# How to test a high voltage diode

#### Gdrumm

Joined Aug 29, 2008
684
A Google search method says to hook up one end of 110v to the cathod end of the diode, then hook the other end of the diode to the neg probe of your meter.
Next, hook the other side of the 110v to the pos probe of the meter, set the meter to 200v ac and turn on the power.

The Meter should read 1/2 of sine wave, or about 55 to 60v = good...

I've tested about 10 of my HV diodes, and all are showing from 119 up to 125v ac one way (supposedly bad). and when reversed, they show 0 volts. To me they are doing what a diode should do. Let current flow one way...

Is there a better way to test these HV diodes?

Thanks,
Gary

#### praondevou

Joined Jul 9, 2011
2,942
THIS looks more like a suitable test setup.

In the setup you described (connected to110VAC), why would inverting the diode give a different result ? Can you post the link you got this information from?

#### SgtWookie

Joined Jul 17, 2007
22,230
While the fellow in that video is using an acceptably low voltage range, he's getting some rather odd results. I agree that if the diode is reverse-biased, you should measure about the same as the supply voltage across the diode. However, if the diode is forward-biased, you should read a rather low voltage (0.7v-1v) across the diode - unless they are REALLY high voltage diodes.

#### praondevou

Joined Jul 9, 2011
2,942
While the fellow in that video is using an acceptably low voltage range, he's getting some rather odd results. I agree that if the diode is reverse-biased, you should measure about the same as the supply voltage across the diode. However, if the diode is forward-biased, you should read a rather low voltage (0.7v-1v) across the diode - unless they are REALLY high voltage diodes.
Yep, we would need to know the model # to compare the obtained Vfd @ the applied current with the informations in the datasheet. I don't know what "HV" means in terms of max reverse voltage......

Joined Dec 26, 2010
2,148
"Stack" rectifiers are quite common for higher voltage rectification, at kilovolts upwards. Here the manufacturer assembles a number of matched junctions in series stacks, somewhat along the lines of the old metal rectifiers. Some high voltage rectifiers are still made this way using selenium, but most are now silicon. A much higher PIV is possible than with a single junction, at the cost of a larger forward drop.

If I had any doubts about the health of such a device, after basic testing I would be inclined to carry out a reverse leakage test at voltages approaching its full rating. Such testing cannot really be advised on here, but I would point out that at any voltage, leakage testing must not be done simply with diode and ammeter in series across the supply - if the diode fails excessive current will blow up the meter. Use a resistor capable of withstanding the full voltage in series with the diode

#### debe

Joined Sep 21, 2010
1,385
When checing Microwave oven diodes I use a Megger tester on 1000V to test them as a multimeter wont work on them.

#### debe

Joined Sep 21, 2010
1,385
Heres how i do it.

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#### sheldons

Joined Oct 26, 2011
613
Heres the schematic for my high voltage diode tester-which can also test capacitors(mw caps and mw diodes and asm rectifiers) ive been using it for years.....it also checks leds too