Volt-ampere characteristic of electronic devices

It would be worthwhile to start the narrative with Edison. This curious husband of science experimented with his incandescent bulb, trying to reach new heights in electric lighting, and invented a diode lamp by accident . In a vacuum, the electrons left the cathode and were carried away towards the second electrode, separated by space. The rectification of the current at that time knew little, but the patented invention eventually found its application. It was then that the volt-ampere characteristic was needed. But first things first.

The volt-ampere characteristic of any electronic device - vacuum, as well as semiconductor - helps to understand how the device behaves when plugged into an electrical circuit. In fact, this is the dependence of the output current on the voltage applied to the device. The predecessor of the diode invented by Edison is designed to cut off negative voltage values, although, strictly speaking, everything will depend on the direction of inclusion of the device in the circuit, but about this some other time, so as not to bore the reader with unnecessary details.

Thus, the current-voltage characteristic of an ideal diode is a positive branch of a mathematical parabola known to most in school lessons. Current through such a device can flow only in one direction. Naturally, the ideal is different from real life, and in practice with negative voltage values there is still a parasitic current called reverse (leakage). It is much smaller than the useful current, called direct, but, nevertheless, it is not necessary to forget about the nonideality of real devices.

The vacuum triode differs from its younger colleague with two electrodes by the presence of a control grid, partitioning across the middle section of the vacuum bulb. A cathode with a special coating facilitating the separation of electrons from its surface served as a source of elementary particles that received the anode. The flow was controlled by the voltage applied to the grid. The current-voltage characteristic of a vacuum triode lamp is very similar to a diode lamp, but with one more refinement. Depending on the voltage on the base, the parabola coefficient undergoes a change, and a family of lines of similar shape is obtained.

Unlike a diode, triodes operate at positive voltages between the cathode and the anode. The required functionality is achieved by manipulating the grid voltage. And, finally, we need to make a last clarification. Since the cathode has a finite ability to emit electrons, then on each characteristic there is a saturation region, where a further increase in voltage no longer leads to an increase in the output current.

Despite the different nature and principles of operation, the current-voltage characteristic of the transistor is not too different from the transistor, only the steepness of the parabola is relatively large. That is why lamp circuits on mature thinking often transferred to a semiconductor base. The order of physical quantities is different, transistors use incomparably lower supply voltages. In addition, semiconductor devices can be controlled by both positive and negative voltages, which gives a greater degree of freedom to designers when designing circuits.

To fully satisfy the requests for the transfer of ready-made solutions, devices with a photoelectric effect were invented. True, if the lamps used its external version, then the improved element base for understandable reasons functions on the basis of the internal photoeffect. The current-voltage characteristic of the photoelectric effect is different in that the value of the output current is shifted, depending on the illumination. The intensity of the light flux is higher, the greater the output current. So phototransistors work, and photodiodes use the reverse current branch. This helps create devices that capture photons and are controlled by external light sources.