I was sitting in the classroom thinking: “this is boring”.

I loved electronics, but now the professor was going on about “N and P materials”.

And some kind of graph that I did not understand.

We were learning about the diode. Which I wanted to learn. But those graphs did nothing for me.

I was falling asleep.

Even though it’s obvious for those who know the basics of electronics - nobody ever told me the fact I’m about to share…

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Once I learned this, everything became much easier:

A diode has something called a forward voltage.

It’s often written as Vf in datasheets.

And here’s the thing:

A diode will have that voltage across its pins when current is flowing in the “forward” direction (from anode to cathode).
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Q: Why is this so important?

Because it makes it easier to see what’s going on in a circuit!

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Example:

You have a circuit with a resistor and a Light-Emitting Diode (LED) with a 2V forward voltage (Vf). That means there will be 2V across the LED. So the rest of the voltage will be across the resistor.

Then you can use Ohm’s law to calculate the current:

The current is equal to the voltage across the resistor, divided by the resistor value.

This is the type of logic thinking I do when I want to figure out what a circuit does.

“I know the voltage here must be X. That means this voltage here must be Y. That means the current must be Z.”

This train of thought was made possible by knowing:

• That the diode has Vf across itself
• That the voltage applied to a circuit always completely drops across the components in the circuit.
• Ohm’s law

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Want to learn these things so that you can make your own reasonings of circuits? The learning track Learn the Basics of Electronics [Members Only] in Ohmify will help you do exactly that.

Keep On Soldering!
Oyvind @ build-electronic-circuits.com