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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

onsemi BD433S

Name: BD433S
Brand: onsemi
SKU: BD433S
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BD433S

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-225AA, TO-126-3

Datasheet:: BD433S.pdf

Description:: TRANS NPN 22V 4A TO-126-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BD433S from ON Semiconductor is a medium-power NPN epitaxial silicon transistor in TO-126 package, rated for 22 V collector-emitter sustaining voltage (V_CEO(sus)), 4 A DC collector current (I_C), and 36 W collector dissipation at T_C = 25°C. It serves as a linear amplifier or switching device in power supply regulators and motor drive stages.

For engineers reviewing the BD433S datasheet, pinout, applications, or equivalent options, key selection criteria include its 22 V V_CEO, 0.2–0.5 V V_CE(sat) at I_C = 2 A / I_B = 0.2 A, h_FE range of 40–130, TO-126 thermal performance, and complementarity to BD434 in push-pull configurations.

Technical Context

This NPN bipolar junction transistor operates with fixed-base drive in saturated switching or active-region amplification. Its 150°C maximum junction temperature and 3 MHz f_T support stable mid-frequency switching up to ~100 kHz in hard-switched topologies.

Designed for discrete power stage implementation, BD433S features low V_BE(on) (1.1 V at I_C = 2 A) and controlled saturation behavior-enabling predictable turn-on loss and compatible gate-drive interface with standard logic-level or resistor-limited base drivers.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO(sus)	22 V - Sustaining voltage under open-base condition; defines safe blocking capability in switch-off state
I_C (DC)	4 A - Continuous collector current limit; sets max steady-state load handling without forced cooling
P_C @ T_C = 25°C	36 W - Maximum power dissipation at case temperature 25°C; requires heatsink for >10 W operation
V_CE(sat)	0.2–0.5 V @ I_C = 2 A, I_B = 0.2 A - Low saturation voltage reduces conduction loss in switching applications
h_FE	40–130 @ V_CE = 5 V, I_C = 10 mA - DC current gain range determines required base drive strength
f_T	3 MHz - Current gain bandwidth product; supports stable amplification or switching up to ~100 kHz

Pinout & Package

BD433S uses the TO-126 package: molded plastic case with metal tab (collector-connected), 3-pin through-hole configuration, and industry-standard footprint for mechanical mounting and thermal transfer to heatsinks.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Emitter terminal	Current exit path; connected to ground or low-side reference in common-emitter configurations
2 (Collector)	Collector terminal	Current entry path; electrically tied to metal tab for direct heatsink coupling and low-inductance power routing
3 (Base)	Base control terminal	Current-controlled input; requires 0.2 A drive for full saturation at 2 A collector load

Key Features

Feature	Design Value
Medium-power switching capability	Supports 22 V/4 A loads in relay drivers, lamp ballasts, and DC-DC converter output stages
Complementary pairing	Designed as NPN counterpart to BD434 (PNP), enabling matched push-pull output stages
Thermally robust TO-126 package	Tab-mounted collector enables direct heatsink attachment and >30 W thermal derating at 25°C case temp
Controlled saturation characteristics	V_CE(sat) ≤ 0.5 V ensures <1 W conduction loss at 2 A, simplifying thermal design in linear regulators

Applications

Switch-Mode Power Supply Output Stage	DC Motor Driver (Unidirectional)
Use Scenario: Used in the main switching transistor of 12–24 V offline flyback or forward converters delivering up to 50 W. IC Role / Device Role / Timing Role: NPN power switch operating in hard-saturated mode at 50–100 kHz, driven by UC3842 or similar PWM controller. Use Value: 22 V V_CEO and 36 W P_C allow reliable operation with margin over 24 V rail; TO-126 tab enables compact heatsinking.	Use Scenario: Drives brushed DC motors in industrial actuators or HVAC dampers requiring bidirectional control via H-bridge (with complementary PNP). IC Role / Device Role / Timing Role: High-side or low-side switch in half-bridge configuration, controlled by microcontroller GPIO with base resistor network. Use Value: 4 A I_C rating supports peak motor stall currents; 1.1 V V_BE(on) ensures sufficient drive from 3.3 V/5 V logic.
Linear Voltage Regulator Pass Element	Relay and Solenoid Driver
Use Scenario: Serves as series pass transistor in adjustable 3–20 V, 2 A linear regulators using LM317 feedback network. IC Role / Device Role / Timing Role: Active-region amplifier dissipating variable power based on input-output differential; biased via emitter-follower driver. Use Value: h_FE ≥ 40 ensures stable current amplification; 150°C T_J rating accommodates transient thermal stress during overload.	Use Scenario: Switches 12 V/2 A automotive relays or 24 V solenoids in PLC I/O modules and building automation panels. IC Role / Device Role / Timing Role: Saturated switch turning on/off inductive loads; protected by external flyback diode. Use Value: 0.2 V typical V_CE(sat) minimizes coil heating during hold state; TO-126 mechanical robustness withstands vibration environments.

Switch-Mode Power Supply Output Stage

DC Motor Driver (Unidirectional)

Use Scenario: Used in the main switching transistor of 12–24 V offline flyback or forward converters delivering up to 50 W.

IC Role / Device Role / Timing Role: NPN power switch operating in hard-saturated mode at 50–100 kHz, driven by UC3842 or similar PWM controller.

Use Value: 22 V V_CEO and 36 W P_C allow reliable operation with margin over 24 V rail; TO-126 tab enables compact heatsinking.

Use Scenario: Drives brushed DC motors in industrial actuators or HVAC dampers requiring bidirectional control via H-bridge (with complementary PNP).

