Introduction And Step-Down Chopper

DC CHOPPERS

It is a circuit which converts D.C voltage into D.C voltage while doing so, the magnitude of output D.C voltage may be less or greater than the magnitude of input voltage. Basically, there are two types of Chopper:

• Step-Up D.C Chopper
• Step-Down D.C Chopper

Step-Down D.C Chopper

It is a circuit which converts D.C voltage into D.C voltage while doing so, the magnitude of output D.C voltage is less in magnitude than that of the input voltage.

The principle of operation of the chopper can be explained from the figure above where the transistor is used as a switching device. When a pulse of certain positive value is provided to the base terminal of the transistor for the period of time t₁ ,it remains in the state of conduction and when a zero value is supplied to it, the transistor switch will be in the open state for a time period t₂.Thus,for the time period of t1, the voltage across the load is V while for other t₂ period the voltage across the load is zero. It can be observed from the figure besides.

Here,

t₁ = ON Time

t₂ = OFF Time

T = t₁ + t₂

F = 1/T

Average value of V_o can be determined as

$$Vo = \int\limits_0^{t1} {Vdt} $$

= V*t1/T

= V*(t1/(t1 + t2))

= k V

Where k is duty cycle. K =(t1/(t1 + t2))

The mode of operation of chopper can be categorized into two types;

1) Constant Frequency Mode

In this mode, time period is kept constant and T_on is varied such that T_on + T_off = T

2) Variable Frequency Mode

In this mode, On time period is kept constant and variable frequency is obtained by varying off time period of the switching device

References

1) TutorialsPoint. power_electronics_quick_guide. n.d. 10 5 2016. <http://www.tutorialspoint.com/power_electronics/images/current_and_voltage_waveform.jpg>.

2) Tutorials Area. Step Down Chopper. n.d. 10 05 2016. <http://www.tutorialsarea.com/EEE/Power Electronics/images/Stepdown chopper.png>.