WO2011057682A1

WO2011057682A1 - Light emitting diode array and method of operation thereof

Info

Publication number: WO2011057682A1
Application number: PCT/EP2010/001790
Authority: WO
Inventors: Woon Bok Kim; Hak Ki See
Original assignee: Intsec Ltd.
Priority date: 2009-11-16
Filing date: 2010-03-22
Publication date: 2011-05-19
Also published as: KR20110053678A

Abstract

A light emitting diode (LED) array is to be connected to an external electrical power source. This array has a predetermined number of LED chips and is connected to a control circuit. The control circuit is adapted to convert power from the electrical power source into a repeating pulse train for driving the LEDs. The repeating pulse train has a sequence of short ON/OFF pulses and a long OFF period. This mode of operation of the LED array avoids thermal problems with the LEDs and therefore, does not require a heat sink as do conventional LED lighting designs. The mode of operation of the LED array provides for an efficient use of the electrical energy. This also avoids a heat sink. In comparison to prior art LED lightings the mode of operation of the LED array is up to 20% to 50% more energy-efficient while at the same time the described LED lighting can be manufactured with reduced costs. The LED lighting described here does hardly heat up. This ascertains a long lifetime with a minimal decay in light output.

Description

Light Emitting Diode Array and Method of Operation Thereof Description

Introduction

Hereinafter, a light emitting diode array and a method of operation thereof is described. Such light emitting diode arrays are intended to replace conventional incandescent light bulbs that use a thin tungsten filament coil in either a vacuum or an inert gas. In these conventional incandescent light bulbs, an electric current passes through the filament, heating it so that it glows and produces light. These traditional incandescent light bulbs are increasingly less popular due to their low efficiency and restricted lifetime. Additionally, there exists legislation for banning such incandescent light bulbs in the future, e.g. in Australia and the European Community.

Background

A Light Emitting Diode (LED) is a solid-state semiconductor device that converts electrical energy directly into light. The semiconductor device is comprised of two regions. A p-region that contains positive electrical charges while an n-region contains negative electrical charges. When voltage is applied to the device and current begins to flow, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths.

Prior Art

Conventionally, a LED array may include optics, a heat sink and a power supply.

Advanced Lumonics, LLC, Boca Raton, FL, USA offers a direct replacement LED light bulb "EvoLux" featuring a Color Rendering Index of 75 for Cool White and 80 for Warm White. This LED light bulb has an active cooling system that employs a long life internal fan to cool a heat sink. The entire housing is encased in ABS plastic. The heat sinks conventionally employed in these and other LED light bulbs are

comparably heavy, volumenous and expensive to manufacture. This results in the entire lighting device being quite costly. Moreover, the fact that cooling is required indicates a less than optimum energy-efficient operation. Finally, the fan is an additional moving mechanical component that can fail. In many applications, LEDs are driven with a source of constant current. Most LEDs have a specified current level that will achieve the maximum brightness for that LED without premature failures. One way to drive a LED is a switch-mode power supply (SMPS). A LED will have a forward voltage drop across its terminals for a given current drive level. The power supply voltage and the LED forward voltage

characteristics determine the SMPS characteristics. Multiple LEDs can be connected in series to increase the forward voltage drop at the chosen drive current level. The SMPS circuitry adopted to regulate current in LED lighting applications are

comparable to those used to control voltage in a power supply application.

Microchip Technology Inc. Chandler, AZ , USA features a LED Lighting Design Guide "Adding Intelligence to Lighting Applications" of September 2008

fwww.microchip.com/ lighting). According to this Design Guide, LED lighting applications can be controlled by a Micro Controller Unit (MCU). One application for a MCU in LED lighting is brightness control. A power LED can be dimmed by reducing the drive current. However, this is not the most efficient way to control the brightness of a LED. A power LED provides the best efficiency at the maximum rated drive current. Better efficiency can be obtained by turning the LED on and off using a low frequency Pulse Width Modulation (PWM) signal. The PWM signal is connected to the enable input of the SMPS control IC. The LED is always driven at the maximum current level when it is switched on.