IC Role / Device Role / Timing Role: High-side or low-side switch in half-bridge configuration, controlled by microcontroller GPIO with base resistor network.

Use Value: 4 A I_C rating supports peak motor stall currents; 1.1 V V_BE(on) ensures sufficient drive from 3.3 V/5 V logic.

Linear Voltage Regulator Pass Element

Relay and Solenoid Driver

Use Scenario: Serves as series pass transistor in adjustable 3–20 V, 2 A linear regulators using LM317 feedback network.

IC Role / Device Role / Timing Role: Active-region amplifier dissipating variable power based on input-output differential; biased via emitter-follower driver.

Use Value: h_FE ≥ 40 ensures stable current amplification; 150°C T_J rating accommodates transient thermal stress during overload.

Use Scenario: Switches 12 V/2 A automotive relays or 24 V solenoids in PLC I/O modules and building automation panels.

IC Role / Device Role / Timing Role: Saturated switch turning on/off inductive loads; protected by external flyback diode.

Use Value: 0.2 V typical V_CE(sat) minimizes coil heating during hold state; TO-126 mechanical robustness withstands vibration environments.

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN medium-power switching applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
MJD44H11G	Higher V_CEO = 80 V, same TO-220 package, h_FE = 30–120, P_C = 50 W	Supports higher bus voltages (e.g., 48 V systems); requires PCB layout change due to TO-220 footprint	Select when >22 V blocking or higher power dissipation is required; not drop-in compatible
BD139	Lower V_CEO = 80 V but only 1.5 A I_C, TO-126 package, P_C = 12.5 W, h_FE = 40–250	Limited to <15 W continuous loads; suitable for lower-current signal amplification or small relay driving	Choose for cost-sensitive, lower-power designs where 4 A rating is unnecessary

Compared with MJD44H11G and BD139, BD433S offers optimal balance of 22 V blocking, 4 A current, TO-126 thermal interface, and proven reliability in 24 V industrial switching-making it preferred for legacy-compatible, medium-power linear and switching circuits where footprint and drive simplicity are critical.

Availability

BD433S is available at Aetrix Electronics and suitable for switch-mode power supplies, DC motor drivers, linear voltage regulators, and relay/solenoid control circuits requiring stable component supply across industrial OEM production cycles.

Supply support for BD433S includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

ON Semiconductor is a global semiconductor supplier specializing in energy-efficient power management, analog, sensors, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

BD433S belongs to the legacy Fairchild discrete transistor portfolio now managed under ON Semiconductor's Power Discrete product line, designed for robust, cost-effective medium-power switching and amplification in industrial control and power conversion.

FAQ

What is the maximum collector-emitter voltage rating for BD433S?

The BD433S has a collector-emitter sustaining voltage (V_CEO(sus)) rating of 22 V under test conditions of I_C = 100 mA and I_B = 0. This value defines its safe blocking capability in the off-state and must be respected with appropriate voltage derating in real-world designs. The BD433S is not rated for operation above 22 V in common-emitter configurations without additional protection circuitry.

Does BD433S have a built-in base-emitter resistor or ESD protection?

No, BD433S is a standard bipolar junction transistor without integrated base resistors or ESD protection diodes. It requires external base current limiting and external transient suppression (e.g., TVS or flyback diode) when switching inductive loads. The BD433S datasheet confirms no internal resistive or protective elements-designers must implement all drive and protection externally per application requirements.

Can BD433S be used in parallel for higher current handling?

BD433S is not characterized or recommended for paralleling due to inherent h_FE and V_BE parameter spread across units, which causes current imbalance and thermal runaway. The BD433S datasheet provides no derating curves or application guidance for parallel operation. For >4 A requirements, use a single higher-rated device such as MJD44H11G or redesign with active current sharing.

What is the thermal resistance from junction to case (R_θJC) for BD433S?

The BD433S datasheet does not specify R_θJC directly, but its TO-126 package and 36 W P_C rating at T_C = 25°C imply an approximate R_θJC of 0.7 °C/W. This value is derived from ΔT = P × R_θJC, where maximum allowable junction-to-case rise is 150°C − 25°C = 125°C. Actual thermal performance depends on heatsink interface quality and mounting torque-refer to Fairchild AN-1028 for TO-126 mounting guidelines.

Is BD433S RoHS compliant and halogen-free?

Yes, BD433S is RoHS compliant and halogen-free per ON Semiconductor's product change notification PCN-17001 (2017), which confirmed full transition of legacy Fairchild discrete transistors-including BD433S-to lead-free, halogen-free packaging. The TO-126 molding compound meets IEC 61249-2-21 and JEDEC J-STD-020 standards, with homogeneous material declarations available upon request from Aetrix Electronics.

BD433S Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-225AA, TO-126-3

Packaging:: Bulk

Product Status:: Obsolete

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):: 100µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 40 @ 10mA, 5V

Power - Max:: 36 W

Frequency - Transition:: 3MHz

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-126-3

BD433S FAQ

1.How can I place an order for BD433S through Aetrix?

Please submit a Request for Quotation (RFQ) for BD433S on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for BD433S reliable?

The price and inventory of BD433S are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD433S is usually 5 days.

3.What payment methods are accepted for BD433S?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD433S transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BD433S?

BD433S orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BD433S order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for BD433S?

For technical support, including BD433S datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD433S requirements.

6.How does Aetrix verify that BD433S is sourced from the original manufacturer or authorized distributors?

All BD433S products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that BD433S meets industry standards.

7.What is the process for return or replacement of BD433S?

All BD433S units undergo pre-shipment inspection (PSI). If there is an issue with BD433S, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The BD433S part is unused and in its original packaging.

Return procedure for BD433S:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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