Patent ID: 7453711

Claim:
A step-up voltage supply unit comprising: a first charge pump unit having a first capacitor, a first double throw switch having a common terminal coupled to one end of said first capacitor, a first terminal coupled to an input terminal whereto input voltage is supplied, and a second terminal coupled to the ground, and a second double-throw switch having a common terminal coupled to another end of said first capacitor, a first terminal, and a second terminal coupled to said input terminal, said second double throw switch operated by the same control signal as said first double throw switch, a first step-up voltage outputting switch for outputting a first step-up voltage from another end of said first capacitor, a second stage charge pump unit having a second capacitor, a third double-throw switch having a common terminal coupled to one end of said second capacitor, a first terminal coupled to the first terminal of said second double throw switch, and a second terminal coupled to the ground, and a fourth double-throw switch having a common terminal coupled to another end of said second capacitor, a first terminal, and a second terminal coupled to said input terminal, said fourth double throw switch operated by the same control signal as said third double throw switch, a second step-up voltage outputting switch for outputting a second step-up voltage from another end of said second capacitor, a last stage charge pump unit having a third capacitor, a fifth double-throw switch having a common terminal coupled to one end of said third capacitor, a first terminal coupled to the first terminal of said fourth double throw switch, and a second terminal coupled to the ground, and a sixth double-throw switch having a common terminal coupled to another end of said third capacitor, a first terminal, and a second terminal coupled to said input terminal, said sixth double throw switch operated by the same control signal as said fifth double throw switch, and a control circuit for outputting an output voltage control signal for synchronizing said first and second double throw switches and said first step-up voltage outputting switch, and switching on and off, when outputting a first step-up voltage of said first stage charge pump unit, synchronizing said first, second, third, and fourth double throw switches and said second step-up voltage outputting switch, and switching on and off, when outputting a second step-up voltage of said second stage charge pump unit, and switching on and off said first, second, third, fourth, fifth and sixth double throw switches and said second step-up voltage outputting switch, when outputting a third step-up voltage of said last stage charge pump unit, wherein said step-up voltage supply unit outputs a third step-up voltage from the first terminal of said sixth double throw switch of said last stage charge pump unit without passing through any output switch.