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BDX33 Darlington Power Transistor Data

Highlight data for the BDX33 NPN Darlington transistor which includes electrical parameters, pinout, package type and many other key transistor datasheet details

The BDX33B and BDX33C are silicon epitaxial-base NPN power transistors in monolithic Darlington configuration mounted in a JEDEC TO-220 plastic package.

They are intended for use in power linear and switching applications and have a maximum dissipation of 70W.

The complementary PNP devices are the BDX34B and BDX34C types which enable the design of complementary power output stages.

Key details and performance parameters for the BDX33 NPN Darlington transistor.

BDX34 transistor datasheet parameters & data
Parameters	Details
Transistor type	70W Darlington NPN
Package type	TO220
V_CBO max (V)	80*
V_CEO max (V)	80*
V_CEsat (V)	2,5V @ I 3 A
I_C max (A)	10
Peak current I_CM max (A)	15
Base current I_B max (A)	0.25
T_J Max °C	150
P_TOT mW	70
DC current gain h_FE	750 min @ 3V
h_fe	100 @ I_C 1A & f = 1MHz
Similar / equivalents

Outline:

Pinout:

Explanation of transistor parameters

Parameter	Explanation
V_CBO Max	Maximum collector-base voltage with emitter open circuit .
V_CEO Max	Maximum collector-emitter voltage with base open circuit.
V_EBO Max	Maximum emitter-base voltage with collector open circuit.
V_CEsat (included where applicable)	The voltage drop across the collector-emitter when the transistor is fully saturated (acting as a closed switch).
I_C Max	Maximum collector current.

Parameter	Explanation
T_J	Maximum junction temperature.
P_TOT Max	Maximum device dissipation normally in free air at 25°C unless other conditions indicated.
f_T Min	Minimum cutoff frequency at which the current gain in a common emitter circuit falls to unity.
C_OB Max	Maximum collector capacitane, normally measured with emitter open circuit.
h_FE	DC current gain for H_FE at I_C. [Note hfe is the small signal gain and although this may be slightly different, the transistor current gain will vary considerably from ne transistor to the next of the same type.]
P_TOT Max	Maximum device dissipation normally in free air at 25°C unless other conditions indicated.

These are the main transistor parameters that have been included in our list. There are others, but these help quantify the main elements of the performance of the transistor.

Read more about . . . . Transistor Data-sheet Specifications & Parameters.

Please note, that the data given is the best estimate we can give within a tabulated summary of this nature. Parameters also vary between manufacturers. Electronics Notes cannot accept any responsibility for errors, inaccuracies, etc, although we do endevaour to ensure the data is as accurate as possible.

Notes and supplementary information

• Availability & sources

The BDX33 is available from a number of stockists and electronic component distributors many of which are given in the table below.

BDX33 Component Distributor, Stock and Pricing

• Further information

Note * There are two versions of the BDX33: the BDX33B which has a V_CBO and V_CEO max of 80V and the BDX33C which has maximum voltages of 100V.

• Internal schematic

When designing with a BDX34, it is very useful to know and understand the internal schematic. The resistors R1 and R2 provide improved switchinga and frequency response and the diode helps provide protection.

The internal schematic provides insight into the operation of the device.

• Notable features

The BDX33 series is an NPN epitaxial silicon power transistor that utilizes the Darlington configuration, making it exceptionally sensitive to small base currents.

Darlington Monolithic Configuration: The device integrates two NPN transistors and two resistors on a single chip, effectively cascading the gain of both transistors (hFE typically 750 minimum at IC=3 A). This allows a tiny base current to control a very large collector current.
High Current and Power Handling: It can handle a continuous collector current (IC) of up to 10 A (with a peak of 15 A) and has a total power dissipation (Ptot) of up to 70 W at a case temperature of 25∘C. This makes it suitable for driving high-power loads.
Integrated Protection Diode: The monolithic structure includes an integrated reverse-biased parallel diode (sometimes called a freewheeling or flyback diode) between the collector and emitter. This diode provides protection against voltage spikes when switching inductive loads like motors and relays.
High Voltage Rating Options: The BDX33 series is available in several variants, such as the BDX33B (80 V VCEO) and the BDX33C (100 V VCEO), offering flexibility for different power supply voltage levels.
Complementary Pair Available: It has complementary PNP counterparts, the BDX34B and BDX34C, which simplifies the design of push-pull or complementary-symmetry power output stages (e.g., in Class B amplifiers).

• Typical applications summary

Application Category	Typical Use Case	Device Feature Utilised
High-Power Switching	Driving high-current DC motors, large solenoids, and high-power relays.	The 10 A collector current capability and 70 W power dissipation (with heatsink) allow it to safely control significant power loads. The built-in protection diode handles inductive kickback.
Power Amplification	Audio amplifier output stages (often in complementary pairs with the BDX34), general-purpose linear power supplies.	The high DC current gain (hFE≥750) enables high input sensitivity, making it efficient for use in linear power applications, and the complementary PNP pair simplifies design.
Industrial Control Interfaces	Interfacing low-power microcontrollers or logic circuits to high-current external peripherals.	The Darlington configuration's ultra-high gain ensures that the small current provided by a logic pin (a few mA or less) is sufficient to fully drive the transistor and switch the 10 A output.
Power Regulation and Control	Pass element in series voltage regulators and current limiting circuits.	The 70 W power capability and TO-220 package (designed for heatsinking) make it robust for handling the heat generated when regulating current or voltage in series pass applications.