Multi-channel driver with switchable bypass capacitors

Abstract

The present invention relates to a lighting unit comprising a power converter for supplying regulated power to a first LED load, the first LED load including at least one LED, the first LED load having a power converter coupled to the power converter and a series combination of a first capacitor and a first switch coupled in series with each other and coupled in parallel with the first LED load, the power converter being configured to operate in a first mode to supply a first amount of the regulated power to the first LED load, the first switch being closed, and in a second mode to supply a second amount of the regulated power to the first LED load, the second amount of the regulated power to the first LED load being less than the first amount of the regulated power to the first LED load, the first switch being open.

Description

Technical Field

[0001] The present invention relates to a lighting unit. In particular, the present invention relates to a lighting unit that provides improved dimming with reduced color point shift.

Background Art

[0002] Today, it is common practice to use light-emitting diodes (LEDs) as light sources for general lighting. Currently, there are many different embodiments in which LEDs are used to provide a desired light color and light intensity. It is desirable that the light intensity of the LED can be controlled to vary from the maximum light output to as low a light output as possible.

[0003] A common way to reduce the light output of an LED is to reduce the average current through the LED by modulating the current through the LED by pulse width modulation (PWM) or by reducing the amplitude of the current, called amplitude modulation. The disadvantage of using amplitude modulation is that at deep dimming, i.e., below about 10% of the maximum LED current, there may be a color shift in the color of the light generated by the LED. In some cases, the color temperature may change by 450K at 5% light output. At higher light output intensities, this color shift is not as severe. When a single LED string emitting light with a single color temperature is used, this color temperature changes when the intensity is reduced and amplitude modulation is applied.

[0004] The object of the present invention is to provide an LED light source having a more stable color temperature over the dimming range of the light source.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The object of the present invention is to provide a lighting unit that provides improved color consistency when the light output is dimmed, such that when the light output is reduced, changes in color or color temperature are not observed, or are not observed to the user. [Means for solving the problem]

[0006] To solve this problem, in the first embodiment of the present invention, - A power supply for supplying regulated power to the first LED load, - The first LED load comprising at least one LED, the first LED load being coupled to the power supply, - A lighting unit having a series combination of a first capacitor and a first switch connected in series with each other, and a series combination connected in parallel with the first LED load, The aforementioned power supply, A first mode in which a first amount of the adjustment power is supplied to the first LED load, wherein the first switch is closed, and A second mode in which a second amount of the adjustment power is supplied to the first LED load, wherein the second amount of the adjustment power supplied to the first LED load is less than the first amount of the adjustment power supplied to the first LED load, and the first switch is opened, and the device is configured to operate in this second mode. A lighting unit is provided in which the power converter is configured to switch from the second mode to the first mode by controlling the switch in linear operation mode.

[0007] This lighting unit has an LED load, which is mounted on a power supply that provides power to the LED load. A capacitor is connected in parallel with the LED load to smooth the current passing through the LED load.

[0008] The inventors' insight is that the color or color temperature deviates the most from the desired color or color temperature, particularly during deeper dimming of the light output. This color temperature or color temperature shift is further referred to as a color point shift. It is desirable to provide a PWM of the LED current at dimming levels to provide the lowest possible color point shift. This can be best done if there is no capacitance in parallel with the LED load, because the capacitor reduces the modulation depth of the PWM current. At deeper dimming levels where a full or significant PWM of the LED load current is desired, the invention disconnects the capacitor by opening a switch in series with it. The power passing through the first LED load is measured or determined, and based on the power exceeding a threshold, it is determined whether to open or close the switch in series with the capacitor. The first switch is opened when the power to the first LED load is below a first threshold, for example, indicating that dimming is being performed, and the first switch is closed when the power to the first LED load is above the first threshold, indicating that dimming is not being performed or that slight dimming is being performed. When the power converter transitions from the second mode to the first mode, the first LED load is shunted by the first capacitor, which is (partially) discharged. The first LED load does not emit light until the first capacitor is fully charged. This results in a dark period during the transition from the second mode to the first mode, which may be observed by the user as flickering and is undesirable. To solve this problem, the present invention provides improved control of the first switch. The first switch operates in its linear operating mode during the transition from the second mode to the first mode. This prevents all current supplied by the power converter from flowing through the capacitor, while allowing a portion of the current to flow through the first LED load, thereby reducing or even eliminating the dark period.

