Diodes Incorporated ZTX851

Overview

ZTX851 from Diodes Incorporated is an NPN silicon planar medium-power high-current transistor with V_CEO = 60 V, continuous I_C = 5 A, peak I_CM = 20 A, V_CE(sat) as low as 100 mV at I_C = 5 A / I_B = 200 mA, and P_tot = 1.2 W at T_amb = 25°C - used in emergency lighting circuits requiring robust switching under sustained load.

For engineers reviewing the ZTX851 datasheet, ZTX851 pinout, ZTX851 application, or ZTX851 equivalent, key selection criteria include verified saturation voltage at high current, thermal resistance (R_th(j-amb) = 150 °C/W), h_FE stability up to 5 A, and TO-92 mechanical compatibility for legacy PCB layouts.

Technical Context

The ZTX851 operates as a medium-power NPN switch optimized for DC and pulsed load control, supporting I_C up to 5 A continuously and 20 A in short pulses (≤2% duty, 300 µs width). Its low V_CE(sat) minimizes conduction loss in battery-backed systems.

It features h_FE = 100–300 across I_C = 10 mA to 10 A (with specified test conditions), f_T = 130 MHz at I_C = 100 mA/V_CE = 10 V, and C_obo = 45 pF at V_CB = 10 V - confirming suitability for medium-speed switching, not RF amplification.

Key Specifications

Pinout & Package

Package: TO-92 (E-Line compatible, 3-lead plastic case). Mounting requires ≥1 inch² copper area for rated P_tot.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN high-current switching applications.

Compared with ZTX851, ZTX853 trades current capability for voltage margin and fits same TO-92 layout, while MJD127 delivers higher current but demands thermal management and board space - making ZTX851 optimal for compact 5 A switching where 60 V rating suffices.

Availability

ZTX851 is available at Aetrix Electronics and suitable for emergency lighting circuits, DC motor starters, industrial annunciator panels, and power supply foldback limiters requiring stable component supply and TO-92 mechanical compatibility.

Supply support for ZTX851 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 and manufacturing operations across Asia and the Americas.

The ZTX series targets medium-power bipolar switching applications, emphasizing ruggedness, consistent h_FE, and thermal reliability in cost-sensitive industrial and lighting systems.

FAQ

What is the maximum safe operating temperature for ZTX851?

The ZTX851 has a specified junction temperature range of –55°C to +200°C. At ambient temperatures above 25°C, power dissipation must be derated linearly per R_th(j-amb) = 150 °C/W - e.g., at 75°C ambient, max P_tot drops to 0.8 W with no heatsink.

Can ZTX851 replace ZTX849 in existing designs?

Yes - ZTX851 is pin-compatible with ZTX849 (both TO-92, E-B-C pinout) and offers identical voltage ratings but higher I_C (5 A vs. 3 A) and lower V_CE(sat). No layout change is needed; verify base drive capability supports 200 mA for full saturation.

Is ZTX851 suitable for PWM motor control?

It supports PWM at frequencies ≤100 kHz with appropriate base drive, given its 130 MHz f_T and 45 ns t_on/1100 ns t_off. However, switching losses increase above 10 kHz due to minority-carrier storage; use with snubbers and fast base turn-off for reliable operation.

Does ZTX851 require a heatsink in standard PCB mounting?

No heatsink is required for ≤1.2 W dissipation at T_amb ≤25°C when mounted on ≥1 inch² of 2-oz copper. Above 25°C ambient or >1.2 W, thermal derating applies - e.g., at 50°C ambient, max power is ~0.8 W without additional cooling.