## 3 Proposed Topology and Operation  
The operational principle for one cell is illustrated in Figure 2. Assume that the voltage of the considered cell rises above a predefined maximum value. At this moment the two LEDs in series (L1, L2) become forward biased, enabling the transistor Q1, bipolar junction transistor (BJT) (PNP) to be turned on. The gate of the N-channel MOSFET Q2 gets pulled up and current flows through the 4W resistor. This is a power resistor since it needs to dissipate the surplus battery power for some time.  
An extra LED is used to inform users that the system is in high-voltage equalization. The LED driver/constant current regulator limits the current to 10 mA and has a negative T-coefficient to protect the LED from thermal runaway at high currents. Note that it tops all cells at a predefined voltage. A detection is added to enable actions, such as balancing and charger cut-off when the cells go beyond the threshold voltage. This detection is located on the right-hand side of the schematic. The over-voltage detection is implemented through an optoisolator, (optocoupler) shown in Figure 3.  
Figure 3: Voltage-sensing circuit of high-voltage equalizing detection (HVED) for eight cells in series.  
Figure 2: High-voltage equalizing detection circuit of one cell.  
For servicing, it is better to know which cell did reach full charge, thus, a visible LED was implemented. As a cell achieves a high voltage, the phototransistor is switched on and allows the conduction of the collector-emitter current. A wired \"Or\" circuit, using transistor Q7, allows the detecting of whether one cell is high and a wired \"AND\" circuit using Q8 detects whether all cells are high. This current originates from a bank- or battery-select, which is a microcontroller signal (5 V) enabling the monitoring of the different battery packs at a certain frequency. This way the amount of signals is reduced from four to one as the packs are not simultaneously monitored, but sequentially monitored. The frequency must be made high enough in order to make sure that during non-monitored dissipation, the cell will not be damaged. In addition, a Bluetooth module is predicted to command the microcontroller to turn on or off the charger when all cells are high via a voice or text message by using a smartphone. Depending on the fastest charger type (within the current limits of the batteries), the resistor might vary.  
Assume only one HVED cell (assume again cell 1) in the pack has reached equalizing mode, or simply put, one cell is high, then the collector of the Q7 BJT is pulled down, enabling a microcontroller to interpret this pull-down as a warning that one cell is high. Please note that the controller has no means of detecting which specific cell is high, thus, the LED is useful for maintenance and fault detection. This information can then be used to disable the charger temporarily and balance the cells amongst each other through a parallel balancing method. During regenerative braking, this method is also used. When all cells are high, the collector of the Q8 BJT is pulled down and the microcontroller is warned that all cells are high. This case will probably only happen when regenerative braking. In a charging situation, most chargers (without individual cell monitoring) will stop when the average peak voltage is high enough, though some cells might be rather low and at the same time other cells too high. By doing this, an important reduction of wires is obtained toward the processor. It can even be further reduced by multiplexing data from series-connected battery sets.