Self-powered LED bypass-switch configuration
A LED string is divided into segments that each have a bypass-switch and a driver for the bypass-switch. The driver is powered by a supply voltage locally generated from the forward-voltages of the LEDs of the segment.
1. An electronic system comprising a plurality of LEDs connected in series,
wherein:
the series is divided into multiple segments;
each specific one of the segments comprises:
a series connection of one or more of the LEDs between first and second nodes of a current path of the specific segment;
a bypass-switch connected between the first and second nodes and in parallel with the one or more LEDs;
a driver for controlling the bypass-switch, the driver having first and second supply terminals;
a capacitance connected between the first and second supply terminals;
wherein
power supply of the driver is locally generated from the current path within the specific segment; and
wherein the local power supply is embodied with a gating element for supply of a current to the capacitance
the gating element is connected between the current path and the capacitance; and
the gating element is operative to generate for the driver a power supply at the capacitance that is derived from a forward-voltage of the one or more LEDs.
2. The system of claim 1 further comprising a monitoring circuit for monitoring a capacitance voltage across the capacitance and for turning off the bypass-switch in dependence on the capacitance voltage.
3. The system of claim 1 , wherein the gating element is a diode having its anode connected to the current path.
4. The system of claim 1 , wherein:
the gating element comprises a sample switch between the current path and the capacitance, and a sample driver for control of the sample switch; and
the sample driver has a third supply terminal connected to the first supply terminal, and a fourth supply terminal connected to the second supply terminal.
5. The system of claim 1 , further comprising a voltage regulator between the capacitance and the first supply terminal.
6. The system of claim 1 , wherein:
the specific segment comprises a voltage up-converter for increasing a voltage between the first and second supply terminals if the bypass-switch in the specific segment is conducting.
7. The system of claim 6 , wherein the up-converter comprises:
a first capacitor and a second capacitor; and
circuitry for connecting the first and second capacitors in parallel between the first and second supply terminals if the bypass-switch in the specific segment is blocking, and for connecting the first and second capacitors in series between the first and second supply terminals if the bypass-switch of the specific segment is conducting.
8. The system of claim 1 , wherein:
a selected one of the segments has two or more LEDs connected in series between the first and second nodes of the current path of the specific segment; and
the power supply is drawn from the current path between a pair of the two or more LEDs.
9. A segment comprising:
a series connection of one or more of the LEDs between first and second nodes of a current path of the segment;
a bypass-switch connected between the first and second nodes and in parallel with the one or more LEDs;
a driver for controlling the bypass-switch, the driver having first and second supply terminals;
a capacitance connected between the first and second supply terminals wherein power supply of the driver is locally generated from the current path within the segment.
wherein
a gating element is present for supply of a current to the capacitance, the gating element is connected between the current path and the capacitance; and
the gating element is operative to generate for the driver a continuous power supply at the capacitance that is derived from a forward-voltage of the one or more LEDs.
10. The segment according to claim 9 , wherein the bypass switch, the driver and the gating element are combined into an integrated circuit.
11. The segment of claim 10 , further comprising a drive-signal level shifter integrated in the integrated circuit.