BJT Switching Speed Control via Conduction Feedback
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Solution Overview
Problem
Switched mode power supplies using bipolar junction transistors (BJTs) face challenges with slower switching speed, mismatched output regulation, and difficulty in accurately detecting abnormal events due to the difference between emitter and collector currents, which affects their efficiency and reliability compared to metal-oxide-semiconductor transistors (MOS).
Innovation Solution
A control method and apparatus that utilize a driver with high-side and low-side drivers, along with a signal converter and condition decider, to detect and control the conduction current through a current-controllable device, adjusting the driving current based on the conduction current to optimize the ON and OFF times of the power switch, including a dead time mechanism to manage the switching process effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a BJT is used as a power switch, then the device structure is simple and the price is low, but the switching speed is slower compared to MOS
Solution Approach 1:
The patent applies preliminary action by pre-charging the base capacitor through a charging current before the BJT switching operation. This ensures that sufficient base charge is available in advance to enable faster turn-on and turn-off speeds, directly addressing the switching speed limitation while maintaining the simple BJT structure
2Loss of energy
If a BJT is used as a power switch, then the conduction loss is low, but the output regulation is mismatched due to the difference between emitter current and collector current
Solution Approach 1:
The patent introduces a current mirror circuit as an intermediary to sense the collector current and generate a corresponding base drive current. This current mirror acts as a mediator that translates the collector current information into appropriate base current control, enabling accurate output regulation while maintaining low conduction loss through the BJT
Solution Approach 2:
The patent implements feedback by using the current mirror to continuously monitor the collector current and adjust the base drive current accordingly. This feedback mechanism ensures that the BJT operates at the optimal point, maintaining accurate output regulation despite the inherent difference between emitter and collector currents
3Device complexity
If a BJT is used as a power switch, then the device structure is simple, but it is difficult to quickly turn ON and OFF the BJT
Solution Approach 1:
The patent applies preliminary action by pre-charging the base capacitor through a charging current before the BJT switching operation. This ensures that sufficient base charge is available in advance to enable faster turn-on and turn-off speeds, directly addressing the switching speed limitation while maintaining the simple BJT structure
Solution Approach 2:
The patent employs periodic action by using alternating charging and discharging current pulses to rapidly switch the BJT state. The charging current quickly charges the base capacitor for turn-on, while the discharging current rapidly discharges it for turn-off, creating a periodic switching pattern that minimizes switching time
Data Source
AI summary
Embodiments disclose control methods and control apparatuses for a switched mode power supply. The switched mode power supply comprises a current-controllable device. A driving current is provided to turn ON the current-controllable device. A conduction current passing through the current-controllable device is detected. The driving current is controlled according to the conduction current. The higher the conduction current the higher the driving current.