BC556A-AP Equivalent & Substitute Parts

Part Overview

The BC556A-AP is a PNP bipolar junction transistor (BJT) manufactured by Micro Commercial Co, designed for general-purpose switching and amplification applications. This component operates at a maximum collector voltage of 65 V with a collector current rating of 100 mA and a maximum power dissipation of 625 mW. The device is housed in a TO-92 through-hole package with formed leads, suitable for conventional PCB assembly methods.

The BC556A-AP is classified as an obsolete product. Identifying equivalent substitute parts is necessary to maintain design continuity, ensure component availability, and support ongoing production or repair requirements for legacy systems utilizing this transistor.

Key Parameters

Parameter	Value	Unit
Transistor Type	PNP	—
Current - Collector (Ic) (Max)	100	mA
Voltage - Collector Emitter Breakdown (Max)	65	V
Vce Saturation (Max) @ Ib, Ic	650 mV @ 5 mA, 100 mA	—
Current - Collector Cutoff (Max)	100	nA
DC Current Gain (hFE) (Min) @ Ic, Vce	120 @ 2 mA, 5 V	—
Power - Max	625	mW
Frequency - Transition	150	MHz
Operating Temperature Range	−55 to +150	°C
Mounting Type	Through Hole	—
Package / Case	TO-92-3 (TO-226AA)	—
RoHS Status	ROHS3 Compliant	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution of the BC556A-AP is determined by strict equivalence across the following critical electrical and mechanical parameters:

Electrical Equivalence Criteria:

Transistor polarity: PNP configuration
Maximum collector current: 100 mA
Maximum collector-emitter breakdown voltage: 65 V
Collector-emitter saturation voltage: 650 mV @ 5 mA, 100 mA
DC current gain (hFE): minimum 110 @ 2 mA, 5 V
Transition frequency: 150 MHz

Mechanical Equivalence Criteria:

Package type: TO-92-3 through-hole configuration with formed leads
Pin compatibility: identical TO-226AA pinout

Compliance Criteria:

RoHS3 compliance required
ECCN classification: EAR99

The BC556ATA manufactured by onsemi meets all specified electrical parameters within acceptable tolerances and maintains identical mechanical compatibility. Both devices share the same base product number (BC556) and are functionally interchangeable within the defined parameter envelope.

Parameter Comparison

Parameter	BC556A-AP (Micro Commercial Co)	BC556ATA (onsemi)	Compatibility
Transistor Type	PNP	PNP	Equivalent
Current - Collector (Ic) (Max)	100 mA	100 mA	Equivalent
Voltage - Collector Emitter Breakdown (Max)	65 V	65 V	Equivalent
Vce Saturation (Max) @ Ib, Ic	650 mV @ 5 mA, 100 mA	650 mV @ 5 mA, 100 mA	Equivalent
Current - Collector Cutoff (Max)	100 nA	15 nA	Compatible (BC556ATA superior)
DC Current Gain (hFE) (Min) @ Ic, Vce	120 @ 2 mA, 5 V	110 @ 2 mA, 5 V	Compatible
Power - Max	625 mW	500 mW	Compatible (BC556A-AP superior)
Frequency - Transition	150 MHz	150 MHz	Equivalent
Operating Temperature Range	−55 to +150 °C	Up to +150 °C	Compatible
Mounting Type	Through Hole	Through Hole	Equivalent
Package / Case	TO-92-3 (TO-226AA)	TO-92-3 (TO-226AA)	Equivalent
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	Equivalent

Engineering Selection Recommendations

BC556ATA (onsemi) as Primary Substitute:

The BC556ATA is the direct functional equivalent for the obsolete BC556A-AP. Both devices maintain identical electrical specifications across all critical parameters including collector current, breakdown voltage, saturation voltage, and transition frequency. The TO-92-3 package pinout is identical, enabling direct mechanical substitution without PCB redesign.

The BC556ATA carries a Last Time Buy product status, indicating limited future availability. Both the original BC556A-AP and the substitute BC556ATA are ROHS3 compliant and classified under ECCN EAR99, ensuring regulatory consistency.

The BC556ATA demonstrates superior leakage current performance (15 nA versus 100 nA), which provides operational margin in low-power applications. The BC556A-AP maintains a higher maximum power rating (625 mW versus 500 mW), which may be relevant in high-dissipation circuit topologies. Circuit design should account for the 125 mW power rating difference when thermal management is critical.

Both devices are suitable for general-purpose switching and amplification applications within the specified electrical envelope. Selection between these parts should be based on component availability, supply chain considerations, and specific application power requirements.

Frequently Asked Questions (FAQ)

Q: Can the BC556ATA directly replace the BC556A-AP without circuit modification?

A: Yes. The BC556ATA is electrically and mechanically equivalent to the BC556A-AP. Both devices share identical collector current (100 mA), breakdown voltage (65 V), saturation voltage (650 mV), and transition frequency (150 MHz) specifications. The TO-92-3 package pinout is identical, permitting direct substitution on existing PCBs.

Q: What is the significance of the different maximum power ratings (625 mW vs. 500 mW)?

A: The BC556A-AP is rated for 625 mW maximum power dissipation, while the BC556ATA is rated for 500 mW. In applications where the transistor operates near maximum power dissipation limits, the BC556A-AP provides additional thermal margin. For typical switching and low-power amplification circuits, this difference is not operationally significant. Thermal analysis of the specific application determines whether this parameter difference affects component selection.

Q: Are both parts RoHS compliant?

A: Yes. Both the BC556A-AP and BC556ATA are ROHS3 compliant, meeting current environmental and regulatory requirements for electronic component manufacturing and use.

Q: What is the difference in leakage current between these parts?

A: The BC556A-AP specifies a maximum collector cutoff current (ICBO) of 100 nA, while the BC556ATA specifies 15 nA. The BC556ATA exhibits lower leakage current, which provides operational advantage in precision analog circuits and low-power applications where leakage current contributes to circuit noise or offset errors.

Q: Why is the BC556A-AP classified as obsolete?

A: The BC556A-AP is no longer in active production by Micro Commercial Co. The BC556ATA from onsemi serves as the current-generation equivalent and is available through active distribution channels, though it carries a Last Time Buy status indicating limited future availability.

Q: Are there any temperature range differences between these parts?

A: The BC556A-AP specifies an operating temperature range of −55 to +150 °C. The BC556ATA specifies operation up to +150 °C. For applications requiring operation below 0 °C, the BC556A-AP provides extended low-temperature capability. For standard industrial and consumer applications operating within 0 to +70 °C, both parts are suitable.

Q: What is the DC current gain (hFE) difference, and does it affect circuit design?

A: The BC556A-AP specifies a minimum hFE of 120 @ 2 mA, 5 V, while the BC556ATA specifies a minimum of 110 @ 2 mA, 5 V. This 10-unit difference is within normal manufacturing tolerance for BJT transistors and does not require circuit redesign. Both values support equivalent amplification and switching performance in standard applications.

Q: Can the BC556ATA be used in high-frequency applications?

A: Yes. Both the BC556A-AP and BC556ATA are rated for 150 MHz transition frequency, supporting high-frequency switching and amplification applications up to this frequency limit. Circuit design should account for parasitic capacitances and layout considerations at frequencies approaching the transition frequency specification.

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