The bipolar transistor can be in an open or closed state, as well as in any of a variety of intermediate states.
To control the state of the transistor is its electrode, called the base or the base.
Remember that a bipolar transistor, in contrast toField, as well as an electronic lamp, is controlled not by voltage, but by current. At the device of structure n-p-n this current should pass in a direction from base to emitter (that is, plus to the base). If the transistor has the structure p-n-p, to open it, pass current in the opposite direction.
Before driving with a transistorLoad, it must be properly connected. Connect the emitter of the transistor directly to the common wire, and its collector - through the load with the power source. If n-p-n structures are used, this source must generate a positive voltage relative to the common wire, and if the structure is p-n-p, then it is negative.
Decide on which regimeOperate the device: analog or key. In the first case, a much larger heat sink will be required. This is due to the fact that a very small current flows through a completely closed transistor, and a very small voltage is applied to the fully open transistor. When the device is partially open, the values of both the voltage and the current are great, although not the maximum. For this reason, the maximum power is allocated to the transistor when it is not fully open.
Calculate what current should be skippedThrough the base-emitter transition of the transistor in order that a certain current begins to flow through the load. To do this, divide the desired load current by the dimensionless parameter of the device, called the current transfer coefficient.
By further increasing the base current, youFind that the load current does not increase further. This means that the transistor is saturated. The higher the load current, the greater the base current required for saturation of a transistor of the same type. If it is necessary to use a transistor in the key mode, always put it into saturation mode, and the heat release on it in the open state will be minimal. Do not, however, the base current be too large so that the device does not begin to heat up from this current.