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A chopper is a.
Time ratio controller
AC to DC converter
DC transformer
High speed semiconductor switch
High speed semiconductor switch
A chopper is essentially a high-speed static semiconductor switch used to convert fixed DC input voltage directly into a variable DC output voltage. It acts as the DC equivalent of an AC transformer, providing step-up or step-down DC voltage control using power switching devices like SCRs, MOSFETs, or IGBTs.
IEEE Std 1662 / IEC 60146
A chopper is essentially a high-speed static semiconductor switch used to convert fixed DC input voltage directly into a variable DC output voltage. It acts as the DC equivalent of an AC transformer, providing step-up or step-down DC voltage control using power switching devices like SCRs, MOSFETs, or IGBTs.
VoтАЛ=╬▒тЛЕVsтАЛ=(TTONтАЛтАЛ)VsтАЛ тАФ Output voltage for a step-down (buck) chopper
VoтАЛ=1тИТ╬▒VsтАЛтАЛ тАФ Output voltage for a step-up (boost) chopper
╬▒=TONтАЛ+TOFFтАЛTONтАЛтАЛ=fтЛЕTONтАЛ тАФ Duty cycle of the chopper switch
A chopper operates by rapidly connecting and disconnecting the load to the constant DC supply using high-speed semiconductor switches. By controlling the duty cycle (TONтАЛ/T), the average output voltage across the load can be continuously varied above or below the input DC source level.
Choppers perform static conversion of DC voltage without magnetic flux linkages (unlike AC transformers).
High switching frequencies (kHz range) allow reduction in the size of external filter inductors and capacitors.
Power electronics devices such as SCRs, MOSFETs, IGBTs, or GTOs serve as the solid-state switching elements.
Time Ratio Control (TRC) and Current Limit Control (CLC) are the primary control strategies used.
High efficiency due to reduced switching losses in static semiconductor devices
Compact size and light weight compared to electromechanical DC motor generators
Fast dynamic response with fine control over average output voltage
Generates high-frequency electrical noise and electromagnetic interference (EMI)
Requires smoothing inductors and filters to limit ripple in output current
DC traction system speed control (electric trains, trolley buses, EVs)
Switched-Mode Power Supplies (SMPS)
Regenerative braking of DC motors
Option A is a control technique (Time Ratio Control) used within choppers, not the definition of the chopper itself.
Option B describes a rectifier, which converts AC to DC.
Option C is a common functional metaphor ('DC Transformer'), but technically incorrect because magnetic transformers rely on Faraday's law and AC flux, whereas a chopper is physically a switching converter.
D is correct тАФ A chopper is fundamentally a static high-speed semiconductor switch that turns ON and OFF rapidly to step up or step down DC voltage.
Remember that while a chopper is often called a 'DC transformer' informally in exams, its physical identity is always a static high-speed semiconductor switch operating on Time Ratio Control (TRC).