Introduction to the LM723 Voltage Regulator

The LM723 is a general-purpose voltage regulator IC that can be used in a wide range of applications. It is designed to provide a stable and adjustable output voltage, making it suitable for powering electronic devices, controlling motors, and regulating power supplies. The LM723 is available in various package types, including TO-100, TO-5, and 14-pin DIP.

Key Features of the LM723

1. Adjustable output voltage range: 2V to 37V
2. Output current capability: up to 150mA
3. Low temperature drift: typically 0.002%/°C
4. Built-in current limiting and thermal shutdown protection
5. Wide operating temperature range: -55°C to +125°C
6. Can be used as a linear or switching regulator
7. Requires few external components for basic operation

Understanding the LM723 Pinout and Internal Block Diagram

To effectively use the LM723 in your circuits, it is essential to understand its pinout and internal block diagram. The LM723 is available in various package types, but we will focus on the 14-pin DIP package for this article.

LM723 Pinout (14-pin DIP)

Pin	Name	Description
1	NC	No Connection
2	ILIM	Current Limit
3	COMP	Compensation
4	VREF	Reference Voltage
5	V-	Negative Supply
6	INV	Inverting Input
7	NI	Non-Inverting Input
8	VOUT	Output Voltage
9	VS	Series Pass Transistor Emitter
10	VC	Series Pass Transistor Collector
11	V+	Positive Supply
12	VZ	Zener Cathode
13	VSS	Substrate
14	NC	No Connection

LM723 Internal Block Diagram

The internal block diagram of the LM723 consists of several key components:

1. Voltage reference: Provides a stable 7.15V reference voltage
2. Error amplifier: Compares the output voltage with the reference voltage and adjusts the output accordingly
3. Series pass transistor: Controls the output current based on the error amplifier’s output
4. Current limiting circuitry: Protects the regulator and load from excessive current
5. Thermal shutdown: Disables the regulator if the internal temperature exceeds a safe limit

Basic LM723 Voltage Regulator Circuit

Now that we have a better understanding of the LM723’s pinout and internal structure, let’s explore a basic voltage regulator circuit using this IC.

Components Required

1. LM723 IC
2. Resistors: R1, R2, and R3
3. Capacitors: C1 and C2
4. Input and output connectors

Circuit Diagram

[Insert a clear circuit diagram showing the connections between the LM723 and external components]

How It Works

1. The input voltage is applied to the V+ pin (pin 11) of the LM723.
2. The voltage reference (pin 4) provides a stable 7.15V reference voltage.
3. The error amplifier (pins 6 and 7) compares the output voltage with the reference voltage.
4. The series pass transistor (pins 9 and 10) controls the output current based on the error amplifier’s output.
5. Resistors R1 and R2 form a voltage divider that sets the output voltage.
6. Resistor R3 and capacitor C1 provide compensation for stable operation.
7. Capacitor C2 improves the transient response and filters the output voltage.

Calculating the Output Voltage

The output voltage of the LM723 regulator circuit can be calculated using the following formula:

Vout = Vref × (1 + R1 / R2)

Where:
– Vout is the desired output voltage
– Vref is the reference voltage (7.15V for the LM723)
– R1 and R2 are the resistor values in the voltage divider

By selecting appropriate values for R1 and R2, you can set the output voltage to the desired level.

Advanced LM723 Voltage Regulator Circuits

While the basic LM723 regulator circuit is suitable for many applications, there are several advanced configurations that can enhance its performance and functionality.

Adjustable Output Voltage with Potentiometer

By replacing the fixed resistor R2 with a potentiometer, you can create an adjustable voltage regulator circuit. This allows you to fine-tune the output voltage within the LM723’s range.

Current Limiting

The LM723 has built-in current limiting circuitry that protects the regulator and load from excessive current. By connecting a resistor between the ILIM pin (pin 2) and ground, you can set the maximum output current.

The current limit can be calculated using the following formula:

Ilim = 0.65V / Rlim

Where:
– Ilim is the desired current limit
– Rlim is the resistor value connected to the ILIM pin

Switching Regulator Configuration

While the LM723 is primarily used as a linear regulator, it can also be configured as a switching regulator to improve efficiency in high-current applications. In this configuration, an external transistor and inductor are used to create a step-down (buck) or step-up (boost) converter.

[Insert a circuit diagram showing the LM723 in a switching regulator configuration]

Applications of the LM723 Voltage Regulator

The LM723 voltage regulator finds applications in various electronic systems, including:

1. Power supplies for electronic devices
2. Motor speed control circuits
3. Battery chargers
4. Voltage Stabilizers
5. Automotive electronics
6. Industrial control systems

Troubleshooting and Tips

When working with the LM723 voltage regulator, keep the following tips in mind:

1. Ensure proper power supply decoupling with capacitors close to the IC.
2. Use heat sinks for high-current applications to prevent thermal shutdown.
3. Pay attention to the maximum ratings of the IC, such as input voltage and output current.
4. Use appropriate compensation components for stable operation.
5. Double-check the pinout and connections before powering up the circuit.

Frequently Asked Questions (FAQ)

1. What is the maximum output current of the LM723 voltage regulator?

2. The LM723 can provide up to 150mA of output current.

3. Can the LM723 be used as a switching regulator?

4. Yes, the LM723 can be configured as a switching regulator for improved efficiency in high-current applications.

5. What is the purpose of the compensation pin on the LM723?

6. The compensation pin (pin 3) is used to connect external components that ensure stable operation of the regulator.

7. How can I adjust the output voltage of the LM723 regulator?

8. The output voltage can be adjusted by changing the values of the resistors in the voltage divider connected to the non-inverting input (pin 7) and the reference voltage (pin 4).

9. What should I do if the LM723 regulator is overheating?

10. Ensure that the regulator is not exceeding its maximum output current rating. Use a heat sink to dissipate excess heat, and provide adequate ventilation for the circuit.

Conclusion

The LM723 voltage regulator is a versatile and reliable IC that has stood the test of time. Its adjustable output voltage, built-in protection features, and ability to be used in both linear and switching regulator configurations make it a popular choice for a wide range of applications. By understanding the LM723’s pinout, internal structure, and circuit configurations, you can effectively utilize this regulator in your electronic projects. Remember to follow best practices, such as proper power supply decoupling and thermal management, to ensure optimal performance and longevity of your LM723-based circuits.