Switching Power Supply Pulse Frequency Modulation Control
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Solution Overview
Problem
Conventional switching power supplies face issues with efficiency, noise, size, manufacturing costs, and reliability due to high harmonic input current specifications, and struggle with controlling output voltage under varying loads, leading to increased diode losses and potential current leading mode breakdowns.
Innovation Solution
A switching power supply design featuring equal primary inductance values in transformers, equal winding ratios, and a control circuit that sets ON-duties and switching frequencies to maintain constant output voltage, using a series resonance circuit and feedback control to prevent current leading mode and optimize efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the winding ratio of transformers is reduced to decrease size, then the transformer size is reduced, but diode losses increase and conversion efficiency deteriorates
Solution Approach 1:
The patent changes the operating parameter from fixed frequency to variable frequency (pulse frequency modulation) to optimize the voltage conversion ratio. By adjusting the switching frequency dynamically, the system achieves the desired voltage transformation without requiring small winding ratios, thereby avoiding increased diode losses while maintaining compact transformer sizes.
Solution Approach 2:
The patent introduces dynamic control of the switching frequency based on feedback from the output voltage. The control circuit continuously adjusts the switching frequency to maintain stable output voltage under varying load conditions, replacing static winding ratio design with dynamic frequency adjustment, which resolves the contradiction between size and efficiency.
2Speed
If the switching frequency is increased to improve response speed, then the response speed is improved, but electromagnetic interference and noise increase
Solution Approach 1:
The patent employs periodic switching action with pulse frequency modulation, where the switching frequency varies periodically based on load conditions. This periodic control allows the system to achieve fast response when needed while operating at lower frequencies during steady-state conditions, thereby reducing electromagnetic interference and noise while maintaining good response characteristics.
3Volume of moving object
If the winding ratio is reduced to minimize component size, then the component size is reduced, but the system becomes susceptible to current leading mode breakdown
Solution Approach 1:
The patent changes the control parameter from fixed winding ratio to variable switching frequency. By using pulse frequency modulation, the system can operate with larger winding ratios that are less susceptible to current leading mode breakdown, while still achieving compact overall size through optimized frequency control and reduced component counts enabled by the variable frequency operation.
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 design allows for efficient voltage control without small winding ratios, reducing diode losses and preventing current leading mode, enhancing reliability and conversion efficiency while minimizing component sizes and heat sink requirements.
Implementation Method 1
By setting the resonance frequency of the series circuit consisting of primary inductance (Lm1 and Lr1) of transformer T1, primary inductance (Lm2 and Lr2) of transformer T2, and capacitor Cr to be much lower than the switching frequency fs, currents IQ1 and IQ2 flowing through MOSFETs Q1 and Q2 are made to rise linearly.
Implementation Method 2
Inductance element Lz resonates partially with capacitor Cs, when MOSFETs Q1 and Q2 conduct switching, to make MOSFETs Q1 and Q2 perform zero-voltage switching.
Implementation Method 3
Transformers T1 and T2 are represented by the respective equivalent circuits including exciting inductance Lm1 and exciting inductance Lm2, leakage inductance Lr1 and leakage inductance Lr2, primary windings Np1 and Np2, and secondary windings Ns1 and Ns2, respectively.
Data Source
AI summary
A switching power supply exhibits high conversion efficiency and facilitates reducing the size thereof. The switching power supply includes a half-bridge circuit including a first series circuit formed of switching devices Q1 and Q2 and connected between the output terminals of a DC power supply; and a second series circuit connecting primary inductance Lr1 of transformer T1, primary inductance Lr2 of transformer T2 and capacitor Cr in series. The second series circuit is connected between the output terminals of the half-bridge circuit, and is made to conduct a series resonance operation. The switching devices Q1 and Q2 is controlled at the ON-duties of 0.5 for reducing the breakdown voltages of rectifying diodes D1 and D2 on the secondary side of transformers T1 and T2 and for improving the conversion efficiency of the switching device.