Patent ID: 9706616
Date: 2017-07-11
CPC Classifications: H05B

Claim:
1. A driver for driving a series arrangement being a variable number of strings of LEDs wherein each string has a capacitor connected in parallel with the respective string, the driver comprising: a controllable current source adapted to be connected in series between the series arrangement and a rectified AC supply, and to source a controllable current through the series arrangement; a current source controller adapted to control the controllable current source, wherein the current source controller is operable to source a relatively lower current when a difference between the voltage across the series arrangement and the voltage of the rectified AC supply is relatively higher and a relatively higher current when the difference is relatively lower, and wherein the relatively lower current is a first relatively lower current; the current source controller being configured to adjust the current in dependence on the charging level of the capacitors, and to source the first relatively lower current in response to the difference being greater than a reference level; and the driver being adapted for operation with a series combination of a resistor and a zener diode having a voltage drop, the series combination being connected in parallel with the current source, wherein the current source controller comprises a current comparator configured to compare the current through the resistor against a reference current, and the reference current has a fixed relationship with the reference level.