MPSA18 Pinout: Complete Guide on How to Use It

What is the MPSA18?

The MPSA18 is a high-voltage, low-power NPN transistor designed for general-purpose amplification and switching applications. It is part of the MPSA series of transistors, which are known for their reliable performance and versatility. The MPSA18 is capable of handling collector-emitter voltages up to 180V and collector currents up to 500mA, making it suitable for a wide range of electronic projects.

MPSA18 Pinout Configuration

To effectively use the MPSA18 transistor, it is essential to understand its pinout configuration. The MPSA18 has three pins: the collector (C), base (B), and emitter (E). The pinout arrangement is as follows:

Pin Number	Pin Name	Description
1	Emitter	The emitter of the transistor
2	Base	The base of the transistor
3	Collector	The collector of the transistor

It is important to note that the MPSA18 has a TO-92 package, which is a common three-lead plastic package used for small-signal transistors. The TO-92 package has a rounded shape with leads arranged in a triangular pattern.

Electrical Characteristics of the MPSA18

To properly design circuits using the MPSA18, it is crucial to understand its electrical characteristics. The following table summarizes the key electrical parameters of the MPSA18 transistor:

Parameter	Symbol	Value
Collector-Emitter Voltage	VCEO	180V
Collector-Base Voltage	VCBO	180V
Emitter-Base Voltage	VEBO	6V
Collector Current	IC	500mA
Collector Dissipation	PC	625mW
DC Current Gain	hFE	50-800
Transition Frequency	fT	100MHz

These electrical characteristics provide a foundation for designing circuits that operate within the MPSA18’s specified limits, ensuring optimal performance and reliability.

MPSA18 as an Amplifier

One of the primary applications of the MPSA18 transistor is as an amplifier. In an amplifier circuit, the MPSA18 is used to increase the strength of a weak input signal, producing a larger output signal. The basic configuration for an MPSA18 amplifier is the common-emitter (CE) amplifier.

Common-Emitter Amplifier

In a common-emitter amplifier, the input signal is applied to the base of the MPSA18, while the output signal is taken from the collector. The emitter is connected to ground or a reference voltage. The following schematic shows a simple common-emitter amplifier using the MPSA18:

In this circuit, the input signal is coupled to the base of the MPSA18 through capacitor C₁. Resistor R₁ sets the base bias current, while resistor R₂ and capacitor C₂ form a voltage divider to provide the necessary base bias voltage. The amplified output signal appears across resistor R_C, which is connected between the collector and the positive power supply voltage (V_CC).

The gain of the common-emitter amplifier can be calculated using the following formula:

A_V = -R_C / R_E

Where:
– A_V is the voltage gain
– R_C is the collector resistor
– R_E is the emitter resistor

By selecting appropriate values for R_C and R_E, you can achieve the desired gain for your amplifier circuit.

MPSA18 as a Switch

Another common application of the MPSA18 transistor is as a switch. In a switching circuit, the MPSA18 is used to control the flow of current through a load, such as a relay, LED, or motor. When a sufficient base current is applied, the MPSA18 turns on, allowing current to flow through the load. When the base current is removed, the MPSA18 turns off, interrupting the current flow.

Simple Switching Circuit

The following schematic shows a simple switching circuit using the MPSA18 transistor:

In this circuit, the MPSA18 is used to control the current flow through an LED. When a sufficient voltage is applied to the base of the MPSA18 through resistor R₁, the transistor turns on, allowing current to flow from the collector to the emitter and through the LED, causing it to illuminate. Resistor R₂ limits the current flowing through the LED to prevent damage.

The base current required to turn on the MPSA18 can be calculated using the following formula:

I_B = (V_CC – V_BE) / R₁

Where:
– I_B is the base current
– V_CC is the supply voltage
– V_BE is the base-emitter voltage drop (typically 0.7V)
– R₁ is the base resistor

By selecting an appropriate value for R₁, you can ensure that sufficient base current is provided to turn on the MPSA18 and control the load.

MPSA18 in Darlington Configuration

The MPSA18 can also be used in a Darlington configuration, which combines two transistors to achieve high current gain. In a Darlington pair, the emitter of one transistor is connected to the base of another transistor, effectively multiplying their individual current gains. This configuration is useful when driving loads that require high currents, such as motors or high-power LEDs.

