Determine the operating point of a diode

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In physics you can be given the task of determining the working point of a diode. To solve the task, you need different equations. The calculation is conclusive and therefore easy to solve after understanding the basic formulas.

The working point of a diode is determined in physics

The calculation of the working point of the diode comes from the area of physics. However, the tasks are only carried out in high-school diploma or calculated at the universities as they are demanding.

  • When applying these calculations, you may need the mathrm command, depending on the nature of the task. This ensures that the font is converted from italic to upright font during a calculation. There are no spaces, umlauts or the ß in the display.
  • The so-called frac, which ensures that a value is mapped to the decimal value, can also be used in the calculation.
  • You can determine the operating point of a semiconductor diode as well as the reverse direction. The tasks set can be very different. You often have to support the calculation with a drawing.
  • If a switch is used, the operating point can change on the characteristic. This makes the tasks very complex. You should first clarify the calculation with a simple example in order to have the basics ready. Then even complex tasks can be solved well.
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You use two equations

To determine the operating point of a diode, you use several formulas. This is because there are usually two unknowns in the calculation that you need to calculate. The two unknowns you are looking for are labeled I and UD.

  1. Use the mesh theorem to work out the equation: U0 = I*R + UD. This equation will benefit if you graph it. The need arises from the fact that the second equation is given by the characteristic curve of the diodes. However, this is not a so-called closed equation, it is only available in a graphic representation.
  2. Draw the following equation in a coordinate system: I = -UD/R + U0/R. This is a straight line with a slope of -1/R. The straight line intersects the so-called ordinate, which is also known as the I axis. The value is U0/R. Both straight lines intersect the characteristic curve of the diodes. This allows you to find the unknowns you need for the equation. This is how you get the values ​​I and UD. It is important that both equations are fulfilled. In the graphic representation of both equations, these are fulfilled at their point of intersection.
  3. In the further performance of the task you need to take into account the barrier layer. The current is specified, but the voltage is not taken into account. You also refer to this specified current as the reverse current. However, the voltage must be below the breakdown voltage. This is because you are not using a zener semiconductor diode.
  4. Now use the mesh law and insert the depletion layer, which is always negative, and the voltage U0, which is also negative, into the equation. In this way you can determine the operating point of a diode.

You can take different temperatures into account when doing the calculations. These affect the voltage dropped by the diode.

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