Active Clamp Isolated Power Supply Burst Frequency Control
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Solution Overview
Problem
Existing isolated power supply apparatuses, particularly AC adapters, face challenges in miniaturization with high output and power density requirements, leading to increased power loss and efficiency decrease when the switching frequency is elevated, especially in medium to light load regions due to the use of active clamp circuits.
Innovation Solution
An isolated power supply apparatus with a semiconductor device for power supply control that includes a transformer, a switching element, an active clamp circuit, and a current-to-voltage converter, which adjusts the switching element's timing and frequency based on load conditions to maintain efficiency, using burst mode operation with fixed switching times and lower frequencies in lighter loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the switching frequency is increased to reduce transformer size and improve power density, then the power loss increases and efficiency decreases
Solution Approach 1:
The patent implements dynamic switching frequency adjustment where the control circuit varies the switching frequency based on real-time detection of transformer inductance changes. When inductance decreases (indicating saturation risk), the frequency is reduced to prevent core saturation and excessive power loss. This dynamic adaptation allows the system to operate at higher frequencies when safe, minimizing transformer size while avoiding power loss when saturation risk exists.
Solution Approach 2:
The patent changes the operating parameters (switching frequency) based on detected conditions. By monitoring transformer inductance and adjusting the switching frequency accordingly, the system optimizes the balance between transformer size and power loss. The control circuit modifies frequency parameters in response to inductance measurements, enabling efficient operation across varying load conditions.
2Power
If the switching frequency is increased to improve power density, then the efficiency significantly decreases in medium load to light load regions
Solution Approach 1:
The patent employs dynamic switching frequency adjustment based on real-time transformer inductance detection. In medium to light load regions, when the control circuit detects inductance changes indicating saturation risk, it automatically reduces the switching frequency to maintain efficiency. This dynamic behavior allows the system to achieve high power density when needed while preserving efficiency when loads are lighter.
Solution Approach 2:
The patent implements a feedback mechanism where the control circuit continuously monitors transformer inductance and uses this information to adjust switching frequency. The detected inductance changes provide feedback about transformer saturation status, enabling the control circuit to optimize frequency selection and maintain high efficiency across varying load conditions while achieving high power density.
3Volume of moving object
If PWM control or quasi-resonant control is used with high switching frequency, then the transformer size is reduced, but the power loss increases
Solution Approach 1:
The patent enhances conventional PWM or quasi-resonant control by adding dynamic frequency adjustment based on transformer inductance detection. The control circuit monitors inductance changes and dynamically modifies switching frequency during operation, allowing the system to achieve high-frequency operation with reduced transformer size while preventing power loss that would occur under saturation conditions.
Solution Approach 2:
The patent replaces fixed mechanical switching frequency settings with an adaptive electronic control system that detects transformer inductance and automatically adjusts frequency. This substitution of fixed parameters with sensor-based adaptive control enables the system to achieve both small transformer size and low power loss by optimizing frequency in real-time based on actual transformer 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 suppresses efficiency loss in medium to light load regions, maintaining high average efficiency by reducing power loss and improving power density through controlled burst frequency and zero-voltage switching techniques.
Implementation Method 1
a transformer for voltage conversion
Implementation Method 2
a current-to-voltage converter element connected in series with the switching element
Data Source
AI summary
An insulated power supply apparatus includes: a transformer; a switching element connected in series with a primary-side winding of the transformer; an active clamp circuit connected between terminals of the winding; and a semiconductor device for power supply control that controls the switching element and the active clamp circuit. A current-to-voltage converter element is connected in series with the switching element. The semiconductor device includes: a circuit that generates a timing to turn off the switching element based on a voltage obtained by conversion by the converter element and a predetermined turn-off threshold level; a circuit that performs ON/OFF control of the switching element in a burst mode at a predetermined load or less; and a circuit that, in the burst mode, changes a burst frequency to be lower as a load current is smaller with the number of switching times of the switching element in one burst cycle fixed.