Electrical circuit with two or more loads

Abstract

A mechanism for powering two loads of a load circuit. The power drawn by each load is controlled by a respective control circuit. The control circuits operate at different frequencies. The mechanism includes an isolating circuit for isolating the power flow to the second load from the difference between the frequencies of the control circuits.

Description

[0001] Electrical circuit with two or more loads

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of electrical circuits, and in particular, to electrical circuits having two or more load arrangements.

[0004] BACKGROUND OF THE INVENTION

[0005] There is a need for electrical circuits comprising two loads that draw power from a same power supply. One suitable example is in the field of lighting, where two different LED loads may wish to draw power from a same power supply.

[0006] There is an ongoing desire to reduce noise in electrical circuits.

[0007] SUMMARY OF THE INVENTION

[0008] It has been recognized that there are circumstances in which two loads may be controlled to draw power from a same power supply at slightly different frequencies, even if designed to operate at the same frequency. This may, for instance, occur if both loads draw power using a pulse-width modulation scheme wherein the pulse-wide modulation is controlled by a respective high frequency signal generated by (different) clocking circuits. A difference in frequency of the high frequency signal may result from (deemed acceptable) manufacturing tolerances between clocking circuits that define the frequency. However, the applicant has recognized that the difference in frequencies causes a ripple or “beat frequency” in the resultant current(s) drawn by the two loads. This problem will be explained in more detail later.

[0009] The underlying idea of the present invention is to provide an isolating circuit to isolate the current drawn by (at least) one of the loads from the current drawn by another one of the loads, given this difference in frequency. This effectively attenuates any ripple in the current drawn by the load resulting from the difference in the operating frequency of the loads.

[0010] The proposed technique thereby reduces the noise in a load circuit comprising two or more loads, and more particularly, reduces the noise in power drawn by the load(s) affected by the isolating circuit.

[0011] The invention is defined by the claims. According to examples in accordance with an aspect of the invention, there is provided a load circuit comprising: an input node configured to connect to a power supply; a first load arrangement electrically coupled to the input node, the first load arrangement comprising a first load and a first control circuit configured to operate at a first frequency and control a power flow from the input node to the first load depending on said first frequency; a second load arrangement, different to the first load arrangement, electrically coupled to the input node, the second load arrangement comprising a second load and a second control circuit configured to operate at a second frequency, different to the first frequency, and control a power flow from the input node to the second load depending on said second frequency, wherein the difference between the first frequency and the second frequency meets one or more certain conditions; and an isolating circuit configured to isolate the power flow from the input node to the second load to be independent of the difference between the first frequency and the second frequency.

[0012] The present disclosure proposes the use of an isolating circuit to isolate the power flow to a second load from a difference between frequencies at which the first and second load are controlled to draw power. Thus, the isolating circuit effectively acts to isolate the current drawn by the second load from the current drawn by the first load. This advantageously reduces, attenuates or removes any ripple in the current drawn by the second load that would otherwise result from the first load drawing / competing current (from the same input power) with the second load -at a different frequency thus varying over the operation time of the first load.

[0013] In some examples, the first control circuit comprises a first internal clocking circuit configured to generate a first oscillating signal at the first frequency; the first control circuit controls the power flow from the input node to the first load in synchronization with the first oscillating signal; the second control circuit comprises a second internal clocking circuit configured to generate a second oscillating signal at the second frequency; and the second control circuit controls the power flow from the input node to the second load in synchronization with the second oscillating signal.

[0014] This approach provides a mechanism for controlling the current flow through the first and second loads at different frequencies. This is advantageous for facilitating separate control of the current flow through the first and second loads. The difference in frequencies of the clocking circuits would result in a ripple in the current drawn by (at least) the second load without the use of the proposed isolating circuit. Thus the present application is preferably applicable with such designs to solve the underlying problem. The isolating circuit may be configured to isolate the power flow from the input node to the second load to be independent of the power flow from the input node to the first load controlled by the first control circuit. This advantageously reduces the effect of a power flow to the first load on the power flow to the second load, thus the power flow to the second load is no longer competed by the first load and would not vary over the operation time of the first load, further reducing a noise of the load circuit.

