Discrete

MOSFETs

The workhorse switch and amplifier of modern electronics.

What is it?

A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a voltage-controlled switch. Applying voltage to the gate enables current flow between drain and source. Used as the switching element in DC-DC converters, motor drivers, power-distribution gating, and signal switching. Available in N-channel (more common, lower RDS(on) per area) and P-channel (simpler high-side driving).

N-channel MOSFET as a low-side switchV+loadDG(gate)SWhen VGS > VGS(th):• channel forms between D and S• current flows: V+ → load → D → S → GND• RDS(on) drops as VGS risesWhen VGS < VGS(th):• channel pinches off• switch is open, load is disconnected
Low-side N-channel MOSFET switch. Pulling the gate above the threshold voltage VGS(th) enables current flow from drain to source, energising the load. Below VGS(th), the channel is off and the load is disconnected.

When do you need it?

  • Switching element in any DC-DC converter (buck, boost, flyback, half-bridge).
  • Motor drivers (BLDC, stepper, brushed DC).
  • Load switches and battery protection.
  • Reverse-polarity protection (ideal-diode circuit with PMOS).
  • Signal-level analog switches (small-signal NMOS like 2N7002 for level shifting, gating).

How to pick the right one

Polarity (N or P)
N-channel for low-side switching or sync-rectifier; P-channel for high-side driving with simple gate drive.
VDS (Drain-Source breakdown)
Must exceed the maximum voltage seen across the switch. 30 V, 40 V, 60 V, 100 V, 150 V, 200 V, 650 V, 800 V common.
RDS(on) at your VGS
Conduction resistance. Lower = less heating but bigger die / cost. Spec'd at VGS = 10 V (logic) or 4.5 V (low-voltage gate).
VGS(max) and VGS(th)
VGS(max) is the rating you must not exceed. VGS(th) is where the MOSFET starts conducting — matters for sub-2 V drive applications.
Qg (Total gate charge)
Energy needed to switch the gate. Smaller Qg = faster switching, lower driver loss. Critical at high fSW.
Package
SOT-23 / SOT-323 / SOT-363 / DFN1006 for small signal; DFN2x2 / DFN3x3 / SO-8 / TO-220 / TO-263 / TOLL for power.

What Magnias offers

Magnias MOSFET portfolio is one of our strongest categories — small-signal NMOS like 2N7002CL (always use 2N7002CL, not 2N7002KL), low-voltage power NMOS for buck synchronous rectifiers, 60-200 V single and dual N-channel for load switches, and 600-800 V super-junction for offline PFC / flyback applications. AEC-Q101 automotive versions widely available. Note: PMH80N650PK is EOL — request our latest 650 V SJ recommendation.

Common questions

Why does the datasheet show RDS(on) at multiple VGS values?
MOSFET on-resistance drops with higher gate drive until it saturates. Pick the VGS that matches your gate-driver output and look at THAT RDS(on) — don't trust the headline 10 V number if you only drive the gate to 4.5 V.
What does 'logic-level' MOSFET mean?
VGS(th) is low enough (typically <2 V) that the part is fully-enhanced by 3.3 V or 4.5 V gate drive. Critical for microcontroller-direct driving.
2N7002 — what variant should I use?
Magnias recommends 2N7002CL, not 2N7002KL — the CL variant is the current-production drop-in.
Why is super-junction better at high voltage?
Charge-balanced columns let the device hold off voltage with less depletion width, so RDS(on) scales much better than planar designs at 500 V+. SJ MOSFETs are the standard for offline PFC and LLC applications.
How do I avoid shoot-through in a half-bridge?
Dead-time between turning off one FET and turning on the other. Minimum dead-time = max(td(off)) + Qg / drive current. Most gate-driver ICs let you program this directly.
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