LED Buck Control Startup Sequencing for Stable Constant Current
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Solution Overview
Problem
In LED control circuits, the current loop of the front-stage isolated DC-DC circuit begins to operate before the current loop of the BUCK circuit performs a closed-loop operation, leading to reduced power output and inability to provide a constant current to the LED load.
Innovation Solution
An LED control circuit with a control unit that includes detection units and a control IC to manage the operation of the BUCK circuit, ensuring it starts only after the isolated DC-DC circuit operates in a constant voltage mode, thereby allowing the BUCK circuit to perform a closed-loop operation and supply a stable constant current to the LED load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the isolated DC-DC circuit operates with both constant voltage module and current limiting protection module, then the circuit can provide constant voltage mode and current limiting protection mode, but the voltage loop and current loop compete with each other causing the current loop to operate prematurely
Solution Approach 1:
The patent applies preliminary action by detecting the output voltage of the isolated DC-DC circuit before enabling the BUCK circuit operation. The control unit checks whether the voltage has reached the predetermined threshold (e.g., 36V) before allowing current loop operation, ensuring the voltage loop completes its startup first. This prevents the current loop from operating prematurely and ensures proper sequencing of circuit operations.
2Ease of operation
If the BUCK circuit starts operation after the isolated DC-DC circuit output voltage rises to a certain value, then the circuits start in sequence, but the output current of the isolated DC-DC circuit increases with the BUCK circuit causing the current loop to operate before the BUCK circuit current loop completes closed-loop operation
Solution Approach 1:
The patent implements feedback by continuously monitoring the output voltage of the isolated DC-DC circuit and using this information to control the startup of the BUCK circuit. The control unit receives feedback about the voltage level and only enables the BUCK circuit when the voltage reaches the predetermined threshold, ensuring proper sequencing. This feedback mechanism prevents the current loop from operating prematurely and ensures the BUCK circuit current loop can complete its closed-loop operation reliably.
3Reliability
If the isolated DC-DC circuit operates in current limiting protection mode, then the output power is reduced to protect electrical components, but the reduced power cannot meet the input power requirements of the BUCK circuit
Solution Approach 1:
The patent applies preliminary action by ensuring the isolated DC-DC circuit completes its voltage loop operation and reaches the predetermined output voltage threshold before the BUCK circuit begins operation. This sequencing prevents the scenario where the current loop operates prematurely and triggers current limiting protection mode. By establishing proper startup sequence, the system ensures sufficient power is available when the BUCK circuit operates, avoiding reduced power output while still maintaining component protection through the designed operating procedures.
Data Source
AI summary
An LED control circuit, comprising: an isolated DC-DC circuit having a first current loop and a voltage loop, said circuit being used for outputting a stable direct current voltage; and a buck circuit having a control unit; wherein the control unit is used for controlling the buck circuit to output constant current, so as to supply power to an LED load, and also used for controlling the buck circuit to not operate when the direct current voltage is less than a preset voltage, and controlling the buck circuit to operate when the direct current voltage is greater than or equal to the preset voltage.