Bipolar Transistor Power Switch Control via Base Current Adjustment
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Solution Overview
Problem
The control of power converters using bipolar transistors as switching devices is complex due to the need for precise timing and current regulation, which is challenging with existing technologies.
Innovation Solution
A control circuit that determines the time instant when the power switch is switched off by detecting the collector current falling to zero, using an auxiliary winding for freewheeling detection, and adjusts the base current based on the storage time to regulate the switching process, ensuring reliable power conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If bipolar transistors are used as power switches instead of MOSFETs, then cost is reduced, but control complexity increases
Solution Approach 1:
The control circuit measures the actual switch-off time of the bipolar transistor and uses this feedback to dynamically adjust the base current in subsequent switching cycles. This closed-loop feedback mechanism enables automatic optimization of the storage time, resolving the control complexity issue while maintaining the cost advantage of bipolar transistors
Solution Approach 2:
The control circuit pre-calculates and applies the appropriate base current level before each switching event based on previously measured storage time characteristics. This preliminary adjustment ensures optimal switching performance is achieved from the start of each cycle, reducing the complexity of real-time control adjustments
2Speed
If the base current is increased to reduce storage time, then switching speed is improved, but peak collector current increases
Solution Approach 1:
The control circuit dynamically adjusts the base current level cycle-by-cycle based on the measured storage time, rather than using a fixed base current. This dynamic adaptation allows the system to achieve the minimum necessary base current for the required storage time, preventing excessive peak collector current while maintaining adequate switching speed
Solution Approach 2:
The control circuit changes the base current parameter adaptively based on measured storage time characteristics. By modifying the base current level according to actual device behavior rather than using a conservative fixed value, the system optimizes the trade-off between switching speed and peak collector current
3Measurement precision
If the storage time is reduced to improve switching response, then switching precision is improved, but control complexity increases
Solution Approach 1:
The control circuit incorporates a feedback loop that measures the actual storage time of the bipolar transistor and automatically adjusts the base current to achieve the desired storage time. This self-regulating feedback mechanism achieves precise storage time control without requiring complex external timing circuits or multiple control signals
Solution Approach 2:
The control circuit uses the bipolar transistor's own storage time characteristic as the basis for adjustment, rather than imposing an external timing reference. The system serves itself by using the measured storage time directly to determine the appropriate base current level, eliminating the need for additional timing components or complex synchronization circuits
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 solution allows for efficient and reliable operation of power converters with bipolar transistors, reducing costs while maintaining peak collector current levels, by accurately controlling the storage time and switching process.
Implementation Method 1
The inductive element, e.g. the transformer, may comprise an auxiliary winding, and the indication of the time instant may be determined based on the evolution of the voltage level at the auxiliary winding
Data Source
AI summary
The present document relates to Direct Current (DC) to DC power converters. In particular, the present document relates to DC to DC power converters which comprise one or more bipolar transistors as power switches. A control circuit configured to control a power switch of a switched-mode power converter is described. The power switch comprises a bipolar transistor. The control circuit is configured to determine an indication of a time instant, at which the power switch is switched off; and to adjust a basis current for controlling the power switch based on the determined indication of the time instant.