BC237 Equivalent & Substitute Parts

Part Overview

The BC237 is an NPN bipolar junction transistor manufactured by onsemi, rated for 45 V collector-emitter breakdown voltage and 100 mA maximum collector current in a TO-92 through-hole package. This device is classified as obsolete, making equivalent and substitute parts necessary for new designs and ongoing production requirements. The BC237 operates across a temperature range of -55°C to 150°C and delivers 350 mW maximum power dissipation with a transition frequency of 200 MHz.

Key Parameters

Parameter	BC237 Specification
Transistor Type	NPN
Voltage - Collector Emitter Breakdown (Max)	45 V
Current - Collector (Ic) (Max)	100 mA
Power - Max	350 mW
Frequency - Transition	200 MHz
DC Current Gain (hFE) (Min) @ Ic, Vce	120 @ 2mA, 5V
Vce Saturation (Max) @ Ib, Ic	600mV @ 5mA, 100mA
Current - Collector Cutoff (Max)	15nA
Operating Temperature	-55°C ~ 150°C (TJ)
Mounting Type	Through Hole
Package / Case	TO-92-3
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution of the BC237 is determined by strict electrical and mechanical compatibility across the following critical parameters:

Primary Substitution Criteria:

Transistor Type: NPN (required match)
Voltage - Collector Emitter Breakdown: minimum 45 V
Current - Collector (Ic) (Max): minimum 100 mA
Mounting Type: Through Hole
Package / Case: TO-92-3 or TO-92 compatible form factor

Secondary Compatibility Factors:

Power dissipation capability: minimum 350 mW
Operating temperature range: must encompass -55°C to 150°C
DC Current Gain (hFE): functional equivalence at specified test conditions
Vce Saturation characteristics: comparable performance at rated conditions

Substitute parts are grouped into two categories based on current handling capacity and package form factor:

Category A - Direct Electrical Equivalents (100 mA rated current): BC550CBU and 2N5232A PBFREE maintain the 100 mA collector current rating with enhanced voltage or power specifications, ensuring drop-in compatibility for standard BC237 applications.

Category B - Higher Current Capability (600 mA to 2 A rated current): 2N4401BU, ZTX450, and ZTX690B provide increased current handling for applications requiring higher collector current while maintaining 45 V voltage rating and through-hole packaging.

Parameter Comparison

Parameter	BC237	BC550CBU	2N5232A PBFREE	2N4401BU	ZTX450	ZTX690B
Transistor Type	NPN	NPN	NPN	NPN	NPN	NPN
Voltage - Collector Emitter Breakdown (Max)	45 V	45 V	50 V	40 V	45 V	45 V
Current - Collector (Ic) (Max)	100 mA	100 mA	100 mA	600 mA	1 A	2 A
Power - Max	350 mW	500 mW	625 mW	625 mW	1 W	1 W
Frequency - Transition	200 MHz	300 MHz	Not specified	250 MHz	150 MHz	150 MHz
DC Current Gain (hFE) (Min) @ Ic, Vce	120 @ 2mA, 5V	420 @ 2mA, 5V	250 @ 2mA, 5V	100 @ 150mA, 1V	100 @ 150mA, 10V	400 @ 1A, 2V
Vce Saturation (Max) @ Ib, Ic	600mV @ 5mA, 100mA	600mV @ 5mA, 100mA	125mV @ 1mA, 10mA	750mV @ 50mA, 500mA	250mV @ 15mA, 150mA	500mV @ 5mA, 1A
Current - Collector Cutoff (Max)	15nA	15nA	30nA	Not specified	100nA	100nA
Operating Temperature	-55°C ~ 150°C	-55°C ~ 150°C	-65°C ~ 150°C	-55°C ~ 150°C	-55°C ~ 200°C	-55°C ~ 200°C
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole
Package / Case	TO-92-3	TO-92-3	TO-92-3	TO-92-3	E-Line-3 (TO-92 compatible)	E-Line-3 (TO-92 compatible)
Product Status	Obsolete	Active	Active	Active	Active	Active
RoHS Status	Non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

BC550CBU is the primary direct substitute for BC237 applications. This part maintains identical collector current (100 mA) and collector-emitter breakdown voltage (45 V) specifications while offering enhanced power dissipation (500 mW versus 350 mW) and higher transition frequency (300 MHz versus 200 MHz). BC550CBU is ROHS3 compliant and carries active product status, ensuring long-term availability and supply chain stability. The identical Vce saturation characteristics (600mV @ 5mA, 100mA) and matching operating temperature range (-55°C to 150°C) provide seamless functional equivalence.

