LM2576 Voltage Regulator Equivalents, Internal Structure, Working Principle and More

Ⅰ. What is LM2576 voltage regulator?

Ⅱ. What are the features of LM2576 voltage regulator?

Ⅲ. Pin configuration of LM2576 voltage regulator

Ⅳ. Internal structure of LM2576 voltage regulator

Ⅴ. How does the LM2576 voltage regulator work?

Ⅵ. Technical parameters of LM2576 voltage regulator

Ⅶ. Selection of peripheral components of LM2576 voltage regulator

Ⅷ. Application circuit of LM2576 voltage regulator

LM2576 is a low-cost, high-efficiency, adjustable-output step-down DC voltage regulator. It can convert the high voltage input from the power supply into low voltage to supply various loads. In this article, we will introduce the features, internal structure, working principle, application circuit, etc. of LM2576 in detail to better understand and use this voltage regulator.

The LM2576 series is a 3A current output step-down switching integrated voltage regulator circuit manufactured by Texas Instruments. It contains a fixed frequency oscillator (52kHz) and a reference regulator (1.23V), and has a complete protection circuit, including current limiting and thermal shutdown circuits, etc. This circuit has a current output capability of 3A and is suitable for voltage stabilization applications that require large current output. It uses built-in components and functions to form an efficient voltage stabilizing circuit with only a few external components.

It integrates a fixed oscillator internally and requires very few peripheral devices to form an efficient voltage regulator circuit. This design greatly reduces the size of the heatsink and often eliminates the need for a heatsink. In addition, the chip provides excellent safety performance with comprehensive protection circuits, including current limit and thermal shutdown circuits. In addition, the chip provides an external control pin (On/Off), making it an ideal replacement for conventional three-terminal type voltage regulator ICs.

Replacements and equivalents:

• CS51411

• LM2575

• LM2596

• LM2940

• MP2307

• LM7805

• It requires relatively few external components, which helps simplify circuit design.

• LM2576 has a wide input voltage range (up to 60V).

• In comparison to linear regulators, the LM2576 typically exhibits enhanced efficiency, leading to a reduction in power consumption and an overall improvement in system efficiency.

• It usually has built-in overheating and short-circuit protection to ensure the safety of the chip under various operating conditions.

LM2576 includes five pins with the following names and functions.

Pin 1 (Vin): The voltage which has to be regulated is provided as input to this pin.

Pin 2 (Output): The regulated output can be obtained through this pin.

Pin 3(Ground): It connects to system ground.

Pin 4 (Feedback): This pin is provided with the feedback voltage based on which the output is regulated.

Pin 5 (On/Off): It connects to ground to activate regulator or connects to Vcc to disable the regulator.

The internal structure of the LM2576 chip includes a set of inductors, a diode, a switching tube and a set of filter capacitors, which are connected through a controller. When the power supply voltage is higher than the output voltage, the chip will begin to convert a high-frequency pulse current and turn on/off the switch tube at a certain duty cycle, thus changing the electromagnetic field and affecting the inductor, and finally outputs a stable DC voltage.

Input voltage detection: The LM2576 first checks the input voltage to ensure that the voltage is within the range that the chip can handle. If the input voltage is out of range, the chip will automatically stop working to protect the circuit and the device.

PWM control: LM2576 uses pulse width modulation (PWM) for voltage conversion. The PWM controller can achieve precise control of the output voltage by adjusting the switching time ratio of the switching tube.

Switch control: LM2576 adjusts the input voltage through the switch to control the output voltage. When the switch tube is turned on, the input voltage is transmitted to the output terminal through the switch tube; when the switch tube is turned off, the input voltage is cut off and the output terminal voltage is 0.

Inductive component: The LM2576 is typically equipped with an inductive component (such as an inductor or transformer) that stores energy and smooths the voltage output. The current change of the inductive element can offset the difference between the input voltage and the output voltage, thereby achieving a stable voltage output.

Feedback control: A feedback control loop is set up in the LM2576 to monitor the output voltage and compare it with the set value. When the output voltage is higher than the set value, the feedback control loop sends a signal to the PWM controller to reduce the output voltage by shortening the conduction time of the switch tube. On the contrary, when the output voltage is lower than the set value, the feedback control loop will increase the output voltage by extending the conduction time of the switch tube.

