Step-Up Chopper With Low Pass Filter
A boost converter is a type of DC-DC converter that increases the voltage level of an input DC source . It operates on the principle of energy storage and transfer. The converter consists of an inductor , a diode ,capacitor and a switch . Initially the switch is closed allowing current to flow through the inductor ,storing energy in its magnetic field. When the switch opens the magnetic field collapses, inducing a voltage across the inductor . The diode conducts , transferring stored energy to the output capacitor effectively boosting the output voltage . By controlling duty cycle of the switch , the output voltage can be regulated .
Case 1
When switch in a step up chopper is in the ON state , it acts as a closed circuit , offering ideally zero resistance to the flow of current . During this ON state , the DC input voltage is applied across the circuit , allowing current to flow through the switch and the inductor . The inductor stores energy in the form of a magnetic field. Let’s us consider that the switch is ON for a duration TON . As current flows through the inductor , it ramps up, and energy is stored in the magnetic field .
Simultaneously, the load connected to the circuit receives a fraction of this energy , leading to an increase in voltage across the load. After the ON state , the switch transitions to the OFF state , the switch is open, and the inductor discharges its stored energy through the load. The diode, typically connected in parallel with the load, allows the current to continue flowing in the same direction. By controlling the ratio of the ON time to the total switching period , the duty cycle , the average output voltage can be adjusted . This ability to regulate the duty cycle enables the step-up chopper to increase the output voltage level compared to the input voltage , making it a versatile component in DC- DC voltage conversion circuits .
When switch S is ON , inductor will starts charging .
VL = Vs
I c + I0 = 0
I c = -I0
Case 2
When switch in a step up chopper is in the OFF state, the polarity of the inductor is reversed. The energy stored in the inductor during the ON state is now released , and it acts as a source , helping to maintain the flow of current in the same direction through the load . This mode contributes to stepping up the output voltage. As the switch is off , the inductor discharges its stored energy, and the diode connected in parallel with the load allows the current to continue flowing in the same direction.
The load resistance plays a crucial role in dissipating the energy released by the inductor. The inductor ,now acting as a source , contributes to the overall output voltage , effectively boosting the voltage across the load. This process of releasing stored energy from the inductor during the off state is essential for achieving a higher output voltage compared to the input voltage . By carefully controlling the ON and OFF times of the switch, the step-up chopper efficiently regulates the energy transfer, making it a valuable component in various applications where voltage conversion and regulation are required .
When switch S is OFF , diode D is forward biased and inductor will starts discharging .
V L = Vs – V0
I c = IL – I0
Since the average voltage across the inductor is zero
V0 (DTs) + (Vs – V0) (1 – D)Ts = 0
V0 = [1 /(1-D)] Vs
Vs * Is = V0 * I0
Is = I0/(1 -D)
Ripple in the Inductor Current
During ON period -:
VL = Vs
L (di L /dt on) = Vs
L (Δ i L/DTs) = Vs
Δ i L = DVs /L f
Ripple in the Output Voltage or Capacitor Voltage
During ON period , capacitor is feeding the load:
I c = -I0
C (d V c /dt) = – I0
C (Δ V c / DTs ) = – I0
Δ V c= DI 0/ f C
Step Up Chopper
Choppers are widely employed in applications like battery charging, voltage regulation in power systems, motor drives, and renewable energy systems. Additionally, choppers can be integrated with filters, such as low-pass filters to reduce voltage ripples and harmonics in the output waveform, ensuring a stable and clean power supply. This feature is particularly important in sensitive electronic devices and applications where a constant and high-quality power source is essential for optimal performance. Overall, choppers play a crucial role in modern power electronics, enabling efficient and controlled power conversion in diverse electrical systems.
Table of Content
- Chopper
- Step-Up Chopper
- Construction
- Working Principle
- Step-Up Chopper With Low Pass Filter
- Advantages
- Disadvantages
- Applications
- Solved Example