WO2008065244A1

WO2008065244A1 - Procedure for producing light by the help of light radiating diodes and a light consisting of light radiating diodes

Info

Publication number: WO2008065244A1
Application number: PCT/FI2007/050623
Authority: WO
Inventors: Mika Nummenpalo; Jyrki Jokinen
Original assignee: Easy Led Oy
Priority date: 2006-11-30
Filing date: 2007-11-20
Publication date: 2008-06-05
Also published as: EP2123123A4; DE202007019404U1; FI9614U1; EP2123123A1; FI118881B

Abstract

This invention relates to a method and a light source for producing light using light-emitting diodes (LEDs) (9). In the method, at least a number of LEDs (9) are connected serially, and the current or voltage passing through the series-connected LEDs (9) is regulated with a regulating element (6). The number of series-connected LEDs (9) is chosen so that the total threshold voltage of the LEDs (9) is lower than or at most equal to the input voltage of the LEDs (9).

Description

PROCEDURE FOR PRODUCING LIGHT BY THE HELP OF LIGHT RADIATING DIODES AND A LIGHT CONSISTING OF LIGHT RADIATING DIODES

This invention relates to a method for producing light using light-emitting diodes, as described in the preamble to claim 1, and to a light source consisting of light-emitting diodes, as described in the preamble to claim 6.

In known technology, light sources or lamps consisting of light-emitting diodes (LEDs) are designed for low-voltage syste.ms, i.e. typically 24 V or 12 V. Thus the power sources are usually ordinary direct voltage sources such as accumulators or batteries, which are perfectly suitable, but only for small-scale use.

Large-scale lighting solutions that comprise several lamps of sufficient luminous efficiency cannot be produced economically or viably using accumulator or battery technology. Therefore larger applications generally use for example ordinary mains current, by placing in between the ordinary alternating voltage current and the light' s LEDs a device such as an adaptor or voltage chopper that reduces the mains voltage, which is for example 230 VAC, and that acts as a separate voltage source. A problem with these solutions is that this kind of adaptor device also consumes electricity, which causes unnecessary energy wastage. In addition, the adaptor devices always contain parts that are subject to wear, such as capacitors, whose useful life is the shortest of all of the components of an adaptor. Furthermore, the adaptor device becomes warm during use, losing energy as heat and causing potential placement problems. All in all, the adaptor increases the cost of the lighting solution, takes up space, and thus makes the use and placement of the light more difficult and reduces the useful life of the light if it malfunctions. US patent applications US2004/0252500 and US2006/0076901 refer to an LED rope light used mainly for decoration, which uses serially connected LEDs and a current regulator that provides the LEDs with steady current and that can be used for controlling for instance the temperature of the LEDs. However, the LED rope lights in the applications also use a separate voltage source according to known technology, which voltage source is mentioned for instance in paragraph [0020] of patent application US2004/0252500, where the voltage source is said to produce voltage in the range 2.1-36 V. Similarly, paragraph [0028] of the same application mentions that the input voltage with a connection according to a certain embodiment of the invention can also be in the range 3-260 V. However, that voltage is direct voltage, and according to the explanation a separate voltage source is still needed to produce it. Therefore the abovementioned problems related to separate voltage sources in solutions according to known technology also apply to the solutions in these patent applications.

Thus a problem shared by known LED lighting solutions based on mains current is the fact that a large part of the input power of the light is lost as thermal loss and conversion loss in the device used for reducing the mains voltage. A further problem is caused by voltage variations in the mains current, which can be up to approx. ±10% of the rated voltage. Therefore at the lowest voltage point, the LEDs of the light source may not light up, because the input voltage is too low to induce a voltage that exceeds the LEDs' threshold voltage. Similarly, the problem of the highest voltage points is overheating of the LEDs, because due to the properties of an LED, the rising of the voltage passing through the LED above the LED' s threshold voltage quickly causes the LED to take up too much current. Overheating of the LEDs causes heat loss and a reduction in the useful lives of the LEDs, or even their breakage. The object of this invention is to remove the problems described above and achieve an optimally inexpensive and simple method for producing light using light-emitting diodes (LEDs) . The object of the invention is also to achieve an optimally inexpensive, simple, reliable, long-life, efficient light source consisting of LEDs, designed to directly use the alternating current coming from the mains (in Europe a rated current of 230 VAC) . The method described in the invention is characterised by what is disclosed in the characterisation part of claim 1. Similarly, the light source according to the invention is characterised by what is disclosed in the characterisation part of claim 6. Other embodiments of the invention are characterised by what is disclosed in the other claims .

