BD437 Equivalent & Substitute Parts

Part Overview

The BD437 is an NPN bipolar junction transistor manufactured by onsemi, rated for 45 V collector-emitter breakdown voltage and 4 A maximum collector current in a TO-126 through-hole package. This device is classified as obsolete, making equivalent and substitute parts necessary for ongoing production and maintenance applications. The BD437 delivers 36 W maximum power dissipation with a 3 MHz transition frequency, suitable for general-purpose switching and amplification circuits operating within specified voltage and current parameters.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	45	V
Current - Collector (Ic) (Max)	4	A
Power - Max	36	W
Frequency - Transition	3	MHz
Vce Saturation (Max) @ Ib, Ic	800 mV @ 300 mA, 3 A	—
DC Current Gain (hFE) (Min) @ Ic, Vce	85 @ 500 mA, 1 V	—
Current - Collector Cutoff (Max)	100	µA
Operating Temperature Range	-55 to 150	°C
Mounting Type	Through Hole	—
Package / Case	TO-126-3	—

Substitute Part Grouping Explanation

Substitution of the BD437 is determined by electrical and mechanical compatibility across the following critical parameters: transistor type (NPN), maximum collector-emitter breakdown voltage, maximum collector current, power dissipation rating, transition frequency, saturation voltage characteristics, DC current gain, and through-hole mounting compatibility. Parts are grouped into three categories based on their relationship to the main device:

Direct Equivalent: Parts maintaining identical electrical specifications and package form factor, differing only in product status or packaging configuration.

Similar Specification: Parts with higher voltage ratings or modified gain characteristics that operate within the same package and mounting type but with different maximum ratings.

Parametric Equivalent: Parts with identical electrical specifications and active product status, suitable for direct replacement in new designs.

Parameter Comparison

Parameter	BD437 (onsemi)	BD437G (onsemi)	BD437TG (onsemi)	BD439G (onsemi)	BD437 (STMicroelectronics)
Transistor Type	NPN	NPN	NPN	NPN	NPN
Voltage - Collector Emitter Breakdown (Max)	45 V	45 V	45 V	60 V	45 V
Current - Collector (Ic) (Max)	4 A	4 A	4 A	4 A	4 A
Power - Max	36 W	36 W	36 W	36 W	36 W
Frequency - Transition	3 MHz	3 MHz	3 MHz	3 MHz	3 MHz
Vce Saturation (Max) @ Ib, Ic	800 mV @ 300 mA, 3 A	800 mV @ 300 mA, 3 A	800 mV @ 300 mA, 3 A	800 mV @ 300 mA, 3 A	600 mV @ 200 mA, 2 A
DC Current Gain (hFE) (Min) @ Ic, Vce	85 @ 500 mA, 1 V	85 @ 500 mA, 1 V	85 @ 500 mA, 1 V	40 @ 500 mA, 1 V	30 @ 10 mA, 5 V
Current - Collector Cutoff (Max)	100 µA	100 µA	100 µA	100 µA	100 µA
Operating Temperature Range	-55 to 150 °C	-55 to 150 °C	-55 to 150 °C	-55 to 150 °C	-55 to 150 °C
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole
Package / Case	TO-126-3	TO-126-3	TO-126-3	TO-126-3	SOT-32-3
Product Status	Obsolete	Active	Active	Active	Not For New Designs
RoHS Status	RoHS Non-Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

For Direct Replacement in Existing Designs: BD437G and BD437TG are suitable direct replacements for the obsolete BD437 (onsemi). Both parts maintain identical electrical specifications including 45 V breakdown voltage, 4 A collector current, 36 W power rating, and 85 minimum DC current gain. BD437G and BD437TG are active products with ROHS3 compliance, addressing the obsolescence and regulatory status of the original device. The primary distinction between these two options is packaging configuration: BD437G is supplied in bulk packaging, while BD437TG is supplied in bulk packaging with identical electrical performance.

For Higher Voltage Applications: BD439G operates at 60 V maximum collector-emitter breakdown voltage while maintaining 4 A collector current and 36 W power dissipation. This part is suitable for applications requiring higher voltage headroom. The DC current gain minimum is reduced to 40 at the specified test conditions, which may affect circuit performance in gain-dependent applications. BD439G is an active product with ROHS3 compliance.

For Alternative Packaging: The STMicroelectronics BD437 offers identical voltage and current ratings but uses a SOT-32-3 package instead of TO-126-3. This part is classified as "Not For New Designs" and features different saturation voltage characteristics (600 mV versus 800 mV) and reduced DC current gain (30 minimum). Physical package differences preclude direct mechanical substitution without circuit board redesign.

Frequently Asked Questions (FAQ)

Q: Can BD437G directly replace the obsolete BD437 from onsemi?

A: Yes. BD437G maintains identical electrical specifications: 45 V breakdown voltage, 4 A maximum collector current, 36 W power dissipation, 3 MHz transition frequency, and 85 minimum DC current gain. Both parts use the TO-126-3 package. BD437G is an active product with ROHS3 compliance, addressing the obsolescence status of the original BD437.

Q: What is the difference between BD437G and BD437TG?

A: BD437G and BD437TG are electrically identical, both maintaining 45 V breakdown voltage, 4 A collector current, and 85 minimum DC current gain. The difference is in packaging configuration: BD437G is supplied in bulk packaging, while BD437TG is also supplied in bulk packaging. Both are active products with ROHS3 compliance and identical TO-126-3 package form factors.

Q: Can BD439G be used as a substitute for BD437?

A: BD439G is a similar specification part with a higher 60 V maximum collector-emitter breakdown voltage compared to the BD437's 45 V rating. Both maintain 4 A collector current and 36 W power dissipation. However, BD439G has a reduced DC current gain minimum of 40 at the specified test conditions, compared to 85 for the BD437. This gain reduction may affect circuit performance in applications where current gain is a critical design parameter. BD439G is suitable for applications requiring higher voltage ratings.

Q: Why is the STMicroelectronics BD437 not recommended as a substitute?

A: The STMicroelectronics BD437 uses a SOT-32-3 package instead of the TO-126-3 package used by the onsemi BD437. This physical package difference prevents direct mechanical substitution without circuit board redesign. Additionally, this part is classified as "Not For New Designs," and it exhibits different electrical characteristics including lower saturation voltage (600 mV versus 800 mV) and reduced DC current gain (30 minimum versus 85 minimum).

Q: Are all substitute parts RoHS compliant?

A: BD437G, BD437TG, and BD439G are all ROHS3 compliant. The original onsemi BD437 is RoHS non-compliant. The STMicroelectronics BD437 is ROHS3 compliant but is classified as "Not For New Designs."

Q: What are the key parameters that determine substitution compatibility?

A: Substitution compatibility is determined by: transistor type (NPN), maximum collector-emitter breakdown voltage, maximum collector current (4 A), power dissipation rating (36 W), transition frequency (3 MHz), saturation voltage characteristics, DC current gain, and through-hole mounting type with TO-126-3 package form factor. Deviations in any of these parameters may affect circuit performance.

Q: Can the BD437 be used in new designs?

A: The original onsemi BD437 is classified as obsolete and is not suitable for new designs. BD437G and BD437TG are active products with ROHS3 compliance and are suitable for new designs. These parts maintain identical electrical specifications and package form factors.

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