Importance of Forward Voltage on a Diode


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When thinking about the forward voltage on a diode there are several items that you might want to consider. First is the obvious power loss across the diode and determining if that loss is circuit effecting.

Let’s say you were designing a full bridge rectifier for a 12V system. In the above picture, each color represents a different direction that current would travel. At any point of the wave it is considered to be utilizing two diodes worth of voltage drop. At 700mV a piece, that is a 1.4V loss of power which is over 10% of your total voltage wasted.

To overcome this, low-voltage circuits will require you to use a germanium diode. These diodes have a lower voltage drop, around 300mV, causing less of an impact on the circuit. Over the years germanium diodes have been replaced with Schottky diodes which provide a similar voltage drop but were proven to be more reliable. Although they typically have lower voltage drops compared to standard silicon diodes, they can’t handle the reverse voltage or max current that they can.

Another item you might want to look at is price. They can be pretty comparable at the surface mount level, with Schottky being slightly more expensive. The through-hole versions of Schottky diodes start at about twice as expensive as standard diodes which can quickly climb as you look for specific characteristics. This might not play a big part for hobbyists who are only looking for a couple to tinker with, but it can add up quick for production uses.

Here is a link to our single diodes: http://www.digikey.com/short/qqzq7n

At the top you can select Schottky or Standard in the Diode Type filter then take a look at the voltage drops in the Voltage - Forward (Vf) (Max) @ If filter.