The bipolar transistor may be open or closed, and in any of a plurality of intermediate states.
To control the state of the transistor serves as its electrode, called the base or base.
Remember that a bipolar transistor, in contrast to thefield, as well as an electronic tube, not controlled voltage and current. In the device structure of n-p-n, this current must pass in a direction from the base to the emitter (i.e., plus database). If the transistor has a p-n-p structure for the current miss its opening in the opposite direction.
Before controlled by transistorload, it must be connected correctly. The emitter of transistor is connected directly to ground and its collector - through the load to a power source. When using the structure of n-p-n, this source would produce a positive voltage relative to the common wire, if the structure of p-n-p, then negative.
Decide which mode shouldwork device: analog or key. In the first case it will require much larger heat sink. This is due to the fact that in a fully enclosed transistor runs very small current, but to fully open a very small applied voltage. When the device is partially open, high, but not maximum, the values of both voltage and current. For this reason, the maximum power allocated to the transistor at a time when it is fully opened.
Calculate how much current is necessary to passvia the base-emitter junction of the transistor to the load began to take a certain current. To do this, the desired load current divide by the dimensionless parameter of the device, called the current transmission rate.
By a further increase in base current, youYou find that on the load current does not increase. This means that the transistor is saturated. The larger the load current, the greater the saturation of the transistor of the same type is required base current. If you need to use a transistor in switching mode, always switch it in saturation mode, and heat it will be minimal in the open state. Do not, however, the base current is too high, that the instrument has not started to heat up by this current.