Boost and linear LED control
A light emitting diode (LED) lighting system includes a switching power converter having an input for coupling to an alternating current (AC) power source, an output, and a switch. The LED lighting system also includes an LED lighting subsystem coupled to receive power from the output of the switching power converter. The LED lighting subsystem includes a current source for one or more LEDs, and the current source has a control node and a sense node. The LED lighting system additionally includes a switch state controller coupled to the switching power converter and coupled to the LED lighting subsystem. The switch state controller controls switching of the switch and varies a control current provided to the control node of the current source based on at least a parameter sensed from the sense node.
1. A light emitting diode (LED) lighting subsystem, comprising:
one or more LEDs;
a current source for the one or more LEDs, the current source including:
a transistor having a control input coupled to a constant voltage source, a first leg coupled to the one or more LEDs and a second leg; and
a current mirror coupled to the second leg of the transistor, the current mirror having a control node, a sense node indicative of an operating point of the LED lighting subsystem, and a transistor size ratio that determines an LED current provided to the one or more LEDs based on a control current received at the control node.
2. The LED lighting subsystem of claim 1 , wherein the one or more LEDs include multiple parallel coupled strings of LEDs.
3. The LED lighting subsystem of claim 1 , wherein the transistor is a NPN transistor.
4. An apparatus comprising:
lighting subsystem of claim 1 ;
a feedback circuit coupled to the sense node; and
a lighting system controller that supplies the control current to the control node of the current mirror.
5. The apparatus of claim 4 , wherein the lighting system controller varies the control current provided to the control node based on an amount of dimming applied to the one or more LEDs by a phase-cut dimmer.
6. The apparatus of claim 4 , wherein the switch state controller varies the control current provided to the control node to constrain current ripple in the one or more LEDs to no more than a predetermined amount.
7. A lighting system controller for a light emitting diode (LED) lighting system illuminating one or more LEDs from AC line voltage, wherein the lighting system controller receives a link voltage and a feedback signal indicative of an operating point of the LED lighting system, and responsive thereto, varies a control current provided to a current source that governs current through the one or more LEDs such that ripple in the one or more LEDs is no more than a predetermined amount.
8. The lighting system controller of claim 7 , wherein the lighting system controller comprises an integrated circuit.
9. The lighting system controller of claim 7 , wherein the lighting system controller further receives as an input a signal indicative of phase-cut dimming applied to the LED lighting system, and responsive thereto, varies the control current based on the signal indicative of phase-cut dimming.
10. The lighting system controller of claim 9 , wherein the signal indicative of phase-cut dimming is a rectified input voltage of the LED lighting system.