BC635 Equivalent & Substitute Parts

Part Overview

The BC635 is an NPN bipolar junction transistor manufactured by onsemi, rated for 45 V collector-emitter breakdown voltage and 1 A maximum collector current in a TO-92-3 through-hole package. This device is classified as obsolete, necessitating identification of equivalent and substitute components for ongoing design support and procurement continuity. The BC635 is suitable for general-purpose switching and amplification applications requiring moderate voltage and current ratings.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	45	V
Current - Collector (Ic) (Max)	1	A
Power - Max	1	W
Frequency - Transition	100	MHz
Vce Saturation (Max) @ Ib, Ic	500 mV @ 50 mA, 500 mA	—
DC Current Gain (hFE) (Min) @ Ic, Vce	40 @ 150 mA, 2 V	—
Operating Temperature (Max)	150	°C
Package / Case	TO-92-3	—
Mounting Type	Through Hole	—

Substitute Part Grouping Explanation

Substitution of the BC635 is determined by the following critical parameters: transistor polarity (NPN), maximum collector-emitter breakdown voltage, maximum collector current, power dissipation rating, and package type (TO-92-3 through-hole). Substitute parts must maintain electrical compatibility within the application's voltage and current requirements while preserving the through-hole mounting interface.

The BC635 has two identified substitute relationships:

Direct Substitute (2N4401BU): This part shares NPN polarity and TO-92-3 packaging. However, the 2N4401BU operates at reduced maximum voltage (40 V versus 45 V) and reduced maximum current (600 mA versus 1 A), with lower power dissipation (625 mW versus 1 W). This part is suitable for applications where the BC635's full voltage and current ratings are not required. The 2N4401BU is currently in active production status.

Similar Substitute (BC636TA): This part shares identical voltage (45 V), current (1 A), power (1 W), and frequency (100 MHz) ratings with the BC635. However, the BC636TA is a PNP transistor, not NPN. This part is suitable only for circuit designs requiring PNP polarity. The BC636TA is classified as Last Time Buy status.

Parameter Comparison

Parameter	BC635	2N4401BU	BC636TA
Transistor Type	NPN	NPN	PNP
Voltage - Collector Emitter Breakdown (Max)	45 V	40 V	45 V
Current - Collector (Ic) (Max)	1 A	600 mA	1 A
Power - Max	1 W	625 mW	1 W
Frequency - Transition	100 MHz	250 MHz	100 MHz
Vce Saturation (Max) @ Ib, Ic	500 mV @ 50 mA, 500 mA	750 mV @ 50 mA, 500 mA	500 mV @ 50 mA, 500 mA
DC Current Gain (hFE) (Min) @ Ic, Vce	40 @ 150 mA, 2 V	100 @ 150 mA, 1 V	40 @ 150 mA, 2 V
Operating Temperature (Max)	150°C	150°C	150°C
Package / Case	TO-92-3	TO-92-3	TO-92-3
Mounting Type	Through Hole	Through Hole	Through Hole
Product Status	Obsolete	Active	Last Time Buy

Engineering Selection Recommendations

For NPN Applications Requiring Full BC635 Ratings:

The BC635 is obsolete. If the application requires 45 V breakdown voltage, 1 A collector current, and 1 W power dissipation with NPN polarity, no direct equivalent from the provided substitute list maintains all specifications. The 2N4401BU is available in active production status but operates at reduced voltage (40 V) and current (600 mA) ratings. Selection of the 2N4401BU is appropriate only when the application circuit operates within these reduced limits.

For PNP Applications with Equivalent Ratings:

The BC636TA provides identical voltage, current, and power ratings to the BC635 but with PNP polarity. This part is suitable for complementary circuit designs. The BC636TA is classified as Last Time Buy, indicating limited future availability.

Compliance and Certification:

The 2N4401BU carries ROHS3 compliance certification. The BC636TA carries ROHS3 compliance certification. Both parts maintain REACH Unaffected status and EAR99 export classification consistent with the BC635.

Frequently Asked Questions (FAQ)

Q: Can the 2N4401BU directly replace the BC635 in all applications?

A: No. The 2N4401BU operates at reduced maximum voltage (40 V versus 45 V) and reduced maximum collector current (600 mA versus 1 A). Substitution is valid only for applications where the circuit operates within these reduced electrical limits.

Q: What is the primary difference between the BC635 and BC636TA?

A: The BC636TA is a PNP transistor, while the BC635 is NPN. Both share identical voltage (45 V), current (1 A), power (1 W), and frequency (100 MHz) ratings. Selection depends on circuit polarity requirements.

Q: Are all substitute parts available in the same TO-92-3 package?

A: Yes. Both the 2N4401BU and BC636TA are supplied in TO-92-3 through-hole packages, maintaining mechanical and pin compatibility with the BC635.

Q: What is the significance of the BC635 being classified as obsolete?

A: Obsolete status indicates the manufacturer has discontinued production. Existing inventory may be available from component distributors, but long-term procurement cannot be guaranteed. Substitute parts in active or Last Time Buy status provide alternative sourcing paths.

Q: Does the 2N4401BU offer any performance advantages over the BC635?

A: The 2N4401BU operates at higher transition frequency (250 MHz versus 100 MHz) and exhibits higher DC current gain (100 versus 40 at specified conditions). However, these advantages are offset by reduced voltage and current ratings.

Q: What is the operating temperature range for each part?

A: The BC635 and BC636TA specify maximum junction temperature of 150°C. The 2N4401BU specifies an operating temperature range of −55°C to 150°C, providing explicit lower temperature specification.

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