[0015] The isolating circuit may be configured to be independent of (any) time-varying overlap between the power flow from the input node to the first load controlled by the first control circuit and the power flow from the input node to the second load controlled by the second control circuit. A difference between the first and second frequencies causes a timevarying overlap between the current drawn by the first load and the current drawn by the second load. In the / each overlapping period, the current drawn by the second load is reduced; in the non-overlapping period, the current by the second load is sufficient. Thus, the current drawn by the second load will vary over time and create a ripple (without the use of the proposed approach). This approach increases the attenuation of the ripple in current drawn by the second load.

[0016] In some examples, the one or more certain conditions include a condition that the difference between the first frequency and the second frequency is greater than zero and less than 100 Hz, preferably 80 Hz. Such small differences are more likely to cause eye- noticeable or user-perceptible ripple (in the current drawn by the second load). In particular, if the loads are LEDs, then a small difference in frequency will result in a noticeable or user- perceptible flicker to the light emitted by the LED(s) of the second load. Approaches are particularly advantageous when used to attenuate ripples caused by small differences in the first and second frequency. The proposed approach is therefore particularly advantageous in attenuating this ripple.

[0017] In some examples, the rated power of the first load is greater than the rated power of the second load. The magnitude of the ripple in the second load is greater when the first load has a higher power rating than the second load. The proposed approach is therefore particularly advantageous to be used in such circumstances.

[0018] The isolating circuit may be configured to provide an isolated power for the second load arrangement at an intermediate node between the input node and the second load arrangement, wherein the second control circuit is adapted to control a power flow from the intermediate node to the second load. This provides a readily implementable approach for the isolating circuit, e.g., using simple electronic components. In some examples, the isolating circuit comprises a unidirectional component, optionally a diode, connected from the input node to the intermediate node, to thereby prevent the first load arrangement from drawing power away from the isolated power via the intermediate node. This approach significantly reduces a chance that the first load will draw power made available for the second load, therefore significantly attenuating any ripple in the current drawn by the second load.

[0019] In some examples, the isolating circuit further comprises an energy buffer component, optionally a capacitor, connected to the intermediate node and configured to store energy for buffering the isolated power at the intermediate node. This maintains a power supply exclusively for the second load, even if the first load is drawing power from the input node, thereby reducing or avoiding a reduction in the (average) power drawn by the second load.

[0020] In an alternative or additional example, the isolating circuit comprises an inductor connected between the input node and the intermediate node, such that the inductor and an optional capacitor form a filter between the input node and the second load arrangement. The inductor acts as a filter to effectively suppress at least of the energy drawn away from the second load by the first load. Moreover, the inductor and optionally the capacitor is a reactive component whose power loss is considerably less than diode. Thus, an advantage of this example is high power efficiency.

[0021] In some examples, the isolating circuit comprises a linear current regulator connected in series with the second load and configured to regulate the current drawn by the second load. This approach facilitates or maintains a current through the second load actively, even when the first load is competing energy from the input node, the linear current regulator would automatically reduce its impedance to maintain a current through the second load, thereby performing an active isolation of the current drawn by the second load from the current drawn by the first load. This approach increases the uniformity of the current drawn by the second load.

[0022] In some examples, the first control circuit comprises a first control node configured to receive a first control signal; the first control circuit controls the power flow from the input node to the first load at a duty cycle responsive to the first control signal and at the first frequency; the second control circuit comprises a second control node configured to receive a second control signal; and the second control circuit controls the power flow from the input node to the second load at a duty cycle responsive to the second control signal and at the second frequency. This approach provides a technique for facilitating independent control of the current drawn by the first and second loads.

[0023] In some examples, the first load comprises one or more first LEDs and the second load comprises one or more second LEDs. Proposed approaches are particularly advantageous for driving loads formed of LEDs, as the current demanded by each load may vary (e.g., depending upon a demanded or desired dimming level) and there is a desire for independent control of the different loads.

