mondrasek;
old stuff:
Every electronics device has an identifier such as 1N4001, 1N914, you need
to look these up in a diode handbook (PDF) file from a semiconductor manufacture.
Almost every diode except for the really-really inexpensive kind has their number
printed on the device. Signal diodes use color banding for the digits of the
numbers but can leave the 1N.. designator off sometimes. You'll often see white,
brown, yellow - 914 - 1N914 germanium signal diodes.
the following will tell you various parameters of the device;
In diodes there will be;
Part Number: 1N4001 the 1Nnnnn - are all common diodes
Function: Power,Signal,Bridge,[forget about the following]=> Zener,tunnel,varicap,trigger,Optoelectronic diodes
Process: silicon, germanium, Schotkey => determines the voltage pedestal
PIV - peak reverse voltage - how much voltage can the diode block before it's damaged for 1N4001 - it is 1KVDc
Hf - what is the half frequency the diode can support - 10Mhz. Where half the AC voltage is lost.
FJC - what is the forward junction capacitance - 15pf.
Iac - what is the maximum forward current - 10Amps.
Ir - what is the leakage current at the maximum voltage - xxmilliamps
Generally signal diodes will have under 1 amp of current capacity, very low junction capacitance,
a relatively low breakdown voltage and possibly a very high Hf frequency.
Power diodes will have a very high forward current, somewhat higher leakage than signal, often
have a very high PIV, and often a low to moderate Hf, and much higher junction capacitance.
Note: The old style desktop computer switching power supplies run at 20KHz to 100KHz
switching frequency. Why: to eliminate the bulk of the magnetic cores from the inductors
and trade off: faster diodes, transistors, scr's etc semiconductor speeds to run efficiently
- yet have to handle high current and wattages. So these scrap supplies are a good source of
power components.
try link:
http://www.jameco.com/ under IC& Semiconductors click on diodes and rectifiers
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On Wikipedia
http://en.wikipedia.org/wiki/Continuity_testerA buzz-light a tool and is like two 1.5Volt batteries and a flashlight bulb with a red and black insulated
alagator clip leads in a circuit - very simple. Often you can solder a big needle to the back of one
to serve as a probe. It is used for checking continuity of non-powered circuits like cables or
inductors. The battery voltage at 3Vdc is low so you don't have to worry about the probe blowing
other stuff like semiconductors or wiring out. But the bulb will not light well at resistances above
100 ohms or so, so is kind of a low ohms meter. A diode or power transistor should allow the bulb to
light in one direction then if you reverse the leads the bulb will not light. Often a signal diode
will not have low enough forward resistance to light the buzz-light in the forward direction and
you will have to use a DVM instead.
You can do a simple experiment with a NPN *power* transistor and a buzz-light, you put the buzz light
between the Emitter(-) and Collector(+) then take a 470 ohm resistor from the Collector to the Base.
The 470 ohm resister would not light the buzz light itself but the current amplification gain of the
transistor (a figure called Beta) allows the current through 470 ohm resistor to light the light. Reverse
the leads for an PNP power transistor.
A power semiconductor that does not do the above behavior this is either "burnt out" or "shorted" as in a
failure mode.
You should also study how a four (4) diode bridge rectifier works, as this is a common multi-device
component. +,-,AC+,AC- (good, looks like you already have.)
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From your latest post;
Interesting solution to the problem mondrasek (very good);
The 1:1 transformer at 50Hz should best have an iron core like the R60 core from
the SGS drive coil... Actually the bemf pulse (you need to at least read about
"Fourier transforms") Harmonics are probably far above the basic 50Hz cycle
repetition rate. Meaning a higher frequency core response of the transformer is
better to let the entire pulse through. More like the difference between 50-60Hz
and audio frequencies.
Another solution would be to put the diodes between the cap. and coil.
The circuit could then only tap into the bemf. But I'm not going to say
it is better than what you've already got. As it stands, the transformer
will effect both directions of current through the coil. This may or may not
solve your timing symmetry difficulties.
Another thing you try do is put the scope's second channel across the batteries
(be careful not to create any "ground loops" ie ground wire conflicts)
and make sure the right polarity pulses are happenning to each of the batteries.
The thing I am concerned about is; "race conditions" where the contacts might
interrupt the circuit path before the pulses get entirely through.
:S:MarkSCoffman