Portable electric lamp having a current limitation device

Abstract

Portable electric lamp including a lighting module, and a compact case containing a power supply for supplying the lighting module and a limitation device for a current delivered by the power supply, the limitation device including a controlled limitation switch coupled between a reference terminal of the power supply and an output terminal of the lighting module, the limitation device being configured so as to determine a supply voltage between an output terminal of the limitation switch and the reference terminal, and to control the limitation switch so that it is in a closed state when the supply voltage is lower than or equal to a desired voltage.

The invention claimed is: 
     
       1. A portable electric lamp comprising:
 a lighting module; and 
 a compact case containing a power supply for supplying the lighting module and a limitation device for a current delivered by the power supply, 
 the limitation device including:
 an operational amplifier; 
 a limitation transistor having a drain that is coupled to an output terminal of the lighting module, and a gate that is coupled to an output of the operational amplifier; 
 a resistive element coupled between a reference terminal of the power supply and a source of the limitation transistor, 
 the operational amplifier having two inputs respectively coupled to terminals of the resistive element and being configured to compare a first input voltage to a second input voltages to determine a supply voltage at the terminals of the resistive element, and to control the limitation transistor so that the limitation transistor is in a closed state when the supply voltage is lower than or equal to a desired voltage; and 
 a controlled safety switch coupled between the output of the operational amplifier and the reference terminal, the controlled safety switch being in a closed state for maintaining the limitation transistor in an opened state when a voltage between the drain and the source of the limitation transistor is higher than a reference voltage. 
 
 
     
     
       2. The portable electric lamp according to  claim 1 , wherein the limitation transistor is a NMOS-type transistor. 
     
     
       3. The portable electric lamp according to  claim 1 , wherein the controlled safety switch is a safety bipolar-type transistor having a base that is coupled to the output terminal of the lighting module, and the reference voltage is equal to the threshold voltage of the controlled safety switch. 
     
     
       4. The portable electric lamp according to  claim 3 , further comprising:
 an additional limitation device for limiting the supply current delivered by the power supply, 
 the additional limitation device comprising:
 an additional operational amplifier having two inputs respectively coupled to terminals of the resistive element and being configured to compare a first input voltage to a second input voltage; and 
 an additional controlled safety switch coupled between said limitation transistor and the output terminal of lighting module, 
 the additional controlled safety switch including a control unit coupled to an output of the additional operational amplifier, the additional operational amplifier being configured to determine the supply voltage and to control the additional controlled safety switch so that the additional controlled safety switch is in a closed state when the supply voltage is lower than or equal to the desired voltage. 
 
 
     
     
       5. The portable electric lamp according to  claim 4 ,
 wherein the additional controlled safety switch is an additional limitation transistor, and 
 wherein the additional limitation device further comprises an additional safety bipolar-type transistor coupled between the output of the additional operational amplifier and the reference terminal, the additional safety bipolar-type transistor being in a closed state for maintaining the limitation transistors in the opened state when the base-emitter voltage of the safety bipolar-type transistors exceeds their threshold voltage.