Germanium Diodes
Germanium Diodes
Learn about the advantages of Germanium Diodes
electronics
Diodes are a very important component of most
alternative energy generating systems - for example in
PV solar panels they are used to stop energy being radiated back out into the night sky from the
battery bank, and in
wind turbine generators they are used to
rectify AC into DC electricity.
Most
diodes are made of
silicon because of its ease of processing and stability, however they have one disadvantage: a
silicon diode has a forward
voltage drop of around
0.7 volts. This means that if you had a 7.0 Volt rated solar panel charging a battery via a silicon diode, only 7 - 0.7 = 6.3 Volts would be seen by the battery - the remainder is
lost as heat in the diode.
In a
Bridge Rectifier the current passes through
two diodes. Therefore the total
forward voltage drop is a whopping
1.4 volts - a significant amount in
low voltage systems.
Germanium Diodes
A
Germanium Diode (such as the
1N34 pictured above) will typically have a forward voltage drop of just
0.3 volts which means they are
much more efficient. Older germanium diodes had a larger leakage of current at a reverse voltage, but now
American Microsemiconductor and others supply a range of improved
low current leakage germanium diodes. Diodes such as the most common 1N34A can cost as little as 5 pence each.
Buy Germanium Diodes
It is not always easy to find
germanium diodes as they are not a very popular item. One of the best ways to obtain them is to purchase
vintage stock made available for sale on
eBay.
At the time of updating this article (August 2008) there were OA47, OA81, OA90, OA91, OAZ210, IS689, 1N34A, 1N42, 1N60, AAZ17, and AA119 germanium diodes all listed for sale - some new and some vintage / used.
Click here to search
eBay UK for
germanium diode, or here to search
eBay USA for
germanium diode.
In the UK
Rapid Electronics often have one or two
germanium diodes - click to view their latest listings.
More Information about Germanium Diodes
While
silicon diodes are resistant to the heat from soldering,
germanium diodes can very easilty be damaged. Therefore a crocodile clip or other suitable
heat sink should be clipped onto the lead between the diode body and the joint to be soldered.
An interesting article about the practical use of
Germanium Diodes in a crystal radio set is here, and discusses the forward
voltage drop of a selection of germanium diodes in real world testing. The
OA47 came out tops with a forward voltage drop of under
250mV.
Article Last Modified: 13:43, 8th Aug 2008Comment on this Article
If you have any comments on this article, please email them to
neil@reuk.co.uk.
I think you should mention the current rating of the Ge diodes: I think several of those you mention (OA47,81,90,91) are very low current ~ about 100mA peak (and much lower continuous) and at high currents they have much higher forward Voltage drop.
I understand there are some high(er) current Ge diodes, which can handle several Amps and maintain low forward V drop, but they are not the little glass beads you show. Which reminds me - Ge components are much less thermally robust than Si.
On a more positive note, one way of getting a Ge diode (esp for higher current) is to use a Ge transistor with base and collector shorted together. I mention this because I see transistors like OC25, OC30, OC35 around occasionally, but not power Ge diodes (though this may be because I've not looked!)
Don, 3rd March 2009 |
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