Patent Publication Number: US-7589475-B2

Title: Electric lamp with enhanced dependability

Description:
This nonprovisional application claims the benefit of U.S. Provisional Application No. 60/814,898, filed Jun. 20, 2006. 
   BACKGROUND OF THE INVENTION 
   The invention relates to an electric lamp comprising at least one light-emitting diode and an electronic power switch connected in series between a power source and the light-emitting diode and controlled by an electronic processing circuit according to the state of a control switch connected to a control input of the electronic processing circuit. 
   STATE OF THE ART 
   As represented in  FIG. 1 , a control switch  1  is conventionally connected between a power source, for example a battery  2 , and a lamp L, to control switch-on and switch-off of the lamp. 
   To enable different operating modes of a lamp, an electronic processing circuit, also supplied by the battery  2  and comprising a control input, can control an electronic power switch. 
   Thus, German utility model DE29600938U describes a lamp, more particularly a bicycle lamp, which is able to light with different intensities. As represented in  FIG. 2 , in this document a control switch constituted by a control button T is connected between the supply voltage Vb and the control input E 1  of the electronic processing circuit  3 . The latter comprises three distinct outputs connected by means of three corresponding resistors to a control electrode of a transistor T 1  forming the electronic power switch. The power level (50%, 75% or 100%) supplied to the lamp L is determined according to how long the button T is kept depressed, by choosing the output activated by the electronic processing circuit  3 . Signalling diodes D connected to further outputs of the electronic processing circuit  3  can indicate the power level of the lamp and/or indicate an insufficient battery charge level. 
   U.S. Pat. No. 6,017,140 also describes a multifunctional bicycle lamp controlled by a control button. In this embodiment, illustrated in  FIG. 3 , the electronic processing circuit  3  is formed by a microprocessor (μP) and the control electrode of transistor T 1  is connected to a single output S 1  of the electronic processing circuit. The control input E 1  is directly connected to the power supply (Vb). The button T is for its part connected, in parallel with a diode, between the control input E 1  and ground. Further outputs, S 2  to S 4 , of the electronic processing circuit are connected to light-emitting diodes. The choice of operating mode is made sequentially according to the number of presses made on the button T: maximum power Pmax on the 1 st  press, distress lighting mode (flashing of the diode connected to the output S 2  or continuous lighting of the diode connected to the output S 3 ) on the 2 nd  press, maximum power Pmax and distress lighting at the same time on the 3 rd  press, half-power (Pmax/2) on the 4 th  press and switch-off on the 5 th  press. The output S 4  enables the state of charge of the battery to be indicated. 
   In a more general manner, the U.S. Pat. No. 6,249,089 describes control of various operating modes of a lamp under the control of a button T constituting the only interface with the user and located outside the power circuit connecting the battery to the lamp. The various operating modes can depend on the number of presses on the button, on the time interval between two presses and/or on how long the button is pressed. 
   A head-mounted lamp with light-emitting diodes marketed by the Petzl Corporation under the trade-mark Tikka Plus® is schematically illustrated in  FIG. 4 . Like the previous lamps, this lamp comprises a control button T between the voltage Vb of the battery and the input E 1  of the processing circuit  3  and the output S 1  of the processing circuit controls the power transistor T 1 . The processing circuit comprises two power supply terminals respectively connected to the voltage Vb of the battery  2  and to ground. The various operating modes are controlled according to the number of presses on the button and/or how long the button is pressed and/or the time interval between 2 presses. 
   In all the above-mentioned embodiments enabling multifunctional operation, any malfunctioning of an electronic component makes the lamp totally unusable. 
   OBJECT OF THE INVENTION 
   The object of the invention is to provide a multifunction lamp not presenting the drawbacks of known lamps. 
   The device according to the invention is characterized in that the control switch is connected in parallel to the electronic power switch and in that the electronic processing circuit comprises state of the control switch detecting means periodically applying fine turn-off pulses to a control electrode of the electronic power switch. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages and features will become more clearly apparent from the following description of particular embodiments of the invention given for non-restrictive example purposes only and represented in the accompanying drawings, in which: 
       FIG. 1  represents a lamp according to the prior art. 
       FIGS. 2 to 4  illustrate various embodiments of multifunctional lamps according to the prior art. 
       FIGS. 5 and 6  illustrate two alternative embodiments of a lamp according to the invention. 
       FIGS. 7 to 10  illustrate for a same state A 1  of the control button T ( FIG. 7 ) the corresponding values of the output voltage Vs of the power transistor T 1  in a prior art lamp according to  FIG. 4  ( FIG. 8 ), the signals A 2  supplied by the output S 1  ( FIG. 9 ) and the corresponding values of the voltage Vs in a lamp according to the invention ( FIG. 10 ). 
   

   DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
   As represented in  FIG. 5 , the control button T is connected in parallel to the power transistor T 1 , which is, as in  FIG. 4 , connected in series between the battery  2  and at least one light-emitting diode (LED) and controlled by the signals A 2  supplied by the output S 1  of the processing circuit  3 . The processing circuit is supplied by battery  2 , as in  FIG. 4 . 
   Input E 1  of the processing  3  circuit is then connected to the point which is common to the power transistor T 1 , to the control button T and to the light-emitting diode (LED). The signals applied to the input E 1  therefore correspond to the output voltage Vs of the power transistor T 1 . 
   In this embodiment, the power switch, connected in series with the light-emitting diode (LED) to the terminals of the battery  2 , thus comprises 2 branches in parallel:
         a 1st branch formed by the control button T, which is normally open,   a 2nd branch formed by the transistor T 1 , controlled by the electronic processing circuit  3 .       

   When the 1st branch is closed, i.e. during a press on the button, the voltage Vs remains constantly equal to the voltage Vb of the battery, whatever the state of the power transistor. When the 1st branch is open, the voltage Vs is controlled by the processing circuit  3  via the power transistor T 1 . 
   The electronic processing circuit  3  further comprises means for detecting and reconstituting the state of the control button T. Indeed, although the input E 1  is connected to the battery  2  by means of the control button T, parallel connection of the control button T and the power transistor T 1  does not enable the electronic processing circuit  3  to read the state of the button directly when the power transistor T 1  is on. To enable the electronic processing circuit to detect and reconstitute the state of the control button T to control the power transistor accordingly, the electronic processing circuit  3  periodically applies fine pulses to the control electrode of the power transistor T 1  switching the power transistor T 1  off and monitors the voltage Vs at the terminals of the light-emitting diode. 
   The power transistor T 1  and the processing circuit  3  are preferably formed by distinct components, as in  FIG. 5 . They can also be integrated in a common electronic chip. In the alternative embodiment illustrated in  FIG. 6 , the electronic chip  4  comprises 3 terminals only. Two power supply terminals are respectively connected to the voltage Vb of battery  2  and to ground and one input/output terminal is connected to the button T and to the lamp (LED). The button T is connected between the power supply terminal connected to the voltage Vb and the input/output terminal. The connections between the power transistor and the electronic processing circuit are made inside the chip  4 . 
   Operation of the lamp according to  FIGS. 5 and 6  is described below with reference to  FIGS. 7 to 10 . These figures enable operation of a prior art lamp according to  FIG. 4  and of a lamp according to  FIG. 5  or  6  to be compared for the same states (A 1 ) of the button T and the same successive lighting modes. 
   In the example represented in  FIG. 7 , the lamp being initially off, control of the lamp is performed by two successive presses respectively between times t 1  and t 2  and between times t 3  and t 4 , then, after a time interval of more than 2 s, by pressing the button T again, between times t 5  and t 6 . The control button T, which is normally open, is therefore only closed between the times t 1  and t 2 , t 3  and t 4 , t 5  and t 6 . 
   In the prior art lamp according to  FIG. 4 , the signals A 1  of  FIG. 7 , representative of the state of the control button T, correspond to the signals applied to the input E 1  of the processing circuit  3 . The electronic processing circuit then supplies controls signals of the power transistor T 1  on its output S 1  successively causing, in the example illustrated in  FIG. 8  which represents the output voltage Vs of the power transistor T 1 , i.e. the voltage at the terminals of the lamp:
         as soon as the 1 st  press is made, i.e. from time t 1 , lighting of the lamp at a maximum lighting level in which the voltage Vs and power are maximum (Vsmax and Pmax),   after two successive short presses, i.e. from time t 3 , switching to an optimum lighting level in which the voltage Vs and the corresponding power decrease (Vsmean and Pmean),   switching-off of the lamp (Vs=0) when the button is pressed again after a time interval (t 4 -t 5 ) of more than 2 s, i.e. at time t 5 .       

