (it is supposed, for example, that the regulated DC voltage provided at the output of Flyback converter stage 130 is substantially 59V). Further, Output stage 135 has two outputs. The first output is the LED current output from terminals “+” and “−” (
Diodes D1 to D4 define a conventional full bridge Rectifier 122 (
It should be noted that the undesirable resonance of the Input stage 120 circuit can be associated with charging capacitors C23, C1, and C4 through inductors L2, L3 and through a relatively small inductor, which is usually provided within TRIAC dimmer 105. These capacitors C23, C1 and C4 may become overcharged, and then they start discharging back through said inductors that can cause a reversal of the power line current, which in turn may turn OFF the TRIAC component of TRIAC dimmer 105. Thus, capacitor C33 has a relatively big capacitance (such as 0.47 μF, i.e., five times bigger) compared to other capacitors. In addition, providing resistor R65 enables limiting capacitor C33 charging, so that it is still charging up, when all the other capacitors of Input stage 120 have finished charging. As a result, according to an embodiment of the present invention, the input current is not reversed, and the TRIAC component stays switched ON (remains stable).
It should be noted that a portion 220 of Phase Decode and PWM Generation stage 126 circuitry, containing transistors Q2 and Q1, zener diodes ZD5 and ZD6, and resistors R11, R12, R10 and R9, is a conventional floating, two terminal network circuit, which requires no external power or bias to function as a current limiter. It can be assumed, for example, that a small current is flowing through the reverse biased half of zener diode ZD5. This will produce a voltage, for example 3.3V (this voltage is desirably kept relatively small, but cannot be any lower because conventional zener diodes of lower voltage become relatively leaky), which is applied across the emitter base of transistor Q2. Resistor R10 limits the current which flows, and as a result, roughly constant current flows out of the collector of transistor Q2, corresponding to the zener diode ZD5 voltage that is applied across said resistor R10. The forward biased half of zener diode ZD5 is used for temperature compensation, and it compensates for the presence of the emitter base junction of transistor Q2. When the substantially constant collector current is outputted from transistor Q2, this current goes through the reverse biased half of zener diode ZD6 and biases transistor Q1, similarly to biasing transistor Q2. As a result, transistor Q1 has a substantially constant collector current, which in turn biases zener diode ZD5. Also, it should be noted that resistors R11 and R12 (which can be high voltage 10 MΩ [MegOhm] resistors) enable providing a relatively tiny leakage current for initiating operation of said portion 220 of circuitry. Further, it should be noted that said portion 220 of circuitry is connected to the AC power line by means of terminal RAIL, and it may be exposed to voltage surges, which can even be 600V, for example. Thus, in order to protect it against such voltage surges, a high voltage resistor R52 of 4.7 KΩ is placed in series with said current limiter 220 and a surge protecting zener diode ZD8 (e.g., 400V surge protecting diode) is placed across it.
