Sanyo Electric Co., Ltd.

Shuhei Kawai

Takao Myono

Tatsuya Suzuki

Takashige Ogata

A driver circuit to obtain a current to drive a light emitting device is reduced in a patterning area and improved in efficiency. A positive power supply voltage Vdd is applied to an anode of a white LED, while a voltage &#x2212;0.5 Vdd from a &#x2212;0.5 Vdd generation circuit is applied to a cathode of the white LED through an N-channel type MOS transistor. The &#x2212;0.5 Vdd generation circuit generates the voltage &#x2212;0.5 Vdd according to a clock &#x3a6; from a clock generation circuit. A voltage of 1.5 Vdd is applied between the anode and the cathode of the white LED, as equivalent to a prior art. Since N-channel type MOS transistors are heavily used in the &#x2212;0.5 Vdd generation circuit, the driver circuit requires less patterning area to obtain the same amount of current to drive the LED as in the prior art. In addition, a parasitic capacitance is reduced to improve efficiency of the driver circuit.

Driver circuit

A leakage path through a parasitic diode in a charge transfer MOS transistor is cut off to prevent increase in the power consumption and loss of control of a charge pump circuit. A first charge transfer MOS transistor and a second charge transfer MOS transistor are N-channel type and are connected in series with each other. A ground electric potential VSS is supplied to a source of the first charge transfer MOS transistor as an input electric potential, and an output electric potential is obtained from an output terminal connected with a drain of the second charge transfer MOS transistor. A back gate of the first charge transfer MOS transistor is set by a first switching circuit to either an electric potential at a connecting node between the first and the second charge transfer MOS transistors or the ground electric potential VSS.

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Gunma, Japan

Shuhei Kawai