Current vs. voltage properties of a diode
The current-voltage, (I-V) Characteristics Curves define the operating As its name suggests, I-V characteristic curves show the relationship between the current flowing Semiconductor diodes are characterized by non-linear current– voltage. Semiconductor diode schematic symbol: Arrows indicate the direction of electron . An equation describes the exact current through a diode, given the voltage. ID characteristic relating diode voltage and current can be described by an exponential relationship: where IS and n are scale factors, and kT/q.
It obeys Ohm's law ; the current is proportional to the applied voltage over a wide range. Its resistanceequal to the reciprocal of the slope of the line, is constant.
Shockley diode equation
A curved I—V line represents a nonlinear resistance, such as a diode. In this type the resistance varies with the applied voltage or current. Negative resistance vs positive resistance: An I—V curve which is nonmonotonic having peaks and valleys represents a device which has negative resistance.
Regions of the curve which have a negative slope declining to the right represent operating regions where the device has negative differential resistancewhile regions of positive slope represent positive differential resistance.
Negative resistance devices can be used to make amplifiers and oscillators.
Tunnel diodes and Gunn diodes are examples of components that have negative resistance. Devices which have hysteresis ; that is, in which the current-voltage relation depends not only on the present applied input but also on the past history of inputs, have I—V curves consisting of families of closed loops.
Each branch of the loop is marked with a direction represented by an arrow. Examples of devices with hysteresis include iron-core inductors and transformersthyristors such as SCRs and DIACsand gas-discharge tubes such as neon lights. I—V curve similar to a tunnel diode characteristic curve.
Current–voltage characteristic - Wikipedia
VBO is the breakover voltage. Memristor I—V curve, showing a pinched hysteresis Gunn diode I—V curve, showing negative differential resistance with hysteresis notice arrows In electrophysiology[ edit ] An approximation of the potassium and sodium ion components of a so-called "whole cell" I—V curve of a neuron. While I—V curves are applicable to any electrical system, they find wide use in the field of biological electricity, particularly in the sub-field of electrophysiology.
In this case, the voltage refers to the voltage across a biological membrane, a membrane potentialand the current is the flow of charged ions through channels in this membrane. The current is determined by the conductances of these channels. In the case of ionic current across biological membranes, currents are measured from inside to outside. That is, positive currents, known as "outward current", corresponding to positively charged ions crossing a cell membrane from the inside to the outside, or a negatively charged ion crossing from the outside to the inside.
Similarly, currents with a negative value are referred to as "inward current", corresponding to positively charged ions crossing a cell membrane from the outside to the inside, or a negatively charged ion crossing from inside to outside. The figure to the right shows an V—I curve that is more relevant to the currents in excitable biological membranes such as a neuronal axon.
The blue line shows the V—I relationship for the potassium ion.
Note that it is linear, indicating no voltage-dependent gating of the potassium ion channel. The yellow line shows the V—I relationship for the sodium ion. A few lucky electrons and holes may happen to pick up a lot of thermal kinetic energy. This gives them enough 'go' to cross the barrier, hence the reversed biassed current is not zero, just very, very small.
Introduction to Diodes And Rectifiers
When the voltage is applied this way round it tends to push the electrons and holes towards the junction. It also reduces the height of the energy barrier and reduces the width of the depletion zone. These effects make it easier for free electrons and holes with modest amounts of thermal kinetic energy to cross the junction.
As a result, we get a sizeable current through the diode when we apply a forward bias voltage. If you look up diodes in a physics book you'll probably find an explanation which finishes up telling you that current through a diode varies exponentially with the applied voltage.
The shape of this exponential curve depends upon various factors which include a 'fiddle factor' called the saturation current. There are two problems with this result.V-I Characteristics of PN Junction Diode
One is that the equation is fairly complicated and quite difficult to use for analysing some circuits. The second problem is that this equation is usually wrong! Being simple souls who like a quiet life, electronic engineers deal with these problems by simplifying things and using whichever of the following three models of the diode suits them. Vd represents the height of the diode barrier when no voltage is applied.
This means that the energy required for an electron or hole to be able to cross the barrier is eVd.