Capacitor regulated high efficiency driver for a light emitting diode
AssigneeInternational Business Machines Corporation
InventorKai D. Feng
Life of this patent
Estimating the term…
Abstract
A high efficiency light emitting diode (LED) driver circuit utilizes a capacitor to regulate the LED driving current. The voltage across the capacitor is monitored to maintain a preselected low threshold voltage on the capacitor, which determines the LED optical emission intensity. The capacitor provides the LED driver current by discharging through the LED during transmission intervals, and the power supply for the device is used only to maintain the capacitor charge level. The LED driver circuit accordingly operates at high efficiency with low power consumption. The LED driver current can be regulated by changing the low and high threshold voltages of the capacitor pump controller, thereby to control the optical intensity of the LED.
Claims20
A driver circuit for a light emitting diode in an optical transmitter which converts an electrical signal into an optical signal, comprising:
- a charge switch;
- a capacitor having a first side connected to a higher voltage terminal of a power supply through said charge switch;
- a discharge switch coupled to a lower voltage terminal of said power supply, a second side of the capacitor being connected to said lower voltage terminal of the power supply, the anode of the light emitting diode being connected to a connection point of the charge switch and the capacitor, the cathode of the light emitting diode being connected to said lower voltage terminal of the power supply through said discharge switch;
- and
- a controller for closing the charge switch to charge the capacitor when a voltage on the capacitor reaches a preset low voltage threshold and for opening the charge switch when the voltage on the capacitor reaches a preset high voltage threshold,
- wherein the discharge switch is closed responsive to an intensity of the electrical signal and the capacitor thereby discharges through the light emitting diode to emit an optical signal corresponding to the electrical signal.
An optical transmitter, comprising:
- a light emitting diode;
- and
- a driver circuit for activating the light emitting diode responsive to an electrical signal, the driver circuit comprising:
- a charge switch;
- a capacitor having a first side connected to a higher voltage terminal of a power supply through said charge switch;
- a discharge switch coupled to a lower voltage terminal of said power supply, a second side of the capacitor being connected to the lower voltage terminal of the power supply, the anode of the light emitting diode being connected to a connection point of the charge switch and the capacitor, the cathode of the light emitting diode being connected to the lower voltage terminal of the power supply through said discharge switch;
- and
- a controller for closing the charge switch to charge the capacitor when a voltage on the capacitor reaches a preset low voltage threshold and for opening the charge switch when the voltage on the capacitor reaches a preset high voltage threshold,
- wherein the discharge switch is closed responsive to an intensity of the electrical signal and the capacitor thereby discharges through the light emitting diode to emit an optical signal corresponding to the electrical signal.
A circuit for a light emitting diode, comprising:
- a first switch;
- a charge storage device having a first side connected to a higher voltage terminal of a power supply through said first switch;
- a second switch coupled to a lower voltage terminal of said power supply, a second side of the charge storage device being connected to the lower voltage terminal of the power supply, the anode of the light emitting diode being connected to a connection point of the first switch and the charge storage device, the cathode of the light emitting diode being connected to said lower voltage terminal of the power supply through said second switch;
- and
- a controller for closing the first switch to charge the charge storage device when a voltage on the charge storage device reaches a preset low voltage threshold and for opening the first switch when the voltage on the charge storage device reaches a preset high voltage threshold.
Dependencies are inferred from the claim text.