WHST06202E0 Single Working Voltage1500 Isolation 8000VDC BMS ISOLATION TRANSFORMER

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In a BMS, an isolation transformer is mainly used for:
(1) High/low-voltage isolation—providing isolated power between the high-voltage battery-pack-side circuits (such as the AFE) and the low-voltage control circuitry, preventing high-voltage leakage from damaging the low-voltage side and ensuring personal safety.
(2) Digital communication isolation—transmitting sampled data between the battery-monitoring chip and the main control MCU via isolated coupling (such as isolated CAN), eliminating common-mode interference and ground loops; this is more common than transmitting analog signals directly through a transformer. In addition, isolation transformers can also be used for signal-feedback isolation in auxiliary power supplies.

A daisy chain (such as isoSPI or a UART daisy chain) connects multiple AFEs end to end in series, so only one pair of isolated signal lines is needed to connect all slave boards. Compared with a parallel bus or star connection, the daisy chain has clear advantages:
(1) It greatly reduces wiring harnesses and connectors, lowering cost and weight.
(2) Electrical isolation is easier to achieve in high-voltage series battery packs (isolation only needs to be done once at the head of the chain).
(3) It supports relatively long-distance transmission. The drawback is that a single-point failure affects downstream nodes, so a fault-tolerance mechanism must be designed.

Because cells differ in manufacturing process, temperature gradient, and aging rate, voltage inconsistencies arise during series charge/discharge. Without balancing, lower-capacity cells will fill up or empty first, reducing the usable capacity of the whole pack and even causing overcharge/over-discharge safety risks. Balancing is divided into passive balancing (dissipating energy through resistors) and active balancing (transferring energy through capacitors or transformers); the goal is to keep cell voltages consistent and extend battery life.

(1) Choose AEC-Q200-certified transformers to ensure automotive-grade reliability.
(2) Use dual-winding or redundant designs to prevent a single-point failure from causing isolation failure. (3) Perform 100% production-line testing of withstand voltage and partial discharge, with a test voltage typically 1.2-1.5 times the rated isolation voltage.
(4) Monitor the transformer's secondary output voltage and immediately trigger a fault report if an abnormality occurs.
(5) Pair with isolation-fault detection circuits (such as missing-resistor detection or window comparators) to meet ASIL B/C requirements.