Flat Transformer Design Guide
A flat transformer, also known as a planar transformer, uses flat copper traces on printed circuit boards instead of round wire windings. This design achieves extremely low profile height, excellent thermal performance, and repeatable parasitic control, making it ideal for high density power converters.
Working Principle
Flat transformers follow the same electromagnetic principles as conventional transformers, but the windings are implemented as multi-turn PCB traces or copper foil. The planar core (usually E, ER, or EI shapes made from high frequency ferrite) encloses the PCB winding layers, providing tight magnetic coupling and predictable leakage inductance.
Key Advantages
| Advantage | Description |
|---|---|
| Low profile | Height below 10 mm typical |
| Excellent thermal | Large surface area dissipates heat |
| Repeatable parasitics | Consistent inter-winding capacitance |
| High power density | Up to several kW in small volume |
| Automated assembly | Compatible with SMT processes |
Key Specifications Table
| Parameter | Typical Value | Note |
|---|---|---|
| Frequency | 200 kHz – 5 MHz | Depends on ferrite grade |
| Power | 10 W – 5 kW | Converter topology dependent |
| Efficiency | 96 – 99% | Careful winding design |
| Isolation | 1 – 5 kV | Creepage and clearance design |
| Core material | Mn-Zn power ferrite | PC40, PC95, N87 grades |
Design Steps
Step 1: Select core shape and size from the power requirement. Step 2: Determine turns ratio and layer stack-up. Step 3: Design PCB winding with proper copper weight and trace width. Step 4: Simulate or measure leakage inductance and AC resistance. Step 5: Verify thermal performance and isolation clearance.
Applications
Flat transformers are used in server power supplies, telecom rectifiers, on-board chargers for EVs, GaN/SiC DC-DC converters, and high power LED drivers.
Sirui Technology Flat Transformers
Shaanxi SiRui Technology Co., Ltd. manufactures custom flat / planar transformers with ISO9001, RoHS, REACH, SGS and CTI certification. We provide design support and fast prototyping for global customers. Send your specifications to sales@sirui-tech.com.
FAQ
Q: What is the minimum height achievable? A: With planar cores and PCB windings, transformer height can be under 8 mm. Q: Do you provide complete planar transformer assemblies? A: Yes, we supply core + PCB winding assemblies ready for integration.