2SD1042 bipolar transistor — Specifications & Equivalents

About the 2SD1042

The 2SD1042 is an NPN bipolar transistor with a collector–emitter voltage (V_CEO) rating of 120 V, a continuous collector current (I_C) of 40 A and a DC current gain (h_FE) of minimum 35. It can dissipate up to 180 W and is rated to a junction temperature of 150 °C. It is supplied in the TO3 package.

At a glance

• Type: NPN bipolar transistor
• Max collector–emitter voltage (V_CEO): 120 V
• Max collector current (I_C): 40 A
• DC current gain (h_FE): minimum 35
• Transition frequency (f_T): 1 MHz
• Power dissipation (P_D): 180 W
• Max junction temperature (T_J): 150 °C
• Package: TO3
• Manufacturer: Multi-source (JIS registered part number)

Typical applications

Judging from its ratings the 2SD1042 is generally applied in power output and driver stages.

A transition frequency (f_T) of 1 MHz indicates the frequency range over which useful current gain remains available.

The quoted current gain of minimum 35 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 120 V, V_CBO 150 V and V_EBO 100 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 180 W, and that figure assumes the datasheet's mounting and ambient conditions — derate it for your own thermal design.

Choosing a replacement for the 2SD1042

A drop-in substitute for the 2SD1042 must be the same NPN type and offer a collector–emitter rating of at least 120 V, a collector current rating of at least 40 A, current gain in the same ballpark as minimum 35 and a transition frequency of at least 1 MHz for the same bandwidth.

Mechanically, check the replacement against the TO3 footprint and confirm the pin order — parts sharing a package outline do not always share a pinout.

Because 2SD1042 is a JIS-registered part number rather than one vendor's proprietary series, it is produced by several manufacturers. Datasheet figures vary slightly between them, so check the datasheet of the brand you actually buy — this also makes like-for-like sourcing easier.

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 2SD1042?

The 2SD1042 is an NPN bipolar junction transistor (BJT). It is rated for 120 V collector-emitter and 40 A continuous collector current.

What is the maximum voltage of the 2SD1042?

Maximum collector-emitter voltage (Vceo) is 120 V, and collector-base (Vcbo) is 150 V.

How much current can the 2SD1042 handle?

Continuous collector current is rated at 40 A, with dissipation limited to 180 W.

What is the hFE of the 2SD1042?

DC current gain (hFE) is quoted as minimum 35. Size base drive from the minimum value so the transistor saturates fully across production spread.

What package does the 2SD1042 come in?

It is listed in TO3. Verify the pinout of the specific variant, as one outline can carry different pin assignments.

What can I use to replace the 2SD1042?

This page lists 17 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.