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The load voltage of a chopper can be controlled by varying the_____.
Duty cycle
Firing angle
Reactor position
All
Duty cycle
A DC chopper is a static power electronic device that converts fixed DC input voltage directly into a variable DC output voltage. The average output (load) voltage is controlled primarily by adjusting the duty cycle D (or ╬▒), which is the ratio of switch ON-time to the total switching period.
IEEE 519 / IEC 60146 Power Converter Standards
A DC chopper is a static power electronic device that converts fixed DC input voltage directly into a variable DC output voltage. The average output (load) voltage is controlled primarily by adjusting the duty cycle D (or ╬▒), which is the ratio of switch ON-time to the total switching period.
VoтАЛ=DтЛЕVsтАЛ=(TONтАЛ+TOFFтАЛTONтАЛтАЛ)VsтАЛ тАФ Average load voltage of a step-down chopper
D=TTONтАЛтАЛ=fтЛЕTONтАЛ тАФ Duty cycle definition (f is switching frequency)
VrmsтАЛ=DтАЛтЛЕVsтАЛ тАФ RMS output voltage of step-down chopper
The chopper operates by rapidly switching a semiconductor switch (like a MOSFET, IGBT, or Thyristor) ON and OFF. During TONтАЛ, the load is connected to the supply source, delivering full input voltage VsтАЛ. During TOFFтАЛ, the load is disconnected (or freewheeling occurs), making the output voltage zero. By controlling TONтАЛ relative to T, the average load voltage VoтАЛ=D├ЧVsтАЛ is varied.
Duty cycle D varies between 0 and 1 (0%тЙдDтЙд100%).
Time Ratio Control (TRC) varies TONтАЛ with constant frequency f, or varies f with constant TONтАЛ.
Firing angle ╬▒ controls AC-to-DC phase-controlled thyristor converters, not DC-to-DC choppers.
High efficiency due to switching operation rather than power dissipation
Fast dynamic response and compact size
Smooth and continuous control of DC voltage
Generates high-frequency electromagnetic interference (EMI)
Requires filter components to smooth output current and voltage ripple
DC motor speed control in electric traction and EV drives
Switched Mode Power Supplies (SMPS)
Regenerative braking systems
Option B (Firing angle) is incorrect: Firing angle ╬▒ controls phase-controlled rectifiers (AC to DC converters).
Option C (Reactor position) is incorrect: Reactors (inductors) limit fault current or ripple, but do not provide active load voltage control.
A is correct тАФ The load voltage of a chopper is directly proportional to its duty cycle D=TONтАЛ/T.
Always remember: Choppers vary output DC voltage using Duty Cycle (D), whereas Phase-Controlled Rectifiers control output DC voltage using Firing Angle (╬▒).