# Does a silicon diode drop voltage by the same amount no matter how large the supply voltage?

Does a silicon diode drop voltage by the same amount no matter how large the supply voltage can get? I mean let's assume I have conducted the experiment in which I have connected only a diode and a resistor across a power supply. I will increase the power supply gently at the beginning, and I will notice the voltage across the diode. At the beginning when the voltage across the diode is below .70 V, I notice a one to one correspondence, that is when the supply voltage is 0.2V, the voltage drop across the diode is 0.2V given that zero current passes through the circuit. After we reach 0.7 voltage drop across the diode, the supply voltage is 10 V then, when I increase further supply voltage, like as high as 30 V, the voltage drop across the diode is just .74V increasing only .04 V when the supply voltage increased 3 times?!

The data isn't mine, I have just googled it.

• You might find my non-return valve analogy useful: lednique.com/what-is-an-led/…. Commented Dec 18, 2023 at 20:05
• Jack - Hi, Re: "The data isn't mine, I have just googled it." Please link to the source of that data, to give the required reference. Thanks. Commented Dec 18, 2023 at 20:35

Yes. Diode does not know if there is 100V or 1000V on one side. It will only have a voltage drop based on current over it.

• What if there was no resistance? Won't that violate Kirchoff's Law?
– Jack
Commented Dec 18, 2023 at 19:51
• @Jack then the diode will explode. The diode does not know if there is a resistance limiting current or not, but the drop of the diode depends on the current through it. Your circuit then just needs to sensible and let a suitable range of current flow. Commented Dec 18, 2023 at 19:54

The data sheet for a diode will have curves showing the Current .vs. Voltage.

E.g. for from the Vishay 1N4148 Small Signal Fast Switching Diode datasheet:

Note the use of a logarithmic scales on the Current .vs. Voltage curves since the current–voltage curve is exponential in accordance with the Shockley diode equation.

Semiconductor diodes has information on the characteristics of semiconductor diodes, which these days as mainly silicon.