Many modern SLIC circuits require a protector with a breakdown voltage that can be modified or programmed. Littelfuse trademarked the name BATTRAX for their line of these sophisticated devices. These devices are not actually SIDACtor devices at all, but specially designed SCR devices in a diode array. The SCR is triggered when a voltage more negative than the reference voltage is detected. This means that the protection voltage is determined by the voltage on the reference pin. Most SLIC circuits still require the protection diodes for positive surges. However, there are some SLIC devices that now ring the telephone line with positive voltages. For these applications Littelfuse also makes positive voltage tracking devices.