LED Driving Circuit with Compensating Capacitor for Ripple Reduction
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Solution Overview
Problem
Existing light-emitting diode (LED) driving circuits using pulse width modulation (PWM) dimming methods suffer from output voltage ripples and slow changes in the closed-loop transfer function due to diode current variations and error amplifier slew rates, leading to unstable operation and inability to quickly minimize ripples.
Innovation Solution
A light-emitting diode driving circuit comprising a control circuit, a transistor switch, and a compensating circuit that generates a pulse drive signal to charge an inductor and deliver current to LEDs, with a compensating circuit performing charging and discharging operations to reduce output voltage ripples through a dimming control signal, allowing for quicker loop transfer function changes and improved phase margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PWM dimming method is applied to control LED brightness, then brightness control capability is improved, but output voltage ripples increase and closed-loop transfer function changes slowly
Solution Approach 1:
The patent introduces a compensating capacitor as an intermediary element connected between the output node and the inverting input terminal of the error amplifier. This compensating capacitor acts as a mediator that provides a feedback path to stabilize the closed-loop transfer function, thereby reducing output voltage ripples while maintaining PWM dimming control capability
Solution Approach 2:
The patent modifies the electrical parameters of the compensation network by adding the compensating capacitor with specific capacitance value. This parameter change alters the frequency response and phase characteristics of the feedback loop, enabling faster closed-loop transfer function changes and better ripple suppression without sacrificing brightness control performance
2Measurement precision
If error amplifier is used in the LED driving circuit, then control precision is improved, but slew rate limits the speed of voltage change
Solution Approach 1:
The compensating capacitor is pre-configured in the feedback path to anticipate and prepare for voltage changes. When the error amplifier needs to respond to load transients or dimming commands, the compensating capacitor is already in place to provide the necessary phase lead and enable faster voltage change without being limited by the error amplifier's slew rate
3Stability of the object's composition
If compensating capacitor voltage changes slowly, then circuit stability is maintained, but ripple reduction capability deteriorates
Solution Approach 1:
The patent creates a dynamic compensation system where the compensating capacitor works in conjunction with the error amplifier to provide adaptive feedback. The compensating capacitor's voltage can change more quickly when needed to suppress ripples, while the overall feedback loop maintains stability through the controlled gain and phase characteristics introduced by the compensation network
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
The solution enables faster brightness control of LEDs, reduces load transients, and minimizes output voltage ripples, resulting in a more stable and efficient LED driving circuit operation with enhanced phase margin.
Implementation Method 1
the transistor switch is activated by the pulse drive signal such that an inductor is charged by an input voltage, in which the inductor is arranged to deliver an inducting current to at least one light-emitting diode when the transistor switch is deactivated
Implementation Method 2
The compensating circuit is coupled between the control circuit and a capacitor provided for reducing ripples of an output voltage corresponding to the inducting current
Data Source
AI summary
A light-emitting diode driving circuit includes a control circuit, a transistor switch and a compensating circuit. The control circuit receives an oscillating signal to generate a pulse drive signal. The transistor switch is activated by the pulse drive signal such that an inductor is charged by an input voltage, in which the inductor is arranged to deliver an inducting current to at least one light-emitting diode when the transistor switch is deactivated. The compensating circuit is coupled between the control circuit and a capacitor provided for reducing ripples of an output voltage corresponding to the inducting current. The compensating circuit performs a charging and discharging operation along with the capacitor when controlled by a dimming control signal provided to control brightness of the light-emitting diode.