Darlington Pair Circuit

The following schematic shows an MPSA18 Darlington pair circuit:

In this circuit, two MPSA18 transistors (Q₁ and Q₂) are connected in a Darlington configuration. The emitter of Q₁ is connected to the base of Q₂, and the collectors of both transistors are tied together. Resistor R₁ limits the base current for Q₁, while resistor R₂ ensures proper turn-off of the Darlington pair.

The total current gain of the Darlington pair can be calculated using the following formula:

β_total = β₁ × β₂

Where:
– β_total is the total current gain of the Darlington pair
– β₁ is the current gain of the first transistor (Q₁)
– β₂ is the current gain of the second transistor (Q₂)

By using the MPSA18 in a Darlington configuration, you can achieve extremely high current gains, making it possible to drive loads with high current requirements.

MPSA18 in Voltage Regulation

The MPSA18 can also be used in voltage regulation circuits to maintain a stable output voltage despite variations in the input voltage or load current. One common voltage regulation circuit using the MPSA18 is the series voltage regulator.

Series Voltage Regulator

The following schematic shows a series voltage regulator using the MPSA18 transistor:

In this circuit, the MPSA18 is used as a pass transistor to control the voltage across the load (R_L). The base of the MPSA18 is connected to a voltage divider formed by resistors R₁ and R₂, which sets the output voltage. The Zener diode (D₁) provides a stable reference voltage for the voltage divider.

The output voltage of the series voltage regulator can be calculated using the following formula:

V_out = V_Z × (1 + R₁ / R₂)

Where:
– V_out is the regulated output voltage
– V_Z is the Zener voltage of D₁
– R₁ and R₂ are the voltage divider resistors

By selecting appropriate values for R₁, R₂, and D₁, you can design a series voltage regulator that provides a stable output voltage for your specific application.

MPSA18 in Audio Circuits

The MPSA18 transistor is also commonly used in audio circuits, such as preamplifiers and power amplifiers. Its high voltage capability and good frequency response make it suitable for audio applications.

Simple Preamplifier Circuit

The following schematic shows a simple preamplifier circuit using the MPSA18 transistor:

In this circuit, the MPSA18 is used as a common-emitter amplifier to amplify the input audio signal. Capacitor C₁ couples the input signal to the base of the MPSA18, while capacitor C₂ couples the amplified output signal to the next stage. Resistors R₁ and R₂ set the bias point for the transistor, and resistor R_E provides emitter degeneration, which helps to stabilize the circuit and improve linearity.

The gain of the preamplifier can be adjusted by changing the values of R_C and R_E. Increasing the value of R_C or decreasing the value of R_E will result in higher gain, while decreasing R_C or increasing R_E will result in lower gain.

Frequently Asked Questions (FAQ)

1. What is the maximum collector-emitter voltage rating of the MPSA18 transistor?

2. The MPSA18 has a maximum collector-emitter voltage rating of 180V.

3. What is the typical current gain (h_FE) range for the MPSA18?

4. The typical current gain range for the MPSA18 is 50-800.

5. Can the MPSA18 be used as a switch?

6. Yes, the MPSA18 can be used as a switch to control the flow of current through a load, such as a relay, LED, or motor.

7. How can I increase the current gain when using the MPSA18?

8. To increase the current gain, you can use the MPSA18 in a Darlington configuration, which combines two transistors to multiply their individual current gains.

9. Is the MPSA18 suitable for audio applications?

10. Yes, the MPSA18 is suitable for audio applications due to its high voltage capability and good frequency response. It can be used in preamplifier and power amplifier circuits.

Conclusion

The MPSA18 transistor is a versatile and widely used NPN bipolar junction transistor that finds applications in amplification, switching, voltage regulation, and audio circuits. By understanding the MPSA18 pinout and its electrical characteristics, you can effectively integrate this transistor into your electronic projects.

This comprehensive guide has covered the basics of the MPSA18, including its pinout configuration, electrical parameters, and various circuit applications. We have explored common-emitter amplifiers, switching circuits, Darlington configurations, voltage regulators, and audio preamplifiers using the MPSA18.

By following the examples and explanations provided in this guide, you should now have a solid foundation for using the MPSA18 transistor in your own projects. Remember to always consider the specific requirements of your application and design your circuits accordingly.

As with any electronic component, it is essential to handle the MPSA18 with care and operate it within its specified limits to ensure optimal performance and longevity. Always refer to the manufacturer’s datasheet for the most up-to-date and accurate information regarding the MPSA18’s characteristics and usage guidelines.

We hope this guide has been informative and helpful in your journey to understand and utilize the MPSA18 transistor. Happy designing and building your electronic projects!