The "MCP1650 Multiple White LED Demo Board" and the "MCP1650 3W White LED Demo Board" use a PIC10F206 MCU. The PIC10F206 device provides the user button interface and generates the PWM control signal for the SMPS IC.

The MCP1650 Multiple White LED Demo Board uses the MCP1650 IC to power nine white LEDs connected in series. A PIC10F202 microcontroller is used to provide the PWM signal to the MCP1650. It also accepts a push button input to adjust the white LEDs to three different intensities of 100%, 50% and 25%.

Problem

In view of the above discussed prior art, it is sought to provide a more energy- efficient, cost-effective, and longer-life operation of LED arrays. Energy-efficiency is defined as the light output of a light source divided by the total electrical power input to that light source, expressed in lumens per watt (Im/W). Solution

Such a more energy-efficient and long-life light emitting diode array is to be connected to an external electrical power source. The LED array has a predetermined number of LED chips and is connected to a control circuit. The control circuit is adapted to convert power from the electrical power source into a repeating pulse train for driving the LEDs of the LED array. The repeating pulse train has a sequence of short ON/OFF pulses and a long OFF period. Preferably, the sequence of short ON/OFF pulses is followed by the long OFF period.

Advantages

This mode of operation of the LED array avoids thermal problems with the LEDs and therefore, does not require a heat sink as do conventional LED lighting designs. More specifically, the mode of operation of the LED array described here lends itself to a very efficient use of the electrical energy fed into the LED lighting described.

Moreover, the heat sink can be avoided due to the energy efficiency of the described LED lighting.

Comparison measurements with LED lightings currently offered and sold in the market show that the mode of operation of the LED array described here is up to 20% to 50% more energy-efficient while at the same time can be manufactured with substantially reduced costs. Another important advantage resides in the fact that the LED lighting described here does hardly heat up. This circumstance ascertains a long lifetime with a minimal decay in light output of the light source.

Embodiments, Variations

The control circuit can be adapted to adjust the sequence of short ON/OFF pulses to have a first duration dl and the long OFF period to have a second duration d2. The control circuit can be further adapted to adjust the ratio dl/d2 of the first duration dl and the second duration d2 from approximately 1/20 to approximately 20/1.

The control circuit can further be adapted to adjust the long OFF period to have a second duration d2 in the range of approximately 200 ps to approximately 5 ms.

The control circuit can even further be adapted to adjust each one of the short ON pulses to have a third duration d3 in the range of approximately 1.5 s to

approximately 40 ps and the short OFF pulses to have a fourth duration d4 in the range of approximately 0.5 * d3 to approximately 40 * d3. The control circuit can further be adapted to adjust the number n of short ON/OFF pulses in the repeating pulse train in the range from approximately 3 to

approximately 250.

For a given light emitting diode array having a given number of LED chips, the control circuit can be adapted to adjust (i) the first duration of the short ON/OFF pulses, (ii) the second duration of the long OFF period, (iii) the third and the fourth durations of each one of the short ON/OFF pulses, (iv) the ratio of the first and the second duration, and / or (v) the number of short ON/OFF pulses in the repeating pulse train to each have a fixed value or a value that varies within a predetermined range during operation of the light emitting diode array.

The control circuit can be adapted to provide the short ON/OFF pulses in the repeating pulse train at an ON-voltage of approximately 1.1 Volt to approximately 5.5 Volt per each of the LED chips in the light emitting diode array. Preferably, the ON- voltage is approximately 2 Volt to approximately 4 Volt per each of the LED chips. This voltage is dependent from the characteristics of the LEDs used in the LED array.

The control circuit can be adapted to provide the short ON/OFF pulses in the repeating pulse train with a current in the range from approximately 10 mA to approximately 250 mA to the light emitting diode array. This current is dependent on the number and the characteristics of the LEDs used in the LED array and can be substantially higher than the 250 mA mentioned earlier. Moreover, the current can be provided by a constant current source in the control circuit that is switched on and off under the control of the control circuit dependent from the characteristics of the LEDs used in the LED array.

