LED Driver Circuit Reducing Glow Currents via Four-Quadrant Switching
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Solution Overview
Problem
Modern circuit arrangements for semiconductor light sources experience undesirable glow currents due to parasitic capacitances, causing them to emit light even when switched off, which is noticeable in dark environments.
Innovation Solution
A circuit arrangement with a four-quadrant switch configuration, including diodes and MOSFETs, along with specific capacitor and resistor configurations, is implemented to reduce glow currents by minimizing parasitic capacitance and impedance, utilizing voltage-dependent switching elements like SIDACs and TVS diodes to further suppress glow currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a diode is connected in series between the DC-DC converter and the output terminal to reduce glow current, then the glow current is significantly reduced, but power losses occur due to the diode's forward voltage drop
Solution Approach 1:
The patent changes the electrical parameters of the circuit by using MOSFETs with dynamically controllable resistance instead of fixed-parameter diodes. The MOSFETs are switched between on and off states to control current flow, eliminating the continuous forward voltage drop losses inherent in diode-based solutions while still preventing glow current effectively.
2Object-affected harmful factors
If a MOSFET is used as a switch to reduce glow current, then the glow current is suppressed, but parasitic capacitances of the MOSFET still allow some glow current to flow
Solution Approach 1:
The patent introduces an intermediary circuit consisting of series-connected MOSFETs and diodes that act as a barrier to glow current. This intermediary configuration creates a four-quadrant switch that blocks reverse current flow more effectively than a single MOSFET, compensating for the parasitic capacitance effects of individual components.
3Ease of operation
If the circuit is permanently connected to mains voltage for permanent switching capability, then switching control is enabled, but parasitic capacitances induce glow current in the semiconductor light sources
Solution Approach 1:
The patent applies preliminary anti-action by pre-configuring the output stage with series-connected MOSFETs and diodes that are specifically designed to block reverse current flow. This pre-configured barrier prevents glow current from flowing through the LED string even when the circuit remains connected to mains voltage, while still allowing controlled switching operation.
4Object-affected harmful factors
If Y-capacitors are connected between the output terminal and ground to reduce glow current, then some glow current is reduced, but the capacitors themselves create voltage fluctuations that can induce glow
Solution Approach 1:
The patent extracts the glow current suppression function from the Y-capacitor and places it in the series path of the output stage using MOSFETs and diodes. By removing the Y-capacitor's glow suppression role and replacing it with active switching components in series, the patent eliminates the voltage fluctuation issue while maintaining effective glow current blocking.
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 glow currents to an imperceptible level in dark environments, improving efficiency and eliminating power losses associated with existing diodes, while maintaining cost-effectiveness through shared driver circuits and efficient energy handling.
Implementation Method 1
a rectifier circuit (140) for converting the AC input voltage into a rectified voltage
Implementation Method 2
a converter circuit (150) for converting the rectified voltage into a current suitable for the semiconductor light sources
Implementation Method 3
Due to parametric capacitances, the mains AC voltage can induce a small current in the semiconductor light sources
Data Source
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AI summary
Circuit arrangement (100) for operating semiconductor light sources (55) having: – a power input (110) for inputting an input AC voltage, – an output (120), having a 1st output connection (122) and a 2nd output connection (124), that is set up to connect a string of semiconductor light sources (55), – a control input (130) for controlling the operation of the circuit arrangement (100) with a control signal (ST), – a rectifier circuit (140) for converting the input AC voltage (UE) into a rectified voltage, – a converter circuit (150) for transforming the rectified voltage into a current (IB) suitable for the semiconductor light sources, – a 1st switch (S1), arranged between the converter circuit (150) and the output (120), for switching the current through the semiconductor light sources, – a 1st diode (15) arranged between the 1st switch (S1) and the output or between the converter circuit and the 1st switch (S1). The known problem of semiconductor light sources glowing in the switched-off state is reduced according to the invention in this case such that it is no longer perceptible in practice.