2N3906 PNP Transistor Pin Diagram, Circuit, Equivalent & Datasheet

The 2N3906 is a commonly used PNP bipolar junction transistor (BJT) that plays a crucial role in electronic circuits. It is a popular choice among circuit designers, hobbyists, and makers for various electronics projects. Motorola Semiconductor introduced the 2N3906, along with its NPN counterpart, the 2N3904, in the 1960s. It is part of the 2N390x series of transistors, which are widely used due to their affordability and versatility. In this article, we'll delve into the 2N3906 pin diagram, circuit, features, where & how to use it and more details.

What is 2N3906?

The 2N3906 is a PNP transistor, meaning the collector and emitter are closed (forward biased) when the base pin is grounded, and they open (reverse biased) when a signal is applied to the base pin. This distinction is where a PNP transistor differs from an NPN transistor; a logic state (blue color) is utilized to switch between Ground and Signal Voltage (Emitter-Base Voltage VBE).

With a gain value ranging from 110 to 300, the 2N3906's amplification capacity is determined. The maximum current that can flow through the Collector pin is 200mA, making it unsuitable for loads consuming more than 200mA. To bias the transistor, current must be supplied to the base pin, limited to 5mA (IB). When fully biased, the transistor allows a maximum of 200mA to flow across the collector and emitter, entering the Saturation Region. The typical voltage allowed across the Collector-Emitter (V­CE) or Base-Emitter (VBE) is approximately 40V and 5V, respectively. When the base current is removed, the transistor enters the Cut-off Region, with the Base Emitter voltage around 5V.

This device is designed for general-purpose amplifier and switching applications with collector currents ranging from 10 mA to 100 mA.

2N3906 Pin Diagram

The 2N3906 is a PNP (Positive-Negative-Positive) transistor, meaning current flows from the emitter to the collector. It features three pins: emitter, base, and collector, each used for different configurations. The transistor operates within a voltage range of -40V DC. The pinout configuration and schematic symbol are illustrated in the following figure.

Features of 2N3906

• Type: Bipolar PNP transistor

• Maximum Collector-Emitter Voltage: 40V

• Maximum Emitter-Base Voltage: 5V

• Maximum Collector-Base Voltage: 40V

• Continuous Collector Current: 200mA

• Operating Temperature Range: -55 to 150°C

• Minimum Forward Current Transfer Ratio: 100

• Transition Frequency: 250MHz

• Maximum Collector Current: 200mA

• Collector Capacitance: 5pF

• Maximum Power Dissipation: 250mW

• Storage Temperature Range: -55 to 150°C

• Collector-Emitter Saturation Voltage: 0.25V

• DC Current Gain: 60

• Maximum DC Current Gain (hFE): 300

• Maximum Base Current (IB): 5mA

• Package: TO-92

Specifications

2N3906 Equivalents/Alternatives

Here is a list of popular transistors that can serve as replacements for the 2N3906:

BC557, BC527, BC558, BC559, 2N2907, BC556, A1015, C945, 2N4403, 9014, MPSA13, MPSA92, MPSA55, and ZTX555.

2N3906 CAD Model

Characteristics curves of 2N3906

common emitter static characteristics of the 2N3906 transistor

The graph illustrates the common emitter static characteristics of the 2N3906 transistor, plotting collector current against collector-to-emitter voltage.

For each base current value, the curve initially appears flat, but then sharply rises as the collector-to-emitter voltage increases.

current gain characteristics of the 2N3906 transistor

The graph displays the current gain characteristics of the 2N3906 transistor, plotting DC current gain against collector current.

For constant voltage values, the DC current gain initially starts at a higher value, then decreases to a lower value as the collector current increases.

How does a 2N3906 transistor work?

The transistor does not conduct unless a bias voltage is applied to its base, allowing holes in the emitter to move towards the base. A PNP transistor is essentially two diodes connected back to back, with two PN junctions: the emitter-base junction and the collector-base junction. The emitter-base junction is forward biased, responsible for transistor conduction, and has a small resistance.

Here's how the 2N3906 operates:

• When the base pin is grounded, the collector and emitter are closed, or forward biased.

• When a signal is applied to the base pin, the collector and emitter are open, or reverse biased.

• With a small amount of light on the LDR, the transistor's base is biased, allowing negative current flow to the base.

• Pressing switch one turns on the MOSFET gate, bringing the base of the 2N3906 low. This allows current to flow from the emitter to the collector, and then to the gate of the FET, latching it on.

