Switching Power Supply Noise Reduction via Resonant Current Control
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Solution Overview
Problem
Conventional current-resonant type switching power supplies experience noise generation due to steep current variations on the primary winding of the transformer, leading to inefficiencies and noise issues from input and output variations.
Innovation Solution
A switching power supply design that sets the on-period of the second switching element longer than half the cycle of the resonant current, ensuring the switching element on the primary side is turned off after the resonant current becomes zero, and uses a pulse ratio control circuit to fix the on-width of one switching element and vary the off-width, or vice versa, to manage switching frequencies and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PWM control is used to regulate output voltage by varying switching element on/off times, then output voltage regulation is achieved, but noise increases due to steep current variations on the primary winding
Solution Approach 1:
The patent employs resonant current periodic action by configuring the switching elements to operate in sync with the resonant frequency of the Lr-Cri circuit. The resonant current naturally oscillates in a sinusoidal pattern, and by timing the switching actions to coincide with specific phases of this resonance cycle, the system achieves soft switching that eliminates steep current transitions while maintaining effective output voltage regulation through periodic energy transfer.
2Measurement precision
If the switching element on the primary side is turned off during energy transmission to the secondary side, then output voltage regulation is improved, but noise increases due to steep current variations
Solution Approach 1:
The patent applies preliminary action by ensuring the resonant current completes its energy transfer cycle before the switching element is turned off. The control circuit is designed to detect when the resonant current has naturally decayed to zero (indicating complete energy transfer to the secondary side) and only then terminates the switching element's conduction period. This preliminary completion of the resonant cycle prevents abrupt current interruption and eliminates voltage spikes.
Solution Approach 2:
The patent converts the potentially harmful resonant oscillations and current variations into a beneficial soft-switching mechanism. By deliberately allowing the resonant current to flow through the switching element and then waiting for its natural decay to zero before turning off the switch, the system transforms what could be harmful high-frequency oscillations into a controlled energy transfer process that achieves zero-voltage switching and eliminates noise.
3Loss of energy
If resonant current flows through the switching element during energy transmission, then efficiency is improved, but noise is generated due to current variations
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the switching element's conduction angle and timing based on the resonant current's amplitude and phase characteristics. The control circuit monitors the resonant current waveform and modifies the switching parameters (turn-on and turn-off timing) to ensure that the switching element conducts only during the appropriate phase of the resonant cycle when current is naturally flowing, thereby achieving soft switching that reduces losses while the natural sinusoidal decay of resonant current eliminates abrupt transitions that cause noise.
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 effectively suppresses noise and achieves high efficiency by ensuring the switching element on the primary side is turned off after the resonant current has been transmitted to the secondary side, reducing current variations and stress on semiconductor components.
Implementation Method 1
a current-resonant circuit formed of a current-resonant capacitor Cri, a resonant reactor Lr, and a primary winding Lp of a transformer T is connected in parallel with the voltage-resonant capacitor Crv. The voltage-resonant capacitor Crv, the current-resonant capacitor Cri, the resonant reactor Lr, and the primary winding Lp of the transformer T collectively constitute a resonant circuit.
Implementation Method 2
The primary winding Lp and a secondary winding Ls are wound so as to generate common-mode voltages.
Data Source
AI summary
A switching power supply includes a first series circuit formed by connecting first and second switching elements in series at both ends of a direct-current power source, a second series circuit formed by connecting a resonant capacitor, a resonant reactor, and a primary winding of a transformer in series at both ends of the switching element, a rectifying-smoothing circuit configured to rectify and smooth a voltage generated on a secondary winding of the transformer, and a control circuit configured to turn the first and second switching elements and on and off alternately based on an output voltage from the rectifying-smoothing circuit. Here, the control circuit sets an on-period of the second switching element to a predetermined time period longer than a half value of a cycle of a resonant current attributable to the resonant reactor and the resonant capacitor, and controls an on-period of the first switching element based on the output voltage from the rectifying-smoothing circuit.