Rohm Co., Ltd.

Shogo Hachiya

Kiyotaka Umemoto

Masaru Sakai

A power supply apparatus includes a switching regulator, a linear regulator, a timer circuit, a control circuit, an inverter, and a switch. The power supply apparatus is a step-down type DC-DC converter which steps down an input voltage inputted to an input terminal and then outputs an output voltage, which has been stepped down, to an output terminal. The timer circuit counts the time elapsed from when a start of the power supply apparatus is instructed by a control signal, and sets an output signal to a high level at a lapse of a predetermined time. When the output signal goes to the high level, the switch turns on and the output voltage is supplied to a power supply terminal of the control circuit.

Power supply

A control signal generating circuit () comprises a comparator () for comparing an output voltage Vwith a reference voltage outputted from a reference voltage source (), a flipflop () set by the output of the comparator (), and a pulse control circuit () which receives an input voltage V, a reference voltage V, and the inverted output of the flipflop (), sets the on time in accordance with the ratio between the input voltage Vand the reference voltage V, and resets the flipflop () when the on time elapses after the output pulse of the flipflop () rises. The output pulse of the flipflop () is outputted as a control signal into a driver logic circuit (). The driver logic circuit () performs on/off control of NMOSs () according to the control signal. Thus, a switching regulator capable of operating at high speed can be realized.

Switching regulator

A DC/DC converter in which the DC output set voltage can be raised includes a switching transistor arranged to input an external power supply voltage, a smoothing circuit, a switching control circuit to which the internal power supply voltage is supplied and arranged to control the switching transistor, a comparison circuit arranged to compare the DC output voltage with a first reference voltage and to output a selecting signal, first and second linear transistors arranged to input the external power supply voltage or DC output voltage in accordance with the selecting signal, and to output the voltage according to the internal power supply control voltage as the internal power supply voltage, and an error amplification circuit arranged to input the internal power supply voltage, compare the internal power supply voltage with the second reference voltage, amplify the error thereof, and output the internal power supply control voltage.

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Kyoto, Japan

Shogo Hachiya