The control circuit can comprise a microcontroller adapted to and programmed to generate the repeating pulse train that has a sequence of short ON/OFF pulses and a long OFF period, wherein parameters of the sequence of short ON/OFF pulses and the long OFF period such as such as the first duration of the short ON/OFF pulses, the second duration of the long OFF period, the third duration of each one of the short ON/OFF pulses, a ratio of the first and the second duration, and/or the number of short ON/OFF pulses in the repeating pulse train are to be programmed into the microcontroller during an initial setting operation of the light emitting diode array via a parameter setting input. The control circuit can further comprise a power supply to be connected to an external electrical power source for supplying electrical power to the light emitting diode array and to the microcontroller. Preferably, the power supply is unregulated and includes a surge and over-voltage protection stage, a line filter stage, an AD/DC conversion stage, and/or a voltage smoothing stage.

The control circuit can also comprise a regulated power supply to be connected to the preferably unregulated power supply to provide an operation voltage to the microcontroller and / or other circuitry. Preferably, the regulated or partially regulated power supply includes a voltage down converter for down converting the output voltage of the preferably unregulated power supply, a voltage stabilizer for stabilizing the down converted voltage and/or a signal conditioner for providing a voltage magnitude detection signal representative of the output voltage of the preferably unregulated power supply to the microcontroller. The microcontroller is preferably adapted to shut down any electrical power to be provided to the LED array when the output voltage of the preferably unregulated power supply is unstable beyond a predetermined, accepted voltage band or if other out-of-specification criteria are detected.

The control circuit can be adapted to provide the peak current and the average current during the short ON/OFF pulses in the repeating pulse train independently. The peak current can be set by a current / voltage limiter and the average current can be set by the setting of the control circuit (e.g. the first, second, third and/or fourth durations).

The microcontroller can also comprise a first output for providing a signal with the repeating pulse train that has the sequence of short ON/OFF pulses and the long OFF to a solid-state power switch. The solid-state power switch provides an amplified electrical power signal to the light emitting diode array to drive the LEDs. The microcontroller can also comprise a second output for providing an operation pulse signal to the voltage down converter.

The control circuit provides the LED driver power signal using a current waveform that is supplied in the most secure current and voltage range. The control circuit can include a control loop, using e.g. an Analog/Digital Converter to sense and control the voltage and the current provided to the light emitting diode array. The LED driver power signal is generated and controlled by the control circuit to operate the LED array efficiently. To this end, the signal timing and shape, the voltage and current of the LED driver power signal can be initially adapted to the respective LED array and then to respective current operating conditions (e.g.

voltage variations of the mains input voltage, over voltage peaks, etc.). To this end, the control circuit is adapted to cease to provide or to reduce the LED driver power signal (i) in case the voltage signal representing the operating voltage for the LED array is unstable, or (ii) in case the operation voltage for the control circuit, especially the microcontroller, is unstable, or (iii) in case of incorrect operation mode settings, or (iv) in case initial there occurs a signal generation error after a predetermined number (e.g. 3 to 10, preferably 5) of repeating pulse trains, or (v) in case there is a (over-)heating in the control circuit. In order to detect any overheating in the control circuit, a temperature sensitive element e.g. a thermistor can be included in the control circuit, sensed and the duration d3 of the ON pulses can be shortened and/or the durations d2, d4 of the short and/or the long OFF pulses can be extended.

The LED driver power signal can be adjusted and the light emitting diode array can be operated when connected to the control circuit as follows:

• Determine the number of LED chips in the LED array.

• Set required voltage / current values for nominally driving the determined number of LED chips in the LED array.

• Sense, adjust and set input voltage of control circuit.

• Sense, adjust and set characteristics of operation pulse signal to the

voltage down converter.

