Definition
The LLC resonant converter is the isolated DC-DC stage found in most modern high-efficiency ASIC and server power supplies. It takes the regulated high-voltage rail produced by the PFC stage (around 375-400V) and steps it down through a transformer to the low-voltage, high-current output that feeds the hashboards. Its name comes from the resonant tank: two inductances (the resonant inductor Lr and the transformer magnetizing inductance Lm) plus a resonant capacitor Cr.
How resonance buys efficiency
Instead of hard-switching the primary MOSFETs against full voltage, the LLC tank shapes the current so that the switches turn on at zero voltage (ZVS) and the secondary rectifiers turn off at zero current (ZCS). This soft-switching behavior slashes switching loss, which is what lets the converter run at high frequency (commonly 200-350kHz) while staying cool. Output regulation is achieved not by varying duty cycle but by shifting the drive frequency above or below the resonant point.
Why it dominates high-power supplies
LLC converters deliver excellent efficiency, low electromagnetic interference, high power density, and a low component count, which is exactly why they win in the multi-kilowatt supplies that mining and AI compute hardware demand. The trade-off is control complexity: frequency-based regulation and resonant-tank design are less forgiving than a simple PWM buck.
The LLC stage relies on the soft-switching concepts covered in our soft switching (ZVS/ZCS) entry, and its low-side output typically uses synchronous rectification to keep conduction loss low at high current.
In Simple Terms
The LLC resonant converter is the isolated DC-DC stage found in most modern high-efficiency ASIC and server power supplies. It takes the regulated high-voltage rail…