Diodes Incorporated FMMT38CTC

Overview

FMMT38CTC from Diodes Incorporated is an NPN silicon planar medium-power Darlington transistor in SOT-23 package, featuring V_CEO = 60 V, h_FE = 5000–10000 at I_C = 100 mA / 500 mA, V_CE(sat) = 1.25 V at I_C = 800 mA / I_B = 8 mA, and P_tot = 330 mW - used for high-gain switching in low-voltage industrial control interfaces.

For engineers reviewing the FMMT38CTC datasheet, FMMT38CTC pinout, FMMT38CTC application, or FMMT38CTC equivalent, key selection criteria include verified Darlington gain linearity at 500 mA, pulsed I_CM = 800 mA capability, SOT-23 thermal derating above 25°C, and documented V_BE(on) = 1.8 V at I_C = 800 mA.

Technical Context

This device implements a monolithic NPN Darlington pair with integrated base-emitter resistor network enabling high DC current gain (h_FE ≥ 5000) while maintaining controlled saturation behavior. It operates with V_EB ≤ 10 V and supports pulsed collector currents up to 800 mA under 2% duty cycle.

The transistor is characterized for operation across –55°C to +150°C junction temperature range, with guaranteed V_CE(sat) ≤ 1.25 V at I_C = 800 mA and I_B = 8 mA, and exhibits <100 nA leakage (I_CBO, I_EBO) at rated blocking voltages.

Key Specifications

Pinout & Package

SOT-23 plastic surface-mount package with standard 3-pin configuration (Emitter, Base, Collector), footprint compatible with JEDEC TO-236AB outline and automated pick-and-place assembly.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-gain Darlington switching applications.

Compared with ZTX851 and MMDT3904, FMMT38CTC delivers 10× higher h_FE and verified 800 mA pulsed capability in the same SOT-23 footprint - making it uniquely suited for space-constrained, high-gain industrial switching where base drive efficiency and voltage margin are critical.

Availability

FMMT38CTC is available at Aetrix Electronics and suitable for industrial relay drivers, LED matrix row controllers, microcontroller GPIO expanders, and thermal-protected solenoid interfaces requiring stable component supply and long-term manufacturability.

Supply support for FMMT38CTC 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 semiconductor company specializing in discrete, analog, and mixed-signal devices for industrial, computing, consumer, and communications markets.

FMMT38CTC belongs to the FMMT38x family of medium-power Darlington transistors designed specifically for high-gain, low-input-drive switching in compact industrial control and interface applications.

FAQ

Is FMMT38CTC pin-compatible with FMMT38A or FMMT38B?

Yes - all FMMT38x variants share identical SOT-23 pinout (Emitter-Base-Collector on pins 1-2-3) and mechanical footprint. However, FMMT38A/B have lower h_FE (500–4000) and are marked "Not Recommended for New Design"; FMMT38CTC is the preferred version for new designs requiring ≥5000 gain.

What is the maximum allowable base resistor value when driving FMMT38CTC from a 3.3 V GPIO?

With V_BE(on) = 1.8 V and required I_B = 8 mA for 800 mA I_C, a 3.3 V source allows R_B ≤ (3.3 V − 1.8 V)/8 mA = 187 Ω. Standard 180 Ω or 220 Ω resistors are commonly used to ensure reliable saturation while limiting base current.

Does FMMT38CTC require a flyback diode when switching inductive loads?

Yes - although V_CEO = 60 V provides margin, inductive kickback from relays or solenoids can exceed this rating. A 1N4148 or similar fast-switching diode must be placed cathode-to-collector, anode-to-ground to clamp transient voltage and protect the transistor's junction.

Can FMMT38CTC operate continuously at 300 mA collector current?

No - the 300 mA rating is the absolute maximum continuous I_C at T_amb = 25°C. At that current, power dissipation reaches ~375 mW (using V_CE(sat) ≈ 1.25 V), exceeding the 330 mW P_tot limit. Derating is required; sustained operation above 250 mA demands heatsinking or forced airflow.