BC558 bipolar transistor — Specifications & Equivalents

About the BC558

The BC558 is a PNP bipolar transistor with a collector–emitter voltage (V_CEO) rating of 25 V, a continuous collector current (I_C) of 0.1 A and a DC current gain (h_FE) of minimum 75. It can dissipate up to 0.5 W and is rated to a junction temperature of 150 °C. It is supplied in the TO92 package.

At a glance

• Type: PNP bipolar transistor
• Max collector–emitter voltage (V_CEO): 25 V
• Max collector current (I_C): 0.1 A
• DC current gain (h_FE): minimum 75
• Transition frequency (f_T): 75 MHz
• Power dissipation (P_D): 0.5 W
• Max junction temperature (T_J): 150 °C
• Package: TO92
• Manufacturer: Multi-source (Pro Electron registered part number)

Typical applications

Judging from its ratings the BC558 is generally applied in small-signal amplification and general-purpose switching.

A transition frequency (f_T) of 75 MHz indicates the frequency range over which useful current gain remains available.

The quoted current gain of minimum 75 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 25 V, V_CBO 30 V and V_EBO 5 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 0.5 W, and that figure assumes the datasheet's mounting and ambient conditions — derate it for your own thermal design.

Choosing a replacement for the BC558

A drop-in substitute for the BC558 must be the same PNP type and offer a collector–emitter rating of at least 25 V, a collector current rating of at least 0.1 A, current gain in the same ballpark as minimum 75 and a transition frequency of at least 75 MHz for the same bandwidth.

Mechanically, check the replacement against the TO92 footprint and confirm the pin order — parts sharing a package outline do not always share a pinout.

Because BC558 is a Pro Electron-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 BC558?

The BC558 is a PNP bipolar junction transistor (BJT). It is rated for 25 V collector-emitter and 0.1 A continuous collector current.

What is the maximum voltage of the BC558?

Maximum collector-emitter voltage (Vceo) is 25 V, and collector-base (Vcbo) is 30 V.

How much current can the BC558 handle?

Continuous collector current is rated at 0.1 A, with dissipation limited to 0.5 W.

What is the hFE of the BC558?

DC current gain (hFE) is quoted as minimum 75. Size base drive from the minimum value so the transistor saturates fully across production spread.

What package does the BC558 come in?

It is listed in TO92. Verify the pinout of the specific variant, as one outline can carry different pin assignments.

What can I use to replace the BC558?

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.