Explore how Current-Mode PWM Controllers work, their principle of operation, and their advantages in power supply systems.
Introduction to Current-Mode PWM Controllers
Current-Mode Pulse Width Modulation (PWM) controllers have become a critical component in various applications, including power supply systems and electronic devices. They control power by adjusting the duty cycle of a PWM signal according to the instantaneous load current, offering fast response, improved line regulation and inherent cycle-by-cycle current limiting.
Working Principle of Current-Mode PWM Controllers
The basic working principle of a current-mode PWM controller involves two primary steps: current sensing and comparison. The controller senses the inductor current and compares it with a reference current. The PWM signal’s duty cycle is then adjusted according to this comparison.
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Current Sensing: The controller senses the inductor current during the ON time of the switch (MOSFET or BJT) in a power supply circuit. This current sensing can be direct or indirect, based on the design of the controller.
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Comparison: The sensed inductor current is then compared to a reference current. This reference current is derived from the output voltage error, which is the difference between the desired and actual output voltage.
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Adjustment: If the inductor current is greater than the reference current, the PWM controller decreases the duty cycle, reducing the output voltage. Conversely, if the inductor current is less than the reference current, the duty cycle is increased, boosting the output voltage.
Advantages of Current-Mode PWM Controllers
Current-mode PWM controllers offer several advantages over their voltage-mode counterparts, including:
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Fast Transient Response: The controller’s fast response to load changes is primarily due to its control based on instantaneous current rather than average current.
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Improved Line Regulation: These controllers provide improved line regulation due to immediate correction of output voltage changes.
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Inherent Over-Current Protection: The cycle-by-cycle current limiting feature of current-mode controllers provides inherent protection against over-current conditions, enhancing the safety of the overall system.
In conclusion, current-mode PWM controllers play a crucial role in enhancing the efficiency and safety of various electronic systems. Understanding their working mechanism is key to leveraging their full potential.
