Resonant converters use LC resonant tanks to achieve zero-voltage switching (ZVS) or zero-current switching (ZCS), eliminating switching loss and enabling much higher efficiency and frequency than hard-switched topologies. These converters are the standard choice for server power, EV chargers and telecom power supplies.
This guide compares the main resonant topologies and their magnetic component requirements.
Shaanxi SiRui Technology Co., Ltd. manufactures resonant transformers and resonant inductors for LLC and series resonant converters. Contact: sales@sirui-tech.com | Web: www.sirui-tech.com
1. Why Resonant Topologies?
Hard-switched converters (buck, boost, flyback) have significant switching loss at high frequency. Resonant converters switch at zero voltage or zero current, reducing switching loss by 80–90%. This enables higher frequency (smaller magnetics), higher efficiency (96%+), lower EMI and higher power density.
2. ZVS vs ZCS
ZVS (Zero-Voltage Switching): switch turns ON when voltage across it is zero. More common for MOSFET-based converters.
ZCS (Zero-Current Switching): switch turns OFF when current through it is zero. Used for IGBT-based converters.
3. Main Resonant Topologies
LLC Resonant Converter
The most popular isolated resonant topology. Uses resonant inductor (Lr), magnetizing inductance (Lm) and capacitor (Cr). ZVS achieved over wide load range. Best for 200 W to 10 kW—telecom, server, EV onboard chargers.
Series Resonant Converter (SRC)
Simpler than LLC. Best for constant load applications and induction heating.
4. Magnetic Component Requirements
- Resonant inductor: stable L over frequency/current, low loss, powder cores preferred
- Resonant transformer: leakage inductance often intentionally used as resonant inductor
- High-frequency winding: litz wire essential to reduce skin and proximity loss
- Frequency range: typically 100 kHz–1 MHz
5. Typical Parameters
| Parameter | Typical Range |
|---|---|
| Switching frequency | 100 kHz–1 MHz |
| Efficiency target | 95–97% |
| Power range | 200 W–10 kW |
6. Sirui-Tech Resonant Magnetics
- LLC resonant transformers: EE, EER, planar cores
- Resonant inductors: powder core, litz wire wound
- Leakage inductance control: precise, for resonant tank integration
Conclusion
Resonant converters enable the highest efficiency and power density in modern power supplies. LLC is the dominant isolated topology for server and EV applications. The magnetic components are the key to performance.
Need resonant magnetics? Contact Sirui-Tech at sales@sirui-tech.com with your topology and power level.