[0024] There is also proposed a lighting device comprising any herein disclosed load circuit and a power supply (to be) connected to the input node of the load circuit. The power supply may be a voltage regulator.

[0025] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0028] Figure 1 illustrates an existing load circuit;

[0029] Figure 2 illustrates example waveforms in the existing load circuit;

[0030] Figure 3 illustrates a proposed load circuit;

[0031] Figure 4 illustrates another proposed load circuit;

[0032] Figure 5 illustrates another proposed load circuit;

[0033] Figure 6 illustrates another proposed load circuit;

[0034] Figure 7 illustrates a proposed lighting device;

[0035] Figure 8 illustrates a known system architecture for light strip;

[0036] Figure 9 illustrates an improved system architecture for light strip according to the invention; and

[0037] Figure 10 illustrates an alternative improved system architecture for light strip according to the invention.

[0038] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The invention will be described with reference to the Figures.

[0040] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0041] The invention provides a mechanism for powering two loads of a load circuit. The power drawn by each load is controlled by a respective control circuit. The control circuits operate at different frequencies. The mechanism includes an isolating circuit for isolating the power flow to the second load from the difference between the frequencies of the control circuits.

[0042] Figure 1 illustrates an existing load circuit 100. The load circuit 100 comprises an input node 101 configured to connect to a power supply VDD; a first load arrangement 110 and a second load arrangement 120.

[0043] The input node 101 effectively provides a bus voltage for the first 110 and second 120 load arrangements.

[0044] The first load arrangement 110 is electrically coupled to the input node 101. The first load arrangement 110 comprises a first load LED1. The first load LED1 may comprise a set or string of one or more first LEDs, here: illustrated as a single LED. The first load arrangement also comprises a first control circuit 115, Ml configured to operate at a first frequency and control a power flow from the input node 101 to the first load LED1 depending on said first frequency.

[0045] The second load arrangement 120 is also electrically coupled to the input node 101. The second load arrangement 120 comprises a second load LED2, different to the first load. The second load LED2 may comprise a set or string of one or more second LEDs (different to the first LEDs), here: illustrated as a single LED. The second load arrangement 120 also comprises a second control circuit 125, M2 configured to operate at a second frequency and control a power flow from the input node 101 to the second load LED2 depending on said second frequency.

[0046] The first control circuit 115 may comprise a first internal clocking circuit 116 (e.g., an oscillator) configured to generate a first oscillating signal at the first frequency. The first control circuit may be configured to control the power flow from the input node to the first load in synchronization with the first oscillating signal. For instance, the first control circuit 115 may comprise a first PWM controller 117 configured to control, using a first drive signal SI, the conduction and un-conduction and thereby the current flow through a switch Ml connected between the input node and the first load LED1. The first PWM controller 117 may control the current flow using a pulse-width modulation (PWM) scheme that operates at the first frequency.

[0047] Similarly, the second control circuit 125 may comprise a second internal clocking circuit 126 configured to generate a second oscillating signal at the second frequency. The second control circuit may control the power flow from the input node to the second load in synchronization with the second oscillating signal.

[0048] For instance, the second control circuit 125 may comprise a second PWM controller 127 configured to control, using a second drive signal S2, the conduction and unconduction and thereby the current flow through a switch M2 connected between the input node and the second load LED2. The second PWM controller 117 may control the current flow using a pulse-width modulation (PWM) scheme that operates at the second frequency.

[0049] The first and second PWM controllers may each control an (average) pulse width responsive to control signals provided by logic circuitry 150. The logic circuitry 150 may, for instance, receive an indication of a desired power to be drawn by each load and define the (average) pulse width for the first and second PWM controllers appropriately.

[0050] Thus, the first control circuit 115 may comprise a first control node 118 configured to receive a first control signal Sci, which may be generated by the logic circuitry 150. The first PWM controller 117 (and therefore the first control circuit) may control the power flow from the input node to the first load at a duty cycle responsive to the first control signal and at the first frequency. This can be achieved through appropriate PWM control of the switch Ml.

