- what is buck converter ?
- how to design buck converter ?
- what are applications of buck converter ?
- how to select components like diode , switch, inductor and capacitor for buck converter ?
- how to select or design gate driver circuit or IC?
- How to use microcontroller for PWM generation?
I hope that after reading this article you will be able to design your own buck converter according to your requirement.
what is buck converter ?
buck converter is non isolated converter which is used to step down DC voltage It is actually serve the purpose of step down DC transformer. Buck converter is used only for low power applications due to some reasons of efficiency issues, inductor size and capacitor size. It is beyond the scope of this article to discuss what is the reason behind . you can find answer of this question from many books on power electronics.Buck converter have very high efficiency for low power applications
Applications of buck converter ?
There are plenty of application of buck converter in switch mode power supplies and many other. some of the applications are given below
How to design buck converter ?
In this section you will learn how to design a Buck converter. before designing buck converter you should have a theoretical knowledge of buck converter. how buck converter works and how to calculate value of inductor, capacitor, frequency and duty cycle of switch. If you don’t know anything about buck converter I recommend you to read chapter 5 of M.H Rashid book on power electronics.
Let’s proceed to practical design of Buck converter. A simple circuit diagram of buck converter with control mechanism is shown below.This is a simple circuit diagram of buck converter you have came across many time while reading about Buck converter in plenty of books.But in practical buck converters there are many other components used to get regulated step down voltage.These books don’t discuss the practical implementation of buck converter. After reading this reading you will be able to design buck converter.
In circuit diagram given below inductor, capacitor and diode can be found easily from market. Inductor should be ferrite core or iron core for high current or power applications. Before selection of diode you should take care of turn on and turn off time of diode. Diode switching time from turn on to turn off and vice versa should be fast. I recommend you to use schotty diode, becuase it have fast reverse recovery time and low forward conduction losses. You can also use another switch instead of diode. This type of buck converter is called synchronous buck converter. Another components used in this circuit diagram is switch. Switch is most important component of any dc to dc converter. By controlling turn on and turn off time of switch we actually control voltage at the output of buck converter. Now the question is how to select this switch?
This switch can be any semicondutor device from transistor, MOSFET and IGBT. Selection of these components depends on power rating of buck converter. Usually MOSFET is used in practical buck converters due to its low on state resistance, high switch frequency and high power handling capability. PWM controller shown in circuit diagram is used to control turn on and turn off time of switch. In other words it is uses to control duty cycle of PWM. PWM stands for pulse width modulation. I have posted a separate article on pulse with modulation. If you don’t know about pulse width modulation and duty cycle I recomend you to read following read before reading this article further.
Now let’s move to another componets need to design buck conveter. If you are using MOSFET as a switch, you can use MOSFET either as low side MOSFET driver or high side MOSFET driver. Now you must be thinking why we need of MOSFET driver when MOSFET can be turn on by applying voltage signan to its base. Bcause MOSFETs are voltage controlled devices. They have high gate to source impedence. To get high swithcing speed of MOSFET gate driving circuit is used. Another reason to use gate driver circuit is that if you are using microcontroller for PWM generation, the output of microcontroller PWM is 5 volt and to drive MOSFET we must apply voltage to gate of MOSFET between 10.5 volt to 12 volt. So gate driver circuit is also used to tranaslate voltage level of PWM square wave. Mosfet can be used either in low side or high. If load is connected to source pin of MOSFET it is called high side configurati0n and if load is connected to drain pin of MOSFET it is called low side configuration. There are many gate drivers IC available in market. But we are using IR2110 of international rectifiers as a gate driver of MOSFET. If you want to know more about gate drivers circuits and How to use IR2110 for high side and low side driver of MOSFET check this article.
Practical example of buck converter :
Now I take a practical example of buck converter and teach you how to design its circuit diagram using IR2110 and PWM using pic microcontroller. Let’s suppose we want to design a buck converter which have input voltage of 12 volt and want to get regulated 5 volt output at the output of buck converter. So
Vin = 12 volt
Vout = 5 Volt
I load = 1 Ampere
By using these value we can easily calculate values of iductor, capacitor and duty cycle of pulse width modulation. In other words turn on or off time of switch. By using formula’s of buck converter you can easily calculate their values. For information about how to calculate values of inductor capacitor and duty , I suggest you yo go through chapter 5, page number 186 of M.H.Rashid book on power electronics. After doing calculations I have found following values of indutor, capacitor and duty cycle :
inductor = 150 uH
capacitor = 200 uF
duty cycle = 42 %
Now I have designed circuit diagram of buck converter using above given values. Circuit diagram is given below. Circuit diagram includes MOSFET IR540, MOSFET driver IR2110 in high side configuration , because load is conned to high side of MOSFET and 10MQ060 schottky diode is used Becuase load current is 1 ampere and its rating more than 1 ampere. PIC16F877A microcontroller is used to generate PWM and read output voltage as feedback. Two resistors are used as a voltage divider to lower the output voltage. Because microcontroller pin can not read voltage more than 5 Volt. PIC16877A analog to digital conveter is used to read this voltage. If yo don’t have idea about programming and use of PIC microcontrollers, I recommend you to used following articles :
Complete circuit diagram of Buck converter is given below :
buck converter simulation in proteus
Video lecture on buck converter simualtion
click here to purchase code and proteus simulation[/button-brown]
I have used IR2112 instead of IR2110 because it is not available in proteus. You can use IR2210 for same ciruit as well. Both MOFET drivers are almost same. Kindly don’t forget to share this article with others. This is what you can do for us in return. Thanks 🙂