US Patent No. 10,512,137

LED DRIVE CIRCUIT


Patent No. 10,512,137
Issue Date December 17, 2019
Title Led Drive Circuit
Inventorship Koji Sonobe, Matsumoto (JP)
Assignee FUJI ELECTRIC CO., LTD., Kawasaki-Shi (JP)

Claim of US Patent No. 10,512,137

1. An LED drive circuit configured to convert an alternating current voltage of an alternating current power source to a direct current voltage necessary to cause light emitting diodes (LEDs) to emit light, and control lighting of the LEDs, the LED drive circuit comprising:a rectifier circuit configured to convert the alternating current power source to a direct current;
a voltage converter circuit, including
a transformer including:
a primary coil on a primary side of the transformer, the primary coil being connected to the direct current voltage converted by the rectifier circuit; and
a secondary coil on a secondary side of the transformer; and
a switching element provided on the primary side of the transformer and configured to convert the direct current voltage converted by the rectifier circuit to a desired magnitude,
wherein the voltage converter circuit is configured to supply the voltage to the LEDs from the second side of the transformer;
a capacitor connected to a node on a path connecting the secondary coil of the transformer and the LEDs;
a control circuit provided on the primary side of the transformer and configured to control an on-duty of the switching element of the voltage converter circuit for supplying a predetermined current to the LEDs via the transformer; and
a current supply circuit connected between the rectifier circuit and the capacitor and configured to supply a starting current to the capacitor,
wherein the control circuit includes:
a feedback terminal connected to one of the LEDs and;
a power supply terminal which is separate and distinct from the feedback terminal, and
wherein the power supply terminal is connected to one end of the capacitor via the node, so as to drive a current to the power supply terminal using an accumulated charge of the capacitor.