# US 5,705,911 A · Charging circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,705,911 A - Document ID: US5705911A - Status: Granted - Kind: A - Application number: 08/757,453 - Filed: 1996-11-27 - Granted: 1998-01-06 - Earliest claimed: 1995-11-30 - Assignees: Sanyo Electric Co., Ltd. - Inventors: Mikitaka Tamai - Web page: https://patentgrep.com/patent/US5705911A ## CPC - H02J 7/663: {using battery or load disconnect circuits (H02J9/002 takes precedence)} - H02J 7/65: against overtemperature - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY ## Abstract An over-charge protection FET and an over-discharge protection FET are connected in series with the rechargeable battery and turned ON or OFF by a control circuit. An ON-OFF switching device is connected between G and S of the over-charge protection FET and controlled by an output signal from the control circuit. An over-charge protection FET drain voltage input circuit is connected to the input side of the ON-OFF switching device. When the drain voltage of the over-charge protection FET is high, the input circuit sets the ON-OFF switching device to the ON state to forcibly set the over-charge protection FET to the OFF state. ## Claims ### Claim 1 A charging circuit for charging a rechargeable battery comprising: (1) an over-charge protection FET having a gate and a source, connected in series with the rechargeable battery, to protect the rechargeable battery from excessive charge; (2) an over-discharge protection FET connected in series with the rechargeable battery and the over-charge protection FET, to protect the rechargeable battery from excessive discharge; (3) a control circuit to prevent excessive charge and discharge of the rechargeable battery by detecting rechargeable battery voltage and controlling the ON-OFF state of the over-charge protection FET and the over-discharge protection FET; (4) an ON-OFF switching device having an input side, connected between the gate and the source of the over-charge protection FET and controlled by an output signal from the control circuit; and (5) a drain voltage input circuit connected to the input side of the ON-OFF switching device, which switches the ON-OFF switching device to the ON state when the drain voltage of the over-charge protection FET is high to forcibly maintain the over-charge protection FET in the OFF state. ### Claim 2 (depends on 1) A charging circuit as recited in claim 1 wherein the ON-OFF switching device is a bipolar transistor. ### Claim 3 (depends on 1) A charging circuit as recited in claim 1 wherein the over-charge protection FET is connected to the negative side of the rechargeable battery through the over-discharge protection FET. ### Claim 4 (depends on 1) A charging circuit as recited in claim 1 wherein the input circuit is provided with a diode. ### Claim 5 (depends on 4) A charging circuit as recited in claim 4 wherein the input circuit is a series connection of a diode and a zener diode. ### Claim 6 (depends on 4) A charging circuit as recited in claim 4 wherein the input circuit is a series connection of a plurality of diode. ### Claim 7 (depends on 4) A charging circuit as recited in claim 4 wherein the input circuit is a series connection of a diode and a bipolar transistor. ### Claim 8 (depends on 4) A charging circuit as recited in claim 4 wherein the input circuit is a series connection of a diode and an FET. ### Claim 9 (depends on 4) A charging circuit as recited in claim 4 wherein the input circuit, which is a diode, is connected between the input side of the ON-OFF switching device and the drain of the over-charge protection FET. ### Claim 10 (depends on 9) A charging circuit as recited in claim 9 wherein the input circuit, which is a diode, is connected between the base of a bipolar transistor, which is the ON-OFF switching device, and the drain of the over-charge protection FET. ### Claim 11 A charging circuit for charging a rechargeable battery comprising: (1) an over-charge protection FET having a gate and a source, connected in series with the rechargeable battery, to protect the rechargeable battery from excessive charge; (2) an over-discharge protection FET connected in series with the rechargeable battery and the over-charge protection FET, to protect the rechargeable battery from excessive discharge; (3) a control circuit to prevent excessive charge and discharge of the rechargeable battery by detecting rechargeable battery voltage and controlling the ON-OFF state of the over-charge protection FET and the over-discharge protection PET; (4) an ON-OFF switching device having an input side, connected, between the gate and the source of the over-charge protection FET and controlled by an output signal from the control circuit; and (5) a drain voltage input circuit connected to the input side of the ON-OFF switching device, which switches the ON-OFF switching device to the ON state when the drain voltage of the over-charge protection FET is high to forcibly maintain the over-charge protection PET in the OFF state, (6) a resistor connecting the gate of the over-charge protection FET to the rechargeable battery; (7) a capacitor connected to said resistor and the gate of the over-charge protection FET to delay gate voltage rise in the over-charge protection FET; and wherein (8) the charging circuit is designed such that when rechargeable battery voltage is abnormally low, the capacitor delays the rise in gate voltage of the over-charge protection FET, the ON-OFF switching device is prevented from turning ON before the gate voltage rises, and the over-charge protection FET is kept in the ON state to allow charging of a rechargeable battery with low battery voltage but no internal short-circuit. ### Claim 12 (depends on 11) A charging circuit as recited in claim 11 wherein the ON-OFF switching device is a bipolar transistor of with its collector connected to the gate of the over-charge protection FET. ### Claim 13 (depends on 12) A charging circuit as recited in claim 12 wherein the capacitor is connected between the positive side of the rechargeable battery and the collector of the bipolar transistor, which is the ON-OFF switching device, and the resistor is connected between the positive side of the rechargeable battery and the collector of the transistor. ### Claim 14 (depends on 11) A charging circuit as recited in claim 11 wherein the over-charge protection FET is connected to the negative side of the rechargeable battery through the over-discharge protection FET. ### Claim 15 (depends on 11) A charging circuit as recited in claim 11 wherein the input circuit is provided with a diode. ### Claim 16 (depends on 15) A charging circuit as recited in claim 15 wherein the input circuit is a series connection of a diode and a zener diode. ### Claim 17 (depends on 15) A charging circuit as recited in claim 15 wherein the input circuit is a series connection of a plurality of diodes. ### Claim 18 (depends on 15) A charging circuit as recited in claim 15 wherein the input circuit is a series connection of a diode and a bipolar transistor. ### Claim 19 (depends on 15) A charging circuit as recited in claim 15 wherein the input circuit is a series connection of a diode and an FET. ### Claim 20 (depends on 15) A charging circuit as recited in claim 15 wherein the input circuit, which is a diode, is connected between the input side of the ON-OFF switching device and the drain of the over-charge protection FET. ### Claim 21 (depends on 20) A charging circuit as recited in claim 20 wherein the input circuit, which is a diode, is connected between the base of a bipolar transistor, which is the ON-OFF switching device, and the drain of the over-charge protection FET.