Patent attributes
A controller in a solid state luminaire implements a nested control loop to drive multiple, parallel-connected, heterogeneous strings of series-connected LEDs using a constant current power supply. The current through each string is independently controlled by a current regulator in series with the LEDs. An inner (current) control loop alters the relative drive strength of each LED string, to achieve desired luminous characteristics, such as CRI, CCT, and the like. An outer (voltage) control loop monitors the output voltage of the power supply, and the total current drawn. The outer control loop adjusts a gain factor applied to the control signals for each current regulator, to control the total current drawn—while maintaining the relative ratios of drive strength between the strings—so as to maintain the power supply output voltage at a substantially constant value.