• Sense, adjust and set characteristics of repeating pulse train that has the sequence of short ON/OFF pulses and the long OFF period. The values of these characteristics and their changes are preferably based on the voltage signal representing the operating voltage for the LED array, or the operation voltage for the control circuit.

• Provide an LED driver power signal for the LED array in the form of the repeating pulse train that has a sequence of short ON/OFF pulses and a long OFF period.

• Cease to provide the LED driver power signal or reduce the LED driver power signal

(i) in case the voltage signal representing the operating voltage for the LED array is unstable, or

(ii) in case the operation voltage for the control circuit, especially the microcontroller, is unstable, or

(iii) in case of incorrect operation mode settings, or

(iv) in case initial there occurs a signal generation error after a predetermined number of repeating pulse trains, or

(v) in case there is an (over-)heating in the control circuit.

A lighting fixture with the mode of operation of the LED array described here can include at least one light emitting diode array connected to the control circuit as described above.

Brief Description of the Drawings

The modes of operation, features, advantages, variations and characteristics of the light emitting diode array to be connected to an external electrical power source, where the light emitting diode array has a predetermined number of LED chips and is connected to a control circuit is described in detail hereinafter with regards to the attached drawings.

Fig. 1 illustrates the general mode of operation of the LED array described here. Fig. 2 illustrates the characteristics of the mode of operation of the LED array described here.

Fig. 3 is a schematic drawing of a circuit diagram that can be used to implement the mode of operation of the LED array described here.

Fig. 4 is a schematic flowchart of a program to operate a LED array described here connected to the control circuit described here.

Detailed Description of the Drawings

Fig. 1 shows a light emitting diode (LED) array 10 to be connected to an external electrical power source (Mains). The embodiment uses a mains voltage of 220 Volt. It is understood, however, that other mains voltages, e.g. 110 Volt are also possible. The light emitting diode array 10 has a predetermined number of LED chips 12 and is connected to a control circuit 30. It is understood that the number of LED chips 12 has an impact on the light output of a light source using the LED array 10. In addition, one or more LED chips 12 can be mounted in a common assembly. The light emitting diode array 10 has all its LED chips 12 electrically connected in series. Therefore, the current flowing through the totality of the LED chips 12 of the LED array 10 is the same. The control circuit 30 is adapted to convert power from the electrical power source (Mains) into a repeating pulse train 40 for driving the LEDs of the LED array 10. This repeating pulse train 40 has a sequence of short ON/OFF pulses 42 and a long OFF period 44 (see also Fig. 2).

The control circuit is adapted to adjust the sequence of short ON/OFF pulses 42 to have a first duration dl and the long OFF period 44 to have a second duration d2. The control circuit 30 is further adapted to adjust the ratio dl/d2 of the first duration dl and the second duration d2 from 0.05 to 20. This is achieved in a preferred embodiment by utilizing a microcontroller as described hereinafter. It is, however, also possible to use a circuit with discrete or integrated active and passive

components. The control circuit 30 is adapted to adjust the long OFF period 44 to have a second duration d2 of approximately 200 ps to approximately 5 ms.

The control circuit 30 is adapted to adjust each one of the short ON pulses 42 to have a third duration d3 of approximately 1.5 ps to approximately 40 ps. The control circuit 30 is also adapted to adjust each one of the short OFF pulses 43 to have a fourth duration d4 of approximately 0.5 * d3 to approximately 40 * d3. These third and fourth durations are set (i) depending on the type of LEDs, (ii) the number of the LEDs 12, (iii) their characteristics and (iv) depending from the duration of the length of the second duration d2 of the long OFF period 44.

The control circuit 30 is adapted to adjust the number n of short ON/OFF pulses 42 in the repeating pulse train 40 in the range from approximately 3 to approximately 250.