The above described portion 220 of Phase Decode and PWM Generation stage 126 circuitry generates a substantially constant current of 1 mA [milliAmpere], when applying voltages from 7V to 500V to Dimming LED driver circuit 110. The purpose of providing said substantially constant current is that whenever the TRIAC component (provided within TRIAC dimmer 105 (
According to an embodiment of the present invention, PWM generation circuit of Phase Decode and PWM Generation stage 126 operates with applying a positive voltage of 13.6V to Vcc Supply 226; applying substantially zero voltage on terminal 11 of said Vcc Supply 226; and applying a reference signal of approximately 7V (e.g., 7.5 Volts) to terminal 2 of amplifier U11 and to terminal 12 of amplifier U14, said reference signal is generated by using a potential divider (consisting of resistors R6, R8) of an input 10V voltage. It should be noted that capacitor C20 makes said 13.6V voltage signal substantially noise free, similarly to capacitor C6 which makes 10V voltage signal (generated by precision regulator U4) substantially noise free. As a result, the noise from the PWM generation circuit is substantially removed, eliminating undesirable fluctuations of light generated by the LED load 115 (
According to another embodiment of the present invention, amplifier U11 has mostly positive feedback through resistor R4. Therefore, if the voltage outputted from terminal 1 of said amplifier U11 is relatively high, then the voltage value of its input terminal 3 is also relatively high compared to the half way point voltage on its other input terminal 2. It should be noted that since the output terminal 1 of amplifier U11 is provided with a substantially constant high voltage, the current flows through resistor R3 into terminal 13 of amplifier U14, which is configured as an integrator. Because terminals 12 and 13 of amplifier U14 need to stay at the same voltage potential, the output terminal 14 of amplifier U14 ramps down at a rate such that the displacement current flowing through capacitor C5 substantially eliminates the current flow through resistor R3. Further, the output from terminal 14 of integrator U14 is applied through resistor R13 to terminal 3 of amplifier U11. This means that a relatively small portion of the terminal 14 voltage is being applied to said terminal 3 (the voltage on terminal 3 of amplifier U11 is not entirely locked to the voltage on terminal 1 of said amplifier U11, since the signal through resistor R13 can pull it around). As the voltage on terminal 14 of integrator U14 starts decreasing, the voltage on terminal 3 of amplifier U11 is pulled down below the reference voltage (e.g., 7V) provided into terminal 2. Then, amplifier U11 flips state with pin 1 switching to its limiting low voltage output. This leads to the linear increase of terminal 14 voltage, until the voltage on terminal 3 is pulled above said reference voltage. After that, the voltage on said terminal 3 is pulled down again, repeating these steps.
It should be noted that terminal 1 of amplifier U11 outputs a square wave signal with 50% duty cycle that has, for example, amplitude in a range of substantially 0.6V and 13.0V. On the other hand, terminal 14 of integrator U14 outputs a waveform, which linearly ramps in a range between high and low voltages (such as 1.0V and 12.6V), wherein said range is predefined by values of resistors R4 and R13. It should be noted that the waveform outputted from integrator U14 first ramps up to the high voltage and then ramps down to the low voltage, and after that it is repeated over again. The frequency of said waveform is predefined by the time constant set according to values of capacitor C5 and resistor R3. It should be noted that capacitor C5 can be made of a temperature stable material, such as COG (It should be noted that in the COG abbreviation, defined by the American Electronics Association, the first letter (“C”) defines the minimum operating temperature, the second letter (“O”) defines the maximum operating temperature, and the third letter (“G”) defines the percentage change in capacitance when applying the above maximum and minimum operating temperatures. Also, for minimizing effects of undesirable tiny leakage currents, said capacitor C5 can have a relatively large capacitance, such as 4700 pF [picoFarad].
According to an embodiment of the present invention, the pedestal voltage outputted from terminal 7 of amplifier U12 is used in conjunction with the ramp voltage provided from terminal 14 of integrator U14 to generate a PWM signal to be outputted from Phase Decode and PWM Generation stage 126. For this, comparator U13 is used for producing a PWM signal train. A problem may be raised, when the pedestal voltage is relatively low and is close to minimum, such as 1V. In such a case, the pedestal voltage clips the bottom tips of the ramp waveform. As a result, even if relatively slight noise or irregularity is present on terminal 7, then such noise is amplified, resulting in reducing the light illumination intensity in a manner, which the human eye interprets as an annoying flickering. For this reason, according to an embodiment of the present invention, it can be undesirable to pulse width modulate a signal down to substantially zero voltage amplitude because usually the last few percent (e.g., 5%) of the signal voltage are noisy, which in turn can produce undesirable light flickering, in terms of human perception. Therefore, according to an embodiment of the present invention, the pulse width modulation of a signal outputted from terminal 7 of comparator U13 can be stopped at a predefined level, for example, at 8% of its full width. As mentioned above, pulse width modulating the signal below this predefined level may generate the undesirable noise, and in turn light flickering. However, it should be noted that the minimum ramp voltage outputted from terminal 14 of integrator U14 can be affected by temperature changes, operational amplifiers gains and offset voltages, and other various factors. Therefore, said minimum terminal 14 ramp voltage is recorded as follows: capacitor C28 is charged up by resistor R58 from the steady 10V voltage terminal, connected to said resistor R58. Bipolar diode D13 is connected to terminal 14 of integrator U14, so that each time the voltage of the ramp waveform (outputted from said terminal 14) goes below the capacitor C28 voltage, said capacitor C28 is discharged and is maintained at 0.7V above the minimum voltage of said ramp waveform.
