Load driving device, and lighting apparatus and liquid crystal display device using the same

Abstract

A light emitting load driving device includes a first constant current source structured to be serially connected to a first light emitting load group; a second constant current source structured to be serially connected to a second light emitting load group; a first load connection terminal structured to be connected to the first light emitting load group; a second load connection terminal structured to be connected to the second light emitting load group; and a control circuit structured to be supplied a first voltage applied to the first load connection terminal, a second voltage applied to the second load connection terminal, and a reference voltage applied to the control circuit, wherein the control circuit is structured to select a minimum voltage between the first voltage and the second voltage, and the control circuit is structured to equalize the minimum voltage and the reference voltage.

What is claimed is: 
     
         1 . A light emitting load driving device comprising:
 a drive current control unit configured to generate a plurality of drive currents to be supplied to each of a plurality of light emitting loads connected in parallel respectively and perform PWM control for the drive currents, wherein   the light emitting load driving device is configured to supply the drive currents by shifting each on period so that the light emitting load in at least one channel is prevented from turning on simultaneously with the light emitting loads of the remaining channels.   
     
     
         2 . The light emitting load driving device according to  claim 1 , wherein
 the light emitting load driving device is configured to supply the drive currents by shifting each on period so that each of the light emitting loads not turn on simultaneously.   
     
     
         3 . The light emitting load driving device according to  claim 2 , wherein
 the light emitting load driving device is configured to turn on the light emitting load of one channel, and turn on the light emitting load of a next channel after the on period has elapsed.   
     
     
         4 . The light emitting load driving device according to  claim 1 , wherein
 the light emitting load driving device is configured to perform not only the PWM control but also current value control of the drive currents.   
     
     
         5 . The light emitting load driving device according to  claim 4 , wherein
 the light emitting load driving device is configured
 to perform the PWM control only, unless on duty of the drive currents has reached an upper limit value, and 
 to perform not only the PWM control but also the current value control, if the on duty has reached the upper limit value. 
   
     
     
         6 . The light emitting load driving device according to  claim 4 , wherein
 the light emitting load driving device is configured to perform the current value control even before on duty of the drive currents reaches an upper limit value.   
     
     
         7 . The light emitting load driving device according to  claim 1 , wherein
 the light emitting load driving device is configured to control the drive currents so that there is a predetermined simultaneous off period until the light emitting load of one channel is turned on after the light emitting load of another channel is turned off.   
     
     
         8 . The light emitting load driving device according to  claim 1 , wherein
 the light emitting load driving device is configured to perform the PWM control according to a luminance control command inputted from a microcomputer.   
     
     
         9 . The light emitting load driving device according to  claim 8 , further comprising:
 a serial interface unit configured to receive the luminance control command and convey the luminance control command to the drive current control unit.   
     
     
         10 . The light emitting load driving device according to  claim 8 , wherein
 the luminance control command includes a data signal indicative of a light emitting load to be turned on, or on duty and drive current value thereof.   
     
     
         11 . The light emitting load driving device according to  claim 1 , wherein
 the light emitting load driving device is configured to perform the PWM control according to PWM signals of each channel inputted from a microcomputer individually.   
     
     
         12 . The light emitting load driving device according to  claim 1 , further comprising:
 A DC/DC converter unit configured to stabilize an input voltage to generate a desired constant voltage.   
     
     
         13 . The light emitting load driving device according to  claim 1 , wherein
 the drive current control unit includes a plurality of constant current sources configured to be serially connected to the light emitting loads.   
     
     
         14 . The light emitting load driving device according to  claim 13 , further comprising:
 a plurality of load connection terminals configured to connect the plurality of light emitting loads and the plurality of constant current sources respectively.   
     
     
         15 . An electronic device comprising:
 the plurality of light emitting loads;   a power supply circuit configured to generate a drive voltage and supply the drive voltage to the plurality of light emitting loads, and   the light emitting load driving device according to  claim 1 .   
     
     
         16 . The electronic device according to  claim 15 , wherein
 the power supply circuit is configured to perform output feedback control of the drive voltage so that among a plurality of detection voltages each voltage level of which varies depending on a magnitude of each forward dropping voltage of the light emitting loads, the lowest detection voltage becomes equal to a predetermined reference voltage.   
     
     
         17 . The electronic device according to  claim 16 , wherein
 the power supply circuit is a step-up/down circuit configured to boost or lower a constant voltage to generate the drive voltage.   
     
     
         18 . The electronic device according to  claim 15 , wherein
 each of the plurality of light emitting loads includes a plurality of light emitting elements connected in series.   
     
     
         19 . The electronic device according to  claim 18 , wherein
 the plurality of light emitting elements include LED.