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High Voltage AC Adapter Detection Circuit

IP.com Disclosure Number: IPCOM000011903D
Original Publication Date: 2003-Mar-25
Included in the Prior Art Database: 2003-Mar-25
Document File: 2 page(s) / 16K

Publishing Venue

IBM

Abstract

Generally, an electric appliance like notebook PC uses AC adapter for power supply. A user should use an appropriate one, but, if AC adapter output plug and electric appliance connector are all-purpose type, there is some possibility that a user can attach another AC adapter which isn't appropriate for use. In that case, if non-appropriate AC adapter is higher voltage output type than appropriate one, electrical parts of appliance may be damaged by de-rating voltage over. Especially, a capacitor may burn. To solve this concern, a zener diode is used on power line which is connected to AC adapter. It can regulate power line voltage, and supply regulated voltage to electrical circuit even if a user attach non-appropriate AC adapter to appliance. But, this method causes power loss, because a zener diode always consumes power. In worst case, a zener diode is broken by over stress.

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High Voltage AC Adapter Detection Circuit

This invention can detect it when an high voltage output AC adapter was attached to electric appliance, and prevent that high voltage is supplied to an electrical circuit.

This invention consists of two circuit.
1) A hardware which can detect high voltage that it is supplied by attached non-appropriate AC adapter to appliance.
2) A hardware which can prevent that high voltage is supplied to an electrical circuit.

<General Circuit> A zener diode (D1) is used on input power line, DC-IN, and it is connected to AC adapter. It can regulate power line voltage, and supply regulated voltage to electrical circuit even if a user attach non-appropriate AC adapter to appliance.

In-Rush Current Protection Circuit is a general circuit to prevent in-rush current when AC Adapter is attached to electric appliance.

<Invention> This invention is explained as follows.

An example circuit can detect 25V, and prevent that 25V is supplied to VPOWERRAIL, when over 25V output type AC Adapter is attached to electric appliance.

(1) Explanation the hardware which detects that high voltage output type AC Adapter was attached to electric appliance.

Q3, R3, R4 detect DC-IN voltage which is supplied by AC Adapter If Q3 gate threshold voltage, Vgs_th characteristic, is 0.8Vmin, Q3 turns on when DC-IN voltage is over 25V.

If DC-IN voltage is under 25V, Q3 is off state.

(2) Explanation the hardware which prevents that high voltage is supplied to an electrical...