ZTX550 Equivalent & Substitute Parts

Part Overview

The ZTX550 is a PNP bipolar junction transistor manufactured by Diodes Incorporated, rated for 45 V collector-emitter breakdown voltage and 1 A maximum collector current. The device is packaged in an E-Line (TO-92 compatible) configuration and is rated for 1 W maximum power dissipation with a transition frequency of 150 MHz. The ZTX550 is classified as obsolete, necessitating identification of active substitute components that maintain functional compatibility within specified electrical and mechanical parameters.

Substiute Parts

ZTX550

Diodes IncorporatedIn Stock: 5202ZTX550 Datasheet

Current PartRFQ

BC32725BU

onsemiIn Stock: 17157BC32725BU Datasheet

MFR RecommendedRFQ

BC32740BU

onsemiIn Stock: 11460BC32740BU Datasheet

MFR RecommendedRFQ

PN4033 PBFREE

Central Semiconductor CorpIn Stock: 935PN4033 PBFREE Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the ZTX550 is determined by the following critical parameters:

Electrical Compatibility Requirements:

• Transistor type must be PNP
• Voltage rating must equal or exceed 45 V collector-emitter breakdown voltage
• Current rating must equal or exceed 1 A maximum collector current
• Power dissipation must equal or exceed 1 W

Mechanical Compatibility Requirements:

• Mounting type must be Through Hole
• Package must be compatible with TO-92-3 or E-Line-3 footprints

Regulatory Compliance:

• RoHS3 compliance required
• REACH unaffected status required

The substitute parts BC32725BU, BC32740BU, and PN4033 PBFREE meet the core electrical requirements for voltage and current ratings. However, each substitute exhibits trade-offs in secondary parameters including power dissipation, transition frequency, and operating temperature range.

Parameter Comparison

Engineering Selection Recommendations

BC32725BU and BC32740BU (onsemi): Both devices are active products with ROHS3 compliance and REACH unaffected status. These substitutes provide 45 V voltage rating matching the ZTX550 specification. However, maximum collector current is reduced to 800 mA and maximum power dissipation is 625 mW. These devices are suitable for applications where the circuit design accommodates the reduced current and power ratings. The BC32740BU provides higher DC current gain (250 @ 100mA, 1V) compared to BC32725BU (160 @ 100mA, 1V), offering improved amplification characteristics. Both devices operate at maximum junction temperature of 150°C, which is lower than the ZTX550 specification of 200°C.

PN4033 PBFREE (Central Semiconductor Corp): This active product maintains the 1 A maximum collector current rating of the ZTX550 and provides enhanced voltage rating of 80 V. The PN4033 PBFREE offers superior transition frequency of 400 MHz compared to the ZTX550 at 150 MHz. However, maximum power dissipation is 625 mW, lower than the ZTX550 specification of 1 W. The device operates at maximum junction temperature of 150°C. The PN4033 PBFREE is ROHS3 compliant and REACH unaffected. This substitute is appropriate for applications requiring higher voltage headroom and faster switching characteristics while accepting reduced power dissipation capability.

All three substitute parts are available in active production status with full regulatory compliance, ensuring long-term supply availability and design continuity.

Frequently Asked Questions (FAQ)

Q: Can BC32725BU or BC32740BU directly replace ZTX550 in all applications?

A: BC32725BU and BC32740BU are electrically compatible for voltage rating (45 V) but provide reduced maximum collector current (800 mA versus 1 A) and power dissipation (625 mW versus 1 W). These substitutes are suitable only for circuits designed to operate within these reduced specifications. Applications requiring the full 1 A current or 1 W power dissipation must use PN4033 PBFREE or verify circuit operation at reduced ratings.

Q: What is the primary limitation of BC32725BU and BC32740BU compared to ZTX550?

A: The primary limitation is reduced maximum collector current (800 mA) and power dissipation (625 mW). Additionally, maximum operating junction temperature is 150°C compared to ZTX550 at 200°C. These devices are suitable for low-power applications but not for high-current or high-temperature environments.

Q: Why does PN4033 PBFREE have lower power dissipation than ZTX550 despite matching current rating?

A: Power dissipation is a separate specification determined by device design and thermal characteristics. PN4033 PBFREE is rated for 625 mW maximum power dissipation while maintaining 1 A current capability. Applications must verify that actual power dissipation remains within this limit through circuit analysis.

Q: Are all substitute parts compatible with TO-92-3 footprints?

A: Yes. BC32725BU, BC32740BU, and PN4033 PBFREE are all packaged in TO-92-3 (TO-226AA) configuration, which is mechanically compatible with E-Line-3 footprints used by ZTX550. Pin assignments are identical for PNP transistors in this package family.

Q: What is the difference between BC32725BU and BC32740BU?

A: Both devices share identical electrical specifications except for DC current gain. BC32740BU provides minimum DC current gain of 250 @ 100mA, 1V, while BC32725BU provides 160 @ 100mA, 1V. BC32740BU offers superior amplification characteristics for the same voltage and current ratings.

Q: Is PN4033 PBFREE suitable for high-frequency applications?

A: PN4033 PBFREE provides transition frequency of 400 MHz, which exceeds ZTX550 at 150 MHz. This device is suitable for applications requiring faster switching speeds. However, the reduced power dissipation rating (625 mW) must be verified against circuit requirements.

Q: Are all substitute parts RoHS3 compliant?

A: Yes. BC32725BU, BC32740BU, and PN4033 PBFREE are all ROHS3 compliant and REACH unaffected, meeting current environmental and regulatory requirements.