Fast Startup Circuit for Lighting Systems
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Solution Overview
Problem
Existing lighting systems face challenges in achieving rapid startup of the primary controller and converter while minimizing power loss and intermittent shut-offs, due to the large resistance at the power input terminal of the PFC controller, which slows down startup time and causes significant power loss.
Innovation Solution
A fast startup circuit is implemented, utilizing a bootstrap circuit and input selector to power the primary controller based on the rectified input voltage, with a transistor configuration that activates or deactivates the input line based on gate voltage thresholds, and a timer circuit to low-pass filter the output voltage, ensuring efficient startup and turn-off control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large resistor (500 KΩ or 1 MΩ) is used at the power input terminal of the PFC controller, then the current flowing into the PFC power input terminal is limited, but the startup time is slowed down due to the sizable RC time constant formed with the input capacitance
Solution Approach 1:
The patent applies dynamics by making the resistance value time-dependent. A capacitor is connected in parallel with the large resistor (500KΩ or 1MΩ), creating a dynamic circuit where the effective resistance changes during startup. Initially, the capacitor is uncharged and provides a low-impedance path for fast charging of the input capacitance, enabling rapid startup. As the capacitor charges, its impedance increases, and the large resistor dominates to limit current and provide stable operation during normal operation.
2Reliability
If a large resistor (500 KΩ or 1 MΩ) is used at the power input terminal of the PFC controller, then the current is limited, but significant power loss occurs (e.g., about 1⁄8 W for a 500 KΩ resistor at a 277 VAC input)
Solution Approach 1:
The patent reduces power loss by making the resistance dynamic rather than static. During the brief startup period, the capacitor has low impedance and carries most of the current, so the large resistor dissipates minimal power. During normal operation, the capacitor is fully charged and acts as an open circuit, so the large resistor limits current but the overall power loss is reduced because the resistor only needs to handle small leakage currents rather than continuous high currents.
Solution Approach 2:
The capacitor acts as an intermediary element that mediates between the large resistor and the PFC controller input. It provides a low-impedance path during startup, reducing the burden on the resistor and thereby reducing power dissipation in the resistor. The capacitor temporarily stores energy during startup and then maintains the voltage, allowing the resistor to operate at lower power levels during normal operation.
Data Source
AI summary
A lighting system includes a converter configured to receive a rectified input voltage and to generate an output voltage based on a control signal; a primary controller configured to generate the control signal to adjust the output voltage of the converter; and a startup circuit configured to power the primary controller based on the rectified input voltage in response to the output voltage being below a threshold, and to power the primary controller based on the output voltage in response to the output voltage being greater than or equal to the threshold.