Insulated Transformer Power Supply for High Power Factor
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Solution Overview
Problem
Existing switching power sources with insulated primary and secondary sides face challenges in achieving a high power factor, particularly when outputting low voltage, as they are not suitable for transformer configurations with insulated windings.
Innovation Solution
A power source device comprising a transformer with insulated primary and secondary windings, a rectifying circuit, an inductor, a rectifying element, a switching element, and a capacitor, where the inductance of the inductor is set to ensure the capacitor voltage is higher than the rectifying circuit output voltage, and the number of turns in the primary windings is adjusted to shape the input current waveform sinusoidally, suppressing peak portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a capacitor input type switching power source is used with a smoothing capacitor at the rear stage of a diode bridge, then the circuit is simple to implement, but the power factor becomes low since input current flows into the transformer only when the diode bridge output voltage exceeds the smoothing capacitor voltage
Solution Approach 1:
An auxiliary winding is introduced as an intermediary element between the main primary winding and the smoothing capacitor. This auxiliary winding, connected in series with the smoothing capacitor, enables the capacitor to be charged during specific intervals when the main primary winding is not conducting, thereby maintaining continuous current flow and improving power factor while preserving circuit simplicity
Solution Approach 2:
The circuit operates by periodically charging the smoothing capacitor through the auxiliary winding during intervals when the main primary winding current is zero. This periodic charging action ensures continuous power transfer and maintains sinusoidal current waveform, improving power factor without complicating the overall circuit structure
2Loss of energy
If a general step-up type power factor correction circuit is used, then the power factor can be improved, but the circuit configuration is not suitable for transformers with insulated primary and secondary sides that output low voltage from several volts to several tens of volts
Solution Approach 1:
The invention applies a localized modification to the transformer configuration by adding an auxiliary winding specifically on the primary side. This local addition enables the transformer to function with insulated primary and secondary sides while outputting low voltage, making the circuit suitable for specific applications without requiring a complete redesign of the transformer structure
Solution Approach 2:
The primary winding is segmented into a main primary winding and an auxiliary winding with different functions. The main primary winding handles the primary power transfer, while the auxiliary winding specifically charges the smoothing capacitor. This segmentation allows the circuit to achieve power factor correction compatible with insulated low-voltage transformers
3Loss of energy
If the number of turns of the first primary winding is made larger than the second primary winding, then the input current waveform can be shaped to suppress peak portions and approximate sinusoidal shape, but the transformer design becomes more complex
Solution Approach 1:
The transformer employs asymmetric winding configurations where the first primary winding has a different number of turns than the second primary winding. This asymmetry is deliberately designed to shape the input current waveform, suppressing peak portions and approximating sinusoidal shape, thereby improving power factor while maintaining a manageable transformer structure
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 configuration enhances the power factor of the switching power source by shaping the input current waveform to resemble a sinusoidal wave, effectively improving power factor and voltage output stability.
Implementation Method 1
a first series circuit in which an inductor and a first rectifying element are connected in series
Implementation Method 2
a first capacitor connected between the other end of the first primary winding and the second output terminal, wherein an inductance of the inductor is set so that a voltage of the first capacitor is higher than an output voltage of the rectifying circuit
Implementation Method 3
a rectifying circuit including a first output terminal and a second output terminal, and configured to fully rectify an AC voltage
Implementation Method 4
a transformer including a first primary winding and a second primary winding, and a secondary winding, and of which a primary side and a secondary side are insulated from each other
Implementation Method 5
a switching element connected between the other end of the second primary winding and the second output terminal, and configured to be switched between an on state and an off state
Data Source
AI summary
A power source device includes a transformer, a rectifying circuit, a series circuit, a switching element and a capacitor. The transformer includes first and second primary windings and a secondary winding. The rectifying circuit includes first and second output terminals and fully rectifies an AC voltage. The series circuit in which an inductor and a rectifying element are connected in series and connected between the first output terminal and a connecting point where one end of the first primary winding and one end of the second primary terminal are connected. The switching element is connected between the other end of the second primary winding and the second output terminal and switched between an on state and an off state. The capacitor is connected between the other end of the first primary winding and the second output terminal. An inductance of the inductor is set so that a voltage of the capacitor is higher than an output voltage of the rectifying circuit.