Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: An LED drive circuit includes a resistor for setting a constant current, a switching power supply circuit for outputting a DC output voltage and a constant-current power supply circuit that receives the DC output voltage and that outputs the constant current to drive the LED. The LED drive circuit reduces, in dim light mode in which the LED is driven by a current less than that in normal light mode, at least one of the oscillation frequencies of an oscillation circuit included in the switching power supply circuit and an oscillation circuit included in the constant-current power supply circuit as compared with the normal light mode.

Abstract: An illumination light emitting element driving circuit includes a power factor improving circuit (2). The power factor improving circuit (2), when a load (illumination light emitting diode 17) of the illumination light emitting element driving circuit is light, performs operation (including stopping the operation) different from operation performed when the load is not light to thereby make power consumption lower than power consumption during the operation performed when the load is not light.

Abstract: To reduce the electric power wasted in an overvoltage protection circuit, a regulator IC 100 incorporates an overvoltage protection circuit 105 that stops the output operation of the regulator when the output voltage Vo becomes higher than a predetermined threshold voltage Vth1. The overvoltage protection circuit 105 includes switch means FET3 that turns on and off the overvoltage protection operation thereof according to a predetermined control signal.

Abstract: 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.

Abstract: 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.

Abstract: To reduce the electric power wasted in an overvoltage protection circuit, a regulator IC 100 incorporates an overvoltage protection circuit 105 that stops the output operation of the regulator when the output voltage Vo becomes higher than a predetermined threshold voltage Vth1. The overvoltage protection circuit 105 includes switch means FET3 that turns on and off the overvoltage protection operation thereof according to a predetermined control signal.

Abstract: 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.

Abstract: 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.

Abstract: A stabilized power supply-use device of the present invention, which is mounted on a switching power supply, is an IC into which power transistors, a control circuit for controlling a base current of the power transistors, and other electronic components are formed, and an overcurrent detecting resistor connected in series with the power transistor is realized by a resister provided externally to the IC. Therefore, as compared to the overcurrent detecting resistor being made up of aluminum wiring patterns inside the IC, the overcurrent detecting resistor of the present invention dramatically decreases variations in value of resistance, whereby it is possible to improve an accuracy of voltage detection and to arbitrarily set a value of resistance. This eliminates the need for a needlessly increased input power capacity in a test based on safety standard and other tests, thereby enabling a switching power supply manufactured at a lower cost.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.