Primary-Side Load Current Detection in Resonant Converters
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Solution Overview
Problem
Existing frequency-controlled resonant converters require extra circuitry on the secondary side of the transformer to detect load currents, which complicates the system and prolongs start-up time, as they need to limit maximum load currents by adjusting switching frequency.
Innovation Solution
The solution involves detecting load currents on the primary side of the transformer using a circuit element and auxiliary circuitry to derive signals representative of the primary and magnetizing currents, combining these signals to obtain a difference signal that reflects the load current, allowing for its measurement and control without additional secondary-side circuitry, thereby reducing start-up time and simplifying current measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If extra circuitry is added on the secondary side to detect load currents, then load current detection accuracy is improved, but device complexity increases
Solution Approach 1:
The patent uses the transformer as an intermediary to transfer load current information from the secondary side to the primary side. By detecting the primary current and subtracting the magnetizing current, the system obtains load current information without requiring direct sensing on the secondary side, thus reducing device complexity while maintaining measurement accuracy.
Solution Approach 2:
The patent creates a copy of the load current signal by reflecting it onto the primary side through the transformer. The detected primary current is a copy that contains load current information, which is then processed by subtracting the magnetizing current component to retrieve the actual load current value.
2Reliability
If switching frequency is increased to limit maximum load current, then load current protection is improved, but start-up time increases
Solution Approach 1:
The patent implements feedback control by continuously monitoring the load current through the primary side detection system and adjusting the switching frequency accordingly. This allows the system to respond dynamically to load conditions, providing protection while enabling faster start-up by avoiding excessive frequency limitations during normal operation.
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 enables reliable protection against excess load currents, reduces power dissipation, and facilitates easier current measurement on the primary side, allowing for faster start-up and efficient operation by monitoring and controlling load currents directly on the primary side.
Implementation Method 1
a transformer having a primary circuit and a secondary circuit, the primary circuit being energisable by an AC signal to induce a secondary AC signal across the secondary circuit
Data Source
AI summary
A resonant converter comprises switching circuitry (1) for supplying pulses, at a controllable frequency, to a resonant circuit so as to power the primary circuit (3, 12) of a transformer (4). The secondary winding (5a, 5b) of the transformer (4) delivers an AC signal which is rectified and then produces a load current. On the primary side, the converter has a resistor (13) for deriving a first electrical signal representative of the current in the primary circuit (3, 12), and an auxiliary winding (14) which is closely coupled to the secondary winding (5a, 5b) and across which an auxiliary voltage is induced as a consequence of the close coupling of the winding (14) to the secondary winding (5a, 5b). A resistor/capacitor combination (16, 17) integrates the auxiliary voltage with respect to time to derive a second electrical signal. Computational circuitry (19) combines the first and second signals so as effectively to subtract the second signal from the first signal to derive a difference signal which is representative of the load current reflected onto the primary side of the transformer (4) and is accordingly representative of the actual load current.