Gas chromatography-mass spectrometry (GCMS) is a method that combines the features of gas chromatography and mass spectrometry to identify different substances within a test sample. Applications of GCMS include environmental analysis, ecological tests, drug analysis, explosives investigation, and identification of unknown samples. A Supersonic Molecular Beam GCMS (SMB-GCMS) is an advanced technique that improves the data quality of conventional GCMS. Electron Ionization (EI) is an ionization method in which energetic electrons interact with gas phase molecules to produce ions. This technique is widely used in mass spectrometry and especially in GCMS instrumentation. In such EI ion source, electrons are produced through thermionic emission by heating a wire filament that has electric current running through it. The electrons are than accelerated (usually to 70 eV) before contacting and ionizing the molecules. In this system the most important parameter is the filament emission current that determines the ionization rate, thus, we need to regulate this current to the pre determined value. On the one hand, we need fast responses control to keep the emission current constant, but on the other hand, we need to protect the filament from damages that occur by large filaments current transients. To control our filament and emission current, we developed a digital circuit based on DSP controller that has several modes of operation. We use a smart algorithm that has a fast response to small signal and a slow response to large signal. In addition we have several protections that prevent the current from reaching unsafe values.