Adjustable Bipolar Voltage Regulator Circuit

Introduction

In the world of electronics, voltage regulators are indispensable components that are used to stabilize the voltage output in various electronic devices. One popular type of voltage regulator circuit is the adjustable bipolar voltage regulator circuit. This circuit utilizes the LM317 and LM337 integrated circuits (ICs) to provide a precise and adjustable output voltage. In this article, we will delve into the working principle of the adjustable bipolar voltage regulator circuit using LM317 and LM337 ICs. We will also discuss the specifications of these ICs separately, highlighting their key features and benefits.

In the following circuit diagram, there is a straightforward circuit that can provide a range of ± 1.2 V to ± 20 V as output. To achieve this, two ICs, namely LM317K and LM337K, are used as the positive and negative voltage regulators, respectively. These ICs come with built-in features such as current limit and power dissipation limit. For the TO-220 package, the maximum dissipation is 15 watts, while for the TO-3 package, it is 20 watts. To ensure proper heat dissipation, it is necessary to mount these ICs on heat sinks capable of efficiently dissipating heat.

Circuit Diagram of Adjustable Bipolar Voltage Regulator

This project can be designed using a few basic components. The circuit diagram of this project is shown below.

**Adjustable Bipolar Voltage Regulator Circuit Diagram**

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Components List of Adjustable Bipolar Voltage Regulator

Following is the list of all components used in this project:

Working Explanation of Adjustable Bipolar Voltage Regulator

The output voltages can be independently adjusted using VR1 and VR2. Additionally, capacitors C5 and C6 are incorporated into the circuit to improve the rejection of a.c. ripple voltage. In the event of a short circuit across the regulator output, C5 comes into play by adjusting the currents in the terminal. If you want to calculate the output, you can use a formula specific to this circuit.

Vout = 1.25 V (1+VR1/R1)

Overview of Major Components:

LM317 IC Specifications:

The LM317 is a positive voltage regulator IC that is commonly used in many applications due to its high reliability and stability. Let’s take a look at its key specifications:

Output Voltage Range: The LM317 IC is capable of providing an adjustable output voltage ranging from 1.25 volts to 37 volts. This flexibility makes it suitable for a wide variety of applications.
Output Current: This IC can deliver a maximum output current of up to 1.5 amperes. It is important to note that for higher output currents, an appropriate heat sink should be utilized to prevent overheating.
Line Regulation: The line regulation of the LM317 IC refers to its ability to maintain a steady output voltage despite changes in the input voltage. It has a typical line regulation value of 0.01% per input volt variation.
Load Regulation: Load regulation is a measure of how well the IC responds to changes in the load current. The LM317 exhibits a typical load regulation value of 0.1% for a 10 mA to 1.5 A current range.
Thermal Regulation: This specification indicates the ability of the LM317 to handle changes in temperature without affecting its output voltage. The typical thermal regulation for this IC is 0.02% per degree Celsius.
Ripple Rejection: The LM317 has a high ripple rejection ratio, with a typical value of 80 dB at 120 Hz. This ensures that any unwanted ripple or noise in the input voltage is minimized in the output voltage.

LM337 IC Specifications:

Similar to the LM317, the LM337 is a negative voltage regulator IC that complements the adjustable bipolar voltage regulator circuit. Let’s explore its key specifications:

Output Voltage Range: The LM337 IC also provides an adjustable output voltage, but in the negative polarity. It can deliver an output voltage ranging from -1.25 volts to -37 volts.
Output Current: The LM337 can safely deliver a maximum output current of 1.5 amperes. As with the LM317, it is crucial to use a heat sink for higher output currents.
Line Regulation: The line regulation of the LM337 IC is similar to that of the LM317, with a typical value of 0.01% per input volt variation.
Load Regulation: The LM337 exhibits a typical load regulation value of 0.3% for a 10 mA to 1.5 A current range. This indicates its ability to maintain a stable output voltage with varying loads.
Thermal Regulation: The thermal regulation of the LM337 is also similar to the LM317, with a typical value of 0.02% per degree Celsius.
Ripple Rejection: The LM337 IC boasts a high ripple rejection ratio, with a typical value of 77 dB at 120 Hz. This ensures efficient filtering of unwanted noise from the input voltage.

Adjustable Bipolar Voltage Regulator Circuit using LM317, LM337 ICs:

Now that we have a good understanding of the specifications of the LM317 and LM337 ICs, let’s examine how they can be used to create an adjustable bipolar voltage regulator circuit.

The circuit diagram for the adjustable bipolar voltage regulator is quite straightforward. It consists of the following components:

LM317 IC: The LM317 IC is connected in the positive voltage regulator configuration. The adjust pin (ADJ) is connected to the resistive voltage divider network, consisting of two resistors (R1 and R2). This allows for precise adjustment of the output voltage within the desired range.
LM337 IC: The LM337 IC is connected in the negative voltage regulator configuration. The adjust pin (ADJ) is also connected to a resistive voltage divider network, similar to the LM317 IC.
Input and Output Capacitors: To enhance the stability and filtering capabilities of the circuit, input and output capacitors are connected across the input and output terminals of both ICs. These capacitors help in reducing noise, improving voltage regulation, and preventing oscillations.
Potentiometer: A potentiometer is connected to the voltage divider network of the LM317 IC. This allows for adjusting the output voltage with ease, providing flexibility in various applications.

Conclusion of Adjustable Bipolar Voltage Regulator

In conclusion, the adjustable bipolar voltage regulator circuit diagram is an efficient and versatile solution for voltage regulation in various electronic applications. This circuit design incorporates the LM317 positive voltage regulator and the LM337 negative voltage regulator, allowing for adjustable positive and negative output voltages. The use of these ICs ensures stability, accuracy, and low dropout voltage, making it suitable for a wide range of power supply requirements.

The LM317 and LM337 ICs are highly reliable and widely available in the market, making them popular choices for voltage regulation circuits. These ICs can handle high current and have built-in thermal overload protection, ensuring safe operation even under demanding conditions. Additionally, they can tolerate a wide input voltage range, making them suitable for both AC and DC power sources.

The adjustable voltage range of this circuit is achieved by properly selecting the resistor values connected to the adjust pin of the ICs. By adjusting the values of these resistors, precise and stable positive and negative voltage outputs can be obtained. Furthermore, the use of high-quality capacitors helps to minimize noise and ripple, ensuring a clean and stable power supply for sensitive electronic components.

The flexibility and effectiveness of this adjustable bipolar voltage regulator circuit make it ideal for a variety of applications, including audio equipment, power supply modules, battery charging circuits, and motor control systems.

Overall, the LM317 and LM337 adjustable bipolar voltage regulator circuit provides a reliable and efficient solution for voltage regulation needs, offering stability, accuracy, and versatility in power supply applications.

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