BSR18A Equivalent & Substitute Parts

Part Overview

The BSR18A is a PNP bipolar junction transistor manufactured by onsemi, housed in a SOT-23-3 surface mount package. This component is rated for 40 V collector-emitter breakdown voltage with a maximum collector current of 200 mA and 350 mW power dissipation. The BSR18A operates across a temperature range of -55°C to 150°C and features a transition frequency of 250 MHz.

The BSR18A is classified as an obsolete product. Equivalent and substitute parts are necessary to maintain design continuity and ensure component availability for new production runs, repairs, and system upgrades where the original part is no longer available through standard distribution channels.

Key Parameters

Parameter	Value	Unit
Transistor Type	PNP	—
Current - Collector (Ic) Max	200	mA
Voltage - Collector Emitter Breakdown (Max)	40	V
Vce Saturation (Max) @ Ib, Ic	400 mV @ 5 mA, 50 mA	—
DC Current Gain (hFE) Min @ Ic, Vce	100 @ 10 mA, 1 V	—
Power - Max	350	mW
Frequency - Transition	250	MHz
Operating Temperature	-55 to 150	°C
Package / Case	SOT-23-3 (TO-236)	—
Mounting Type	Surface Mount	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitute parts for the BSR18A are classified into two categories based on electrical parameter alignment:

Direct Substitutes maintain identical electrical specifications within the critical operating parameters: 40 V collector-emitter breakdown voltage, 200 mA maximum collector current, 250 MHz transition frequency, and equivalent saturation characteristics. These parts are pin-compatible and functionally interchangeable in the SOT-23-3 package.

Similar Substitutes share the same package and mounting type but differ in one or more electrical parameters. These parts operate at higher voltage ratings (45 V), higher collector current capabilities (500 mA or 100 mA), or lower transition frequencies (100 MHz). Similar substitutes are suitable only when the application circuit can tolerate these parameter variations without performance degradation.

The following parameters determine substitution eligibility:

Transistor polarity (PNP)
Package type (SOT-23-3 / TO-236)
Mounting method (Surface Mount)
Operating temperature range (-55°C to 150°C minimum)
Collector-emitter breakdown voltage (40 V minimum)
Maximum collector current (200 mA minimum)

Parameter Comparison

Part Number	Manufacturer	Product Status	Ic Max (mA)	Vce Breakdown (V)	hFE Min @ Ic, Vce	Power Max (mW)	Frequency (MHz)	Package	RoHS Status
BSR18A	onsemi	Obsolete	200	40	100 @ 10 mA, 1 V	350	250	SOT-23-3	—
MMBT3906LT1G	onsemi	Active	200	40	100 @ 10 mA, 1 V	300	250	SOT-23-3	ROHS3 Compliant
SMMBT3906LT1G	onsemi	Active	200	40	100 @ 10 mA, 1 V	300	250	SOT-23-3	ROHS3 Compliant
SMMBT3906LT3G	onsemi	Active	200	40	100 @ 10 mA, 1 V	300	250	SOT-23-3	ROHS3 Compliant
BC807-16LT1G	onsemi	Active	500	45	100 @ 100 mA, 1 V	300	100	SOT-23-3	ROHS3 Compliant
BC807-16LT3G	onsemi	Active	500	45	100 @ 100 mA, 1 V	300	100	SOT-23-3	ROHS3 Compliant
BC807-25LT1G	onsemi	Active	500	45	160 @ 100 mA, 1 V	300	100	SOT-23-3	ROHS3 Compliant
BC807-25LT3G	onsemi	Active	500	45	160 @ 100 mA, 1 V	300	100	SOT-23-3	ROHS3 Compliant
BC807-40LT1G	onsemi	Active	500	45	250 @ 100 mA, 1 V	300	100	SOT-23-3	ROHS3 Compliant
BC807-40LT3G	onsemi	Active	500	45	250 @ 100 mA, 1 V	300	100	SOT-23-3	ROHS3 Compliant
BC857ALT1G	onsemi	Active	100	45	125 @ 2 mA, 5 V	300	100	SOT-23-3	ROHS3 Compliant

Engineering Selection Recommendations

Direct Substitutes (Recommended Primary Selection)

The MMBT3906LT1G, SMMBT3906LT1G, and SMMBT3906LT3G are direct electrical equivalents to the BSR18A. All three parts maintain identical collector current (200 mA), collector-emitter breakdown voltage (40 V), DC current gain (100 @ 10 mA, 1 V), and transition frequency (250 MHz) specifications. These parts are manufactured by onsemi and are classified as Active products, ensuring long-term availability.

