Project Background
The customer, an automotive audio solution provider based in South China, supplies 4×65W Class D amplifier modules to OEM car manufacturers. The original design used generic audio transformers, which exhibited high total harmonic distortion at full power output with 12.8V supply, particularly noticeable in the low-frequency range. Additionally, transient distortion caused by core saturation occurred during cold start at -40℃.
Technical Challenges
- Limited space inside the vehicle required the transformer to fit the existing PCB layout with a height not exceeding 24mm;
- Operating temperature range of -40℃ to +105℃ demanded stable magnetic performance with minimal drift;
- Must pass dielectric withstand voltage testing above 1500V as well as automotive-grade vibration and thermal cycling verification;
- Tight project timeline: only 8 weeks from design confirmation to mass production.
Our Solution
We replaced the original silicon steel core with a high-permeability permalloy core, redesigned the turns ratio and interlayer structure, and switched to a high-temperature-resistant resin during the vacuum impregnation process:
- Redesigned the turns ratio to match the customer's amplifier gain curve, reserving a 30% margin for magnetic flux density in the low-frequency range;
- Utilized sectional winding with double-layer insulating tape, reducing interlayer capacitance by approximately 25% and improving phase shift in the high-frequency range;
- Grounded the metal shielding case to suppress switching noise coupling from the amplifier;
- Delivered the first samples within 3 days, and the customer proceeded to small-batch trial production after bench testing.
Delivered Results
- Total harmonic distortion at full power reduced from 0.8% to within 0.15%, with the most significant improvement in the low-frequency range;
- No core saturation during cold start at -40℃, and inductance drift remained below 3% after 500 thermal cycles;
- All dielectric withstand voltage tests passed at 1500V/1min, with 80,000 units delivered in mass production and a batch defect rate below 0.3‰;
- The customer subsequently switched another subwoofer amplifier on the same platform to this series as well.