BJT Charge Pump Drive Circuit for LED Power Supply
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Solution Overview
Problem
Conventional power stage configurations for LED-based light bulbs, such as the buck-boost power stage, provide limited control over energy conversion and are costly due to the need for high-voltage switches, which are expensive and difficult to incorporate into small bulbs.
Innovation Solution
The use of bipolar junction transistors (BJTs) as switches in the power stage, which are lower cost than field effect transistors (FETs) and can generate a power supply voltage for controllers, allowing for feedback loops and efficient energy conversion by controlling base current through timing adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional buck-boost power stage configuration is used, then energy conversion is achieved, but device complexity and cost increase due to requirement of high-voltage switches
Solution Approach 1:
The patent extracts the high-voltage switching function from the conventional buck-boost power stage by using the BJT's inherent high-voltage capability and reverse recovery time, eliminating the need for separate high-voltage MOSFETs and complex control circuitry. The BJT directly handles high-voltage switching while the charge pump generates necessary base drive voltages.
Solution Approach 2:
The BJT serves multiple functions simultaneously: it acts as the primary power switch, generates auxiliary power during reverse recovery through the charge pump, and enables dimmer compatibility. This multi-functionality reduces the overall component count and system complexity compared to conventional designs.
2Power
If high-voltage switches are used in conventional power stages, then power conversion is achieved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive high-voltage MOSFETs with cheaper BJT transistors that can handle high voltages. The BJT's shorter lifetime in terms of switching cycles is compensated by the charge pump's ability to rapidly recharge the base, effectively extending operational life while reducing component cost.
Solution Approach 2:
The BJT's reverse recovery process automatically generates the charge necessary to recharge the base during the off-state, creating a self-sustaining mechanism that eliminates the need for external high-voltage base drive circuitry and reduces overall system cost.
3Ease of manufacture
If BJT is used as switch in power stage, then manufacturing cost is reduced, but base drive voltage requirement increases complexity
Solution Approach 1:
The charge pump acts as an intermediary device that converts the BJT's reverse recovery current into the high voltage needed for base drive. This mediator bridges the gap between the low-voltage control circuitry and the high-voltage BJT switching operation, simplifying the overall control architecture.
Solution Approach 2:
The patent converts the BJT's reverse recovery phenomenon, which is typically considered a harmful effect causing voltage spikes and EMI, into a beneficial source of charge for base drive. The reverse recovery current is routed through the charge pump to generate the necessary base voltage, turning a disadvantage into an advantage.
4Power
If conventional power stages are used, then power supply is provided, but power dissipation increases
Solution Approach 1:
The charge pump operates continuously during the BJT's off-state, capturing and storing energy from the reverse recovery current that would otherwise be dissipated. This continuous energy capture and transfer to the base reduces overall power dissipation in the power stage.
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
BJTs enable lower-cost LED light bulb implementations with improved energy conversion efficiency and reduced power dissipation, facilitating dimmer compatibility and efficient power supply generation for LED-based light bulbs.
Implementation Method 1
Charge pump-based drive circuitry for bipolar junction transistor (BJT)-based power supply
Data Source
AI summary
A bipolar junction transistor (BJT) may be used to generate a supply voltage for operating a controller, such as a lighting controller for a LED-based light bulb. A base of the BJT may receive current generated from the supply voltage to control operation of the BJT. Although the base of the BJT would be at a lower voltage than the emitter, a base drive circuit may be coupled between the emitter and the base of the BJT to increase the voltage. As one example, the base drive circuit may be a charge pump. In another example, the BJT may function as its own charge pump. In yet another example, a positive and a negative base current of the BJT may be independently controlled to regulate an output supply voltage VDD from the BJT.