[0009] When dimming is not performed, or when a limited amount of dimming is performed, it may be desirable to leave the capacitor in parallel with the LED so that the current passing through the LED load is filtered and smoothed. This can be beneficial in environments where high-frequency flickering, such as the PWM frequency, needs to be avoided at high light output, for example, when used near a barcode scanner.

[0010] In a further example, the lighting unit is: - A second switch for adjusting the current passing through the first LED load, wherein the first LED load is connected in series with the power supply and the second switch, - A second LED load comprising at least one LED, wherein the power supply is configured to supply the regulated power to the second LED load, - A series combination of a second capacitor and a third switch connected in series with each other, and a series combination connected in parallel with the second LED load, - A fourth switch for adjusting the current passing through the second LED load, wherein the second LED load further comprises the power supply and a fourth switch coupled in series with the fourth switch, The power supply is adapted to supply regulated power to the second LED load, and the power supply is A third mode in which the first amount of the adjustment power is supplied to the second LED load, wherein the third switch is closed, and A fourth mode is configured to supply a second amount of the adjustment power to the second LED load, wherein the second amount of the adjustment power supplied to the second LED load is less than the first amount of the adjustment power supplied to the second LED load, and the third switch is opened.

[0011] Two parallel LED strings, each having its own parallel capacitor, also suffer from color point shift across the dimming range. In this example, each LED string has its own capacitor and its own switch in series with the corresponding capacitor. The third switch is opened when the power to the second LED load is below a second threshold, for example, indicating that dimming is taking place, and the third switch is closed when the power to the second LED load is above the second threshold, indicating that dimming is not taking place or that only slight dimming is occurring. In this example, the first and second LED loads can independently decide whether to open or close their respective first and fourth switches. This can be particularly interesting if the control of the first switch is located near the first LED load and the control of the fourth switch is located near the second LED load. This can result in the switches, capacitors, switches, and LED load controls for either the first or second LED load being grouped together, or at least very close together, on the same printed circuit board, for example.

[0012] The use of the second and fourth switches allows for independent current control of the current flowing through each LED load by modulating the current flowing through the LED load.

[0013] Another possibility is that both the first switch and the third switch are controlled by a single controller. This could result in the first switch and the third switch being turned on and off simultaneously.

[0014] In a further example, the lighting unit further comprises a first unidirectional element, preferably a second unidirectional element, wherein the first unidirectional element is configured to supply the adjustment power to the first LED load and the first capacitor, and the second unidirectional element is configured to supply the adjustment power to the second LED load and the second capacitor.

[0015] Using the first unidirectional element to supply the regulated power to the first LED load and the first capacitor makes it possible for the string voltages to be different between the first LED load and the second LED load. Without the first unidirectional element, undesirable current may flow, for example, from the first capacitor coupled to the first LED load which has a higher string voltage, to the second LED load which has a lower string voltage.

[0016] In a further example, the power supply is a current source configured to supply a regulating current.

[0017] Preferably, the power supply is a current source, since the light output of the LEDs in the LED load is directly related to the amount of current flowing through the LEDs. The currents flowing through the first LED load and the second LED load can be used to determine whether the first switch and / or the second switch need to be opened or closed. The currents flowing through the first LED load and the second LED load may represent the power supplied to the first LED load and the second LED load by the power supply.

[0018] In a further example, the lighting unit further includes a fifth switch coupled between the output of the current source and ground reference so that no regulating current is supplied to the first LED load.

[0019] The addition of the fifth switch can enable deeper dimming of the light output of the first LED load and the second LED load. The fifth switch can shunt the current supplied by the current source and separate it from the first LED load and the second LED load.

[0020] In a further example, the first LED load has a red LED.

