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Protection method against reverse current from AC adapter to Docking connector

IP.com Disclosure Number: IPCOM000011904D
Original Publication Date: 2003-Mar-25
Included in the Prior Art Database: 2003-Mar-25
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Abstract

Disclosed is a circuit for a protection method against reverse current from AC adapter to Docking-connector. Notebook PC has a Docking-connector to connect the Docking-Station to expand the function of a Notebook PC. When the Docking-Station is not attached, the AC adapter voltage is applied to the power-supply-pins which exist inside the Docking-connector. A mechanical shutter was needed to the Notebook PC to hide the Docking-connector for safety but the circuit can prevent the danger by a electrical method without a mechanical shutter.

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Protection method against reverse current from AC adapter to Docking connector

In this invention;
(1) FET is added between the Notebook PC's AC adapter connector and the Docking-connector to prevent the reverse current.
(2) A detect signal which controls the reverse-current-protection FET, is generated when the Notebook PC and the Docking-Station are connected. This signal is made when one of the pins in the Docking-connector connects with the Ground(GND).
(3) While the Docking-Station is not attached, the detect signal is inactive and the Docking-connector is electrically separated from the AC adapter.
(4) When the Docking-Station is attached, the detect signal generates and the reverse-current-protect FET is activated. Thus, it enables the Docking-Station to supply power for the Notebook PC.
(5) There is a danger of FET smoke and fire in power line because of the FET's incomplete activation which is caused by the connector's bad electrical contact. A protector is added for the perfect solution for this problem.
(6) The protection function detects the abnormal heat by a thermistor, which is placed near the reverse-current-protection FET, and shuts down the system by activating the thermal protection circuit. It forces all the FETs in the power line to stop at once and prevents the reverse-current-protection FETs from smoke and fire.

In summary;
(1) Protect the reverse current from the AC adapter to the Docking-connector in the Notebook PC.
(2) Reduce the mechanical shutter which was necessary to hide the power-supply-pins.
(3) Since there is no need to use the mechanical shutter , it mekes the Notebook PC thinner.
(4) Electrical separation is safer solution because in case using mechanical shutter, it is impossible to protect the reverse-direction current when the user opened the shutter deliberately.

A reverse-current protection FET(Q8) is added be...