Electrical Engineering ⇒ Topic : Thyristor Choppers

Thyristor Choppers

If a high-speed switch is inserted between the D.C. source and the load the fixed voltage of a D.C. source can be converted into an adjustable average voltage across the load. This high- speed switch is called the chopper. A chopper is a D.C. to D.C. convertor and its basic circuit is shown in Fig.(a) and (b).

                             (a) Basic circuit                                                                                   (b) Output voltage

                                                                               Fig.  (b) Voltage chopping 

The average value of load voltage or output voltage V₀ for a resistance load

From the above equation it can be concluded that following are the three ways of obtaining the variable mark-space ratio or time-on to time-off ratio (time ratio control TRC) for voltage ' control :

• By varying the duration of on-time with respect to off-time keeping the total time period T constant;
• By keeping the on-time constant and varying the frequency;
• By adjustment of both.