Flyback Converter Primary-Side Control Voltage Accuracy
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Solution Overview
Problem
Conventional primary-side-control flyback switching power supplies face challenges in accurately maintaining output voltage stability, especially when operating in continuous current mode (CCM), due to voltage drops on the secondary side, which cannot be completely eliminated by existing error correction techniques.
Innovation Solution
An apparatus and method that includes an output voltage error detection unit, a correction amount calculation unit, a reference voltage generation unit, and a PWM control unit to detect the auxiliary winding voltage after a secondary conduction period starts, calculate the secondary voltage drop based on primary current, and adjust the switching element to maintain constant output voltage by adding a correction amount to the target voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional primary-side-control flyback switching power supplies are used, then cost and number of parts are reduced, but output voltage accuracy deteriorates due to secondary side voltage drops
Solution Approach 1:
The patent applies preliminary action by calculating the secondary voltage drop in advance based on primary current characteristics before the secondary conduction period ends. The control circuit computes the voltage drop amount during the secondary conduction period and uses this pre-calculated value for error correction, rather than attempting to measure the actual secondary voltage after the drop occurs. This allows the system to compensate for the voltage drop proactively, maintaining output voltage accuracy while using the simplified primary-side-control topology without secondary voltage sensing components.
2Measurement precision
If existing error correction techniques are used, then output voltage control is improved in discontinuous current mode, but accuracy deteriorates in continuous current mode due to inability to completely eliminate secondary voltage drop errors
Solution Approach 1:
The patent implements dynamics by adapting the error correction method based on the operating mode. The control circuit dynamically determines whether the power supply is operating in discontinuous current mode (DCM) or continuous current mode (CCM) and applies appropriate correction strategies. In DCM, the circuit uses sampling at the end of secondary conduction, while in CCM, it uses real-time calculation based on primary current. This dynamic adaptation allows accurate output voltage control across both operating modes, resolving the contradiction between precision and versatility.
Solution Approach 2:
The patent changes the correction parameter from fixed sampling-based correction to dynamic calculation-based correction. By using the primary current waveform characteristics and calculating the secondary voltage drop in real-time, the system adjusts the correction amount according to actual operating conditions. This parameter change enables accurate compensation in both DCM and CCM, where conventional fixed correction methods fail in CCM due to the persistent secondary current.
3Stability of the object's composition
If secondary voltage drop correction is attempted, then output voltage stability is improved, but device complexity increases due to additional control circuit functions
Solution Approach 1:
The patent applies universality by making the primary-side-control circuit perform multiple functions: it simultaneously controls the switching element, detects primary current characteristics, calculates secondary voltage drop, and performs error correction all within a single control integrated circuit. The control circuit uses the auxiliary winding voltage for both timing detection (when secondary conduction starts) and as part of the feedback mechanism. This multi-functionality achieves output voltage stability without adding separate dedicated correction hardware, thus limiting the increase in device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution ensures accurate output voltage control in both discontinuous current mode (DCM) and continuous current mode (CCM), effectively minimizing errors caused by secondary side voltage drops, thereby maintaining stable output voltage regardless of operating conditions.
Implementation Method 1
a transformer to convert an input voltage on a primary side into a direct-current output voltage on a secondary side based on switching of a switching element
Data Source
AI summary
An output voltage error detection unit outputs an auxiliary winding voltage generated across an auxiliary winding having the same number of turns as a secondary winding a certain period after a secondary conduction period starts. A correction amount calculation unit calculates a secondary voltage drop caused by a secondary current flowing in the conduction period based on a primary current flowing when the conduction period starts and outputs a calculation result as a correction amount. A reference voltage generation unit generates a reference voltage by adding the correction amount to the output voltage. A control unit generates a feedback signal to minimize the error between the auxiliary winding voltage obtained after a certain delay period and the reference voltage. A PWM signal generation unit controls a PWM signal based on the feedback signal, adjusts switching of the switching element, and maintains the output voltage at a constant level.