Electrical – Schottky diode / Rectifier Diode difference and how to test them

diodesmultimeterrectifierschottky

I have 3 diodes that I would like to test

  • 1x USD935
  • 2x USD2009

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USD935 is identified by its datasheets as a "Power Schottky Rectifier Diode". I cannot find the datasheet of the USD2009 but they have similar test readings. So I'm assuming they are also a "Power Schottky Rectifier Diodes"

I am a bit confused by the name, as I thought a Schottky diode and Rectifier Diode were 2 different things. (different symbols).
Some make a distinction between the 2 , others say that a Schottky diode can be used as a rectifier.

To add to the confusion, I have them out of circuit and read that they can be tested using a multimeter in Ohms mode, as well as using the Diode function of the multimeter.

I tested them and got the following results

Diode test

  • black lead kathode / red lead anode : 0.18v (beep)
  • Black lead anide / red lead kathode : OLD

Resistanse test

  • black lead kathode / red lead anode : 170k ohm
  • Black lead anide / red lead kathode : 1k ohm

In terms of interpreting the results I found the following :

  • In How to Test a Diode Rectifier a forward voltage of 0.5 to 0.8 volts is mentioned when using the diode function of the multimeter. (mine is only 0.18v).
  • They also say that with the resistance test (black lead on the anode and the red lead on the kathode) there should be an OL where instead I have 1k ohm.
  • In How to Test a Schottky Diode it is mentioned that Shottky diodes can be tested using the continuity test on the diode. Is that the case ? With mine there is no continuity between the anode and kathode.

Are my diodes bad, or am I misinterpreting the test-results / executing the test in the wrong way?

Best Answer

Looking at how Microsemi makes part numbers

USDaavv aa is the Max Amps and vv is the reverse V rating so USD2009 20A 9V is obsolete.

Diode, Rs is inverse to Imax but V=0 capacitance increases with Rs such that in same voltage family Rs*C = constant.

The way to test them is to pulse current thru them and measure peak voltage drop @ 25'C or so a VI plot with pulses so temp. rise does not reduce Vf much.

They should all be 0.3V @ 1A but different at 10A.

Being metallized on one electrode Schottky diodes are approx 50% of Vf of Silicon Diodes but much higher leakage Rp.

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