For a given light emitting diode array 10 having a given number of LED chips, the control circuit 30 is adapted to adjust the first duration dl of the short ON/OFF pulses 42, the second duration d2 of the long OFF period 44, the third duration d3 of each one of the short ON pulses 42, the fourth duration d4 of each one of the short OFF pulses 43, the ratio dl/d2 of the first dl and the second duration d2, and/or the number of short ON/OFF pulses 42, 43 in the repeating pulse train 40 to each have a fixed value or a value that varies within a predetermined range during operation of the light emitting diode array 10. The control circuit 30 is adapted to provide the short ON/OFF pulses 42, 43 in the repeating pulse train 40 at an ON-voltage of approximately 1.1 V to approximately 3.5 V per each of the LED chips 12 in the light emitting diode array 10 and with a current in the range from approximately 10 mA to approximately 250 mA or higher.

The control circuit 30 comprises a microcontroller 50 adapted and programmed to generate the repeating pulse train 40 that has a sequence of short ON/OFF pulses 42, 43 followed by a long OFF period 44. Parameters of the sequence of short ON/OFF pulses 42, 43 and the long OFF period 44 such as such as the first duration dl of the sequence of short ON/OFF pulses 42, 43, the second duration d2 of the long OFF period 44, the third duration d3 of each one of the short ON pulses 42, the fourth duration d4 of each one of the short OFF pulses 43, a ratio dl/d2 of the first dl and the second duration d2, and / or the number n of short ON/OFF pulses 42, 43 in the repeating pulse train 40 are to be programmed into the microcontroller 50 during an initial setting operation of the light emitting diode array 10 via a parameter setting input 52.

As can be seen in Fig. 3, the control circuit 30 comprises a power supply 54 to be connected to the external electrical power source Mains for supplying electrical power to the light emitting diode array 10 and to the microcontroller 50. A current limiter 52 is used to limit the electrical power fed to the light emitting diode array 10. A resistor can implement this current limiter 52, however, this current limiter 52 can also be implemented as an active circuit. In the illustrated embodiment, the power supply 54 is unregulated and includes a surge and over-voltage protection stage, a line filter stage, an AD/DC conversion stage, and a voltage smoothing stage. The latter components of this power supply 54 are not illustrated in further detail.

The control circuit 30 further comprises a regulated power supply 56 to be connected to the unregulated power supply 54 to provide an operation voltage to the

microcontroller 50. In the present embodiment, the regulated power supply 56 includes a voltage down converter 58 for down converting the output voltage of the unregulated power supply 54, a voltage stabilizer 62 for stabilizing the down converted voltage, and a signal conditioner 64 for providing a voltage magnitude detection signal representative of the output voltage of the unregulated power supply 54 to the microcontroller 50. The microcontroller 50 is programmed and adapted to shut down or reduce any electrical power to be provided to the light emitting diode array 10 when the output voltage of the unregulated power supply 54 is instable beyond a predetermined, accepted voltage band.

The microcontroller 50 comprises a first digital output 1 for providing a signal including the repeating pulse train that has the sequence of short ON/OFF pulses followed by a long OFF period to a solid-state power switch 70. The solid-state power switch 70 provides an amplified electrical power signal to the light emitting diode array 10. A second digital output 2 of the microcontroller 50 is used for providing an operation pulse signal having a variable frequency to a signal driver 72 and from there to the voltage down converter 58. This down converter 58 is flexible in that it can provide an output voltage and output current that can vary. As such, this down converter 58 can be a power source to various components of the control circuit 30 including the LED array 10.

Fig. 4 illustrates a flowchart of a method of adjusting and operating a light emitting diode array 10 connected to the control circuit 30 as described above. This method includes the following steps:

Determine the number of LED chips in the LED array.

Set required voltage / current values for nominally driving the determined number of LED chips in the LED array. This is preferably done in a register or memory of the microcontroller.

Sense, adjust and set input voltage of control circuit. This is preferably done in a register or memory of the microcontroller.

Sense, adjust and set characteristics of operation pulse signal to the voltage down converter. This is preferably done in a register or memory of the microcontroller. Sense, adjust and set characteristics of repeating pulse train that has a sequence of short ON/OFF pulses and a long OFF period based on the voltage signal representing the operating voltage for the LED array, or the operation voltage for the control circuit, or in case there is a (over-) heating in the control circuit. This is preferably done in a register or memory of the microcontroller.