[0021] In a further example, the first LED load has a phosphor-converted LED.

[0022] In a further example, the second LED load has a phosphor-converted LED.

[0023] The first LED load and the second LED load may have several types of LED loads. The examples shown are red, amber, green or blue LEDs, but phosphor-converted LEDs for creating warm white or cold white effects are also possible.

[0024] In a further example, the string voltage of the first LED load is greater than the string voltage of the second LED load.

[0025] In the lighting circuit according to the present invention, it is possible to have the first string voltage greater than the second string voltage, which enables an increase in the design freedom when designing the LED load.

[0026] In a further example, the lighting unit has a controller for controlling the first switch and the second switch.

[0027] A single controller can be used to control the first and second switches. The controller can also be used to control the third, fourth, and fifth switches. The controller may also have several building blocks, each of which can be used to control a single switch. This allows for localized integration of the building blocks near the corresponding switches.

[0028] In a further example, the controller is configured to provide a dimming function for the light output of the first LED load, and the controller is configured to control the second switch to modulate the current passing through the LED load.

[0029] The controller may be used to receive a dimming signal that enables the lighting unit to perform the dimming function.

[0030] In a further example, the controller is configured to further control the third and fourth switches.

[0031] In a further example, the controller is configured to provide a dimming function for the light output of the second LED load, and the controller is configured to control the third switch to modulate the current passing through the LED load.

[0032] Similar to providing dimming functionality to a single LED load, the controller may also be used to receive dimming signals that enable the lighting unit to perform the dimming functionality for both the first LED load and the second LED load.

[0033] In a further example, the power supply is adapted to supply maximum output power, and is configured to operate in the second mode when the regulated power is less than 25% of the maximum output power, preferably less than 10% of the maximum output power.

[0034] Below 25% of the maximum output power of the power supply, a threshold may be reached indicating that the power supply operates in the second mode. This allows the capacitor in the LED load to be disconnected by opening the first and / or fourth switch.

[0035] Preferably, this threshold is less than 10% of the maximum output power of the power supply, but it may also be within the range of 10% to 25%, such as 15% or 20% of the maximum output power of the power supply.

[0036] In a further example, the first switch has a semiconductor switch.

[0037] Preferably, the first switch is a semiconductor switch such as a bipolar transistor or a metal-oxide-film field-effect transistor (MOSFET). The second, third, fourth, and fifth switches may also be semiconductor switches. [Brief explanation of the drawing]

[0038] For a better understanding of the present invention and to more clearly illustrate how it can be carried out, the accompanying drawings are referenced here, as merely one example. [Figure 1] This shows an example of the current implementation of the lighting unit. [Figure 2] An embodiment of the lighting unit according to the present invention is shown. [Figure 3] An embodiment of the lighting unit according to the present invention is shown. [Figure 4] Further improvements to the embodiment of the lighting unit according to the present invention are shown. [Modes for carrying out the invention]

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

[0040] The detailed descriptions and specific examples illustrate exemplary embodiments of the apparatus, systems, and methods, but are for illustrative purposes only and should not be understood as being intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems, and methods of the invention will be better understood from the following description, the appended claims, and the appended drawings. It should also be understood that the figures are for illustrative purposes only and are not drawn to scale. It should also be understood that throughout the figures, the same reference numerals are used to indicate the same or similar parts.

