How to Test a Schottky Diode with a Multimeter
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How to test a Schottky diode with a multimeter: use diode mode on a part that is out of its circuit, read it once in each direction, and expect a lower forward number than a silicon rectifier gives. A working Schottky still shows a number one way and OL the other, according to Fluke’s diode procedure. This guide uses the 1N5817 to 1N5819 data sheets to show why the number is lower, why leakage matters more, and what the sources do not say.
Electrical safety first
Work on mains circuits can kill, so a Schottky check belongs on the bench. Vishay’s sheet lists low-voltage inverters, freewheeling, DC/DC converters and polarity protection as typical uses for its Schottky parts. Even so, this guide covers only a loose part, or a low-voltage circuit that is powered off, and it does not describe work inside equipment that plugs into a wall outlet. In the Klein MM400 manual, ignoring the warnings can result in severe injury or death, and voltages above 25 V AC RMS or 60 V DC are called a shock hazard. Panel and service work belongs to a licensed electrician; the homeowner workbook from the Electrical Safety Foundation International says to always contact a qualified, licensed electrician for electrical work in your home.
The meter’s CAT rating (measurement category) must suit the circuit, and Fluke advises choosing a meter rated for the highest category you might meet. The rating comes only from the meter’s label or manual; the Klein MM400 manual lists CAT III 600V. Where neither the manual nor the label states a rating, call the meter unrated. Fluke also says to assume every component in a circuit is energized until you have positively discharged it. No part of this guide calls any meter safe for household mains.
Quick answer
- Take the Schottky out of the circuit, or confirm a low-voltage circuit is off and discharged.
- Diode mode, red lead on the anode, black lead on the cathode: write down the forward number. Swap the leads: the display should show OL.
- Expect the forward number to be lower than for a silicon rectifier. The sources do not give a meter range for Schottky parts, so compare with a known good part of the same type.
- OL both ways points to an open part, and the same low reading both ways points to a short. Leakage and voltage rating are not proven by this check.
What makes a Schottky different
The Micro Commercial Components application note on Schottky rectifiers lists the main advantages as a very low forward voltage drop and switching speeds that approach zero time. It names the costs as well. Reverse leakage currents are many times higher than in pn-junction rectifiers, the maximum junction temperature is typically 125 to 175 °C against about 200 °C for pn junctions, and Schottky rectifiers seldom exceed 100 volts in working peak reverse voltage. The note adds that a metal with a low energy barrier height minimizes forward voltage, but restricts high-temperature operation and brings very high reverse leakage.
The Electronics Notes tutorial describes the same trade. It gives a turn-on voltage of around 0.2 to 0.3 volts for Schottky rectifiers and about 0.6 to 0.7 volts for standard silicon diodes. It lists high reverse leakage, limited reverse voltage and limited junction temperature as the drawbacks. That tutorial is a secondary source, and this guide used it only to confirm what the manufacturer note and the data sheets show.
What the data sheets say, side by side
The table sets the 1N5817 to 1N5819 Schottky family against the 1N4001 to 1N4007 silicon rectifier family. Both are in the same DO-41 package type, which makes the comparison fair. Each Schottky figure appears on both the Vishay and Diodes Incorporated sheets unless noted; the silicon figures come from the Diodes Incorporated sheet.
| Item | 1N4001 to 1N4007 (silicon rectifier) | 1N5817 / 1N5818 / 1N5819 (Schottky) | Our calculation |
|---|---|---|---|
| Repetitive reverse voltage | 50 to 1000 V | 20 / 30 / 40 V | 40 ÷ 1000 = 4 percent of the top silicon rating |
| Forward voltage at 1.0 A (maximum) | 1.0 V | 0.450 / 0.550 / 0.600 V | 0.450 ÷ 1.0 = 45 percent; 0.600 ÷ 1.0 = 60 percent |
| Reverse current at rated voltage, 25 °C | 5.0 µA | 1.0 mA | 1.0 mA ÷ 5.0 µA = 200 times |
| Reverse current at 100 °C | 50 µA | 10 mA | 10 mA ÷ 50 µA = 200 times |
| Rise in leakage from 25 °C to 100 °C | 50 ÷ 5.0 = 10 times | 10 ÷ 1.0 = 10 times | Same factor on both sheets |
| Cathode marking | Cathode band | Cathode band (Diodes Incorporated); color band denotes the cathode end (Vishay) | Same marking convention |
Two sources differ in a small detail. The Vishay sheet lists a second forward-voltage condition at 3.1 A, while the Diodes Incorporated sheet lists 3.0 A. The maximum values at that second condition, 0.750, 0.875 and 0.900 V, match on both. The Schottky’s lower forward voltage is real, at 40 to 55 percent below the silicon figure at the same current, and so is its 200-times leakage.
