# Voltage drop, Forward voltage and Forward Voltage drop

Joined Mar 3, 2015
19
In the continuous quest to familiarize myself with electronic circuits, I have come across 3 terms that I'd appreciate some help to clear in my head. So, Voltage drop, Forward voltage and Forward Voltage drop. Are we talking about the same thing here?

Here's an example, trying to figure out what resistor I should use in the circuit:

Say I am using a 9V battery to power a circuit with a LED that in the datasheet says that the Forward voltage is 2V. The led has the typical Forward current of 20mA.

So, R = V(9-2) / 20mA = 7V / 20mA = 350 Ohms

Is the above correct? If so, what is the voltage drop about, and furthermore, what is the Forward voltage drop?

Thanks!
John

#### Dodgydave

Joined Jun 22, 2012
10,322
yes correct, use a 330 ohms resistor preferred value. Leds have a voltage drop of 1.8 to 3.6V depends on the colour.

#### crutschow

Joined Mar 14, 2008
29,828
Forward Voltage Drop and Forward Drop are the same, and both refer to the Voltage Drop across the device (diode or LED) in the forward (conducting) direction.

#### WBahn

Joined Mar 31, 2012
26,398
You may also encounter the term "diode drop" to mean this same thing. Different people use different terms and may use the same terms to mean different things in different situations. The assumption (and it's an unconscious one most of the time) is that someone reading it will be sufficiently familiar with the concepts to extract the right meaning from the context of where and how the terms are used. It usually works just fine because that is something that humans tend to be very good at. But it does make it hard for someone that is new to field and hasn't learned the jargon yet.