2N4240 bipolar transistor — Specifications & Equivalents

About the 2N4240

The 2N4240 is an NPN bipolar transistor with a collector–emitter voltage (V_CEO) rating of 300 V, a continuous collector current (I_C) of 2 A and a DC current gain (h_FE) of 30–150. It can dissipate up to 35 W and is rated to a junction temperature of -65 to +200°C. It is supplied in the TO-66 package.

At a glance

• Type: NPN bipolar transistor
• Max collector–emitter voltage (V_CEO): 300 V
• Max collector current (I_C): 2 A
• DC current gain (h_FE): 30–150
• Power dissipation (P_D): 35 W
• Max junction temperature (T_J): -65 to +200°C
• Package: TO-66
• Manufacturer: Multi-source (JEDEC registered part number)

Typical applications

Judging from its ratings the 2N4240 is generally applied in power output and driver stages and high-voltage switching such as offline converters and lamp drivers.

The quoted current gain of 30–150 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 500 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 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 2N4240

A drop-in substitute for the 2N4240 must be the same NPN type and offer a collector–emitter rating of at least 300 V, a collector current rating of at least 2 A and current gain in the same ballpark as 30–150.

Mechanically, check the replacement against the TO-66 footprint and confirm the pin order — parts sharing a package outline do not always share a pinout.

Because 2N4240 is a JEDEC-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 2N4240?

The 2N4240 is an NPN bipolar junction transistor (BJT). It is rated for 300 V collector-emitter and 2 A continuous collector current.

What is the maximum voltage of the 2N4240?

Maximum collector-emitter voltage (Vceo) is 300 V, and collector-base (Vcbo) is 500 V.

How much current can the 2N4240 handle?

Continuous collector current is rated at 2 A, with dissipation limited to 35 W.

What is the hFE of the 2N4240?

DC current gain (hFE) is quoted as 30–150. Size base drive from the minimum value so the transistor saturates fully across production spread.

What package does the 2N4240 come in?

It is listed in TO-66. Verify the pinout of the specific variant, as one outline can carry different pin assignments.

What can I use to replace the 2N4240?

No verified equivalents are listed yet. Choose a part of the same polarity that meets or exceeds every rating above and shares a compatible package and pinout.