How to test it, step by step
- Remove the part from the circuit. Fluke starts with power off and no voltage at the diode, notes that charged capacitors can leave voltage in a circuit, and says it may be necessary to remove one end of the diode.
- Find the cathode. Both Schottky data sheets mark it with a band.
- Put the meter in diode mode. Fluke calls Diode Test mode almost always the best approach.
- Read forward. Fluke defines forward bias as the red lead on the anode and the black lead on the cathode. Write down the number.
- Read reverse. Swap the leads. Fluke says a good diode shows OL when reverse biased.
- Compare. Fluke advises comparing readings with a known good diode when using its resistance-mode method. Our suggestion is to do the same in diode mode with a Schottky of the same part number, because the sources give no meter range for these parts.
How to read a low forward number
Fluke gives 0.5 to 0.8 V for common silicon diodes and 0.2 to 0.3 V for some germanium diodes. The Klein MM400 manual says 200 to 700 mV indicates forward bias. The Schottky data sheets give 0.45 to 0.60 V as a maximum at 1.0 A, and the Klein manual’s diode-test current is 1.5 mA maximum. Our own ratio of data-sheet current to meter current is 1.0 ÷ 0.0015, about 667. Kuphaldt’s textbook chapter says a diode-check reading is typically below the normal 0.7 V for silicon and 0.3 V for germanium because the meter’s current is trivial. So the number on your display may be lower than any figure on the sheets, and it may sit below the 200 mV bottom of the Klein manual’s window.
Three traps follow from that. A low Schottky reading can look like a germanium diode, because the Fluke germanium range and the Electronics Notes turn-on range overlap at 0.2 to 0.3 V. It can look like a short if you expect a silicon-style number. It may also sit below a manual’s stated window, and the sources do not say whether that is normal for a Schottky. The cure is the same each time: look at the pattern. A good part gives a number one way and OL the other. A short gives the same answer both ways, which Fluke puts at about 0.4 V and the Klein manual at approximately 0 mV. An open part gives OL both ways.
The meter’s voltage against a Schottky’s rating
A Schottky blocks far less voltage than a silicon rectifier, so the meter’s reverse test is a bigger share of its rating. The table divides the Klein MM400’s 3.0 V DC open-circuit voltage, and the 3.9 V cap in the Fluke 87 manual, by each Schottky’s repetitive reverse voltage. The formula is test voltage ÷ rated voltage × 100. Every figure is our own arithmetic.
| Part | Rated reverse voltage | 3.0 V as a share | 3.9 V as a share |
|---|---|---|---|
| 1N5817 | 20 V | 15 percent | 19.5 percent |
| 1N5818 | 30 V | 10 percent | 13 percent |
| 1N5819 | 40 V | 7.5 percent | 9.75 percent |
Compare the 1N4007 at 1000 V, where 3.0 V is 0.3 percent. A Schottky that reads OL in reverse is blocking at 7.5 to 15 percent of its rating on the 3.0 V figure, while a silicon rectifier is checked at a sliver of its rating. That is a modest comfort, not proof. The data-sheet leakage figures of 1.0 mA and 10 mA apply at the full rated voltage, and the sheets we opened do not say what a good Schottky leaks at 3 V. They also do not say whether a leaky Schottky would show a number instead of OL in reverse on a meter.
Leakage, temperature and what the sheets imply
The data sheets give leakage at two temperatures, 1.0 mA at 25 °C and 10 mA at 100 °C, a factor of 10. The silicon rectifier sheet shows the same factor of 10, from 5.0 µA to 50 µA. So heat raises leakage on both kinds of diode, but the starting point for the Schottky is 200 times higher. The MCC note ties that to the barrier metal: lower forward voltage comes with higher leakage and a lower temperature ceiling.
The practical reading is that a Schottky’s reverse behavior is the part a plain meter check can speak to least. Vishay lists a maximum junction temperature of 125 °C and Diodes Incorporated an operating range up to 125 °C, while the silicon sheet’s range tops out at 150 °C. MCC says typical Schottky junction ratings run 125 to 175 °C. A part that has run hot in service therefore has a narrower temperature margin than a silicon part. A meter will not show that margin. A bench supply, a resistor and a voltmeter can measure forward voltage at a chosen current, a method Kuphaldt’s chapter mentions, but the sources we opened give no values for a Schottky and this guide does not invent them.
Testing a Schottky on a board
On a board, a Schottky has other parts around it. Fluke says an in-circuit reading can be false and that it may be necessary to lift one end of the diode. The Fluke 87 manual says the resistance displayed is the total through all possible paths between the probes, and Kuphaldt says parallel components affect any reading. If the board belongs to mains-powered equipment, stop and hand it to a qualified person. For continuity checks on the same board, see how to use a continuity tester.
