AC-DC Power Supply Control Circuit for Sinusoidal Input Current
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Solution Overview
Problem
Traditional constant on-time control methods for switching power supplies result in non-sinusoidal input current waveforms, leading to high total harmonic distortion (THD) and suboptimal power factor (PF), which are not suitable for modern energy-saving requirements.
Innovation Solution
A control circuit for AC-DC power supplies that includes a PWM signal generating circuit and a reference voltage generating circuit, which generates a PWM signal based on the inductor current and input voltage to control the power stage circuit, ensuring the input current waveform matches the input voltage waveform, thereby achieving sinusoidal input current and reduced THD.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If constant on-time control method is used, then control simplicity is maintained, but input current waveform distortion increases leading to high THD
Solution Approach 1:
The patent changes the control parameter from fixed on-time to variable on-time that adapts to input voltage variations. The control circuit dynamically adjusts the on-time of the switching transistor based on the instantaneous input voltage, transforming the control strategy from static to dynamic parameter adjustment, thereby achieving sinusoidal input current while maintaining circuit simplicity.
Solution Approach 2:
The patent implements a feedback mechanism where the control circuit continuously monitors the input voltage and adjusts the switching duty cycle accordingly. This closed-loop control ensures that the input current follows the sinusoidal waveform of the input voltage, reducing THD while keeping the control structure relatively simple through intelligent feedback regulation.
2Device complexity
If traditional switching control is used, then circuit structure remains simple, but power factor is suboptimal
Solution Approach 1:
The patent introduces dynamic control to a previously static circuit structure. By making the switching on-time variable and adaptive to input conditions, the circuit dynamically optimizes its operation to achieve high power factor without adding complex circuit topologies, thus improving energy utilization while maintaining structural simplicity.
3Object-generated harmful factors
If sinusoidal input current is achieved through advanced control, then THD is reduced, but control complexity increases
Solution Approach 1:
The patent replaces complex mechanical or analog control mechanisms with a simplified digital or microcontroller-based control system. This substitution enables sophisticated sinusoidal current control and THD reduction through software algorithms while keeping the hardware structure relatively simple, achieving low THD without proportionally increasing overall system complexity.
Data Source
AI summary
A control circuit for controlling an AC-DC power supply, can include: a pulse-width modulation (PWM) signal generating circuit configured to generate a PWM signal in accordance with a reference voltage and a current sampling signal representing an inductor current flowing through an inductor of the AC-DC power supply, and to control a power stage circuit of the AC-DC power supply in accordance with the PWM signal; and a reference voltage generating circuit configured to generate the reference voltage based on an input voltage of the AC-DC power supply.