Patent ID: 9544960
Date: 2017-01-10
CPC Classifications: H05B,Y02B

Claim:
1. An apparatus for driving light emitting diodes (LEDs) comprising: a first terminal that receives an alternating current (AC) input voltage; a second terminal that receives the AC input voltage, wherein an input voltage magnitude is present between the first terminal and the second terminal; a rectifier coupled to the first terminal and to the second terminal; a current sense resistor; a first string of N LEDs, wherein the rectifier is coupled through the current sense resistor to the first string of LEDs, and wherein the current sense resistor is directly connected to the first string of LEDs; a second string of 2N LEDs, and a third string of 4N LEDs, wherein during a first time period a first current flows through the first string of LEDs but no current flows through the second or third string of LEDs, wherein during a second time period a second current flows through both the first string of LEDs and through the second string of LEDs but not through the third string of LEDs, wherein during a third time period a third current flows through the third string of LEDs but not through either of the first string of LEDs or the second string of LEDs, wherein N is a positive nonzero integer, wherein the first string of LEDs, the second string of LEDs and the third string of LEDs are connected in series, and wherein the input voltage magnitude during the second time period is greater than the input voltage magnitude during the first time period.