Totem-Pole PFC Reverse Current Limiting via Drain-Source Sensing
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Solution Overview
Problem
Totem pole PFC circuits are vulnerable to reverse currents generated by sudden changes in AC input voltage, such as lightning strikes or voltage surges, which can damage power switches and diodes.
Innovation Solution
A control circuit for totem pole PFC circuits that includes a switch control circuit, a comparing circuit, and a logic circuit to generate control signals for high side and low side power switches, effectively turning them off when reverse currents are detected to prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional current sensing devices are added to detect reverse currents, then the reliability of power switch protection is improved, but the device complexity and power loss increase
Solution Approach 1:
The power switch itself provides the sensing function through its intrinsic drain-source voltage characteristics. When reverse current flows, the voltage across the drain-source terminals naturally indicates the reverse current condition, eliminating the need for external sensing devices. The control circuit monitors this self-generated voltage signal to detect and protect against reverse current.
Solution Approach 2:
The patent extracts the current sensing function from separate external devices and integrates it into the power switch's own operational characteristics. By monitoring the drain-source voltage of the existing power switch, the system obtains reverse current detection capability without adding separate sensing components.
2Reliability
If additional current sensing devices are added to detect reverse currents, then the reliability of power switch protection is improved, but the power loss increases
Solution Approach 1:
The power switch provides its own protection mechanism by generating detectable voltage signals during reverse current conditions. This self-service approach eliminates the need for additional active sensing components that would consume power, thereby reducing overall system power loss while maintaining protection reliability.
3Reliability
If the control circuit turns off power switches quickly when reverse current is detected, then the reliability is improved, but the response time may affect circuit operation
Solution Approach 1:
The control circuit is configured to detect reverse current conditions and immediately initiate switch turn-off action. By having the control logic ready and the switching mechanism prepared, the system can respond rapidly to reverse current threats, minimizing damage while the quick response itself becomes part of the protective action rather than a detrimental factor.
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 limits reverse currents, protecting the power switches and diodes from damage, while also reducing power loss and improving circuit efficiency by eliminating the need for additional current sensing devices.
Implementation Method 1
The first comparing circuit is coupled to the first pin and the third pin and configured to generate a high side off signal by comparing a first voltage indicative of a drain-source voltage of the high side power switch with a first threshold voltage
Data Source
AI summary
A control circuit for a totem pole PFC circuit with a low side power switch coupled between a switching node and a reference ground. The control circuit includes fourth pins. The first pin is coupled to the switching node. The second pin is coupled to the switching node through a first unidirectional device. The third pin is coupled to a control terminal of the low side power switch. The fourth pin is configured to be coupled to the reference ground. The control circuit is configured to control the turning-off of the low side power switch based on a first voltage indicative of a drain-source voltage of the low side power switch.