Active Clamp Circuit Steering Network Switching Loss Reduction
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Solution Overview
Problem
Conventional switched mode power converters face limitations in reducing switching losses and leakage inductance-related losses, especially at higher output power ranges and higher switching frequencies, due to current ringing and increased RMS current, which can lead to increased costs and inefficiencies.
Innovation Solution
An active clamp circuit with a steering diode network and an offset element is used, where the clamp switch is controlled to turn on near the end of the power switch's OFF time, transferring charge from leakage inductance to clamp capacitance, and the offset element manages voltage across the clamp switch to minimize switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional passive clamp circuits are used, then the switch is protected from voltage damage, but switching losses and RMS current increase due to current ringing
Solution Approach 1:
The patent introduces an active clamp circuit with a clamp switch and clamp capacitance as an intermediary between the power switch and the high-voltage node. This active clamp circuit actively controls the voltage transition and absorbs the leakage inductance energy, preventing current ringing while reducing switching losses. The clamp switch acts as a mediator that shapes the voltage waveform to enable zero-voltage switching of the power switch.
Solution Approach 2:
The patent changes the operating parameters of the clamp circuit by using an active switch instead of a passive diode, allowing dynamic control of the clamp voltage and current. The clamp switch is controlled to turn on at specific timing to achieve zero-voltage switching, and the clamp capacitance is sized to provide the necessary voltage clamping while minimizing RMS current. This parameter optimization reduces both switching losses and conduction losses.
2Productivity
If switching frequency is increased to improve productivity, then output power delivery improves, but leakage inductance-related losses and current ringing increase
Solution Approach 1:
The patent converts the harmful effect of leakage inductance into a beneficial one by using the leakage inductance energy to charge the clamp capacitance during the clamp switch's on-time. This stored energy is then returned to the circuit during the next switching cycle, reducing the need for additional energy from the input source and decreasing overall losses. The leakage inductance that causes ringing is transformed into an energy storage element that supports zero-voltage switching.
3Loss of energy
If active clamp circuit is used to reduce switching losses, then efficiency improves, but device complexity increases
Solution Approach 1:
The active clamp circuit performs multiple functions: it protects the power switch from overvoltage, enables zero-voltage switching to reduce switching losses, absorbs leakage inductance energy, and provides a controlled path for clamp current. By integrating these functions into a single circuit topology with the clamp switch and clamp capacitance, the patent reduces overall circuit complexity compared to using separate protection and loss-reduction circuits.
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 reduces switching losses and RMS current, allowing for zero-voltage switching and minimizing the voltage across the clamp switch, thereby enhancing the efficiency and reducing costs associated with output capacitors.
Implementation Method 1
the clamp switch is controlled to turn on near the end of the power switch's OFF time, transferring charge from leakage inductance to clamp capacitance
Implementation Method 2
the offset element manages voltage across the clamp switch to minimize switching losses
Implementation Method 3
allowing for zero-voltage switching and minimizing the voltage across the clamp switch
Data Source
AI summary
A power converter, comprising an energy transfer element, an output of the power converter, a power switch, an active clamp circuit, and a first controller. The active clamp circuit comprising a capacitance, a steering diode network coupled to the capacitance and configured to transfer a charge to the capacitance, a clamp switch coupled to the capacitance and configured to transfer the charge stored in the capacitance to the energy transfer element, and an offset element coupled to the clamp switch and configured to provide a path to discharge a capacitance associated with the clamp switch. The first controller configured to output a clamp drive signal to control the turn on and turn off of the clamp switch and a primary drive signal to control the turn on and turn off of the power switch.