Diode Question

[Grant Richter]

> 
> Here are two dumb questions about diodes:  I know that the voltage drop 
> across diodes connected in series is additive (two diodes in series:
voltage 
> drop + voltage drop = 1.2 volts).  This behavior is similar to that of 
> current through series resistors, as per Mr. Ohm.  My question:  If you 
> connect two diodes in parallel (with both diodes biased in the same 
> direction), does the Ohm's Law analogy still apply?  That is, will the 
> voltage drop across them divide in half (from .6 volts to .3 volts)?  
> (similar to the behavior of current through parallel resistors)

The answer is no. The two parallel connected diode will share current
flow based on the voltage drop, the one with the lowest voltage drop will
conduct the majority of the current. This is why you can not just parallel
LEDs from a single resistor. They do make monolithic matched diodes
and LEDs that can be paralleled and share current approximately equally.

> 
> Second question:  is the voltage drop across a Germanium diode different
than 
> the drop across a Silicon diode?
> 
The voltage drop across a silicon diode is generally between 600 and 700
millivolts
depending on construction, temperature and amount of current flow.
Note that the voltage drop can go as high as 1 to 1.2 volts at high current
flows
(above one ampere).
Shottky diodes are more heavily doped and have lower voltage drops
at the expense of greater reverse leakage.

Germanium diodes generally have voltage drops between 200 and 250
millivolts depending on construction, temperature and amount of current
flow.