Full-link ESD and Surge Protection Solution for Off-highway Agricultural EV OBC + BMS

Off-highway electric vehicles such as agricultural tractors, construction machinery, and mining equipment operate in EMC environments far harsher than passenger vehicles. The vehicle's high-voltage powertrain, consisting of the OBC (on-board charger) + BMS (battery management system), is highly susceptible to communication interruption, chip breakdown, and complete system shutdown.

The OBC and BMS are the core modules for the vehicle's electrical energy interaction. The entire system has three high-risk points: the high-voltage power loop, low-voltage control communication interfaces, and the exposed charging gun interface. These three types of interfaces have significantly different electrical operating conditions and must be protected with dedicated TVS/ESD array components matched to each.

To address the severe pulse interference conditions of off-highway agricultural vehicles, Leiditech offers a complete AEC-Q101 automotive-grade protection solution. The components feature four core performance advantages: small size, low clamping voltage, low leakage current, and high surge withstand capability.

整车电气链路核心单元示意图

The tractor's overall electrical system consists of two core electronic control units as follows:

· OBC (On-Board Charger): Includes AC input from the charging gun, CAN communication bus, 12V auxiliary power supply, and high-voltage DC output to the battery pack.

· High-voltage battery pack + BMS (Battery Management System): Covers the HV bus, BMS acquisition CAN communication, cell balancing sampling lines, high-voltage interlock loop, and temperature acquisition sampling lines.

Supporting load devices: HV PDU (high-voltage power distribution unit), high-voltage to low-voltage DC/DC, drive motor inverter, electric PTO, air conditioning compressor, and other equipment. During start/stop, these devices generate high-power surges in reverse, which propagate interference to the OBC and BMS main control boards.

OBC On-Board Charger Sub-Interface ESD and Surge Protection Solution

As the vehicle's external charging entry point, the OBC faces primary interference threats from grid lightning surges and power port EFT bursts. It is divided into four types of interfaces:

1. AC charging gun input interface (AC220V mains input)

Leiditech uses high-throughput varistors (MOV) in combination with ceramic gas discharge tubes (GDT) for surge protection on 220V AC power interfaces. Depending on the environment the power supply is in, different protection levels are selected. Commonly used components include MOV 14D471K/20D471K/25D471K and GDT 2R600-8L, meeting IEC 61000-4-5 test levels from 4KV to 8KV.

2. OBC On-board CAN Communication Interface

Leiditech uses the multi-channel integrated automotive-grade device SMC24Q for protection (targeting the Littelfuse AQ24CANA), with capacitance <50pF, ensuring signal integrity while passing ESD testing. The common-mode choke LDW43T-513T filters out common-mode interference. The solution meets IEC 61000-4-2 Level 4, achieving contact discharge of 30kV and air discharge of 30kV .

3. OBC 12V low-voltage auxiliary power interface

This solution is specifically designed for 12V automotive power interfaces, suitable for harsh onboard electrical environments. It meets ISO 7637-2 5a/5b load dump test requirements while providing ISO 10605-2 Level 4 ESD protection (contact discharge ±15kV, air discharge ±25kV). The PPTC resettable fuse provides overcurrent protection, paired with a low-loss Schottky diode (S-SK54C) for reverse polarity protection, comprehensively suppressing spike interference and transient surges on the power line, ensuring stable and reliable operation of downstream automotive electronic equipment.

4. OBC high-voltage DC output port (to battery pack HV bus)

Leiditech recommends the 5.0SMDJ440CA device, featuring a VRWM of 440V, suitable for a nominal 358V battery pack (within 400V full charge), with a maximum clamping voltage Vc of 713V. It absorbs high-voltage plug/unplug arcs and motor back-EMF spikes.

Advantages: AEC-Q101 qualified automotive-grade wide temperature range -55 to 125°C, SMC package compatible with compact OBC control boxes.

Battery Pack BMS Sub-Interface ESD and Surge Protection Solution

As the core of battery safety control, the BMS involves sampling lines, balancing lines, CAN communication, high-voltage interlock, and temperature acquisition lines — most of which are long wiring harnesses. In field operating conditions, electrostatic coupling is strong. Without proper protection, failures such as individual cell sampling failure, balancing loss of control, and false high-voltage power-off alarms can occur.

1. BMS vehicle CAN communication interface (interfacing with OBC and vehicle controller): Long vehicle CAN harnesses couple ESD and conducted surges from drive motor start/stop. Protection solution is the same as the OBC onboard CAN communication interface.

2. Cell voltage sampling / balancing acquisition lines (BMS internal acquisition channels): Transient pulses from cell balancing switching, harness friction ESD, and aggravated device leakage at low temperatures.

Leiditech recommends single-channel ground-referenced ESD protection using the single-channel device GBLC05C in SOD323 package, with junction capacitance Cj < 10pF. A single cell has a full charge voltage of 4.2V; the 5V withstand voltage provides sufficient margin. This absorbs ESD from plug/unplug and harness friction without leaking current during normal operation that would pull down cell voltage. Meets IEC 61000-4-2 Level 4, achieving contact discharge of 30kV and air discharge of 30kV.

3. BMS HV bus positive/negative main terminals (interfacing with HV PDU): Risk from reverse high-voltage surges generated by drive motor startup, electric PTO, and air conditioning compressor, as well as arcing spikes from HV relay disconnection.

Leiditech's multi-channel low-leakage SMC24Q array is suitable for CAN communication and multi-channel sampling signal ports. The protection solution addresses the three key requirements of harsh agricultural operating environments, compact ECU design, and vehicle-level EMC compliance, providing full-link ESD and surge protection from the charging gun input to the internal battery pack sampling lines, ensuring long-term stable operation of agricultural electric equipment and reducing field downtime and maintenance costs.

Leiditech focuses on the R&D of automotive EMC protection solutions, offering a full range of automotive-grade ESD, TVS, and other components. We support domestic substitution and customized EMC rectification solutions, with extensive engineering implementation cases, stable and controllable delivery, and an in-house laboratory available for customers' free preliminary testing.