Buck-Boost Converter

Today on this blog, we will see the introduction of the Buck-boost converter. Buck-boost converters are a type of power mode switch. It can provide a controlled DC output from the source voltage or higher or less than the output voltage you want. This can be especially helpful in battery-operated applications where the battery power starts above what you want but lowers when the battery drains. 


The Buck-boost converter is a type of DC-to-DC converter with an output voltage that may be greater or less than the input voltage. It is a voltage converter that goes up or down. The buck-boost converter is similar to a flyback converter, and a single inductor is used in place of the transformer. There are two types of converters in buck-boost converter: buck converter and one boost converter.

The input voltage is less than the output voltage (Vin <Vout). This indicates that the current output is lower than the current input. Hence the buck booster is a step-up mode.

Vin < Vout and Iin > Iout

The input voltage is greater than the output voltage (Vin > Vout). It follows that the output current is greater the input current. Hence the buck-boost converter is a step-down mode.

Vin > Vout and Iin < Iout

Formula of Output voltage (Vo) = -Vin * D/ (1-D)

The negative sign shows that the polarity of the output voltage is reversed.


It is made up of MOSFET (switch), diode, inductor, capacitor, DC voltage source. PWM pulses are given to the MOSFET, which switches it ON and OFF, and that’s how the output voltage is adjusted, and the output voltage which we are getting out of it is a reversed polarity which means if a positive voltage is given at input, the output voltage will be of negative value.

Mode 1:- Switch is ON, Diode is OFF

In this case, when the switch is closed, the inductor starts charging, due to the switching circuit closure provides zero resistance to current flow and the inductor starts charging, and charges up to its maximum level.

The inductor stores charges when the switch is ON and when the power switch is OFF, the polarity of the Inductor slows down so that the power flows through the load and diode and back to the inductor. So the current direction with the inductor remains the same.

Mode 2:- Switch is OFF, Diode is On

In this mode the polarity of the inductor is reduced and the energy stored in the inductor is released and finally dispersed against the load and this helps to maintain the flow of energy in the same load with the load and increase the output. The voltage as an inductor now operates as a source in conjunction with the input source.


  • Battery Charger / USB Charging Ports for Portable Devices:

Everyone wants their smartphone, tablet, or portable battery pack to charge quickly without heating their portable devices. A BUCK compatible converter can be used for this application. Generally, the mobile device's charging port is a micro USB port.


The voltage generated by a solar panel does not change constantly, it varies according to the intensity of the sunlight, for example the electric power of a solar panel can range from 10V to 18V and requires charging. a battery with a normal voltage of 12V and then we need to reduce 18V to 12V and increase 10V to 12V. This fixed output voltage is detected by a close loop system.

  • AMOLED Displays (Active Matrix OLED) for Portable Devices:

 Enabling AMOLED displays on portable devices requires flexible DC-DC converters that provide high power efficiency and robust output voltage.


➨It performs step-up or step-down voltage using least components.
➨It offers lower operating duty cycle.
➨It offers greater efficiency through wide input and output voltage ranges.
➨It is cheap compare to most of the converters.


➨High gain cannot be achieved with this type of converter as efficiency does not work for maximum gain (i.e., very small duty cycle or large duty cycle).

➨No isolation from the input side to the output side which is very important for most operating systems.


Today's sophisticated systems continue to add additional functions that require multiple power supply levels. We can use DC-DC switch converters in many applications. With this simple process and parameter / application reference, system designers can choose the best converter for any application.

Power supply & voltage regulators

Leave a comment

All comments are moderated before being published