Zero-Current Detection Circuit Using Opposing MOSFETs
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Solution Overview
Problem
Current zero-current detection methods in phase-cut dimming systems, particularly those using Schottky diodes, suffer from significant power losses and high costs at higher currents, leading to heat buildup and potential operational issues.
Innovation Solution
A circuit with two parallel branches of MOSFETs, where one MOSFET's current path direction is opposite to the other, allows for accurate zero-current detection with reduced power losses by minimizing the duration of current flow through body diodes, thereby reducing heat generation and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Schottky diodes are used for zero-current detection in phase-cut dimming systems, then zero-current detection can be implemented, but significant power losses and heat buildup occur at higher currents
Solution Approach 1:
The patent changes the operating parameters of the detection circuit by using MOSFETs with very low on-resistance (e.g., 10 milliohms or less) instead of Schottky diodes. This parameter change reduces the voltage drop and power losses during current conduction while maintaining zero-current detection capability through the body diode's reverse recovery characteristics.
Solution Approach 2:
The patent employs MOSFETs that can handle high currents with minimal power loss, effectively replacing the role of Schottky diodes. The MOSFETs' low on-resistance allows them to conduct current efficiently during the on-state, and their body diodes provide the necessary reverse recovery for zero-current detection, eliminating the need for separate Schottky diodes and reducing overall power losses.
2Reliability
If Schottky diodes are used for zero-current detection, then detection function is provided, but manufacturing costs increase
Solution Approach 1:
The patent integrates multiple functions into the MOSFETs: they serve as both the main switching elements for phase-cut dimming and as the detection circuit elements for zero-current detection. The body diodes of the MOSFETs provide the necessary reverse recovery characteristics for detection, eliminating the need for separate Schottky diodes and reducing component count and manufacturing costs.
Solution Approach 2:
The patent merges the detection circuit with the main power switching circuit by using the same MOSFETs for both purposes. The body diodes of the MOSFETs are utilized for zero-current detection, combining the detection function with the power switching function in a single component, thereby reducing overall system cost and complexity.
3Loss of energy
If MOSFETs are used instead of triacs for phase-cutting, then power losses are reduced and controllability is improved, but circuit complexity increases
Solution Approach 1:
The patent employs MOSFETs with intrinsic body diodes that automatically provide the necessary reverse recovery characteristics for zero-current detection. The MOSFETs self-regulate their switching behavior based on the body diode's recovery characteristics, reducing the need for additional external components and simplifying the overall circuit design despite using MOSFETs instead of triacs.
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 enables reliable, energy-efficient zero-current detection in phase-cut AC systems, improving accuracy and reducing manufacturing costs by minimizing power losses and heat generation.
Implementation Method 1
During those half-waves when the MOSFETs T1, T2 is not operating as a switch it allows the electric current to pass through via its body diode
Implementation Method 2
at least one primary switch arranged in said current path for implementing leading edge type phase-cutting of the input AC, the at least one primary switch arranged to operate alternatingly in one of a conductive and a non-conductive state
Data Source
Figure 1(a)~1(c)
Figure 2~5
Figure 6a~7
AI summary
A circuit for providing a leading edge type phase-cut alternating current (AC) to a load is provided. The circuit comprises a current path for coupling a load to an input AC supply, at least one primary switch arranged in said current path for implementing leading edge type phase-cutting of the input AC, the at least one primary switch arranged to operate alternatingly in one of a conductive and a non-conductive state in accordance with at least one first control signal, and a detection circuit arranged in said current path, arranged to provide a zero current detection signal for indicating the end of a half-wave in said phase-cut AC. The detection circuit comprises two parallel branches and a first MOSFET arranged in a first branch of said two parallel branches and a second MOSFET in a second branch of said two parallel branches such that the direction of the current path from the source to the drain through the first MOSFET is opposite to that of the second MOSFET, wherein one or both of the first MOSFET and the second MOSFET are arranged to receive respective second control signals for switching into one of a conductive state and a non-conductive state.