   In the lamp according to  FIG. 5  or  6 , the processing circuit modifies the signals A 2  applied by its output S 1  to the control electrode of the power transistor T 1 , so as to periodically apply fine turn-off pulses thereto. When the 1 st  press is made on the button T, at time t 1 , the light-emitting diode (LED) and the processing circuit input E 1  are directly connected to the battery by the 1 st  branch of the switch. The signal Vs, initially at zero, then switches to the voltage Vsmax=Vb. As previously, the lamp thus lights at its maximum lighting level when the 1 st  press is made on the button. The processing circuit  3 , in response to the passage to Vb of the voltage applied to its input E 1 , then makes the signal A 2 , which is initially at zero, go to a maximum value A 2  max so as to close the 2 nd  branch of the switch. 
   The processing circuit  3  then periodically sets the signal A 2  to zero during very short times, for example 1 ms every 100 ms. This periodically causes turn-off of the power transistor T 1 . However, although the 2 nd  branch (T 1 ) of the power switch is then periodically open, so long as the control button T remains closed (between times t 1  and t 2 ), the 1 st  branch (T) of the power switch remains constantly closed and the voltage Vs remains at its maximum value Vsmax=Vb. The light-emitting diode (LED) is in fact directly connected by the button T to the battery. The signal Vs therefore remains unchanged (at Vsmax) until the control button T is released by the user, at time t 2 . 
   At time t 2 , the 1 st  branch of the switch opens, but the voltage Vs, which henceforth only depends on the state of the power transistor T 1 , remains at Vsmax, according to the value of the voltage A 2  which has been applied thereto since time t 1 . However, the voltage Vs then periodically drops to zero, thus causing microbreaks, when fine turn-off pulses are applied to its control electrode. The duration of the fine pulses is chosen such that the periodic microbreaks of the lamp, caused by these fine pulses resetting the voltage Vs to zero and corresponding to simultaneous opening of the two branches of the power switch, are not perceptible to the eye of the user. 
   When the button T is pressed again, at time t 3 , the power transistor T 1  is again short-circuited by the button T and the fine turn-off pulses are no longer transmitted to the voltage Vs, which remains unchanged. 
   Before release of the button T at time t 4 , the processing circuit  3  has however detected the state (A 1 ) of the control button T from the signals Vs applied to its input E 1 . When the voltage Vs is not zero, the presence of fine resetting pulses or microbreaks in the signal Vs in fact means that the button T is open. The absence of pulses during a longer time than the interval between two fine turn-off pulses means on the other hand that the button T is closed and short-circuits the power transistor T 1 . The processing circuit can thus reconstitute the signals illustrated in  FIG. 7  and use these reconstituted signals to control the power transistor T 1 . 
   In the example represented in  FIG. 9 , the processing circuit makes the control signal A 2  of the power transistor T 1  switch to its mean value A 2  mean between the times t 3  and t 4 , after a 2 nd  press on the button T has been detected by the absence, from the time t 3 , of fine zero resetting pulses in the signal Vs applied to its input E 1 . As the button T short-circuits the power transistor T 1  up to time t 4 , the voltage Vs nevertheless remains at its maximum value Vsmax=Vb up to time t 4  and can only switch to the value Vsmean at time t 4 , when the button T is released. 
   In the example represented, the button is no longer actuated up to time t 5 . During the period t 4 -t 5 , the signals A 2  and Vs therefore remain unchanged and the processing circuit  3  considers that no new press has been exerted on the button T due to the constant presence of the fine zero resetting pulses in the signal Vs. 
   When the button T is pressed again, at time t 5 , the voltage Vs automatically reverts to the value Vb until the button is released at time t 6 . During the period t 5 -t 6 , the turn-off pulses are no longer transmitted to the voltage Vs. The electronic processing circuit  3  can consequently rapidly detect this new press on the button and modify the control signal A 2  to take account of this new press. In the example represented in  FIG. 9 , the period t 4 -t 5  being more than 2 s, the electronic processing circuit sets the signal A 2  to zero as soon as this new press is detected (between times t 5  and t 6 ) to turn the power transistor T 1  off and thus switch off the lamp as soon as the button is released, at time t 6 . 
   In an alternative embodiment, a limiting resistor R (represented by a broken line in  FIG. 5 ) is connected in series with the button T in the 1 st  branch of the power switch. This limits flash effects due to the button T being pressed, when switching from one operating mode to another. Indeed, as illustrated in  FIG. 10  between times t 5  and t 6 , in the absence of this resistor R, any press on the button T automatically applies the voltage Vb to the terminals of the light-emitting diode. Inserting the limiting resistor R on the other hand enables the current flowing through the button, and consequently the power in the light-emitting diode, to be limited when the button T is pressed. The value of the limiting resistor R is for example chosen such that the power transmitted to the light-emitting diode by the button T corresponds to the minimum power of the lamp. 
   The processing circuit  3  of  FIGS. 5 and 6  can therefore reconstitute the state of the button and detect all the presses, determine the number of times the button is pressed, for how long (short press, long press), and the durations of the time intervals between presses to control operation of the lamp accordingly. 
   Connecting the control button T in parallel with the power transistor and periodic turn-off of the power transistor T 1 , by fine pulses, thus enhances the dependability of the lamp in the event of failure of an electronic component, while enabling the lamp to be controlled according to the number of presses and/or the pressing time and/or the time interval between presses on the control button, which remains the sole interface with the user. In the event of failure of one of the electronic components of the lamp, the user can still use the lamp, for example at its maximum power, by pressing on the button T. 
   The processing circuit  3  can provide the fine turn-off pulses continuously or only after a first press has been detected (when switching from Vs to Vb).