[0041] Figure 1 shows an example of a lighting unit as currently implemented. Power supply 1 is used to convert the primary power supply into regulated power for the load. The primary power supply may be a normal mains power supply operating at, for example, 230V 50Hz or 120V 60Hz. In other examples, the primary power supply may be a DC power supply such as a battery or a DC grid. The regulated power to the load is supplied to the LED load LED1 and capacitor C1. Capacitor C1 is provided in parallel with the LED load LED1 to filter and remove any ripple current that would otherwise flow through the LED load LED1. Current flows through the LED load LED1, which results in a specific light output. To reduce the light output, the current through the LED load LED1 needs to be reduced. This can be done by reducing the amplitude of the current generated by power converter 1. The amplitude of the current can be reduced in at least two ways, but more ways are possible. The first way is to reduce the amplitude of the current by amplitude modulation. In this case, the amplitude of the current is gradually reduced until it reaches the desired amount of current. This amplitude modulation has significant disadvantages. The lower the current level, the greater the color point shift of the light output by the LED load LED1. The color temperature of the light output is first determined by the type of LED used. Changing the amplitude of the current results in a color point shift. Using pulse width modulation in the current flowing through the LED load LED1 results in a constant amplitude of the LED current, but the pulse width determines the average current supplied to the LED load LED1. Therefore, it is preferable to use pulse width modulated current for the LED load LED1 to achieve dimming of the light output. The use of the term pulse width modulation is intended in its broadest sense, where the on-off ratio of pulses over time determines the average LED current, and does not necessarily require, for example, fixed-frequency pulse width modulation. Consequently, pulse width modulation is intended here to include, for example, pulse frequency modulation, pulse duration modulation, pulse position modulation, and binary code modulation.Generally, pulse width modulation (PWM) encompasses all methods of dimming LED current that have reduced color shift compared to amplitude dimming of LED current. A pulse width modulated current can be generated by a power converter 1. This pulse width modulated current is supplied to a capacitor C1 and an LED load LED1. Capacitor C1 is used to filter and remove ripple from the current flowing to the LED load LED1, ensuring a stable LED current is generated. This is beneficial in situations where flicker should be prevented. Cameras and barcode scanners may react to light with flicker frequencies generated by pulse width modulation. When dimming is performed, capacitor C1 causes the pulse width modulated current to behave more like amplitude modulation, resulting in a shift in the color point of the light emitted by the LED load LED1. An improved lighting unit is desired that can provide less flicker to ensure good operation where a camera or barcode scanner is used, and that can provide reduced color shift when the light output is dimmed.

[0042] Figure 2 shows an example of an embodiment according to the present invention. The power converter 1 supplies power to an LED load LED1 and a capacitor C1. A first switch SW1 is in series with the capacitor C1. The series combination of capacitor C1 and the first switch SW1 is coupled in parallel with the LED load LED1. The power converter 1 is configured to provide dimming of the light output of the LED load LED1 by reducing the current supplied to the LED load LED1. In a first operating mode of the power converter 1, the power converter 1 supplies pulse-width modulated current to the LED load LED1 and the capacitor C1. In this first operating mode, the first switch SW1 is closed. The first operating mode is, for example, an operating mode in which the power converter 1 supplies power to the LED load LED1 such that the light output of the LED load LED1 is within a range between the maximum light output and 25% of the light output.

[0043] When the light output is reduced to, for example, less than 25%, the power converter 1 can operate in a second operating mode. In this second operating mode, the current to the LED load LED1 is further reduced. In this second operating mode, the first switch SW1 is opened so that the capacitor C1 cannot receive any power supplied by the power converter 1. The filtering and stabilization of the current through the LED load LED1 performed by the capacitor C1 in the first operating mode is not performed in the second operating mode because the capacitor C1 cannot filter and stabilize the current through the LED load LED1. Instead, the pulse width modulated current generated by the power converter 1 is supplied directly to the LED load LED1, which causes flickering in the light output. Since the light output is dimmed, the effect of the light flicker is no longer significant for, for example, a camera or barcode scanner.

[0044] The pulse-width modulated current can maintain a constant amplitude throughout the dimming range, and the average current through the LED load LED1 can be controlled by controlling the duty cycle of the current. In other examples, the amplitude of the current may be changed throughout the dimming range in conjunction with the control of the duty cycle. This combination of amplitude modulation and pulse-width modulation still provides a reduction in color point shift.

[0045] The first switch SW1 may be controlled by a controller 2 that determines whether the power converter 1 operates in a first operating mode or a second operating mode. If the controller 2 determines that the power converter 1 operates in the first operating mode, the controller 2 closes the first switch SW1. If the controller 2 determines that the power converter 1 operates in the second operating mode, the controller 2 closes the first switch SW1.