[0051] Similarly, the second control circuit may comprise a second control node 128 configured to receive a second control signal Sc2, which may be generated by the logic circuitry 150. The second PWM controller 127 (and therefore the second control circuit) may control the power flow from the input node to the second load at a duty cycle responsive to the second control signal Sc2 and at the second frequency. This can be achieved through appropriate PWM control of the switch M2.

[0052] The switch(es) Ml, M2 may be formed from FETs, such as MOSFETS, or any other suitable form of electrically controllably switching device (e.g., any suitable transistor such as a BJT). In practice, the control circuits 115 and 125 are usually implemented by integrated circuits (IC) that are the same model since their general function of generating a PWM signal to control the gate of a MOSFET is substantially the same. The applicant has recognized that even if the same batch of ICs are used wherein the first and second frequencies are designed to be identical to one another, in practice, there may be a discrepancy between the two frequencies of the two controllers due at least to manufacturing tolerances. A flicker or ripple problem will occur or result when a difference between the first frequency and the second frequency will meet one or more certain conditions, e.g., the difference will be nonzero and less than a predetermined percentage (e.g., 1% or 5%) of the first frequency and / or a predetermined frequency value (e.g., 100 Hz or more preferably 80 Hz).

[0053] This discrepancy in the frequencies will effectively cause the respective currents drawn by each load to have a phase shift with one another that varies with time. Put another way, there will be a time-varying overlap between the time(s) at which the first load draws power and the time(s) at which the second load draws power. Since each load arrangement draws power from the same input node 101, this varying phase shift leads to the two loads drawing current from the input node in a time-varying manner. When the first and second load draw current at a same time, then the voltage at the input node will be naturally pulled down (due to the drawing of charge) to a greater extent than if the first and second loads do not draw current at a same time. Usually, the response time of the power supply that supplies the voltage VDD is not fast and is not able to compensate for the pulled down voltage in time. This effect is particularly enhanced if the rated power of the first load is greater than the rated power of the second load (such that the first load draws more power than the second load).

[0054] As there is a variation in the phase shift, the magnitude of the current drawn by the second load will change over time. More particularly, over time, this will cause a ripple to occur in the current drawn by the first and second loads. If the rated power of the first load is greater than the rated power of the second load, this ripple is more noticeable in the current drawn by the second load. If the first / second load is an LED, any such ripple will cause the LED to flicker.

[0055] Figure 2 illustrates example waveforms for electrical signals within the existing load circuit 100. Each waveform represents a current (I) over time (t).

[0056] A first waveform illustrates the first drive signal SI, which operates at a first frequency. A second waveform illustrates the second drive signal S2, which operates at a second frequency. A third waveform illustrates the current ILEDI through the first load. A fourth waveform illustrates the current ILED2 through the second load. In the illustrated scenario, the first load has a higher rated power than the second lower and the second frequency is (slightly) larger than the first frequency (e.g., but within an acceptable tolerance for an oscillator).

[0057] As illustrated in Figure 2, when the first load and second load draw current at a same time, the current drawn by the second load will drop. As the first and second frequencies are different, the amount of current drawn by the second load will change for each cycle of the second drive signal. This effectively causes a ripple in the (time-averaged) current drawn by the second load, as represented with a dotted line 250. For example, in the beginning, the first load and the second load draw power (e.g., are turned on) at the same time thus the current drawn by the second load is relatively small. Due to the frequency difference, the overlap between the time at which the second load and the first load draws power will gradually reduce (i.e., the second load will draw power in more and more different time duration with respect to the firstload). The (moving average) current to the second load will thereby gradually increase. Those skilled in the art would understand that, even not shown, as time passes by, the situation will reverse and the overlapping will become more again, and the (moving average) current drawn the second load will gradually decrease. This will repeat and causes the ripple.

[0058] Put another way, there will be a time-varying overlap between the power flow from the input node to the first load controlled by the first control circuit and the power flow from the input node to the second load controlled by the second control circuit.

[0059] Of course, it will be appreciated that an analogous ripple is also induced in the (time-averaged) current drawn by the first load. If the rated power of the first load is greater than the rated power of the second load, then this ripple will naturally have a reduced magnitude (compared to the ripple in the second load) and is less visible. Nonetheless, it is noted that this ripple will, in any event, exist.