The method and light source according to the invention will later be referred to collectively as the solution according to the invention, for simplicity. A benefit of the solution according to the invention is that the light's power source can directly be the alternating current coming from the mains, which leaves out the voltage-reducing solutions that increase energy consumption, cost, space utilisation and susceptibility to faults. Further benefits are the reliability of the LEDs' lighting up when the light is switched on, and the effective prevention of the heating up and possible damage of the LEDs, thanks to protection from under- and overvoltage. Another benefit is the connection system of the solution according to the invention, which permits the use of a lower voltage than normal mains voltage over the light's current regulator, which means that the heating up and the need for power handling capacity of the current regulator are not as great as in other solutions. A further benefit is the opportunity of using ordinary, affordable dimming devices for adjusting the brightness of the light. Below, the invention is described in detail using application examples, by referring to the appended figures, in which

Figure 1 shows a light solution according to the invention in simplified form, and

Figure 2 shows an advantageous circuit diagram of a light according to the invention, in simplified form.

Figure 1 shows a typical separate light source 1 that can be connected to the mains current with a connector, but the light source can just as well be for example a lamp unit in a street light, connected directly to the mains current without a separate connector, or another type of light. The light source 1 includes at least an electrical connection 2, with which the light is connected to an ordinary electrical network, such as a network with a rated value of 230 VAC. In addition, the light 1 has a control part 3, which involves for example at least a rectifier 5, which is designed to convert the 230 V alternating voltage to an essentially equivalent direct voltage using full-wave rectification. The actual light-radiating part of the light consists of a number of serially connected light-emitting diodes (LEDs) 9, which, connected in this way, form the light source's LED unit 4, with for example 64 series-connected and essentially identical LEDs 9. For use in lighting, the most favourable LEDs are white LEDs. Furthermore, the light source 1 includes a current regulator acting as a regulating element 6, which regulates the current passing through the LEDs in the LED unit 4, and favourably also a reflector 10 that reflects and focuses the light produced by the LED unit 4.

Figure 2 shows a beneficial connection according to the invention, in simplified form. Because LEDs 9 only work with direct voltage, the 230 V alternating voltage coming from the electrical network through connector 2 is arranged to be converted into direct voltage with a full-wave rectifier 5 included in the light source 1. The full-wave rectified direct voltage received from the rectifier 5 is directly conducted, without a need for reducing voltage, to the LEDs 9 that together form the LED unit 4. Direct current can only flow in one direction through the LEDs 9, and the flow direction is marked with arrows in Figure 2. In addition the light source 1 comprises at least a current regulator 6, placed after the LEDs 9 in the LED unit 4 in the direction of flow of the current, as well as the current regulator's set voltage resistor 7 or other similar set value adjuster.

Depending on the LEDs' properties, the threshold voltage of the ordinary LEDs 9 that emit white light, used in the LED unit 4 of the light source 1, is typically for example approx. 3.2-3.6 V. If the voltage fed to the LEDs is below this threshold voltage, the LEDs do not have enough current to emit light and therefore they do not light up when switched on. In using LEDs with a threshold voltage of for example 3.2 V, the total threshold voltage for the LED unit 4 consisting of series-connected LEDs 9 is the sum of all the threshold voltages. Therefore, if the number of LEDs 9 in the LED unit 4 is set to 64, the total threshold voltage of the LED unit 4 is 204.8 V. That is the lowest input voltage that will make the LEDs 9 in the example's LED unit 4 light up. If the electrical network's voltage rating is 230 V and the allowable voltage variation is for example 10%, the voltage coming from the network varies in the range 207-253 V.

