Small high-voltage "blue" capacitors on the output stage often leak or short. How to Disable/Bypass (For Diagnostics ONLY)
Monitors voltage levels via COMP pins to trigger protection. Pin 15 provides a signal when a fault occurs. BD9766FV - Mouser Electronics
In these cases, replacement is the only fix. The IC is relatively inexpensive and readily available from major distributors.
DC-AC Inverter Control IC, the primary protection-related pins are Pin 21 (SCP1) Pin 22 (SCP2) bd9766fv protection pin
Aged or broken lamps draw uneven current, triggering the IS1/IS2 inputs.
The "protection pin" consolidates the logic for these safety features. It is not simply an input; it is a bidirectional pin that both senses faults and signals a shutdown.
The BD9766FV uses several pins to monitor and manage fault conditions: Pin 21 (SCP1) & Pin 22 (SCP2): These are connected to external capacitors that set the Timer Latch Small high-voltage "blue" capacitors on the output stage
The protection pin is left unconnected or the pull-up resistor is missing. The BD9766FV requires an external pull-up to VREF (typically 5V) for normal operation.
Here is a step-by-step explanation of how the protection pin works:
The BD9766FV uses a system. When a fault (such as a lamp failure, open transformer, or shorted MOSFET) is detected through the IS (Current Sense) or VS (Voltage Sense) pins, the IC begins charging the capacitors on the SCP pins. BD9766FV - Mouser Electronics In these cases, replacement
Always connect a 10kΩ to 100kΩ resistor from the protection pin to VREF. If the pin is left floating, internal leakage can keep it high, disabling the protection comparator.
The is far more than a simple enable line—it is the central nervous system for fault handling in your DC-DC converter. By understanding its latch vs. hiccup behavior, respecting layout guidelines, and properly sizing external pull-ups and timing capacitors, you can design a power supply that is both efficient and failsafe.