[0060] The present disclosure provides a mechanism for reducing, attenuating or removing the ripple from the current drawn by at least the second load. In particular, the present disclosure proposes the use of an isolating circuit configured to isolate the power flow from the input node to the second load to be independent of the difference between the first frequency and the second frequency.

[0061] Figure 3 illustrates a proposed load circuit 300. Elements of the proposed load circuit that are identical to the load circuit previously described retain their reference numerals.

[0062] The load circuit 300 further comprises an isolating circuit 350. The isolating circuit is configured to isolate the power flow from the input node 101 to the second load LED2 to be independent of the difference between the first frequency and the second frequency. More specifically, in the illustrated example, the isolating circuit 350 is configured to provide an isolated power for the second load arrangement 120 at an intermediate node 301 located between the input node 101 and the second load arrangement 120. Accordingly, the second control circuit 125 is adapted to control a power flow from the intermediate node 301 to the second load LED2.

[0063] In the illustrated example, the isolating circuit comprises a unidirectional component DI (here: a diode) connected from the input node 101 to the intermediate node 301. In this way, the first load is unable to draw power from the isolated power defined at the intermediate node 301, thereby reducing or attenuating any change to the (average) power drawn by the second load LED2.

[0064] The isolating circuit 350 may further comprise an energy buffer component Cl (here: a capacitor) connected to the intermediate node 301 and configured to store energy for buffering the isolated power at the intermediate node. This provides a buffered power from which the second load can draw power.

[0065] An alternative energy buffer component to a capacitor is a battery or cell arrangement. Another alternative energy buffer component is an inductor connected between the diode and the intermediate node. Of course, some examples may include a combination of a capacitor and an inductor.

[0066] One alternative to a diode DI, for use as the unidirectional component, is a switch (e.g., a synchronously controlled switch). This switch should be carefully controlled, for example, to be turned on when the first load LED1 is turned off or does not draw power so as to allow the voltage at the input node (i.e., the power supply VDD) to charge the capacitor Cl.

[0067] In the illustrated examples, the isolating circuit 350 comprises a unidirectional component DI in the form of a diode and an energy buffer component Cl in the form of a capacitor. The diode DI has an anode connected to the input node 101 and a cathode connected to the intermediate node 301.

[0068] In use, as the first load draws current from the input node 101, the voltage at the input node 101 may drop below the voltage of the intermediate node 301. At this point in time, the voltage at the cathode of the diode DI will be higher than the voltage at the anode. The diode will therefore prevent current flow between the input node 101 and the intermediate node 301, such that the energy buffer component Cl takes over the providing of power to the second load (if required) until the voltage at the input node 101 rises again. The diode may then conduct once more, and charge the energy buffer component Cl. The cycle will be iteratively repeated, thereby keeping the current drawn by the second load stable.

[0069] In the above described example, the isolating circuit is implemented by the diode which may has some power loss due to the forward voltage on the diode.

[0070] Figure 4 illustrates another proposed load circuit 400. Elements of the proposed load circuit that are identical to any load circuit previously described retain their reference numerals.

[0071] In this approach, the load circuit again comprise an isolating circuit 450 connected between the input node 101 and an intermediate node 401. More specifically, in the illustrated example, the isolating circuit comprises an inductor LI connected between the input node 101 and the intermediate node 401. The isolating circuit thereby forms a filter between the input node and the second load arrangement 120.

[0072] The inductor acts to suppress, at least partially, the energy drawn by the first load arrangement from the second load arrangement. Using an inductor L to act as the filter between the first and second load arrangements (e.g., rather than a unidirectional component such as a diode) has increased efficiency and reduced power losses since the inductor is a reactive component.

[0073] More specifically, the inductor will act to suppress, attenuate or smooth any change in current drawn by the second load arrangement (as an inductor will oppose any sudden changes in current). This effectively acts as a filter to isolate the current drawn by the second load arrangement from any current drawn by the first load arrangement.

