Experiment

Aim of the experiment

i. To understand the basic circuit and operation of a simple Boost Converter.

ii. To study Continuous, Discontinuous and Boundary Conduction Modes of the Boost

Converter by varying.

a. Duty cycle

b. Switching frequency

c. Load

Required components and equipments

1. MOSFET Irf740

2. Driver IC IR2110

3. Inductor

4. Capacitor

5. Diode

6. Resistive load

Theory

A DC-DC converter(chopper) is a device that accepts a DC input voltage and produces a DC output

voltage. Typically the output produced is at a different voltage level than the input. In addition,

DC-to-DC converters are used to provide noise isolation, power bus regulation, etc. Here we are

going to study boost converter.

A boost converter (step-up converter) is a power converter with an output dc voltage greater

than its input dc voltage. Since power (V*I) must be conserved, the output current is lowered

from the source current. It is a class of switching-mode power supply (SMPS) containing at

least two semiconductor switches (a diode and a transistor) and at least one energy storage

element. Filters made of inductor and capacitor combinations are often added to a converter’s

output to improve performance. Fig 2.1 shows the power circuit schematic of a boost converter.

Boost Converter Schematic Diagram

The basic principle of a boost converter consists in 2 distinct states .

1) In the On-state, the switch SW is closed, resulting in an increase in the inductor

current.

Fig.2 Switch is closed

2) In the Off-state, the switch is open and the only path offered to inductor current is through the

fly back diode D, the capacitor C and the load R. It results in transferring the energy

compilrd on the On-state into capacitor.

Fig.3 Switch is open

The boosting of voltages in the boost converter can be related through the following

equation

Vo = Vi

/ (1-D)

The above relation shows that in case of D=0 there will be no boosting.

Note: Avoid D=0 and D=1 keep the range of duty cycle 10 % to 90 %

Procedure

Construct the circuit as shown in the fig.1. Do the changes as instructed below.

Varying Duty Cycle

Set the duty ratio at 50%, switching frequency at 100kHz and RL

= 1kΩ.

1. Vary the duty ratio from 10 % to 90 % (in steps of 10%). Draw the input and output wave

forms.

2. Measure the average output voltage for the corresponding duty ratio.

3. Calculate the theoretical average output voltage for the corresponding duty ratios.

Varying the frequency

1. Set the duty ratio to 50 %.

2. Measure the peak-peak output ripple voltage.

3. Repeat the above procedure for different switching frequencies (1kHz, 2kHz, 3kHz). Draw the

corresponding input and output wave forms.

Circuit1

Fig. 4 Boost converter

Observation:

Varying Duty Cycle

Observe and make a copy of the switch input voltage, output ripple voltage, output current and

capacitor current waveforms.

Varying Duty Cycle

Observe and make a copy of the sw input voltage, output ripple voltage, output current and

capacitor current waveforms and draw it on the given graph paper.

S.No Vin Vo f δ L C Load Ripples Remarks

1.(H)

1.(S)

2. (H)

2.(S)

3. (H)

3.(S)

Varying the frequency

Observe and make a copy of the switch input voltage, output ripple voltage, the output current

and capacitor current waveforms and draw it on the given graph.

Varying Duty Cycle

Observe and make a copy of the sw input voltage, output ripple voltage, output current and

capacitor current waveforms and draw it on the given graph paper.

S.No Vin Vo f δ L C Load Ripples Remarks

1.(H)

1.(S)

2. (H)

2.(S)

3. (H)

3.(S)

Conclusion :