A transistor AND gate outputs a small current when one of the inputs is HIGH. Why does this happen?
This is because of the base current. The current comes from the signal source.

Also, note that the demonstrated schematic is simply wrong. The proper AND gate has to amplify the signal, so with similar technique you can only build NAND element. If you need AND - simply make one NAND and then invert the output signal once more.







simulate this circuit &ndash; Schematic created using CircuitLab