Sharp Kabushiki Kaisha Corporation

Katsumi Inaba

Hirohisa Warita

Tomohiro Suzuki

Atsushi Kanamori

Toshiyuki Fujita

Naoki Fukunaga

Hiroyuki Shoji

Mitsuru Mariyama

Yasuhiro Maruyama

Masakazu Ikeda

Tsutomu Satoh

Kohji Hisakawa

Tsutomu Satou

An LED drive circuit is an LED dive circuit that receives an alternating voltage to drive an LED, and includes a current remove portion that removes a current from a current supply line that supplies an LED drive current to the LED. If an input current to the LED drive circuit is an unnecessary current, the LED does not light because of current removal by the current remove portion. If the input current to the LED drive circuit turns into the LED drive current from the unnecessary current, the current remove portion decreases the amount of current removed.

LED drive circuit, LED illumination component, LED illumination device, and LED illumination system

To reduce the electric power wasted in an overvoltage protection circuit, a regulator ICincorporates an overvoltage protection circuitthat stops the output operation of the regulator when the output voltage Vo becomes higher than a predetermined threshold voltage Vth. The overvoltage protection circuitincludes switch means FETthat turns on and off the overvoltage protection operation thereof according to a predetermined control signal.

Regulator and electronic apparatus therewith

In a switching power supply circuit, completion of discharging of a capacitance provided in a soft-start circuit requires a period longer than a cycle with which an activating/deactivating portion switches switching control operation of a driving portion (which performs switching control to turn on/off a switching device provided in a stepping-up DC-DC converter) between an activated state and a deactivated state. Moreover, the soft-start circuit is prevented from performing soft-start operation until discharging of the capacitance is completed. Furthermore, the activating/deactivating portion prevents the switching control operation of the driving portion from being switched from the deactivated state to the activated state from a time point that constant voltage feeding operation of a constant voltage portion (which feeds, to a comparing portion that sends an output signal to the driving portion, a constant voltage as the drive voltage) is switched from the deactivated state to the activated state until a predetermined period elapses.

Switching power supply circuit and electronic apparatus provided therewith

The voltage booster type switching power supply circuit is provided with a drive circuit for controlling a switching element, a start/stop circuit for turning the drive circuit on and off according to a brightness control signal for adjusting a brightness of a light source of a liquid crystal display device, an output voltage detection circuit for detecting whether the output voltage is greater than a predetermined voltage and feeding out a result as a comparison result signal, and a soft-start circuit that does not operate when the comparison result signal is active on the rising edge of the brightness control signal, and that operates so as to increase the output voltage gradually when the comparison result signal is inactive on the rising edge of the brightness control signal.

Power supply circuit having soft start

A switch selects an inputted direct-current voltage at rising of the inputted direct-current voltage, and selects an outputted voltage after the rising of the outputted voltage, for an input to the constant voltage circuit which supplies power to a control circuit. Therefore, once the step-up operation is carried out in a state where the inputted direct-current voltage is at or greater than the operation voltage of the control circuit, the power source of the control circuit is switched to the side of the outputted voltage which has been increased even when the inputted direct-current voltage decreases. Consequently, the voltage of the power source of the control circuit stays at or greater than the operation voltage of the control circuit, and the stabilized power circuit can carry out a proper operation. This function prevents the operation from being inadequate due to a decrease of the inputted direct-current voltage, and a proper operation can be carried out. Further, a signal of the hysteresis comparator is used for the switching for an input of the constant voltage circuit which supplies the power source to the control section. Thus, the circuit can be simplified.

Switched-capacitor-type stabilized power circuit

A control section controls a switch to a charge period so as to charge a voltage-increasing capacitor at a start up. Then, the control section controls the switch to a voltage-increasing period so as to increase a voltage by a voltage-increasing capacitor and charges the output capacitor. The switching section alternately switches the charge period and the voltage-increasing period so that the charged voltage of the output capacitor, i.e., the output voltage is always stabilized within a range of the output voltage in a steady state. Here, a soft start circuit controls the switching section to carry out the switching operation so that the charged voltage always becomes not more than the output voltage in the steady state at the start-up.

Stabilized power unit

In the regulated power supply circuit, an overcurrent detection circuit detects the flow of an overcurrent through a transistor acting as an output control element and supplies a result of the detection to a cut-off operation prohibition circuit. During non-startup time of the regulated power supply circuit, the cut-off operation prohibition circuit simply relays a result of the overcurrent detection circuit detecting an overcurrent to a cut-off circuit without introducing any changes to the result. The cut-off circuit increases a base potential of the transistor according to the result of the detection of an overcurrent to cut off the output of the transistor. It is ensured that the output voltage rises even if the overcurrent detection circuit has activated the cut-off circuit upon detection of the overcurrent temporarily passing through the transistor during a startup. Therefore, the cut-off operation prohibition circuit prohibits the cut-off circuit from performing the cut-off operation from the outset to the end of the startup. Hence, a regulated power supply circuit can be provided which, even if an overcurrent is detected, develops no loss in the transistor during non-startup time.

Growing community of inventors

Tondabayashi, Japan

Katsumi Inaba