1. Schottky diode

Schottky diodes should be preferred because of their forward voltage drop, fast switching speed, and short reverse recovery time. In contrast, ordinary rectifier diodes such as 1N4000 and 1N5400 are not suitable for this application.

2. Energy storage inductor

The DC flow of the inductor directly determines the output current. The LM2576 can operate in either continuous or discontinuous operating modes. When the current flowing through the inductor remains continuous, it is a continuous operating mode; when the inductor current drops to zero within a switching cycle, it is a discontinuous operating mode.

3. Input capacitance

It is recommended to choose low ESR aluminum or tantalum capacitors as bypass capacitors to prevent large transient voltages from appearing at the input end. At the same time, when the input voltage fluctuates greatly and the output current is high, we should choose a capacitor with a larger capacity, such as 470μF to 10000μF. The rms current value of the capacitor must be at least 1/2 of the DC load current. For safety reasons, the rated withstand voltage of the capacitor must be 1.5 times the maximum input voltage. In addition, we cannot choose ceramic capacitors because this will cause serious noise interference.

4. Output capacitance

It is recommended to use low ESR tantalum capacitors between 1μF and 470μF. However, please note that excessive capacitance can cause damage to the device under certain conditions (such as open load or disconnected input). COUT is usually used for output filtering and improving loop stability. However, if the ESR of the capacitor is too low, the feedback loop may become unstable, causing the output to oscillate. This is almost a common feature of voltage regulators, including LDOs and others.

The LM2576 voltage stabilizing circuit is shown in the figure below. This IC is used to build a 5V 3A switching regulator. The circuit uses basic electronic components such as LM2576 and IN5822 diodes, as well as 100uF inductors and capacitors of different capacities (such as 1000uf and 100uf) to achieve stable output.

The above circuit is very simple for designing power digital circuits. Because it is a digital circuit, we chose to use a high power of 10 watts. The power supply required for the circuit is 5V, 3A. Once we apply it to a car, it can power a circuit from the car's cigarette lighter. However, it is suitable for the 12V voltage standard. So to ensure the circuit operates properly, we need to use 3A of current to reduce the voltage to 5V. The input voltage range of this circuit is 7V to 40V, and the operating frequency is also high, making it very suitable for applications that require high-power digital circuits.

Due to the built-in cooler, the LM2576 does not generate heat, so it can be used continuously for long periods of time. In addition, it has the ability to change different integrated circuits. The voltage levels may vary for different integrated circuits. For example, the LM2576 has an output of 3.3Vdc, while other models have outputs of 5Vdc, 12Vdc, or 15Vdc. Additionally, the LM2576 has an output range of 1.23Vdc to 37Vdc.

Frequently Asked Questions

1. What is LM2576 current regulator?

The LM2576 series of regulators are monolithic integrated circuits ideally suited for easy and convenient design of a step−down switching regulator (buck converter). All circuits of this series are capable of driving a 3.0 A load with excellent line and load regulation.

2. What is the use of LM2576?

The LM2576 series of regulators are monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator, capable of driving 3-A load with excellent line and load regulation.

3. What is the difference between LM2596 and LM2576?

The higher internal frequency allows the use of a smaller inductor and capacitor on the output reduces the size and weight of your passives. The newer also LM2596 also have a low power idle mode. However, the LM2576 has a variant available for higher input voltages.

4. What power supply uses LM2576?

The LM2576-Adj (PS1) can accept input voltages up to 40V, but REG1 (78L09) can tolerate the maximum of 35V (absolute maximum rating) at the input. REG1 plays an important role in the stability of the amplifier (IC1), therefore reducing 10V from the input voltage threshold is a wise decision.

5. How does LM2576 work?

LM2576 is one kind of voltage regulator and it is also called a buck converter. This is mainly used like a pre-regulator within the linear regulators. This kind of regulator is a modified version of switching power supplies wherever it includes all functions required to decrease the voltage of the circuit.