Regulated power supply voltage and triac hold-up current for a switching power converter

1. A method, comprising:

while a phase-cut dimmer switch operates to dim a lighting from an LED powered by a switching power converter;

sourcing a current through a current source into a first node;

responsive to an internal power supply voltage being below a maximum level, switching on a first switch connected between the first node and a storage capacitor to maintain a bleed current for the phase-cut dimmer switch until the storage capacitor is charged to a desired level for the internal power supply voltage;

responsive to the internal power supply voltage being at or above the maximum level, switching on a second switch connected between the first node and ground to maintain the bleed current for the phase-cut dimmer switch; and

regulating an output voltage for the switching power converter by cycling a power switch coupled to a rectified input voltage.

2. The method of claim 1 , wherein sourcing the current through the current source comprises sourcing the current through a current mirror.

3. A switching power converter, comprising:

a current mirror configured to drive a current into a first node;

a storage capacitor for storing a power supply voltage;

a first switch connected between the first node and the storage capacitor;

a second switch connected between the first node and ground;

a dimming detector configured to detect a dimming from a phase-cut dimmer switch; and

a controller powered by the power supply voltage, the controller being configured to switch on the first switch and to switch off the second switch responsive to the power supply voltage being below a maximum level and to a dimming detection by the dimming detector and to switch off the first switch and switch on the second switch responsive to the power supply voltage being at or above the maximum level and to the dimming detection by the dimming detector.

4. The switching power converter of claim 3 , further comprising:

a power switch;

an inductor having a first terminal coupled to an input node;

a cascode transistor coupled between the inductor and the power switch;

a resistor coupled between the input node and a second node; and

a zener diode coupled between the second node and ground, wherein the second node is coupled to a gate of the cascode transistor.

5. The switching power converter of claim 4 , further comprising an LED coupled to the input node.

6. (The switching power converter of claim 4 , wherein the power switch comprises an NMOS transistor.

7. The switching power converter of claim 4 , wherein the power switch comprises a bipolar junction transistor.

8. The switching power converter of claim 5 , further comprising an output diode coupled between the LED and a second terminal for the inductor.