Linear-Mode MOSFET Switching for Multi-Group LED Peak Current Control
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Solution Overview
Problem
LED drivers experience unwanted peak-currents when switching between LED groups with different forward voltages, potentially damaging the switched LED group.
Innovation Solution
An LED driver with a control unit that switches LED groups between nominal and transition modes, using capacitors and resistors to manage current flow during transitions, reducing peak currents by controlling gate-to-source voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the switch is quickly switched from one LED group to another LED group with different forward voltage, then the switching speed is improved, but peak current is generated which may damage the LED group
Solution Approach 1:
Before switching the main switch from one LED group to another, the control unit first sets the switch to a transition mode with a first gate-source voltage that is lower than the nominal gate-source voltage. This preliminary action prepares the switch to gradually conduct current, preventing sudden peak current when switching to an LED group with lower forward voltage, while still allowing relatively fast switching operation.
Solution Approach 2:
The control unit dynamically changes the gate-source voltage parameter of the switch between different operating states: a first gate-source voltage during transition mode (lower than nominal) to limit current during switching, and a second nominal gate-source voltage during nominal mode for full conduction. This parameter change allows the switch to adapt its conductivity during the switching process, enabling fast switching while controlling peak current.
2Object-affected harmful factors
If the gate to source voltage of the switch is reduced during transition mode, then peak current is reduced, but the switching time is extended
Solution Approach 1:
The switching process is divided into two distinct periodic phases: a transition mode phase with reduced gate-source voltage to limit peak current, followed by a nominal mode phase with full gate-source voltage for complete conduction. This periodic action structure allows the system to manage peak current during the critical transition phase while minimizing the total switching time by quickly transitioning to full conduction mode once the peak current risk is mitigated.
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
Mitigates peak currents during LED group transitions, ensuring safe and efficient operation of LED fixtures by limiting current flow during transient periods.
Implementation Method 1
The LED fixture further comprises a capacitor arranged in a parallel connection to the plurality of LED groups. Such a capacitor is applied in order to reduce a high frequency which may occur on the current supplied to the LED groups otherwise.
Implementation Method 2
control the operation mode of the switch of the LED group between a nominal mode, wherein the switch operates in a closed nominal state or an open nominal state, and a transition mode, wherein the switch operates in a semi-closed state, wherein the gate to source voltage of the switch of the LED group is lower than the gate to source voltage of the respective switch when operated in the nominal mode
Data Source
AI summary
An LED driver configured to control a LED fixture comprising a plurality of LED groups is described, each LED group comprising at least one LED forming a series connection with a switch, wherein the plurality of LED groups are arranged in a parallel connection, the LED fixture further comprising a capacitor arranged in a parallel connection to the plurality of LED groups, the LED driver comprising:a power converter for converting an input power from a power source to a current which is provided to the plurality of LED groups;a control unit configured to control the power converter to provide the current to the plurality of LED groups, and wherein the control unit is further configured tocontrol an operation mode of the switch of the LED group between a nominal mode, wherein the switch operates in a closed nominal state or an open nominal state, anda transition mode, wherein the switch operates in a semi-closed state, wherein a gate to source voltage of the switch of the LED group is lower than the gate to source voltage of the respective switch when operated in the nominal mode,switch the current from flowing through a first LED group to flowing through a second LED group, wherein the first LED group has a higher forward voltage than the second LED group, by switching the switch of the first LED group in the open nominal state and the switch of the second LED group in the semi-closed state during a transient period.