High efficiency low power capacitor charged DC driver
View Patent ↗A high efficiency low power DC driver apparatus is presented for powering a light source, with a capacitive divider circuit receiving an AC input and providing a divided AC output, a rectifier provide a DC output below ten watts, output terminals coupleable to one or more light sources, and a linear regulator coupled in series with the light source to regulate a drive current flowing through the series circuit.
1. A high efficiency low power DC driver apparatus for powering a light source, comprising:
an input including first and second input terminals coupleable to an AC power supply;
a capacitive divider circuit including first and second capacitances coupled in series between the input terminals and coupled with one another at an intermediate node, the capacitive divider circuit receiving an AC input at the input terminals and providing a divided AC output at the intermediate node;
a rectifier operatively coupled with the intermediate node to receive and rectify the divided AC output to provide a DC output at a pair of DC output nodes at a power level of less than 10 watts;
an output including a pair of driver output terminals coupleable to at least one light source, a first one of the driver output terminals being coupled with a first one of the DC output nodes; and
a linear regulator coupled between a second one of the driver output terminals and a second one of the DC output nodes to couple the light source and the linear regulator in a series circuit between the DC output nodes, the linear regulator being operative to regulate a drive current flowing through the series circuit.
2. The driver apparatus of claim 1 , where the linear regulator comprises:
a field-effect transistor with drain and source terminals coupled in the series circuit and a gate terminal operative to control the current flowing between the drain and source terminals;
a sense resistance coupled in the series circuit; and
an op amp circuit with an input coupled with the sense resistance to sense a voltage across the sense resistance and an output controlling a voltage applied to the gate terminal of the field-effect transistor to regulate the drive current flowing through the series circuit.
3. The driver apparatus of claim 2 , where the linear regulator further comprises a capacitance in the op amp circuit to control a rise time of the drive current flowing through the series circuit for soft-starting the driver apparatus.
4. The driver apparatus of claim 2 , where a ratio of the first and second capacitances of the capacitive divider is set such that the linear regulator regulates only during startup.
5. The driver apparatus of claim 1 , where the linear regulator comprises:
a three-terminal regulator with an input terminal coupled with one of the DC output nodes, an output terminal coupled with one of the driver output terminals, and an adjustment terminal;
a first resistance coupled between the output terminal and the adjustment terminal; and
a second resistance coupled between the adjustment terminal and the other one of the driver output terminals;
where the three-terminal regulator regulates a voltage between the driver output terminals to regulate the drive current flowing through the series circuit.
6. The driver apparatus of claim 5 , where the second resistance of the linear regulator is adjustable for dimming the lighting device.
7. The driver apparatus of claim 5 , where a ratio of the first and second capacitances of the capacitive divider is set such that the linear regulator regulates only during startup.
8. The driver apparatus of claim 1 , where the linear regulator is operative to control a rise time of the drive current flowing through the series circuit for soft-starting the driver apparatus.
9. The driver apparatus of claim 1 , where the linear regulator is adjustable for dimming the lighting device.
10. The driver apparatus of claim 9 , where a ratio of the first and second capacitances of the capacitive divider is set such that the linear regulator regulates only during startup and for dimmed operation of the lighting device.
11. The driver apparatus of claim 1 , where a ratio of the first and second capacitances of the capacitive divider is set such that the linear regulator regulates only during startup.
12. The driver apparatus of claim 11 , where a ratio of the first capacitance divided by the second capacitance of the capacitive divider is greater than 2.
13. The driver apparatus of claim 12 , where the ratio of the first capacitance divided by the second capacitance of the capacitive divider is 3.
14. The driver apparatus of claim 1 , where a ratio of the first capacitance divided by the second capacitance of the capacitive divider is greater than 2.
15. The driver apparatus of claim 14 , where the ratio of the first capacitance divided by the second capacitance of the capacitive divider is 3.
16. The driver apparatus of claim 1 , where the linear regulator is a non-switching regulator.