LED Driving Circuit Dynamic Reference Current for Fast Deep Dimming Start
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Solution Overview
Problem
LED lamps experience slow starting speed during deep dimming due to low starting speed issues caused by small reference voltage and high output capacitance, leading to inefficient charging of the output capacitance for forward voltage drop.
Innovation Solution
An LED driving circuit and method that includes a reference generating circuit and a current adjusting circuit, which sample output voltage and current signals to select appropriate reference current signals, allowing for rapid starting by adjusting the conduction state of the adjusting tube or switching power supply, using discrete or continuous analog signals to manage current flow effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the output capacitance is increased to achieve high power factor, then the power factor is improved, but the starting speed becomes slow due to slow charging of the output capacitance
Solution Approach 1:
The patent applies dynamics by making the reference current signal variable rather than fixed. The reference current signal dynamically changes based on the output voltage level: it is larger when output voltage is small (during starting) and smaller when output voltage is large (during normal operation). This dynamic adjustment allows the circuit to achieve both high power factor (with large output capacitance) and fast starting speed (with large reference current during starting).
Solution Approach 2:
The patent changes the parameter of reference current signal from a fixed value to a variable value that depends on output voltage. By sampling the output voltage and selecting appropriate reference current signals based on voltage thresholds, the system optimizes the charging current of the output capacitance during starting while maintaining proper current regulation during normal operation, thus resolving the contradiction between power factor and starting speed.
2Adaptability or versatility
If the reference voltage is decreased to enable deep dimming, then the dimming capability is improved, but the starting speed becomes slow due to insufficient charging current
Solution Approach 1:
The patent makes the reference current signal dynamic based on the dimming level represented by the output voltage. During deep dimming (low output voltage), the system automatically selects a larger reference current signal to enable fast starting. During normal operation (high output voltage), a smaller reference current signal is used to maintain the desired dimming level. This dynamic adaptation allows deep dimming capability while maintaining fast starting performance.
Solution Approach 2:
The patent implements preliminary action by detecting the output voltage level and pre-selecting the appropriate reference current signal before the starting process begins. The reference generating circuit continuously samples the output voltage and prepares the corresponding reference current signal, ensuring that when starting is needed, the appropriate current is already ready, thus achieving fast starting even in deep dimming conditions.
3Speed
If a large reference current is used during starting, then the starting speed is improved, but the stress on the adjusting tube increases
Solution Approach 1:
The patent applies dynamics by making the reference current signal adaptive to the operating conditions. A larger reference current signal is used only when needed (during starting when output voltage is small), and a smaller reference current signal is used during normal operation. This dynamic adjustment achieves fast starting speed while avoiding excessive stress on the adjusting tube during steady-state operation.
Solution Approach 2:
The reference generating circuit periodically samples the output voltage and switches between different reference current signals based on the sampled voltage level. This periodic monitoring and switching ensures that large current is applied only during the brief starting period when needed, and normal operation uses appropriate current levels, thus achieving fast starting without sustained high stress on the adjusting tube.
Data Source
AI summary
The present disclosure provides an LED driving circuit and an LED driving method, which may be applied to a switching power supply driving circuit and a linear driving circuit. The LED driving circuit includes an adjusting tube and a driving control circuit of the adjusting tube. The adjusting tube receives an input voltage, and the driving control circuit adjusts the adjusting tube to output an output current to be expected. A reference generating circuit samples an output voltage of the LED driving circuit to obtain an output voltage sampling signal and a reference current signal corresponding to the output voltage sampling signal. A current adjusting circuit samples the output current to obtain an output current sampling signal, receives the corresponding reference current signal, and controls a conduction state of the adjusting tube according to the output current sampling signal and the reference current signal.