BSR18B Equivalent & Substitute Parts

Part Overview

The BSR18B is a PNP bipolar junction transistor manufactured by onsemi, housed in a SOT-23-3 surface mount package. This device is rated for 40 V collector-emitter breakdown voltage with a maximum collector current of 200 mA and 230 mW power dissipation. The BSR18B is classified as obsolete, making equivalent and substitute parts necessary for new designs and ongoing production requirements. Substitute parts must maintain electrical compatibility within the specified parameter ranges while offering active product status and modern manufacturing support.

Key Parameters

Parameter	BSR18B Value	Unit
Transistor Type	PNP	—
Voltage - Collector Emitter Breakdown (Max)	40	V
Current - Collector (Ic) (Max)	200	mA
Power - Max	230	mW
Vce Saturation (Max) @ Ib, Ic	400mV @ 5mA, 50mA	V
DC Current Gain (hFE) (Min) @ Ic, Vce	110 @ 10mA, 1V	—
Operating Temperature Range	-55 to 150	°C
Package / Case	SOT-23-3	—
Mounting Type	Surface Mount	—
Product Status	Obsolete	—

Substitute Part Grouping Explanation

Substitute parts for the BSR18B are selected based on strict electrical and mechanical compatibility criteria. The primary substitution logic follows these parameters:

Critical Matching Parameters:

Transistor Type: PNP (all substitutes must be PNP)
Package: SOT-23-3 surface mount (mechanical compatibility)
Voltage Rating: Minimum 40 V collector-emitter breakdown voltage
Current Rating: Minimum 200 mA collector current capacity
Power Dissipation: Minimum 230 mW
Operating Temperature: -55°C to 150°C minimum range

Substitution Categories:

Direct Electrical Match (Same Ratings): Parts with identical or superior electrical specifications and matching saturation characteristics qualify as direct substitutes. The MMBT3906LT1G and MMBT3906LT3G meet the exact electrical requirements of the BSR18B with identical Vce saturation at the same test conditions.

Higher Current Capacity Substitutes: Parts rated for higher collector current (500 mA to 800 mA) with 40 V or 45 V breakdown voltage operate within the BSR18B's electrical envelope. These include MMBT4403LT1G, BC807-16LT1G, BC807-16-7-F, BC807-40-7-F, and BCW68GLT1G. These devices provide design margin for applications requiring higher current capability.

Lower Current Capacity Substitutes: The BC857CLT1G and BC857B-7-F are rated for 100 mA maximum collector current. These parts are suitable only for applications where the circuit design operates at or below 100 mA, representing a subset of BSR18B applications.

All substitute parts maintain the SOT-23-3 package format, surface mount technology, and operating temperature range of -55°C to 150°C or better. Active product status and RoHS3 compliance are prioritized for long-term availability and regulatory compliance.

Parameter Comparison

Part Number	Manufacturer	Ic (Max) mA	Vce(br) V	Power mW	Vce Sat @ Ib, Ic	hFE (Min) @ Ic, Vce	Freq MHz	Status	Package
BSR18B	onsemi	200	40	230	400mV @ 5mA, 50mA	110 @ 10mA, 1V	—	Obsolete	SOT-23-3
MMBT3906LT1G	onsemi	200	40	300	400mV @ 5mA, 50mA	100 @ 10mA, 1V	250	Active	SOT-23-3
MMBT3906LT3G	onsemi	200	40	300	400mV @ 5mA, 50mA	100 @ 10mA, 1V	250	Active	SOT-23-3
MMBT4403LT1G	onsemi	600	40	300	750mV @ 50mA, 500mA	100 @ 150mA, 2V	200	Active	SOT-23-3
BC807-16LT1G	onsemi	500	45	300	700mV @ 50mA, 500mA	100 @ 100mA, 1V	100	Active	SOT-23-3
BC857CLT1G	onsemi	100	45	300	650mV @ 5mA, 100mA	420 @ 2mA, 5V	100	Active	SOT-23-3
BCW68GLT1G	onsemi	800	45	225	1.5V @ 30mA, 300mA	120 @ 10mA, 1V	100	Active	SOT-23-3
BC807-16-7-F	Diodes Incorporated	500	45	310	700mV @ 50mA, 500mA	100 @ 100mA, 1V	100	Active	SOT-23-3
BC807-40-7-F	Diodes Incorporated	500	45	310	700mV @ 50mA, 500mA	250 @ 100mA, 1V	100	Active	SOT-23-3
BC857B-7-F	Diodes Incorporated	100	45	300	650mV @ 5mA, 100mA	220 @ 2mA, 5V	200	Active	SOT-23-3
BC857BE6327HTSA1	Infineon Technologies	100	45	330	650mV @ 5mA, 100mA	220 @ 2mA, 5V	250	Last Time Buy	SOT-23-3

Engineering Selection Recommendations

Primary Substitutes (Recommended for Direct Replacement):

The MMBT3906LT1G and MMBT3906LT3G are the optimal substitutes for the BSR18B. Both parts are manufactured by onsemi, maintain identical electrical specifications including collector current (200 mA), breakdown voltage (40 V), and saturation voltage characteristics. These devices offer active product status with RoHS3 compliance and unlimited moisture sensitivity level (MSL 1). The increased power dissipation rating (300 mW versus 230 mW) and higher transition frequency (250 MHz) provide design margin without requiring circuit modifications.

