Electricity: measuring and testing – Fault detecting in electric circuits and of electric components
Reexamination Certificate
2002-10-02
2003-09-23
Le, N. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
C324S550000, C340S638000, C361S057000
Reexamination Certificate
active
06624638
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the electric supply of light-emitting loads, in particular light-emitting diode (LED) lamps. More specifically, the present invention is concerned with electric circuits and methods required for remote monitoring of LED lamps.
BACKGROUND OF THE INVENTION
Light-emitting diode (LED) lamps are becoming more and more popular in automotive traffic lights, railway signal lights and other applications Their lower power consumption is an attractive feature, but the main reason for their popularity is their long life (100 000 hours) compared to standard incandescent lamps (5 000 hours). Manifestly, these features allow important reduction in maintenance costs.
In certain applications, such as railway signal lights, these lamps may be used, as those skilled in the art would know, for main line signalling and/or grade crossing signaling. Grade crossing signals are usually situated in populated areas such as road intersections. Remote monitoring of the LED lamps in grade crossing signals is therefore not necessary. Main line signals, on the other hand, can be installed in remote areas, which are not easily accessible. Remote monitoring for checking the integrity of the lamps signals is therefore common practice.
For lamps equipped with standard incandescent bulb, electrical integrity can be easily verified. If the filament of the incandescent bulb is in normal condition, current flows through the bulb according to Ohm's law (I=V/R). Otherwise, if the filament is open, no current flows through the bulb and it should be replaced.
For LED lamps, however, LED current is controlled by a power supply. Current characteristics are therefore not identical in a LED lamp and in an incandescent lamp. In a LED lamp, alternative current (ac) line voltage is rectified and then converted to a suitable level by a dc—dc (direct current) converter, which also regulates LED current. In case of LED failure, or failure of any other electrical component in the LED lamp, it is possible for the power supply to continue drawing current at or near the nominal current value, even if the LED's are not emitting any light. Remote monitoring systems could therefore see the LED lamp as functioning correctly when in reality it is not. This situation is not acceptable since it can lead to very hazardous train operations and cause major accidents.
Another problem, related to LED lamps and their power supplies and controllers, is caused by electric components which retain residual voltage differentials after power is removed from the LED lamp. The resulting characteristic is that a LED lamp will effectively light up when the power applied to it reaches a first high level while it will be turned off only when the power reaches a second lower level. The resulting problem is that if a certain power is induced by, for example, other nearby cables, the LED lamp could remain on while in fact it should be off. This could also lead to dangerous situations.
These particularities of LED lamps limit their widespread use in situations where they need to be remotely monitored such as in railway main line signalling applications.
OBJECTS OF THE INVENTION
An object of the present invention is therefore to allow LED lamps to become compatible with remote detection systems designed for monitoring of incandescent lamps.
Another object of the invention is to provide LED lamp circuitry which will emulate an incandescent lamp's behaviour upon remote monitoring of the LED lamp.
Yet another object of the invention is to provide a control circuit for enabling/disabling the power supply to LED lamps in relation to the level of the line voltage.
SUMMARY OF THE INVENTION
More specifically, in accordance with the present invention, there is provided a fuse blow-out circuit for establishing a short circuit between first and second voltage and current supply lines to blow out a protection fuse through which a current supplied to a light-emitting load by the first and second lines flows, this fuse blow-out circuit comprises:
a timer means responsive to the voltage across the first and second lines for producing a time-representative signal after a certain period of time;
means connected to the timer means for preventing production of the time-representative signal in response to the current supplied to the light-emitting load; and
means for establishing a current path between the first and second lines in response to the time-representative signal.
Accordingly, when no current is supplied to the light-emitting load, the current path is established and provides the short circuit between the first and second lines that will blow out the protection fuse and emulate an open circuit of a defective incandescent lamp.
Also in accordance with the present invention, there is provided a fuse blow-out circuit for establishing a short circuit between first and second voltage and current supply lines to blow out a protection fuse through which a current supplied to a light-emitting load by the first and second lines flows. This fuse blow-out circuit comprises:
a resistor and a capacitor connected in series between the first and second lines, this resistor having a given resistance value, and this capacitor having a given capacitance value and a capacitor charge period dependent on the given resistance value and the given capacitance value;
a trigger circuit connected in parallel with the capacitor, and comprising a first controllable switch member closed in response to the current supplied to the light-emitting load to discharge the capacitor; and
a second controllable switch member defining a current path between the first and second lines and closed in response to a given voltage amplitude across the capacitor.
Therefore, in the absence of current supplied to the light-emitting load for a duration equivalent to the capacitor charge period, the given voltage amplitude across the capacitor is reached to thereby close the second switch member, establish the current path and provide the short circuit between the first and second lines that will blow out the protection fuse and emulate an open circuit of a defective incandescent lamp.
Further in accordance with the present invention, there is provided a power supply unit responsive to alternating voltage and current from an ac source for supplying a dc voltage and current to a light-emitting load, comprising:
a rectifier unit rectifying the alternating voltage and current from the ac source and supplying the rectified voltage and current to first and second voltage and current supply lines;
a protection fuse through which the alternating current from the ac source is supplied to the rectifier unit;
a converter of the rectified voltage and current into the dc voltage and current supplied to the light-emitting load;
a fuse blow-out circuit as described above, for establishing a short circuit between the first and second voltage and current supply lines to blow out the protection fuse; and
a controller of the converter in response to the rectified voltage on the first and second lines.
The present invention also relates to a cold filament detection circuit connected between first and second lines through which a voltage and current supply source supplies voltage and current to a light-emitting load, the voltage and current supply source having a set up time during which no current is supplied to the light-emitting load. This cold filament detection circuit comprises:
a resistor;
means for connecting the resistor between the first and second lines in response to the voltage on the first and second lines to thereby establish through this resistor a current path between the first and second lines; and
means for disconnecting the resistor from between the first and second lines in response to the current supplied to the light-emitting load.
Accordingly, during the set up time no current is supplied to the light-emitting load and the current path is established through the resistor to emulate the impedance of an incandescent lamp, and when current is
Darby & Darby
Gelcore LLC
Le N.
Nguyen Vincent Q.
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