L7812CV Voltage Regulator: Block Diagram, Specifications, Application and Design Considerations

Ⅰ. Overview of L7812CV

Ⅱ. L7812CV block diagram

Ⅲ. How does L7812CV work?

Ⅳ. L7812CV specifications

Ⅴ. Application cases of L7812CV

Ⅵ. Design considerations of L7812CV

Ⅶ. How to judge the quality of L7812CV

The L7812CV is a three-terminal positive voltage regulator with multiple fixed output voltage options. This voltage regulator is capable of stably converting a high voltage of approximately 14V to 35V into a 12V DC voltage output. The L7812CV provides local on-card scaling, thereby solving the distribution issues associated with single-point scaling. Additionally, it features internal current limiting, thermal shutdown, and safe area protection, making it rugged and durable. With sufficient heat dissipation, the L7812CV can provide an output current of more than 1A. Although it is primarily designed for fixed voltage regulation, it can also provide adjustable voltage and current with external components.

Alternatives and equivalents:

• BA17812T

• LM7812CT

• MC78M12ACTG

• MC78M12CTG

L7812CV is a circuit based on a linear voltage regulator. Its working principle can be simply described as: within the specified input voltage range, the unstable input voltage is stably converted into a 12V DC voltage output through the built-in voltage adjustment mechanism, while providing a stable current at the output end.

1. Internal structure

The internal structure of L7812CV consists of three main parts: input stage, output stage and voltage stabilization stage. Among them, the input stage consists of input filter capacitor C1 and overvoltage protection diode D1, which is used to filter the input voltage and protect it from overvoltage. The output stage consists of components such as output capacitor C2 and output diode D2, whose function is to ensure the stability of the output current. The voltage stabilization stage is mainly composed of key components such as voltage regulator tubes and comparators, and is responsible for adjusting the unstable input voltage to a constant 12V DC output voltage.

2. Basic principle

The basic principle of L7812CV is to adjust the input voltage by using a voltage stabilizing circuit to output a stable voltage. The working principle of this voltage stabilizing circuit is based on feedback control technology to ensure that the voltage at the output is not affected by fluctuations in input voltage and load current. Specifically, L7812CV uses negative feedback control technology, which compares the voltage at the output terminal with the reference voltage, and then feeds the comparison result back to the control circuit to control the voltage at the output terminal.

• Part Status: Active

• Package / Case: TO-220

• Packaging: Tube

• Polarity: Positive

• Line Regulation: 120 mV

• Load Regulation: 100 mV

• Input Voltage: 14V ~ 35V

• Output Voltage: 12 V

• Quiescent Current: 4.4 mA

• Operating Temperature: 0°C ~ 125°C

• Manufacturer: ST Microelectronics

• Mounting Style: Through Hole

• Number of Outputs: 1 Output

• Length/Width/Height: 10.4 mm/4.6 mm/9.15 mm

• Product Category: Linear Voltage Regulators

Some application cases of L7812CV are listed below:

1. Medical devices

In medical devices, the L7812CV is used to provide stable +12V power supply for driving various critical medical sensors and monitoring devices. These devices have extremely high requirements for power supply stability. With its stable power output, the L7812CV provides strong support for the accurate measurement and monitoring of medical equipment, enabling doctors to more accurately understand the patient's condition and formulate precise and effective treatment plans accordingly.

2. LED lighting system

In the LED lighting system, the stabilized power output of L7812CV ensures that the LED lamps and lanterns obtain precise voltage and current during operation, thus ensuring the normal operation and long life of the LED lamps and lanterns. Through the regulation of L7812CV, LED fixtures can maintain stable brightness and color in various working environments, providing a long-lasting and reliable light source for the lighting system.

3. Computer power

In desktop computers, servers and other computing devices, the L7812CV is commonly used to stabilize the +12V power line. This power line can be used to supply devices such as motherboards, hard disk drives, optical drives, fans, etc., to ensure that they receive a stable voltage during operation.

