diodes

[dash]

what is the best way of checking diodes rated at 1000v,200amp. a multimeter does not give consistent reading with identical diodes,any thoughts or suggestions greatly appreciated.thanks

 

[CarlPugh]

Years ago worked at a company that used a high voltage transformer, a series resistor to limit the current to 1 mA maximum, a low value resistor to display the current through the diode and an oscilloscope. (1 mA is probably OK for large diodes, less than 1 mA should be used for small diodes)
The oscilloscope was set up to display the current through the diode on the horizontal axis and the voltage across the diode on the vertical axis.

This circuit never caused any diode failures during our tests. However cannot guarantee that it will not cause diode failure with other type diodes.

Of course a multimeter with diode test function is much easier and will catch most diode failures.

The diodes now are probably more consistent, but back then there was a lot of difference between diodes, even when testing the same part number.

 

[maged541946]

Hi,
For such a high rating diode it is better to determine whatit is you need to know.
If a simple GO/NO GO test a digital mutimeter with a diode test or a simple 3volt DC source and a 100 ohms resistor and an LED or any indicator will do.

If a good one is needed to determine then the reverse leakage current should be measured and compared with data sheets, as sometimes after use, some diodes start gaining reverse leakage as a result of overheating, this reverse leakage may cause extra heat and so on till it fails.

if breakdown voltage is needed (1000V) a reverse high voltage from a transformer, small one is better as they have internal limiting current effect. a series large resistor and high power, say 10K and at least 25 Watts, note that you use half cycle for power. If such a resistor is hard to find and expensive you can replace it with 5 220V AC light bulbs ( or 10 110VAC) each is 10-40 watt but they MUST HAVE THE SAME RATING, do not mix different watts.

Use 2 1000v dides to get the DC you will apply to the diode under test in reverse mode, once the lamps start to glow, the diode under test is in break down and the lamps will protect it. you may just apply a voltage and see if diode is ok or no.

 

[rjgoebel]

Will such a diode test work in-circuit? Or will this only really work if you remove the diode from the circuit and then put in the series resistor. Im also assuming you need a voltage source or current source to make the 1mA current flow through the diode.



Jim Goebel,
Electrical Engineer
Mid-West Forensics, Inc.

 

[sreid]

Expensive but Tektronix offers high voltage, high current Curve Tracers.

http://www.tek.com/Measurement/cgi-...her_tm/curve_tracers/home.html&FrameSet=curve