Lossless Over-Current Detection Circuit for Royer Oscillators
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Solution Overview
Problem
Conventional over-current detection circuits for Royer oscillators and push-pull converters suffer from inefficiency due to power loss in sense resistors and complexity in transformer construction, lacking effective short-circuit protection and requiring cumbersome hardware additions.
Innovation Solution
A lossless over-current detection circuit using complementary switching transistors, diodes, and a voltage-divider circuit with a thermistor, which generates an over-current signal without carrying load current and is less sensitive to transistor gain variations, enabling easier transistor selection and reduced power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sense resistors are added to each half of the Royer oscillator for current monitoring, then over-current detection capability is improved, but power loss increases and efficiency deteriorates
Solution Approach 1:
The patent extracts the over-current detection function from the main power path by using a separate detection circuit that monitors voltage at the common anode of diodes rather than placing resistors in series with the load current. This separates the detection function from the power-carrying path, eliminating the power loss associated with sense resistors while maintaining detection capability.
Solution Approach 2:
The patent introduces diodes as intermediary elements that allow voltage monitoring without carrying the full load current. The diodes act as mediators between the power path and detection circuit, enabling over-current detection through voltage drops across the diodes rather than through resistive sensing of the load current itself.
2Reliability
If leakage inductance is added to the transformer by separating primary and secondary windings for over-current limitation, then switching transistor gain selection is improved, but device complexity and manufacturing time increase
Solution Approach 1:
The patent extracts the over-current protection function from the transformer structure itself and implements it through a separate electronic detection circuit using diodes and resistors. This removes the need to modify the transformer by separating windings or adding leakage inductance, thereby reducing device complexity while maintaining protection capability.
Solution Approach 2:
The patent replaces the mechanical/physical approach of using transformer leakage inductance for over-current limitation with an electronic detection and control system. Instead of relying on magnetic coupling characteristics, the system uses electronic voltage monitoring and switching control to achieve over-current protection.
3Loss of energy
If sense resistors with low resistance values are used to mitigate power loss, then power loss is reduced, but sensitivity to noise increases
Solution Approach 1:
The patent uses diodes as intermediary elements that provide a more robust detection mechanism compared to low-value sense resistors. The diode voltage drops provide a clearer signal that is less susceptible to noise, while the detection circuit monitors these voltage drops rather than directly sensing small resistor voltage drops.
Solution Approach 2:
The patent performs preliminary voltage monitoring at the common anode of the diodes before the current reaches the switching transistors. This early detection point provides a stronger signal with better noise characteristics compared to monitoring after the switching transistors, where noise from the switching operations would interfere with the detection.
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
The solution provides efficient short-circuit protection with reduced power loss and simplified transistor selection, enhancing the reliability and efficiency of Royer oscillators and push-pull converters.
Implementation Method 1
a first resistor, a first diode including a first anode and a first cathode, and a second diode including a second anode and a second cathode. The first anode and the second anode are connected to each other and are connected to the voltage input via the first resistor. The first cathode is connected to the first switching transistor and the second cathode is connected to the second switching transistor such that the connection of the first and second anodes provides an over-current signal that is related to the current in the first and second switching transistors.
Data Source
AI summary
A circuit including over-current protection includes a voltage input, first and second switching transistors that are complementarily switched and that receive current from the voltage input, a first resistor, a first diode including a first anode and a first cathode, and a second diode including a second anode and a second cathode. The first anode and the second anode are connected to each other and are connected to the voltage input via the first resistor. The first cathode is connected to the first switching transistor and the second cathode is connected to the second switching transistor such that the connection of the first and second anodes provides an over-current signal that is related to the current in the first and second switching transistors.