The MMBT3906LT1G is supplied in Cut Tape (CT) & Digi-Reel® packaging with 608,935 pieces in stock. The SMMBT3906LT1G and SMMBT3906LT3G are supplied in Tape & Reel (TR) packaging with 95,300 and 8,420 pieces in stock respectively. Both SMMBT variants carry AEC-Q101 automotive qualification, making them suitable for automotive and high-reliability applications.

All direct substitutes are ROHS3 compliant and carry REACH Unaffected status, meeting modern regulatory requirements. The minor reduction in maximum power dissipation from 350 mW to 300 mW does not affect functional compatibility in applications designed for the BSR18A.

Similar Substitutes (Conditional Selection)

The BC807 series (BC807-16LT1G, BC807-16LT3G, BC807-25LT1G, BC807-25LT3G, BC807-40LT1G, BC807-40LT3G) and BC857ALT1G are suitable substitutes only when circuit design permits higher voltage ratings and different current or frequency characteristics.

BC807 variants support 500 mA collector current and 45 V collector-emitter breakdown voltage, with transition frequency of 100 MHz. These parts are appropriate for applications where the BSR18A's 200 mA current limit or 250 MHz frequency is not a design constraint. The BC807-40 variants offer the highest DC current gain (250 @ 100 mA, 1 V).

The BC857ALT1G supports only 100 mA maximum collector current and is suitable only for low-current applications where the BSR18A's 200 mA capability is not required.

All similar substitutes are Active products with ROHS3 compliance and REACH Unaffected status.

Frequently Asked Questions (FAQ)

Q: Can MMBT3906LT1G directly replace BSR18A in all applications?

A: Yes. The MMBT3906LT1G maintains identical electrical specifications for collector current (200 mA), collector-emitter breakdown voltage (40 V), DC current gain (100 @ 10 mA, 1 V), and transition frequency (250 MHz). Both parts use the SOT-23-3 package with identical pinout. The 50 mW reduction in maximum power dissipation (from 350 mW to 300 mW) does not affect functional compatibility in standard applications.

Q: What is the difference between MMBT3906LT1G, SMMBT3906LT1G, and SMMBT3906LT3G?

A: All three parts are electrical equivalents with identical specifications. The primary differences are packaging format and automotive qualification. MMBT3906LT1G is supplied in Cut Tape & Digi-Reel format for standard applications. SMMBT3906LT1G and SMMBT3906LT3G are supplied in Tape & Reel format and carry AEC-Q101 automotive qualification for use in automotive and high-reliability systems.

Q: Can BC807 series parts replace BSR18A?

A: BC807 series parts are suitable substitutes only when the application circuit can tolerate higher collector current capability (500 mA vs. 200 mA), higher collector-emitter breakdown voltage (45 V vs. 40 V), and lower transition frequency (100 MHz vs. 250 MHz). If the circuit design depends on the BSR18A's 250 MHz frequency response or 200 mA current limit, BC807 variants are not appropriate substitutes.

Q: Is BC857ALT1G compatible with BSR18A?

A: BC857ALT1G is not a suitable substitute for BSR18A. The BC857ALT1G supports only 100 mA maximum collector current, which is insufficient for applications requiring the BSR18A's 200 mA capability. Use BC857ALT1G only in low-current applications where 100 mA maximum current is acceptable.

Q: Are all substitute parts RoHS compliant?

A: Yes. All direct and similar substitute parts listed are ROHS3 compliant and carry REACH Unaffected status, meeting current regulatory requirements for electronic components in most markets.

Q: What packaging options are available for direct substitutes?

A: Direct substitutes are available in two packaging formats. MMBT3906LT1G is supplied in Cut Tape (CT) & Digi-Reel format, suitable for automated pick-and-place assembly. SMMBT3906LT1G and SMMBT3906LT3G are supplied in Tape & Reel (TR) format, also suitable for automated assembly. All three use the SOT-23-3 package with identical mechanical dimensions and pinout.

Q: What is the operating temperature range for substitute parts?

A: All substitute parts operate across the temperature range of -55°C to 150°C (junction temperature), matching the BSR18A specification. This range is suitable for industrial, commercial, and automotive applications.

Q: Are substitute parts available in high volume?

A: Yes. Direct substitutes maintain substantial inventory levels. MMBT3906LT1G has 608,935 pieces in stock, SMMBT3906LT1G has 95,300 pieces, and SMMBT3906LT3G has 8,420 pieces available. These inventory levels support both new production and replacement requirements.

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