onsemi ZTX749_J61Z

Overview

ZTX749 from Fairchild Semiconductor is a PNP low-saturation bipolar junction transistor (BJT) designed for high-current switching in power management and linear regulation circuits, featuring V_CEO = −25 V, I_C = −2 A continuous, V_CE(sat) = −300 mV at I_C = −1 A / I_B = −100 mA, and h_FE ≥ 70 at I_C = −50 mA, used in DC-DC converter output stages and relay drivers.

For engineers reviewing the ZTX749 datasheet, pinout, applications, or equivalent options, key selection criteria include verified PNP polarity, TO-226 package thermal resistance (R_θJA = 125°C/W), guaranteed h_FE range across I_C = −50 mA to −2 A, and confirmed BVEBO = −5 V for base-emitter reverse protection in bidirectional control interfaces.

Technical Context

The ZTX749 operates as a medium-power PNP BJT with fixed emitter-base and collector-base junction structures optimized for low V_CE(sat) under high forward current. Its h_FE varies from 70–300 depending on I_C, and it maintains stable breakdown ratings: BV_CEO = −25 V, BV_CBO = −35 V, BV_EBO = −5 V.

Thermal design relies on its TO-226 package's R_θJA = 125°C/W and maximum T_J = +150°C, with PD = 1 W derated above 25°C ambient. C_obo = 100 pF at V_CB = −10 V supports moderate-frequency switching up to f_T = 100 MHz at I_C = −100 mA.

Key Specifications

Pinout & Package

Package: TO-226AE (also designated TO-92 variant with straight leads), epoxy-molded plastic case with 3-terminal through-hole mounting. Dimensions conform to JEDEC TO-226 standard: body height 4.70 mm, lead spacing 1.40 mm, overall length 7.73 mm.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP switching transistor applications.

Compared with MJD2955 and ZTX750, the ZTX749 uniquely balances TO-226 mountability, −300 mV saturation, and 70–300 h_FE range - making it optimal for space-constrained, medium-current PNP switching where thermal budget and board area are critical.

Availability

ZTX749 is available at Aetrix Electronics and suitable for DC-DC converters, industrial relay drivers, linear voltage regulators, and overvoltage protection circuits requiring stable component supply with consistent parametric performance across production lots.

Supply support for ZTX749 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

Fairchild Semiconductor was a U.S.-based semiconductor manufacturer specializing in power discrete devices, analog ICs, and optoelectronics before its acquisition by ON Semiconductor in 2016.

The ZTX749 belongs to Fairchild's legacy ZTX series of general-purpose bipolar transistors engineered for cost-sensitive, medium-power linear and switching applications in industrial controls and power supplies.

FAQ

What is the maximum continuous collector current rating for ZTX749?

The ZTX749 has a maximum continuous collector current rating of −2 A at T_A = 25°C. This rating assumes proper PCB copper area and ambient conditions; derating applies above 25°C per the R_θJA = 125°C/W thermal resistance. At I_C = −2 A, V_CE(sat) rises to −500 mV, increasing conduction loss to 1 W - the device's absolute PD limit.

Does ZTX749 support high-frequency switching applications?

The ZTX749 has an f_T of 100 MHz at I_C = −100 mA and V_CE = −5 V, indicating usable gain up to ~10 MHz. However, its relatively high C_obo = 100 pF and −500 mV V_CE(sat) at high current make it best suited for PWM frequencies below 500 kHz - such as in 24 V industrial SMPS or motor control gate drivers - rather than RF or MHz-class digital switching.

What is the pin configuration of ZTX749 in TO-226 package?

The ZTX749 uses standard TO-226AE (TO-92) pinout: Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector, viewed from flat side with leads down. This matches JEDEC MO-034 and is identical to ZTX750 (NPN) pinout - allowing shared footprint layout when both polarities are used, though biasing must be inverted.

Can ZTX749 replace BC557 in existing designs?

ZTX749 is not a direct replacement for BC557 due to higher current capability (−2 A vs. −100 mA), larger package (TO-226 vs. TO-92), and different h_FE profile (70–300 vs. 125–800). While electrically functional in low-current roles, its thermal mass and saturation behavior differ significantly - requiring validation of base drive, layout clearance, and transient response in any BC557 upgrade path involving ZTX749.

What is the guaranteed minimum h_FE for ZTX749 at I_C = −1 A?

The ZTX749 guarantees h_FE ≥ 75 at I_C = −1 A, V_CE = −2 V, per its official datasheet. This value is measured under pulsed conditions (≤300 µs, ≤2% duty cycle) to avoid self-heating effects. For DC operation at −1 A, design margins should account for h_FE degradation near T_J = +150°C, where gain may fall to ~60% of room-temperature value.