MOSFETs in Mining Hardware

Power stage MOSFETs used in hash board buck converters — high-side and low-side switching, common ICs, multimeter testing procedures, and failure modes.

Overview

MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) are the power switching elements in hash board buck converter circuits. Each voltage domain on a hash board has at least two MOSFETs — a high-side switch and a low-side switch — that together convert the 12V input to the sub-0.4V core voltage required by the ASIC chips.

MOSFET failures are one of the most common hardware faults on hash boards, second only to ASIC chip failures. A single shorted MOSFET can take down an entire voltage domain and, in the worst case, dump 12V directly into the ASIC chips, causing catastrophic damage.

High-Side and Low-Side Switching

Every buck converter power stage consists of two MOSFETs working in alternation:

High-Side MOSFET

Connects the 12V input to the inductor during the "on" phase
Switches on for a very short time each cycle (2-3% duty cycle for mining voltages)
Must handle the full input voltage (12V) across drain-source
Requires a gate driver that can supply voltage above the input rail (bootstrap circuit)

Low-Side MOSFET

Provides a current path from the inductor to ground during the "off" phase
Carries current for most of the switching cycle (97-98% of the time)
Sees lower voltage stress but higher RMS current than the high-side
Gate is referenced to ground, making it easier to drive

        12V Input
            │
    ┌───────┤
    │  [High-side MOSFET]  ←── Gate Driver
    │       │
    │       ├─── Switching Node ─── [Inductor] ─── Vout (0.3V)
    │       │                                         │
    │  [Low-side MOSFET]   ←── Gate Driver        [Caps]
    │       │                                         │
    └───────┴───── GND ──────────────────────────── GND

When a high-side MOSFET fails short (drain-source shorted), 12V is applied directly to the output rail. This destroys every ASIC chip in the voltage domain within milliseconds. Always check for this condition before applying power to a board under repair.

Common MOSFETs in Mining Hardware

MOSFET	Manufacturer	Vds Max	Rds(on)	Id Max	Package	Found In
BSC010N04LS	Infineon	40V	1.0 mOhm	100A	TDSON-8	Antminer S19 series
FDMS3600S	ON Semi	40V	1.8 mOhm	80A	Power56	Antminer S17, T17
IPB019N08N3	Infineon	80V	1.9 mOhm	90A	D2PAK	Whatsminer M30S
BSC016N04LS	Infineon	40V	1.6 mOhm	86A	TDSON-8	Antminer S19 XP
TPHR8504PL	Toshiba	40V	0.82 mOhm	120A	SOP Advance	Antminer S21
AON6504	Alpha & Omega	40V	1.4 mOhm	85A	DFN 5x6	Avalon boards

Key Parameters

Vds (Max Drain-Source Voltage): Must exceed the input voltage with margin. 40V rating is standard for 12V input miners.
Rds(on) (On-Resistance): Lower is better — determines power loss and heat generation. Mining MOSFETs are in the 0.8-2.0 milliohm range.
Id (Max Drain Current): Must handle the full domain current. Typically 80-120A rating for 30-50A actual load.
Package: Thermal performance depends on the package. Exposed-pad packages (TDSON, D2PAK) provide better heat dissipation.

How to Test MOSFETs with a Multimeter

MOSFET testing with a multimeter provides a quick pass/fail assessment. It cannot verify all parameters (switching speed, Rds(on) accuracy), but it reliably detects the most common failure modes: short circuits and open circuits.

Preparation

Disconnect all power from the hash board
Wait at least 60 seconds for capacitors to discharge
Set your multimeter to diode mode (displays forward voltage drop)
Identify the MOSFET pins: Gate (G), Drain (D), Source (S)

For common mining MOSFETs in TDSON-8 or similar packages:

Pin 1-3: Source
Pin 4: Gate
Pin 5-8 + Exposed Pad: Drain

Test the Body Diode (Drain to Source)

Every N-channel MOSFET has an internal body diode from source to drain:

Red probe on Source, Black probe on Drain: Should read 0.3V to 0.6V (body diode forward voltage)
Red probe on Drain, Black probe on Source: Should read OL (open line — diode is reverse biased)

If both directions read near 0V: The MOSFET is shorted (most common failure) If both directions read OL: The MOSFET may be open (less common)

Test Gate Isolation

The gate should be electrically isolated from both drain and source:

Probe between Gate and Source: Should read OL in both directions
Probe between Gate and Drain: Should read OL in both directions

If any reading is near 0V: The gate oxide has failed — MOSFET must be replaced

Switching Test (Optional)

This verifies the MOSFET can actually turn on:

Touch the red probe to Gate and Drain simultaneously for a moment — this charges the gate capacitor
Now measure Drain to Source — should read a low voltage (MOSFET is now "on" from the stored gate charge)
Short Gate to Source to discharge the gate — now Drain to Source should return to showing the body diode

This test works because the multimeter's test voltage (typically 2-3V) is enough to partially charge the gate of most N-channel MOSFETs. It does not work reliably on all MOSFETs but is a useful quick check.

Common Failure Modes

1. Short Circuit (Drain-Source)

The most common MOSFET failure in mining hardware. The drain-source junction fails short, creating a permanent conductive path. For a high-side MOSFET, this means 12V appears directly on the output rail.

Causes:

Electrical overstress (voltage spike or overcurrent)
Thermal runaway (insufficient cooling, degraded thermal pad)
Avalanche breakdown from inductive transients

Diagnosis: Diode mode test shows near 0V between drain and source in both directions.

Impact:

High-side short: 12V on the domain output — catastrophic ASIC damage
Low-side short: Domain output pulled to ground — domain dead but ASICs may survive

2. Open Circuit (Drain-Source)

Less common than short circuits. The MOSFET fails open and no longer conducts current.

Causes:

Bond wire failure from thermal cycling
Extreme overcurrent event that vaporized the die

Diagnosis: Body diode test shows OL in both directions. Domain output is 0V because no current can flow.

3. Gate Oxide Failure

The thin gate oxide layer breaks down, creating a short between the gate and channel.

Causes:

Electrostatic discharge (ESD) during handling
Voltage overshoot on the gate driver signal
Manufacturing defect

Diagnosis: Diode mode shows a low reading between gate and source or gate and drain.

In-Circuit Considerations

When testing MOSFETs in-circuit (still soldered to the board), other components connected in parallel can affect your readings. A low resistance reading between drain and source may be caused by a shorted ASIC chip on the output rail, not a failed MOSFET. To conclusively test a MOSFET, desolder at least the drain or source connection to isolate it.

If you suspect a MOSFET failure but the in-circuit test is ambiguous:

First disconnect the inductor from the switching node — this isolates the MOSFET pair from the load
Test the drain-source of each MOSFET with the inductor disconnected
If the MOSFETs test good, the short is downstream (likely a shorted ASIC chip)

Replacement Notes

MOSFETs in TDSON-8 and D2PAK packages have large exposed thermal pads — use generous flux and hot air at 280-300°C
Always replace MOSFETs in pairs (high-side and low-side together) if one has failed short, as the partner MOSFET may have been damaged by the fault current
Verify the replacement matches the original Vds, Rds(on), and package
After replacement, test the domain output voltage before reconnecting the ASIC load
If a high-side MOSFET shorted, inspect every ASIC chip in the domain for damage before powering on

Found In These Miners

MOSFETs are present in every voltage domain on every hash board:

Antminer S19 Series — BSC010N04LS / BSC016N04LS
Antminer S21 — TPHR8504PL
Whatsminer M50 — IPB019N08N3
Whatsminer M30S — IPB019N08N3

MOSFETs in Mining Hardware

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