Driving circuit and illumination device having light-emitting elements

Abstract

The present invention discloses a driving circuit including a rectifying circuit and a first current-controlling circuit. Input terminals of the rectifying circuit are connected to output terminals of an AC power source. The first current-controlling circuit and a plurality of light-emitting elements be driven are connected in series, and then are connected between two output terminals of the rectifying circuit. The driving circuit further includes a plurality of switches and a switch-controlling circuit; the switches are connected in parallel with two terminals of one or some light-emitting elements connected in series to form many light-emitting element subunits. Control-signal output terminals of the switch-controlling circuit are connected to control terminals of the switches respectively, to control the switches in an ON-OFF state according to an instantaneous value of a DC voltage outputted from the rectifying circuit, for controlling an amount of light-emitting elements which should be lighten.

What is claimed is: 
     
       1. A driving circuit for light-emitting elements, comprising a rectifying circuit with output terminals, a first current-controlling circuit, a plurality of light-emitting groups each comprising a switch and a light-emitting elements subunit with one or more serially connected light-emitting elements, and a switch-controlling circuit; wherein said first current-controlling circuit is connected between said rectifying circuit's output terminals and further connected in series with each of said light-emitting subunits, and said switch-controlling circuit is in connection with said switch in each of said light-emitting groups for setting said switch in an ON-OFF state according to instantaneous value of DC voltage from said rectifying circuit and thereby controlling how many of said emitting elements are to be lighten at any given moment;
 wherein the amount of the switches is n; a m-th switch being connected in parallel with two terminals of Am light-emitting elements connected in series to form a m-th light-emitting element subunit; m is from 1 to n; the n light-emitting element subunits are connected in series, and a sum of amounts of light-emitting elements comprised in each of the n light-emitting element subunit is N1; 
 wherein the switches are divided into three portions, the first portion being the switches prior to the k-th switch, the second portion being the k-th switch, the third portion being the switches after the k-th switch, k being an integer and 1<k<n; when m is in a range from 1 to k−1, Am is 2 m-1 ; when m=k, Ak is any number less than 2 k-1 ; when m is in a range from k+1 to n, Am is a sum of a basic number and a compensation number; the basic number is double of A m-1  and each of the compensation numbers is any integral number from 0 to 2 k-1 −Ak, and the sum of the compensation numbers is not greater than 2 k-1 −Ak; whereby the light-emitting elements of any number from 1 to N1 can be controlled to be lighten. 
 
     
     
       2. The driving circuit according to  claim 1 , wherein said light-emitting element is selected from the group consisting of light-emitting diodes, organic light-emitting diodes, polymer light-emitting diodes and laser diodes. 
     
     
       3. The driving circuit according to  claim 2 , wherein the switch-controlling circuit calculates the amount of the light-emitting elements to be lighten by taking an integral part of a calculated result according to a formula of: 
       
         
           
             
               
                 
                   U 
                   - 
                   
                     Δ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     U 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                 
                 
                   U 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   0 
                 
               
               , 
             
           
         
         wherein, 
         U represents an instantaneous value of the DC voltage outputted from the rectifying circuit; 
         U1 represents an operation voltage required by the first current-controlling circuit operating steadily; and 
         U0 represents an operation voltage of a single light-emitting element. 
       
     
     
       4. The driving circuit according to  claim 3 , wherein the switch-controlling circuit controls an amount of light-emitting elements be lighten according to a following method that comprises:
 1) the switch-controlling circuit converting the amount of the light-emitting elements to be lighten into a binary number with n bits; 
 2) the switch-controlling circuit controlling the n switches according to n bits of binary number respectively, wherein a m-th bit of the binary number from right to left correspondingly controls the m-th switch; while the m-th bit is 0, the m-th switch is correspondingly controlled in the ON state; while the m-th bit is 1, the m-th switch is correspondingly controlled in the OFF state. 
 
     
     
       5. The driving circuit according to  claim 1  further comprises n1 switches, one terminal of each of the n1 switches is connected to a cathode of a N1-th light-emitting element, and another terminal of each of the n1 switches is connected to a connection terminal between a cathode and an anode of any two consecutive light-emitting elements. 
     
     
       6. The driving circuit according to  claim 1 , wherein the sum N1 of the amounts of the light-emitting elements comprised in each of the light-emitting element subunits is less than the amount N of the light-emitting elements of the driving circuit to be driven. 
     
     
       7. The driving circuit according to  claim 1 , further comprises a charge-discharge circuit which includes a charge-discharge switch, a charge-discharge capacitor and a second current-controlling circuit connected in series;
 one terminal of the charge-discharge circuit is connected to an cathode of a 
 
       
         
           
             
               
                 N 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 1 
               
               - 
               
                 
                   
                     Uc 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   - 
                   
                     Δ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     U 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                 
                 
                   U 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   0 
                 
               
               - 
               th 
             
           
         
       
       light-emitting element, and integral part of the result of 
       
         
           
             
               
                 
                   Uc 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
                 - 
                 
                   Δ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   U 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
               
                 U 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 0 
               
             
           
         
       
       is taken; the other terminal of the charge-discharge circuit is connected to a negative terminal of the rectifying circuit;
 wherein, 
 Uc1 represents a charge-discharge operation voltage of the charge-discharge capacitor; 
 U2 represents an operation voltage of the second current-controlling circuit; 
 U0 represents an operation voltage of a single light-emitting element. 
 
     
     
       8. The driving circuit according to  claim 1 , wherein at least one of the rectifying circuit, the first current-controlling circuit, the light-emitting elements, the switches and the switch-controlling circuit are integrated on an IC chip. 
     
     
       9. An illumination device having light-emitting elements, comprises a driving circuit according to  claim 1  and a plurality of light-emitting elements connected in series.