BD437S Equivalent & Substitute Parts

Part Overview

The BD437S is an NPN bipolar junction transistor manufactured by onsemi, rated for 45 V collector-emitter breakdown voltage and 4 A maximum collector current. This device is packaged in TO-126-3 through-hole configuration with a maximum power dissipation of 36 W and transition frequency of 3 MHz. The BD437S is classified as obsolete, necessitating identification of active equivalent and substitute components for new designs and ongoing production support.

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	600mV @ 200mA, 2A	—
DC Current Gain (hFE) (Min) @ Ic, Vce	30 @ 10mA, 5V	—
Current - Collector Cutoff (Max)	100	µA
Operating Temperature (Max)	150	°C
Mounting Type	Through Hole	—
Package / Case	TO-225AA, TO-126-3	—
RoHS Status	ROHS3 Compliant	—

Substitute Part Grouping Explanation

Substitution of the BD437S is determined by electrical and mechanical compatibility across the following critical parameters:

Primary Substitution Criteria:

Transistor Type: NPN
Voltage - Collector Emitter Breakdown (Max): 45 V minimum
Current - Collector (Ic) (Max): 4 A minimum
Power - Max: 36 W minimum
Mounting Type: Through Hole
Package / Case: TO-126-3 or equivalent TO-225AA

Substitution Categories:

Direct Equivalents maintain identical electrical specifications and packaging, enabling pin-for-pin replacement without circuit modification.

Parametric Equivalents meet or exceed all critical electrical parameters while maintaining mechanical compatibility. These components function identically in circuit applications despite minor specification variations.

Similar Alternatives share the same transistor type, voltage rating, and package but operate at reduced current or power levels. These components are suitable only for applications where the reduced current or power rating does not exceed circuit requirements.

Parameter Comparison

Part Number	Manufacturer	Product Status	Ic (Max) [A]	Vce Breakdown (Max) [V]	Power (Max) [W]	Frequency [MHz]	hFE (Min) @ Ic, Vce	Package	Operating Temp (Max) [°C]
BD437S	onsemi	Obsolete	4	45	36	3	30 @ 10mA, 5V	TO-126-3	150
BD437G	onsemi	Active	4	45	36	3	85 @ 500mA, 1V	TO-126	150
BD437TG	onsemi	Active	4	45	36	3	85 @ 500mA, 1V	TO-126	150
BD437	STMicroelectronics	Not For New Designs	4	45	36	3	30 @ 10mA, 5V	SOT-32-3	150
BD437S	Fairchild Semiconductor	Active	4	45	36	3	30 @ 10mA, 5V	TO-126-3	150
2N5190G	onsemi	Active	4	40	40	2	25 @ 1.5A, 2V	TO-126	150
BD135G	onsemi	Active	1.5	45	1.25	—	40 @ 150mA, 2V	TO-126	150
BD135	STMicroelectronics	Active	1.5	45	1.25	—	40 @ 150mA, 2V	SOT-32-3	150

Engineering Selection Recommendations

For Direct Replacement (Pin-for-Pin Compatible):

BD437G (onsemi) and BD437TG (onsemi) are active direct equivalents to the obsolete BD437S. Both components maintain 4 A collector current, 45 V breakdown voltage, 36 W power rating, and 3 MHz transition frequency. BD437G and BD437TG are ROHS3 compliant and suitable for new designs. The primary difference is packaging designation (TO-126 versus TO-126-3), which does not affect electrical performance or mechanical fit in standard through-hole applications.

BD437S manufactured by Fairchild Semiconductor is an active parametric equivalent with identical electrical specifications and TO-126-3 packaging. This component provides direct substitution capability and is ROHS3 compliant.

For Applications Tolerating Reduced Current or Power:

BD135G (onsemi) and BD135 (STMicroelectronics) are active alternatives rated for 1.5 A maximum collector current and 1.25 W power dissipation. These components maintain 45 V breakdown voltage and through-hole TO-126 or SOT-32-3 packaging. Selection of BD135 variants is appropriate only when circuit requirements do not exceed 1.5 A collector current.

For Applications Tolerating Reduced Voltage Rating:

2N5190G (onsemi) is an active alternative rated for 40 V breakdown voltage (5 V lower than BD437S) with 4 A collector current and 40 W power dissipation. This component is suitable only when the 40 V rating meets circuit voltage requirements.

Avoid:

BD437 (STMicroelectronics) is classified as "Not For New Designs" and uses SOT-32-3 packaging, which differs from the standard TO-126-3 configuration. This component is not recommended for new applications.

Frequently Asked Questions (FAQ)

Q: Can BD437G directly replace BD437S in existing designs?

A: Yes. BD437G maintains identical electrical specifications (4 A, 45 V, 36 W, 3 MHz) and through-hole mounting. The packaging designation difference (TO-126 versus TO-126-3) does not affect mechanical or electrical compatibility in standard circuit applications.

Q: What is the difference between BD437G and BD437TG?

A: Both components are manufactured by onsemi and share identical electrical ratings (4 A, 45 V, 36 W, 3 MHz). The designation suffix indicates different packaging or tape-and-reel configurations. Electrical performance and pin compatibility are equivalent.

Q: Can BD135G substitute for BD437S?

A: BD135G is not a direct substitute. While both are NPN transistors with 45 V breakdown voltage and through-hole packaging, BD135G is rated for only 1.5 A maximum collector current and 1.25 W power dissipation, compared to BD437S at 4 A and 36 W. BD135G is suitable only for applications where collector current does not exceed 1.5 A.

Q: Why is the Fairchild Semiconductor BD437S listed as active when the onsemi BD437S is obsolete?

A: Different manufacturers maintain separate product lifecycles. The Fairchild Semiconductor BD437S remains in active production with identical electrical specifications and TO-126-3 packaging, providing a direct alternative to the obsolete onsemi version.

Q: What is the significance of the hFE (DC Current Gain) differences between BD437S and BD437G?

A: BD437S specifies minimum hFE of 30 at 10 mA and 5 V, while BD437G specifies minimum hFE of 85 at 500 mA and 1 V. These measurements occur at different operating points. Both specifications are within the same device family and do not prevent substitution. Circuit designs should verify that the specified gain meets application requirements at the intended operating point.

Q: Are all listed substitutes ROHS3 compliant?

A: All active substitute components listed (BD437G, BD437TG, BD437S by Fairchild, 2N5190G, BD135G, and BD135 by STMicroelectronics) are ROHS3 compliant. The obsolete onsemi BD437S and STMicroelectronics BD437 are also ROHS3 compliant.

Q: Can 2N5190G replace BD437S in high-voltage applications?

A: 2N5190G is rated for 40 V breakdown voltage, which is 5 V lower than BD437S at 45 V. This component is suitable only for applications where the maximum circuit voltage does not exceed 40 V. For circuits requiring the full 45 V rating, 2N5190G is not appropriate.

Q: What packaging options are available for BD437 equivalents?

A: Active equivalents are available in TO-126 and TO-126-3 through-hole packages (onsemi BD437G, BD437TG, Fairchild BD437S). STMicroelectronics offers BD437 in SOT-32-3 packaging, though this device is not recommended for new designs. All packages are through-hole configurations suitable for standard PCB mounting.

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