Switching Power Supply Control Circuit for Transformer Buzzing
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Solution Overview
Problem
Conventional switching power supply apparatuses face challenges in reducing power consumption in standby mode without increasing volume or manufacturing costs, and struggle to prevent buzzing and respond quickly to load changes, especially when handling AC input voltages and power factor correction.
Innovation Solution
A switching power supply apparatus that employs a switching control circuit for pulse frequency modulation (PFM) control with a fixed ON-period under light loads and pulse width modulation (PWM) control with adjustable ON-periods based on AC power supply voltage, using hysteresis comparators to differentiate between high and low voltage systems, and includes features for quick load response and overload protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the switching frequency is lowered to reduce power consumption in standby mode, then power consumption is reduced, but the transformer may buzz due to low-frequency operation
Solution Approach 1:
The patent changes the ON-period parameter of the switching device based on the detected AC power supply voltage. When high voltage (e.g., 200V) is detected, a shorter ON-period is used, and when low voltage (e.g., 100V) is detected, a longer ON-period is used. This parameter adjustment ensures the switching frequency remains above the buzzing threshold while maintaining appropriate power transfer efficiency for each voltage system.
Solution Approach 2:
The patent detects the AC power supply voltage in advance before entering standby mode and pre-adjusts the ON-period of the switching device accordingly. This preliminary action ensures that when the power supply enters standby mode with lowered switching frequency, the ON-period is already optimized to prevent transformer buzzing, thus resolving the contradiction before it occurs.
2Use of energy by moving object
If the ON-period is extended to improve power transfer under light load, then power consumption is reduced, but the response time to load changes increases
Solution Approach 1:
The patent dynamically adjusts the ON-period of the switching device based on real-time detection of AC power supply voltage and load conditions. Rather than using a fixed ON-period, the system adapts the ON-period length according to the detected voltage system (high or low voltage), optimizing both power transfer efficiency and response time for each operating condition.
Solution Approach 2:
The patent implements a feedback mechanism where the AC power supply voltage is continuously detected and fed back to the switching control circuit. Based on this feedback, the control circuit adjusts the ON-period to maintain optimal performance. This feedback loop ensures that when load changes occur, the system can quickly adapt the ON-period to maintain appropriate response time while minimizing power consumption.
3Device complexity
If a single power supply apparatus is used instead of two separate apparatuses, then volume and manufacturing cost are reduced, but power consumption in standby mode increases
Solution Approach 1:
The patent designs a single power supply apparatus that can universally handle both high voltage (200V) and low voltage (100V) AC power supplies by detecting the input voltage and automatically adjusting the ON-period of the switching device. This multi-functional design eliminates the need for separate power supply apparatuses for different voltage systems while maintaining low power consumption in standby mode through optimized switching control.
Solution Approach 2:
The patent changes the operating parameters (ON-period) of the single power supply apparatus based on the detected AC voltage level. This allows one apparatus to efficiently operate across different voltage systems by adjusting its timing parameters, achieving the functionality of multiple specialized apparatuses with a single versatile unit that maintains low standby power consumption.
4Use of energy by moving object
If the switching frequency is changed discontinuously between two frequencies, then power consumption is reduced, but the transformer buzzing problem persists due to frequency transitions through the buzzing range
Solution Approach 1:
Instead of changing switching frequency discontinuously between two fixed frequencies, the patent changes the ON-period parameter which indirectly adjusts the switching frequency. By detecting the AC voltage system and selecting appropriate ON-period values, the system ensures the switching frequency remains continuously above the buzzing threshold while adapting to different voltage inputs, avoiding the harmful frequency transition range.
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 reduces power consumption in standby mode, prevents buzzing, and ensures quick response to load changes, while being applicable to power factor correction (PFC) systems and handling varying AC input voltages effectively.
Implementation Method 1
a switching control circuit for conducting a pulse frequency modulation control (PFM control), in which an ON-period of a switching device is fixed
Implementation Method 2
the switching control circuit conducts a pulse width modulation control (PWM control)
Implementation Method 3
using hysteresis comparators to differentiate between high and low voltage systems
Implementation Method 4
employs the voltage obtained by rectifying the output from an AC power supply for an input thereof
Data Source
AI summary
A switching power supply apparatus employing a voltage obtained by rectifying an output from an AC power supply, as an input thereof includes a switching control circuit. The switching control circuit conducts a PFM control having a fixed ON-period of a switching device when a load is judged to be light based on a load signal indicating the load, and a PWM control when the load is judged not to be light. The switching control circuit changes the ON-period based on whether the AC power supply is a high voltage system or a low voltage system.