Totem-Pole PFC Skip-Mode Control for Output Overvoltage
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Solution Overview
Problem
Totem pole power factor correction (PFC) circuits face challenges in reducing electromagnetic interference (EMI) and preventing over-voltage when operating in low-power modes, leading to unregulated output voltages exceeding device power ratings.
Innovation Solution
The method involves controlling a PFC circuit by detecting polarity changes in the input voltage and applying a pulse sequence to EMI capacitors to manage voltage transitions, using a combination of PWM signals and pulse sequences to maintain regulated output voltages, even in skip-mode operations, while disabling the slow-leg portion during light-load conditions to reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the slow-leg portion is disabled during light-load conditions to reduce power consumption, then power efficiency is improved, but unregulated output voltages exceed device power ratings causing over-voltage damage
Solution Approach 1:
The controller proactively detects polarity changes in the input voltage and preemptively applies pulse sequences to the EMI capacitors before over-voltage conditions can develop. This preliminary action charges or discharges the EMI capacitors to appropriate voltage levels, preventing unregulated output voltages from exceeding device ratings when the slow-leg is disabled during light-load operation.
Solution Approach 2:
The EMI capacitors serve as intermediary energy storage elements between the input voltage and the output load. By controlling the voltage on these capacitors through pulse sequences, the system mediates the voltage transition and prevents direct over-voltage exposure to the output devices, enabling safe disablement of the slow-leg portion during light-load conditions.
2Object-affected harmful factors
If EMI capacitors are used to reduce electromagnetic interference, then EMI is reduced, but voltage transitions during polarity changes cause over-voltage peaks
Solution Approach 1:
The controller continuously monitors the voltage on the EMI capacitors and dynamically adjusts the pulse sequence application in response to detected polarity changes. This feedback mechanism ensures that the EMI capacitors are charged or discharged at the appropriate moments, maintaining voltage regulation while preserving the EMI filtering function.
Solution Approach 2:
The controller applies pulse sequences to the EMI capacitors periodically synchronized with the AC line frequency and polarity transitions. This periodic action ensures that voltage transitions occur in a controlled manner during each half-cycle, reducing EMI while preventing over-voltage peaks through rhythmic voltage management.
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 effectively reduces EMI and prevents over-voltage peaks, ensuring the PFC circuit operates within safe voltage limits during low-power modes while maintaining efficiency and compliance with industry standards.
Implementation Method 1
applying a pulse sequence to a second transistor of the fast-leg portion of the PFC circuit to change a voltage on an EMI capacitor from a first voltage corresponding to the first half cycle to a second voltage corresponding to a second half cycle
Data Source
AI summary
During a light load (or no-load) operation of a totem pole power factor correction circuit (i.e., PFC), a pulse width modulation (PWM) controller can operate in a skip mode. Further, the PWM controller may disable portions of the PFC to reduce standby power consumption. In this mode, and in this disabled configuration, the output of the PFC may be peak charged over time to a voltage that could be damaging or destructive. This peak charging results from the PFC circuit's inability to fully charge/discharge EMI capacitors between half cycles of the input line voltage. The present disclosure provides circuits and methods to fully charge/discharge the EMI capacitors to prevent peak charging the output.