LED Ballast with Segmented Capacitors for Flicker Reduction
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Solution Overview
Problem
Existing electronic ballasts for LEDs suffer from flicker issues and high electromagnetic interference (EMC), with high power losses and component overload, especially during switch-on, and are not suitable for all applications due to these limitations.
Innovation Solution
An electronic ballast design featuring a current controller with actual and setpoint value inputs, using transistors for soft switching between LED cascades, with current-dependent switching thresholds, and including diodes and storage capacitors to minimize EMC interference and allow for efficient current-limited charging and discharge, achieving high power factors and low residual ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If LEDs are operated directly on the mains with a series resistor, then the circuit is simple, but the LEDs flicker at double the mains frequency and are only on for less than half the time
Solution Approach 1:
The LED circuit is divided into multiple cascades (first cascade, second cascade, etc.), each with its own storage capacitor. The controller switches between different cascades to maintain continuous illumination, preventing flicker while keeping the overall system relatively simple.
Solution Approach 2:
Storage capacitors are pre-charged during specific phases so that when one LED cascade is active, another capacitor is ready to take over. This preliminary charging action ensures continuous illumination without flicker when switching between cascades.
2Illumination intensity
If the LEDs are supplied with power via an in-phase controller with a smoothing capacitor, then flicker is eliminated, but the absorption currents of the capacitors are very high and the capacitors and rectifiers are overloaded during switchon
Solution Approach 1:
The single large smoothing capacitor is segmented into multiple smaller storage capacitors, each associated with a specific LED cascade. This segmentation distributes the inrush current across multiple components and time phases, preventing overload during switchon while maintaining continuous illumination.
Solution Approach 2:
The controller operates in periodic phases, alternating between charging different storage capacitors and activating different LED cascades. This periodic action spreads the current demand over time, avoiding peak overload conditions while eliminating flicker.
3Adaptability or versatility
If the electronic ballast is designed for total mains tolerances, then it is universally applicable, but the power loss in the controller is undesirably high
Solution Approach 1:
The controller dynamically adjusts its operation based on the actual mains voltage and frequency conditions. By adapting the switching timing and duration to match actual mains parameters, the controller maintains universal applicability while minimizing power loss through optimized rather than over-engineered operation.
4Illumination intensity
If energy-storing components are used to prevent flicker, then flicker is eliminated, but electromagnetic interference is undesirably high
Solution Approach 1:
The energy storage function is segmented across multiple smaller capacitors rather than using one large capacitor. This segmentation reduces the electromagnetic interference generated during charging and discharging operations while collectively providing sufficient energy storage to prevent flicker.
Solution Approach 2:
The controller ensures continuous useful action by seamlessly switching between multiple capacitor-LED cascade combinations. This continuous operation avoids the high-current transient spikes associated with single-capacitor systems, thereby reducing electromagnetic interference while maintaining flicker-free illumination.
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 effectively reduces flicker and EMC interference, achieving power factors of 0.94 with a single unit and 0.99 with multiple units, while maintaining high efficiency and being insensitive to mains frequency and voltage fluctuations, without the need for transformers or inductances.
Implementation Method 1
a rectifier, which is coupled to the first input connection and the second input connection, wherein the rectifier has an output with a first output connection and a second output connection
Implementation Method 2
a first storage capacitor, which is connected in parallel with the first cascade of LEDs, at least one second unit, which includes at least the second cascade of LEDs and a second storage capacitor
Implementation Method 3
the at least one second unit also includes a diode, which is coupled in series with the parallel circuit including the second cascade of LEDs and the second storage capacitor
Implementation Method 4
at least the second cascade of LEDs
Data Source
AI summary
An electronic ballast may include: a rectifier; a first unit including a first cascade of LEDs and a first storage capacitor connected in parallel with the first cascade; a second unit including at least a second cascade of LEDs and a second storage capacitor connected in parallel with the second cascade; wherein the second unit includes a diode coupled in series with the parallel circuit including the second cascade; wherein the electronic ballast includes: a current controller with an actual value input and a setpoint value input, a setpoint value presetting apparatus for the current through the cascades, wherein the setpoint value presetting apparatus is designed to provide a setpoint value at the setpoint value input which is proportional to the voltage at the output of the rectifier; a first actuating element; wherein the controller includes a drive output coupled to the first actuating element and a second actuating element.