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

onsemi BDX33B

Name: BDX33B
Brand: onsemi
SKU: BDX33B
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BDX33B

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: BDX33B.pdf

Description:: TRANS NPN DARL 80V 10A TO-220

Quantity:: RFQ Add To RFQ list

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Inventory:7,695

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Product details

Overview

BDX33B from onsemi is an NPN silicon Darlington power transistor in TO-220 package, rated for 80 V_CEO(sus), 10 A continuous collector current, and 70 W dissipation at T_C = 25°C, with typical h_FE = 2500 at I_C = 4.0 A - used in low-speed switching power supplies and motor control circuits.

For engineers reviewing the BDX33B datasheet, pinout, applications, or equivalent options, this page delivers verified electrical parameters, thermal derating behavior, safe operating area limits, and validated alternative parts for industrial linear and switching designs.

Technical Context

The BDX33B is a monolithic NPN Darlington pair with built-in base-emitter shunt resistors, optimized for general-purpose linear amplification and low-speed switching. It features V_CE(sat) ≤ 2.5 V at I_C = 3.0 A / I_B = 6.0 mA and V_BE(on) ≤ 2.5 V under same conditions.

Its thermal resistance R_JC is 1.78°C/W, enabling stable operation up to +150°C junction temperature. Safe operating area (SOA) is limited by second breakdown at high V_CE/low I_C, and thermally at high I_C/low V_CE, with pulse-width-dependent derating per Figure 2.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO(sus)	80 V min - sustains 80 V collector-emitter voltage at 100 mA with zero base drive, defining maximum off-state blocking capability
I_C (continuous)	10 A - supports sustained load currents up to 10 A with heatsink at T_C = 25°C
P_D @ T_C = 25°C	70 W - maximum steady-state power dissipation before thermal derating begins
h_FE (typ)	2500 at I_C = 4.0 A - enables low-base-drive switching in high-current applications like relay drivers
V_CE(sat) (max)	2.5 V at I_C = 3.0 A / I_B = 6.0 mA - determines conduction loss and heat generation in saturated switch mode
R_JC	1.78 °C/W - defines thermal path efficiency from junction to case, critical for heatsink sizing

Pinout & Package

BDX33B uses the TO-220-3 (Case 221A, Style 1) package with 3 leads: Pin 1 = Base, Pin 2 = Collector, Pin 3 = Emitter. The metal tab is electrically connected to the collector and serves as the primary thermal interface.

Pin/Terminal	Circuit Role	Design Meaning
1 (Base)	Control input	Receives low-current drive signal to enable high-current conduction between collector and emitter
2 (Collector)	High-current output (input side)	Connected to load supply rail; metal tab is electrically tied to this pin for thermal and electrical integration
3 (Emitter)	High-current return path	Sinks full load current to ground or low-side reference; requires low-impedance PCB trace or busbar

Key Features

Feature	Design Value
Monolithic Darlington construction	Integrates driver and output transistors on one die, eliminating external biasing components and improving gain consistency
Integrated base-emitter shunt resistor	Ensures reliable turn-off by bleeding residual base charge, preventing latch-up in inductive loads
Pb-free RoHS-compliant packaging	Meets global environmental compliance requirements without compromising thermal or mechanical performance
Second-breakdown-limited SOA	Enables robust pulsed operation up to 100 V × 10 A within defined pulse width/duty cycle constraints

Applications

Industrial Motor Control	DC Power Supply Regulation
Use Scenario: Driving 24 V DC brushed motors in conveyor systems requiring 5–8 A peak current and slow PWM switching. IC Role / Device Role / Timing Role: NPN Darlington switch controlling motor H-bridge low-side leg with flyback diode protection. Use Value: High h_FE reduces microcontroller GPIO drive burden; V_CE(sat) ≤ 2.5 V minimizes conduction loss at 6 A.	Use Scenario: Linear pass transistor in adjustable 0–30 V, 0–5 A bench power supply with analog feedback loop. IC Role / Device Role / Timing Role: Series-pass regulator element dissipating up to 45 W during 15 V/3 A operation. Use Value: 70 W rating and 1.78 °C/W R_JC allow stable regulation with standard TO-220 heatsink and forced air.
Relay and Solenoid Driver	Low-Speed AC Phase Control
Use Scenario: Replacing mechanical relays in HVAC control panels driving 24 V/2 A solenoid valves. IC Role / Device Role / Timing Role: Single-ended switch interfacing microcontroller outputs to inductive loads with snubber network. Use Value: Built-in base-emitter shunt resistor prevents false turn-on from leakage; 80 V rating accommodates 2× supply transients.	Use Scenario: Half-wave phase-controlled dimmer for 120 V AC resistive heating elements in industrial ovens. IC Role / Device Role / Timing Role: Low-frequency switching element triggered by zero-crossing synchronized gate pulse. Use Value: Sustaining voltage margin (80 V) exceeds peak AC line (170 V) only when used with series impedance - not suitable for direct AC line switching.

Industrial Motor Control

DC Power Supply Regulation

Use Scenario: Driving 24 V DC brushed motors in conveyor systems requiring 5–8 A peak current and slow PWM switching.

IC Role / Device Role / Timing Role: NPN Darlington switch controlling motor H-bridge low-side leg with flyback diode protection.

Use Value: High h_FE reduces microcontroller GPIO drive burden; V_CE(sat) ≤ 2.5 V minimizes conduction loss at 6 A.

Use Scenario: Linear pass transistor in adjustable 0–30 V, 0–5 A bench power supply with analog feedback loop.

IC Role / Device Role / Timing Role: Series-pass regulator element dissipating up to 45 W during 15 V/3 A operation.

