Vishay Siliconix IRF840A

Overview

IRF840A from Vishay Siliconix is a 500 V, 8.0 A N-channel power MOSFET in TO-220AB package, featuring 0.85 Ω R_DS(on) at V_GS = 10 V, 38 nC total gate charge, and 510 mJ single-pulse avalanche energy - designed for high-voltage switching in offline SMPS and UPS systems.

For engineers reviewing the IRF840A datasheet, IRF840A pinout, IRF840A application, or IRF840A equivalent, this discrete power transistor supports robust unclamped inductive switching, offers characterized C_oss eff. (56 pF), and delivers stable performance across -55 °C to +150 °C junction temperature range with validated dV/dt ruggedness up to 5.0 V/ns.

Technical Context

The IRF840A employs planar vertical DMOS technology optimized for high-voltage hard-switching topologies. Its gate threshold voltage (2.0–4.0 V) enables standard 10 V gate drive compatibility, while low Q_gd/Q_g ratio (18/38 nC) supports fast turn-off and reduced Miller-induced shoot-through risk in bridge configurations.

Thermal design is enabled by R_thJC = 1.0 °C/W and R_thCS = 0.50 °C/W, allowing 125 W continuous dissipation at T_C = 25 °C. The integrated body diode exhibits t_rr = 422–633 ns and Q_rr = 2.16–3.24 μC under 100 A/μs dI/dt, supporting moderate-frequency freewheeling in forward and half-bridge converters.

Key Specifications

Pinout & Package

IRF840A uses the industry-standard TO-220AB package with isolated tab (drain-connected), 3-pin through-hole mounting, and 1.0 °C/W junction-to-case thermal resistance. Mounting torque: 10 lbf·in (1.1 N·m) for 6-32 or M3 screw.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage N-channel MOSFET applications.

Compared with STP5NK50ZFP and IXTH8N50L, the IRF840A balances proven ruggedness, standardized TO-220AB mechanical fit, and sufficient 8.0 A/125 W capability for cost-sensitive 500 V SMPS - making it a field-proven choice where avalanche reliability and dV/dt immunity outweigh marginal R_DS(on) or Q_g advantages.

Availability

IRF840A is available at Aetrix Electronics and suitable for switch mode power supplies, uninterruptible power supplies, and high-speed industrial switching applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant sourcing.

Supply support for IRF840A includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Vishay Siliconix is a global leader in discrete semiconductors, specializing in high-reliability MOSFETs, diodes, and optoelectronics for power, signal, and sensing applications.

The IRF840A belongs to Vishay's legacy high-voltage power MOSFET product line, engineered for ruggedness and consistency in offline AC/DC conversion, motor control, and industrial power switching.

FAQ

What is the maximum continuous drain current for the IRF840A at 100 °C case temperature?

The IRF840A supports 5.1 A continuous drain current at T_C = 100 °C, per its linear derating curve from 8.0 A at 25 °C. This value is confirmed in the Absolute Maximum Ratings table and reflects thermal limitation of the TO-220AB package. Designers must verify heatsink sizing using R_thJC = 1.0 °C/W and ambient conditions. The IRF840A remains within safe SOA limits up to this current when operated with proper gate drive and layout.

Does the IRF840A have a fully characterized body diode for synchronous rectification?

No - the IRF840A body diode is specified for freewheeling and clamping, not synchronous rectification. Its t_rr (422–633 ns) and Q_rr (2.16–3.24 μC) are characterized for hard-switched recovery, but reverse recovery is not optimized for zero-voltage switching. The IRF840A datasheet does not specify forward voltage softness or reverse recovery softness factor. For synchronous rectification, dedicated low-Q_rr MOSFETs such as the SiR872DP should be considered instead of the IRF840A.

Is the IRF840A suitable for use in a half-bridge configuration without a Miller clamp?

Yes - the IRF840A's specified peak dV/dt immunity of 5.0 V/ns provides margin against false turn-on in typical half-bridge layouts with moderate layout care. Its 18 nC Q_gd and 9.0 nC Q_gs yield a favorable Q_gd/Q_gs ratio (~2.0), reducing Miller feedback sensitivity. However, for >200 kHz operation or high dV/dt nodes (>3 V/ns), a dedicated Miller clamp or negative gate turn-off remains recommended. The IRF840A has been widely deployed in 50–100 kHz half-bridges without clamps.

What is the effective output capacitance (C_{oss eff.}) of the IRF840A and why is it important?

The IRF840A specifies C_{oss eff.} = 56 pF, measured across V_DS = 0 V to 400 V. Unlike static C_oss, this value represents the fixed capacitance yielding the same energy storage and switching timing as the nonlinear actual C_oss. It is essential for calculating turn-off loss (E_off ≈ ½ × C_{oss eff.} × V_DS² × f_sw) and designing resonant transitions in LLC or phase-shifted full-bridge converters. This parameter is explicitly defined and tested for the IRF840A.

Can the IRF840A replace the original IRF840 in existing designs?

Yes - the IRF840A is a direct enhancement of the IRF840, with identical pinout, package, and voltage/current ratings, plus improved gate, avalanche, and dV/dt ruggedness. Key specs including V_DS = 500 V, R_DS(on) = 0.85 Ω, Q_g = 38 nC, and E_AS = 510 mJ are either identical or improved. No PCB or schematic changes are required. The IRF840A maintains full backward compatibility while offering higher reliability in demanding switching environments.