4. Power supplies

The L7812CV is often used to build various types of power supplies, such as for computers, communication equipment, audio equipment, and test instruments. In these applications, the L7812CV stabilizes the input voltage from an unstable DC power source (such as a battery or AC adapter) and outputs a stable +12V voltage.

5. Industrial control systems

In industrial control systems, the L7812CV can be used to provide a stable +12V power supply for driving various sensors, actuators, controllers and other devices. For example, it can be used in systems such as PLC (Programmable Logic Controller) and DCS (Distributed Control System), etc. PLC is responsible for receiving input signals, processing them according to preset logic programs, and outputting control signals to drive actuators to realize industrial automation control. DCS, on the other hand, provides efficient and safe control of large-scale industrial processes through decentralized control and centralized management. These systems have extremely high power requirements and need a stable voltage to ensure the accuracy and reliability of the control signals.

The L78 Series of fixed voltage regulators feature thermal overload protection, which activates to disable the circuit in cases of excessive power overload, internal short-circuit protection to cap the maximum current flow through the circuit, and output transistor safe-area compensation, diminishing the output short-circuit current as voltage across the pass transistor rises. In many low current applications, compensation capacitors are not required. However, it is recommended that the regulator input be bypassed with capacitor if the regulator is connected to the power supply filter with long lengths, or if the output load capacitance is large. An input bypass capacitor should be selected to provide good high frequency characteristics to insure stable operation under all load conditions. A 0.33 µF or larger tantalum, mylar or other capacitor having low internal impedance at high frequencies should be chosen. The bypass capacitor should be mounted with the shortest possible leads directly across the regulators input terminals. Normally good construction techniques should be used to minimize ground loops and lead resistance drops since the regulator has no external sense lead.

Incorporating an operational amplifier enables fine-tuning to achieve higher or intermediary values while maintaining regulation traits. The resulting minimum voltage from this setup exceeds the regulator voltage by 2 volts. The circuit of a high current voltage regulator (the figure shown below) can be modified to provide supply protection against short circuit by adding a short circuit sense resistor, RSC, and an additional PNP transistor. The current sensing PNP must be able to handle the short circuit current of the three terminal regulator. Therefore a four ampere plastic power transistor is specified.

Methods to determine whether L7812CV is good or bad include the following:

1. Appearance inspection: Check the external appearance of L7812CV, including whether the solder joints and pins are damaged, oxidized or otherwise abnormal. These cosmetic abnormalities may hint at internal problems.

2. Replacement test: If a spare L7812CV is available, we can directly replace it into the circuit and test the performance of the circuit again. If the problem is solved after replacement, it means that the original L7812CV may be bad.

3. Thermal test: When observing the temperature of L7812CV during operation, if its temperature is moderate, there is no overheating, and it maintains operation within the specified temperature range, then it can be considered to be working normally. However, if the L7812CV overheats abnormally, this may be a warning sign that its internal components may be damaged or otherwise faulty.

4. Overload test: Test the overload capability of L7812CV by connecting a load to its output port. It's probably good if it can supply the appropriate current within specified parameters and keep the output voltage stable. If the output voltage drops or becomes unstable under normal load, it's probably bad.

5. Voltage test: Use a multimeter or oscilloscope to measure the output voltage of the L7812CV. If the output voltage is around +12V and remains stable as the load changes, it's probably normal. If the output voltage is unstable, below +12V, or has no output at all, it may be bad.

Frequently Asked Questions

1. What is a voltage regulator used for?

It regulates voltage during power fluctuations and variations in loads. It can regulate AC as well as DC voltages. A voltage regulator usually takes in higher input voltage and emits a lower, more stable output voltage.

2. What is L7812CV?

The L7812CV is a three-terminal positive voltage regulator. This regulator can provide local on-card regulation, eliminating the distribution problems associated with single point regulation.

3. What is the function of L7812CV?

L7812CV is a L78 series three-terminal positive regulator in TO-220 package and fixed 12V output voltage, making it useful in a wide range of applications. This regulator can provide local on-card regulation, eliminating the distribution problems associated with single point regulation.