Totem-Pole PFC Control for Single-Turn Inductor Discharge
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Solution Overview
Problem
Existing totem-pole PFC circuits require multiple switch turn-ons, leading to high power consumption in the bootstrap capacitor, increasing circuit costs and volume, which hinders miniaturization.
Innovation Solution
The method delays the discharge switch of the PFC inductor by a specified threshold duration when the previous switching period is less than a specified duration, ensuring it is turned on only once during a switching period, reducing bootstrap capacitor power consumption and enabling full input range ZVS.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switch is turned on multiple times in a switching period, then the PFC inductor can be fully discharged, but the bootstrap capacitor power consumption increases and its volume increases
Solution Approach 1:
The patent applies preliminary action by predicting whether the PFC inductor needs to be discharged before actually turning on the switch. The controller determines the inductor current state in advance and only activates the discharge switch when necessary, avoiding unnecessary switch operations and bootstrap capacitor power consumption.
Solution Approach 2:
The patent uses feedback by continuously monitoring the PFC inductor current and using this information to control the discharge switch. The controller adjusts the switch operation based on real-time inductor current feedback, ensuring the inductor is discharged only when needed and reducing bootstrap capacitor power consumption.
2Reliability
If the bootstrap capacitor capacitance value is increased to support multiple switch turn-ons, then the circuit can operate normally, but the capacitor volume increases and device miniaturization is hindered
Solution Approach 1:
The controller predicts the need for inductor discharge in advance and prepares the discharge switch operation accordingly. This preliminary determination ensures the switch is turned on only when necessary, allowing the use of a smaller bootstrap capacitor while maintaining circuit operation stability.
Solution Approach 2:
The patent changes the operational parameters of the discharge switch from fixed multiple turn-ons to conditional single turn-on based on inductor current state. This parameter change reduces the power consumption requirements of the bootstrap capacitor, enabling the use of a smaller capacitance value and reducing capacitor volume.
3Productivity
If the switching frequency is increased beyond maximum specified frequency, then the switching period decreases, but the switching frequency should be limited to avoid excessive speed
Solution Approach 1:
The controller predicts whether the PFC inductor needs to be discharged before the switching period ends. By determining this in advance, the controller can extend the current switching period slightly if needed, ensuring the switching frequency remains below the maximum specified frequency while still achieving complete inductor discharge.
Solution Approach 2:
The patent dynamically adjusts the switching period based on the predicted need for inductor discharge. When the inductor current state indicates discharge is needed, the switching period is extended appropriately, creating a dynamic switching frequency that adapts to circuit conditions while remaining within specified limits.
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 power consumption in the bootstrap capacitor, allowing for a smaller device footprint and broader application scenarios while maintaining efficient zero-voltage switching.
Implementation Method 1
a bootstrap capacitor in a bootstrap circuit coupled to the switch
Implementation Method 2
a PFC inductor in the totem-pole PFC circuit; duration of previous charging of the PFC inductor and duration of previous discharging of the PFC inductor
Implementation Method 3
maintaining efficient zero-voltage switching
Data Source
Figure 1~2(a)
Figure 2(b)~2(c)
Figure 2(d)~3
AI summary
A method for controlling a totem-pole PFC circuit is provided. When an alternating current of an input end of a totem-pole PFC circuit is in a positive half period, if a previous switching period is less than specified duration, after charging of a PFC inductor is completed, a switch that enables the PFC inductor to be discharged is first delayed for specified threshold duration, and then the switch that enables the PFC inductor to be discharged is turned on, so that the switch that enables the PFC inductor to be discharged is turned on only once. In an existing PFC application, when an input voltage is in a positive half period, a switch that enables a PFC inductor to be discharged needs to be turned on twice. Compared with the existing PFC circuit, the totem-pole PFC circuit in this application allows the switch that enables the PFC inductor to be discharged to be turned on only once, so that power consumption of a bootstrap capacitor in a bootstrap circuit connected to a gate of a switch S1 can be reduced. The bootstrap capacitor does not need to increase a volume. This reduces circuit costs, and facilitates miniaturization of a device installed with the totem-pole PFC circuit.