BC550A A1G Equivalent & Substitute Parts

Part Overview

The BC550A A1G is an NPN bipolar junction transistor manufactured by Taiwan Semiconductor Corporation, designed for small-signal amplification applications. This device operates at a maximum collector voltage of 45 V with a collector current rating of 100 mA and power dissipation of 500 mW in a Through Hole TO-92 package. The BC550A A1G is classified as obsolete, making equivalent substitute parts necessary for ongoing production and maintenance applications. Active equivalent devices are available from alternative manufacturers including Fairchild Semiconductor and onsemi, offering compatible electrical and mechanical specifications with current product status.

Key Parameters

Parameter	BC550A A1G
Transistor Type	NPN
Current - Collector (Ic) Max	100 mA
Voltage - Collector Emitter Breakdown (Max)	45 V
Current - Collector Cutoff (Max)	15 nA (ICBO)
DC Current Gain (hFE) Min @ Ic, Vce	110 @ 2 mA, 5 V
Power - Max	500 mW
Operating Temperature	-65°C ~ 150°C (TJ)
Mounting Type	Through Hole
Package / Case	TO-92-3 (TO-226AA)
Product Status	Obsolete
RoHS Status	ROHS3 Compliant

Substitute Part Grouping Explanation

Substitution of the BC550A A1G is determined by strict electrical and mechanical parameter matching within the NPN small-signal bipolar transistor category. The critical parameters that define substitution eligibility are:

Electrical Parameters:

Transistor Type: NPN (required match)
Maximum Collector Current: 100 mA (required match)
Maximum Collector-Emitter Breakdown Voltage: 45 V (required match)
Maximum Collector Cutoff Current: 15 nA (required match)
Minimum DC Current Gain: 110 @ 2 mA, 5 V (minimum threshold)
Maximum Power Dissipation: 500 mW (minimum threshold)

Mechanical Parameters:

Mounting Type: Through Hole (required match)
Package Type: TO-92-3 (required match)

All substitute parts listed meet or exceed these core electrical specifications. Substitute parts may feature enhanced performance characteristics such as higher transition frequency (300 MHz versus unspecified for BC550A A1G), higher power ratings, or higher DC current gain values. These enhancements do not compromise compatibility in applications designed for the BC550A A1G baseline specifications.

Parameter Comparison

Parameter	BC550A A1G	BC547ATA	BC547BTA	BC547BTF	BC547CTA	BC547CTFR	BC550CTA
Transistor Type	NPN	NPN	NPN	NPN	NPN	NPN	NPN
Current - Collector (Ic) Max	100 mA	100 mA	100 mA	100 mA	100 mA	100 mA	100 mA
Voltage - Collector Emitter Breakdown (Max)	45 V	45 V	45 V	45 V	45 V	45 V	45 V
Current - Collector Cutoff (Max)	15 nA	15 nA	15 nA	15 nA	15 nA	15 nA	15 nA
DC Current Gain (hFE) Min @ Ic, Vce	110 @ 2 mA, 5 V	110 @ 2 mA, 5 V	200 @ 2 mA, 5 V	200 @ 2 mA, 5 V	420 @ 2 mA, 5 V	420 @ 2 mA, 5 V	420 @ 2 mA, 5 V
Power - Max	500 mW	500 mW	625 mW	500 mW	500 mW	500 mW	500 mW
Frequency - Transition	Not specified	300 MHz	300 MHz	300 MHz	300 MHz	300 MHz	300 MHz
Operating Temperature	-65°C ~ 150°C	150°C	-55°C ~ 150°C	150°C	150°C	150°C	150°C
Mounting Type	Through Hole	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	TO-92-3	TO-92-3	TO-92-3
Product Status	Obsolete	Active	Active	Active	Active	Active	Active
RoHS Status	ROHS3 Compliant	Not specified	Not specified	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

All listed substitute parts are qualified replacements for the BC550A A1G based on electrical and mechanical parameter compatibility. Selection among available substitutes should be based on the following criteria:

Product Status and Availability: All substitute parts carry Active product status, ensuring ongoing availability and manufacturing support. The BC550A A1G is classified as Obsolete, making substitution necessary for new designs and ongoing production.

Compliance and Certifications: BC547BTF, BC547CTA, BC547CTFR, and BC550CTA are ROHS3 Compliant with REACH Unaffected status, matching the compliance profile of the original BC550A A1G. These parts are suitable for applications requiring regulatory compliance documentation.

