Bipolar transistors come in n-p-n and p-n-p structures. It is most convenient to switch them on according to the common emitter scheme. Depending on the application, the transistor can be made to operate in a key or linear mode.
Instructions
Step 1
Regardless of which mode the transistor will operate in, connect its emitter to the common wire directly, and the collector to the power bus through the load. If the device has an n-p-n structure, there should be a positive voltage on the power rail, and if the p-n-p structure is negative. Ensure that the transistor parameters (allowable on-state current, allowable off-state voltage, power dissipation) are sufficient to control the load that is connected to it.
Step 2
To open the transistor in the key mode, apply a supply voltage to its base through a resistor. Select its resistance so that the base current is slightly higher than the number that will be obtained if the rated load current is divided by the gain of the transistor. If the base current is too low, the device will overheat, because it will not be fully open, and if it is too large, from the base current itself.
Step 3
To put the transistor in analog mode, apply a bias to the base. To do this, also connect it to a power source through a resistor, but this time select its resistance so that the voltage at the collector of the transistor relative to the common wire is equal to half of the supply. Then about 50% of the power will be dissipated on the load, and the remaining 50% on the device itself. Use a radiator to keep it from overheating.
Step 4
When operating a transistor under conditions of temperature change in a wide range, it will be necessary to ensure thermal stabilization of its mode. To do this, connect the upper terminal of the bias resistor to the collector rather than to the power bus.
Step 5
Apply a variable control signal to the base of the transistor operating in linear mode through a capacitor. If the stage is not an output stage, use a resistor as the load, and remove the output signal from the collector also through a capacitor. In this form, it can be fed to the next stage.