According to the invention, the number of LEDs 9 in the LED unit 4 should be chosen taking into account the threshold voltage of the LEDs 9 used, as well as the input voltage, so that the total threshold voltage of the LED unit 4 is always lower than or at most equal to the lowest point in the electrical network's input voltage variation range. Then the total threshold voltage of the LED unit 4 is always lower than or at most equal to the input voltage, regardless of the source of the input voltage. Favourably, the total threshold voltage should be suitably lower than the lowest voltage point in the electrical network' s input voltage variation range. According to the example above, if the threshold voltage for each LED 9 is 3.4 V, the number of series- connected LEDs should be for example 60, making the total threshold voltage of the LED unit 4 204 V, which is suitably lower than the lowest voltage in the electrical network' s variation range. By changing the number of LEDs 9 in the LED unit 4, the total threshold voltage of the LED unit 4 can be adapted to any input voltage. This method provides a certain safety margin for voltage variation, which makes the lighting up of the LEDs 9 reliable regardless of variations in the electrical network voltage.

When the voltage rises to an LED's threshold voltage, the LED lights up and uses a certain amount of current while it is lit, typically for example 20 mA. If the voltage going over the LED rises above the threshold voltage, the LED uses significantly more current than the abovementioned 20 mA, which makes the LED heat up and soon break. For this reason, the current coming to the LEDs must be limited using either a voltage regulator or a current regulator. In the solution according to the invention, the current going to the LEDs 9 in the LED unit 4 is limited with a current regulator 6 connected to the light source 1, according to known technology. The advantage of the current regulator is that it can be used to set a specific current that the LEDs take up, regardless of the voltage, which means that the voltage is automatically regulated at the same time. Therefore the current regulator ensures that the voltage cannot rise too high, which keeps the voltage going through the LEDs 9 in the LED unit 4 at an optimal level even if the network' s voltage should rise higher in its variation range than the total threshold voltage of the LED unit 4.

According to the invention, the current regulator 6 is placed in the direction of flow of the direct current after the LEDs 9 in the LED unit 4, so that the inlet of the current regulator 6 is connected to the outlet of the LED unit 4, and the current regulator's 6 outlet is connected to a rectifier 5, in order to form a closed circuit over the LEDs 9. Connected in parallel to the current regulator 6 is a voltage set resistor 7, which sets the amount of current to be fed to the LEDs 9 in the LED unit 4, for example at the abovementioned 20 mA. Because the current regulator 6 is placed after the LEDs 9 in the LED unit 4 (in the direction of flow of current) , the voltage passing through the current regulator 6 is only a part of the original input voltage, i.e. equivalent to the original input voltage minus the total threshold voltage of the LEDs 9 in the LED unit 4. For example, in this case, the voltage passing through the current regulator 6 is only 230 - 204.8 V = 25.2 V. This arrangement has the benefit that the current regulator can be smaller than usual, it heats up less and therefore it lasts longer.

The solution according to the invention also allows for easy adjustment of the brightness of the light. An ordinary thyristor-based brightness control device 8 i.e. dimmer, indicated with a dot-and-dash line, is connected in Figure 2 for example to the input voltage before the light's rectifier

5. The LEDs' brightness control is based on momentarily switching off the input voltage from the LEDs, which makes the LEDs go out briefly. This is only visible to the eye, however, as a dimming of the light.

According to the procedure of the invention, a number of LEDs 9 are connected serially to form an LED unit 4, and these series-connected LEDs 9 are connected to the electrical network through at least one rectifier 5, which converts the alternating current coming from the network into direct current. According to the invention, the number of series-connected LEDs 9 in the LED unit 4 is chosen so that the total threshold voltage of the series-connected

LEDs 9 in the LED unit 4 is essentially lower than or at most equal to the input voltage coming into the LEDs 9. Favourably, the total threshold voltage of the LEDs 9 should be essentially lower than or at most equal to the lowest voltage point in the electrical network' s input voltage variation range. In addition, the voltage fed to the current regulator 6 is essentially lower than the original input voltage by the sum of the LEDs' 9 threshold voltages.

Those skilled in the art will see that the invention is not limited to the example given above, but can be varied within the scope of the patent claims given below. What is essential is that the serial connection of the LEDs is designed taking into account the LEDs' specific threshold voltage as well as the input voltage, and set so that a suitable safety margin is always in place to guarantee the lighting up of the LEDs despite variations in the input voltage, and that the input voltage does not have to be reduced with separate added components but the light can be used directly with rectified network voltage. It can also be that the total threshold voltage of the series-connected LEDs is approximately equal to the input voltage. However, this may make the abovementioned safety margin smaller, which may reduce the reliability of the LEDs' lighting up.

