BC33725 NPN Bipolar Junction Transistor Equivalent & Substitute Parts

Part Overview

The BC33725 is an NPN bipolar junction transistor manufactured by onsemi, rated for 45 V collector-emitter breakdown voltage and 800 mA maximum collector current. The device is packaged in a TO-92-3 through-hole configuration with a maximum power dissipation of 625 mW and transition frequency of 100 MHz. The BC33725 is classified as obsolete, making identification of equivalent and substitute components necessary for ongoing design support and production continuity. Active alternatives with identical or superior electrical characteristics are available from multiple manufacturers.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Collector Current (Max)	800	mA
Collector-Emitter Breakdown Voltage (Max)	45	V
Vce Saturation (Max)	700 mV @ 50 mA, 500 mA	—
Collector Cutoff Current (Max)	100	nA
DC Current Gain (hFE Min)	160 @ 100 mA, 1 V	—
Power Dissipation (Max)	625	mW
Transition Frequency	100	MHz
Operating Temperature (Max)	150	°C
Mounting Type	Through Hole	—
Package	TO-92-3	—

Substitute Part Grouping Explanation

Substitution of the BC33725 is determined by matching the following critical electrical and mechanical parameters:

Electrical Matching Criteria:

Transistor type: NPN
Collector current rating: 800 mA minimum
Collector-emitter breakdown voltage: 45 V minimum
DC current gain (hFE): 160 minimum at specified conditions
Power dissipation: 625 mW minimum
Transition frequency: 100 MHz minimum

Mechanical Matching Criteria:

Mounting type: Through Hole
Package compatibility: TO-92-3 or TO-92 compatible configurations

Substitute parts are classified into two categories:

Direct Equivalents: Parts with identical electrical specifications and compatible packaging. These provide one-to-one replacement capability without circuit modification.

Similar Equivalents: Parts with equal or superior electrical performance in one or more parameters but potentially different package designations or thermal characteristics. These require verification of physical fit within the application.

Parameter Comparison

Parameter	BC33725 (onsemi)	BC33725BU (Fairchild)	ZTX450 (Diodes Inc.)	BC337-25BK (Diotec)
Transistor Type	NPN	NPN	NPN	NPN
Ic (Max)	800 mA	800 mA	1 A	800 mA
Vce Breakdown (Max)	45 V	45 V	45 V	45 V
Vce Saturation (Max)	700 mV @ 50 mA, 500 mA	700 mV @ 50 mA, 500 mA	250 mV @ 15 mA, 150 mA	700 mV @ 50 mA, 500 mA
Icbo (Max)	100 nA	100 nA	100 nA	100 nA
hFE (Min)	160 @ 100 mA, 1 V	160 @ 100 mA, 1 V	100 @ 150 mA, 10 V	160 @ 100 mA, 1 V
Power (Max)	625 mW	625 mW	1 W	625 mW
Frequency - Transition	100 MHz	100 MHz	150 MHz	100 MHz
Operating Temperature (Max)	150°C	150°C	200°C	150°C
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole
Package	TO-92-3	TO-92-3	E-Line (TO-92 compatible)	TO-92
Product Status	Obsolete	Active	Active	Active

Engineering Selection Recommendations

BC33725BU (Fairchild Semiconductor): This part is the primary direct equivalent. It maintains identical electrical specifications across all critical parameters including collector current, breakdown voltage, saturation voltage, current gain, power dissipation, and transition frequency. The TO-92-3 package provides direct mechanical compatibility. Product status is active with established supply chain availability. This part is suitable for direct replacement in all applications where the BC33725 was originally specified.

BC337-25BK (Diotec Semiconductor): This part meets all electrical parameter requirements with identical ratings for collector current, breakdown voltage, saturation voltage, current gain, power dissipation, and transition frequency. The TO-92 package is mechanically compatible with TO-92-3 applications. Product status is active. This part is suitable for direct replacement with verification of physical fit within the application enclosure.

ZTX450 (Diodes Incorporated): This part exceeds the electrical specifications of the BC33725 in collector current (1 A vs. 800 mA), power dissipation (1 W vs. 625 mW), and transition frequency (150 MHz vs. 100 MHz). The operating temperature range extends to 200°C. The E-Line package is designated as TO-92 compatible. Product status is active. This part is suitable for applications requiring enhanced performance margins, with verification that the E-Line package dimensions accommodate the original TO-92-3 footprint.

Frequently Asked Questions (FAQ)

Q: Can BC33725BU be used as a direct replacement for BC33725?

A: Yes. BC33725BU is manufactured by Fairchild Semiconductor and provides identical electrical specifications across all parameters: 800 mA collector current, 45 V breakdown voltage, 700 mV saturation voltage, 160 minimum hFE, 625 mW power dissipation, and 100 MHz transition frequency. The TO-92-3 package is mechanically identical. No circuit modifications are required.

Q: What is the difference between BC337-25BK and BC33725?

A: BC337-25BK matches all electrical specifications of BC33725 but is packaged in TO-92 instead of TO-92-3. Both packages are through-hole configurations with compatible pin configurations. Physical dimensions should be verified for fit within the application. BC337-25BK is manufactured by Diotec Semiconductor and carries active product status.

Q: Why is ZTX450 listed as a substitute if it has different specifications?

A: ZTX450 exceeds the electrical requirements of BC33725 in three parameters: collector current (1 A vs. 800 mA), power dissipation (1 W vs. 625 mW), and transition frequency (150 MHz vs. 100 MHz). These superior ratings provide additional performance margin. The E-Line package is designated as TO-92 compatible. ZTX450 is suitable for applications where enhanced performance is beneficial or where thermal headroom is required.

Q: Are all substitute parts RoHS compliant?

A: BC33725BU and ZTX450 carry ROHS3 compliance certification. BC337-25BK lists RoHS status as not applicable. All parts carry REACH Unaffected or Vendor Undefined status. Compliance requirements should be verified against specific application and regional standards.

Q: What is the inventory status of substitute parts?

A: BC33725BU (Fairchild) has 25,400 pieces in stock. BC337-25BK (Diotec) has 5,736 pieces in stock. ZTX450 (Diodes Incorporated) has 1,600 pieces in stock. The original BC33725 (onsemi) has 980 pieces in stock but is classified as obsolete.

Q: Can ZTX450 be used in high-temperature applications?

A: ZTX450 is rated for operating temperatures up to 200°C, compared to 150°C for BC33725. This extended temperature range makes ZTX450 suitable for applications requiring operation at elevated temperatures. Circuit design should account for the different saturation voltage characteristics at high current levels.

Q: Are there package dimension differences between TO-92-3 and E-Line?

A: Both TO-92-3 and E-Line are through-hole packages with three leads. E-Line is designated as TO-92 compatible. Physical dimensions should be verified against the specific application PCB layout and component mounting constraints before substitution.

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