On electronics repair forums, one of the most discussed topics is disabling the protection pin on the LX1692 to force the backlight to stay on. This is considered a diagnostic technique or a last-resort repair, not a best practice.
While not a sensor pin, the Enable pin is part of the protection logic. If the system microcontroller detects a fault elsewhere, it pulls this pin low to force the LX1692 into shutdown mode. lx1692 protection pin
The protection pin often reads voltage from a resistive divider connected to the lamp return or the transformer’s secondary. As resistors drift in value (common in older electronics), the voltage on the protection pin can creep up to 1.5V or higher, falsely triggering shutdown. On electronics repair forums, one of the most
| State | PROT Pin Voltage | IC Outputs (PWM) | |---|---|---| | Normal | ~5V | Switching | | Fault detected (first few cycles) | ~5V (no change) | Switching | | Fault confirmed | 0V | Hi-Z (off) | | After ( V_CC ) reset | ~5V (rising edge) | Switching resumes | The protection pin often reads voltage from a
Internally, the PROT pin is connected to:
Normal Operation: The pin is pulled high (≈5V) by the internal current source. Fault Condition: The IC turns on the internal open-drain transistor, grounding the PROT pin (≈0V). Latch: Once the PROT pin is pulled low (by internal or external means), the IC latches off all PWM outputs. The only way to restart is to cycle the ( V_CC ) power (power-on reset).
Old lamps draw more current than new ones. The LX1692 monitors current balance between two lamps. An imbalance causes a DC offset that eventually triggers the protection pin. Fix: Replace lamps or balance transformers.