Secondary-Side MOSFET Control Using Snubber Voltage Feedback
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Solution Overview
Problem
Existing methods for controlling the disconnection time of MOSFET transistors in DC-DC voltage converters are inefficient, particularly at high frequencies, due to measurement delays and inaccuracies in detecting zero crossing and forward voltage, leading to significant conduction and reverse recovery losses.
Innovation Solution
A circuit apparatus with a snubber circuit and automatic control circuit that adjusts the disconnection time of the MOSFET transistor based on the voltage across a storage element in the snubber circuit, optimizing the switch-off time to minimize losses by detecting and adjusting the voltage difference across the snubber circuit elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current measurement is used to detect zero crossing, then disconnection time can be controlled, but measurement delays and signal processing delays occur leading to loss of time and increased device complexity
Solution Approach 1:
The patent introduces a current mirror circuit as an intermediary that replicates the primary side current on the secondary side. This current mirror provides a direct, real-time representation of the current without requiring measurement and signal processing delays, enabling accurate zero crossing detection while maintaining real-time response.
Solution Approach 2:
The patent replaces the mechanical/electronic measurement and signal processing system with a direct electrical coupling approach. Instead of measuring current and processing signals to detect zero crossing, the system uses the current mirror to directly provide the current information, eliminating the need for complex measurement and processing circuits.
2Loss of energy
If forward voltage measurement is used to control disconnection time, then switching element can be turned off at optimal time, but inductive voltage drops dominate during steep edges requiring complex inductance compensation
Solution Approach 1:
The patent uses the current mirror circuit as an intermediary to indirectly sense the current state without directly measuring the forward voltage across the switching element. This avoids the problem of inductive voltage drops dominating the measurement, as the current mirror provides a clean representation of the current that can be used to determine the optimal disconnection time without complex compensation.
3Loss of energy
If MOSFET transistors with lower resistance are used, then conduction losses are reduced, but measurement accuracy requirements increase to mV range
Solution Approach 1:
The current mirror circuit serves as an intermediary that allows the system to monitor current without directly measuring the small voltage drops across the low-resistance MOSFET. By mirroring the current and using this mirrored signal for control decisions, the system avoids the need for high-precision mV-range voltage measurements while still achieving optimal switching control.
4Loss of time
If signal processing latency is reduced, then disconnection time control improves, but gate actuation latency remains an obstacle
Solution Approach 1:
The patent implements preliminary action by using the current mirror to continuously track and represent the current state in real-time, preparing the control system with accurate current information before the zero crossing occurs. This allows the control circuit to predict and prepare for the optimal disconnection point without being constrained by signal processing latency, improving both response time and reliability.
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 switching losses by optimizing the disconnection time, minimizing energy storage in parasitic capacitances and reducing reverse recovery losses, thereby improving the efficiency of the DC-DC voltage converter across various operating points.
Implementation Method 1
The snubber circuit is interconnected with the rectifier circuit and is designed to store resonant oscillation energy occurring in the rectifier circuit
Implementation Method 2
The channel of the MOSFET transistor is actively turned on, i.e. switched on so that it is electrically conductive, while a current is flowing through the intrinsic diode of the MOSFET transistor. The relatively low forward voltage of the conducting channel compared to the intrinsic diode of the MOSFET transistor reduces losses considerably
Implementation Method 3
the reverse recovery losses of the intrinsic diode can be drastically reduced
Data Source
AI summary
The invention relates to a circuit apparatus (10) for controlling the current flow of the secondary side (20) of a direct voltage converter, comprising: a controllable switch element (1) having a first connection (1a), a second connection (1c) and a control connection (1b); a snubber circuit, which is electrically coupled to the source connection (1a) and the second connection (1c); and a control circuit (5), which is designed to control a deactivation time of the controllable switch element (1) via the control connection (1b); wherein the control circuit (5) is electrically coupled to the snubber circuit and is designed to control the deactivation time according to an electrical parameter of the coupling.