Battery management circuit maintaining cell voltages between a minimum and a maximum during charging and discharging
A battery management circuit maintains voltage balance during charging and discharging of a multi-cell, series connected battery stack. The circuit allows the entire energy content of the battery stack to be drained, as opposed to just monitoring the cells and turning off the discharge when the first cell voltage drops below a predetermined threshold. The circuit also provides high efficiency voltage balancing during charging of the battery stack conserving energy and keeping the temperature of the battery pack to a minimum.
1. A battery management circuit, comprising:
a plurality of cell connections whereby a corresponding plurality of battery sections are connectable in series between a load output and ground such that the positive terminal of each battery section in the series is connected to the negative terminal of the subsequent battery section in the series, except that the negative terminal of the first battery section in the series is connected to ground and that the positive terminal of the last battery section is connected to the load output;
balancing circuitry connected across a plurality N of the cell connections whereby, when a corresponding plurality of battery sections are connected thereto to drive a load connected at the load output and when activated, the balancing circuitry is configured to provide a supplemental current across the connections of one or more weaker ones of the battery sections from one or more stronger ones of the battery sections;
a controller circuit connected to the cell connections to monitor the charge level of batteries connected thereto and connected to the balancing circuitry to activate the balancing circuitry in response to detecting one or more of the battery sections being discharged below a first level; and
charging circuitry connected to the controller circuit, coupled to the cell connections, and having an AC input,
wherein in response to the controller circuit detecting the voltage across the plurality of cell connections being at or below a second level of discharge, the controller circuitry activates the charging circuitry, where the second level of discharge is a minimum allowable terminal voltage of the batteries.
2. The battery management circuit of claim 1 , wherein each of the cell connections allow for connection of a plurality of batteries connected in series.
3. The battery management circuit of claim 1 , wherein the balancing circuitry includes:
a plurality of N first windings of a transformer each connected across a corresponding one of the cell connections;
a plurality of N first diodes through which each of a corresponding one of the first windings are connected to the positive terminal connection of a corresponding cell connection;
a switch connected to the controller circuit; and
a second winding of the transformer connected between the load output and, through the switch, ground, wherein the first windings and second winding are part of the same transformer.
4. The battery management circuit of claim 3 , wherein the switch is a low voltage dmos transistor connected between the second winding and ground and having a gate connected to the controller circuit.
5. The battery management circuit of claim 4 , wherein, when the balancing circuitry is activated, the controller circuit applies a series of pulse to the gate of the dmos transistor.
6. The battery management circuit of claim 1 , further comprising:
a load switch connected to the controller circuit, through which load output is connectable to the load,
wherein in response to the controller circuit detecting the voltage across the plurality of cell connections being at or below the second level, the controller circuitry opens the load switch.
7. The battery management circuit of claim 1 , wherein the balancing circuitry includes:
a plurality of N first windings each connected across a corresponding one of the cell connections; and
a plurality of N first diodes through which each of a corresponding one of the first windings are connected to the positive terminal connection of a corresponding cell connection; and
wherein the charging circuitry includes:
a first switch connected to the controller circuit;
a second winding connected between ground and, through the first switch, the load output, wherein the first windings and second winding share a common core;
a bridge rectifier having the AC input;
a switching converter connected to the bridge rectifier and inductively coupled to the first windings.
8. The battery management circuit of claim 7 , wherein the first switch comprises a pair of dmos transistors connected in series between the second winding and the load output and having gates connected to the controller circuit.
9. The battery management circuit of claim 7 , wherein the switching converter includes:
a second switch connected to the controller circuit and connected across the bridge rectifier; and
a third winding connected, through the second switch, across the bridge rectifier and sharing a common core with the first windings and second winding.
10. The battery management circuit of claim 9 , wherein the second switch is a dmos transistor having a gate connected to the controller circuit.