LM723 Project: A Comprehensive Guide

Oct 22, 2025 by Jhon Lennon 37 views

Hey guys! Today, we're diving deep into the fascinating world of the LM723 voltage regulator. If you're an electronics enthusiast, a hobbyist, or an engineering student, chances are you've stumbled upon this versatile little chip. The LM723 is an adjustable voltage regulator IC that's been around for ages, and it's still super relevant for a wide range of projects. We're going to explore everything from the basics of the LM723 to building some cool projects with it. So, grab your soldering iron, and let's get started!

Understanding the LM723 Voltage Regulator

So, what exactly is the LM723? At its core, the LM723 is a monolithic integrated circuit designed for use as a voltage regulator. It can provide both positive and negative output voltages and can be adjusted to supply a wide range of voltages and currents, making it incredibly versatile for various applications. This chip is essentially a complete voltage regulator, except for the external components needed to set the voltage and current levels. The LM723's popularity stems from its reliability, ease of use, and the fact that it's relatively inexpensive.

The LM723 includes several key components inside its package, including a reference voltage source, an error amplifier, a series pass transistor driver, and current limiting circuitry. These components work together to maintain a stable output voltage, regardless of changes in input voltage or load current. The reference voltage is a stable voltage source that the error amplifier uses as a benchmark. The error amplifier compares the output voltage to a fraction of the reference voltage and adjusts the pass transistor drive accordingly. The pass transistor acts like a variable resistor, controlling the amount of current that flows to the output. The current limiting circuitry protects the regulator from overloads and short circuits, preventing damage to the chip and the connected circuitry.

One of the most significant advantages of the LM723 is its flexibility. By selecting appropriate external resistors and capacitors, you can configure it to operate in a variety of modes, including as a linear regulator, a switching regulator, or even a current source. The input voltage can range from around 9.5V to 40V, and it can supply output voltages from 2V to 37V, with output currents up to 150mA without an external pass transistor. With an external transistor, the output current can be increased to several amps. This makes it suitable for powering microcontrollers, op-amps, and other electronic circuits that require a stable and regulated voltage supply. For those who want to learn more, datasheets are readily available online. These datasheets provide detailed information on the chip's specifications, pin configurations, and application circuits. They are an invaluable resource when designing and building your LM723-based projects.

Key Features and Specifications of the LM723

Let's break down the key features and specs that make the LM723 such a popular choice for voltage regulation. Understanding these details will help you use the chip effectively in your projects. Here are some essential specifications:

Input Voltage Range: The LM723 can handle a wide input voltage range, typically from 9.5V to 40V. This allows it to be used with various power sources, including batteries, wall adapters, and rectified AC voltage.
Output Voltage Range: It can provide output voltages from 2V to 37V. This adjustability makes it suitable for powering various electronic circuits that require different voltage levels.
Output Current: Without an external pass transistor, the LM723 can supply output currents up to 150mA. With an external transistor, the output current can be increased to several amps, making it suitable for higher-power applications.
Internal Reference Voltage: The chip has an internal reference voltage of around 7.15V. This stable reference voltage is used by the error amplifier to maintain a consistent output voltage.
Current Limiting: The LM723 includes built-in current limiting circuitry to protect the regulator and connected circuits from overloads and short circuits. This feature is essential for preventing damage and ensuring the reliability of your projects.
Thermal Overload Protection: Some versions of the LM723 also include thermal overload protection, which shuts down the regulator if it gets too hot. This feature adds an extra layer of safety, preventing the chip from being damaged by excessive heat.

The key features of the LM723 include its high ripple rejection, low temperature drift, and excellent line and load regulation. High ripple rejection means that the regulator can effectively filter out noise and voltage fluctuations from the input voltage, providing a clean and stable output voltage. Low-temperature drift means that the output voltage remains relatively stable over a wide range of temperatures, ensuring consistent performance in different environments. Excellent line and load regulation means that the output voltage remains stable despite changes in the input voltage or load current. These features make the LM723 a reliable choice for applications where a stable and regulated voltage supply is essential.

