Transformer Control Winding for Precise BJT Oscillation Control
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Solution Overview
Problem
Self-oscillating power converters using bipolar junction transistors (BJTs) face challenges in accurately controlling the oscillation frequency, leading to unpredictable performance and increased costs when transitioning to field effect transistors (FETs) for improved control.
Innovation Solution
A controller with bidirectional electronic switches and diodes, magnetically coupled to the load and drive windings, allows for precise control of BJTs by creating effective short-circuits without diodes, reducing voltage drop and leakage inductance, enabling efficient control of BJTs in self-oscillating power converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If self-oscillating converters use bipolar junction transistors with tolerance-prone components, then cost is reduced, but oscillation frequency control precision deteriorates
Solution Approach 1:
The patent implements a control winding magnetically coupled to the drive winding, forming a feedback mechanism that senses the oscillation state and actively regulates the BJT switching. This feedback loop compensates for component tolerances in real-time, maintaining precise frequency control while using inexpensive BJTs and standard tolerance components.
Solution Approach 2:
The patent dynamically adjusts the control winding current parameters to regulate oscillation frequency. By changing the current magnitude and timing in the control winding, the system can precisely control the BJT switching frequency despite variations in other component parameters, resolving the contradiction between component tolerance and frequency precision.
2Reliability
If additional windings and diodes are added to control oscillations, then oscillation regulation improves, but leakage inductance increases and control efficiency decreases
Solution Approach 1:
The patent combines the control function with the existing transformer structure by winding the control winding on the same core as the drive winding. This integration allows oscillation control to be achieved within the existing magnetic circuit without adding separate control inductors, thereby avoiding excessive leakage inductance while maintaining effective regulation.
Solution Approach 2:
The control winding serves multiple functions: it provides feedback sensing, regulates oscillation frequency, and controls BJT switching. This multi-functionality allows effective oscillation regulation without requiring additional dedicated control components that would increase leakage inductance and reduce efficiency.
3Manufacturing precision
If field effect transistors are used instead of bipolar junction transistors, then control precision improves, but manufacturing cost increases
Solution Approach 1:
The patent uses a feedback control mechanism that compensates for the limited control characteristics of BJTs. The control winding continuously senses and adjusts the base current, effectively providing precise control comparable to FETs while maintaining the cost advantage of using inexpensive BJT devices.
Solution Approach 2:
The control system uses the load current itself to provide feedback through the control winding, creating a self-regulating mechanism. This self-service approach eliminates the need for external control circuits or more expensive transistors, achieving precise control through the intelligent use of existing circuit elements.
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 controller effectively regulates the oscillations of BJTs, allowing for precise control of frequency and start characteristics, reducing costs by maintaining BJTs while achieving performance comparable to FET-based systems.
Implementation Method 1
A controller with bidirectional electronic switches and diodes, magnetically coupled to the drive and load windings, allows for precise control of BJTs
Implementation Method 2
creating effective short-circuits across the control winding, enabling better regulation of the oscillations
Data Source
AI summary
This invention relates to a circuit for controlling a power converter featuring BJTs, through use of a control winding on the transformer that provides the base drive for the BJTs. This controller can control the control winding current, thus modifying the commutating of the current or stopping the oscillations. It can provide unidirectional shorts to prevent commutation and can also provide an initial power pulse to control the start or operation of the power converter.