Simple 5V Switch Mode Power Supply Circuit using IC LM2674

This circuit is like a power adapter for your electronics but more efficient.

It takes electricity that is a bit too strong usually higher than 5V and converts it to a perfect 5V.

This 5V is just the right amount of power for many electronics, like those little computer boards you use for your projects.

The special chip in this circuit LM2674 is super easy to use and makes sure the 5V coming out are steady and reliable.

So, you can use this circuit to power your electronics without worrying about damaging them with strong electricity.

Circuit Working:

Parts List:

This circuit utilizes a 5-volt Switch Mode Power Supply, employing an IC from national semiconductor renowned for its expertise in designing ICs for switch mode power supplies.

These devices are typically easy to implement thanks to the comprehensive documentation available.

One common example uses the LM2671 or LM2674.

Components are readily available for 3.3V, 5V, and 12V outputs, with an option for a presettable voltage.

These supplies can handle currents up to 500mA within their specified application boasting a high switching frequency of 260 kHz.

The key advantage lies in the minimal need for low value inductors and capacitors resulting in high efficiency and compact dimensions.

Typically, efficiency reaches 90% and can even reach 96%.

Both ICs offer protection against current and temperature overloads.

The LM2671 offers additional features like soft start and the ability to synchronize with an external clock, enabling synchronization of multiple supplies for better electromagnetic compatibility EMC control.

The circuit shown provides a 5V output with a current up to 500mA.

Diode D1 is a schottky type with a voltage rating of Uco≥45V and a current rating of Imax≥3A.

Formulas:

The LM2674 IC, which is intended to be a simple solution to step down voltage regulation is used in the formula for the 5V switch mode power supply circuit above.

Although the LM2674 integrates a lot of capabilities to streamline the design process, it might be useful to know the following fundamental formula for performance analysis and component selection:

Inductor value L:

L = (V_out * (V_in – V_out)) / (ΔI * f_sw)

where,

• L is henrys inductance.
• V_out is the output voltage 5V.
• V_in the input voltage, ranges from 8V to 40V.
• ΔI inductor ripple current, is usually between 20 and 40 percent of output current.
• f_sw the LM2674s switching frequency, is typically 260 kHz.

The maximum output current (500mA in this example) should be less than the inductor current rating.

Selection of Output Capacitors:

Value of the output capacitor C3:

The intended output voltage ripple determines the value of the output capacitor.

Generally speaking, ripple is reduced with a bigger capacitor.

C3 = I_out / (ΔV_out * f_sw)

where,

• C3 is the output capacitance in farads
• I_out is the output current 500mA
• ΔV_out is the desired output voltage ripple
• f_sw is the switching frequency of the LM2674

Efficiency Calculation

η = (P_out / P_in) * 100%

where:

• η is the efficiency in percentage
• P_out is the output power (Vout * Iout)
• P_in is the input power (Vin * Iin)

Note:

This is a condensed summary, consult the LM2674 datasheet for accurate computations and the best possible design, and think about utilizing simulation tools.

How to Build:

To build a 5V Switch Mode Power Supply Circuit using IC LM2674 follow the below mentioned connections steps:

Select Component Values:

• Choose the values of the inductor, capacitors and resistors based on the LM2674 datasheet and your specific requirements output voltage, current etc.

Circuit Layout:

• Design the circuit layout on a breadboard or PCB following the recommended layout guidelines from the LM2674 datasheet.

Connect Components:

• Connect the components according to the circuit diagram provided in the LM2674 datasheet or the application notes.

Input and Output Connections:

• Connect the input voltage source typically a DC power supply to pin 7 of the LM2674 and the load output to the pin 8.

Testing:

• Power up the circuit and measure the output voltage and current to ensure they meet your requirements.
• Monitor the temperature of the LM2674 and ensure it remains within safe limits.

Finalization:

• Once you have verified that the circuit is working correctly finalize the layout and connections.
• Consider adding a heat sink to the LM2674 if it tends to get hot during operation.

Note:

It is important to refer to the LM2674 datasheet and application notes for detailed instructions and specifications specific to your application.

Conclusion:

To conclude, the LM2674 IC offers a basic and efficient solution for creating a 5V switch mode power supply.

Its simplicity and reliability make it a popular choice for a wide range of applications requiring a stable 5V output.

References:

LM2674 SIMPLE SWITCHER