Systems and methods for balancing multi-cell batteries with a transformer and a rectifier circuit

1. A method for balancing energy stored in a plurality of cells of a battery having a first terminal and a second terminal, the method comprising:

identifying a subset of the plurality of cells having a voltage below a preselected threshold;

identifying remaining ones of the plurality of cells having a voltage equal to or greater than the preselected threshold

repeatedly open and close a primary switch coupled between the first terminal of the battery and a transformer comprising a primary winding and a plurality of secondary windings, wherein each secondary winding is coupled to one of the plurality of cells via a secondary switch of a plurality of secondary switches and a rectifier circuit, wherein the primary winding is coupled between the first terminal and the second terminal of the battery, and wherein the rectifier circuit rectifies a signal received from a corresponding one of the secondary windings; and

closing a subset of the plurality of secondary switches coupled to the identified subset of the plurality of cells and opening remaining ones of the plurality of secondary switches coupled to the identified remaining ones of the plurality of cells while the primary switch is being repeatedly opened and closed.

2. A battery balancing circuit comprising:

a battery comprising a plurality of cells coupled in series, a first terminal and a second terminal;

a transformer comprising a primary winding and a plurality of secondary windings, wherein each secondary winding is coupled to one of the plurality of cells via a secondary switch of a plurality of secondary switches and a rectifier circuit, wherein the primary winding is coupled between the first terminal and the second terminal of the battery, and wherein the rectifier circuit is configured to rectify a signal received from a corresponding one of the secondary windings;

a primary switch in series with the primary winding of the transformer; and

a control circuitry coupled to the primary switch, the plurality of secondary switches, and each of the plurality of cells, and configured to control an open/close state of each of the primary switch and the plurality of secondary switches,

wherein the control circuitry is further configured to:

identify a subset of the plurality of cells having a voltage below a preselected threshold;

identify remaining ones of the plurality of cells having a voltage equal to or greater than the preselected threshold;

close a subset of the plurality of secondary switches coupled to the identified subset of the plurality of cells and open remaining ones of the plurality of secondary switches coupled to the identified remaining ones of the plurality of cells; and

repeatedly open and close the primary switch while the identified subset of the plurality of cells are closed and the remaining ones of the plurality of secondary switches are opened.

3. The circuit of claim 2 , wherein the control circuitry is configured to:

detect an imbalance condition in at least one cell of the plurality of cells.

4. The circuit of claim 3 , wherein the control circuitry is configured to:

measure a voltage at each of the plurality of cells; and

actuate, repeatedly, the primary switch such that energy is transferred from the battery to the subset of the plurality of cells.

5. The circuit of claim 3 , wherein the imbalance condition is selected from the group consisting of an under-voltage and an over-voltage.

6. The circuit of claim 2 , wherein the control circuitry is configured to actuate the primary switch at a preselected frequency and with a preselected duty cycle.

7. The circuit of claim 2 , wherein the control circuitry is configured to:

energize the primary winding by switching the primary switch; and

provide a path for energy from the primary winding to the subset of the plurality of cells by switching the subset of the plurality of secondary switches.

8. The circuit of claim 2 , wherein each of the rectifier circuits comprise a full wave rectifier.

9. The circuit of claim 8 , wherein the full wave rectifier comprises a center tapped full wave rectifier including at least two diodes.

10. The circuit of claim 2 , wherein each secondary winding is connected to a corresponding rectifier circuit and a corresponding secondary switch is connected between the corresponding rectifier circuit and a corresponding cell of the battery.

11. The circuit of claim 2 , wherein each of the rectifier circuits consist of a diode.