Semiconductor Components Industries, LLC

Shuhei Kawai

Feng Xu

Yoshio Fujimura

Tomoyuki Goto

Iwao Fukushi

Noriaki Okada

Masahiro Maruki

Kojima Hiroyuki

Hiroyuki Kojima

Kazuhiko Saito

A control circuit of a light-emitting element comprises a rectifying unit which full-wave rectifies an alternating current power supply, a clock generator which generates and outputs a clock signal (CLK), a first comparator which compares a comparison voltage (CS) corresponding to a current flowing to the light-emitting element and a reference voltage (REF), and a switching element which is set to an ON state in synchronization with the clock signal (CLK) and which is set to an OFF state when the comparison voltage (CS) becomes greater than the reference voltage (REF) at the first comparator, to switch the current flowing to the light-emitting element. In this structure, a period of the clock signal (CLK) generated in the clock generator is varied, to reduce or inhibit noise.

Control circuit of light emitting element

In accordance with an embodiment, a control circuit for controlling a light emitting diode includes a first switching circuit having first and second inputs and an output and a second switching circuit having at least first and second inputs and an output, the first input coupled to the second input of the first switching circuit. Another embodiment includes a method for reducing flicker by generating an adjusted rectified voltage in response to a TRIAC dimmer signal from a TRIAC dimmer and a switching current in response to the adjusted rectified voltage being greater than a first reference voltage. The switching current is decreased in response to the adjusted rectified voltage becoming less than the first reference voltage. The TRIAC dimmer is turned off in response to decreasing the switching current.

Method for mitigating flicker

In accordance with an embodiment, a light emitting element driving circuit includes a comparator having an input connected to smoothing circuit and an output connected to a voltage-dividing circuit through a transistor. A drain-to-source resistance of the transistor is connected in parallel with a portion of the voltage dividing circuit. An output signal of the voltage dividing circuit is connected to another comparator that generates a drive transistor drive signal. The drive transistor is connected to one or more light emitting elements. In accordance with another embodiment, a reference voltage is generated in response to a rectified signal and compared with a sense voltage to generate a drive signal that is used to drive the drive transistor. Light is emitted from the one or more light emitting elements in response to the drive signal and the rectified voltage being greater than the forward voltage drops of the one or more light emitting elements.

Light emitting element driving circuit

In a control circuit for a light-emitting device, a reference voltage generation circuit detects a full-wave rectified voltage and generates a first voltage as well as generating a second voltage by converting the rectified voltage into a DC voltage. A voltage corresponding to a difference between the first voltage and the second voltage or a voltage corresponding to a ratio of the first voltage to the second voltage is generated as a reference voltage by a subtraction circuit or by a division circuit, respectively. As a result, a change in amplitude of the reference voltage can be suppressed when amplitude of the rectified voltage is varied due to a variation in an AC input voltage supplied from an AC power supply.

Light-emitting device control circuit

A switching-control circuit to control switching of a transistor whose input electrode is applied with an input voltage, and turn off the transistor, when an output current from the transistor is greater than a reference current, includes: a reference-voltage-generating circuit to generate such a first-reference voltage that the reference current is reduced with reduction in an output voltage; a comparing circuit to compare a voltage corresponding to the output current with the first-reference voltage; and a driving circuit to turn on/off the transistor based on a feedback voltage corresponding to the output voltage and a second reference voltage corresponding to a target level so that the output voltage reaches the target level, when the comparing circuit determines that the output current is smaller than the reference current, and turn off the transistor when the comparing circuit determines that the output current is greater than the reference current.

Switching control circuit

Control circuit of light-emitting element

A TRIAC dimmer gates an AC waveform from an AC power source in proportion to a control signal and outputs a TRIAC pulse having part of the waveform missing. The TRIAC pulse is rectified and is applied to an LED array and the drive current flowing to the LED array is detected at a current detection resistor. The drive current value and a predetermined value are compared at a comparator and in accordance with the comparison result thereof the control transistor is turned off. Then, the TRIAC pulse is converted to a DC voltage signal and in accordance with the obtained DC voltage signal the drive current value or the predetermined value input by the comparator are changed. Furthermore, instead of the TRIAC pulse, a PWM pulse supplied from an external source may also be utilized.

Growing community of inventors

Ota, Japan

Shuhei Kawai