Provide an operation pulse signal having a variable frequency to a signal driver and from there to the voltage down converter. This frequency varies in order to regulate the output voltage of the voltage down converter into a stabilize voltage range.

Provide an LED driver power signal for the LED array in the form of the repeating pulse train that has a sequence of short ON/OFF pulses and a long OFF period.

Cease to provide the LED driver power signal or reduce the LED driver power signal (i) in case the voltage signal representing the operating voltage for the LED array is unstable, or (ii) in case the operation voltage for the control circuit, especially the microcontroller, is unstable, or (iii) in case of incorrect operation mode settings, or (iv) in case initial there occurs a signal generation error after a predetermined number of repeating pulse trains, or (v) in case there is a (over-) heating in the control circuit

This light emitting diode array is to be connected to an external electrical power source. This array has a predetermined number of LED chips and is connected to a control circuit. The control circuit is adapted to convert power from the electrical power source into a repeating pulse train for driving the LEDs. The repeating pulse train has a sequence of short ON/OFF pulses and a long OFF period. This mode of operation of the LED array avoids thermal problems with the LEDs and therefore, does not require a heat sink as do conventional LED lighting designs. The mode of operation of the LED array provides for an efficient use of the electrical energy. This also avoids a heat sink. In comparison to prior art LED lightings the mode of operation of the LED array is up to 20% to 50% more energy-efficient while at the same time the described LED lighting can be manufactured with reduced costs. The LED lighting described here does hardly heat up. This ascertains a long lifetime with a minimal decay in light output.

It is understood that not only upper and lower limits of the numerical value ranges referred to herein are disclosed, but also every numerical value between these limits

Claims

1. A light emitting diode (LED) array to be connected to an external electrical power source, wherein the light emitting diode array

- has a predetermined number of LED chips and is connected to a control circuit,

- the control circuit is adapted to convert power from the electrical power source into a repeating pulse train for driving the LEDs of the LED array, and the repeating pulse train

- has a sequence of short ON/OFF pulses (42, 3) and a long OFF period (44).

2. The light emitting diode array according to claim 1, wherein the control circuit is adapted to adjust the sequence of short ON/OFF pulses to have a first duration (dl) and the long OFF period to have a second duration (d2), and the control circuit is adapted to adjust the ratio (dl/d2) of the first duration (dl) and the second duration (d2) from 1/20 to 20/1.

3. The light emitting diode array according to claim 1 or 2, wherein the control circuit is adapted to adjust the long OFF period to have a second duration (d2) of

approximately 20 ms to approximately 65 ms.

4. The light emitting diode array according to claim 1, 2 or 3, wherein the control circuit is adapted to adjust each one of the short ON pulses (42) to have a third duration (d3) of approximately 1.5 ps to approximately 40 ps and each one of the short OFF pulses (43) to have a fourth duration (d4) of approximately 0.5 * d3 to approximately 20 * d3.

5. The light emitting diode array according to one or more of claims 1 to 4, wherein the control circuit is adapted to adjust the number (n) of short ON/OFF pulses (42, 43) in the repeating pulse train in the range from approximately 3 to approximately 250.

6. The light emitting diode array according to one or more of claims 1 to 5, wherein, for a given light emitting diode array having a given number of LED chips, the control circuit is adapted to adjust

- the first duration (dl) of the short ON/OFF pulses,

- the second duration (d2) of the long OFF period,

- the third duration (d3) of each one of the short ON pulses (42), - the fourth duration (d4) of each one of the short OFF pulses (43),

- the ratio (dl/d2) of the first (dl) and the second duration (d2), and/or

- the number (n) of short ON/OFF pulses in the repeating pulse train,

to each have a fixed value or a value that varies within a predetermined range during operation of the light emitting diode array.

