Buck-Flyback Power Supply Control Without Optocouplers
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Solution Overview
Problem
Conventional switching power supplies with single-stage designs face challenges in achieving high power factor and efficient voltage regulation without using optocouplers for galvanic isolation, leading to increased component costs and power losses.
Innovation Solution
A power factor-corrected step-down flyback converter with an auxiliary winding on the transformer is used to regulate the output voltage, where the voltage induced in the auxiliary winding is measured at specific instantaneous values of the pulsating DC input voltage to control the switching element, eliminating the need for an optocoupler and allowing for synchronous current and voltage curves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a optocoupler is used for galvanic separation to regulate output voltage, then voltage regulation is achieved, but device complexity and cost increase
Solution Approach 1:
The patent removes the optocoupler from the circuit by extracting the galvanic separation function. The auxiliary winding directly provides a voltage signal that reflects the output voltage, eliminating the need for optical isolation while maintaining voltage regulation capability.
Solution Approach 2:
The auxiliary winding serves multiple functions: it provides galvanic separation, enables output voltage regulation, and eliminates the need for separate optocoupler components. This multi-functional approach reduces overall device complexity.
2Object-generated harmful factors
If a two-stage structure with separate PFC level is used, then power factor is improved, but device complexity and installation space increase
Solution Approach 1:
The patent combines the PFC function and output voltage regulation into a single integrated circuit stage. The auxiliary winding on the transformer provides both power factor correction and voltage feedback, merging what would traditionally require separate PFC circuitry and control components.
Solution Approach 2:
The single circuit stage performs multiple functions: power factor correction, voltage transformation, and output voltage regulation. This multi-functional design eliminates the need for separate PFC level and reduces installation space.
3Productivity
If voltage induced in auxiliary winding is measured at varying current values, then regulation responds to voltage changes, but measurement precision decreases
Solution Approach 1:
The patent employs periodic sampling of the auxiliary winding voltage at specific instants during the switching cycle. By measuring at predetermined current values (e.g., when current is zero or at specific thresholds), the system achieves consistent measurement precision while maintaining responsive voltage regulation.
Solution Approach 2:
The control system predeterminedly selects specific measurement points in the switching cycle where the auxiliary winding voltage provides accurate information about output voltage. This preliminary selection of measurement timing ensures precision while maintaining regulation effectiveness.
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 approach enables a single-stage switching power supply with integrated power factor correction and good control behavior, reducing component expenditure and achieving a high power factor close to 1, while minimizing installation space, weight, and costs.
Implementation Method 1
a voltage induced in a auxiliary winding of the transmission can also be used in order to regulate the secondary output voltage primarily
Data Source
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AI summary
The invention relates to a method for controlling the output voltage (U=) of a switched-mode power supply with a power factor-corrected buck-flyback converter comprising a transformer (6), wherein the buck-flyback converter is supplied with a pulsating DC voltage (Uin) on its input side. The method is characterized in that the transformer (6) has, in addition to a primary winding (61) and a secondary winding (62), an auxiliary winding (63), wherein a value of a voltage (Uind) induced in the auxiliary winding (63) is used as a reference variable for controlling the output voltage (U=), and wherein the value used for control is determined at a predetermined instantaneous value of the pulsating DC voltage (Uin). The invention further relates to a switched-mode power supply with a control module (51) configured to carry out such a method.