[0074] The isolating circuit 450 may further comprise a (second) capacitor C2, e.g., connected between the intermediate node 401 and a ground or reference voltage. The capacitor acts as an energy storage device to provide charge or power for driving the second load arrangement when it draws current.

[0075] The inductor LI and the (second) capacitor effectively act together as an LC filter. The arrangement of the inductor LI and (second) capacitor C2 provides a L-type low- pass filter. This acts to filters out any ripple (resulting from the first load arrangement drawing current), whilst allowing the DC component of the power supply at the input node 101 to pass through to the second load arrangement.

[0076] The specific illustrated arrangement of the LC filter (formed from the inductor LI and the (second) capacitor C2) provides a L-type low-pass filter with a high output impedance. Figure 5 illustrates another proposed load circuit 500. Elements of the proposed load circuit that are identical to any load circuit previously described retain their reference numerals.

[0077] In this approach, the load circuit again comprise an isolating circuit 450 configured to isolate the power flow from the input node to the second load to be independent of the difference between the first frequency and the second frequency.

[0078] More specifically, in this approach, the isolating circuit comprises a linear current regulator Is (or current source) connected in series with the second load LED2 and configured to regulate the current drawn by the second load. Thus, the current through the second load is directly regulated using the linear current regulator Is.

[0079] In the illustrated example, the current regulator Is replaces the switch previously used to control the power flow through the second load.

[0080] The use of the current regulator significantly reduces the dependence of the current through the second load on the voltage at the input node. This provides a significantly more stable current flow through the second load.

[0081] The proposed architecture effectively combines the advantages of constant voltage (CV) and constant current (CC). This is particularly advantageous for load circuits in which each load is a set or string of LEDs. In particular, for high power LEDs, CV is better than CC in dimming depth / high resolution and current accuracy at low dimming level, etc., and for low power light source, CC is better than CV in immunity from the bus voltage fluctuation.

[0082] Thus, there is a particular advantage when the first load has a higher rated power than the second load, as the first load can be driven using a CV technique, with the second load being driven using a CC technique.

[0083] Previously disclosed approaches make use of a single isolating circuit for effectively isolating the current drawn by the second load arrangement from the difference between the first and second frequencies (i.e. , the current drawn by the first load arrangement). This reduces the effect of a (time-averaged) ripple induced in the current drawn by the second load arrangement. As previously explained, it is also recognized that a difference between the first and second frequencies will cause a similar ripple to occur in the first load arrangement. The size of this ripple is relatively small if the first load has a greater rated power than the second load. Nonetheless, it may be advantageous to also isolate the current drawn by the first load arrangement from the difference between the first and second frequencies. Accordingly, some load circuits may further comprise a second isolating circuit (different to the second isolating circuit) configured to isolate the power flow from the input node to the second load to be independent of the difference between the first frequency and the second frequency.

[0084] As an example, the second isolating circuit may be connected between the input node and a second intermediate node. The second isolating circuit may thereby be able to provide a (second) isolated power for the first load arrangement at the second intermediate node located between the input node and the first load arrangement. Accordingly, the first control circuit may be adapted to control a power flow from the second intermediate node to the first load.

[0085] The second isolating circuit may be embodied or structured in a similar manner to any previously described isolating circuit. In a load circuit comprising the isolating circuit and the second isolating circuit, although possible, the two isolating circuits do not need to take the same structure or layout (e.g., the isolating circuit may be embodied using a linear current regulator and the second isolating circuit may be embodied as a filter comprising an inductor).

[0086] Figure 6 illustrates one example variant to a previously described load circuit 600, which further comprises a second isolating circuit 650. Elements of the proposed load circuit that are identical to the load circuit previously described retain their reference numerals.

[0087] The second isolating circuit 650 is connected between the input node 101 and a second intermediate node 601. The isolating circuit is thereby able to provide a (second) isolated power for the first load arrangement at the second intermediate node 601 located between the input node 101 and the first load arrangement 110. Accordingly, the first control circuit 115 is adapted to control a power flow from the second intermediate node 601 to the first load LED1.

