IRF520 MOSFET: Threshold Voltage Is Not a Gate-Drive Rating
The IRF520 MOSFET is frequently discussed beside Arduino switching modules, but its threshold voltage is not a promise of low-loss operation from a GPIO. Read the on-resistance test conditions, thermal limits and actual driver circuit before using it to control a load.
Read the gate voltage beside the resistance
The referenced Vishay IRF520 datasheet specifies its maximum drain-source on-resistance at a gate-source voltage of 10 V. That condition matters as much as the resistance number. Applying 3.3 V or 5 V to a gate is not the same test condition, even if the load appears to turn on. Do not present the device as unconditionally suitable for direct logic-level drive.
Understand what threshold actually measures
The threshold test is made at a very small specified drain current, 250 microamps in the linked datasheet. It indicates the onset of conduction under that test, not a gate voltage for switching the advertised load current efficiently. Typical transfer curves are also not a guaranteed maximum resistance specification for every part and temperature.
Separate a module label from its circuitry
A board sold as a MOSFET driver may contain little more than a transistor, terminals, indicator and resistors. Check whether it includes a real gate driver and what voltage reaches the gate relative to the source. An illuminated input LED says nothing about MOSFET conduction loss or whether the load voltage is close to its intended value.
Calculate losses from appropriate conditions
For a fully enhanced switch, conduction loss is approximately current squared times on-resistance, using a resistance valid for the gate voltage and temperature. Switching losses and inductive energy add further constraints. A datasheet current figure based on controlled case temperature is not a breadboard continuous-current allowance. Include heat removal and the safe operating area in the design.
Inspect the complete low-side circuit
Verify gate, drain, source and exposed-tab connections for the exact manufacturer package. Provide a defined gate-off state and a drive path appropriate to switching frequency. An inductive load needs suitable suppression and energy handling; the internal body diode is not a universal replacement for a correctly designed external protection network.
Choose a better fit when needed
If only low-voltage logic drive is available, consider a MOSFET with guaranteed resistance at the actual gate voltage or a suitable driver arrangement. Compare current, voltage, heat, gate charge and protection together. This guide is for small low-voltage learning circuits, not mains switching or a validated high-power controller.Newest in the store
Availability and illustration note
No matching product was found in the checked Epro catalog for this topic on 19 October 2026. This article therefore does not quote an Epro price or claim stock. The original illustration shows conceptual signal flow only, not a complete circuit or a photograph of a supplied product. Obtain a documented component or carrier with a known pinout and electrical specification.
Frequently asked questions
Does a 2–4 V threshold make IRF520 a 3.3 V power switch?
No. Threshold is measured at a small test current and does not guarantee low resistance at 3.3 V.
Does a module input LED prove low switching loss?
No. Measure and evaluate the actual gate-source voltage, load current and drain-source voltage under safe conditions.
Related Epro reading
Review breadboard connections before assembling a prototype. For controller expansion, the Mega 2560 pin guide explains why pin names and electrical limits must be checked together.
Technical references and test limitations
This guide uses the documentation linked below. The procedures are for a controlled, low-voltage learning setup; no independent hands-on test of the particular seller board is claimed. Record the actual part markings, wiring and firmware version before drawing conclusions from a test.