Further, those skilled in the art will see that the solution according to the invention is suitable for various assemblies, which may include for example serially and parallel-connected LED units.

Those skilled in the art will also see that the connection according to the invention and the number of LEDs can vary from the examples given above. For example, a rectifier is not needed when the input voltage is a direct current.

Those skilled in the art will also see that the connection according to the invention can also vary from the above example in that the current regulator can be placed before the LED unit in the direction of flow of the current. That would feed the whole input voltage through it, however, which means that the current regulator would have to be more powerful and more expensive, according to known technology.

Further, those skilled in the art will see that the regulating element that limits the current passing through the LEDs, i.e. the current regulator, can be replaced by a regulating element that limits the voltage passing through the LEDs, i.e. a voltage regulator.

Claims

1. A method for producing light with light-emitting diodes (LEDs) (9), in which method a number of LEDs (9) are connected in a series, and the current or the voltage passing through the series-connected LEDs (9) is regulated with a regulating element (6), characterised in that the number of series-connected LEDs (9) is chosen so that the total threshold voltage of the LEDs (9) is lower than or at most equal to the input voltage of the LEDs (9) .

2. A method according to claim 1, characterised in that the input voltage of the series-connected LEDs (9) is taken from an electrical network, and that the number of series- connected LEDs (9) is chosen so that the total threshold voltage of the LEDs (9) is lower than or at most equal to the lowest voltage point of the voltage variation range of the electrical network's input voltage.

3. A method according to claims 1 or 2, characterised in that the current going to the LEDs (9) is regulated after the LEDs (9) in the direction of the current, with a regulating element (6) placed after the LEDs (9), such as a current regulator, and that a voltage that is essentially lower than the input voltage by the amount of total threshold voltage of the series-connected LEDs (9) , is conducted to the current regulator (6) .

4. A method according to any of the claims above, characterised in that the voltage fed to the LEDs (9) is rectified, if necessary, before being fed to the LEDs (9).

5. A method according to any of the claims above, characterised in that the rectified mains current with a voltage rating essentially of 230 V is fed to an LED unit (4) formed by 64 series-connected LEDs (9) , from where the current is conducted to a current regulator (6), which is used to regulate the current coining in to the LEDs (9) according to a predetermined value, after the LEDs (9) in the direction of flow of the current.

6. A light source for producing light with light-emitting diodes (LEDs) (9), which light source consists at least of an LED unit (4) made up of a number of LEDs (9) connected in a series, as well as a regulating element (6) that regulates the current or the voltage passing through the LEDs (9), characterised in that the number of the series-connected LEDs (9) is chosen so that the total threshold voltage of the LEDs (9) is lower than or at most equal to the input voltage of the LEDs (9) .

7. A light source according to claim 6, characterised in that the input voltage of the series-connected LEDs (9) is fitted to be taken from an electrical network, and that the number of series-connected LEDs (9) is chosen so that the total threshold voltage of the LEDs (9) is lower than or at most equal to the lowest voltage point of the voltage variation range of the electrical network's input voltage.

8. A light source according to claims 6 or 7, characterised in that the regulating element (β) is a current regulator placed after the LEDs (9) in the direction of the current, which regulator is fitted to regulate the current fed to the LEDs (9) after the LEDs (9) in the direction of the current, and that a voltage that is essentially lower than the input voltage by the amount of total threshold voltage of the series-connected LEDs (9) is arranged to be conducted to the current regulator (6).

9. A light source according to claims 6, 7 or 8, characterised in that the LED unit (4) consisting of series- connected LEDs (9) is connected to an electrical network through a rectifier (5) , which is fitted to convert the alternating current coining from the network into a direct current using full-wave rectification.

10. A light source according to any of the claims 7-9 above, characterised in that the inlet of the current regulator (β) is connected to the outlet of the LED unit (4) and that the outlet of the current regulator (6) is connected to the rectifier (5) in order to create a closed circuit over the

LEDs (9), and that connected in parallel to the current regulator (6), there is a voltage set resistor (7) by which the amount of current fed to the LEDs (9) of the LED unit

(4) is arranged to be set, and that the LED unit (4) is equipped with 64 series-connected LEDs (9) .