Zener Diode Tester

[mr.sky]

Can someone recommend a good Zener Diode Tester.
I know there is one out there that is a Kit. But cannot
remember where from.
As you guys know, cannot test zeners with multimeter.

[Evil Lurker]

Re: Zener Diode Tester

Been thinking bout this one for a while... considered using modified version of a typical bistable 555 timer circuit and a couple of transistors and resistors to charge up a capacitor.

When the momentary "on" button is pressed the output of the timer would go high applying power to the base of a simple ten cent TO-92 NPN transistor starting the capacitor charge cycle. Also at the same time the capacitor would completely discharge thru the other connection on the momentary button switch. This may sound strange but most button switches that I see are dual pole single throw... only when the button is released would the capacitor actually begin to charge. Of course to prevent the transistor from going poof there would be a resistor limiting the input current to the capacitor when the button's contacts are closed.

As the capacitor charges up it will eventually reach a point where the zener diode begins to conduct. Part of the current flowing thru the zener would be fed into to the base of another NPN transistor (perhaps a germanium amplifier type) which would serve to pull the reset pin of the 555 timer low turning off the supply power to the capacitor. Configured in this manner the 555 timer would act as a crude combination "flip-flop-sample-and-hold" thing and measuring when the zener conducts should be as simple as measuring the voltage across the capacitor leads. It could also be used to detect "leaky" zeners and other regular small switching or rectifier diodes.

The power supply could for the circuit could also be ridiculously simple... just a bunch of dollar store 9v batteries hooked in series coupled with the right transistor and capacitor and you could test about anything you wanted.

[mr.sky]

Re: Zener Diode Tester

Here is a Schematic of one.

http://gsuryalss.files.wordpress.com...ode-tester.gif

[tom66]

Re: Zener Diode Tester

You could also use a 1:2 step down or isolating mains transformer with a meg-ohm resistor in series. That would allow you to apply up to +/-160V to the device; plot the result on the scope to see where the current peaks and you have the breakdown voltage.

[budm]

Re: Zener Diode Tester

All you need is a variable power supply that can go up to 20Vdc if the Zener you are testing are not more than 18V.
Just hook up 500 Ohm 1/2 W with the Zener you want to test, Plus to Cathode through the resistor, Negative to Anode, put meter across the Diode to read the Zener voltage. If the Zener is good you should see as you turn up the power supply, the voltage will not get any higher, that will be the Zener voltage. You also check the forward junction just like regular Diode.

[mr.sky]

Re: Zener Diode Tester

All you need is a variable power supply that can go up to 20Vdc if the Zener you are testing are not more than 18V.
Just hook up 500 Ohm 1/2 W with the Zener you want to test, Plus to Cathode through the resistor, Negative to Anode, put meter across the Diode to read the Zener voltage. If the Zener is good you should see as you turn up the power supply, the voltage will not get any higher, that will be the Zener voltage. You also check the forward junction just like regular Diode.

Zener diode is in Panasonic A-board, not sure of voltage, etc. Panasonic
Schematic does not show what type of Zener it is.
I know it has a red band, then green. I have seen some on Ebay,
but not sure if they are any good. Thanks guys for input.