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US4806789A
Expired / Lapsed
US
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Power select circuit
Assignee: Toshiba Corp
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Filing: 1988-03-29
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Granted: 1989-02-21
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Expires: 2008-03-29
Abstract
Abstract A first node is connected to an external power source via a switch. A second node is connected to an internal power source whose voltage is lower than that of the external power source. The first and second nodes are connected to an output node via first and second MOSFET switches. The output node is connected to a semiconductor circuit. The potentials at the first and second nodes are compared with each other by a voltage comparator connected between the output node and ground. A MOSFET is quickly turned on and off in response to the potential at the first node.
Inventors
- 👤 Kazuhisa Sakihama
- 👤 Takuya Fujimoto
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 15:57
CPC Classifications
H; H03; H03K; H03K17/00; H03K17/51; H03K17/56; H03K17/60; H02; H02M; H02M3/00; H02M3/02; H02M3/04; H02M3/10; H02M3/145; H02M3/155; H02M3/156; H02M3/158; G; G11; G11C; G11C5/00; G11C5/14; G11C5/141; G11C5/143
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
252 words
A power source select circuit comprising: first MOSFET whose source is connected to a first power voltage input terminal, and drain and back gate are connected to a power voltage output terminal; second MOSFET whose source is connected to a second power voltage input terminal, and drain and back gate are connected to said power voltage output terminal; a voltage comparator for comparing the potentials at said first and second power voltage input terminals, and for determining the output value on the basis of the comparison result; a first means, connected to said first MOSFET and said voltage comparator for rendering said first MOSFET conductive when a potential difference between said first power voltage input terminal and ground, is larger than that between said second power voltage input terminal and ground, a second means, connected to said second MOSFET and said voltage comparator, for rendering said second MOSFET conductive when a potential difference between said first power voltage input terminal and ground is smaller than that between said second power voltage input terminal and ground wherein said voltage comparator further comprises: a third MOSFET for blocking the flow of a constant current in said voltage comparator when said first power voltage input terminal is at a potential near ground potential; and a fourth MOSFET connected to said first power voltage input terminal and the output of said voltage comparator for stabilizing the output voltage of said voltage comparator when said first power voltage input terminal is at a potential near ground potential.
Claim 2
Dependent Claim
252 words
A power source select circuit comprising: first MOSFET whose source is connected to a first power voltage input terminal, and drain and back gate are connected to a power voltage output terminal; second MOSFET whose source is connected to a second power voltage input terminal, and drain and back gate are connected to said power voltage output terminal; a voltage comparator for comparing the potentials at said first and second power voltage input terminals, and for determining the output value on the basis of the comparison result; a first means, connected to said first MOSFET and said voltage comparator for rendering said first MOSFET conductive when a potential difference between said first power voltage input terminal and ground, is larger than that between said second power voltage input terminal and ground, a second means, connected to said second MOSFET and said voltage comparator, for rendering said second MOSFET conductive when a potential difference between said first power voltage input terminal and ground is smaller than that between said second power voltage input terminal and ground wherein said voltage comparator further comprises: a third MOSFET for blocking the flow of a constant current in said voltage comparator when said first power voltage input terminal is at a potential near ground potential; and a fourth MOSFET connected to said first power voltage input terminal and the output of said voltage comparator for stabilizing the output voltage of said voltage comparator when said first power voltage input terminal is at a potential near ground potential.
Claim 3
Dependent Claim
35 words
The power source select circuit according to claim 1, in which said second MOSFET is used as a switch interconnected between an internal power source and a semiconductor circuit through said power voltage output terminal.
Claim 4
Dependent Claim
34 words
The power source select circuit according to claim 1, in which the potential at said first power voltage input terminal is set to be higher than that at said second power voltage input terminal.
Claim 5
Dependent Claim
25 words
The power source select circuit according to claim 1, further comprising a resistive means connected between said first power voltage input terminal and ground potential.
Claim 6
Dependent Claim
30 words
The power source select circuit according to claim 1, in which the source of said first MOSFET is connected to said first power voltage input terminal via an ON/OFF switch.
Claim 7
Dependent Claim
30 words
The power source select circuit according to claim 4, in which the source of said first MOSFET is connected to said first power voltage input terminal via an ON/OFF switch.
Claim 8
Dependent Claim
29 words
The power source select circuit according to claim 1, in which said voltage comparator is connected between said first power voltage input terminal and ground through said third MOSFET.
Claim 9
Dependent Claim
25 words
The power source select circuit according to claim 7, in which said third MOSFET includes a gate connected to said first power voltage input terminal.
Claim 10
Dependent Claim
44 words
The power source select circuit according to claim 8, in which said fourth MOSFET includes a source connected to the power voltage output terminal and a drain connected to an output of a circuit of which a current is blocked by the third MOSFET.
Claim 11
Dependent Claim
34 words
The power source select circuit according to claim 9, in which said fourth MOSFET includes a gate which is connected, together with the gate of said third MOSFET, to first power voltage input terminal.
References Cited (Backward Citations)
US4527076A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-02-21 | 1992-08-22 | 1993-02-21 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-02-21 | 1996-08-22 | 1997-02-21 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-02-21 | 2000-08-22 | 2001-02-21 | $7700.00 | Window Closed / Lapsed |