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Shockley Diode Calculator

Use the Shockley diode calculator to obtain the I-V characteristic of a real or ideal diode.

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Diode current11.8719 mAI_s(e^(V/nV_T) − 1) at 0.6 V
Thermal voltage V_T25.8649 mVkT/q at 300.15 K — about 25.9 mV at room temperature, and it scales with ABSOLUTE temperature
Voltage for ten times the current59.5562 mVabout 60 mV per decade at room temperature — this is the number to remember, and it is why a diode looks like a fixed 0.7 V drop over a wide current range
Dynamic resistance at this current2.1787 ΩnV_T ÷ I — the small-signal slope, which falls as the current rises
At 0.4 V5.2041 µAa -200 mV change gives a 0× current change
At 0.5 V248.5608 µAa -100 mV change gives a 0× current change
At 0.7 V567.0295 mAa 100 mV change gives a 47.8× current change

The formula

I = I_s(e^(V/nV_T) − 1); I_D = ½k(V_GS − V_th)²

Exponential, square law, and why it matters

A diode's current rises exponentially with voltage — about a decade for every 60 mV at room temperature. That steepness is why a diode behaves like a fixed 0.7 V drop over a wide current range, and why driving one from a voltage source is destructive: 60 mV of error is a factor of ten in current.

A MOSFET in saturation follows a square law in the overdrive voltage, which is far gentler. That makes MOSFETs easier to bias and much better at paralleling, helped by their threshold falling with temperature so a hot device turns on harder and shares current — whereas a hot bipolar takes more current and runs hotter still.

The bipolar result worth knowing is that voltage gain depends on the collector current and the load resistor, not on beta. Since beta varies threefold between nominally identical parts and drifts with temperature, that independence is what makes bipolar amplifiers designable at all. The fixed-base-resistor bias shown here sets base current rather than collector current, so it inherits all of beta's variability — which is why real circuits use an emitter resistor and a divider.

The thermal voltage kT/q scales with absolute temperature, so every one of these relations shifts as a device warms. Hard-coding 25 mV is a room-temperature approximation, not a constant.