Power Supply Control Circuit Using Auxiliary Winding Feedback
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Solution Overview
Problem
In power supply systems using synchronous rectifiers, the primary side controller lacks accurate estimation of output voltage, leading to improper regulation and inefficiency.
Innovation Solution
A power supply control circuit that utilizes an auxiliary winding to generate a voltage sample signal representative of the output voltage, allowing for improved feedback and regulation by detecting changes in the signal during the off-time of the power switch, enabling accurate control of the primary side current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If primary side controller is used without auxiliary winding feedback, then device complexity is reduced, but output voltage regulation accuracy deteriorates
Solution Approach 1:
An auxiliary winding is introduced as an intermediary element on the primary side that indirectly provides feedback information about the output voltage. The auxiliary winding couples magnetically to the transformer and generates a voltage proportional to the primary current, which serves as a mediator to infer secondary side conditions without direct electrical connection.
Solution Approach 2:
The auxiliary winding creates a copied version of the primary voltage waveform that can be processed to extract information about the output voltage. By sampling and processing this copied signal, the controller obtains an estimate of the output voltage without requiring direct feedback from the secondary side.
2Loss of energy
If synchronous rectifier is used, then power conversion efficiency is improved, but control difficulty increases due to lack of direct feedback
Solution Approach 1:
A feedback mechanism is implemented using the auxiliary winding signal. The controller samples the auxiliary winding voltage during the off-time of the primary switch, processes this signal to estimate the output voltage, and uses this estimated feedback to adjust the duty cycle and control parameters, thereby maintaining stable operation of the synchronous rectifier.
Solution Approach 2:
The controller performs preliminary sampling of the auxiliary winding signal during the off-time of the primary switch before the next switching cycle begins. This preliminary action allows the controller to prepare the feedback information and adjust control parameters in advance, ensuring continuous and stable control of the synchronous rectifier.
3Measurement precision
If direct secondary side feedback is used, then output voltage regulation accuracy is improved, but device complexity and isolation requirements increase
Solution Approach 1:
The feedback function is segmented into two parts: the auxiliary winding on the primary side that captures voltage information, and the signal processing circuitry that extracts output voltage estimates from this information. This segmentation allows feedback to be obtained without requiring a complete secondary-to-primary feedback path, reducing complexity and isolation requirements.
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 enhances the accuracy of output voltage regulation by using the voltage sample signal as feedback, improving the control of the power switch and maintaining the output voltage within a desired range, even in the absence of direct secondary side feedback signals.
Implementation Method 1
A power supply control circuit that utilizes an auxiliary winding to generate a voltage sample signal representative of the output voltage
Data Source
AI summary
In one embodiment, a power supply controller, or alternately a semiconductor device having a power supply controller, may have a first circuit configured to form a sense signal that is representative of a signal from an auxiliary winding of a transformer. A feedback circuit may be configured to allow the sense signal to increase in response to a turn-off of the power switch, to subsequently detect a second increase of the sense signal prior to subsequently turning on the power switch, and to form a feedback signal as a value of the sense signal responsively to the second increase of the sense signal.