Electronic – what is the load line and operating point used for in practical

diodesloadnon-linear

I have a hard time understanding what an operating point and load line represent and why do we need them at all.

After reading some wikibedia,

  • What I got is this load line represent response of the linear circuit attached to the diode for changing in voltage across it.

But, this doesn't seem to answer my question about

  • why do we even need this and what does it represent exactly in a little more simple detail.

Best Answer

Load lines are useful in understanding and calculating the operating point of a circuit which would otherwise require complex calculations. Diodes have a non-linear relationship between I and V and we often use an approximation such as "2 V drop across the LED" when making calculations. We can do better if we have a load line chart.

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Figure 1. A simple LED circuit.

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Figure 2. Loadlines for various resistors on 5 V supply. Image source: LEDnique.

Here we can quickly calculate the operating point of an LED.

  • If we used a 180 Ω resistor on a RED LED we would expect to get 18 mA through the LED.
  • If we wanted 10 mA through a blue LED we can see that the 270 Ω resistor would do the job.

No calculations involved (once the graph has been created). To create the graph draw the lines from the supply voltage point on the V-axis and the \$ \frac V R \$ point on the I-axis.

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