GB2543750A

GB2543750A - LED strips, method of making an LED light, and drive circuits especially for the LED strips

Info

Publication number: GB2543750A
Application number: GB1518620.8A
Authority: GB
Inventors: Frederick Fellerman Bernard
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-10-21
Filing date: 2015-10-21
Publication date: 2017-05-03
Also published as: GB201518620D0

Abstract

A flexible elongate strip 2 of insulating material with light emitting diodes (LEDs) 3 placed along the base layer connected in series with a conductor 4. The strip can be taken apart in small sections, and reconnected with connectors 5. Each section has a resistor wired in series with the LEDs. The strip or tape can be cut to desired length and provided with a drive circuit to allow an AC mains power supply to be used. The strip can be wrapped around a central core to create a light fixture. A drive circuit can be connected, comprising a rectifier to rectify a mains supply voltage and apply DC voltage across the LED strip, and a current limiting capacitor.

Description

TITLE: LED strips, method of making an LED light and drive circuits especially for the LED strips

The present invention relates to LED strips, method of making an LED light, and drive circuits for the LED strips. LED strip are well known. Such known strips have an elongate basie layer carrying spaced LEDs. Groups of adjacent LEDs (e.g. groups of 3 or 6 adjacent LEDs) are wired in series, but each group is wired in parallel to one another. Groups are spaced by connectors which can be severed in half.

According to one aspect of the present invention there is provided an LED strip comprising an elongate base layer of insulating material, and plurality of LED spaced along the base layer, and each LED being connected in series. Preferably the LED strip is formed at least one metre in length, e.g. made in a continuous length and cut to lengths such as 3 metres. Preferably connectors are provided between groups of LEDs such between groups of 6 or 3 LEDs. Preferably a resistor is wired in series with groups of LEDs.

According to another aspect of the invention there is provided a method of making a an LED light comprising taking an LED strip as above defined and cutting it to provide a sub-strip of LEDs with the length of the sub-strip being chosen to have the number of LEDs required to give the desired lumens output, and providing a drive circuit to drive the LEDs from an AC mains supply. Preferably the sub-strip is wound around a core. The core may be a truncated cone shape or bulb shape. The invention relates to a light made by this method

According to a third aspect of the invention there is provided a drive circuit for an LED strip or sub-strip as defined above comprising: a) a rectifier to rectify a mains supply voltage and apply the DC voltage across the strip or substrip, and b) a current limiting capacitor to limit the current through the LEDs.

Preferably the φ smoothing capacitor is provided to smooth the rectified mains supply. Preferably wherein the LED voltage is less than the rectified voltage. A fourth aspect of the invention relates to a drive circuit for an array of LEDs comprising: a) a rectifier to rectify a mains supply voltage and apply the DC voltage across the LED array, said rectifier having no smoothing capacitor, and b) a current limiting capacitor to limit the current through the LEDs.

Preferably wherein the LED voltage is less than the rectified voltage.

Embodiments of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 shows a view of a strip of LEDs,

Figure 2 shows a sub-strip from the strip of Figure 1 used to make a light,

Figure 3 shows a first drive circuit of the sub-strip of Figure 2, and Figure 4 shows a second drive circuit of the sub-strip of Figure 2.

Referring to Figure 1 there is shown an LED strip 1 comprising an elongate base layer 2 of insulating material such as plastics, and plurality of LED 3 spaced along the base layer, and each LED being connected in series by a conductor 4. Preferably the LED strip is formed at least one metre in length e.g. 5 metres, and made on a continuous basis. Preferably connectors 5 are provided between groups of LEDs such between groups of 3 (or 6) LEDs. Preferably a resistor (not shown) is wired in series with groups of LEDs to provide a more even overall resistance value to groups of LEDs. There may typically be 60 or 30 LED per linear metre of base layer.

When making a light, a sub-strip of one or more groups of 3 (or 6) LED can be cut from the long LED strip 1 with cuts passing through connectors 5 so that each sub-strip has part of a connector 5 at each end to connect the sub-strip to a power supply.

As shown in Figure 2, there is shown a method of making a an LED light comprising taking an LED sub-strip 10 of LEDs from strip 1 of Figure l,with the length of the sub-strip being chosen to have the number of LEDs required to give the desired lumens output. For example the sub-strip might have 48 LEDs wired in series. The sub-strip 10 is wound around a core in the form of a plastics truncated conical cone 11 (or other bulb type shape), and a drive circuit 12 is provided to drive the LEDs from an AC mains supply through a bayonet (or screw) fitting 13. The invention also relates to a light made by this method.

What is good about the method is that only one type of LED strip 1 need be manufactured from which lights with different lumens outputs can be created simply by selecting the number of LEDs in a sub-strip.

