High-frequency Schottky diode failures, used in switching power supplies—what does the multimeter measure?

ID: 219842

Description:

Steps:

1. Some notes on Schottky diodes, or high-frequency diodes, or fast switching diodes, which are widely used in switched-mode power supplies. When these diodes fail, they short-circuit, causing the power supply to stop oscillating and making the device appear dead. This is the first thing to check in switched-mode power supplies, as it is a very common fault.
2. It has already happened to me with several devices where a diode failure left the unit dead, for example:
3. Photo 2: CREATE MILK FROTHER STUDIO milk frother, does not turn on, Schottky diode fault.
4. PANASONIC Inverter NN-SD28HS microwave - Dead, no power, switched-mode power supply Schottky diode fault.
5. Photo 3: Repair of electronic module DA1-B5780116000 for EQUATION dehumidifier, Type: YL-2A15BT, does not turn on.

6. Measurement of a Schottky diode IN GOOD CONDITION, OK, properly biased: Negative - Cathode / Positive - Anode. In these diodes, you will find that the measurement provided by the multimeter in ohms is lower than in other diodes; THE FORWARD VOLTAGE DROP is from 0.2 to 0.348 Volts (Even though we are using the ohms scale).
7. When reverse-biased, it behaves like any diode; it DOES NOT conduct electricity.
8. A faulty Schottky diode will show a resistance of 0 ohms or very close to it, a "short circuit" in both forward and reverse bias. Therefore, it is relatively simple to locate.

9. Schottky diodes are very useful, for example, as reverse-polarity protection diodes in devices. In the following document, I use them with an IKEA alarm clock that has 2 batteries in parallel to prevent sulfation.
10. DEKAD Alarm Clock - IKEA battery holder sulfated - Modification and improvement to prevent the problem.
11. Explanatory video, measuring rectifier diodes; the methodology for Schottky diodes is the same.
12. End of Guide.