Protection circuit and battery pack

Abstract

A secondary battery is protected from being overcharged and excess discharge current by a simple circuit. A comparator (CMP1) compares a charging voltage (Vc) of the secondary battery (6) with a reference voltage (Vref1) and detects overcharge. A transistor (Q1) turns on and turns on a heater (R2) when overcharge is detected by the comparator (CMP1). A PTC element (SW1) turns off when it is heated by the heater and reaches a prescribed operation temperature (Tsw1), and interrupts a charging current. When the discharge current from the secondary battery (6) is excessive, the PTC element (SW1) self-heats by the discharge current and turns off when it reaches the operation temperature (Tsw1) and interrupts the discharge current.

Description

technical field [0001] The present invention relates to a protection circuit and a battery pack for protecting a secondary battery from overcharging or excessive discharge current. Background technique [0002] 12 is a circuit diagram showing the structure of a battery pack (Battery Packing) according to the background art. A battery pack 101 shown in FIG. 12 has a protection circuit 102 and a secondary battery 103 . The secondary battery 103 is, for example, a lithium ion (Lithium ION) secondary battery, a lithium polymer (Lithium Polymer) secondary battery, a nickel metal hydride (NickelHydrogen) secondary battery, or a nickel cadmium (Nickel Cadmium) secondary battery, etc. secondary battery. If such a secondary battery is overcharged or discharged with an excessively large current, it will lead to deterioration of characteristics such as cycle life, swelling and deformation of the battery, and the like. Here, the battery pack 101 has a protection circuit 102 that prot...

AI Technical Summary

Problems solved by technology

[0012]However, in the protection circuit 102 shown in FIG. 12, since the FET contains a parasitic diode, it is impossible to use one FET to cut off the discharge current and the charge in which the current flows in different directions. current, so it is necessary to have FET106 to cut off the discharge current and FET107 to cut off the charge current

Moreover, a reference voltage source 108 and a comparator 110 are required to detect overcharge, a reference voltage source 109, a comparator 111, and a resistor 112 are required to detect an excessive discharge current, and output signals based on the comparators 110 and 111 are required. Since the logic circuit 113 turns on (ON) / off (OFF) the two FETs 106 and 107, there is a disadvantage that the circuit scale of the protection circuit 102 is too large

[0013] In addition, in the structure shown in FIG. 13 or FIG. 14, the secondary battery is protected from overcharging by connecting a temperature switch that operates according to the temperature of the PTC element and the like in series with the secondary battery to protect the secondary battery from overcharging. Low accuracy, for example, when using a charging device with poor charging voltage control accuracy to charge the battery pack, if the secondary battery is continuously charged with a charging current that does not rise in temperature rapidly, the temperature switch may not act. However, the secondary battery is overcharged, resulting in deterioration of the characteristics of the secondary battery, swelling or deformation of the battery, etc.

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