LM2678 Based 5V DC-DC Buck Converter Circuit

This is LM2678 Based 5V DC-DC Buck Converter Circuit

It makes 5V DC-DC buck converter.

Buck converter changes high voltage to low voltage by switching.

LM2678 IC chip is very efficient step-down regulator and it can give 5A output current.

Circuit efficiency is more than 90% and it works good with load and voltage changes.

LM2678 IC have three fixed output like 3.3V, 5V, 12V and also have adjustable output.

It has features like thermal shutdown, current limit and ON/OFF control.

Power input is from 8V to 40V DC.

This article show how circuit work, design calculation and to build 5V buck circuit with LM2678.

Circuit Working:

Parts List:

Circuit uses IC LM2678 step-down regulator chip.

Input voltage is from 8V to 40V change to steady 5V output.

This regulator works as switch mode with more efficient than normal linear.

Input DC voltage is from 8V to 40V.

Three capacitors C1, C2, C3 clean input voltage and reduce noise and spikes.

LM2678 IC control voltage and switch current through inductor L1 fast.

Capacitor C4 connect pin 2 for frequency stable.

Inductor L1 save energy when switch ON and give energy when switch OFF to keep current flow.

Pin 7 is ON/OFF switch and if connected to ground the regulator turn OFF.

Diode D1 give path for current when switch is OFF and saves energy.

Capacitors C6 and C7 smooth output and makes stable 5V DC.

Formulas with Calculations:

Formulas for LM2678 5V buck converter:

Inductor l calculate by:

l = (Vout * (Vin – Vout)) / (f * Iout * Vin * k)

where,

• Vout is 5V output
• Vin is 12V input
• Iout is 5A output current
• f is 260kHz switching frequency
• k is 0.3 current ripple factor

Put values:

l = (5 * (12 – 5)) / (260000 * 5 * 12 * 0.3) = 22µH

Output capacitor Cout calculate by:

Cout = (Iout * k) / (f * Vripple)

where,

• Iout is 5A
• k is 0.3
• f is 260kHz
• Vripple is 50mV

Put values:

Cout = (5 * 0.3) / (260000 * 0.05) = 115µF

Use two 180µF capacitors for better performance.

How to build:

To build a LM2678 Based 5V DC-DC Buck Converter Circuit follow the below steps:

• Connect pin 1 of IC1 LM2678 to 5V output voltage
• Connect pin 2 of IC1 to input voltage 8V to 40V
• Connect pin 3 of IC1 to one side of capacitor C5 and other side of C5 to pin 1 of IC1
• Connect pin 4 of IC1 to GND
• Connect pin 6 of IC1 to join point of inductor L1 and positive of capacitor C6
• Pin 7 is ON/OFF switch
• Connect positive of capacitors C1, C2, C3 in parallel from pin 2 of IC1 and negatives to GND
• Connect capacitor C4 between pin 2 of IC1 and GND
• Connect diode D1 cathode to junction of pin 1 and pin 3 of IC1 and anode to GND
• Connect positive of capacitors C6 and C7 in parallel from junction of L1 and 5V output and negatives to GND
• Connect inductor L1 between diode D1 cathode and positive of capacitor C6

Conclusion:

LM2678 Based 5V DC-DC Buck Converter Circuit is strong step-down regulator.

It gives 5A output with high efficiency.

Switching design is less with heat loss.

Circuit is good for microcontrollers, battery devices, and industrial electronics.

Use right parts like inductor, capacitors, diode for better performance and for stable work.

References:

LM2678 SIMPLE SWITCHER® High Efficiency 5-A Step-Down Voltage Regulator