BC857B Equivalent & Substitute Parts

Part Overview

The BC857B is a PNP bipolar junction transistor manufactured by STMicroelectronics in SOT-23-3 surface mount packaging. This device is rated for 45 V collector-emitter breakdown voltage, 100 mA maximum collector current, and 250 mW power dissipation. The BC857B operates at frequencies up to 100 MHz with a maximum junction temperature of 150°C.

The BC857B is classified as an obsolete product. Equivalent and substitute parts are necessary to maintain design continuity, ensure component availability, and support ongoing production requirements. Substitute devices must maintain electrical compatibility within the specified parameter ranges while meeting current manufacturing and compliance standards.

Key Parameters

Parameter	Value	Unit
Transistor Type	PNP	—
Voltage - Collector Emitter Breakdown (Max)	45	V
Current - Collector (Ic) (Max)	100	mA
Power - Max	250	mW
Frequency - Transition	100	MHz
Operating Temperature (Max)	150	°C
Package / Case	SOT-23-3	—
Mounting Type	Surface Mount	—
Vce Saturation (Max) @ Ib, Ic	650 mV @ 5 mA, 100 mA	—
DC Current Gain (hFE) (Min) @ Ic, Vce	220 @ 2 mA, 5 V	—

Substitute Part Grouping Explanation

Substitute parts for the BC857B are classified into two categories based on electrical parameter compatibility:

Direct Electrical Equivalents maintain all critical electrical parameters within the BC857B specification envelope. These parts are suitable for direct replacement without circuit modification:

Maximum collector current: 100 mA
Collector-emitter breakdown voltage: 45 V
Power dissipation: 250 mW or greater
Transition frequency: 100 MHz or greater
Operating temperature range: minimum 150°C maximum junction temperature
Package: SOT-23-3 surface mount

Higher-Performance Alternatives exceed one or more electrical parameters while maintaining backward compatibility. These parts operate within the BC857B electrical envelope and are suitable for applications where enhanced performance is acceptable:

Maximum collector current: 500 mA (exceeds 100 mA requirement)
Power dissipation: 310 mW (exceeds 250 mW requirement)
Transition frequency: 200 MHz (exceeds 100 MHz requirement)

All substitute parts maintain PNP transistor type, SOT-23-3 package compatibility, and surface mount mounting configuration.

Parameter Comparison

Part Number	Manufacturer	Ic (Max) mA	Vce(br) V	Power mW	fT MHz	hFE @ 2mA, 5V	Vce Sat mV	Product Status	RoHS
BC857B	STMicroelectronics	100	45	250	100	220	650	Obsolete	Non-compliant
BCW70LT1G	onsemi	100	45	225	—	215	300	Active	ROHS3 Compliant
BC807-16-7-F	Diodes Incorporated	500	45	310	100	100	700	Active	ROHS3 Compliant
BC807-40-7-F	Diodes Incorporated	500	45	310	100	250	700	Active	ROHS3 Compliant
BC857,215	Nexperia USA Inc.	100	45	250	100	125	650	Active	ROHS3 Compliant
BC857,235	NXP USA Inc.	100	45	250	100	125	650	Active	Active
BC857A RFG	Taiwan Semiconductor Corporation	100	45	200	100	125	650	Active	ROHS3 Compliant
BC857A,215	Nexperia USA Inc.	100	45	250	100	125	650	Active	ROHS3 Compliant
BC857A-7-F	Diodes Incorporated	100	45	300	200	125	650	Active	ROHS3 Compliant
BC857ALT1G	onsemi	100	45	300	100	125	650	Active	ROHS3 Compliant
BC857B-7-F	Diodes Incorporated	100	45	300	200	220	650	Active	ROHS3 Compliant

Engineering Selection Recommendations

Direct Replacement Priority

BC857B-7-F (Diodes Incorporated) provides the closest electrical match to the BC857B. This part maintains identical collector current (100 mA), collector-emitter breakdown voltage (45 V), saturation voltage (650 mV), and DC current gain (220 @ 2 mA, 5 V). The device offers enhanced power dissipation (300 mW versus 250 mW) and transition frequency (200 MHz versus 100 MHz), providing design margin without requiring circuit modification. Product status is active with ROHS3 compliance.

Equivalent Electrical Performance

BC857ALT1G (onsemi) and BC857A-7-F (Diodes Incorporated) deliver equivalent electrical performance within the BC857B specification envelope. Both maintain 100 mA collector current, 45 V breakdown voltage, and 650 mV saturation voltage. These parts feature active product status and ROHS3 compliance. BC857ALT1G provides 300 mW power dissipation at 100 MHz transition frequency. BC857A-7-F offers 300 mW power dissipation at 200 MHz transition frequency with extended operating temperature range (-65°C to 150°C).

