2SA844-D-AP Equivalent & Substitute Parts

Part Overview

The 2SA844-D-AP is a PNP bipolar junction transistor manufactured by Micro Commercial Co, designed for small-signal switching and amplification applications. Specified for 55 V collector-emitter breakdown voltage, 100 mA maximum collector current, and 300 mW power dissipation in a through-hole TO-92 package. The device is classified as obsolete, necessitating identification of active equivalent alternatives that maintain functional compatibility within specified electrical parameters.

Substiute Parts

2SA844-D-AP

Micro Commercial CoIn Stock: 10222SA844-D-AP Datasheet

Current PartRFQ

BC556BTA

Fairchild SemiconductorIn Stock: 18331BC556BTA Datasheet

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BC557ATA

Fairchild SemiconductorIn Stock: 860BC557ATA Datasheet

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BC557BTA

onsemiIn Stock: 6210BC557BTA Datasheet

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BC557BTF

onsemiIn Stock: 41658BC557BTF Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution of the 2SA844-D-AP is determined by equivalence in the following electrical and mechanical parameters:

Primary Substitution Criteria:

• Transistor polarity: PNP type required
• Collector current rating: 100 mA minimum
• Collector-emitter breakdown voltage: Must equal or exceed 55 V
• Package type: TO-92-3 through-hole configuration
• Mounting compatibility: Through-hole lead formation

Secondary Compatibility Factors:

• Power dissipation capability
• Transition frequency
• DC current gain (hFE)
• Saturation voltage characteristics
• Operating temperature range

Substitute parts are grouped based on voltage rating capability. Parts with collector-emitter breakdown voltage equal to or greater than 55 V are direct functional equivalents. Parts with lower voltage ratings are listed with voltage derating considerations.

Parameter Comparison

Engineering Selection Recommendations

BC556BTA (Fairchild Semiconductor)

BC556BTA is the primary substitute for applications where the 55 V collector-emitter breakdown voltage specification is critical. This device exceeds the original specification at 65 V, providing voltage margin. All current and power ratings are equivalent or superior. The device is active in production with ROHS3 compliance. Transition frequency is reduced to 150 MHz compared to the original 200 MHz specification.

BC557BTA and BC557BTF (onsemi)

Both BC557BTA and BC557BTF are active production alternatives from onsemi. These devices operate at 45 V collector-emitter breakdown voltage, which is 10 V below the original 2SA844-D-AP specification. Selection of these parts requires circuit analysis to confirm that the reduced voltage rating is acceptable for the intended application. Both devices maintain 100 mA collector current and TO-92-3 package compatibility. BC557BTF has significantly higher inventory availability. Both are ROHS3 compliant.

BC557ATA (Fairchild Semiconductor)

BC557ATA operates at 45 V collector-emitter breakdown voltage with reduced DC current gain (110 minimum at 2 mA, 5 V versus 250 minimum for the original part). This device is suitable only for applications where the lower voltage rating and reduced gain are acceptable. Active production status and ROHS3 compliance are confirmed.

Voltage Rating Considerations

Applications operating at or near 55 V require BC556BTA. Applications with maximum operating voltages below 45 V may use BC557 series devices. Circuit design review is necessary to confirm voltage derating acceptability.

Frequently Asked Questions (FAQ)

Q: Can BC557 series devices directly replace the 2SA844-D-AP in all applications?

A: BC557 series devices (BC557ATA, BC557BTA, BC557BTF) operate at 45 V collector-emitter breakdown voltage, which is 10 V lower than the 2SA844-D-AP specification of 55 V. Direct replacement is possible only in circuits where the maximum operating voltage does not exceed 45 V. Circuit analysis is required to confirm voltage compatibility.

Q: What is the primary advantage of BC556BTA over BC557 series alternatives?

A: BC556BTA provides 65 V collector-emitter breakdown voltage, exceeding the original 2SA844-D-AP specification of 55 V. This device is the preferred substitute for applications requiring the full voltage rating or operating near the original specification limit.

Q: Are all substitute parts available in the same TO-92-3 package?

A: Yes. All substitute parts listed (BC556BTA, BC557ATA, BC557BTA, BC557BTF) are packaged in TO-92-3 through-hole configuration with identical lead formation, ensuring mechanical and pin compatibility with the original 2SA844-D-AP.

Q: How does the transition frequency difference affect circuit performance?

A: The 2SA844-D-AP specifies 200 MHz transition frequency, while all substitute parts specify 150 MHz. This 50 MHz reduction may impact high-frequency switching applications. Circuit performance at the intended operating frequency must be verified during design validation.

Q: What is the significance of the DC current gain (hFE) differences?

A: The 2SA844-D-AP specifies minimum hFE of 250 at 2 mA and 12 V. BC557BTA and BC557BTF specify 200 at 2 mA and 5 V. BC557ATA specifies 110 at the same conditions. Lower gain values require increased base drive current for equivalent collector current. Circuit bias design may require adjustment.

Q: Are all substitute parts RoHS3 compliant?

A: BC557BTA and BC557BTF are confirmed ROHS3 compliant. BC556BTA and BC557ATA do not list RoHS status in the provided specifications. Compliance verification with the component supplier is recommended for applications requiring RoHS certification.

Q: What inventory considerations apply to these substitutes?

A: BC557BTF has the highest inventory availability at 41,626 pieces. BC556BTA has 18,244 pieces available. BC557BTA has 6,200 pieces. BC557ATA has 779 pieces. Inventory levels should be confirmed with the supplier for production requirements.