Battery protection circuit
First Claim
1. A battery protection circuit for a device employing a rechargeable battery to protect said battery from damage due to deep discharge thereof, said circuit comprising:
- (a) a rechargeable battery having a battery voltage and a dropout voltage at which no further discharge of said battery is desirable;
(b) load means operable by current from said battery;
(c) a load drive transistor connecting said load means across said battery and operable to allow current flow through said load means upon the application of suitable drive current to a base of said drive transistor;
(d) switching means connected across said battery and to the base of said transistor, said switching means providing said suitable base drive current when said battery voltage exceeds said dropout voltage by a selected degree;
said switching means reducing said base drive in response to said battery voltage approaching said dropout voltage whereby the current through said drive transistor is reduced resulting in said load means operating at noticeably diminished capacity to warn of the need to recharge said battery; and
said switching means ceasing to provide said base drive in response to said battery voltage decreasing to said dropout voltage to prevent deep discharge of said battery;
(e) a voltage sensing resistor connected to one terminal of said battery;
(f) regenerative switch means connected between said sensing resistor and the other terminal of said battery;
said regenerative switch means being turned on by a voltage across said sensing resistor above a selector level and being turned off upon said voltage across said sensing resistor decreasing below said selected level;
(g) said regenerative switch means having an output terminal providing a base drive voltage related to the level of said battery voltage;
(h) a base resistor connecting said output terminal to the base of said drive transistor such that said base drive current flows through said base resistor when said switch is turned on whereby said drive transistor conducts current through said load means;
(i) said base resistor having a resistance selected such that said load is operated at noticeably diminished capacity as said dropout voltage is approached to warn of the need to recharge said battery; and
(j) said sensing resistor having a resistance selected such that said regenerative switch means is turned off upon said battery voltage decreasing to said dropout voltage whereby said base drive current ceases and said drive transistor is cut off thereby cutting off the flow of current through said load means to prevent further discharge of said battery.
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Accused Products
Abstract
A battery protection circuit particularly for portable lamps employing rechargeable batteries is provided to prevent overdischarge of the batteries and includes a bulb drive transistor connecting a bulb across the battery with a switch interposed between one side of the battery and the bulb, a voltage sensing resistor connected to one side of the switch, a regenerative switch connected between the sensing resistor and the other side of the battery, and the regenerative switch including an output terminal connected by a base resistor to the base of the drive transistor. The regenerative switch includes a pair of transistors connected and cooperating such that when one of the transistors is turned on, the other is caused to be turned on, the transistors, further, maintaining each other on. As the dropout voltage of the battery is approached, the base drive of the drive transistor decreases which causes the bulb to become dim to thereby warn of the discharged state of the battery. At the dropout voltage, the voltage across the sensing resistor, which is substantially in parallel with the base-emitter junction of one of the switch transistors, is reduced to a level which is not sufficient to maintain the sensing transistor on whereby the switch transistors are turned off, resulting in the turn-off of the drive transistor so that the battery is protected from overdischarge.
48 Citations
11 Claims
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1. A battery protection circuit for a device employing a rechargeable battery to protect said battery from damage due to deep discharge thereof, said circuit comprising:
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(a) a rechargeable battery having a battery voltage and a dropout voltage at which no further discharge of said battery is desirable; (b) load means operable by current from said battery; (c) a load drive transistor connecting said load means across said battery and operable to allow current flow through said load means upon the application of suitable drive current to a base of said drive transistor; (d) switching means connected across said battery and to the base of said transistor, said switching means providing said suitable base drive current when said battery voltage exceeds said dropout voltage by a selected degree;
said switching means reducing said base drive in response to said battery voltage approaching said dropout voltage whereby the current through said drive transistor is reduced resulting in said load means operating at noticeably diminished capacity to warn of the need to recharge said battery; and
said switching means ceasing to provide said base drive in response to said battery voltage decreasing to said dropout voltage to prevent deep discharge of said battery;(e) a voltage sensing resistor connected to one terminal of said battery; (f) regenerative switch means connected between said sensing resistor and the other terminal of said battery;
said regenerative switch means being turned on by a voltage across said sensing resistor above a selector level and being turned off upon said voltage across said sensing resistor decreasing below said selected level;(g) said regenerative switch means having an output terminal providing a base drive voltage related to the level of said battery voltage; (h) a base resistor connecting said output terminal to the base of said drive transistor such that said base drive current flows through said base resistor when said switch is turned on whereby said drive transistor conducts current through said load means; (i) said base resistor having a resistance selected such that said load is operated at noticeably diminished capacity as said dropout voltage is approached to warn of the need to recharge said battery; and (j) said sensing resistor having a resistance selected such that said regenerative switch means is turned off upon said battery voltage decreasing to said dropout voltage whereby said base drive current ceases and said drive transistor is cut off thereby cutting off the flow of current through said load means to prevent further discharge of said battery. - View Dependent Claims (2, 3, 4)
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5. A battery protector circuit for a device employing a rechargeable battery;
- said circuit for protecting said battery from damage due to deep discharge thereof;
said circuit comprising;(a) a rechargeable battery having a battery voltage and a dropout voltage at which no further discharge of said battery is desirable; (b) load means operable by current from said battery; (c) a load drive transistor connecting said load means across said battery and operable to allow current flow through said load means upon the application of suitable drive current to a base of said drive transistor; (d) a voltage sensing resistor connected to one terminal of said battery; (e) regenerative switch means connected between said voltage sensing resistor and the other terminal of said battery, said switch means being turned on upon the voltage across said sensing resistor exceeding a selected level and being turned off upon said voltage across said sensing resistor decreasing below said selected level; (f) said switch means having an output terminal providing a base drive voltage related to the level of said battery voltage; (g) a base resistor connecting said output terminal to the base of said drive transistor such that base drive current flows therethrough when said switch means is turned on whereby said drive transistor conducts current through said load means; (h) said base resistor having a resistance selected such that said load is operated at noticeably diminished capacity as said dropout voltage is approached to warn of the need to recharge said battery; and (i) said sensing resistor having a resistance selected such that said switch means is turned off upon said battery voltage decreasing to said dropout voltage whereby said base drive current ceases and said drive transistor is cut off thereby cutting off the flow of current through said load means to prevent further discharge of said battery. - View Dependent Claims (6, 7, 8, 9, 10, 11)
- said circuit for protecting said battery from damage due to deep discharge thereof;
Specification