SBT42 bipolar transistor — Specifications & Equivalents

About the SBT42

The SBT42 is an NPN bipolar transistor with a collector–emitter voltage (V_CEO) rating of 300 V, a continuous collector current (I_C) of 0.5 A and a DC current gain (h_FE) of minimum 40. It can dissipate up to 0.35 W and is rated to a junction temperature of 150 °C. It is supplied in the SOT23 package.

At a glance

• Type: NPN bipolar transistor
• Max collector–emitter voltage (V_CEO): 300 V
• Max collector current (I_C): 0.5 A
• DC current gain (h_FE): minimum 40
• Transition frequency (f_T): 50 MHz
• Power dissipation (P_D): 0.35 W
• Max junction temperature (T_J): 150 °C
• Package: SOT23

Typical applications

Judging from its ratings the SBT42 is generally applied in small-signal amplification and general-purpose switching and high-voltage switching such as offline converters and lamp drivers.

A transition frequency (f_T) of 50 MHz indicates the frequency range over which useful current gain remains available.

The quoted current gain of minimum 40 determines the base drive needed: divide your target collector current by the minimum h_FE, not the typical figure, when sizing the base resistor.

Biasing and absolute maximum ratings

Absolute-maximum breakdown limits are V_CEO 300 V, V_CBO 300 V and V_EBO 6 V (magnitudes). The emitter–base rating is the easiest to overlook and is often only a few volts, so protect the junction against reverse drive.

Dissipation is capped at 0.35 W, and that figure assumes the datasheet's mounting and ambient conditions — derate it for your own thermal design.

Choosing a replacement for the SBT42

A drop-in substitute for the SBT42 must be the same NPN type and offer a collector–emitter rating of at least 300 V, a collector current rating of at least 0.5 A, current gain in the same ballpark as minimum 40 and a transition frequency of at least 50 MHz for the same bandwidth.

Mechanically, check the replacement against the SOT23 footprint and confirm the pin order — parts sharing a package outline do not always share a pinout.

Where the application switches inductive loads or runs near the voltage limit, keep extra headroom rather than choosing a part that only just meets the original numbers.

Frequently asked questions

What is the SBT42?

The SBT42 is an NPN bipolar junction transistor (BJT). It is rated for 300 V collector-emitter and 0.5 A continuous collector current.

What is the maximum voltage of the SBT42?

Maximum collector-emitter voltage (Vceo) is 300 V, and collector-base (Vcbo) is 300 V.

How much current can the SBT42 handle?

Continuous collector current is rated at 0.5 A, with dissipation limited to 0.35 W.

What is the hFE of the SBT42?

DC current gain (hFE) is quoted as minimum 40. Size base drive from the minimum value so the transistor saturates fully across production spread.

What package does the SBT42 come in?

It is listed in SOT23. Verify the pinout of the specific variant, as one outline can carry different pin assignments.

What can I use to replace the SBT42?

This page lists 10 candidate equivalents matched on electrical ratings and package. Any replacement should meet or exceed the original voltage, current and dissipation figures and use a compatible drive level.