Tapped single-stage buck converter LED driver
Systems, devices and methods are described herein. An integrated light emitting diode (LED) lighting system includes an electronics board. An alternating current (AC) input is disposed on the electronics board. Multiple strings of LED devices are disposed on the electronics board, each having an individual voltage threshold. A buck converter is disposed on the electronics board and is electrically coupled to provide a direct current (DC) current based on an AC current at the AC input. A switching circuit is disposed on the electronics board and is electrically coupled to the strings of LED devices to apply the DC current to each of the strings in a sequence beginning at a time when an instantaneous voltage level at the AC input reaches the individual threshold voltage of a first one of the strings of LED devices in the sequence.
1. An integrated light emitting diode (LED) lighting system comprising:
an alternating current (AC) input configured to receive a sinusoidal input voltage;
a load circuit comprising:
a first plurality of LED devices coupled in parallel with a first capacitive element and a second plurality of LED devices coupled in parallel with a second capacitive element, the first plurality of LED devices and the second plurality of LED devices being coupled together at a first location, and
a switching element coupled in series with the first and second capacitive elements on a first electrical path between the location and a first node;
a single stage buck converter circuit, electrically coupled between the AC input and the first plurality of LED devices, configured to provide a drive current to the load circuit; and
a switching circuit on a second electrical path between the first location and a second node, the switching circuit comprising an input electrically coupled to a second location between the AC input and the single stage buck converter circuit to sense an instantaneous voltage of the sinusoidal input voltage and configured to close the second electrical path to divert the drive current at the first location away from the second plurality of LED devices along the second path when the instantaneous voltage is less than a threshold voltage of the load circuit and to open the second electrical path when the instantaneous voltage is greater than the threshold voltage of the load circuit.
2. The system of claim 1 , wherein the threshold voltage of the load circuit equals a total threshold voltage of the first and second plurality of LED devices.
3. The system of claim 1 , wherein the switching circuit comprises a switch coupled to the first location and a comparator coupled to the switch, and the comparator is configured to switch the switch to an on state to disconnect the second plurality of LED devices from the drive current in response to the instantaneous voltage dropping below the threshold voltage of the load circuit.
4. The system of claim 1 , wherein each of the first plurality of LED devices and the second plurality of LED devices comprises a plurality of LED devices electrically coupled together in at least one of in series and in parallel.
5. The system of claim 1 , further comprising a rectifier element coupled to the single stage buck converter circuit.
6. A method comprising:
receiving a signal having an alternating current (AC) and a sinusoidally varying voltage;
converting the AC to a direct current (DC) using a single stage buck converter circuit;
supplying the DC from the single stage buck converter circuit to a series string of a first plurality of LED devices and a second plurality of LED devices, the first plurality of LED devices and the second plurality of LED devices being coupled together at a first location on a first electrical path;
sensing an instantaneous voltage of the sinusoidal input voltage at a second location between the AC input and the single stage buck converter circuit;
maintaining a switch, on a second electrical path between the first location and a node, in an ON state to close the second electrical path and divert the DC current along the second electrical path to by-pass the second plurality of LED devices when the instantaneous voltage is below a threshold voltage of the first and second plurality of LED devices;
maintaining the switch in an OFF state to open the second electrical path when the instantaneous voltage is greater than the threshold voltage of the first and second plurality of devices; and
supplying the second plurality of LEDs with a current from an alternate source when the DC current is diverted.
7. The method of claim 6 , wherein the diverting the DC current further comprises diverting the DC current on a condition that the instantaneous voltage is between a threshold voltage of the first plurality of LED devices and the threshold voltage of the series string of the first plurality of LED devices and the second plurality of LED devices.
8. The system of claim 1 , wherein the switching element is one of a diode and an active switching device.
9. The method of claim 6 , wherein the current from the alternate source is supplied by a capacitive element.
10. The method of claim 6 , wherein the diverting the DC current does not short the first and second plurality of LED devices.
11. The system of claim 1 , wherein the threshold voltage of the load circuit is constant.
12. The method of claim 6 , wherein the threshold voltage is constant.