EP1667492A1

EP1667492A1 - Lighted status indicator for electric, electronic and similar equipment

Info

Publication number: EP1667492A1
Application number: EP04425895A
Authority: EP
Inventors: Antonio Coppola
Original assignee: Signal Lux MDS Srl
Current assignee: Signal Lux MDS Srl
Priority date: 2004-11-26
Filing date: 2004-11-26
Publication date: 2006-06-07

Abstract

A lighted status indicator for electric, electronic and similar equipment, comprising at least one LED (2) of the super bright type and a feeding circuit (3) adapted to submit LED (2) to passage therethrough of a current having an operating intensity equal to a fraction of the standard intensity provided for operation of the same LED (2) under conditions of maximum light emission. The feeding circuit (3) comprising a diode (5), set in parallel with respect to LED (2), and a resistor (4).

Description

The present invention relates to a lighted status indicator for electric, electronic and similar equipment.
A lighted status indicator has the function of making a user aware of the state of electric or electronic equipment: for example, a green light may indicate a correct operation, a red light a failure, etc.. Lighted indicators of the type in reference are present on household appliances, such as refrigerators and vacuum cleaners, on light switches, on personal computers.
It is known that in lighted status indicator a first type of light source may consist of microlamps of a 3-6 mm diameter which contain a gas and in which an electric discharge takes place.
These microlamps are connected in an alternating-current circuit the supply voltage of which, included between standard values of 110V and 380V at 50 Hz, is reduced to the necessary flashover voltage of said microlamps, usually of about 90V, by an appropriate resistor having a resistance of a value approximately included between 48 and 270Kohm.
Practically, said microlamps are able to supply a light intensity of about 8-13 millicandles (mcd) and have an average lifetime of about 15 thousand hours.
The above mentioned prior art has some drawbacks.
In fact, first of all, it allows light sources to be made available that are characterized by a limited range of colours, i.e. generally only red, green, more seldom blue, since other colours would involve use of expensive gases capable of greatly increasing the microlamp costs to such an extend that they would be no longer competitive.
In particular, it is to be pointed out that it is not possible to obtain a white light but only a light of a colour tending to yellow.
In addition, the average lifetime of said microlamps can be inappropriate for some applications, also because brightness of same has a tendency to be reduced with use, due to formation of deposits on the inner surface of the small transparent bulbs forming the lamp bodies, and to lose steadiness due to arising of flickering phenomena.
In order to overcome at least some of the drawbacks of the microlamps briefly described above, utilisation of a second type of light source is also known which is based on use of LEDs, i.e. light-emitting diodes, of the type capable of supplying a light intensity of about 10mcd.
These LEDs not only offer availability of a wide range of colours among which white, but also have an average lifetime of about 50 thousand hours, i.e. a lifetime that is more than three times higher than the lifetime of gas-discharge microlamps, while maintaining a steady light with a constant intensity.
One of such light-emitting diodes is known from document US6543904B1 which discloses an illuminating element for vehicles provided with an intermediate element containing the activation electronics for activating the LED. The illuminating element is mounted on a printed circuit board by means of a contact socket.
However said LEDs too have some drawbacks.
First of all, there is a need for a rather complicated feeding circuit to enable them to be connected with an electric network having the standardized line voltages, varying between 110 and 230V at 50Hz.
In the above mentioned feeding circuit in fact, in addition to a first diode disposed in series with the LED itself, the presence of a capacitor and a first resistor disposed in parallel, and of a second resistor and a second diode suitably interposed between the other components is provided.
The capacitor and first resistor perform the function of reducing voltage and current to the values required by the LED, 2V and 20mA (milliampere) for example, whereas the second resistor and second diode discharge possible voltage peaks present in the network.
Practically, the necessary presence of said feeding circuit made up of many components increases the cost of the LED alone to be used as the light source, to a rather important extent.
It will be also recognised that the sizes of the feeding circuit associated with the LED make it impossible to use the same in status indicators the maximum diameter of which must not overcome 7 mm.
Finally, it is also to be pointed out that, specifically, the feeding circuit of the gas-discharge lamp, due to the presence of the resistor, produces heat to an important amount and therefore gives rise to useless high temperatures, in addition to energy losses.
It is also known, from document US2002/0140379A1, a LED lighting device comprising several extra LEDs such that, as the LEDs of the lighting device degrade over time, more LEDs can be turned on thus allowing a constant luminosity to be maintained. Such LEDs are of the super bright type and are used at full current for a fractional time.
Under this situation, the technical task underlying the present invention is to devise a lighted status indicator for electric, electronic and similar equipment that is capable of substantially obviating the mentioned drawbacks.
Within the scope of this technical task, it is an important aim of the invention to devise a lighted status indicator that, in addition to enabling a constantly steady light emission devoid of flickering phenomena, which can be of any colour and therefore also white, is of very high useful lifetime too, much higher than that obtainable with standard LEDs, but at much more reduced production costs as compared with those of said LEDs.
The technical task mentioned and the aims specified are substantially achieved by a lighted status indicators according to one or more of the appended claims.
Description of two preferred but not exclusive embodiments of a lighted status indicators in accordance with the invention is now given hereinafter with the aid of the accompanying drawings, in which:

Fig. 1 diagrammatically shows a first embodiment of a lighted status indicator in accordance with the invention;
Fig. 2 is a perspective view of a second embodiment of the lighted status indicator; and
Fig. 3 shows the wiring diagram of the feeding circuit of the status indicator seen in Figs. 1 and 2.

