Connector-less Charging Circuit Using Active Clamp for Leakage Energy Recycling
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Solution Overview
Problem
Existing connector-less charging methods for portable electronic devices are inefficient due to the use of low frequency transformers, which result in large and ineffective chargers for higher frequency applications.
Innovation Solution
A high-frequency connector-less charging circuit utilizing a transformer with a primary and secondary side, where a primary switch connects and disconnects from ground during a duty cycle, and an active clamp circuit recycles leakage energy back to the source, enabled by a PWM controller, allowing for efficient charging without a physical connector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If low frequency transformers are used for connector-less charging, then leakage energy is minimized, but the transformer size becomes large and charging efficiency decreases
Solution Approach 1:
The patent changes the operating frequency parameter from low frequency (line frequency) to high frequency (600 kHz to 1 MHz), which fundamentally alters the transformer design requirements. At high frequencies, smaller transformers can achieve the same power transfer with reduced leakage inductance effects, resolving the contradiction between minimizing leakage energy and reducing transformer size.
Solution Approach 2:
The patent introduces dynamic control through PWM switching and active clamp circuits that adaptively manage the transformer operation. The primary switch and active clamp circuit dynamically adjust the magnetic flux and recycle leakage energy back to the source, enabling efficient operation at high frequencies with smaller transformer sizes.
2Volume of stationary object
If high frequency operation is used for connector-less charging, then transformer size is reduced and charging speed is improved, but leakage energy increases and requires active management
Solution Approach 1:
The patent converts the harmful leakage energy at high frequencies into a beneficial resource by using the active clamp circuit to recycle it back to the source. The active clamp transistor and capacitor capture the leakage energy during the switch-off period and return it to the input, transforming the high-frequency disadvantage into an efficiency advantage.
Solution Approach 2:
The active clamp circuit implements a feedback mechanism where the voltage across the clamp capacitor is monitored and used to control the clamp transistor timing. This feedback ensures optimal recycling of leakage energy, maintaining high efficiency at high operating frequencies while keeping the transformer size small.
3Ease of operation
If connector-less charging is implemented, then connection time is eliminated and ease of operation is improved, but coupling efficiency decreases due to large spacing
Solution Approach 1:
The patent uses periodic PWM switching at high frequency (600 kHz to 1 MHz) to create time-varying magnetic fields that enhance coupling between the primary and secondary transformers. This periodic excitation allows efficient energy transfer despite the physical spacing required for connector-less operation, maintaining both convenience and efficiency.
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
Enables smaller transformer size and efficient power transfer at higher frequencies, improving charging speed and efficiency for portable devices, and allowing open-loop operation without the need for output inductors or voltage monitoring.
Implementation Method 1
a transformer having a primary side for coupling a charging voltage to a secondary side of the transformer
Implementation Method 2
An active clamp circuit connected to the primary side of the transformer recycles leakage energy from the transformer back to the source
Data Source
AI summary
A connector-less charging circuit includes a transformer having a primary side associated with a secondary side. A primary switch is responsive to a control signal for connecting the transformer to ground during a first portion of a duty cycle, and disconnecting the transformer from ground during the second portion of the duty cycle. An active clamp circuit connects to the primary side of the transformer for recycling leakage energy from the transformer back to the source responsive to the control signal during the second portion of the duty cycle. A PWM controller generates the control signal to both the active clamp circuit and the primary switch.