When selecting an LM723 for your project, it's essential to consider the specific requirements of your application. Check the datasheet to ensure that the chip can handle the input voltage, output voltage, and output current required by your circuit. Also, consider whether you need any additional features, such as thermal overload protection or adjustable current limiting. By carefully considering these factors, you can choose the right LM723 for your needs and ensure that your project performs reliably.

Pin Configuration

Okay, let's talk pins! Understanding the pin configuration of the LM723 is crucial for connecting it properly in your circuits. The LM723 typically comes in a 14-pin dual in-line package (DIP). Here's a breakdown of the most common pins and their functions:

Non-Inverting Input (+IN): This is one of the inputs to the error amplifier. It's typically connected to a voltage divider that samples the output voltage.
Inverting Input (-IN): This is the other input to the error amplifier. It's usually connected to a reference voltage or another voltage divider.
Voltage Control (VC): This pin is used to adjust the output voltage. It can be connected to a potentiometer or another voltage source to fine-tune the output.
VREF (Reference Voltage): This pin provides a stable reference voltage, typically around 7.15V. It's used as a benchmark for the error amplifier.
Current Limit (CL): This pin is used to set the current limit. It's typically connected to a resistor that determines the maximum output current.
Current Sense (CS): This pin is used to sense the output current. It's connected to the load through a small resistor.
V+(Positive Supply Voltage): This is the positive supply voltage input. It's typically connected to a voltage source between 9.5V and 40V.
V-(Negative Supply Voltage or Ground): This is the negative supply voltage input or ground. It's typically connected to ground.
Output Voltage (VO): This is the output voltage. It's connected to the load.
Output (Collector): this pin is the collector of the output transistor
Compensation: This pin is used for frequency compensation to stabilize the regulator and prevent oscillations.
NC (No Connection): This pin is not connected internally and can be left floating.
Zener: This pin connects to the Zener diode which help in voltage regulation.
Frequency Compensation: This pin is used for frequency compensation to stabilize the regulator and prevent oscillations.

When working with the LM723, it's important to consult the datasheet for the specific pinout of your particular package. Different manufacturers may use slightly different pin configurations, so it's always best to double-check. Also, be sure to use proper soldering techniques to avoid damaging the chip or creating short circuits. A little bit of care and attention to detail can go a long way in ensuring the success of your project.

Basic LM723 Circuit Configurations

Alright, let's dive into some basic circuit configurations using the LM723. These configurations will give you a solid foundation for building more complex projects. We'll cover a few common setups, including a basic positive voltage regulator, a negative voltage regulator, and a current source.

Positive Voltage Regulator

This is the most common configuration for the LM723. It provides a stable positive output voltage. Here's how it works:

The input voltage is connected to the V+ pin (pin 7).
The output voltage is taken from the VO pin (pin 9).
A voltage divider is connected between the output and the inverting input (-IN, pin 2) to sample the output voltage.
The non-inverting input (+IN, pin 1) is connected to the reference voltage (VREF, pin 4) through a resistor.
The current limit resistor is connected between the current limit (CL, pin 5) and current sense (CS, pin 6) pins.

The output voltage is determined by the values of the resistors in the voltage divider. By adjusting these resistor values, you can set the output voltage to the desired level. The current limit resistor determines the maximum output current. If the output current exceeds this limit, the regulator will reduce the output voltage to prevent damage.

Negative Voltage Regulator

The LM723 can also be configured as a negative voltage regulator. The main difference is the way the voltage divider and reference voltage are connected. Here's how to set it up:

The input voltage is connected to the V+ pin (pin 7).
The output voltage is taken from the VO pin (pin 9).
A voltage divider is connected between the output and the non-inverting input (+IN, pin 1) to sample the output voltage.
The inverting input (-IN, pin 2) is connected to the reference voltage (VREF, pin 4) through a resistor.
The current limit resistor is connected between the current limit (CL, pin 5) and current sense (CS, pin 6) pins.

