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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

Diodes Incorporated FMMT458TC

Name: FMMT458TC
Brand: Diodes Incorporated
SKU: FMMT458TC
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: FMMT458TC

Manufacturer:: Diodes Incorporated

Category:: Single Bipolar Transistors

Package:: TO-236-3, SC-59, SOT-23-3

Datasheet:: FMMT458TC.pdf

Description:: TRANS NPN 400V 0.225A SOT-23-3

Quantity:: RFQ Add To RFQ list

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Inventory:8,234

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Product details

Overview

FMMT458TC 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 = 400V. It delivers stable h_FE up to 300 at I_C = 100mA and supports fast switching with t_on = 135ns and t_off = 2260ns, used in flyback snubber circuits and HV DC-DC bias supplies.

For engineers reviewing the FMMT458TC datasheet, FMMT458TC pinout, FMMT458TC application, or FMMT458TC equivalent, key selection criteria include verified 400V V_CEO, SOT23 thermal resistance (R_θJA = 250°C/W), h_FE consistency across 1–100mA, ESD HBM rating of 4kV, and complementary PNP pairing with FMMT558.

Technical Context

This NPN bipolar junction transistor operates in linear and switching modes with guaranteed BV_CEO ≥ 400V and V_BE(sat) ≤ 0.9V at I_C = 50mA/ I_B = 5mA. Its f_T = 50MHz enables use in medium-frequency switch-mode control loops.

The device features low leakage (I_CBO, I_EBO, I_CES ≤ 100nA at rated voltages) and robust transient thermal impedance (197°C/W junction-to-lead), validated under pulsed conditions (≤300µs, ≤2% duty cycle).

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	400V - Enables direct use in 380V AC rectified bus and offline SMPS primary-side snubbers
I_C (cont.)	225mA - Supports sustained current in auxiliary bias windings and gate drive isolators
P_D	500mW - Requires minimal PCB copper area (15×15mm 1oz FR-4) for thermal management
h_FE	100–300 - Maintains predictable base drive requirements across 1–100mA operating range
t_off	2260ns - Limits switching losses in <200kHz flyback and resonant converters
ESD HBM	4000V - Reduces handling sensitivity during SMT assembly and board-level test
C_obo	5pF - Minimizes capacitive coupling in high-dv/dt gate driver feedback paths

Pinout & Package

Package: SOT23 - Surface-mount plastic package with matte tin-plated leads, moisture sensitivity level 1, UL 94V-0 rated molding compound, weight ≈ 0.008g.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Current sink terminal	Connected to ground or low-side return path; lowest voltage node during conduction
2 (Base)	Control input	Receives current-limited drive (max 200mA) to saturate or cut off the transistor
3 (Collector)	High-voltage output node	Handles up to 400V reverse bias; routed away from sensitive analog traces per layout guidelines

Key Features

Feature	Design Value
400V breakdown rating	Guaranteed V_CEO and V_CBO ≥ 400V ensures margin over 380V DC link in universal-input SMPS
High h_FE consistency	h_FE = 100–300 across 1–100mA enables single-base-resistor design for multiple load conditions
SOT23 thermal performance	R_θJL = 197°C/W allows direct solder-point thermal relief without added heatsinking
Green RoHS compliance	Halogen- and antimony-free (<900ppm Br/Cl, <1000ppm Sb) meets automotive and industrial environmental mandates

Applications

Industrial Flyback Snubber

AC-DC Auxiliary Bias Supply

Use Scenario: Clamps voltage spikes across transformer primary during MOSFET turn-off in 20–100kHz flyback converters.

IC Role / Device Role / Timing Role: NPN transistor configured as active clamp switch, triggered by RC-delayed base drive synchronized to primary current zero-crossing.

Use Value: Replaces passive RCD networks, reducing power loss by >30% and enabling tighter V_CE regulation at 400V stress levels.

Use Scenario: Provides isolated +12V/50mA bias for PWM controller ICs in offline AC-DC power supplies.

IC Role / Device Role / Timing Role: Linear regulator pass element driven by Zener-referenced base circuit, operating in active region with fixed V_CE ≈ 3V.

Use Value: Delivers stable output with <2% line/load regulation across 85–265V AC input, leveraging h_FE stability to minimize base current variation.

High-Voltage Signal Switching

Automotive LED Driver Reference

Use Scenario: Switches 200–400V logic-level signals in PLC I/O modules and HV sensor interface circuits.

IC Role / Device Role / Timing Role: High-side or low-side level translator, biased into saturation with I_B/I_C = 1/10 ratio for minimal V_CE(sat).

Use Value: Achieves V_CE(sat) ≤ 500mV at I_C = 50mA, reducing heat generation in densely packed DIN-rail enclosures.

Use Scenario: Serves as current reference transistor in constant-current LED drivers for commercial vehicle lighting.