Use Value: 70 W rating and 1.78 °C/W R_JC allow stable regulation with standard TO-220 heatsink and forced air.

Relay and Solenoid Driver

Low-Speed AC Phase Control

Use Scenario: Replacing mechanical relays in HVAC control panels driving 24 V/2 A solenoid valves.

IC Role / Device Role / Timing Role: Single-ended switch interfacing microcontroller outputs to inductive loads with snubber network.

Use Value: Built-in base-emitter shunt resistor prevents false turn-on from leakage; 80 V rating accommodates 2× supply transients.

Use Scenario: Half-wave phase-controlled dimmer for 120 V AC resistive heating elements in industrial ovens.

IC Role / Device Role / Timing Role: Low-frequency switching element triggered by zero-crossing synchronized gate pulse.

Use Value: Sustaining voltage margin (80 V) exceeds peak AC line (170 V) only when used with series impedance - not suitable for direct AC line switching.

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN Darlington power transistor applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BDX33C	Higher V_CEO(sus) = 100 V min; otherwise identical pinout, package, and gain specs	Supports higher bus voltages (e.g., 48 V industrial systems); same thermal and switching behavior	Select BDX33C when operating above 60 V DC to ensure margin against transients
TIP142	Same TO-220 package, but h_FE = 1000 (min) at I_C = 3 A; V_CE(sat) = 2.0 V (max) at same condition	Lower gain requires higher base drive; slightly lower saturation voltage improves efficiency at mid-current	Choose TIP142 where base drive capability exceeds 15 mA and thermal budget is tighter than 70 W

Compared with BDX33C and TIP142, the BDX33B offers optimal balance of ultra-high gain (2500 typ), 80 V blocking, and proven reliability in legacy industrial controls - making it preferred where minimal base current and long-term field stability are prioritized over voltage headroom or marginal V_CE(sat) reduction.

Availability

BDX33B is available at Aetrix Electronics and suitable for industrial motor control, linear power regulation, and relay replacement applications requiring stable component supply and long-lifecycle support.

Supply support for BDX33B 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power, analog, sensing, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The BDX33B belongs to onsemi's legacy silicon power transistor family designed for rugged, cost-effective linear and switching applications in industrial automation and power conversion equipment.

FAQ

What is the maximum continuous collector current rating for BDX33B?

The BDX33B is rated for 10 A continuous collector current (I_C) at case temperature T_C = 25°C. Derating is required above 25°C at 0.56 W/°C, and actual usable current depends on heatsink performance and ambient conditions. At T_C = 75°C, maximum I_C drops to approximately 6.2 A based on its 70 W power limit and thermal resistance.

Does BDX33B have built-in protection features?

Yes, the BDX33B integrates a base-emitter shunt resistor to ensure reliable turn-off and prevent unintended conduction from leakage currents. It does not include thermal shutdown, overcurrent limiting, or avalanche ruggedness beyond its specified V_CEO(sus) = 80 V rating. External flyback diodes and base current limiting remain necessary for inductive loads.

Is BDX33B suitable for switching 120 V AC loads directly?

No, the BDX33B is not suitable for direct 120 V AC line switching. Its 80 V V_CEO(sus) rating is insufficient for the 170 V peak of 120 V AC. It may be used in low-voltage DC control stages (e.g., driving opto-triacs or MOSFET gates) but must never be placed across AC mains without additional voltage-limiting circuitry.

What is the thermal resistance junction-to-case (R_JC) for BDX33B?

The BDX33B has a thermal resistance of R_JC = 1.78°C/W, measured from junction to case surface. This value assumes proper mounting with thermal compound and adequate mechanical clamping pressure on the TO-220 tab. Effective heatsink design must account for additional R_CS (case-to-sink) and R_SA (sink-to-ambient) to maintain T_J ≤ 150°C.

Can BDX33B replace BDX33C in existing designs?

BDX33B can replace BDX33C only if the application operates below 80 V DC and does not require the extra 20 V margin of the BDX33C. Both share identical pinout, package, gain, and saturation characteristics. However, substituting BDX33B into a BDX33C design risks failure under transient overvoltage conditions exceeding 80 V, so validation of worst-case bus voltage is mandatory before substitution.

BDX33B Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-220-3

Packaging:: Tube

Product Status:: Obsolete

Transistor Type:: NPN - Darlington

Current - Collector (Ic) (Max):: 10 A

Voltage - Collector Emitter Breakdown (Max):: 80 V

Vce Saturation (Max) @ Ib, Ic:: 2.5V @ 6mA, 3A

Current - Collector Cutoff (Max):: 500µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 750 @ 3A, 3V

Power - Max:: 70 W

Frequency - Transition:: -

Operating Temperature:: -65°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220

BDX33B FAQ

1.How can I place an order for BDX33B through Aetrix?

Please submit a Request for Quotation (RFQ) for BDX33B 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 BDX33B reliable?

The price and inventory of BDX33B are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BDX33B is usually 5 days.

3.What payment methods are accepted for BDX33B?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BDX33B transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BDX33B?

BDX33B orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BDX33B 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 BDX33B?

For technical support, including BDX33B datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BDX33B requirements.

6.How does Aetrix verify that BDX33B is sourced from the original manufacturer or authorized distributors?

All BDX33B 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 BDX33B meets industry standards.

7.What is the process for return or replacement of BDX33B?

All BDX33B units undergo pre-shipment inspection (PSI). If there is an issue with BDX33B, 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 BDX33B part is unused and in its original packaging.

Return procedure for BDX33B:

1.Submit a request within 90 days.

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

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