DaveC wrote in news: snipped-for-privacy@news.eternal-september.org:
You sound like a man who imagines that by scrunchign his shoulders, no-one will mind when he passes annopyingly several times through the same doorway.
And no. To test a zener you need to try a reverse voltage. Try a variable voltage through a 10K resistor. A sine wave off a 30V transformer will do, just look for the clipping voltages on a scope (or DC voltmeter if you add a capacitor in parallel with the diode). Vz equals peak-peak voltage minus about 0.58V. You may also have to remove one end of it from the circuit to be certain.
Lostgallifreyan wrote in news:Xns9DFE5D70DE9FCzoodlewurdle@216.196.109.145:
Evidently my turn to pass annoying through the same doorway...
Scratch that, the rest stands though, you just have to do the test once for each polarity of that diode. (You'll only see both peaks at once if you have a zero-referenced AC voltage, and even then that capacitor idea wouldn't apply, and I made it more complex than it needs to be, you only need to see the zener peak to know...).
Variable DC supply, 1 meg resistor, series circuit with diode reverse- biased. Watch the diode voltage as you increase the supply voltage. When it levels off, you've reached reverse breakdown.
Even without the "variable" this can work. Use a high enough DC voltage.
There is a method with a scope, resistor and AC supply but it is much more complex for a novice (assuming)
Variable DC supply, 1 meg resistor, series circuit with diode reverse- biased. Watch the diode voltage as you increase the supply voltage. When it levels off, you've reached reverse breakdown.
Do this: Variac out 1 ------[R: 1M]-------o-------scope +in | [DUT] Variac out 2 --------------------o-------scope -in
When the diode conducts forward, you'll see ~ .6V at the diode. When the diode is biased, reversed, the other half-cycle will go to the full voltage; as the voltage is increased, if you hit the diode's breakdown voltage, the peak will start to flatten. THe polarity you'll see will depend on your scope hookup; I'd use Common (i.e., AC neutral, with maybe a safety ground) for "Variac out 2", and scope ground for "scope -in".
hmmmm... Now you are pushing my memory hard!!...LOL
Let's see.
Make a series circuit with the resistor (R) at the top and the component at the bottom. Feed the whole thing with an AC voltage supply, top to bottom.
You will need a scope with horizontal input as well as the usual vertical input and a floating ground or full differential input somwehere. (you work out the logic .. maybe a floating AC voltage supply would be enough)
Hook the vertical input across the resistor and the horizontal input across the component. Maybe the grounds together in the middle of components and floating supply are good for that??? Been a few years.
Now your vertical trace on the scope indicates current (IR drop in the resistor). The horizontal trace indicates voltage drop across the component. You will get the single curve of a component tracer on your scope.
***Component curves*****shorted = vertical line
**open = horizontal line
**resistor same as R = 45 degree line
**capacitor = circle... me thinks round indicates matching impedance with R at 60Hz??
** inductor = circle same as cap above??
**zener no current at lower voltages = horiz. line; no voltage increase at higher voltages = vertical line = visible knee at zener voltage - use calibrated scales for measurement
**avalanche diode = horizonatal line with foldback and shows current (vertical at higher end)
Try it! So simple it stinks but is very visible clue. Watch your scope grounding.
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