US 5,856,756 AGranted

Internal voltage generating circuit

AssigneeOki Electric Industry Co., Ltd.

InventorsKatsuhiko Sasahara, Yuki Hashimoto

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Abstract

An internal voltage generating circuit for generating an internal voltage VINT from an input external voltage VEXT is provided to stabilize the internal voltage. When the external voltage VEXT is less than or equal to a first boundary voltage VT1 or a second boundary voltage VT2 (>VT1), a constant voltage VINTN independent on the external voltage VEXT, which is produced by a constant voltage generator is outputted therefrom. When the external voltage VEXT is greater than or equal to the first boundary voltage VT1 or the second boundary voltage VT2, a variable voltage (>VINTN) linearly increased with an increase in VEXT, which is produced by a variable voltage generator, is outputted therefrom. When a detecting means detects that the external voltage VEXT has been increased to VT2 or higher, the characteristic of the internal voltage is switched from a constant voltage characteristic to a variable voltage characteristic. On the other hand, when the detecting means detects that the external voltage VEXT has been reduced to VT1 or lower, the characteristic of the internal voltage is changed from the variable voltage characteristic to the constant voltage characteristic.

An internal voltage generating circuit for generating an internal voltage from an external voltage applied to an external terminal, the circuit comprising

a reference voltage generator for generating a reference voltage;
a constant voltage generator, coupled to the reference voltage generator, for generating a constant voltage based on the reference voltage;
a variable voltage generator for generating a variable voltage which is larger than the constant voltage and increases linearly with an increase in the external voltage;
an output circuit for outputting the internal voltage, wherein the generated internal voltage is the constant voltage when the external voltage is in a lower voltage range, and wherein the generated internal voltage is the variable voltage when the external voltage is in a upper voltage range higher than the lower voltage range, a boundary voltage being defined between the lower voltage range and the upper voltage range, the boundary voltage being a first boundary voltage when the internal voltage is the variable voltage and being a second boundary voltage higher than the first boundary voltage when the internal voltage is the constant voltage;
detecting circuit connected to the external terminal, for detecting the level of the external voltage, outputting a determination signal having a first logical value or a second logical value, changing the value of the determination signal from the first logical value to the second logical value when the detecting circuit detects that the level of the external voltage has risen from within the lower voltage range to at least the second boundary voltage, and changing the value of the determination signal from the second logical value to the first logical value when the detecting circuit detects that the level of the external voltage has been reduced from within the upper voltage range at least to the first boundary voltage;
and
a voltage circuit connected to the detecting circuit and the output circuit, for providing the constant voltage to the output circuit when the determination signal has the first logical value, and for providing the variable voltage to the output circuit when the determination signal has the second logical value.

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Abstract

Claims17