BD433S NPN Bipolar Junction Transistor Equivalent & Substitute Parts

Part Overview

The BD433S is an NPN bipolar junction transistor manufactured by onsemi, rated for 22 V collector-emitter breakdown voltage and 4 A maximum collector current in a TO-126-3 through-hole package. This device is classified as obsolete, necessitating identification of active equivalent and substitute components for ongoing design requirements and production continuity.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Current - Collector (Ic) Max	4	A
Voltage - Collector Emitter Breakdown (Max)	22	V
Vce Saturation (Max) @ Ib, Ic	500mV @ 200mA, 2A	—
Current - Collector Cutoff (Max)	100	µA
DC Current Gain (hFE) Min @ Ic, Vce	40 @ 10mA, 5V	—
Power - Max	36	W
Frequency - Transition	3	MHz
Operating Temperature (TJ)	150	°C
Mounting Type	Through Hole	—
Package / Case	TO-126-3	—

Substitute Part Grouping Explanation

Substitution of the BD433S is determined by the following critical parameters:

Parametric Equivalents maintain identical electrical specifications across all key ratings: collector current (4 A), collector-emitter breakdown voltage (22 V), saturation voltage (500mV @ 200mA, 2A), DC current gain (40 @ 10mA, 5V), power dissipation (36 W), transition frequency (3 MHz), and through-hole TO-126-3 package configuration. These parts are direct functional replacements with no circuit redesign required.

Functional Substitutes share the same transistor type (NPN), mounting technology (through-hole), and package family (TO-126) but differ in one or more electrical parameters. The BD437G operates at higher voltage ratings (45 V breakdown) while maintaining the same collector current (4 A) and power dissipation (36 W). Functional substitutes require circuit analysis to confirm compatibility within the application's voltage and current operating envelope.

Parameter Comparison

Parameter	BD433S (onsemi)	BD433S (Fairchild)	BD437G (onsemi)
Transistor Type	NPN	NPN	NPN
Current - Collector (Ic) Max	4 A	4 A	4 A
Voltage - Collector Emitter Breakdown (Max)	22 V	22 V	45 V
Vce Saturation (Max) @ Ib, Ic	500mV @ 200mA, 2A	500mV @ 200mA, 2A	800mV @ 300mA, 3A
Current - Collector Cutoff (Max)	100 µA	100 µA	100 µA
DC Current Gain (hFE) Min @ Ic, Vce	40 @ 10mA, 5V	40 @ 10mA, 5V	85 @ 500mA, 1V
Power - Max	36 W	36 W	36 W
Frequency - Transition	3 MHz	3 MHz	3 MHz
Operating Temperature (TJ)	150°C	150°C	-55°C ~ 150°C
Mounting Type	Through Hole	Through Hole	Through Hole
Package / Case	TO-126-3	TO-126-3	TO-126-3
Product Status	Obsolete	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
REACH Status	REACH Unaffected	REACH Unaffected	REACH Unaffected

Engineering Selection Recommendations

BD433S (Fairchild Semiconductor) is the primary parametric equivalent for the obsolete onsemi BD433S. This part maintains identical electrical specifications and package configuration while offering active product status. Both devices are ROHS3 compliant and REACH unaffected, ensuring regulatory compliance continuity.

BD437G (onsemi) functions as an active substitute where circuit voltage ratings permit. The BD437G provides higher collector-emitter breakdown voltage (45 V versus 22 V), expanded operating temperature range (-55°C to 150°C), and higher DC current gain (85 @ 500mA, 1V). The increased saturation voltage (800mV @ 300mA, 3A) and different gain measurement conditions require circuit validation. This part is suitable for applications where the higher voltage rating provides design margin or where the expanded temperature range is required.

Selection between parametric equivalents and functional substitutes depends on application voltage and current requirements. Parametric equivalents require no circuit modification. Functional substitutes require verification that the application voltage envelope does not exceed 45 V and that the higher saturation voltage does not degrade circuit performance.

Frequently Asked Questions (FAQ)

Q: Can the BD433S (Fairchild) directly replace the BD433S (onsemi)?

A: Yes. Both parts are parametric equivalents with identical electrical specifications, saturation characteristics, DC current gain, and TO-126-3 package configuration. Direct substitution is supported without circuit modification.

Q: Under what conditions can the BD437G substitute for the BD433S?

A: The BD437G can substitute when the application circuit operates at voltages not exceeding 45 V and when the higher saturation voltage (800mV @ 300mA, 3A versus 500mV @ 200mA, 2A) does not compromise circuit performance. The BD437G's higher DC current gain (85 @ 500mA, 1V) may alter bias point calculations in circuits with fixed base resistors.

Q: Are all substitute parts in the same package?

A: Yes. All listed parts use the TO-126-3 through-hole package, ensuring mechanical and thermal compatibility in existing PCB layouts and heat sink configurations.

Q: What is the difference in operating temperature range between these parts?

A: The BD433S (both manufacturers) operates to a maximum junction temperature of 150°C. The BD437G extends the minimum operating temperature to -55°C, providing a full -55°C to 150°C range. This expanded range is relevant only for applications requiring low-temperature operation.

Q: Are there compliance differences between the substitute parts?

A: No. All listed parts are ROHS3 compliant and REACH unaffected, maintaining identical regulatory status for procurement and environmental compliance.

Q: How do the DC current gain specifications differ?

A: The BD433S specifies minimum hFE of 40 at 10mA collector current and 5V Vce. The BD437G specifies minimum hFE of 85 at 500mA collector current and 1V Vce. These different measurement conditions reflect different device design characteristics and require circuit analysis to determine impact on bias stability.

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