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Boost Converter


Boost Converter


The boost converter is a power converter and found in many applications where input voltage is not sufficient to drive the application.
Boost Converter
Boost Converter Assembled Circuit
Let see more details about boost converter;

What is Boost Converter?

  • A boost converter is a type of DC-to-DC power converter that steps up the applied input voltage and steps down the current.
  • In other words, we can say that a boost converter is a DC to DC converter with an output voltage higher than the applied input voltage.
  • A boost converter sometimes also called as “step-up converter” as it "steps up" the applied input voltage.
  • Here the output current is lower than the applied source current to save power or to get more efficiency.
  • It is a type of switched-mode power supply which contains a diode, a FET, an inductor and an electrolytic capacitor.

What is the use of Boost Converter

  • Switched mode power supplies can be used for many types of applications such as; DC - DC converters.
  • Many times to run the motors, to operate tools, to charge the battery bank, etc. we need high DC voltage.
  • But mostly the available DC voltage (mostly from battery) is not sufficient to run these applications we need a higher DC voltage as compare to applied DC input voltage.
  • To run the high power applications, we can use many batteries by connecting in series and parallel combination, but this solution will consume more space and will also increase the cost.
  • By using the Boost Converter, we can boost the battery voltage, AC- DC rectifier voltage, DC generators voltage, etc. to required high voltage.
  • But with the increase in output voltage there is decrease in output current.

Boost Converter Circuit

Figure at below shows the basic circuit of a Boost converter.

Boost Converter
Boost Converter Circuit
  • In this we can see that a MOSFET M1 is used as switching device, an inductor L1 is used for storing the energy, Diode D1 which conducts when it is forward bias and at last an Electrolytic capacitor C1 is used to store the charge.
  • We can see that the used components are same but their placement in the circuit has been rearranged.

Working of Boost Converter

Below images and explanations clears the working of boost converter;

Working of Boost Converter when switch is ON

Working of Boost Converter
Working of Boost Converter when switch is ON
  • In above figure we can see that a pulse input is applied to the MOSFET. When high voltage is available at MOSFET gate, it starts to conduct.
  • As MOSFET conducts, it will make current to pass from drain to source terminal of MOSFET and hence inductor L1 start to stores the energy as the current passes through it, i.e. from power supply’s +ve to -ve terminal.
  • Inductor L1 stores energy in the form of the magnetic field.
  • No current passing through the diode D1, capacitor C1 and through the load which have high impedance as compare to the MOSFET’s drain to source path.
Working of Boost Converter when switch is OFF

Working of Boost Converter
Working of Boost Converter when switch is OFF
  • In above figure we can see that when low pulse voltage is available at MOSFET gate, it didn’t conduct.
  • As MOSFET not conducts, it will make current not to pass from drain to source terminal of MOSFET.
  • Because of MOSFET’s fast ON and OFF switching a sudden drop in current will appear, which will generate a back e.m.f. in opposite direction in inductor L1.
  • So, two voltages will appear across inductor L1. First is applied input voltage and second is back e.m.f.
  • Now inductor starts to pass the current through forward biased diode D1.
  • This current charges further the electrolytic capacitor C1 and further it is applied to the connected load.
  • Capacitor C1 will charge with the voltage, “Input voltage + back e.m.f. voltage”.
Working of Boost Converter when switch is again ON

Working of Boost Converter
Working of Boost Converter when switch is again ON
  • In above figure we can see that when again high pulse voltage is available at MOSFET gate, it starts to conduct.
  • When MOSFET is ON the D1 acts as reverse biased i.e. cathode of D1 diode is more positive, because it is connected to the capacitor C1 and it is already fully charged.
  • As the diode D1 is not conducting, the load at output will get voltage from capacitor C1, until it discharges.
  • Capacitor fully drains and it will recharge again when the MOSFET M1 switch OFF again.
  • That’s why we get constant output voltage across the load.

Modes of operation of Boost converter

There are three modes of operation of boost converter;

  • Continuous conduction mode (CCM)
In this mode of boost converter mode, the current flowing through inductor never goes to zero. In other words, we can say that the inductor partly discharges the current before the start of the new switching cycle.

  • Discontinuous conduction mode (DCM)
In this mode of boost converter, the current flowing through inductor goes to zero. In other words, we can say that the inductor is fully discharged at the end of present switching cycle.

  • Critical conduction mode (CRM)
The critical conduction mode works in the boundary of CCM and DCM.

Please refer below link of our previous article to get more details about modes of operation of boost converter;

"Power Factor Correction and its modes of operation"

Boost Converter IC UC3854

UC3854 is High Power Factor Preregulator and widely used in the power factor correction applications i.e. for active PFC. Where it controls switching of MOSFET to get high voltage at the output.

Please refer our previous articles to get more details about boost converter design, boost converter calculations and boost converter schematic using UC3854;

"Design of Boost Converter using UC3854"

Boost Converter IC L6562

The L6562 is a transition mode PFC controller and widely used in power factor correction and lighting applications.

Please refer our previous article to get more details about boost converter calculations using L6562;

"Critical Conduction Mode Boost Converter Calculations using L6562"

Application of Boost Converter

  • In most of DC power supplies they are used to boost low voltage to high voltage.
  • In lighting applications to drive LED lamps, Fluorescent lamps and Halogen lamps.
  • In automobile application for battery charging.
  • In charging of battery bank.
  • It can be seen in regenerative braking of DC motors.
  • In Power Factor Correction

Conclusion

Boost converter is widely used power converter topology. We can use it in the applications where available input voltage is not sufficient to drive the circuit properly. With the implementation of boost converter, we can achieve high voltage at the output but also it decreases the output current because the output wattage is constant.

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