Abstract: A battery protection circuit is provided that includes current monitoring circuit. The current monitoring circuit senses current flowing to or from a rechargeable cell. When the current exceeds a maximum value, the current monitoring circuit actuates, whereby opening a transistor. The transistor has a resistor couple in parallel. When the transistor opens, current is forced through the resistor coupled in parallel with the transistor, thereby limiting the current to a maximum value. The current monitoring circuit also simulates an overcurrent condition in the safety circuit. The overcurrent condition causes a disconnect switch to open, thereby disconnecting the cell(s) from the external terminals.

Abstract: A cell balancing circuit monitors the voltage between serially connected cells and compares it to a reference voltage. From that comparison, the cell balancing circuit sources or sinks current into a midpoint node between rechargeable cells to keep the cells balanced during the charging process. In one preferred embodiment, the cell balancing circuit includes an op-amp, connected in a unity gain configuration. A voltage divider establishes a reference voltage equal to the average of the two cell voltages. The op-amp compares this average to the measured voltage at the midpoint node. When the average voltage exceeds the voltage at the midpoint node, the op-amp sources current into the midpoint node. When the average voltage falls below the voltage at the midpoint node, the op-amp sinks current from the midpoint node. By sourcing or sinking current, the cell balancing circuit allows the lesser charged cell to catch up with the more fully charged cell.

Abstract: This invention includes a circuit for displaying charge status to a user. The circuit includes circuitry for comparing a supply or reference voltage to a cell voltage, circuitry for sensing charging current and circuitry for displaying at least one of three charging states to a user. The circuit compares the supply or reference voltage to the cell voltage while sensing current. If the difference between the supply or reference voltage is great, and current is small, the circuit indicates a trickle charging mode. If the charging current is large, the circuit indicates rapid charge. If the difference between the supply or reference voltage is small, and the current is small, the circuit indicates a top off mode. The circuit preferably includes a plurality of comparators for both sensing and comparing the voltages and currents. A pair of light emitting diodes preferably indicates the state of charge to the user.

Abstract: A battery protection circuit is provided that includes a safety circuit and an overpower circuit. The safety circuit monitors the voltage and current of at least one rechargeable cell within the battery pack, and disconnects the cell(s) from the external terminals of the battery pack when either the voltage becomes too high or low, or when excessive current is being drawn from the battery pack. The overpower circuit monitors the power being delivered to or sourced from the battery pack to the load. The overpower circuit actuates when the power exceeds a predetermined threshold, thereby simulating an overcurrent condition in the safety circuit. The overcurrent condition causes a disconnect means, like a transistor, to open, thereby disconnecting the cell(s) from the external terminals. The battery protection circuit then latches in this disconnected state until a load is removed from the terminals of the battery pack.

Abstract: This invention includes a circuit for displaying charge status to a user. The circuit includes circuitry for comparing a supply or reference voltage to a cell voltage, circuitry for sensing charging current and circuitry for displaying at least one of three charging states to a user. The circuit compares the supply or reference voltage to the cell voltage while sensing current. If the difference between the supply or reference voltage is great, and current is small, the circuit indicates a trickle charging mode. If the charging current is large, the circuit indicates rapid charge. If the difference between the supply or reference voltage is small, and the current is small, the circuit indicates a top off mode. The circuit preferably includes a plurality of comparators for both sensing and comparing the voltages and currents. A pair of light emitting diodes preferably indicates the state of charge to the user.