BC237G NPN Bipolar Junction Transistor Equivalent & Substitute Parts

Part Overview

The BC237G is an NPN bipolar junction transistor manufactured by onsemi, rated for 45 V collector-emitter breakdown voltage and 100 mA maximum collector current. This device is packaged in a TO-92 (TO-226-3) through-hole configuration and is classified as obsolete. Due to its obsolete product status, equivalent and substitute parts with active availability are necessary for ongoing design support and production requirements. Substitute parts maintain electrical compatibility within specified parameter ranges while offering improved availability and active product support.

Substiute Parts

BC237G

onsemiIn Stock: 833BC237G Datasheet

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BC550CBU

onsemiIn Stock: 2948BC550CBU Datasheet

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ZTX450

Diodes IncorporatedIn Stock: 1682ZTX450 Datasheet

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ZTX690B

Diodes IncorporatedIn Stock: 1864ZTX690B Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution of the BC237G is determined by electrical parameter compatibility across three critical dimensions: voltage rating, current rating, and power dissipation capability. All substitute parts must maintain the 45 V collector-emitter breakdown voltage specification to ensure safe operation in the original circuit application. The 100 mA collector current specification establishes the minimum current handling requirement; substitute parts may exceed this rating without functional degradation in circuits designed for the BC237G.

Substitutes are grouped into two categories based on current and power handling:

Category 1 (Direct Electrical Equivalents): Parts maintaining 100 mA maximum collector current and comparable power dissipation (350–500 mW range). These parts are suitable for direct replacement in applications where current and power requirements match the original specification.

Category 2 (Higher Current Capability): Parts rated for collector currents exceeding 100 mA (1 A or 2 A) with proportionally increased power dissipation (1 W). These parts are suitable for applications requiring higher current handling or where circuit redesign permits utilization of enhanced specifications.

All substitute parts maintain NPN transistor type, through-hole mounting, and TO-92-compatible packaging. Frequency response, DC current gain, and saturation voltage characteristics are provided for circuit performance verification.

Parameter Comparison

Engineering Selection Recommendations

BC550CBU Selection Criteria:

The BC550CBU is an active product from onsemi offering direct electrical equivalence to the BC237G. Both devices share identical voltage (45 V), current (100 mA), and saturation voltage specifications. The BC550CBU provides enhanced frequency response (300 MHz versus 200 MHz) and increased power dissipation capability (500 mW versus 350 mW). This part is ROHS3 compliant and maintains REACH unaffected status. Selection of BC550CBU is appropriate for applications requiring direct pin-compatible replacement with improved performance margins and active product support.

ZTX450 Selection Criteria:

The ZTX450 is an active product from Diodes Incorporated rated for 1 A collector current and 1 W power dissipation. This part maintains the 45 V voltage specification and TO-92-compatible packaging. The ZTX450 is suitable for applications where the original BC237G circuit can accommodate higher current capability or where circuit redesign permits utilization of enhanced specifications. This part is ROHS3 compliant, REACH unaffected, and rated for extended operating temperature range (-55°C to 200°C). Selection is appropriate when higher current handling is required or when design flexibility permits specification upgrade.

ZTX690B Selection Criteria:

The ZTX690B is an active product from Diodes Incorporated rated for 2 A collector current and 1 W power dissipation. This part maintains the 45 V voltage specification and TO-92-compatible packaging. The ZTX690B is suitable for applications requiring significantly higher current capability than the original BC237G specification. This part is ROHS3 compliant, REACH unaffected, and rated for extended operating temperature range (-55°C to 200°C). Selection is appropriate for high-current applications or where circuit redesign permits substantial specification upgrade.

All substitute parts maintain REACH unaffected status, ensuring regulatory compliance across global markets. ROHS3 compliance of active substitute parts supports modern manufacturing and environmental requirements.

Frequently Asked Questions (FAQ)

Q: Can BC550CBU be used as a direct replacement for BC237G in all applications?

A: Yes, BC550CBU provides direct electrical equivalence for voltage (45 V), current (100 mA), and saturation voltage specifications. Both parts are packaged in TO-92-3 configuration and are pin-compatible. The BC550CBU offers enhanced frequency response (300 MHz) and power dissipation (500 mW), providing improved performance margins without circuit modification.

Q: What is the primary difference between BC550CBU and ZTX450?

A: BC550CBU maintains 100 mA maximum collector current and is optimized for low-signal applications. ZTX450 is rated for 1 A collector current and 1 W power dissipation, making it suitable for higher-current applications. ZTX450 uses E-Line packaging (TO-92 compatible) rather than standard TO-92-3. Selection depends on circuit current requirements and available design flexibility.

Q: Are ZTX450 and ZTX690B physically interchangeable with BC237G?

A: ZTX450 and ZTX690B use E-Line-3 packaging, which is TO-92 compatible. Physical interchangeability is confirmed for through-hole mounting applications. However, electrical specifications differ significantly: ZTX450 handles 1 A and ZTX690B handles 2 A, compared to BC237G's 100 mA rating. Substitution is appropriate only when circuit design accommodates higher current capability.

Q: Why is BC237G classified as obsolete?

A: BC237G is listed as obsolete by onsemi. Active substitute parts (BC550CBU, ZTX450, ZTX690B) provide equivalent or enhanced functionality with ongoing manufacturer support, improved compliance certifications, and assured long-term availability.

Q: What compliance certifications should I verify for substitute parts?

A: All substitute parts maintain REACH unaffected status. BC550CBU, ZTX450, and ZTX690B are ROHS3 compliant. Verify compliance requirements for your specific application and regional market before final part selection.

Q: Can I use ZTX690B in a circuit designed for BC237G without modification?

A: ZTX690B is electrically compatible at the 45 V voltage specification and maintains TO-92-compatible packaging. However, ZTX690B is rated for 2 A collector current compared to BC237G's 100 mA. Substitution is valid only if circuit design permits higher current operation or if the circuit operates at currents below 100 mA, where ZTX690B performance is derated.

Q: What is the operating temperature advantage of ZTX450 and ZTX690B?

A: ZTX450 and ZTX690B are rated for -55°C to 200°C operating temperature, compared to BC237G's -55°C to 150°C range. This extended upper temperature limit provides 50°C additional thermal margin, beneficial for high-temperature applications or environments with elevated ambient conditions.

Q: How do saturation voltage specifications affect circuit performance?

A: Saturation voltage (Vce sat) determines voltage drop across the transistor in saturated switching mode. BC237G and BC550CBU specify 600 mV saturation voltage, while ZTX450 specifies 250 mV and ZTX690B specifies 500 mV. Lower saturation voltage reduces power dissipation and heat generation in switching applications. Verify saturation voltage compatibility with circuit design requirements.