7. The light emitting diode array according to one or more of claims 1 to 6, wherein the control circuit is adapted to provide the short ON/OFF pulses in the repeating pulse train at an ON-voltage of approximately 1.1 V to approximately 4.0 V per each of the LED chips in the light emitting diode array.

8. The light emitting diode array according to one or more of claims 1 to 7, wherein the control circuit is adapted to provide the short ON/OFF pulses in the repeating pulse train with a current in the range from approximately 10 mA to approximately 250 mA or more to the light emitting diode array (10).

9. The light emitting diode array according to one or more of claims 1 to 8, wherein the control circuit comprises a microcontroller adapted to and programmed to generate the repeating pulse train that has a sequence of short ON/OFF pulses followed by a long OFF period, wherein parameters of the sequence of short ON/OFF pulses and the long OFF period such as such as the first duration (dl) of the short ON/OFF pulses, the second duration (d2) of the long OFF period, the third duration (d3) of each one of the short ON pulses, the fourth duration (d4) of each one of the short OFF pulses, a ratio (dl/d2) of the first (dl) and the second duration (d2), and/or the number of short ON/OFF pulses in the repeating pulse train are to be programmed into the microcontroller during an initial setting operation of the light emitting diode array via a parameter setting input.

10. The light emitting diode array according to one or more of claims 1 to 9, wherein the control circuit 30 comprises a power supply to be connected to an external electrical power source for supplying electrical power to the light emitting diode array and to the microcontroller, and wherein the power supply is preferably unregulated and includes

- a surge and over-voltage protection stage,

- a line filter stage,

- an AD/DC conversion stage, and/or

- a voltage smoothing stage.

11. The light emitting diode array according to one or more of claims 1 to 10, wherein the control circuit comprises a regulated power supply to be connected to the preferably unregulated power supply to provide an operation voltage to the microcontroller, wherein the regulated power supply preferably includes

- a voltage down converter for down converting the output voltage of the preferably unregulated power supply,

- a voltage stabilizer for stabilizing the down converted voltage, and/or

- a signal conditioner for providing a voltage magnitude detection signal representative of the output voltage of the preferably unregulated power supply to the microcontroller, and wherein

the microcontroller is adapted to shut down any electrical power to be provided to the light emitting diode array when the output voltage of the preferably unregulated power supply is instable beyond a predetermined, accepted voltage band.

12. The light emitting diode array according to one or more of claims 1 to 11, wherein the microcontroller comprises

- a first output for providing a signal with the repeating pulse train that has the sequence of short ON/OFF pulses followed by a long OFF period to a solid-state power switch, wherein the solid-state power switch provides an amplified electrical power signal to the light emitting diode array, and

- a second output for providing an operation pulse signal to the voltage down converter.

13. Method of adjusting and operating a light emitting diode array connected to the control circuit according to one or more of claims 1 - 12, comprising the following steps:

(a) determine the number of LED chips in the LED array;

(b) set required voltage / current values for nominally driving the LED chips in the LED array;

(c) sense, adjust and set input voltage of control circuit;

(d) sense, adjust and set characteristics of operation pulse signal to the voltage down converter;

(e) sense, adjust and set characteristics of repeating pulse train that has a

sequence of short ON/OFF pulses and a long OFF period based on the voltage signal representing the operating voltage for the LED array, or the operation voltage for the control circuit, or in case there is a (over-)heating in the control circuit;

(f) provide an LED driver power signal for the LED array in the form of the

repeating pulse train that has a sequence of short ON/OFF pulses and a long OFF period and/or

(g) cease to provide the LED driver power signal or reduce the LED driver power signal (i) in case the voltage signal representing the operating voltage for the LED array is unstable, or (ii) in case the operation voltage for the control circuit, especially the microcontroller, is unstable, or (iii) in case of incorrect operation mode settings, or (iv) in case initial there occurs a signal generation error after a predetermined number of repeating pulse trains, or (v) in case there is a (over-) heating in the control circuit.

14. A lighting fixture including at least one light emitting diode array connected to a control circuit according to one or more of the preceding apparatus and/or operated according to the preceding method claims.