Hi, I'm learning Bipolar Junction Transistor and need help to confusion which arise so I will keep posting questions which I don't understand to this thread. Thank you in advance. So my questions start: When using hybrid pi model and t model, we determine the dc operating point first. In one example, I saw that they make vi=0. My question is that should all sources be made zero to find dc currents? Also, determining dc operating point means only finding dc collector current or do we find other currents (such as dc emitter current) or voltages?