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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?

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2 Answers 2

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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USDaavv aa is the Max Amps and vv is the reverse V rating so USD2009 20A 9V is obsolete.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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  • \$\begingroup\$ And what about the diode test using a multimeter ? Is that an option and can a conclusion be made based on the results in the question ? \$\endgroup\$
    – ddewaele
    Jan 17, 2020 at 5:50
  • \$\begingroup\$ Only to verify it is a Schottky voltage of <0.2 @ 1mA, that does not measure Rs or C \$\endgroup\$
    – Tony Stewart EE75
    Jan 17, 2020 at 5:52
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A Schottky diode is objectively refers to a specific type of diode. A rectifier diode is a more ambiguous term that points towards expected application more than anything else. It doesn't objectively mean anything too specific.

The "rectifier" just indicates it was designed to conduct current in forward bias rather than reverse bias (like zeners or TVS), and maybe that it conducts enough current for power applications as opposed to signal applications.

The symbol for a rectifier diode is just the symbol for a regular diode.

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  • \$\begingroup\$ Thx for clearing up the terminoloy. Any thoughts on the testing part + results using a multimeter ? \$\endgroup\$
    – ddewaele
    Jan 17, 2020 at 5:54
  • \$\begingroup\$ @ddewaele If I was so curious to test them, I wouldn't use a multimeter resistance or diode test function. I would use a constant current source and then use the multimeter to measure voltage and currents and calculate everything else. \$\endgroup\$
    – DKNguyen
    Jan 17, 2020 at 19:21

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