According to an embodiment of the present invention, in order to generate a PWM signal, amplifier U13 (that operates as a comparator) is presented with the ramp waveform on its input terminal 10. Then, its other input terminal 9 is presented with the higher voltage than the voltage of said terminal 7 or than the voltage on capacitor C28. Schottky diodes D12 are used to implement the “OR” function, and if it is assumed that they have a forward voltage of 0.3V, then the minimum voltage that is presented to terminal 9 of comparator U13 is the minimum ramp voltage, such as the voltage in a range from 0.3V to 0.7V. In addition, it should be noted that in spite of the fact that Schottky diodes D13 and D12 can have different temperature coefficients, the output PWM signal remains substantially stable as long as the value of capacitor C28 is minimized (e.g., it has a capacitance of 1 μF). Further, resistor R59 and capacitor C29 are connected to terminal 10 of comparator U13 to set a relatively long time constant (˜1 sec) to the terminal 10 voltage, so that the noise can be maximally reduced. As a result, when the slider of TRIAC dimmer 105 is moved down, the output PWM signal from Phase Decode and PWM Generation stage 125 narrows the output current (provided into LED load 115) to a level of about 8%, for example. It should be noted that the PWM signal is substantially noise free.
According to an embodiment of the present invention, the voltage which comes out of terminal 8 of comparator U13 is a PWM signal having, for example, the 12V amplitude, which has a width proportional to the capacitor C7 voltage, but which narrows down, for example, to approximately 8% pulse width regardless of how small a duty cycle of the TRIAC component (provided within TRIAC dimmer 105) goes down to. This PWM signal is applied through optocoupler U2 to the output of Phase Decode and PWM Generation stage 126. As a result, when the slider of TRIAC dimmer 105 is moved down, the pulse width of the output current goes down substantially smoothly until about 8%, and then it stays at this level, regardless of how low said slider is moved down. This prevents possible light flickering. It should be further noted that another issue can be adjusting values of resistors R4, R13 and R45, so that when TRIAC dimmer 105 outputs a maximal voltage signal (e.g., 115Volts) into Input stage 120, the voltage on output terminal 7 of amplifier U12 will remain above the maximum voltage of the ramp waveform provided from terminal 14 of integrator U14. This means that when the slider of TRIAC dimmer 105 is moved down, at first there is no response, and then there can be a linear progression, for example, down to 8%, and after that once again there can be no response. This allows using different types of TRIAC dimmers that can have different maximum output voltages, for example, in a range from 95V to 115V for 120V TRIAC dimmers (the minimum output voltage of conventional TRIAC dimmers usually varies from 35V to 4V). Therefore, according to an embodiment of the present invention, the output voltage/current signal achieved with each TRIAC dimmer starts off at the 100% setting and as the slider of said each TRIAC dimmer is moved down, the output pulse width voltage/current signal goes down to 8%, regardless of the TRIAC dimmer type.
It should be noted that, when a TRIAC component within conventional TRIAC dimmer 105 turns ON, it may turn ON momentarily at full voltage, even when a dim level is set. Thus, a problem can arise when the current limiter circuit (defined by zener diodes ZD5, ZD6, transistors Q1 and Q2, and resistors R9 to R12) is exposed to this full voltage burst and charges up capacitor C7 correspondingly, so as a result dimming LED driver 110 (
According to an embodiment of the present invention, an information input to Flyback converter stage 130 is provided from optocoupler U6 (
According to another embodiment of the present invention, the input pulsating DC RAIL voltage of the Flyback converter may be, for example, only 4V RMS (Root Mean Square) instead of the normal 120V RMS, thereby enabling deep dimming (e.g., up to 0.1% of the full light intensity). For this, Flyback converter stage 130 can have the following modifications.
