PWM Control Circuit for Flyback Converter Line Regulation
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Solution Overview
Problem
Existing LED driving circuits face challenges in maintaining line regulation characteristics when input voltage magnitude changes, leading to instability in output voltage.
Innovation Solution
A PWM control circuit that stores the peak value of a feedback signal from the secondary side output for one period and inverts it to generate a reference signal, which is then compared with a reference waveform to produce a PWM control signal, improving line regulation by adjusting the on-time of the power transistor switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PWM control is used with error amplifier, then constant voltage/current structure is implemented, but line regulation characteristics deteriorate when input voltage magnitude changes
Solution Approach 1:
The patent stores the peak value of the feedback signal in advance using a sample-and-hold circuit before it is needed for PWM control. This preliminary action allows the stored peak value to be used as a reference for the next period's PWM control, enabling the system to compensate for input voltage changes proactively rather than reactively, thus improving line regulation characteristics.
Solution Approach 2:
The patent implements a feedback mechanism where the peak value of the secondary side output feedback signal is detected, stored, and then used as a reference signal for PWM control. This closed-loop feedback approach allows the system to automatically adjust the PWM duty cycle based on actual output conditions, improving both line regulation and output voltage stability.
2Reliability
If peak value storage and inversion is implemented, then line regulation is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple functions into integrated circuit blocks: the peak detector, sample-and-hold circuit, and inverter are merged into a compact PWM control circuit module. The feedback signal processing path is integrated with the PWM generation path, allowing peak value storage and reference signal generation to occur within the same circuit architecture without requiring separate standalone components for each function.
Solution Approach 2:
The stored peak value serves multiple purposes: it acts as a reference signal for PWM control, provides feedback for output regulation, and enables compensation for input voltage variations. This multi-functional use of the stored peak value reduces the need for additional dedicated components, thereby limiting the increase in device complexity while achieving improved line regulation.
Data Source
AI summary
Disclosed herein are a PWM control circuit, a flyback converter, and a PWM control method. The PWM control circuit includes: a peak storing and reference signal generating unit storing a peak value of one period of a feedback signal from a secondary side output and inverting the peak signal and outputting the inverted peak signal as a reference signal; and a PWM control signal generating unit generating a PWM control signal by using an output obtained by comparing the reference signal with a reference waveform from the peak storing and reference signal generating unit. In addition, the flyback converter including the same and the method for controlling PWM are proposed.