Apparatus – Measuring apparatus
Circuit with common emitter
The task is constructed so as to be able to measure the output (collector) characteristic and transfer characteristic (current) characteristic, especially to determine current gain common emitter configuration β - Defined by equation (1). For those interested in the job will probably be extended in the future as well as the possibility of measuring the input transistor characteristic.
A way of measuring this role is based directly on the principle of a transistor. Second NPN transistor is connected in common emitter configuration (see Fig. 1). When connecting the transistor emitter is connected in the emitter junction forward biased and the collector in the reverse direction. Base circuit and the collector circuit have a common terminal of the transistor - emitter (hence the name: the circuit with common emitter).
Fig. 1 – Diagram of the Circuit with common emitter
In circuit transistor emitter can achieve maximum power gain in comparison with other activations transistor because there amplifies the voltage and current. Power amplification then can take values from 103 to 104. That is the reason why the circuit with common emitter is so often used.
The characteristics of the transistor
Measurement of transistor characteristics is the measuring of the electric element called two-port. We measured the dependence of the input voltage UB and current IB (base circumference) and the dependence of voltage UCE and current IC on the output (collector circuit). Searched characteristic are determined by interaction between these variables - of course precisely specified under applicable definitions of transistor characteristics (eg. the necessity compliance with a constant voltage, etc.).
It was used the bipolar transistor 2N3055 for this experiment. This transistor is quite often used as a power output stages of different amplifiers. These transistors and their characteristics are well documented thanks to it. It can therefore be acquired experimental the values compare well with the values of the catalog or data sheet. Furthermore, the limit parameters are far the maximum voltages and currents which can be achieved in this experiment, a remote – therefore there is no risk of damage to the transistor, and even in case that the remote experiment accidentally unchecked.
Apparatus
Transistor 2N3055 is connected to the experimental USB board K8055 (see Fig. 2). Voltage-based transistor is configured using the output of the first DA converter USB board K8055. The next DA output of the same experimental board serves as a variable source voltage for the collector circuit. This allows you adjusted the size of both the voltage on the known values. Both DA output of the USB board K8055 are boosted, the current for collector circuit is added from an external power supply. Conversely, for reading electrical values is a pair of inputs AD converters, which is also equipped with a USB experimental board. These ADCs are used as ampermeters for loading flowing currents in the two circuits and a voltmeter to determine the voltage between the collector and emitter UCE.
Fig. 2 – Connection of the transistor to the inputs
and outputs of the K8055 board
The control panel allows tasks using a pair of sliders (see below) to set the voltage at the base and collector. It is therefore also affected by the size and the size of the base-current voltage between the collector and ground, thereby enabling adjustment of voltage UCE between the emitter and collector. In retrospect, it is loaded on the control panel real size of electrical currents and voltages UCE (or Base voltage UB).
The measured data are stored in a couple of different tables (each for one possible measurement of the characteristic). These series of values can be displayed in graph directly on the control panel, or can be individually saved as a CSV file and then subsequently processed in any spreadsheet.
This experiment is not equipped with a webcambecause in this experiment apparatus can not observe anything specific.
Video tutorial
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