Switching Power Supply Control Stabilizing Frequency
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Solution Overview
Problem
Switching power supplies using the PFM method face instability and significant changes in switching frequency when load conditions change, leading to inefficient removal of higher harmonics due to the 100% duty cycle during low load conditions and 0% duty cycle during high load conditions.
Innovation Solution
A switching power supply control apparatus that employs a gate control circuit with serial delay circuits, exclusive OR circuits, and flip-flop circuits to ensure the switching element performs ON/OFF operations within each clock period, regardless of comparator output states, thereby stabilizing the switching frequency and reducing harmonic fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PFM method is used to control switching power supply, then stability is improved, but switching frequency changes significantly when operating conditions change
Solution Approach 1:
The patent applies dynamics by making the switching frequency adjustable based on operating conditions. The control circuit dynamically changes the switching frequency according to the output voltage level and load conditions, transitioning between a first switching frequency for normal operation and a second switching frequency for abnormal conditions (such as startup or overload), thereby resolving the contradiction between maintaining stability and adapting to changing operating conditions.
Solution Approach 2:
The patent changes the parameter of switching frequency based on operating conditions. By detecting abnormal conditions (such as output voltage being too high or too low) and adjusting the switching frequency parameter accordingly, the system maintains stable operation across different load conditions while preventing harmful harmonic frequencies.
2Object-affected harmful factors
If duty control is exercised to keep switching frequency within predetermined range, then harmonic disturbances are reduced, but device complexity increases
Solution Approach 1:
The patent employs periodic action by using a clock signal to generate periodic switching cycles. The control circuit uses this periodic clock signal to regulate the switching frequency, ensuring that switching operations occur at predetermined intervals and frequencies. This approach effectively suppresses harmonic disturbances while maintaining relatively simple circuit implementation through regular periodic control.
3Reliability
If switching element operates at 100% duty during low load, then output voltage is maintained, but harmonic frequency fluctuations increase
Solution Approach 1:
The patent applies preliminary anti-action by detecting abnormal operating conditions (such as startup or overload where output voltage may be too high or too low) before they cause harmful harmonic frequency fluctuations. When such conditions are detected, the control circuit preemptively adjusts the switching frequency to a second frequency, preventing the generation of harmful harmonics while maintaining proper output voltage.
Data Source
AI summary
According to embodiments, a switching power supply control apparatus causes a switching element to perform an ON/OFF once in each period of a clock signal, when an output voltage of a switching power supply formed by charging a capacitor with a current of a choke coil that stores/releases current energy in conjunction with the ON/OFF operation of the switching element is adjusted by exercising ON/OFF control of the switching element based on comparator output that compares the output voltage with a reference voltage.