Active Clamp Circuit Reduces Voltage Stress in Flyback Converters
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Solution Overview
Problem
Flyback converters face challenges with high voltage stress on the primary switch due to large drain voltages and energy loss associated with leakage inductance, which reduces efficiency and stresses the primary switch.
Innovation Solution
An active clamp circuit with a clamp capacitance, diode, and clamp switch is introduced, controlled by a controller to discharge and charge the clamp capacitance exclusively through the clamp switch and diode during non-conduction phases of the converter switch, limiting voltage stress and enhancing efficiency by allowing zero voltage switching and quasi-resonant operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a clamp circuit is added to limit voltage stress on the primary switch, then the voltage stress on the primary switch is reduced, but the device complexity increases
Solution Approach 1:
The patent introduces a clamp circuit as an intermediary component between the primary switch and the high voltage stress. The clamp circuit includes a clamp switch, clamp capacitance, and diode that work together to limit the voltage across the primary switch by providing an alternative current path during switching transitions, thereby protecting the primary switch from excessive voltage stress while adding controlled complexity to the system
Solution Approach 2:
The clamp circuit is activated in advance during the non-conduction phase of the converter switch to prepare for the upcoming voltage stress. The controller closes the clamp switch before the primary switch turns on, allowing the clamp capacitance to charge and ready the clamp circuit to immediately limit voltage stress when the primary switch transitions, preventing damage before it occurs
2Reliability
If the clamp switch is closed during non-conduction phase to discharge clamp capacitance, then voltage stress on primary switch is reduced, but energy loss increases
Solution Approach 1:
The patent converts the harmful energy that would normally be dissipated as loss during clamp circuit operation into a beneficial resource. By closing the clamp switch during the non-conduction phase, the stored energy in the clamp capacitance is discharged into the storage inductance rather than being wasted. This recovered energy is then available to be transferred to the output during the conduction phase, transforming what would be energy loss into useful output energy and improving overall converter efficiency
Solution Approach 2:
The clamp circuit design recovers energy that would otherwise be discarded during the switching cycle. The clamp capacitance stores energy during the converter switch conduction phase, and this energy is recovered by discharging it into the storage inductance during the non-conduction phase through the closed clamp switch, rather than letting it dissipate. This recovery mechanism reduces net energy loss and improves converter 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
The active clamp circuit reduces voltage stress on the primary switch, increases converter efficiency, and enables operation in quasi-resonant mode for improved low power performance, minimizing switching losses and energy loss from leakage inductance.
Implementation Method 1
The active clamp circuit includes a clamp capacitance, a diode, and a clamp switch, with the clamp capacitance and the clamp switch being coupled in a circuit path
Implementation Method 2
the diode being coupled across the clamp switch... to cause the clamp capacitance to be charged from the storage inductance exclusively through the diode
Implementation Method 3
The power converter is coupled to the active clamp circuit, and includes a storage inductance coupled in a circuit path with a converter switch... to cause the clamp capacitance to be discharged into the storage inductance
Data Source
AI summary
An active clamp circuit includes a clamp capacitance and a clamp switch coupled in a circuit path, and a diode coupled across the clamp switch.