According to an embodiment of the present invention, it is desirable that Flyback converter stage 130 is able to start from as low an input voltage as possible in order to enable relatively deep dimming (e.g., up to 0.1% of the full light intensity). For this reason, resistors R35, R36 and R37 are set to the lowest possible values, such as 16 KΩ each for operation on a 120V AC power line. This allows start up of the Flyback converter at as low a voltage as possible, subject to the limitation of power dissipation in said resistors R35, R36 and R37. Thus, as much current as possible comes through these resistors at start up, and in turn, charges capacitor C10. When the voltage on said capacitor C10 raises up to about 12V, then PFC controller U3 starts operating, and runs briefly using the energy stored on capacitor C10. On the other hand, when capacitor C10 voltage gets down to about 10V, the operation of PFC controller U3 is terminated and the whole procedure repeats about 100 μsec (microseconds) later. During this brief operation, capacitor C13 gets charged up. It may require several of these charging procedures before capacitor C13 is charged up to about 16V, at which point 15V zener diode ZD4 breaks down and transistor Q5 gets biased on, causing the current to flow through diode D8 into capacitor C10. At this point, PFC controller U3 is continuously operated and capacitor C13 becomes charged up almost instantaneously to about 45V-50V. It should be noted that amplifiers U11 to U14, and precision regulator U4 (
According to another embodiment of the present invention, in order to substantially shut down operation of system 100 (
According to still another embodiment of the present invention, resistors R16, R17, R18 and R28 define a potential divider, which produces on terminal 3 of PFC controller U3 a reduced amplitude “image” of the incoming AC power line voltage. The multiplier circuit inside said PFC controller U3 tries to emulate this “image” in the input current, which is further drawn and sensed on its terminal 4. In other words, it tries to make the input current “mirror” the input AC power line voltage.
Further, it should be noted that diode ZD3 limits excessive voltage excursions between the inputs of the internal amplifier provided within PFC controller L6562; this helps maintain stability of said PFC controller as it is turnedturn ON.
A conventional TRIAC component (provided within TRIAC dimmer 105) has to be provided with a certain minimum amount of current, which is required to keep it operating. When LEDs of LED load 115 (
According to another embodiment of the present invention, HV9910B chip is used to apply amplitude modulation in addition to pulse width modulation to the output of Output stage 135 (defined by terminals “+” and “−”), when the output is dimmed below approximately 8%, as described below.
It should be noted that when the TRIAC dimmer 105 slider is being moved past the region where its output AC voltage is reduced to around 20V, the voltage on capacitor C12 remains initially constant, while the power being supplied from TRIAC dimmer 105 to dimming LED driver circuit 110 (
It is assumed, for example, that the output power RAIL voltage, provided from terminal “+”, is set to 60V with respect to the common negative RAIL of the output circuit (terminal “−”). Also, zener diode ZD7 can have, for example, 47V rating. As a result, the voltage on the anode of said zener diode ZD7 is 13 Volts (60V−47V=13V). According to an embodiment of the present invention, potentiometer resistors R41 and R64 divide this voltage down on terminal 7 of HV9910B chip to approximately 270 mV. The flyback converter stage circuit 130 (
According to an embodiment of the present invention, when the light output is instructed to be reduced and finally turn OFF, then zener diode ZD7 turns OFF substantially cleanly. The voltage on terminal 7 of the HV9910B chip is relatively abruptly reduced to zero. The resulting drop in power consumption from LED load 115 causes the output voltage to jump up a fraction of a second later. Zener diode ZD7 turns back ON, and the whole process repeats after, for example, 100 milliseconds, producing undesirable light flashing. According to an embodiment of the present invention, this can be prevented by adding 10 MΩ [MegOhm] resistor R66 as shown. This degrades the characteristics of zener diode ZD7, so that it is unable to switch OFF cleanly. As a result, the light goes out relatively smoothly. Because of the power drawn by resistor R53, the Flyback converter 131 (
According to an embodiment of the present invention, resistors R39, R40, R47 and R48 define the output current. Each time transistor Q4 is switched ON, the current rises until a preset critical voltage is obtained across these resistors. Then, transistor Q4 is switched OFF again for a predetermined period of time predefined by resistor R44. It should be noted that the current through inductor L1 has likely not gone to zero before transistor Q4 is switched ON again. So, when transistor Q4 switches ON, the current starts flowing substantially instantaneously through resistors R39, R40, R47 and R48.