How Does 2N3906 Work in the PNP Circuit?

Here is a circuit for using a PNP transistor, such as the 2N3906, as a switch or amplifier.

The emitter of the transistor is connected to +3V. The base of the transistor is connected to a normally open pushbutton. When the pushbutton is not pressed, no current flows into the base of the transistor, so it is fully on. As a result, the LED connected to the collector of the PNP transistor will be on. However, when the push button is pressed, the transistor turns off, and the LED shuts off. This happens because the base voltage becomes greater than the emitter voltage, blocking current flow.

This is the basic operation of a PNP transistor circuit.

Where and How to Use 2N3906

Where to Use 2N3906

The 2N3906 is a widely used PNP transistor, similar to the BC557 but with a higher collector-to-emitter voltage rating, making it suitable for toggling high voltage loads. However, with a gain value of only 300, it is not ideal for amplifier circuits.

If you need a PNP transistor to switch high voltage loads up to 0.2A, the 2N3906 might be the right choice.

How to Use 2N3906

The 2N3906 is typically used as a switching device. In the saturation region, it is fully conductive, while in the cut-off region, it does not conduct at all. By default, a PNP transistor like the 2N3906 is in the ON state, but it is not considered fully ON until the base pin is grounded. Applying ground to the base pin reverse biases the transistor, turning it ON. Providing a supply to the base pin stops current flow between the emitter and collector, turning it OFF.

To protect the transistor, a resistor is added in series with it. The value of this resistor (RB) can be calculated using the formula:

RB = VBE / IB

For the 2N3906, the value of VBE is 5V, and the maximum base current (IB) is 200mA. Therefore, the value of the resistor can be calculated based on these values. In the circuit below, when the base emitter voltage (VBE) is 0V (Grounded), the PNP transistor conducts and the motor rotates. If the voltage is made high (5V), the motor stops rotating. It's important to connect the loads to the collector side for PNP transistors, and ensure that the load current is less than 200mA (here 140mA).

2N3906 Schematic

Example as a switch

According to the figure above, when the switch is closed, both LEDs will be on, indicating that both junctions are forward biased and current flows from the emitter to the collector, causing the LEDs to glow brightly. Conversely, when the switch is open, both junctions will be reversed biased, and no current will flow from the emitter to the collector, resulting in the LEDs being off. A 10kΩ resistor is connected in series with the base to limit the base current.

2N3906 Applications

• Suitable for TV and home appliance equipment.

• Small load switch transistor with high gain and low saturation voltage.

• Used to switch high voltage low current loads.

• Optimal for loads with high peak voltage up to 40V.

• Various switching applications.

• High-frequency inverter and converter circuits.

• Making sirens or dual LED or lamp flashers.

• Can be used in Darlington pairs.

• General-purpose audio amplifiers.

2N3906 Circuit

Delay and Rise Time Test Circuit

Total shunt capacitance of test jig and connectors

Storage and Fall Time Equivalent Test Circuit

Total shunt capacitance of test jig and connectors

2N3906 Package

2N3906 Projects

Low light Detector using 23906 with LDR

This circuit operates by detecting low light levels, activating the LED connected between the collector and ground. When the surrounding light is dim, emitter current travels from the emitter to the collector, illuminating the LED along its path.

In the provided circuit diagram, a 2N3906 transistor functions as a switch to control the LED, depending on the ambient light. The entire circuit runs on a 9V power supply.

A 5.6 K Ohm resistor is placed between the load (LED) and ground to safeguard the LED from excessive current. Determining the appropriate resistor value is straightforward using Ohm’s law.

When light intensity on the LDR is high (resulting in low resistance), the transistor base remains unbiased, and no negative current flows to the base. Consequently, the 2N3906 transistor remains in a cut-off state, and the LED remains unlit.

In contrast, when there is low light on the LDR (high resistance), the transistor base becomes biased, allowing negative current to flow to the base. This biasing current drives the 2N3906 into saturation, causing the LED to illuminate.

2N3906 Datasheet 

Download 2N3906 Datasheet PDF.

2N3906 vs. 2N2222 vs. 2N3904

Final Words

The 2N3906 PNP transistor is a versatile and reliable component that is widely used in electronic circuits. Its low cost, high reliability, and ease of use make it a popular choice among hobbyists and professionals alike. With high gain and low noise characteristics, it is well-suited for various applications, including switching and amplification. By understanding how to properly use and maintain the 2N3906 transistor, you can ensure that your circuits perform reliably and efficiently.

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