Totem-Pole PFC Ballast Control Circuitry
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Solution Overview
Problem
Totem Pole boost topologies for power factor correction in lighting converters face challenges such as high control effort, increased component count, and complex driving schemes due to floating switch nodes, which complicate current sensing and protection.
Innovation Solution
The control circuitry is placed on a floating potential, isolated from ground, allowing for a simple shunt-resistor for current sensing and reducing the complexity of driving schemes, with a low-voltage supply and communication interface on the same floating potential, enabling higher switching frequencies and smaller inductive components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the control circuitry is placed on ground potential with conventional driving schemes, then the design is simpler, but the switching losses increase and the component count increases
Solution Approach 1:
Instead of placing the control circuitry on ground potential and using complex level-shifting drivers, the patent inverts the approach by placing the control circuitry on floating potential. This eliminates the need for complex high-side driving schemes and allows direct control of the totem-pole switches, reducing both switching losses and overall system complexity.
Solution Approach 2:
The control circuitry is placed on the same floating potential as the switching nodes, creating equipotential conditions. This eliminates voltage potential differences between the control circuit and switching nodes, allowing direct control without complex level-shifting circuits and reducing switching losses.
2Device complexity
If the control circuitry is placed on floating potential, then the driving scheme complexity is reduced, but the isolation from ground potential increases design difficulty
Solution Approach 1:
The floating potential control circuitry serves multiple functions: it directly controls the totem-pole switches, provides inherent current sensing through the shunt resistor, and eliminates the need for separate level-shifting circuits. This multi-functionality simplifies the overall design despite the floating potential configuration.
Solution Approach 2:
The floating potential control circuitry inherently provides its own reference potential and simplifies current sensing by directly measuring the current through the shunt resistor without needing additional ground-referenced sensing circuits. The system serves itself by using the floating potential as both the control reference and the sensing reference.
3Volume of moving object
If higher switching frequencies are used, then the converter size is reduced, but the switching losses increase
Solution Approach 1:
The patent employs periodic zero-voltage switching (ZVS) in the totem-pole configuration, where the switches are turned on at the zero-voltage crossing points of the AC input. This periodic ZVS action allows high switching frequencies to be used without incurring significant switching losses, as the voltage across the switches is zero at the moment of switching.
Data Source
AI summary
The invention relates to a ballast (101) for lighting means, comprising an actively switched power factor correction stage (102), which is implemented in a Totem Pole boost topology, comprising a control circuit (103), which issues control signals for driving switches of the PFC stage (102), wherein the control circuit (103) is on a floating potential and galvanically isolated from a ground potential of the ballast (101).