Buck Converter

A buck converter is a DC-DC switching regulator that steps a higher voltage down to a lower one. On an ASIC mining hashboard, buck converters are what bridge the gap between the PSU's 12V rail and the very low voltage the hashing chips actually run at — typically somewhere in the 0.3–1.2V range at the chip, depending on generation and clock. (Its counterpart, a boost converter, steps voltage up; hashboards almost exclusively use the step-down buck topology.)

One converter per voltage domain

The chips on a hashboard are split into voltage domains, and each domain has its own buck stage delivering a precisely regulated rail to that cluster of chips. These converters move serious current — often 20A or more per domain — in a cramped, hot space, so they are among the most thermally stressed parts on the board.

Why they fail

A buck converter is built from a switching regulator IC, high-current MOSFETs, an inductor, output capacitors, and current-sense resistors. Heat cycling and overcurrent kill the MOSFETs and dry out the capacitors, which collapses or destabilizes a domain's rail and drops the board's hashrate. Reading each domain's voltage with a meter is how technicians localize a failed converter before rework.

The measurement workflow is detailed in our voltage-domain measurement guide and the broader hashboard repair deep dive.

Where Converters Actually Sit on an Antminer Board

The real power chain on modern Antminer hashboards has more stages than “12V in, core voltage out.” The PSU's 12–15 V rail passes a MOSFET switch, then a boost stage raises it to roughly 19–25 V depending on model; from that boosted rail, per-domain regulators produce the working voltages. On the S21 and S21 XP, most domains are fed by LDO chains (typically three LDOs per domain producing 1.2 V signaling and 0.8 V core rails), while the domains at the top of the chain get dedicated MP2019 converters delivering 2.0–2.5 V to their LDOs. Because the chips in a domain sit in series, the domain voltage equals per-chip voltage times chips per domain — about 0.36 V on an S19 (2 chips/domain), ~1.2 V on an S21 (9 chips/domain), ~1.04 V on an S21 XP (7 chips/domain). Regulation is per-domain, never per-chip.

How a Buck Stage Works

A buck converter chops the input with a high-side MOSFET switching tens to hundreds of kilohertz, feeding an inductor that smooths the chopped waveform into steady current, with output capacitors absorbing the ripple; a control IC adjusts the switching duty cycle against feedback so the output holds its setpoint as load swings. The duty cycle is roughly output over input voltage — the elegance of the topology is that energy is switched rather than burned, so efficiency stays high even across a large step-down. Contrast the LDO used inside each domain: a linear regulator that drops voltage by dissipating the difference as heat — simple and clean, but only sensible for small voltage drops, which is exactly how hashboards deploy them.

Diagnosing a Dead or Sagging Domain

Converter faults localize well with a bench methodology. First verify the boost output (expect ~19–25 V per model); no boost means no domains anywhere, and the suspects are the boost IC, MOSFET, inductor, or diode. With boost present, sweep the domain test points: healthy domains sit within ±50 mV of each other, a domain 100 mV+ low indicates a partial short (failed chip, blown capacitor, or a dying regulator), and a high or absent reading points to an open — cracked solder or a failed regulator output. On high-side domains, check the MP2019-class buck output (2.0–2.5 V) before blaming chips. A thermal camera accelerates all of this: a shorted MOSFET or LDO glows, an open one stays cold. Work through it systematically with the ASIC fault finder before any iron touches the board.

See measurement points in the diode & voltage reference.