[0088] More specifically, in the illustrated example, the second isolating circuit 650 comprises a (second) inductor L2 connected between the input node 101 and the second intermediate node 601. The second isolating circuit thereby forms a filter between the input node 101 and the second load arrangement 110.

[0089] The second isolating circuit acts in a similar way to the first isolating circuit, so as to reduce or attenuate any ripple in the (average) current drawn by the first load as a result of the second load arrangement drawing current.

[0090] The load circuit illustrated in Figure 6 can be modified in a way that one or both of the inductors LI and L2 are replaced by diode. Such a modification will result in at least one isolating circuit that is similar to the isolating circuit of the load circuit illustrated in Figure 3. Proposed approaches are particularly advantageous when employed to attenuate a ripple (in the second load) that results from a slight mismatch between the first frequency and the second frequency. Thus, proposed approaches are particularly suited when the difference between the first frequency and the second frequency is greater than zero and less than 100 Hz, preferably 80 Hz.

[0091] Previously disclosed approaches comprise only a first and second load arrangement. However, other load circuits may comprise more than two load arrangements, each comprising a respective (different) load. Each load arrangement may comprise a respective (different) control circuit configured to operate at a respective (different) frequency to the first frequency. Thus, each load (of each load arrangement) is associated with a respective (different) frequency.

[0092] In such examples, the isolating circuit may be configured to isolate the power flow from the input node to two or more of the loads to be independent of the difference between the first frequency and each respective frequency associated with the two or more loads.

[0093] In some examples, the load circuit may comprise a plurality of separate isolating circuits, each isolating circuit configured to isolate the power flow from the input node to a different set of one or more of the loads to be independent of the difference between any frequency associated with any load in the said set and any frequency associated with at least one (e.g., any) load not in said set. Each isolating circuit may be embodied as previously described. In some examples, if the load circuit comprises a plurality of isolating circuits, at least one isolating circuit may be configured to cascade from another isolating circuit.

[0094] Figure 7 illustrates a proposed lighting device 700.

[0095] The lighting device 700 comprises any previously disclosed load circuit 300, 400, 500, 600, in which the first load comprises one or more first LEDs and the second load comprises one or more second LEDs.

[0096] The lighting device 700 also comprises a power supply Vs to be connected to the input node of the load circuit. The power supply Vs may, for instance, be a voltage regulator.

[0097] The applicant believes that, although it may be known to place a diode between parallel LED branches, this has not used in combination with the LED branches controlled by controllers with frequency variance, and this has not been for solving the ripple problem caused thereby. Therefore this is an unobvious combination.

[0098] The present application further proposes another innovation. Figure 8 shows a diagram of a long / linear lighting system such as light strip. PSU is a power supply unit that provides a supply voltage. The PSU contains a power factor correction unit and the supply voltage usually contains a AC mains frequency ripple. The RF&control block converts the supply voltage into a bus voltage which also contains at least some AC mains frequency ripple. The bus voltage is provided to the light strip which comprises a plurality of LED unit cells connected in a daisy chain of 10M (meters). The problem is that there is wire resistance on the electrical wire in among the plurality of LED unit cells, and the wire resistance gradually increases the ratio of the AC mains frequency ripple in the bus voltage along the daisy chain from the start at the PSU side to the opposite side. This AC mains frequency ripple cause flicker in the light generated by the LED unit cells at the opposite side.

[0099] One embodiment of the invention proposes to add a smooth circuit at the opposite side to remove the AC mains frequency ripple in the bus voltage. In one embodiment, the smooth circuit is implemented by a linear voltage regulator, or low drop out (LDO) voltage regulator. In an alternative embodiment, the smooth circuit can also be implemented by a buffer capacitor. The smooth circuit smooths the AC mains frequency ripple and provides a more stable voltage to the LED unit cells at the opposite side (the last 5 meters) of the daisy chain, and the flicker the LED unit cells is reduced. The LED unit cells at the start side (the first 5 meters) of the daisy chain is still powered by the RF&control block as before.

