Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
  • H02H9/04—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage
  • H02H9/042—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage comprising means to limit the absorbed power or indicate damaged over-voltage protection device
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
  • H02J7/0029—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety or protection devices or circuits
  • H02J7/00302—Overcharge protection
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
  • H02J7/0029—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety or protection devices or circuits
  • H02J7/00308—Overvoltage protection
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
  • H02J7/0029—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety or protection devices or circuits
  • H02J7/0031—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety or protection devices or circuits using battery or load disconnect circuits

Definitions

• the present invention generally relates to overpower protection systems and more particularly to protection systems for protecting rechargeable elements, such as rechargeable batteries.
• rechargeable battery packs such as lithium battery packs
• a smart electronic circuit This smart circuit is connected in series with the battery cells in the pack for protecting the battery cells against being overcharged. Specifically, the smart circuit switches off the pack when the voltage reaches beyond the maximum limit of 4.1 volts per cell. The smart circuit also switches off the pack when the voltage drops below the minimum limit of 2.7 volts per cell. The switching off is made by a FET going high resistance. Chargers specifically designed for these packs usually operate under constant current at a voltage below 4.8 volts so they cannot drive the voltage of the battery cells up to 5.3 volts, at which point the cells are subjected to internal degradation as will be more detailed described below in connection with Fig. 1.
• Figure 1 shows a typical charging curve (the voltage across the battery vs. time) of a lithium battery pack when the smart circuit fails to provide the necessary protection. As illustrated in Fig. 1 , this curve is divided into three areas: areas I, II and III.
• the first area is represented by the region: V ⁇ 4.5 volts.
• V ⁇ 4.5 volts When a lithium battery is being charged in this area, a lithium battery is in the safe operating mode. In this area, the temperature of the battery remains below 60°C to 70°C and the pressure inside the battery remains below 3 bars.
• the second area is represented by the region: 4.5 volts ⁇ V ⁇ 5.3 volts.
• the battery When charging is in this area, the battery operates in a dangerous mode. In this area, the pressure inside the battery rises from 3 bars to 10 bars and temperature of the battery increases beyond 70°C. Moreover, in this area, the battery might even explode.
• the third area is represented by the region: V > 5.3 volts. At this stage, it is too late to save the battery, and the battery is subjected to internal degradation and will explode.
• the present invention provides a novel protection system that prevents a rechargeable battery from being overcharged into a dangerous operating mode.
• the novel protection system may generally be used as a backup system in conjunction with a smart electronic circuit which, when functioning in its normal mode, protects the battery cells against being overcharged.
• this novel protection system should preferably integrated into the battery cells. It could also be used as part of the battery pack electronics or part of the charger.
• the novel protection system will be activated before the battery voltage reaches 5.3 volts.
• a novel protection method of the present invention is also disclosed.
• a rechargeable battery is coupled, in parallel, to a voltage dependent resistive element, such as a zener diode or a diac, having a threshold voltage (e.g., 4.3 volts) just below the maximum operating voltage of the battery (e.g., 4.5 volts for a lithium battery).
• a protection element such as a positive temperature coefficient (PTC) device, a thermal fuse, or a bimetallic breaker, etc., is coupled in series with the battery or with the parallel circuit of the battery and the voltage dependent resistive element. If overcharging starts to occur and the smart circuit fails to function, the current flowing in the voltage dependent resistive element will activate the protection element to thereby halt the charging operation.
• PTC positive temperature coefficient
• a rechargeable battery is coupled in series with a fuse and in parallel with a power MOSFET transistor which is preferable thermally coupled to an overcharge detection device.
• the -3- overcharge detection device will drive the power MOSFET. As soon as the battery voltage exceeds 4.5 volts, the power MOSFET will be activated to short the battery cells, causing the fuse to blow, thus isolating the battery. Either a thermal fuse or a regular fuse may be used in this embodiment. If a PTC device is used instead of a fuse, it will trip and limit the fault current to a low leakage current.
• the battery By connecting a protection element in series with the battery, the battery is also protected from external shorting during transportation, for example.
• a rechargeable battery is coupled in parallel with an overcharge detection device and a thyristor.
• the overcharge detection device provides control to the thyristor.
• a first fuse is connected between a charger and the thyristor, and a second fuse is connected between the thyristor and the overcharge detection device.
• the thyristor will be activated to short the battery, causing the fuses to blow and thus disconnecting the charger from the battery.
