External power source to main battery power sources switch

Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail

Patent

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Details

455127, 307 66, H04B 104

Patent

active

058624937

ABSTRACT:
A switching circuit (30) in a portable telephone connects a gate of a field-effect transistor (Q1) to a voltage below the transistor's gate threshold voltage when the voltage at a first power source terminal (B) falls below a threshold voltage, thus disconnecting the first power source terminal (B) from a portable telephone power input terminal (B+) and connecting a second power source terminal (A) to the power input terminal (B+). The threshold voltage is set at a voltage above the minimum supply voltage of the portable telephone. The first power source terminal may be connected to a main battery and the second power source terminal may be connected to an adapter such as a battery eliminator adapter, hands-free adapter, or mobile transceiver adapter. This switching circuit prevents a call in progress from being disconnected when power sources are exchanged during a GSM burst.

REFERENCES:
patent: 4451742 (1984-05-01), Aswell
patent: 4962523 (1990-10-01), Tanaka
patent: 5036532 (1991-07-01), Metroka et al.
patent: 5335263 (1994-08-01), Tsunehiro et al.
patent: 5498913 (1996-03-01), Moritani
patent: 5511234 (1996-04-01), Ha
patent: 5608273 (1997-03-01), Bartlett et al.

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