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Power source switchover method for high voltage battery

IP.com Disclosure Number: IPCOM000012591D
Original Publication Date: 2003-May-19
Included in the Prior Art Database: 2003-May-19
Document File: 3 page(s) / 14K

Publishing Venue

IBM

Abstract

A battery for Notebook PC is classified by the number of internal battery cells which are connected in series. And battery output voltage is set by it. As for Li+ battery, maximum output voltage of 3S battery (three cells) is 12.6V, and in case of 4S (four cells) battery, it is 16.8V.

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Power source switchover method for high voltage battery

The following is the method of switchover of power supply in the case of "maximum battery voltage is higher than AC adapter voltage".

To support "maximum battery voltage is higher than AC adapter voltage", it should be prepared six circuits.
[1] A FET (or switch) for dividing the route from AC adapter to the system, and a FET (or switch) for dividing the route from battery to the system.
[2] A circuit which can detect the existence of AC adapter, and outputs the result.
[3] A circuit which receives the result of [2], and controls FETs of [1].
[4] A FET which can prevent the leakage voltage from battery when AC adapter supplies power to the system.
[5] A circuit which judges if AC adapter can supply power, and outputs the result.
[6] A circuit which receives the control signal of [3] and the result of [5], and controls FET of [4].

An example circuit is shown as Figure 1. As the definition, AC adatper is 16.0V and 4S battery voltage is 16.8V.

1) Explanation for [1] To divide power source route, two FETs should be prepared. One is for dividing the route from AC adapter to the system, and it is Q1, DCIN FET. The other is for dividing the route from battery to the system, and it is Q2, BATTIN FET.

Power from AC adapter is supplied to system through Q1, and power from battery is supplied through

Q2.

The direction of the body diode should be from AC adapter (battery) to the system. It can prevent AC adapter voltage flows to battery, and battery output voltage flows to AC adapter.

2) Explanation for [2] U1, AC adapter detection circuit, detects the existence of AC adapter, and outputs the result to

-EXTPWR.

When AC adapter is attached to the system, -EXTPWR is Low. And when AC adapter is removed, -EXTPWR is High.

3) Explanation for [3] U2, Load Switch Controller, recieves -EXTPWR, and outputs DCIN_DRV and BATOUT_DRV. DCIN_DRV controls Q1, and BATOUT_DRV controls Q2.

When -EXTPWR is Low (it means AC adapter is attached to the system), U2 outputs High to

   DCIN_DRV, and outputs Low to BATOUT_DRV. As the result, Q1 turns on and Q2 turns off. So, Power for the system is supplied from AC adapter.

When -EXTPWR is High (it means AC adapter is removed from the system), U2 outputs Low to

   DCIN_DRV, and outputs High to BATOUT_DRV. As the result, Q1 turns off and Q2 turns on. So, Power for the system is supplied from Battery.

In the case of "maximum battery output voltage is lower than AC adapter voltage", the control method of switchover of power supply can design
by using [1], [2] and [3].

But, in the case of "maximum battery output voltage is higher than AC adapter voltage", it should add the following circuit, [4], [5] and [6].

1

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4) Explanation for [4] A FET Q3, 4S_support, divides power source route from battery to the system.

4S battery output voltage is higher than 16.0V AC adapter. So, battery voltage flows to the system through the body diode of Q2, even if AC adapter is attached to...