IXYS SMPS Solution

SMPS topology selection depends on power level and requirements: (1) Flyback - best for <150W, simple, low cost, good for multiple outputs

(2) Forward - good for 100-500W, better transformer utilization than flyback

(3) Half-bridge/Full-bridge - for 500W-5kW, efficient, good for high power

(4) LLC resonant - for 100W-1kW, very high efficiency, excellent for server PSUs

(5) Buck/Boost - for DC-DC conversion, simple, efficient. Consider input voltage range, output requirements, efficiency targets, and cost constraints. Contact LiTong FAE for topology recommendations.

Flyback for <150W, LLC for high-efficiency 100W-1kW, bridge topologies for >500W.

EMI minimization techniques for SMPS: (1) Soft switching - use resonant topologies or snubbers to reduce dV/dt and dI/dt

(2) Gate drive - optimize gate resistance to control switching speed

(3) Layout - minimize loop areas in high di/dt paths, use ground planes

(4) Filtering - use proper input and output filters with X and Y capacitors

(5) Shielding - use shielded inductors and transformers

(6) Soft recovery diodes - IXYS fast recovery diodes feature soft recovery to reduce EMI. Start with good layout practices - this is the most cost-effective EMI mitigation strategy.

Use soft switching, optimize layout, and select soft recovery diodes to minimize EMI.

Synchronous rectification (SR) replaces diodes with MOSFETs for output rectification: (1) Benefits - reduces rectification losses from 0.5-1V diode drop to I²×Rds(on), improves efficiency 2-5%

(2) Applications - recommended for outputs <12V or currents >10A

(3) Control - requires SR controller IC to drive MOSFET gates with proper timing

(4) Challenges - adds complexity, requires careful timing to avoid shoot-through. For 5V/20A output, SR can save 10-15W compared to diode rectification. IXYS offers low-Rds(on) MOSFETs ideal for SR applications.

Use SR for low-voltage high-current outputs (<12V, >10A) to improve efficiency.

SMPS MOSFET selection criteria: (1) Voltage rating - 1.5-2x maximum drain voltage including spikes

(2) Current rating - based on thermal constraints, not just maximum current

(3) Rds(on) - lower is better for conduction losses, but consider cost

(4) Gate charge (Qg) - lower Qg reduces gate drive losses and enables faster switching

(5) Output capacitance (Coss) - affects switching losses in hard-switched topologies

(6) Body diode - check reverse recovery for bridge topologies. For high-frequency designs (>200kHz), prioritize low Qg. For high-current designs, prioritize low Rds(on). IXYS provides devices optimized for various SMPS applications.

Balance Rds(on) and Qg based on operating frequency and current requirements.

SMPS magnetic component selection: (1) Transformers - for isolated topologies (flyback, forward, LLC), design for operating frequency, power level, and voltage ratios

(2) Inductors - for buck, boost, and output filters, calculate inductance based on ripple current requirements

(3) Core material - ferrite for high frequency (>50kHz), powdered iron for lower cost applications

(4) Winding - use litz wire for high frequency to reduce skin effect

(5) Gap - gapped cores prevent saturation in inductors and flyback transformers. Work with magnetic component suppliers or use design software. LiTong FAE can provide guidance on magnetic design for IXYS-based SMPS.

Design magnetics for operating frequency and power level; use ferrite cores for high frequency.