DC Current Gain Characteristics: BC547ATA provides the closest DC current gain match at 110 @ 2 mA, 5 V, identical to the BC550A A1G specification. BC547BTA, BC547BTF, BC547CTA, BC547CTFR, and BC550CTA feature higher DC current gain values (200 to 420 @ 2 mA, 5 V), which exceed the minimum requirement and provide enhanced amplification characteristics in small-signal applications.

Power Dissipation: BC547BTA offers 625 mW maximum power dissipation, exceeding the 500 mW baseline. All other substitutes maintain the 500 mW specification. Selection of BC547BTA is appropriate for applications requiring additional thermal margin.

Temperature Operating Range: BC547BTA specifies -55°C ~ 150°C operating temperature, providing extended low-temperature performance compared to the BC550A A1G specification of -65°C ~ 150°C. For applications requiring operation below -55°C, the BC550A A1G baseline specification should be referenced against specific application requirements.

Packaging and Inventory: All substitute parts are supplied in TO-92-3 Through Hole packages with formed leads, ensuring mechanical compatibility with existing PCB designs. Inventory availability ranges from 1,308 to 46,986 pieces across substitute options.

Frequently Asked Questions (FAQ)

Q: Can BC547 series transistors directly replace BC550A A1G in existing designs?

A: Yes. BC547ATA, BC547BTA, BC547BTF, BC547CTA, and BC547CTFR are direct electrical and mechanical equivalents to the BC550A A1G. All devices share identical maximum collector current (100 mA), collector-emitter breakdown voltage (45 V), collector cutoff current (15 nA), and TO-92-3 package configuration. Pin-to-pin compatibility is maintained across all substitute parts.

Q: What is the difference between BC547 and BC550 series transistors?

A: BC547 and BC550 series transistors are functionally equivalent NPN small-signal devices with identical electrical ratings. The primary distinction is manufacturer designation and DC current gain grading. BC550CTA maintains the BC550 series designation while meeting all BC550A A1G electrical specifications. BC547 series parts from onsemi and Fairchild Semiconductor provide equivalent performance with higher DC current gain values in certain grades.

Q: Does higher DC current gain in substitute parts affect circuit operation?

A: Higher DC current gain does not compromise circuit operation in applications designed for the BC550A A1G baseline specification of 110 @ 2 mA, 5 V. Substitute parts with DC current gain values of 200 to 420 @ 2 mA, 5 V provide enhanced amplification characteristics. Circuit designs that do not depend on specific current gain matching will operate identically with substitute parts. Applications requiring precise current gain control should reference the specific grade selected.

Q: Are all substitute parts ROHS3 compliant?

A: BC547BTF, BC547CTA, BC547CTFR, and BC550CTA are explicitly ROHS3 Compliant. BC547ATA and BC547BTA do not specify ROHS compliance status in available documentation. For applications requiring ROHS3 compliance certification, select from BC547BTF, BC547CTA, BC547CTFR, or BC550CTA.

Q: What is the significance of the TO-92-3 package designation?

A: TO-92-3 is a three-lead Through Hole package with formed leads, identical across all listed parts. This package designation ensures mechanical and electrical compatibility with existing PCB designs. The TO-92-3 package accommodates standard 0.1-inch lead spacing and is compatible with conventional through-hole soldering processes.

Q: Can BC547BTA be used in applications requiring extended temperature range?

A: BC547BTA specifies an operating temperature range of -55°C ~ 150°C, which is narrower than the BC550A A1G specification of -65°C ~ 150°C. For applications requiring operation below -55°C, BC547BTA is not suitable. BC547ATA, BC547BTF, BC547CTA, BC547CTFR, and BC550CTA specify 150°C maximum operating temperature without lower temperature limits in provided documentation. Applications requiring -65°C minimum operating temperature should reference original BC550A A1G specifications or contact manufacturers for extended temperature grade availability.

Q: What packaging options are available for substitute parts?

A: All substitute parts are supplied in TO-92-3 Through Hole packages with formed leads. BC547ATA is supplied in Bulk packaging. BC547BTA is supplied in Bulk packaging. BC547BTF, BC547CTA, BC547CTFR, and BC550CTA are supplied in Cut Tape (CT) packaging. Packaging format does not affect electrical or mechanical compatibility; selection depends on procurement and assembly process requirements.

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