LED Driver Dual-Loop Overvoltage Protection Circuit
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Solution Overview
Problem
Existing LED driving circuits face challenges in providing reliable overvoltage protection due to large tolerances in voltage sensing and reference voltages, which can lead to inaccurate detection of overvoltage conditions and potential damage to electrolytic capacitors.
Innovation Solution
The implementation of a second control loop that directly connects the output capacitor to the control terminal of the main switch, triggering at or slightly below the minimum tolerance 'allowable maximum voltage' of the output capacitor, ensures that the voltage on the output capacitor is not allowed to exceed safe levels, thereby preventing capacitor blowup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a voltage divider with high voltage rating resistors is used for OVP sensing, then the sensing accuracy is improved, but the component size increases significantly
Solution Approach 1:
The voltage sensing function is divided into two independent paths: a first control circuit for normal OVP operation and a second control circuit for catastrophic failure protection. Each path uses resistors sized appropriately for its function, avoiding the need for large high-voltage resistors in the primary OVP path.
Solution Approach 2:
A second control circuit acts as an intermediary backup mechanism that activates when the first control circuit fails. This intermediary circuit uses a different resistor configuration (R5, R6) that does not require large high-voltage rating resistors, thus solving the size problem while maintaining protection capability.
2Measurement precision
If voltage sensing tolerances are reduced to improve protection accuracy, then the OVP threshold detection is improved, but the complexity of the voltage divider and reference voltage circuits increases
Solution Approach 1:
The protection function is segmented into two control circuits with different detection thresholds and tolerances. The first control circuit handles normal OVP with standard tolerances, while the second control circuit provides backup protection with its own tolerance characteristics, eliminating the need to reduce tolerances in the primary circuit.
Solution Approach 2:
The system uses different voltage thresholds and tolerance parameters for the two control circuits. The second control circuit is designed with a threshold (Vref2) and tolerance characteristics suited for catastrophic failure protection, allowing the first circuit to maintain standard, simpler parameters.
3Reliability
If the OVP threshold is set below the minimum tolerance 'allowable maximum voltage' to ensure protection, then the safety margin is improved, but the risk of false triggering increases
Solution Approach 1:
The protection ranges are segmented between two control circuits: the first circuit operates in the normal OVP range with higher threshold, and the second circuit operates in the catastrophic failure range with lower threshold. This segmentation allows each circuit to be optimized for its specific range, reducing false triggering while ensuring protection.
Solution Approach 2:
The second control circuit is pre-configured with a lower threshold that activates only in extreme conditions. This preliminary setup ensures that the circuit will trigger before the capacitor reaches its maximum tolerance voltage, providing a safety margin without causing false triggering during normal operation.
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
This dual-overvoltage protection mechanism significantly reduces the risk of electrolytic capacitor blowup by ensuring that the output capacitor voltage does not exceed safe levels, even in the presence of large tolerances in the primary overvoltage protection system.
Implementation Method 1
the voltage on E-CAP (usually output voltage) is detected, and if it is too high, the driver operates in a power-reducing mode wherein the main switch of the LED driver is turned open or its duty cycle is reduced
Implementation Method 2
An inductor L3 is magnetically coupled to the boost inductor L2 with a coil ratio of n:1, wherein n stands for the number of coils in the inductor L2 divided by the number of coils in the inductor L3. A voltage adder is formed by a diode D14 and a capacitor C3. In a charging phase of the boost converter when the switch M2 is close, the inductor L3 is induced with a voltage 1/n of the input voltage/the positive voltage (left terminal is positive) on the inductor L2
Implementation Method 3
A voltage adder is formed by a diode D14 and a capacitor C3. In a charging phase of the boost converter when the switch M2 is close, the inductor L3 is induced with a voltage 1/n of the input voltage/the positive voltage (left terminal is positive) on the inductor L2 and stores it on the capacitor C3. And in a freewheeling phase, the inductor L3 is induced with a voltage 1/n of the negative voltage freewheeling voltage (left terminal is negative) on the inductor L2. This voltage is added with the previously stored voltage on the capacitor C3 and output to a buffer capacitor C4 via a diode D11
Data Source
AI summary
To provide a safer over voltage protection, it is provided a driving circuit for a light emitting source, comprising an input adapted to receive a power supply; a conversion circuit, adapted to convert the power supply and provide a converted power, comprising a power switch (M2); an output, adapted to output the converted power; an output capacitor (C2) connected at the output; a first control circuit coupled to the output and connected to the power switch (M2), adapted to sense a voltage corresponding to the voltage on the output capacitor and control the power switch operate in a power-reducing mode to reduce the converted power when the voltage corresponding to the voltage on the output capacitor sensed by the first control circuit exceeds a first level; and a second control circuit (D15) connected to the output capacitor (C2) and connected to a control terminal of the power switch (M2), adapted to sense a voltage at the output capacitor (C2) and damage and make the power switch (M2) unoperational permanently when the voltage at the output capacitor (C2) sensed by the second control circuit exceeds a second level.