Totem-Pole PFC Stage With Auxiliary Capacitor for Line Dropout Hold-Up
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Solution Overview
Problem
The bulk capacitor size in SMPS is significant due to the need for high energy storage during AC line dropouts, limiting power density and efficiency, and existing solutions either underutilize capacitor energy or increase complexity with additional components.
Innovation Solution
A power factor correction (PFC) stage with a totem-pole converter and an auxiliary capacitor, where the auxiliary capacitor is coupled in parallel with the output capacitor during normal operation and to the input inductor during line dropouts, allowing the first pair of power switches to operate as a DC-DC boost converter under peak current control, extending hold-up time and reducing capacitor size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the bulk capacitor size is increased to deliver full power during AC line dropout, then the hold-up time is extended, but the power density is reduced and the PFC stage size increases
Solution Approach 1:
The patent divides the energy storage function into two separate capacitors: a bulk capacitor for normal operation and an auxiliary capacitor specifically for LDO events. This segmentation allows each capacitor to be optimized for its specific function, reducing the total capacitance required while maintaining the hold-up time requirement.
Solution Approach 2:
The auxiliary capacitor is pre-charged to a higher voltage than the bulk capacitor during normal operation. When an LDO event occurs, this pre-charged auxiliary capacitor immediately discharges to support the bus voltage, providing preliminary energy that extends the effective hold-up time without requiring a larger bulk capacitor.
2Volume of stationary object
If the minimum voltage for the bulk capacitor is lowered to utilize more stored energy, then the capacitor size can be reduced, but the DC-DC stage efficiency decreases due to wide input voltage range
Solution Approach 1:
The auxiliary capacitor acts as an intermediary energy source during LDO events. It provides the additional voltage support needed to maintain optimal input voltage for the DC-DC stage, allowing the bulk capacitor to discharge to lower voltages without compromising DC-DC efficiency. The auxiliary capacitor mediates between the bulk capacitor and DC-DC stage, protecting the DC-DC stage from wide voltage variations.
3Duration of action of stationary object
If an auxiliary storage capacitor and additional conversion circuit are added to support bus energy during LDO, then the hold-up time is extended, but the device complexity increases due to additional inductors and switches
Solution Approach 1:
The auxiliary capacitor is integrated into the existing PFC circuit topology and serves multiple functions: it provides energy during LDO events, maintains bus voltage stability, and works in conjunction with the existing power switches and inductors. The existing power switches are controlled to perform dual functions during different operating modes, reducing the need for additional dedicated components.
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 the size of the bus capacitor while maintaining efficient power delivery during line dropouts, enhancing power density and reducing complexity by utilizing the auxiliary capacitor's energy more effectively.
Implementation Method 1
an auxiliary capacitor having a lower capacitance than the output capacitor... a circuit configured to couple the auxiliary capacitor in parallel with the output capacitor in a first state and to the input inductor in a second state
Implementation Method 2
a totem-pole converter comprising an input inductor for coupling to ac mains, a first pair of power switches, a second pair of power switches... operate the first pair of power switches as a DC-DC boost converter
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A power factor correction (PFC) stage, controller, and control method are described. The PFC stage includes: a totem-pole converter having an input inductor for coupling to ac mains, first and second pairs of power switches, and an output capacitor for coupling to a bus; an auxiliary capacitor having a lower capacitance than the output capacitor; and a circuit configured to couple the auxiliary capacitor in parallel with the output capacitor in a first state and to the input inductor in a second state; and a controller. If a line drop out (LDO) condition is detected on the bus, the controller sets the circuit in the second state and operate the first pair of power switches as a DC-DC boost converter under peak current control. If no LDO condition is detected on the bus, the controller sets the circuit in the first state and operate the totem-pole converter under average current control.