How does a synchronous buck converter regulate output voltage in continuous conduction mode?
1 Answer
A synchronous buck converter is a type of DC-DC power converter used to step down voltage levels efficiently. It operates by switching a series of transistors (usually MOSFETs) on and off to control the energy transfer from the input voltage source to the output load.
In continuous conduction mode (CCM), the inductor current never fully reaches zero during each switching cycle. Here's how a synchronous buck converter regulates the output voltage in CCM:
Reference Voltage and Error Amplification: The first step is to compare the actual output voltage with a desired reference voltage. The difference between these two voltages is the error voltage.
Feedback Loop and Error Amplifier: The error voltage is then fed into an error amplifier, which amplifies the error signal. The amplified error voltage is used to control the switching of the power transistors.
Pulse Width Modulation (PWM) Control: The amplified error voltage from the error amplifier is used to generate a pulse width modulated (PWM) signal. This PWM signal determines the ON and OFF times of the high-side and low-side synchronous rectifiers (usually MOSFETs) in the buck converter.
Synchronous Rectification: The synchronous rectifiers, which are usually MOSFETs, are used to replace the traditional diodes in a non-synchronous buck converter. They provide lower conduction losses during the rectification process.
Inductor Current Control: During the ON time of the high-side synchronous rectifier, current flows from the input source through the inductor, and energy is stored in the inductor's magnetic field. During the OFF time, the inductor current flows through the output load.
Inductor Energy Transfer: The energy stored in the inductor's magnetic field during the ON time is transferred to the output load during the OFF time. This energy transfer results in a regulated output voltage.
Voltage Feedback Loop: As the output voltage starts to approach the desired reference voltage, the error voltage decreases. This reduction in the error voltage causes the PWM control to adjust the duty cycle of the synchronous rectifiers, modulating the energy transfer to maintain the desired output voltage.
Steady-State Regulation: The process continues in a feedback loop, with the error voltage being continuously adjusted to maintain the output voltage at the desired level. The duty cycle of the synchronous rectifiers is controlled based on the error voltage, ensuring that the output voltage remains regulated even under varying load conditions.
In summary, a synchronous buck converter in continuous conduction mode regulates the output voltage by continuously adjusting the duty cycle of the synchronous rectifiers based on a feedback loop that compares the actual output voltage with a desired reference voltage. This regulation process ensures that the output voltage remains stable and closely follows the reference voltage.
In continuous conduction mode (CCM), the inductor current never fully reaches zero during each switching cycle. Here's how a synchronous buck converter regulates the output voltage in CCM:
Reference Voltage and Error Amplification: The first step is to compare the actual output voltage with a desired reference voltage. The difference between these two voltages is the error voltage.
Feedback Loop and Error Amplifier: The error voltage is then fed into an error amplifier, which amplifies the error signal. The amplified error voltage is used to control the switching of the power transistors.
Pulse Width Modulation (PWM) Control: The amplified error voltage from the error amplifier is used to generate a pulse width modulated (PWM) signal. This PWM signal determines the ON and OFF times of the high-side and low-side synchronous rectifiers (usually MOSFETs) in the buck converter.
Synchronous Rectification: The synchronous rectifiers, which are usually MOSFETs, are used to replace the traditional diodes in a non-synchronous buck converter. They provide lower conduction losses during the rectification process.
Inductor Current Control: During the ON time of the high-side synchronous rectifier, current flows from the input source through the inductor, and energy is stored in the inductor's magnetic field. During the OFF time, the inductor current flows through the output load.
Inductor Energy Transfer: The energy stored in the inductor's magnetic field during the ON time is transferred to the output load during the OFF time. This energy transfer results in a regulated output voltage.
Voltage Feedback Loop: As the output voltage starts to approach the desired reference voltage, the error voltage decreases. This reduction in the error voltage causes the PWM control to adjust the duty cycle of the synchronous rectifiers, modulating the energy transfer to maintain the desired output voltage.
Steady-State Regulation: The process continues in a feedback loop, with the error voltage being continuously adjusted to maintain the output voltage at the desired level. The duty cycle of the synchronous rectifiers is controlled based on the error voltage, ensuring that the output voltage remains regulated even under varying load conditions.
In summary, a synchronous buck converter in continuous conduction mode regulates the output voltage by continuously adjusting the duty cycle of the synchronous rectifiers based on a feedback loop that compares the actual output voltage with a desired reference voltage. This regulation process ensures that the output voltage remains stable and closely follows the reference voltage.