Switched mode power converter and method of operating the same

Abstract

A switched mode power converter is disclosed, together with a method for operating the same. The power converter is adapted to be operable in the boundary conduction mode, and operation is interruptible in the absence of any load requirement.

1 . A method of controlling a switched mode power converter including an inductor and a switch and providing an output current for LED applications, the method including the sequential steps of:
 decreasing the current through the inductor from a maximum value to zero, and   immediately thereafter increasing the current through the inductor from zero to the maximum value,   
       and further including the steps of
 providing an interruption by forcing the switch to be open in response to a first change in a converter control signal, which first change is indicative of an absence of a requirement for every one of a plurality of LED loads, and 
 ending the interruption by ending the forcing open of the switch in response to a second change in the converter control signal, which second change is indicative of a recommencement of a requirement for one of any one and a plurality of the plurality of LED loads. 
 
     
     
         2 . The method of  claim 1 , further comprising a further step of smoothing the output current with a smoothing capacitor. 
     
     
         3 . The method of  claim 1 , wherein a presence or an absence of an (i)th one of the LED loads is determined by a control signal PMW(i)_on, and the converter control signal corresponds to a logical combination AND of the PMW(i)_on control signals. 
     
     
         4 . The method of  claim 1 , wherein a presence or an absence of the requirement for an (i)th one of the LED loads is determined by a control signal PMW(i)_on, and the control signal corresponds to a logical combination NOT AND of the PMW(i)_on control signals. 
     
     
         5 . The method of  claim 1 , wherein a presence or an absence of the requirement for an (i)th one of the LED loads is determined by a control signal PMW(i)_off, and the converter control signal corresponds to a logical combination NOT OR of the PMW(i)_off control signals. 
     
     
         6 . The method of  claim 1 , wherein a presence or an absence of the requirement for an (i)th one of the LED loads is determined by a control signal PMW(i)_off, and the control signal corresponds to a logical combination OR of the PMW(i)_off control signals. 
     
     
         7 . An integrated circuit for controlling a boundary conduction mode switched mode power supply and adapted to operate according to the method of  claim 1 . 
     
     
         8 . A switched-mode power converter for LED application, adapted for operation in boundary conversion mode, and for interruption of operation in an absence of a requirement for every one of a LED loads. 
     
     
         9 - 11 . (canceled) 
     
     
         12 . A DC-DC converter for driving at least one, comprising:
 an integrated circuit having both a switch mode power circuit and a temperature sensing circuit for providing an output indicating a temperature of said integrated circuit, the arrangement being such that, in use, said integrated circuit consumes power, some of which power is dissipated in said integrated circuit as heat causing a rise in said internal temperature,   wherein a change in said output from said temperature sensing circuit is used by said integrated circuit to adjust said consumed power so that said internal temperature may be controlled.   
     
     
         13 . A DC-DC converter as in  claim 12 , wherein said integrated circuit is configured to de-rate said consumed power when said output indicates an increase in said internal temperature, so that said power dissipated in said integrated circuit is reduced. 
     
     
         14 . A DC-DC converter as in  claim 12 , wherein said switch-mode power circuit is for supplying a substantially constant average current to at least one said LED, wherein said converter comprises a circuit for controlling said switch-mode power circuit so as to adjust said consumed power whilst leaving said average current substantially unaffected, so that a visual appearance of said at least one LED appears unaffected. 
     
     
         15 . A DC-DC converter as in  claim 12 , wherein the integrated circuit is configured to compare said output from said internal temperature sensing circuit with a first temperature level and a second temperature level higher than said first temperature level, and if said internal temperature is higher than said first temperature level and lower than said second temperature level, to adjust said consumed power in proportion to a difference between said output and said first temperature level. 
     
     
         16 . A DC-DC converter as in  claim 15 , wherein said integrated circuit is configured to effect a substantially linear increase in a ripple voltage of said switch-mode power circuit as said internal temperature increases from said first temperature level to said second temperature level. 
     
     
         17 . A DC-DC converter as claimed in  claim 12 , further comprising a hysteretic levels controller circuit for setting at least one of a peak voltage level and a valley voltage level, which peak and valley levels determine said ripple voltage of said switch-mode power circuit. 
     
     
         18 . A DC-DC converter as in  claim 17 , wherein said internal temperature sensing circuit is adapted to supply said output to said hysteretic levels controller circuit that is configured to increase a magnitude of a ripple voltage of said switch-mode power circuit so that the switching frequency is reduced. 
     
     
         19 . A DC-DC converter as in  claim 18 , wherein said hysteretic levels controller circuit is configured to raise said peak voltage level and lower said valley voltage level in response to increasing internal temperature, thereby reducing said switching frequency to effect de-rating of said consumed power. 
     
     
         20 . A DC-DC converter as in  claim 19 , wherein said hysteretic levels controller circuit is configured to raise said peak and lower said valley voltage levels by a same amount, so that said average current is unaffected by de-rating of said consumed power. 
     
     
         21 . A DC-DC converter as in  claim 12 , further comprising a control logic circuit for adjusting the average current output by said converter by controlling an on period and an off period of each commutation cycle of said switch-mode power circuit. 
     
     
         22 . A DC-DC converter as in  claim 21 / 10 , wherein said control logic circuit is configured either to increase said off period to de-rate said consumed power or to increase said on period to de-rate said consumed power in response to an increase in said internal temperature as indicated by said output. 
     
     
         23 . A DC-DC converter as in  claim 22 , wherein said control logic circuit is configured respectively to control said on period by adjusting a peak current level in said switch-mode power circuit or to control said off period (by adjusting a valley current level in said switch-mode power circuit to compensate for a respective decrease or increase in said average current output by said converter.