A bipolar transistor can be on or off, or in any of a variety of intermediate states. To control the state of the transistor, its electrode, called the base or base, serves.
Instructions
Step 1
Remember that a bipolar transistor, unlike a field-effect transistor, and also a vacuum tube, is not controlled by voltage, but by current. For an n-p-n device, this current must flow from base to emitter (that is, plus to base). If the transistor has a p-n-p structure, pass the current in the opposite direction to open it.
Step 2
Before controlling the load with a transistor, it must be connected correctly. Connect the emitter of the transistor directly to the common wire, and its collector through the load to the power supply. If n-p-n structures are used, this source should generate a positive voltage with respect to the common wire, and if p-n-p structures are used, then negative.
Step 3
Decide in which mode the device should work: analog or key. In the first case, a much larger heat sink is required. This is due to the fact that a very small current flows through a fully closed transistor, and a very small voltage is applied to a fully open transistor. When the device is partially open, both voltage and current are large, although not maximum. For this reason, the greatest power is allocated to the transistor precisely when it is not fully open.
Step 4
Calculate how much current must be passed through the base-emitter junction of the transistor in order for a certain current to begin 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.
Step 5
By further increasing the base current, you will find that the load current does not increase further. This means the transistor is saturated. The higher the load current, the higher the base current is required to saturate a transistor of the same type. If it is necessary to use the transistor in the key mode, always put it into saturation mode, and the heat generation on it in the open state will be minimal. Do not make the base current too high, however, to prevent the instrument from heating up from this current.