Secondary Substitutes (Higher Current Applications):

For applications requiring higher current capacity, the MMBT4403LT1G, BC807-16LT1G, BC807-16-7-F, and BC807-40-7-F provide 500 mA to 600 mA collector current ratings while maintaining 40 V to 45 V breakdown voltage. These parts are suitable when the circuit design can accommodate higher saturation voltages or when additional current margin is beneficial. All maintain active product status and RoHS3 compliance.

Tertiary Substitutes (Lower Current Applications):

The BC857CLT1G, BC857B-7-F, and BC857BE6327HTSA1 are limited to 100 mA maximum collector current. These parts are applicable only to circuit designs operating at or below 100 mA. The BC857BE6327HTSA1 carries Last Time Buy status, indicating limited future availability.

Compliance and Availability Considerations:

All recommended substitutes maintain RoHS3 compliance and REACH unaffected status. onsemi-manufactured parts (MMBT3906LT1G, MMBT3906LT3G, MMBT4403LT1G, BC807-16LT1G, BC857CLT1G, BCW68GLT1G) offer the highest inventory levels and long-term availability. Diodes Incorporated parts (BC807-16-7-F, BC807-40-7-F, BC857B-7-F) provide alternative sourcing with active status. The Infineon BC857BE6327HTSA1 should be avoided for new designs due to Last Time Buy status.

Frequently Asked Questions (FAQ)

Q: Can the MMBT3906LT1G directly replace the BSR18B without circuit modifications?

A: Yes. The MMBT3906LT1G maintains identical electrical specifications for collector current (200 mA), breakdown voltage (40 V), and saturation voltage (400 mV @ 5 mA, 50 mA). Both use the SOT-23-3 package. The increased power rating (300 mW versus 230 mW) and higher transition frequency (250 MHz) provide additional design margin. No circuit modifications are required.

Q: Why are BC807 and BC857 series parts listed as substitutes if they have different current ratings?

A: The BC807 and BC857 series are included because they meet the minimum electrical requirements for the BSR18B application envelope. The BC807-16LT1G and BC807-40-7-F provide 500 mA capacity, exceeding the BSR18B's 200 mA requirement. The BC857CLT1G and BC857B-7-F are suitable only for applications operating at 100 mA or below. Substitution validity depends on the specific circuit's current requirements.

Q: What is the difference between BC807-16-7-F and BC807-40-7-F?

A: Both parts are manufactured by Diodes Incorporated with identical electrical ratings (500 mA, 45 V, 100 MHz). The primary difference is DC current gain: BC807-16-7-F specifies 100 @ 100 mA, 1V while BC807-40-7-F specifies 250 @ 100 mA, 1V. The BC807-40-7-F provides higher current gain, which may be beneficial in switching applications requiring lower base drive current.

Q: Is the BCW68GLT1G suitable for the BSR18B application?

A: The BCW68GLT1G provides 800 mA collector current capacity with 45 V breakdown voltage, exceeding the BSR18B's electrical requirements. However, the saturation voltage is significantly higher (1.5 V @ 30 mA, 300 mA versus 400 mV @ 5 mA, 50 mA). This part is suitable only if the circuit design can accommodate the higher saturation voltage drop. The lower power rating (225 mW) is also a consideration.

Q: Why is the BSR18B obsolete and what does this mean for procurement?

A: The BSR18B is classified as obsolete, indicating onsemi has discontinued production and will not accept new orders. Existing inventory may be available from authorized distributors, but long-term supply is not guaranteed. Substitution to active parts such as MMBT3906LT1G or MMBT3906LT3G is necessary for new designs and ongoing production to ensure supply chain continuity.

Q: Are all substitute parts RoHS3 compliant?

A: Yes. All substitute parts listed maintain RoHS3 compliance and REACH unaffected status, meeting current regulatory requirements for electronic components in most jurisdictions.

Q: What is the significance of the SOT-23-3 package specification?

A: The SOT-23-3 package is a three-terminal surface mount package with standardized pin configuration and footprint. All substitute parts use this identical package, ensuring mechanical and electrical compatibility with existing PCB designs without layout modifications.

Q: Can I use the MMBT4403LT1G in place of the BSR18B for all applications?

A: The MMBT4403LT1G is electrically compatible with the BSR18B for applications operating at or below 200 mA collector current. However, the higher saturation voltage (750 mV @ 50 mA, 500 mA versus 400 mV @ 5 mA, 50 mA) may affect circuit performance in precision switching or analog applications. Verification of circuit operation at the higher saturation voltage is necessary.

Q: What is the difference between Cut Tape (CT) and Tape & Reel (TR) packaging?

A: Cut Tape and Tape & Reel are distribution formats, not component specifications. Both formats contain identical parts in the same SOT-23-3 package. Cut Tape is supplied in smaller quantities on individual tape strips, while Tape & Reel is supplied in continuous reel format for high-volume automated assembly. Electrical and mechanical specifications are identical.

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