Fwd. Voltage drop across silicon diode

[Tparker]

Looked at a few datasheets on the 1N400X series of diodes but did not see any specs. on voltage drop. Is there a standard voltage drop across all silicon diodes and is the amount of the drop current dependent?

[Externet]

Hi.
Yes, it is 0.6 V to 0.7 V current dependent.
Schottky diodes are around 0.4 V drop
Miguel

[Chris Smith]

Silicon diodes are 0.3v
Germanium are 0.7v<p>Oops, flip flop<p>[ April 05, 2004: Message edited by: Chris Smith ]</p>

[Tparker]

Is the voltage drop any more/less depending on current? Suppose you have a 50 volt 3 amp silicon diode that has 250 ma. thru the circuit, would the voltage drop be the same if 3 amps were thru the circuit?

[Externet]

Hi Tparker.
Yes, forward voltage drop is current dependent.<p>The bottom left image here... <p>http://uweb.superlink.net/bhtongue/7dio ... odeCv.html<p>...shows drops for germanium and silicon; as you can see the voltage drop varies around the knee depending on the current flowing.
Miguel

[k7elp60]

Something else to note is that the voltage drop for a specific current will vary between diodes also. This is important as if per chance one has to parallel diodes to increase the current capabilites of the circuit the diodes need to be matched, otherwise one or more diodes will carry more of the current.

[Tparker]

Thanks guys for your input. The diodes will be used in an automotive LED warning light application to prevent feedback.

[Rodney]

I'm afrain Mr. Smith has it backwards. The silicon diodes are typically about .7 volts, germanium typically about .4 volts. Yes, it does increase as current increases.

[Chris Smith]

Already stated that Rodney!...... "Oops, flip flop" followed.

[Dean Huster]

OK. Since we were given an actual diode (1N400x), we can give actual, true specifications and not a bunch of generalized slop.<p>The Motorola data sheet on the 1N400x series of rectifier diodes says that the forward drop can be as much as 1.0v at a forward current of the rated 1 ampere. This will conform to Miguel's answer that the forward drop is dependent upon the forward current. At lesser currents, the drop will be less, dropping to 0.7 or 0.6v when the forward current is more like 100ma or less. By the way, a diode with a 0.7v drop with 1a of current will be dissipating 700mW and will get hotter than a firecracker. Diodes that are running anywhere near their rated current should be mounted off a PCB as you would a power resistor.<p>Miguel, Schottky (hot carrier) diodes have drops less than that of germanium types, usually hovering around 0.1 to 0.2 volts. The do have the problem of a lot higher leakage in the reverse direction as opposed to the leakage found in other diode types.<p>Dean