With reference to the drawings, the lighted status indicator in accordance with the invention is generally identified with reference numeral 1.
It comprises at least one LED 2 of the super bright type, also called "high-efficiency LED", that, as known, is able to ensure an average duration of about three hundred thousand hours.
LED 2 can be selected from the LEDs of the above mentioned type with a diameter of 3 to 5 mm and characterised by a maximum light emission included between 50 and 16000 mcd when said LEDs are passed through by a standard current intensity of about 20mA.
In an original manner, LED 2 is submitted to passage of a current therethrough which has an operating intensity equal to a fraction of said standard intensity obtained by a simple feeding circuit 3. Corresponding to this operating current intensity is a light intensity that is reduced to few units or some tens of millicandles adapted for use in the indicators being the object of the invention.
The feeding circuit comprises a resistor 4 and a diode 5 consisting of components provided with rheophores (see Fig. 2) or disposed internally of an integrated circuit (see Fig. 1) and consisting of components suitable for surface mounting. Diode 5 is set in parallel with respect to LED 2; in the preferred and illustrated form, resistor 4 is set in series with respect to the parallel between diode 5 and LED 2.
For example, should the feeding circuit 3 be connected with an alternating-current network with a voltage included between 110 and 230V at 50 Hz, resistor 4 may have a resistance included between 50 and 200Kohm, preferably of about 120kohm.
LED 2, preferably selected from LEDs with a 3 mm diameter and capable of approximately supplying a 340mcd current with 20mA, is in this case passed through by an operating current intensity of few milliamperes. For instance, the current intensity is included between 0.2 and 5mA. Preferably, the current intensity is of about 1mA to which, just as an indication, a light emission of 17mcd corresponds, which value is adequate for a standard status indicator.
The invention achieves important advantages.
In fact, first of all, the status indicator in accordance with the invention has a very high operating lifetime, without any reduction in light emission, not only higher than that of indicators with gas-discharge microlamps, but also higher than when light sources formed of LEDs of standard type are used, which LEDs in any case cannot be used for said status indicators due to their sizes.
In addition, it is to be pointed out that the status indicator in accordance with the invention comprises a very simple feeding circuit, only formed of one diode and one resistor. This structural simplicity is made possible by the fact that operation of said LED takes place with a much lower current intensity than that considered as the standard operating current and therefore under operating conditions that do not require additional components to protect the LED from possible voltage and current peaks present in the network, and this practically results in very reduced and competitive production costs as compared with other types of status indicators.
Furthermore, these status indicators have a tendency to heat up to a very reduced extent.
Finally, it will be appreciated that the status indicators in accordance with the invention can be such produced that they give rise to light emissions of any colour.

Claims

A lighted status indicator for electric, electronic and similar equipment, characterized in that it comprises at least one LED (2) of the super bright type and a feeding circuit (3) adapted to submit said LED (2) to passage therethrough of a current having an operating intensity equal to a fraction of the standard intensity provided for operation of the same LED (2) under conditions of maximum light emission; said feeding circuit (3) comprising a resistor (4) and a diode (5); at least said diode (5) being set in parallel with respect to said LED (2).
A lighted status indicator as claimed in claim 1, characterised in that said resistor (4) is set in series with respect to the parallel formed by said diode (5) and said LED (2).
A lighted status indicator as claimed in claim 1, characterised in that said resistor (4) and diode (5) consist of components provided with rheophores.
A lighted status indicator as claimed in claim 1, characterised in that said resistor (4) and diode (5) consist of components suitable for surface mounting.
A lighted status indicator as claimed in claim 1, characterised in that said resistor (4) and diode (5) are inserted internally of an integrated circuit.
A lighted status indicator as claimed in claim 1, characterised in that said LED (2) is selected from the LEDs having a light emission included between 50 and 16000mcd with a standard current intensity of about 20mA.
A lighted status indicator as claimed in claim 1 or 6, characterised in that the operating current intensity to which said LED is submitted is included between 0.2 and 5mA, preferably being of 1mA.
A lighted status indicator as claimed in claim 1, characterised in that said resistor (4) has a resistance included between 50 and 200Kohm and preferably of 120Kohm.