2N5232A PBFREE serves as an alternative direct substitute with superior voltage rating (50 V versus 45 V) and enhanced power capability (625 mW). This part is manufactured by Central Semiconductor Corp and maintains 100 mA collector current. The lower Vce saturation (125mV @ 1mA, 10mA) indicates improved switching performance. ROHS3 compliance and active status support modern design requirements. The extended operating temperature range (-65°C to 150°C) provides additional thermal margin.

2N4401BU is suitable for applications requiring higher collector current (600 mA) while maintaining 40 V minimum voltage rating. This part offers significantly increased power dissipation (625 mW) and higher transition frequency (250 MHz). ROHS3 compliance and active status ensure supply availability. Selection of 2N4401BU is appropriate when circuit design permits higher current capability without exceeding thermal or power constraints.

ZTX450 and ZTX690B are E-Line package variants manufactured by Diodes Incorporated, offering TO-92 compatible form factors with substantially higher current ratings (1 A and 2 A respectively). Both parts maintain 45 V voltage rating and provide 1 W power dissipation. These devices are ROHS3 compliant with active product status and extended operating temperature range (-55°C to 200°C). Selection of these parts is appropriate for applications requiring significant current amplification or where thermal headroom is critical.

All substitute parts maintain through-hole mounting compatibility and NPN transistor type equivalence. Selection should be based on specific circuit current requirements, thermal constraints, and compliance mandates rather than on the obsolete status of BC237 alone.

Frequently Asked Questions (FAQ)

Q: Can BC550CBU directly replace BC237 in existing PCB designs without layout modifications?

A: Yes. BC550CBU maintains identical TO-92-3 package geometry and pin configuration as BC237. No PCB layout changes are required. The part is a direct mechanical and electrical substitute for applications operating at or below 100 mA collector current.

Q: What is the primary difference between BC550CBU and 2N5232A PBFREE?

A: Both parts are direct 100 mA equivalents. BC550CBU (onsemi) offers higher DC current gain (420 @ 2mA, 5V) and faster transition frequency (300 MHz). 2N5232A PBFREE (Central Semiconductor) provides higher voltage rating (50 V) and lower Vce saturation (125mV @ 1mA, 10mA), indicating superior switching characteristics. Selection depends on whether gain or switching performance is prioritized in the application.

Q: When should 2N4401BU be selected instead of BC550CBU?

A: 2N4401BU is selected when circuit design requires collector current exceeding 100 mA. This part is rated for 600 mA maximum collector current and provides 625 mW power dissipation. The 40 V voltage rating remains adequate for most BC237 applications. 2N4401BU is not a direct substitute but rather an upgraded alternative for higher-current designs.

Q: Are ZTX450 and ZTX690B compatible with standard TO-92 PCB footprints?

A: ZTX450 and ZTX690B use E-Line-3 package format, which is mechanically compatible with TO-92 footprints. However, verification of pin spacing and lead diameter compatibility with existing PCB designs is required before implementation. These parts are suitable for new designs or PCB revisions that accommodate E-Line packaging.

Q: What compliance advantage do substitute parts offer over BC237?

A: All substitute parts are ROHS3 compliant, whereas BC237 is RoHS non-compliant. For applications subject to RoHS directives or customer compliance requirements, any of the substitute parts (BC550CBU, 2N5232A PBFREE, 2N4401BU, ZTX450, or ZTX690B) satisfy regulatory mandates. BC237 cannot be used in new designs targeting RoHS-compliant end products.

Q: Is operating temperature range a critical factor in substitute selection?

A: Operating temperature range should be verified against application requirements. BC237, BC550CBU, and 2N4401BU are rated -55°C to 150°C. 2N5232A PBFREE extends to -65°C. ZTX450 and ZTX690B extend to 200°C. Selection of extended-range parts is necessary only if circuit operation exceeds 150°C or falls below -55°C.

Q: Can BC237 be used in new production designs?

A: No. BC237 is classified as obsolete. New designs must utilize active substitute parts to ensure long-term supply chain stability and compliance with current regulatory standards. BC550CBU is the recommended primary substitute for direct replacement applications.

Q: What is the significance of Vce saturation differences between substitute parts?

A: Vce saturation determines voltage drop across the transistor in saturated switching mode. Lower Vce saturation (2N5232A PBFREE at 125mV) reduces power dissipation and heat generation in switching applications. Higher Vce saturation (2N4401BU at 750mV) may require circuit design consideration in low-voltage applications. Selection depends on whether the application operates in linear or saturated switching mode.

Q: Are all substitute parts available in bulk packaging?

A: Yes. All substitute parts listed are available in bulk packaging. Inventory levels vary: BC550CBU (2,860 pcs), 2N5232A PBFREE (17,706 pcs), 2N4401BU (9,900 pcs), ZTX450 (1,600 pcs), and ZTX690B (1,808 pcs). Availability should be confirmed with suppliers for production volume requirements.

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