5V Boost Converter

Hello,

Today I like to share to you something about power-supply. For electronic hobbyists the 5V power-supply is an important one.  Most of all digital circuits works in 5V.  So 5V power source is an important one. Here I explain how create a 5V power supply from the 3.7V Li-ion cell. It is a portable device. It is also work as the power bank for mobile phones. So we need a circuit which increase the voltage from 3.7V to 5V. This job is done by a boost converter (DC -DC boost converter). The boost converter produce a voltage which is higher than the input voltage. So it is an amazing circuit for beginners.

For SMPS circuit, visit my previous blog, https://0creativeengineering0.blogspot.com/2018/12/ni-mh-battery-charger-for-230v.html

Boost Converter

From the name it is clear that it is a device which boost (increase) the input voltage. Here the voltage is increased but the total energy is conserved. So for increasing the voltage, it consume more power (current from source) from the source. So the total energy is conserved. The extra energy taken from the battery is stored in the capacitor or an inductor and it delivered to the output in a series manner. So the output voltage increases (series connection increases voltage). It's operation is divided into two phases, in first phase the element charges from the source (store energy) and in the second phase element discharges the energy to the eternal output. So at the discharging time the output get the sum of two energies, that is from the source and from the element. So the output is boosted. This charging and discharging process is done in  faster speed, which is done by using a high frequency oscillator (KHz). This is the basic working principle of boost converter. Note that, the boost converter is not a free energy device it satisfies the law of conservation of energy. There is no free energy devices in the universe😈. It is only in the fools mind.

NOTE: The above mentioned boost converter concept is only for beginners. So it is an introduction only. The inductive boost converter is little bit different than the above mentioned. It explain later. 

Boost Converter Using Inductor

The above block diagram indicate an ideal boost converter using an inductor. It contain two parts, first is a charging and discharging circuit for inductor and the second is the rectifier and filter circuit. In the figure the switch is indicates the semiconductor switch (transistor, mosfet) in the practical circuit. The inductor used here is a ferrite core inductor. Because the inductor frequency of operation is in the range of KHz.

Working of Boost Converter

The given figure indicates the two phases in the working. First phase is the charging and the second phase is the discharging. The graph indicates the current in the inductor at that time. 

Charging Phase

In this phase the switch is at close position. So current is flowing through the inductor. So the inductor current increases exponentially from zero to maximum which shows in the graph. So the inductor stores energy in its magnetic field. The diode D is in reverse bias state. So no current through it. The output voltage is the voltage in the capacitor. 

Discharging Phase

In this phase the switch is in open state.  So here the inductor connected series to the source. So the inductor changes its polarity for discharging. So now the source voltage and inductor voltage act series to the load. So the diode D is in forward biased. So it conduct electricity. So the output load get a higher voltage than at the input. Because, the inductor voltage add up to the source voltage in this state. So the output capacitor charged at a higher voltage. So the output voltage stable at this voltage.

Boost Converter Block Diagram

The given block diagram indicate a practical boost converter. The oscillator is the heart of this circuit. The oscillator produce the necessary high frequency signal. This is modulated by the PWM modulator. The modulation carried out based on the output voltage. The modulation is done for control the output voltage. Basically in PWM modulator, it controls the duty cycle of the oscillator signal. So by modulation we can control the energy output easily. By controls the energy we can easily control and stabilize the output voltage. Then the PWM signal is given to the power transistor base. It give the high current to the inductor. Then the output rectifier and filter produce a stable DC voltage. The feedback circuit is a resistor potential divider set-up for taking a output feedback for changing the duty cycle(PWM).

Circuit Diagram

The circuit diagram is given below. My circuit is based on a DC-DC converter IC MC34063. The IC have all the necessary components inside it. It also contain a power transistor inside. So we need only very few external components. For more IC details download the datasheet. The capacitor C3 control the oscillator frequency. The resistor R4 and R5 are create the feedback network and it controls the output voltage. Here it is designed for 5V. The diode is a high speed schottky diode. The inductor determines the output current capability. This IC have a maximum of 1.5 A capacity.

I made a new 5V boost converter circuit by using a 6 legged small SMD IC. It is capable of delivering a current of 2A and work from 2V. It is better than this circuit. Please visit it. The link is given below,

https://0creativeengineering0.blogspot.com/2019/05/diy-tiny-5v-2a-boost-converter-simple.html