Optimizing High-Voltage Discharge Circuits for EV Applications

How Firstohm Reduced Component Count by 80% with High Power Anti-Surge Resistors

In high-voltage EV systems, conventional discharge resistor arrays often consume excessive PCB space, increase assembly complexity, and reduce overall reliability. This case study highlights how Firstohm’s SWM Series (Anti-Surge Wire Wound MELF Resistors) replaced a 20-piece R-chip array in an EV Power Distribution Unit (PDU) discharge circuit with only 4 resistors — achieving an 80% reduction in component count, improved thermal stability, and greater design flexibility for compact discharge circuit layouts.

Best Solution for Discharge Circuits

Firstohm recommended the SWM Series (Anti-Surge Wire Wound MELF Resistors) as a replacement for the resistor array. These resistors are engineered for high power density, exceptional pulse and surge resistance, and long-term thermal stability.

Key Benefits of Using SWM series in High-Voltage Discharge Applications

  • Space savings – More PCB room for other components in compact designs
  • Lower BOM cost – Fewer parts and reduced assembly time
  • Improved reliability – Fewer solder joints, lower failure risk
  • Thermal stability – Consistent performance under repeated high-voltage surges
  • Applicable for EV, renewable energy, and industrial inverter applications, offering both technical and commercial advantages

Case Study – EV OBC Discharge Circuit Optimization: 80% Fewer Components

  • Discharge Condition: 1000V → 60V within 1 second
  • Capacitance: 210 μF
  • Original Design: 20 pcs 1KΩ 1206 R-Chip resistors (5 series × 4 parallel)
  • Optimized Design: 4 pcs SWM resistors (2 series × 2 parallel)

Results: Significant PCB space savings, simplified assembly, fewer potential failure points — delivering higher performance and reduced total cost.

Firstohm Anti-Surge Wire Wound MELF Resistor (SWM): Possessing multiple-country welding point patents, this resistor delivers enhanced product reliability, excellent pulse withstand capability, cost-effectiveness, and a compact form factor. It is particularly well-suited for use as a pre-charge resistor ordischarge resistor in high-power applications.

The specifications of Anti-Surge Wire Wound MELF Resistors (SMD) are as follows:

Meet Firstohm at electronica India 2025

If you’d like to explore the technical advantages of the SWM Series Anti-Surge Wire Wound MELF Resistors, please visit our official website: www.firstohm.com
Or connect with us in person at Booth H5.B111, electronica India 2025 (17–19 September, BIEC, Bengaluru).