LED Driver Circuit Slew Rate Improvement via PWM Voltage Sampling
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Solution Overview
Problem
The pulse width modulation method for LED light emitting devices experiences a delay in output voltage and slew rate degradation due to power-on delay of the operational amplifier, leading to increased power consumption when trying to address this issue.
Innovation Solution
The solution involves an LED light emitting device with a current control switch and an operational amplifier that samples output voltage during the on state of the pulse width modulation signal, charges a capacitor, and maintains output voltage using the sampled voltage during the off state, with switching units connecting the capacitor to the operational amplifier's terminals to improve channel current slew rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a large current is supplied to the operational amplifier to solve power-on delay, then the response speed is improved, but power consumption increases
Solution Approach 1:
The capacitor is charged in advance during the on-state of the PWM signal before the off-state begins. This preliminary charging action ensures that when the PWM signal transitions to off-state, the operational amplifier immediately has the necessary voltage stored in the capacitor, eliminating power-on delay without requiring excessive current supply during the transition period.
Solution Approach 2:
The capacitor acts as an intermediary energy storage element between the power supply and the operational amplifier. Instead of directly supplying large current to the operational amplifier during transition, the capacitor mediates by releasing stored energy, thereby reducing the instantaneous current demand and associated power consumption while still achieving fast response.
2Speed
If the operational amplifier output voltage is sampled and capacitor is charged during on state, then slew rate is improved, but device complexity increases
Solution Approach 1:
The capacitor serves multiple functions: it stores energy during the on-state, provides voltage during the off-state, and enables fast slew rate operation. The switching unit also performs dual roles by controlling both the capacitor charging/discharging and the operational amplifier output. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in device complexity while achieving improved slew rate.
Data Source
AI summary
The present invention relates to an LED light emitting device and a driving method, and discloses a technology that may improve a slew rate of a channel current flowing through an LED channel when driving with a pulse width modulation method. For this, the present invention includes an LED channel consisting of a plurality of LED elements that are consecutively and serially connected, a current control switch that is connected to the end of the LED channel and performs a switching operation, and an operational amplifier that controls the switching operation of the current control switch according to a pulse width modulation signal. The LED driver samples an output voltage at the operational amplifier when the pulse width modulation signal is in an on state, and maintains the output voltage of the operational amplifier when the pulse width modulation signal is in an off state.