• the fuses have a delay feature such that upon shorting the battery there is a predetermined delay before the fuses blow. This delay feature prevents accidental shorting of the battery that lasts for only a very short period of time.
• Figure 1 shows a charging curve of a lithium battery
• the present invention provides a protection system that protects, during a charging operation, a rechargeable battery against being overcharged into a dangerous operating mode.
• the protection system may be used as a back up system and will generally be used in conjunction with a smart power circuit which will monitor the charge of the battery.
• the smart power circuit is commercially available, for example, as MAX745 or MAX846A product from Maxim Integrated Products, Sunnyvale, California.
• this protection system could be incorporated into the battery itself, or it could be used as part of the pack electronics or part of the charger.
• FIGS. 2A-2C show the basic circuit embodiments according to the present invention.
• a rechargeable battery 10 such as a lithium battery with a maximum operating voltage of 4.5 volts is coupled, in parallel, to a voltage- dependent resistive element, such as a 4.1 volt zener diode 20, forming a parallel circuit.
• the parallel circuit is coupled in series with a protection element 26, such as a PTC device, a thermal fuse or a bimetallic breaker. Protection element 26 is preferably thermally coupled to zener diode 20 in order to accelerate the activation
• a parallel circuit of a charger 30 and a smart circuit 31 are connected in series with the parallel combination of battery 10 and zener diode 20.
• Charger 30 is also connected to a power source (not shown).
• protection element 26 is connected in series with the parallel circuit of battery 10 and zener diode 20, the total amount of fault current flows in protection element 26 and therefore the protection element will be activated faster.
• Figures 2B and 2C show variations of the embodiment of Fig. 2A.
• the power dissipation in the zener diode is a large value between 1 to 4 watts, the power dissipation can cause an efficient thermally-assisted tripping of the protection element.
• the protection element and the zener diode may be hybridized to improve the thermal coupling.
• a constant current DC charger (which is generally the case)
• the current begins to charge battery 10 because of its low internal resistance. If the smart circuit fails to operate, as soon as the battery voltage reaches 4.3 volts, a small current is diverted into zener diode 20 which maintains the voltage at 4.3 volts. If the charge current becomes higher, the differential resistance of the zener diode will decrease by accepting more and more current to maintain a 4.3 volt constant voltage over the battery. In this case, the zener diode is in runaway mode and the zener diode is heated up. The heat dissipated by the zener diode makes the protection element trip faster, thus avoiding overcharging the battery into a dangerous operating mode.
• FIG. 3 shows another embodiment of the invention in which an opto- coupler 50 is used.
• Opto-coupler 50 includes a receiving element, such as a phototransistor 52 of PNP type, and a transmitting element, such as an LED (light- emitting diode) 56.
• a receiving element such as a phototransistor 52 of PNP type
• a transmitting element such as an LED (light- emitting diode) 56.
• rechargeable battery 10 is coupled, in parallel, to the series combination of zener diode 20 with a 3-volt rating, for example, and LED 50 to form a first parallel circuit.
• a protection element 26, such as a fuse, a PTC device or a bimetallic breaker, is coupled in series with the first parallel circuit.
• Phototransistor 52 is coupled in parallel with the combination of protection element 26 and the first parallel circuit to form a second parallel circuit.
• the parallel circuit of a charger 30 and a smart circuit 31 is coupled in parallel with the second parallel circuit.
• Fig. 3 operates according to principles similar to those described above. Under normal conditions, the current in the zener diode 20 is not sufficient to light LED 56. However, if a fault occurs, e.g., a high voltage charger is used, the current in zener diode 20 will increase and thus activate opto-coupler 50 which in turn shunts battery 10. This causes protection element 26 to activate to thereby disconnect battery 10.
• FIG 4 shows yet another embodiment of the invention.
• rechargeable battery 10 is coupled in parallel with an overcharge detection device 60, such as an overvoltage detection device, Model No. TV54VN, (e.g., packages SOT 23B-3 or SOT89-3), manufactured by Telcom Semiconductor, Inc., Crawley, West Wales, England.
• the parallel circuit of battery 10 and detection device 60 is coupled in series with a protection element 58, which may be a fuse, a thermal fuse or a PTC device.
• the combination of battery 10, detection device 60 and protection element 58 is coupled in parallel with a power MOSFET transistor 80, such as Motorola MTD 3055EL, case 369A- 10.
• the parallel circuit of a smart circuit 31 and a charger 30 is coupled to battery 10 in parallel.
• Charger 30 is also connected to a power source (not shown).
• MOSFET 80 is biased by a resistor 76 and driven by detection device 60 via transistor 74.
• Detection device 60 includes a constant current generator 62, which supplies current to a 4.5-volt zener diode 64.
• the voltage of zener diode 64 is compared with the battery voltage using an operational amplifier 72 as a comparator. When the battery voltage reaches 4.5 volts, comparator 72 outputs a positive voltage which turns off transistor 74, which then turns on MOSFET 80. This causes battery 10 to be shunted. Thus, a high current flows in protection element 58.
