Aijiren II Preparative Autosampler User Manual Page 220 All common TTL circuits operate with a 5 V power supply. A TTL signal is defined as "low" N O T E or L when between 0 V and 0.8 V and "high" or H when between 2.0 V and 5.0 V (with respect to the ground terminal). Aijiren II Preparative Autosampler User Manual