[0046] Figure 3 provides another example of a lighting unit according to the present invention. The lighting unit has a power converter 1 that supplies power to a first load and a second load. The first load may be a first LED load LED1, and the second load may be a second LED load LED2.

[0047] Furthermore, the power converter 1 can supply power to the first capacitor C1 and the second capacitor C2. A first switch SW1 is in series with the first capacitor C1. The series combination of the first capacitor C1 and the first switch SW1 is coupled in parallel with the first LED load LED1. The power converter 1 is configured to supply stable power to the first LED load LED1 and the second LED load LED2. It is desirable to adjust the current through the first LED load LED1 and the current through the second LED load LED2 independently of each other. The second switch SW2 is used to adjust the current through the first LED load LED1. The second switch SW2 is arranged in series with the power converter 1 and the first LED load LED1.

[0048] A third switch SW3 is connected in series with the second capacitor C2. The series combination of the second capacitor C2 and the third switch SW3 is connected in parallel with the second LED load LED2. A fourth switch SW4 is used to regulate the current passing through the second LED load LED2. The fourth switch SW4 is placed in series with the power converter 1 and the second LED load LED2.

[0049] Preferably, the current adjustment performed by the second switch SW2 and the fourth switch SW4 is carried out by controlling the switches so that the current adjustment is performed by pulse width modulation of the current passing through the LED load.

[0050] In this case as well, the power converter can operate in a first operating mode and a second operating mode. In the first operating mode of the power converter 1, the power converter 1 supplies current to the first LED load LED1 and the first capacitor C1. In this first operating mode, the first switch SW1 is closed.

[0051] The first operating mode is, for example, an operating mode in which the power converter 1 supplies power to the first LED load LED 1 such that the light output of the first LED load LED 1 is within a range between the maximum light output and 25% of the light output, preferably 10% of the light output.

[0052] When the light output of the first LED load LED1 is reduced to, for example, less than 25%, the power converter 1 may operate in a second operating mode. In this second operating mode, the current to the first LED load LED1 is further reduced. In this second operating mode, the first switch SW1 is opened so that the first capacitor C1 cannot receive any power supplied by the power converter 1.

[0053] The power converter 1 is further adapted to operate in a third and fourth operating mode.

[0054] In the third operating mode of the power converter 1, the power converter 1 supplies current to the second LED load LED2 and the second capacitor C2. In this third operating mode, the third switch is closed.

[0055] The third operating mode is, for example, an operating mode in which the power converter 1 supplies power to the second LED load LED2 such that the light output of the second LED load LED2 is within a range between the maximum light output and 25% of the light output, preferably 10% of the light output.

[0056] When the light output of the second LED load LED2 is reduced to, for example, less than 25%, the power converter 1 may operate in a fourth operating mode. In this fourth operating mode, the current to the second LED load LED2 is further reduced. In this fourth operating mode, the third switch SW3 is opened so that the second capacitor C2 cannot receive any power supplied by the power converter 1.

[0057] In the example shown, power to the first LED load LED1 and the second LED load LED2 is controlled in four operating modes, which, for example, allow control of only the first switch SW1 or the third switch SW3. The operating modes may be combined such that the first switch SW1 and the third switch SW3 are opened or closed simultaneously. For example, the light output of both the first LED load LED1 and the second LED load LED2 may be reduced so that the power converter 1 operates in the second and fourth operating modes. In this example, the first switch SW1 and the third switch SW3 are opened simultaneously.

[0058] The first controller 2 may be used to control the first switch SW1 and the second switch SW2. The second controller 3 may be used to control the third switch SW3 and the fourth switch SW4. The first controller 2 can be located near the first switch SW1 and the second switch SW2. The second controller 3 can be located near the third switch SW3 and the fourth switch SW4. This may allow for the integration of the switches and controllers into an integrated circuit.

[0059] In other examples, a single controller 2 can be used to control the first, second, third, and fourth switches. The single controller 2 can also be used to control the power converter 1. Since all control parameters are transmitted to a single control unit, the single controller 2 allows for easier control of the switches and the power converter 1.

