Reverse Engineering the LIDL LED Driver: A Guide to Constant Current Circuitry

Overview

This technical teardown deconstructs a LIDL LIDL LED light fitting to analyze its internal power delivery system. While the chassis is functionally unserviceable—earning it the label of "landfill tech"—the internal driver presents a surprisingly robust implementation of an isolated constant current supply. Understanding this circuit matters for hardware enthusiasts who want to repurpose high-quality power components from otherwise disposable consumer electronics.

Prerequisites

To follow this logic, you should understand:

• AC/DC Rectification: How bridge rectifiers convert mains voltage.
• Isolated vs. Non-Isolated: The safety implications of transformer-based separation.
• Constant Current Regulation: Why LEDs require specific amperage (260mA) rather than fixed voltage.

Key Components & Tools

• KP11191: The primary switching controller chip managing the power conversion.
• Transformer: Provides galvanic isolation with triple-insulated windings.
• ES2G Diode: A high-speed rectifier used on the secondary output side.
• Fusible Resistor: Acts as a sacrificial safety component (15 ohm) during catastrophic failure.
• Low ESR Capacitor: High-frequency electrolytic capacitor (47µF, 50V) critical for stability.

Code Walkthrough: The Schematic Logic

We can represent the driver's power logic through this functional pseudocode flow:

void driveLEDs() {
    // Input Stage: Safety and Rectification
    apply_mains_power(230V_AC);
    pass_through(fusible_resistor_15ohm);
    bridge_rectify(); // Convert to DC
    
    // Filtering Stage
    filter_noise(inductor_4_7mH, filter_capacitor_220nF);
    
    // Controller Loop (KP11191)
    while (power_on) {
        float current = sense_current(resistor_1_5ohm);
        if (current < target_260mA) {
            switch_mosfet(ON); // Energize transformer
        } else {
            switch_mosfet(OFF); // Collapse field to secondary
        }
        monitor_ovp(pin_10k_resistor); // Check for open circuit
    }
}

The KP11191 monitors the secondary side via the collapsing magnetic field in the transformer. It uses a 1.5 ohm current sense network to maintain a steady 260mA output, even as the forward voltage of the LED string fluctuates between 25V and 40V.

Syntax Notes

• Current Sensing: The controller uses two 3-ohm resistors in parallel to achieve 1.5 ohms. This distributes heat and allows for fine-tuning the output current.
• Snubber Network: A diode-resistor-capacitor (RCD) snubber protects the internal MOSFET from voltage spikes during high-speed switching.

Practical Examples

• Driver Salvage: Remove the driver from the "landfill" housing to power 9-13 one-watt LEDs in a custom enclosure.
• Repair: If the light flickers, replace the output low ESR capacitor, as this is the most common point of failure due to thermal stress.

Tips & Gotchas

• Heat Transfer: The manufacturer glues the driver to the metal case. When repurposing, ensure adequate airflow since the driver is rated for 10W.
• ID Identification: To read faint markings on the KP11191 chip, rub a small amount of thermal paste (zinc oxide) over the surface and wipe it clean to highlight the etched text.