• protection element 58 If a fuse (such as AVX-Kyocera distributed by a British company Farnell) is used as protection element 58, it will blow and disconnect battery 10, thus preventing the battery from exploding. If a PTC device is used as protection element 58 instead of a fuse, the PTC will trip and reduce the high current to a low leakage current, thus preventing the battery from exploding.
• a fuse such as AVX-Kyocera distributed by a British company Farnell
• comparator 72 outputs a negative voltage which turns on transistor 74, which causes power MOSFET 80 in off state.
• a constant current charger may be used without danger. Assuming the maximum charge current of battery 10 is 2C where C is the battery capacity specified by the manufacturer, if the charge current exceeds 2C, the fuse will blow and disconnect battery 10 from charger 30. However, if the charge current is within 2C but the charge voltage is higher than 4.5 volts, detection device 60 will detect the fault and shunt battery 10, causing the fuse to blow.
• a constant voltage charger may also be used without danger in the embodiment of Fig. 4. If the voltage of charger 30 is too high and a charge current higher than 2C is induced, the fuse will blow and prevent the battery from exploding. On the other hand, if the charge current is less 2C but the voltage across the battery is greater than 4.5 volts because of the high voltage of charger 30, then overvoltage detection device 60 will play its role by shunting the battery and blowing the fuse. If a PTC device is used in place of the fuse, the PTC device will trip, thus protecting the battery.
• protection element 58 such as a thermal fuse or PTC device
• power MOSFET 80 the wiring may be simpler. This is because MOSFET 80 has a common connection point with the protection element. Thus, for example, a thin trace may be used as a thermal fuse, which makes thermal coupling of the trace to MOSFET 80 easier.
• all the components are preferably surface mounted devices (SMD).
• FIG. 5 shows a further embodiment of the invention.
• rechargeable battery 10 such as a lithium ion battery
• an overcharge detection device 90 such as an overvoltage detection device, Model No. TC54VC, commercially available from Telcom Semiconductor, Inc., Crawley, West Wales, England.
• Detection device 90 includes a constant current generator 62, a zener diode 64, resistors 66 and 68, operational amplifier 72, a p-type field effect transistor (FET) Q1 and an n-type FET Q2.
• FET field effect transistor
• the parallel circuit of battery 10 and detection device 90 is coupled in series with a first protection element 94.
• An output of detection device 90 provides control over a thyristor (SCR) 96 via a resistor R1.
• a second protection element 98 is connected in series with the parallel circuit of the first protection element 94, thyristor 96, detection device 90 and battery 10.
• a charger 30 is to be connected to the overall circuit. Charger 30 is also connected to a power source (not shown).
• each of the two protection elements 94 and 98 may be a fuse with a delay feature, such as a SMD Slo-Blo fuse 2A, commercially available from Littlefuse in Des Plaines, Illinois. Such a fuse typically has a delay of approximately 20 ms upon occurrence of a high current before it blows.
• R1 may be a SMD resistor with a resistance value of 22 k ⁇ .
• An example of thyristor 96 may be a ST 1220-600B thyristor, commercially available from ST Microelectronics in St. Genis Pouilly, France.
• charger 30 Under normal conditions, charger 30 provides a regulated voltage of 4.3 V and supplies a current of 2 A via protection elements 94 and 98 to battery 10.
• a detected voltage Vd is compared with a reference voltage Vref, using an operational amplifier 72 as a comparator. In this case, the detected voltage Vd is below the reference voltage Vref.
• comparator 72 outputs a positive voltage which will turn on transistor Q2, while transistor Q1 remains off. Since there is no current flowing through resistor R1 , thyristor 96 is not activated. Therefore, normal charging operation is performed.
• a wrong charger i.e., a charger with a high voltage rating (e.g., a 12 V charger)
• the battery voltage Vbat will exceed 4.3 V after Vd exceeds Vref.
• comparator 72 outputs a negative voltage which turns on transistor Q1 , while transistor Q2 is off. This causes a current to flow through resistor R1 and to the gate of thyristor 96.
• thyristor 96 is activated and shorts the battery and the charger.
• a high current is drawn from the battery and the charger through thyristor 96 to ground.
• the high current causes protection elements 94 and 98 to blow, thus disconnecting the wrong charger from the battery.
• the delay feature of protection elements prevents accidental shorting of the battery that lasts for only a very short period of time.
• the circuit in this embodiment is used with a primary protection system which could be a smart circuit.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Charge And Discharge Circuits For Batteries Or The Like (AREA)
• Secondary Cells (AREA)
• Protection Of Static Devices (AREA)

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Publications (1)

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Cited By (10)

Families Citing this family (3)

Citations (7)

• 1999
  • 1999-04-14 AU AU35586/99A patent/AU3558699A/en not_active Abandoned
  • 1999-04-14 WO PCT/US1999/008109 patent/WO1999056374A1/en active Application Filing
  • 1999-04-15 TW TW088106025A patent/TW516261B/zh not_active IP Right Cessation

Patent Citations (7)

Non-Patent Citations (2)

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