Circuit Diagram Symbols | Lucidchart Common circuit diagram symbols. Our circuit diagram symbol library is schematic and includes many icons commonly used by engineers. From transistors to logic gates, you’ll find icons that are modeled to international standards. Our icons are grouped into different symbol families, outlined below. Circuit Icons - 873 free vector icons - flaticon Circuit free vector icons in SVG, PSD, PNG, EPS format or as ICON FONT. Thousands of free icons on the largest database of free vector icons! Download over 873 icons of circuit in SVG, PSD, PNG, EPS format or as webfonts.