One possible drive circuit 20 is shown in Figure 3. A light with sub-strip 21 of 48 LEDs wired in series can create a light with an LED voltage of 192V, and with a lumen output equivalent to a standard 120W light bulb.

The LEDs are powered by an AC 240V supply 22 which is rectified by rectifiers 23A,23B,23C,23D and smoothed by a smoothing capacitor 24. A current limiting capacitor 25 allows the LED sub-strip 21 to be driven by the higher rectified 240Vsupply. Because the LEDs are wired in series, this causes voltage to be raised and the current to be lowered. This results in a high power factor of say 0.87 for the 48 LED sub-strip. The current normally required by the LEDs is limited by the capacitor 25.

The circuit further comprises an inductor 26 to absorb voltage peaks, and a resistor 27 which allows the LEDs to be dimmable.

Smoothing capacitor 24 has hitherto been regarded as essential as its removal causes the LEDs to be pulsed with the rectified mains, rather than the smoothed capacitor current, and consequently the lumens output is virtually doubled from the specified value. This cannot be allowed because the LEDs life would be reduced..

As shown in Figure 4, it has been found that the capacitor 24 can be removed if the current limiting capacitor 25 is decreased in value so the current is reduced to approx 43mA. I.e. 60/log24. This reduced LED power is advantageous to long LED life and at the same time the specified lumens are raised from 301m/LED to approx 301og24.401m/LED.

This means that removing the smoothing capacitor results in both the increase in lumens and the reduction in current - (power) - at the same time so that the Efficacy rises to approx 2401m/w.

So we can say that the selected 48 LEDs having a normal output of 1440 lumens is raised to nearly 20001umens such that the effective lamp equivalent wattage rises from 90 to 120w.

In the circuits, the sub-strip 21 has 48 LEDs with a specific lumen output. It is envisaged that different lights could be made with different lumen outputs, and the value of the current limiting capacitor would be selected to improve the lumen output to a level which will not be detrimental the LEDs.

The invention may take a form different to that specifically described above. For example instead of cutting a desired length of a strip to create a single sub-strip of the required number of LEDs, several sub-strips of LEDs could be wired in series with each other, and several such sub-strips arranged in an array make a light.

The use of a drive circuit such as shown in Figure 4 may be used to drive an array of LEDs not formed as a sub-strip formed from a strip as shown in Figure 1. The invention thus also relates to a drive circuit for an array of LEDs comprising: a) a rectifier to rectify a mains supply voltage and apply the DC voltage across the LED array, said rectifier having no smoothing capacitor, and b) a current limiting capacitor to limit the current through the LEDs.

Further modifications will be apparent to those skilled in the art without departing from the scope of the present invention.

Claims

1. An LED strip comprising an elongate base layer of insulating material, and plurality of LED spaced along the base layer, and each LED being connected in series.

2. An LED strip according to claim 1, wherein the LED strip is formed at least one metre in length.

3. An LED strip according to claim 1 or 2, wherein connectors are provided between groups of LEDs such between groups of 6 or 3 LEDs.

4. An LED strip according to claim 1,2 or 3, wherein a resistor is wired in series with groups of LEDs.

5. A method of making a an LED light comprising taking an LED strip according to any of claims 1 to 4, and cutting it to provide a sub-strip of LEDs with the length of the sub-strip being chosen to have the number of LEDs required to give the desired lumens output, and providing a drive circuit to drive the LEDs from an AC mains supply.

6. A method according to claim 5, wherein the sub-strip is wound around a core.

7. A method according to claim 6, wherein the core is a truncated cone shape or bulb shape.

8. A light made by the method of claim 5,6 or 7.

9. A drive circuit for an LED strip or sub-strip according to any preceding claim comprising: a) a rectifier to rectify a mains supply voltage and apply the DC voltage across the strip or substrip, and b) a current limiting capacitor to limit the current through the LEDs.

10. A drive circuit according to claim 9 wherein no smoothing capacitor is provided to smooth the rectified mains supply. j

11. A drive circuit according to claim 9 or 10, wherein the LED voltage is less than the rectified voltage.

12. A drive circuit for an array of LEDs comprising: a) a rectifier to rectify a mains supply voltage and apply the DC voltage across the LED array, said rectifier having no smoothing capacitor, and b) a current limiting capacitor to limit the current through the LEDs.

13. A drive circuit according to claim 12, wherein the LED voltage is less than the rectified voltage.

14. An LED strip substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

15. A method of making a light substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

16. A drive circuit for an LED strip or sub-strip substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

17. A drive circuit for an array of LEDs substantially as hereinbefore described with reference to and as shown in the accompanying drawings.