In this configuration, the output voltage is negative with respect to ground. The voltage divider samples the negative output voltage and feeds it back to the non-inverting input of the error amplifier. The error amplifier compares this voltage to the reference voltage and adjusts the output voltage accordingly.

Current Source

The LM723 can also be configured as a constant current source. This is useful for applications where you need to supply a fixed amount of current to a load, regardless of changes in the load resistance. Here's how to set it up:

The input voltage is connected to the V+ pin (pin 7).
The load is connected in series with a current sense resistor.
The voltage across the current sense resistor is fed back to the inverting input (-IN, pin 2) of the error amplifier.
The non-inverting input (+IN, pin 1) is connected to a reference voltage.
The output is taken from the output pin (pin 10).

In this configuration, the error amplifier adjusts the output voltage to maintain a constant current through the load. The current is determined by the voltage across the current sense resistor and the value of the resistor. By adjusting the reference voltage or the value of the current sense resistor, you can set the output current to the desired level.

Example LM723 Projects

Now for the fun part – building some projects! Here are a couple of cool project ideas using the LM723 to get your creative juices flowing.

Adjustable Power Supply

One of the most common and useful projects you can build with the LM723 is an adjustable power supply. This project allows you to set the output voltage to any desired level within the chip's range. This is incredibly handy for testing different circuits and powering various electronic devices. The key components you'll need include the LM723 IC, a potentiometer for adjusting the voltage, resistors for setting the voltage range, capacitors for stability, and a transformer and rectifier circuit to provide the input voltage. Additionally, you can add a digital display to monitor the output voltage accurately. Constructing an adjustable power supply with the LM723 is an excellent way to gain practical experience with voltage regulation and circuit design. It's a project that is both educational and highly functional for any electronics enthusiast.

Battery Charger

Another fantastic project is a battery charger. The LM723 can be configured to charge various types of batteries, such as lead-acid, Ni-Cd, and Li-ion. The basic principle involves using the LM723 to provide a constant voltage or constant current to the battery, depending on the charging requirements. For a constant voltage charger, the LM723 is configured to maintain a steady voltage across the battery terminals, while for a constant current charger, it ensures a consistent current flows into the battery. Additional components such as diodes, resistors, and capacitors are used to fine-tune the charging parameters and protect the battery from overcharging. Building a battery charger with the LM723 not only enhances your understanding of power electronics but also provides a practical solution for charging your electronic devices efficiently and safely.

Tips and Tricks for Working with the LM723

Before we wrap up, here are a few tips and tricks to keep in mind when working with the LM723:

Read the Datasheet: Always, always, always read the datasheet! It contains a wealth of information about the chip's specifications, pin configurations, and application circuits.
Use a Heat Sink: If you're running the LM723 at high currents, be sure to use a heat sink to prevent it from overheating. Excessive heat can damage the chip and cause it to malfunction.
Use Proper Decoupling: Use decoupling capacitors close to the power supply pins to reduce noise and improve stability. A 0.1uF capacitor is typically a good choice.
Double-Check Your Connections: Before applying power, double-check all of your connections to make sure they're correct. Incorrect connections can damage the chip and other components.
Start Simple: When starting a new project, start with a simple circuit and gradually add complexity as you gain experience. This will help you troubleshoot any issues more easily.

Conclusion

So, there you have it – a comprehensive guide to the LM723 voltage regulator! We've covered everything from the basics of the chip to building some cool projects with it. The LM723 is a versatile and reliable IC that's perfect for a wide range of applications. Whether you're a beginner or an experienced electronics enthusiast, I encourage you to give it a try. With a little bit of practice, you'll be building awesome LM723-based projects in no time. Happy tinkering!