[0060] The first controller 2, the second controller 3, or a single controller 2 may be, but are not limited to, a microcontroller, a field-programmable gate array (FPGA), or a discrete control solution.

[0061] Preferably, the lighting unit has a first unidirectional element D1 that enables regulated power from the power converter 1 to be supplied to the first LED load LED1. This first unidirectional element D1 is positioned between the output of the power converter 1 and the input of the first LED load LED1. The input of the first LED load LED1 may be the anode of the LED.

[0062] Preferably, the string voltage of the first LED load LED1 is greater than the string voltage of the second LED load LED2. The first unidirectional element D1 prevents current from flowing from the first capacitor C1 to the second LED load LED2, otherwise due to the voltage difference.

[0063] Preferably, the lighting unit also has a second unidirectional element D2 that allows regulated power from the power converter 1 to be supplied to the second LED load LED2. This second unidirectional element D2 is positioned between the output of the power converter 1 and the input of the second LED load LED2. The input of the second LED load LED2 may be the anode of the LED. The function of the second unidirectional element D2 is similar to that of the unidirectional element D1, but it is combined with the second LED load LED2 instead of the first LED load LED1.

[0064] The use of the first and second unidirectional elements allows the user to mount any type of LED load without having to take into account the difference in string voltage.

[0065] Although the first unidirectional element D1 and the second unidirectional element D2 are shown as diodes, MOSFETs can also be used, which interrupt current when reverse-biased and allow current to flow when forward-biased. This can reduce losses in the unidirectional elements.

[0066] Preferably, a unidirectional element is used when any of the first, second, third, or fourth switches is a MOSFET. The MOSFET has an intrinsic body diode that may cause undesirable current to flow, for example, from the first capacitor C1 to the second LED load LED2.

[0067] Figure 4 shows an improved version of the lighting unit example shown in Figure 3. Features with the same reference numerals as in Figure 3 are identical. An additional fifth switch SW5 is provided. This fifth switch SW5 is located between the output of the power converter 1 and the return path, for example, to ground. The fifth switch SW5 substantially shunts the first LED load LED1 and the second LED load LED2 so that no current flows from the power converter 1 to the first LED load LED1 and the second LED load LED2 when the fifth switch SW5 is closed.

[0068] In the example shown, the LED load LED1 is shown and described as a single LED, but it should be understood that multiple LEDs can be used as the LED load LED1. LEDs can be coupled in various configurations, such as in series, parallel, or a combination thereof.

[0069] In the example shown, the second switch SW2 and the fourth switch SW4 are located below the LED load. It should be understood that the second switch SW2 and the fourth switch SW4 can also be located above the LED load so that they can regulate the current passing through the first LED load LED1 and the second LED load LED2. The shown positions of the second switch SW2 and the fourth switch SW4 are preferred because the switches can be easily controlled in these positions.

[0070] In the examples shown, any of the first, second, third, and fourth switches may be, but are not limited to, a semiconductor switch, such as a MOSFET or bipolar transistor, or an electromechanical switch.

[0071] In the examples shown, the power converter 1 may be a current source or a voltage source. A current source is a power converter 1 that adjusts the current at its output. The current source attempts to maintain the generated current at a constant level, and the voltage at the output of the current source is the result of the load impedance and the amount of adjustment current. A voltage source is a power converter 1 that adjusts the voltage at its output. The voltage source attempts to maintain the generated voltage at a constant level, and the current at the output of the voltage source is the result of the load impedance and the amount of adjustment voltage.

[0072] In the example shown, it is preferable that the power converter 1 is configured to transition from the second mode to the first mode by controlling the first switch SW1 in linear operation mode.

[0073] It is also preferable that the power converter 1 be configured to transition from the second mode to the first mode by controlling the third switch SW3 in linear operation mode.

[0074] In the example shown, the first controller 2, the second controller 3, or a single controller 2 may be used to control the second switch SW2 to provide modulation of the current through the first LED load LED1 so that the dimming function of the light output of the first LED load LED1 is activated. In addition, or instead, the first controller 2, the second controller 3, or a single controller 2 may be used to control the fourth switch SW4 to provide modulation of the current through the second LED load LED2 so that the dimming function of the light output of the second LED load LED2 is activated.

