Totem-Pole PFC Current Sense Shunt Switching Circuit
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Solution Overview
Problem
Conventional totem-pole PFC circuits face efficiency limitations due to diode voltage drops and suffer from reverse current issues that cause damage and malfunction in current sense transformers, leading to high costs and power losses.
Innovation Solution
A current sensing circuit with a shunt switch mechanism is implemented to disable the current sensing circuit during freewheeling phases, using transformer windings and shunt switches to prevent reverse voltage stresses and reduce unwanted signals, allowing for lower-cost magnetic components and improved efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sense transformer is used in a totem-pole PFC circuit, then current sensing is achieved, but reverse current flow during freewheeling phases causes damage and malfunction
Solution Approach 1:
The patent extracts the harmful reverse current path from the current sense transformer by introducing a dedicated freewheeling path through the shunt switch. During freewheeling phases, the shunt switch provides an alternative current path that bypasses the transformer, preventing reverse current damage while maintaining accurate current sensing during active phases.
Solution Approach 2:
The shunt switch is activated in advance before reverse current can damage the transformer. The controller monitors the switching phase and proactively enables the shunt switch during freewheeling phases, preventing the harmful effect before it occurs. This preliminary action protects the transformer from reverse voltage stresses and current damage.
2Reliability
If Hall sensors are used to sample current in totem-pole PFC, then reverse current issues are avoided, but the solution becomes bulky and costly
Solution Approach 1:
Instead of using expensive Hall sensors that measure current indirectly through magnetic fields, the patent uses a copy of the existing current path through the current sense transformer. By routing the freewheeling current through a separate shunt switch path, the system maintains the simplicity and cost-effectiveness of transformer-based sensing while achieving the reliability of Hall sensor solutions.
Solution Approach 2:
The patent segments the current sensing function into two distinct paths: one for active phases using the current sense transformer, and another for freewheeling phases using the shunt switch. This segmentation allows each component to operate within its optimal range, maintaining simplicity while solving the reverse current problem.
3Productivity
If the current sensing circuit remains active during freewheeling phases, then continuous monitoring is achieved, but unwanted signals and voltage stresses increase
Solution Approach 1:
The patent implements periodic action by selectively enabling the current sense transformer only during active phases and disabling it during freewheeling phases. The shunt switch is activated periodically during freewheeling phases to provide the necessary current path while keeping the transformer inactive. This periodic activation maintains monitoring continuity where needed while eliminating unwanted signals when the transformer is disabled.
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 prevents damage and malfunction caused by reverse current flow, reduces power losses, and lowers the cost of magnetic components, enhancing the overall efficiency of the totem-pole PFC circuit.
Implementation Method 1
a second transformer winding magnetically coupled to the first winding and configured to deliver current from the first winding to a current sense terminal
Data Source
AI summary
A power converter is provided with a totem-pole power factor correction (PFC) circuit for bridgeless line rectification, and current sensing circuit that can be selectively disabled to reduce unwanted current sense signal components and undesirable current transformer voltage stresses. The totem-pole PFC has at least a first leg with first and second switching elements coupled in series. A PFC inductor is coupled between an AC input on a first end and a node between the switching elements. The current sensing circuit includes a first transformer winding coupled in series with the first switching element, a second transformer winding magnetically coupled to the first winding and configured to deliver current from the first winding to a current sense terminal during an active phase for the first switching element, and a shunt circuit configured to disable the current sensing circuit during a freewheeling phase for the first switching element.