[0100] The smooth circuit can draw voltage signal also on the bus as shown in figure 9. In this case, the amplitude of the voltage is enough but the ripple is too large. Alternatively, as shown in figure 10, the PSU or the RF&control block can provide a supply voltage to the smooth circuit / LDO block in a separate wire different from the Vbus connected to the LED unit cells at the start side.

[0101] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0102] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0103] If the term "adapted to" is used in the claims or description, it is noted the term "adapted to" is intended to be equivalent to the term "configured to". If the term "arrangement" is used in the claims or description, it is noted the term "arrangement" is intended to be equivalent to the term "system", and vice versa.

[0104] Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A load circuit comprising: an input node configured to connect to a power supply; a first load arrangement electrically coupled to the input node, the first load arrangement comprising a first load and a first control circuit configured to operate at a first frequency and control a power flow from the input node to the first load depending on said first frequency; a second load arrangement, different to the first load arrangement, electrically coupled to the input node, the second load arrangement comprising a second load and a second control circuit configured to operate at a second frequency, different to the first frequency, and control a power flow from the input node to the second load depending on said second frequency, wherein the difference between the first frequency and the second frequency meets one or more certain conditions; and an isolating circuit configured to isolate the power flow from the input node to the second load to be independent of the difference between the first frequency and the second frequency.

2. The load circuit of claim 1, wherein: the first control circuit comprises a first internal clocking circuit configured to generate a first oscillating signal at the first frequency; the first control circuit controls the power flow from the input node to the first load in synchronization with the first oscillating signal; the second control circuit comprises a second internal clocking circuit configured to generate a second oscillating signal at the second frequency; and the second control circuit controls the power flow from the input node to the second load in synchronization with the second oscillating signal.

3. The load circuit of claim 1 or 2, wherein the isolating circuit is configured to isolate the power flow from the input node to the second load to be independent of the power flow from the input node to the first load controlled by the first control circuit.

4. The load circuit of claim 3, wherein the isolating circuit is configured to be independent of time-varying overlap between the power flow from the input node to the first load controlled by the first control circuit and the power flow from the input node to the second load controlled by the second control circuit.

5. The load circuit of any of claims 1 to 4, wherein the one or more certain conditions include a condition that the difference between the first frequency and the second frequency is greater than zero and less than 100 Hz, preferably 80 Hz.

6. The load circuit of any of claims 1 to 5, wherein the rated power of the first load is greater than the rated power of the second load.

7. The load circuit of any of claims 1 to 6, wherein the isolating circuit is configured to provide an isolated power for the second load arrangement at an intermediate node between the input node and the second load arrangement, wherein the second control circuit is adapted to control a power flow from the intermediate node to the second load.

8. The load circuit of claim 7, wherein the isolating circuit comprises a unidirectional component, optionally a diode, connected from the input node to the intermediate node, to thereby prevent the first load arrangement from drawing power away from the isolated power via the intermediate node.

9. The load circuit of any of claims 7 to 8, wherein the isolating circuit further comprises an energy buffer component, optionally a capacitor, connected to the intermediate node and configured to store energy for buffering the isolated power at the intermediate node.

10. The load circuit of claim 1, wherein the isolating circuit comprises an inductor connected between the input node and the intermediate node, such that the inductor and an optional capacitor form a filter between the input node and the second load arrangement.

11. The load circuit of any of claims 1, 7, 8 or 10, wherein the isolating circuit comprises a linear current regulator connected in series with the second load and configured to regulate the current drawn by the second load.

12. The load circuit of any of claims 1 to 11, wherein: the first control circuit comprises a first control node configured to receive a first control signal; the first control circuit controls the power flow from the input node to the first load at a duty cycle responsive to the first control signal and at the first frequency; the second control circuit comprises a second control node configured to receive a second control signal; and the second control circuit controls the power flow from the input node to the second load at a duty cycle responsive to the second control signal and at the second frequency.

13. The load circuit of claims 1 to 12, wherein the first load comprises one or more first LEDs and the second load comprises one or more second LEDs.

14. A lighting device comprising the load circuit of claim 13, and a power supply to be connected to the input node of the load circuit.

15. The lighting device of claim 14, wherein the power supply is a voltage regulator.

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