If you want to compare how meters label the diode function, our diode and continuity meter comparison lists what each listing states. For a different special-purpose diode check, with a reverse breakdown stage, see how to check a zener diode. For auto-ranging meters in general, see auto-ranging digital multimeters.
Mistakes to avoid
- Judging by a silicon number. The Schottky sheets show forward drops of 45 to 60 percent of the silicon figure at 1.0 A.
- Reading the data-sheet voltage as the expected display. The data-sheet current is about 667 times the Klein test current.
- Calling a low reading a short without swapping the leads. A short reads the same both ways.
- Treating OL in reverse as a leakage test. The sheets quote leakage at full rated voltage, in milliamps.
- Testing in circuit. Fluke says in-circuit readings can be false.
- Applying a silicon part’s rating. The family tops out at 40 V on the sheets, and MCC says Schottky rectifiers seldom exceed 100 V.
How we chose
We built this guide around the 1N5817 to 1N5819 family because two manufacturers publish sheets for it that we could read on 2026-10-21, and because a silicon family from the same package type gives a fair comparison. We opened the Vishay and Diodes Incorporated Schottky sheets, the Diodes Incorporated silicon sheet, the Micro Commercial Components note, the Electronics Notes tutorial, a Fluke diode guide, a Fluke safety guide, the Klein MM400 manual, the Fluke 87 manual, the Kuphaldt chapter on LibreTexts and an Electrical Safety Foundation International workbook. Figures appear only if one of those pages states them.
What we could not verify
The sources we opened do not give a multimeter reading range for a good Schottky diode, so the guide offers a method rather than a number. They do not say what a leaky Schottky shows in reverse, what a good one leaks at a few volts, or how a reading shifts with temperature. The Klein manual’s forward window is written for diodes in general, and the sources do not say whether a Schottky falls inside it. The data sheets show forward-voltage curves as charts, and no values are taken from them here. Dual and multi-lead Schottky packages are outside this guide. The Electronics Notes page is a tutorial, not a manufacturer document, so its 0.2 to 0.3 V figure is context only.
FAQ
What does a good Schottky diode read in diode mode?
The sources we opened do not give a range. Expect a lower forward number than a silicon rectifier and OL in reverse, and compare with a known good part of the same type. The data sheets list 0.45 to 0.60 V as a maximum at 1.0 A, which is a different test current from the meter’s.
Why does my Schottky read lower than a regular diode?
Its forward drop is lower by design. MCC lists a very low forward voltage drop as a primary advantage, and the data sheets show 0.45 to 0.60 V against 1.0 V for the silicon family at 1.0 A.
Can a multimeter find a leaky Schottky diode?
The sources we opened do not describe a meter reading for leakage. The data sheets quote leakage at the full rated voltage, 1.0 mA at 25 °C and 10 mA at 100 °C, which is far from what diode mode applies.
How can I tell a good Schottky from a shorted one?
Read it both ways. A good part gives a number one way and OL the other, while a short gives the same low answer both ways, according to Fluke and the Klein manual.
Which end is the cathode on a Schottky?
The band. The Vishay sheet says the color band denotes the cathode end, and the Diodes Incorporated sheet lists a cathode band. The red lead goes on the other end for the forward reading.
Bottom line
Test a Schottky in both directions with the same meter, trust the pattern of a number and OL over any single value, and remember that its leakage is the one thing diode mode cannot measure.
Sources
- https://www.vishay.com/docs/88525/1n5817.pdf (opened 2026-10-21)
- https://www.diodes.com/assets/Datasheets/ds23001.pdf (opened 2026-10-21)
- https://www.diodes.com/assets/Datasheets/ds28002.pdf (opened 2026-10-21)
- https://mccsemi.com/pdf/applicationnotes/Introduction%20to%20Schottky%20Rectifier.pdf (opened 2026-10-21)
- https://www.electronics-notes.com/articles/electronic_components/diode/schottky-barrier-diode-power-rectifier.php (opened 2026-10-21)
- https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-test-diodes (opened 2026-10-21)
- https://data.kleintools.com/sites/all/product_assets/documents/instructions/klein/MM400_1390110ART_WEB.pdf (opened 2026-10-21)
- https://workforce.libretexts.org/Bookshelves/Electronics_Technology/Electric_Circuits_III_-_Semiconductors_(Kuphaldt)/03%3A_Diodes_and_Rectifiers/3.02%3A_Meter_Check_of_a_Diode (opened 2026-10-21)
- https://www.fluke.com/en-us/learn/blog/safety/multimeter-guide (opened 2026-10-21)
- https://ghblp.org/wp-content/uploads/2018/09/ESFI-Electrical-Safety-Workbook-compressed.pdf (opened 2026-10-21)
- https://assets.fluke.com/manuals/87______umeng0800.pdf (opened 2026-10-21)
