US 5,350,951 AGranted

Voltage change circuit for a microcomputer

AssigneeMitsubishi Denki Kabushiki Kaisha

InventorKiyoshi Adachi

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Abstract

A microcomputer including first, a voltage change circuit which includes circuitry for selecting one of two voltages applicable to a PROM and, second, leak current prevention circuitry for preventing a current from leaking from a first terminal at a first voltage through first and second switching elements to a second terminal. The leak current prevention circuitry can be a transistor whose source, drain and gate are tied to the first terminal, to the gate of the second switching element and to the second terminal, respectively. The leak current prevention circuitry operates to cut off the second switching element which the voltage at the second terminal is zero. The circuitry for selecting can be two series circuit, each consisting of a diode and two transistors. The series circuits are interconnected and responsive to a voltage selecting signal.

Claims3

Dependent claims

A voltage change circuit for a microcomputer comprising:

a first terminal driven at a first voltage;
a first switching element, coupled to said first terminal and to a common wire, for switching said first voltage to said common wire;
a second terminal driven at a second voltage, said second voltage being one of 0 volts and a voltage higher than said first voltage;
a second switching element, coupled to said second terminal and to said common wire, for switching said second voltage to said common wire, said second switching element having a control input;
and
selecting means, coupled to said first and second switching elements, for closing a selected one of said first and second switching elements, and
leak current preventing means, receiving said second voltage as input and coupled to said second switching element, for generating a leak current preventing signal for said control input of said second switching element, said leak current preventing signal for preventing said second switching element from closing when said second voltage is 0, preventing current from flowing to said second terminal through said second switching element.

4 more elements

Dependencies are inferred from the claim text.