Diodes Incorporated FMMT458QTA

Overview

FMMT458QTA from Diodes Incorporated is a 400V NPN high-voltage transistor in SOT23 package, rated for 225mA continuous collector current and 1A peak pulse current, with 500mW power dissipation and V_CEO/V_CBO = 400V. It delivers stable h_FE up to 300 at I_C = 100mA and supports high-voltage switching in flyback converters, relay drivers, and industrial control interfaces.

For engineers reviewing the FMMT458QTA datasheet, FMMT458QTA pinout, FMMT458QTA application, or FMMT458QTA equivalent, key selection criteria include verified 400V breakdown voltage, SOT23 thermal performance (R_θJA = 250°C/W), V_CE(sat) ≤ 500mV at I_C = 50mA/ I_B = 6mA, and complementary PNP pairing with FMMT558.

Technical Context

This NPN bipolar junction transistor operates in linear and saturated switching modes, with guaranteed BV_CEO and BV_CBO ≥ 400V under pulsed test conditions (≤300µs, ≤2% duty cycle). Its h_FE spans 100–300 across I_C = 1mA to 100mA, supporting precise current gain control in high-impedance base-drive circuits.

Thermal design relies on R_θJL = 197°C/W (junction-to-lead) and validated derating down to zero power at +150°C ambient. ESD robustness includes 4kV HBM and ≥400V MM ratings, enabling use in non-isolated industrial environments without additional protection circuitry.

Key Specifications

Pinout & Package

Package: SOT23 - Molded plastic, halogen/antimony-free, matte tin-plated leads, moisture sensitivity level 1, weight ≈ 0.008 g.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage NPN transistor applications.

Compared with ZTX458 and MMBT4401, FMMT458QTA uniquely balances 400V withstand, SOT23 mountability, and h_FE stability-making it the only viable choice for 277V AC-derived 380V DC industrial switching where both voltage headroom and thermal predictability are mandatory.

Availability

FMMT458QTA is available at Aetrix Electronics and suitable for industrial relay drivers, AC-DC flyback controllers, and high-voltage LED string drivers requiring stable component supply and long-term manufacturing continuity.

Supply support for FMMT458QTA 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

Diodes Incorporated is a global manufacturer of discrete semiconductors and analog ICs, headquartered in Plano, Texas, with design, manufacturing, and sales operations across Asia, Europe, and North America.

FMMT458QTA belongs to Diodes' high-voltage bipolar transistor product line, engineered specifically for industrial and automotive auxiliary power systems where reliability under sustained 400V stress and consistent gain across temperature are critical.

FAQ

What is the maximum safe operating voltage for FMMT458QTA in continuous DC applications?

The FMMT458QTA is rated for V_CEO = 400V and V_CBO = 400V under pulsed test conditions (≤300µs, ≤2% duty cycle). For continuous DC operation, design must maintain V_CE ≤ 400V with appropriate safety margin-typically ≤320V-to account for transients, temperature drift, and long-term reliability per JEDEC JESD78 guidelines.

Can FMMT458QTA be used in avalanche mode?

No. The FMMT458QTA is not characterized or qualified for controlled avalanche operation. Its SOA curve (Figure 1) shows no second breakdown region beyond 400V, and datasheet specifications do not define avalanche energy (E_AS) or ruggedness testing. Use only within specified V_CEO/V_CBO limits with external clamping if voltage overshoot is expected.

How does the SOT23 package affect thermal performance in high-current switching?

In SOT23, FMMT458QTA achieves R_θJA = 250°C/W on 15×15mm FR-4 with 1oz copper. At I_C = 225mA and V_CE(sat) = 500mV, power dissipation is ~113mW, resulting in ~28°C junction rise above ambient-well within the -55°C to +150°C operating range. Larger copper areas or thermal vias further improve this.

Is FMMT458QTA pin-compatible with FMMT458TA or FMMT458TC?

Yes. All FMMT458 variants-including QTA, TA, and TC-share identical SOT23 mechanical dimensions, pinout (E-B-C), and electrical specifications. Differences are limited to packaging format (reel size/tape width) and internal quality screening; no circuit-level redesign is needed when substituting between them.