[0075] A person skilled in the art will be able to understand and achieve, in carrying out the claimed invention, other variations of the disclosed embodiments by studying the drawings, specification and appended claims. In the claims, the word “has” does not exclude other elements or steps, and singular notation does not exclude plurality. The mere fact that certain means are listed in different dependent claims does not mean that combinations of these means cannot be used favorably. No reference numeral in the claims should be construed as limiting the scope.

Claims

1. A power converter for supplying regulated power to the first LED load, The first LED load includes at least one LED, and the first LED load is coupled to the power converter, A lighting unit having a series combination of a first capacitor and a first switch connected in series with each other, and a series combination connected in parallel with the first LED load, The aforementioned power converter A first mode in which a first amount of the adjustment power is supplied to the first LED load, wherein the first switch is closed, and A second mode in which a second amount of the adjustment power is supplied to the first LED load, wherein the second amount of the adjustment power supplied to the first LED load is less than the first amount of the adjustment power supplied to the first LED load, and the first switch is opened, and the device is configured to operate in this second mode. A lighting unit configured such that the power converter switches from the second mode to the first mode by controlling the first switch in linear operation mode.

2. A second switch for adjusting the current passing through the first LED load, wherein the first LED load is connected in series with the power converter and the second switch, A second LED load comprising at least one LED, wherein the power converter is configured to supply the adjusted power to the second LED load, A series combination of a second capacitor and a third switch connected in series with each other, and a series combination connected in parallel with the second LED load, A fourth switch for adjusting the current passing through the second LED load, wherein the second LED load further comprises the power converter and a fourth switch connected in series with the fourth switch, The power converter is adapted to supply regulated power to the second LED load, and the power converter is, A third mode in which the first amount of the adjustment power is supplied to the second LED load, wherein the third switch is closed, and The lighting unit according to claim 1, which is configured to operate in a fourth mode in which a second amount of the adjustment power is supplied to the second LED load, wherein the second amount of the adjustment power supplied to the second LED load is less than the first amount of the adjustment power supplied to the second LED load, and the third switch is opened.

3. The lighting unit according to claim 2, further comprising a first unidirectional element and a second unidirectional element, wherein the first unidirectional element is configured to supply the adjustment power to the first LED load and the first capacitor, and the second unidirectional element is configured to supply the adjustment power to the second LED load and the second capacitor.

4. The lighting unit according to claim 1, wherein the power converter is a current source configured to supply an adjustment current.

5. The lighting unit according to claim 4, further comprising a fifth switch coupled between the output of the current source and a ground reference so that no adjustment current is supplied to the first LED load.

6. The lighting unit according to claim 1, wherein the first LED load has a red or amber LED.

7. The lighting unit according to claim 1, wherein the first LED load has a phosphor conversion LED.

8. The lighting unit according to claim 2, wherein the second LED load has a phosphor conversion LED.

9. The lighting unit according to claim 2, wherein the string voltage of the first LED load is greater than the string voltage of the second LED load.

10. The lighting unit according to claim 2, further comprising a controller for controlling the first switch and the second switch.

11. The lighting unit according to claim 10, wherein the controller is configured to provide a dimming function for the light output of the first LED load, and the controller is configured to control the second switch to modulate the current passing through the first LED load.

12. The lighting unit according to claim 10, as dependent on claim 2, wherein the controller is further configured to control the third switch and the fourth switch.

13. The lighting unit according to claim 12, wherein the controller is configured to provide a dimming function for the light output of the second LED load, and the controller is configured to control the fourth switch to modulate the current passing through the second LED load.

14. The lighting unit according to claim 1, wherein the power converter is adapted to supply maximum output power, and is configured to operate in the second mode when the regulated power is less than 25% of the maximum output power.

15. The lighting unit according to any one of claims 1 to 14, wherein the first switch is a semiconductor switch.

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