BJT Reverse Recovery Compensation in LED Bulb Drivers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional power stages for alternative lighting devices, such as LED-based bulbs, face limitations in controlling energy conversion from line voltage, leading to high costs and difficulties in incorporating high voltage switches, especially in small bulbs, due to the need for expensive high voltage switches and limited control over energy conversion.
Innovation Solution
Employing a bipolar junction transistor (BJT) as a switch in the power stage, coupled to a line voltage, and using a controller to measure and compensate for the reverse recovery time period of the BJT to maintain a desired average output current, thereby dynamically adjusting switching times to reduce errors in peak current delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional high voltage switches are used in power stages, then voltage control capability is improved, but device cost and complexity increase significantly
Solution Approach 1:
The patent introduces a BJT as an intermediary switching device between the microcontroller and the high voltage power stage. The BJT is controlled by low-voltage PWM signals from the microcontroller while handling high voltage current switching, thereby mediating between the low-voltage control domain and high-voltage power domain. This eliminates the need for complex high-voltage MOSFET gate drive circuits and isolation components, reducing overall system complexity while maintaining voltage control capability.
2Device complexity
If BJT reverse recovery time is not compensated, then circuit simplicity is maintained, but current control precision deteriorates
Solution Approach 1:
The patent implements preliminary action by measuring the BJT reverse recovery time during an initial calibration phase and storing this value for subsequent compensation. The system performs a one-time characterization of the BJT's reverse recovery characteristics, then uses this pre-measured data to compensate for current control errors during normal operation. This approach maintains circuit simplicity during runtime while achieving high current control precision through pre-acquired compensation parameters.
Solution Approach 2:
The patent employs feedback by continuously monitoring the actual current output and comparing it with the desired current, then using the pre-measured reverse recovery time to calculate and apply appropriate compensation adjustments. The system measures the reverse recovery time and uses this information to dynamically adjust the PWM duty cycle or switching timing, creating a closed-loop control system that maintains high current control precision without adding complex real-time measurement circuitry.
Data Source
AI summary
A turn-off transition time period, also referred to as a reverse recovery time period, may be compensated for by a controller of a power stage including a bipolar junction transistor (BJT). The reverse recovery time period may be measured in one switching cycle and a subsequent switching cycle may include compensations based on the measured reverse recovery time period. That is the switching on and off of the BJT may be compensated to obtain a desired average output current to a load. When the reverse recovery time period is known, an error in the peak current obtained due to the reverse recovery time period may be calculated. The calculated error may be used to offset the target peak current for controlling the switching of the BJT to begin a turn-off transition of the BJT earlier in a switching cycle and thus reduce error in peak current at the BJT.