IC Role / Device Role / Timing Role: Precision current mirror master device, matched to slave transistor via shared V_BE and thermal coupling on same die substrate.

Use Value: Maintains ±3% current accuracy over -40°C to +125°C ambient, supported by low I_CBO ≤ 100nA at 320V.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
ZTX458	V_CEO = 300V (lower than FMMT458TC's 400V); h_FE min = 100 at I_C = 10mA only	Not suitable for 380V DC bus designs; limited to ≤265V AC-derived rails	Select only when system max V_CE < 280V and thermal derating margin is available
MMBT4401	V_CEO = 40V (severely underspecified); I_C = 600mA but unsafe above 50V	Cannot replace in HV snubber or bias roles; restricted to low-voltage logic-level switching	Reject for any application requiring >100V blocking capability

Compared with ZTX458 and MMBT4401, FMMT458TC uniquely sustains 400V V_CEO with verified h_FE >100 up to 100mA and 5pF C_obo, making it the only viable choice for compact, thermally constrained 380V DC bus auxiliary circuits.

Availability

FMMT458TC is available at Aetrix Electronics and suitable for industrial flyback snubbers, AC-DC auxiliary bias supplies, and high-voltage signal switching requiring stable component supply and full RoHS/Green compliance.

Supply support for FMMT458TC 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, specializing in high-reliability power management, signal integrity, and protection solutions.

The FMMT458TC belongs to Diodes' high-voltage bipolar transistor product line, engineered for robust operation in offline power conversion, industrial control, and automotive-qualified auxiliary circuits (with Q-grade variant FMMT458Q).

FAQ

What is the maximum safe operating voltage for FMMT458TC in continuous DC mode?

The FMMT458TC is rated for V_CEO = 400V and V_CBO = 400V under DC conditions at T_A = +25°C. Derating is required above 25°C ambient: power dissipation drops linearly to zero at +150°C, and voltage capability remains stable per JEDEC JESD78 guidelines for bipolar transistors. No additional external clamping is needed below 400V DC.

Can FMMT458TC be used as a direct replacement for FMMT558 in complementary circuits?

No - FMMT458TC is an NPN transistor while FMMT558 is its complementary PNP counterpart. They share identical SOT23 packaging and voltage/current ratings (400V, 225mA), but opposite polarity and biasing requirements. Interchanging them would reverse circuit functionality and likely cause immediate failure due to incorrect current flow direction.

Does FMMT458TC require a heatsink in standard SOT23 mounting?

No heatsink is required when mounted on a 15×15mm 1oz copper FR-4 PCB per datasheet test condition. Its R_θJA = 250°C/W and R_θJL = 197°C/W allow full 500mW dissipation at T_A ≤ +75°C. For operation above 75°C ambient or >300mW continuous power, localized copper pour or thermal vias are recommended instead of discrete heatsinks.

Is the FMMT458TC marking code "458" sufficient for full part identification?

Yes - "458" is the official product type marking code for all FMMT458 variants (TA, TC, Q-grade). The suffix (e.g., "TC") denotes reel size and packing quantity (10,000 pcs on 13-inch reel), not electrical or thermal differences. Electrical specs, package dimensions, and reliability data are identical across TA, TC, and Q-grade versions.

FMMT458TC Specifications

Product attributes: Attribute value

Manufacturer:: Diodes Incorporated

Series:: -

Package/Case:: TO-236-3, SC-59, SOT-23-3

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 225 mA

Voltage - Collector Emitter Breakdown (Max):: 400 V

Vce Saturation (Max) @ Ib, Ic:: 500mV @ 6mA, 50mA

Current - Collector Cutoff (Max):: 100nA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 100 @ 50mA, 10V

Power - Max:: 500 mW

Frequency - Transition:: 50MHz

Operating Temperature:: -55°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-23-3

FMMT458TC FAQ

1.How can I place an order for FMMT458TC through Aetrix?

Please submit a Request for Quotation (RFQ) for FMMT458TC on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for FMMT458TC reliable?

The price and inventory of FMMT458TC are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for FMMT458TC is usually 5 days.

3.What payment methods are accepted for FMMT458TC?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for FMMT458TC transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for FMMT458TC?

FMMT458TC orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your FMMT458TC order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for FMMT458TC?

For technical support, including FMMT458TC datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your FMMT458TC requirements.

6.How does Aetrix verify that FMMT458TC is sourced from the original manufacturer or authorized distributors?

All FMMT458TC products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that FMMT458TC meets industry standards.

7.What is the process for return or replacement of FMMT458TC?

All FMMT458TC units undergo pre-shipment inspection (PSI). If there is an issue with FMMT458TC, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The FMMT458TC part is unused and in its original packaging.

Return procedure for FMMT458TC:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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