It is disclosed a lighted microindicator for electric, electronic and similar equipment comprising at least one LED (2) of the type having a high light emission and a feeding circuit (3) adapted to submit the 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 LED (2) itself under conditions of maximum light emission.
The present invention relates to a lighted microindicator for electric, electronic and similar equipment.
A lighted microindicator 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 microindicators 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.
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 microindicators 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.
Under this situation, the technical task underlying the present invention is to devise a lighted microindicator 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 microindicator 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 microindicator that is characterised in that it comprises at least one LED of the high-light-emission type and one feeding circuit adapted to submit said LED to passage of a current therethrough that has an operating intensity equal to a fraction of the standard intensity provided for operation of the same LED under conditions of maximum light emission.
Description of two preferred but not exclusive embodiments of a lighted microindicator in accordance with the invention is now given hereinafter with the aid of the accompanying drawings, in which:
With reference to the drawings, the lighted microindicator in accordance with the invention is generally identified with reference numeral 1.
It comprises at least one LED 2 of the high-light-emission 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 set in series with respect to LED 2 and consisting of non rheophore components (see Fig. 2) or disposed internally of an integrated circuit (see Fig. 1) and consisting of components suitable for surface mounting.
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 microindicator.
The invention achieves important advantages.
In fact, first of all, the microindicator 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 microindicators due to their sizes.
In addition, it is to be pointed out that the microindicator 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 microindicators.
Furthermore, these microindicators have a tendency to heat up to a very reduced extent.
Finally, it will be appreciated that the microindicators in accordance with the invention can be such produced that they give rise to light emissions of any colour.