Boost Regulator Tutorial: Topology Working

Boost Regulator Tutorial:

The boost regulator gives higher output voltage than the input voltage. It is similar to that of setup chopper.
The circuit diagram of the boost converter is shown below:

Boost Converter Operation:

To understand the operation, assume that the switch is turned on and conducts from 0 to T/2.

  • So during that time, the current flows in the inductor (Vs - L - SW).
  • The inductor stores the energy during this period.
  • During this period, the output voltage and current is maintained by the filter capacitor ( ie, energy is transferred from capacitor to load).

Please refer the wave forms figure. At the time T/2, the switch is turned off.

  • So the inductor generates a large voltage L.di/dt with the polarity shown in the above figure.
  • Due to this, the anode terminal of the diode got high voltage ( ie, forward biased condition).
  • Thus the diode D starts conducting and maintains the load current.
  • Remember that during this time (T/2 to T) the energy is transferred from inductor to capacitor and load.

Boost converter Operation Summary:

When the switch is on,

  • The diode D1 is reverse biased, and Vin is applied across inductor, L1.
  • Current builds up in the inductor to a peak value, either from zero current in a discontinuous mode, or an initial value in the continuous mode.

When the switch turns off,

  • The voltage across L1 reverses, causing the voltage at the diode to rise above the input voltage.
  • The diode then conducts the energy stored in the inductor, plus energy direct from the supply to the smoothing capacitor and load.
  • Hence, Vo is always greater than Vin, making this a step-up converter.

Features of Boost Topology:

  • It ‘boosts’ the voltage to a higher level.
  • Its output voltage VO is always higher than the input voltage VIN for steady-state operation.
  • The converter consists of an inductor L, a power MOSFET, a diode D1, a filter capacitor C, and a load resistor RL.
  • The switch S is turned on and off at the switching frequency fs = 1/T with the ON duty ratio D = ton/T, where ton is the time interval when the switch S is ON.
  • The boost converter can operate in either continuous or discontinuous conduction mode, depending on the waveform of the inductor current.
  • The boost converter is a step-up circuit.
  • It has only a transformer-less version.
  • It can be operated in either CCM or DCM.
  • Its advantage is that the input current has a continuous (non-pulsating) waveform.
  • It is easy to drive the MOSFET in the boost converter because the gate is referenced to ground.
  • The converter should not be used at D close to 1 because of its poor efficiency.
  • The peak-to-peak current through the filter capacitor is very high; it is equal to the peak-to-peak value of the diode current IDM.

Advantages of Boost converter:

  1. It will set up the output voltage without a transformer.
  2. It gives high-efficiency due to single switch operation.

Disadvantages of Boost Converter:

  1. High peak current flows through to switch.
  2. Output voltage is highly sensitive to changes in duty cycle.
  3. Large inductor and capacitor is required to provide ripple free output.


  1. The boost topology is very popular for capacitive load applications such as photo-flashers and battery chargers.
  2. Furthermore, the continuous input current makes the boost a popular choice as a pre-regulator, placed before the main converter.
  3. The main functions being to regulate the input supply and to greatly improve the line power factor.

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Read More:
DC - DC Chopper: Principle of Operation 
Step Up Chopper - Basics, Operation, Application 
DC to AC Converter - Inverter - An Introduction 
Zener Diode Basics, Operation, Characteristics 

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