![]() ![]() This ratio of C-E current to B-E current is the basic gain of the transistor. The gain, and hence the useful properties, of a BJT come from the fact that is only takes a little current to muck up the reverse biased junction such that it allows a lot more C-E current to flow. However, the special property of a BJT is that a little current thru the base messes up the insulating capability of the reverse biased junction. The reverse biased junction doesn't allow any (except for small leakage we will ignore) current to flow. You apply a voltage accross C-E and with the base open nothing happens. ![]() As for the C-B junction, keeping that reverse biased is fundamental to how BJTs operate.Ī BJT is basically a reverse biased junction that can be made selectively leaky. To keep it off, you want to not forward bias the B-E junction. Whether you do depends on what you want the transistor to do. You don't need to forward bias the B-E junction. ![]()
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