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:
- It will set up the output voltage without a transformer.
- It gives high-efficiency due to single switch operation.
Disadvantages of Boost Converter:
- High peak current flows through to switch.
- Output voltage is highly sensitive to changes in duty cycle.
- Large inductor and capacitor is required to provide ripple free output.
- The boost topology is very popular for capacitive load applications such as photo-flashers and battery chargers.
- Furthermore, the continuous input current makes the boost a popular choice as a pre-regulator, placed before the main converter.
- The main functions being to regulate the input supply and to greatly improve the line power factor.
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