![]() For a lot of transistors (at room temperature) we can estimate this drop to be about 0.6V.Īnother reality bummer: there won't be perfect conduction between emitter and collector. There are many abbreviations for this voltage drop - V th, V γ, and V d are a few - and the actual value varies between transistors (and even further by temperature). The voltages from base to emitter (V BE), and the from base to collector (V BC) set the transistor's mode:īecause the junction from base to emitter looks just like a diode, in reality, V BE must be greater than a threshold voltage to enter saturation. To determine which mode a transistor is in, we need to look at the voltages on each of the three pins, and how they relate to each other. Current flows from emitter to collector (not, exactly, the purpose transistors were designed for). Reverse-Active - Like active mode, the current is proportional to the base current, but it flows in reverse.Active - The current from collector to emitter is proportional to the base current.No current flows from collector to emitter. Cut-off - The transistor acts like an open circuit.Current freely flows from collector to emitter. Saturation - The transistor acts like a short circuit.(When we talk about current flow through a transistor, we usually mean current flowing from collector to emitter of an NPN.) They have four distinct modes of operation, which describe the current flowing through them. Unlike resistors, which enforce a linear relationship between voltage and current, transistors are non-linear devices. Share on Twitter Share on Facebook Pin It Operation Modes ![]()
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