The assignee for this patent, patent number 8766561, is
Reporters obtained the following quote from the background information supplied by the inventors: "The present invention relates generally to lighting devices for driving a semiconductor light-emitting element such as a light-emitting diode (LED), and associated illumination fixtures. More particularly, the present invention relates to LED lighting devices with an output impedance element and associated control circuitry for stabilizing an optical output.
"Lighting devices for driving a semiconductor light-emitting element are known in the art which can control an optical (lighting) output across a wide range, from a very weak optical output to an optical output of a rated current. One example includes a circuit configuration with a current divider connected in parallel with the semiconductor light-emitting element and diverting a driving current flowing to the semiconductor light-emitting element. A resistor, a current regulation diode or a thermistor may be used as specific examples of the current divider.
"A typical application of such a technique, such as may be used in an inspection light source for a solid-state image sensing element, includes an LED driver circuit for sending a relatively small current to an LED with high accuracy. The driver circuit may include a D/A converter and an analog driver. Such an LED driver circuit is relatively expensive and inefficient, making it unsuitable for many illumination fixtures as would be used in homes and offices. Further, power losses due to the current divider are simply disregarded.
"In another example, a switching power supply device as known in the art for controlling a semiconductor light-emitting element across a wide range of lighting outputs performs constant current control for outputs near a rated current (high end of the lighting range) so as to match an output current of a switching power supply with a target current value, and performs constant voltage control for outputs at the low end of the lighting range so as to match an output voltage of the switching power supply with a target voltage value.
"According to this technique, as compared to the first technique described above, power loss is decreased due to the switching power supply device. However, because the technique requires both a feedback control system for constant current control used in the vicinity of the rated current and a feedback control system for constant voltage control used in the very weak optical output, the circuit configuration disadvantageously becomes complicated and expensive."
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "An object of the present invention is to provide a semiconductor light-emitting element lighting device which is relatively inexpensive but yields stable lighting control across a wide range from a rated current (high end of the lighting output range) to the very weak optical output (low end of the lighting output range) of a semiconductor light-emitting element, such as an LED.
"In an embodiment of the present invention, a lighting device is provided with output impedance control to stabilize an optical output across a wide current range. A switching power supply generates the output current, with switching control circuitry to determine switching frequency and an on-duty time for an associated switch, and to turn on/off the switch according to the determined frequency and on-duty time. An impedance element is coupled across output terminals for the lighting device, with an impedance value set so that the load current is larger than the current flowing to the impedance element at maximum on-duty time of the switch and the current flowing to the impedance element is larger than the load current at minimum on-duty time. The impedance element may be a variable impedance element, wherein an impedance control circuit adjusts the variable impedance such that an impedance value for minimum on-duty time of the switch is smaller than that for a maximum on-duty time.
"According to the present invention, even when the lighting device for driving the semiconductor light-emitting element by the switching power supply circuit has a limitation in the control range of the on-duty time of the switching element, the current flowing to the semiconductor light-emitting element can be stably controlled in a wide range and lighting can be stably controlled from the vicinity of the rated current to a very weak optical output."
For more information, see this patent: Esaki, Sana;
Keywords for this news article include: Electronics, Semiconductor,
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