Switching Power Supply Light Load Zero-Current Detection
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Solution Overview
Problem
Conventional switching power supply devices face challenges in maintaining a high power factor when the load is light, especially when zero current detection becomes difficult due to smaller resonance voltages, leading to discrepancies in switching frequency control and increased losses.
Innovation Solution
A switching power supply device with a control circuit that includes a load state detection part, a zero-current detection and frequency reduction part, and a restart timer, which adjusts the switching frequency and turn-ON timing of the switching element based on load state, ensuring reliable power factor correction even when zero current detection is not possible.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the switching frequency is reduced when the load is light to improve power factor, then power factor correction is improved, but zero current detection becomes unreliable due to smaller resonance voltages
Solution Approach 1:
The patent introduces an auxiliary coil as an intermediary element that generates a detection signal proportional to the inductor current. This auxiliary coil works in conjunction with a comparator to provide reliable zero current detection even when the main resonance voltage becomes too small at reduced switching frequencies. The auxiliary coil acts as a mediator that translates the inductor current into a detectable voltage signal.
Solution Approach 2:
The patent changes the detection parameter from directly measuring the small resonance voltage to measuring the auxiliary coil voltage which is proportional to the inductor current. This parameter change allows reliable detection of zero current conditions even when the primary resonance voltage amplitude becomes very small at light loads and reduced switching frequencies.
2Loss of energy
If the switching element turn-ON timing is delayed to reduce switching frequency under light load, then power factor correction is improved, but discrepancies in switching control increase when zero current detection fails
Solution Approach 1:
The auxiliary coil and comparator combination acts as a reliable intermediary detection system that provides consistent zero current detection signals regardless of the switching frequency or load conditions. This eliminates discrepancies in switching control by providing a stable reference for determining turn-ON timing, ensuring consistent operation across all load conditions.
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
The solution effectively prevents power factor reduction and switching losses by synchronizing the turn-ON timing of the switching element with the load state, maintaining efficient operation even under light load conditions.
Implementation Method 1
energy is stored in the inductor 3 as a result of the current flowing to the inductor 3 increasing when the switching element 4 is turned ON. When the switching element 4 is turned OFF, current flows from the inductor 3 to the output capacitor 6 as a result of the diode 5 being conductive, and the energy stored in the inductor 3 is released to the output side.
Implementation Method 2
an inductor 3 of which one end is connected to a diode bridge circuit 2 that performs full-wave rectification on an input alternating current voltage AC
Implementation Method 3
a diode 5 that is connected to the other end of the inductor 3 and that forms a current path between the inductor 3 and an output capacitor 6 when the switching element 4 is OFF, thereby achieving the prescribed output direct current voltage Vout to the output capacitor 6
Data Source
AI summary
The present invention provides, in one aspect, a restart timer that turns a switching element ON when it is not possible to turn the switching element ON via a zero-current detection and frequency reduction part, and specifically includes: a frequency reduction part that reduces a switching frequency of the switching element by delaying the turn-ON timing of the switching element by the zero-current detection and frequency reduction part when a light load state is detected; and a timer adjustment part that lengthens the restart time of the restart timer by synchronizing with the turn-ON timing of the switching element that was delayed by the frequency reduction part.