Boost and linear LED control

1. A light emitting diode (LED) lighting system comprising:

a switching power converter having an input for coupling to an alternating current (AC) power source, an output having a link voltage, and a switch;

an LED lighting subsystem coupled to receive power from the output of the switching power converter, the LED lighting subsystem including a current source for one or more LEDs, wherein the current source has a control node that determines an LED current through the one or more LEDs;

a sense node in the LED lighting subsystem indicative of whether the link voltage is sufficient to maintain a selected LED current; and

a switch state controller coupled to the switching power converter and coupled to the LED lighting subsystem, wherein 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.

2. The LED lighting system of claim 1 , wherein the switching power converter is a boost-type switching power converter.

3. The LED lighting system of claim 1 , wherein the switch state controller varies the control current provided to the control node to constrain current ripple in the LED current provided to the one or more LEDs to no more than a predetermined amount.

4. The LED lighting system of claim 1 , wherein the current source comprises:

a transistor having a control input coupled to a constant voltage source and couplable to the one or more LEDs; and

a current mirror coupled to the transistor that determines an LED current provided to the one or more LEDs based on the control current.

5. The LED lighting system of claim 1 , wherein the parameter sensed from the sense node is a sensed voltage.

6. The LED lighting system of claim 1 , and further comprising a phase-cut dimmer from which the switching power converter receives an AC input.

7. The LED lighting system of claim 6 , wherein the switch state controller further varies the control current provided to the control node based on an amount of dimming applied by the phase-cut dimmer.

8. A method for a light emitting diode (LED) lighting system, the method comprising:

providing a link voltage to a LED lighting subsystem through a switching power converter coupled to an alternating current (AC) power source, wherein the LED lighting subsystem includes one or more LEDs, a sense node, and a current source for one or more LEDs, the current source having a control node;

the current source generating an LED current for the one or more LEDs based on a control current received at the control node of the current source; and

generating a control signal that controls switching of a switch of the switching power converter and varies the control current provided to the control node of the current source based on at least a parameter sensed from the sense node.

9. The method of claim 8 , wherein providing the link voltage comprises providing the link voltage through a boost-type switching power converter.

10. The method of claim 8 , wherein:

the LED lighting system further includes a phase-cut dimmer; and

the method further comprises varying the control current provided to the control node based on an amount of dimming applied by the phase-cut dimmer.

11. The method of claim 8 , and further comprising varying the control current provided to the control node to constrain current ripple in the LED current provided to the one or more LEDs to no more than a predetermined amount.

12. The method of claim 8 , wherein the parameter sensed from the sense node is a sensed voltage.