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Constant voltage generating circuit having step-up circuit

  • US 5,499,183 A
  • Filed: 11/30/1994
  • Issued: 03/12/1996
  • Est. Priority Date: 11/30/1993
  • Status: Expired due to Fees
First Claim
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1. A constant voltage generating circuit comprising:

  • a step-up circuit of a charge pump type for generating a predetermined high voltage by action of a charge pumping in response to a clock signal;

    a high voltage output terminal connected to an output of said step-up circuit for outputting the generated high voltage;

    a clamp circuit connected between said high voltage output terminal and a first voltage supply terminal, said clamp circuit including a clamp element and a first MOSFET of a first channel type having a drain and a gate interconnected to each other, said first MOSFET and said clamp element being connected in series between said high voltage output terminal and said first voltage supply terminal;

    a charge detecting circuit reset by a reset signal and operating to generate a charge detection signal when a current having flowed through said clamp circuit reaches a predetermined value, said charge detecting circuit including a second MOSFET of said first channel type having a source connected to said high voltage output terminal and a gate connected to the gate and the drain of said first MOSFET, a third MOSFET of a second channel type opposite to said first channel type, having a gate and a drain connected in common to a drain of said second MOSFET, and a source connected to said first voltage supply terminal, a fourth MOSFET of said first channel type having a source connected to a second voltage supply terminal and a gate connected to receive an inverted signal of said reset signal, a fifth MOSFET of said second channel type having a drain connected to a drain of said fourth MOSFET, a gate connected to said gate of third MOSFET, and a source connected to said first voltage supply terminal, a capacitor connected between said drain of said fifth MOSFET and said first voltage supply terminal, an invertor having an input connected to said drain of said fifth MOSFET and an output for outputting said charge detection signal, and a sixth MOSFET of said second channel type having a drain connected to said drain of said fifth MOSFET, a gate connected to said output of said invertor, and a source connected to said first voltage supply terminal;

    a clock control circuit responding to said charge detection signal so as to stop application of said clock signal to said step-up circuit.

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