Nexperia Alternatives

BC857,215 and BC857A,215 (Nexperia USA Inc.) maintain electrical compatibility with identical voltage and current ratings. Both parts feature automotive-grade qualification (AEC-Q101) and ROHS3 compliance. DC current gain is specified at 125 @ 2 mA, 5 V, which is lower than the BC857B specification (220 @ 2 mA, 5 V) but remains within acceptable design margins for most applications.

Higher-Current Applications

BC807-40-7-F (Diodes Incorporated) supports applications requiring higher collector current (500 mA maximum). This part maintains 45 V breakdown voltage and 100 MHz transition frequency. DC current gain is specified at 250 @ 100 mA, 1 V. Saturation voltage increases to 700 mV at higher current levels. This device is suitable only for circuits designed to accommodate increased current capability.

Compliance Considerations

All recommended substitute parts maintain ROHS3 compliance status, addressing regulatory requirements for new designs. The BC857B is classified as RoHS non-compliant, making substitution necessary for applications subject to RoHS directives. All substitute parts maintain REACH unaffected status and EAR99 export classification consistent with the original device.

Frequently Asked Questions (FAQ)

Q: Can BC857B-7-F directly replace BC857B in existing designs?

A: Yes. BC857B-7-F maintains identical electrical parameters for collector current (100 mA), collector-emitter breakdown voltage (45 V), saturation voltage (650 mV), and DC current gain (220 @ 2 mA, 5 V). Enhanced power dissipation (300 mW) and transition frequency (200 MHz) provide additional design margin. SOT-23-3 package compatibility ensures mechanical interchangeability.

Q: What is the difference between BC857A and BC857B variants?

A: The primary difference is DC current gain specification. BC857B specifies minimum hFE of 220 @ 2 mA, 5 V. BC857A variants specify minimum hFE of 125 @ 2 mA, 5 V. Both maintain identical voltage (45 V), current (100 mA), and power (250 mW) ratings. BC857A devices are suitable for applications with less stringent gain requirements.

Q: Are BC807 series parts suitable replacements for BC857B?

A: BC807-16-7-F and BC807-40-7-F are higher-performance alternatives, not direct replacements. These parts support 500 mA collector current versus 100 mA for BC857B. Saturation voltage increases to 700 mV at rated current. Use BC807 series only in circuits designed to accommodate higher current capability and saturation voltage characteristics.

Q: What is the significance of the packaging designation differences (SOT-23-3 versus TO-236-3)?

A: SOT-23-3 and TO-236-3 refer to the same physical package. Both designations describe a three-terminal surface mount package with identical pin configuration and footprint. Parts specified with either designation are mechanically interchangeable on standard PCB layouts.

Q: Does BCW70LT1G provide equivalent performance to BC857B?

A: BCW70LT1G maintains electrical compatibility for voltage (45 V) and current (100 mA) ratings. Saturation voltage is significantly lower (300 mV @ 500 µA, 10 mA versus 650 mV @ 5 mA, 100 mA for BC857B). DC current gain is specified at 215 @ 2 mA, 5 V, closely matching BC857B. Power dissipation is 225 mW, slightly below BC857B specification. This part is suitable for applications where lower saturation voltage is beneficial.

Q: Why do some substitute parts specify transition frequency as "—" (not provided)?

A: BCW70LT1G does not provide transition frequency specification in available documentation. This parameter is not required for all applications. For designs requiring specific frequency response, select parts with documented transition frequency specifications (100 MHz or greater).

Q: Are automotive-qualified variants (BC857,215 and BC857A,215) necessary for non-automotive applications?

A: Automotive qualification (AEC-Q101) is not required for non-automotive applications. These parts are suitable for general-purpose use. Automotive-qualified variants provide additional process control and reliability documentation beneficial for safety-critical applications. Selection should be based on application requirements rather than qualification status alone.

Q: What is the impact of RoHS compliance on part selection?

A: All active substitute parts maintain ROHS3 compliance. The original BC857B is RoHS non-compliant. For new designs or applications subject to RoHS directives, select ROHS3-compliant alternatives. Existing designs using BC857B may continue operation, but new production should transition to compliant substitutes.

Q: Can parts with different DC current gain specifications be used interchangeably?

A: DC current gain variation affects circuit biasing and amplification characteristics. Parts with hFE of 220 (BC857B, BC857B-7-F, BC807-40-7-F) are directly interchangeable. Parts with hFE of 125 (BC857A variants) require circuit verification to ensure adequate biasing and gain margins. Parts with hFE of 215 (BCW70LT1G) are suitable for most applications with minor gain variation tolerance.

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