STEF033 Electronic Fuse for 3.3V Line STMicroelectronics STEF033 Electronic Fuse for 3.3V Line is optimized for monitoring output current and input voltage. The STEF033 is connected in series to the 3.3V rail and is able to protect the electronic circuitry on its output from overcurrent and overvoltage. The STEF033 has controlled delay and turn-on time. When an overload condition occurs, the device limits the output current to a predefined safe value. If the anomalous overload condition persists, it goes into an open state, disconnecting the load from the power supply.