In addition, it should be noted that inductor L1, diode D6, resistor R69, capacitor C19, zener diode ZD9, resistor R68, capacitor C26, resistor R44 and resistor R67 define a conventional buck circuit. When transistor Q4 is switched ON, the current is pulled through LEDs load 115, resistor R69 and inductor L1, ramping up until the voltage across resistor R39 is enough to trigger CS (Current Sense) terminal 2 of HV9910B chip. Then, transistor Q4 is switched OFF for an interval predefined by the value of resistor R44. While said transistor Q4 is switched OFF, the current circulates through inductor L1, LEDs load 115 and diode D6. Capacitor C19 smoothes out the voltage signal across LEDs load 115, so that the ripple of said voltage signal is minimized, and the current flowing through said LEDs load 115 is mostly DC current.
It should be noted that when more LEDs are being driven by means of the HV9910B chip, then the output LEDs current is supposed to be the same as when fewer LEDs are being driven. However, the HV9910B chip has limitations and changing a number of LEDs within LED load 115 from twelve LEDs to one LED may increase the output current by 20%, for example. Therefore, to improve the uniformity of the output current, according to an embodiment of the present invention, the zener diode ZD9 and resistor R68 are provided. When there is a relatively large number of LEDs (e.g., twelve LEDs), the DC voltage across said zener diode ZD9 and resistor R68 is relatively low, such as 20V. On the other hand, when LED load 115 contains only one LED, then the voltage across said zener diode ZD9 and resistor R68 is approximately 56V (output 60V voltage minus 4V across said one LED). If zener diode ZD9 is set up, for example, to be 22V, then it substantially is not conducting when said LED load 115 contains said relatively large number of LEDs, (e.g., twelve LEDs). However, as the number of LEDs is decreased, the higher current flows through resistor R68 into terminal 2 of the HV9910 chip, which is its current sensing terminal. Applying a current bias to said terminal 2 has an effect of lowering the current at which transistor Q4 is switched OFF at the end of each cycle, and hence it has an effect of lowering the current being supplied to LED load 115. This is known as a feedforward circuit. (the settings of the circuit are changed according to the connections (e.g., LEDs) sensed). According to an embodiment of the present invention, as a result of the above, the output LED current is substantially independent of LED load 115 (independent of a number of LEDs), and can be within a relatively small tolerance, such as 5%.
According to an embodiment of the present invention, capacitor C26 operates with resistor R57 as an RC (Resistor-Capacitor) filter. Extraneous capacitance of Output stage circuit 135 leads to an initial spike through transistor Q4, when it is turned ON for the first time. Therefore, the time constant of said RC filter smoothes out this spike.
Also, resistor R69 is used to limit surges when LED load 115 is switched into Output circuit stage 135. For 18 W power, for example, the value of said resistor R69 can be approximately 1Ω, thus limiting the instantaneous output current to about 55 A, which is much less disruptive to the electronic circuit, than the possible “infinity” current.
The circuit defined by zener diode ZD7, resistors R41 and R66, and capacitor C31 is an application circuit for the HV9910B chip. The properties of this circuit are that as long as sufficient power is being provided to Input stage 120 (
According to an embodiment of the present invention, less than 0.05% of the light illumination output can be still obtained substantially without flicker or shimmer.
Below is presented a table with sample characteristics of electronics components/units of system 100 (
While some embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be put into practice with many modifications, variations and adaptations, and with the use of numerous equivalents or alternative solutions that are within the scope of persons skilled in the art, without departing from the spirit of the invention or exceeding the scope of the claims.
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| Number | Date | Country |
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| Number | Date | Country | |
|---|---|---|---|
| 20100134038 A1 | Jun 2010 | US |
