1N5822 Schottky Diode Reverse Direction Voltage Drop Test: Is 3V Drop and LED Glow Normal?

Good day. I bought a 1N5822 diode. Setting the multimeter to the diode test position, it enters that everything is OK, but I also wanted to check what voltage drop it has.
I used a 9V battery. I put the diode in series with the multimeter and the drop was about 0.14V. I set the diode in the reverse direction and to my amazement the multimeter showed a voltage of about 3V.
I also did a test with two 1.5V batteries and an LED diode and when the Schottki diode is set in the reverse direction, the LED light brightens slightly.
Is it normal?

piechnat wrote:

I also did a test with two 1.5V batteries and an LED diode and when the Schottki diode is set in the reverse direction, the LED light brightens slightly.
Is it normal?

It is possible - each diode in the reverse direction passes a small current, the so-called reverse current. The LED diode is a very sensitive element and it starts to glow at a current of the order of microamperes, so even a small reverse current is able to stimulate such a sensitive diode to light.

http://html.alldatasheet.com/html-pdf/2819/MOTOROLA/1N5822/1301/5/1N5822.html

Graph number 9. According to me at 8V 25 ° C something will flow between 0.05 and 0.1mA, which is quite a lot for the sensitivity of the led.

The limit voltage is 40V and then at e.g. 100 ° C almost 10mA will flow.

The reverse current of conventional silicon rectifier diodes is smaller by several orders of magnitude.

piechnat wrote:

Is it normal?

This is normal, but the diode may already be damaged (overheated).

When you tested it by connecting 9V in the forward direction without any resistor, the structure got hot.
When you took measurements later in the dam direction, the structure has not yet cooled down.
According to the catalog, a typical reverse current is 0.5mA at 25 ° C, and as much as 20mA at 100 ° C.

OKAY. Thanks for the answers.
Now I'm a little confused. In the beginner's courses, the operation of the diode is shown in a more binary type
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When connected in series: 3V battery + multimeter + Schottky diode + LED (blue), leads 2.5mA, and in the reverse direction 0.01mA. I have no idea what that means.
Is there any test to be sure to exclude diode damage?
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I have a battery powered Arduino via a pulse converter.
This diode is to isolate the Arduino from the output of the converter module when I temporarily connect the USB. If the diode is conducting something in the reverse direction, will this "something" not damage the inverter or cause a short circuit? Because that's what I want to protect myself from.

piechnat wrote:

In the beginner's courses, the operation of the diode is shown in a more binary type

This is for a perfect diode.
In order not to confuse you on the courses, they say so, because the diodes are different and different diodes have different reverse currents. Typically it is several hundred microamps.

If this 9V battery was a 6F22, there is no chance that the 1N5822 diode could hurt - it lasts 3A, this battery gives much less, even in the alkaline version.

What it lets in in the reverse direction should not damage either the converter or the Arduino. Perhaps it can damage the LED that is turned on.

Quote:

Is there any test to be sure to exclude diode damage?

Compare with the catalog parameters, after all, the manufacturer writes this documentation for something

If the manufacturer states that there will be no more than 2mA at 40V, then any LED with more is defective.

2mA is a lot, but high reverse current is typical for Schottky diodes. Usually in these diodes it is so that the better the parameters in the forward direction (lower voltage drop), the worse in the reverse direction (reverse current). In these 2mA, the manufacturer has left some reserve, so it is very unlikely to meet a diode with as much as 2mA.

In pn diodes, the reverse currents are much lower (nA) and there are also diodes so good that they have less than 1pA, of course, it also depends on the size of the diode structure, and thus indirectly on the catalog maximum current.

As a curiosity, I can say that LEDs have one of the lowest leakage currents, provided that no light is falling on them, sometimes peak detectors are built on them (with an amplifier that eliminates a large voltage drop)

Don't taxi a young adept. The diode is ok in the directory. The table is not precise. Again I refer to the chart (link in my first post)

This reverse current has no practical significance in this application and you can safely use this diode.

Quote:

Don't taxi a young adept. The diode is ok in the directory. The table is not precise. Again I refer to the chart (link in my first post)

The table is not precise? - do you know what you are talking about? the documentation contains typical and guaranteed parameters, in the chart they are typical, in the table guaranteed. If someone asks what current to expect, look at the graph. However, when asked how to check if the diode is not damaged, you need to look at the table. Because although the typical value is in the order of 0.05-0.1mA, the manufacturer only guarantees that it will be lower than 2mA.

I would say the table is very illustrative. But agreement, as a simplified version, may be. The chart family appeals to me more.

jaszczur1111 wrote:

I would say the table is very illustrative. But agreement, as a simplified version, may be. The chart family appeals to me more.

You really don't understand why this table is there. Even the translation doesn't help.

I don't need a translation. I know english. Thanks for making me aware of my mental disability. How sad that people have to deal with idiots like me.

I understand it as follows: To check the diode, we look at the table. We measure the reverse current and compare. If it is higher than in the table, the diode is defective according to the manufacturer.

And now we take the graph. We measure the diode, the diode has a deviation from the graph. According to our own whim, we define whether such a diode is still useful for us or not. Because even if it has twice the reverse current, it will not interfere with most applications.

Both methods are appropriate, only the contractual limit is included in the table. Unfortunately, the table contains only two temperature values. So we have to bring the element to this. Using the chart, we can ignore heating to 25C or 100C. This is the advantage of the chart, at least from my point of view.

Moderated By Dzimi:

Please limit the statements to the topic of the ongoing discussion only.

Quote:

I don't need a translation. I know english. Thanks for making me aware of my mental disability. How sad that people have to deal with idiots like me.

I did not want to lower your self-esteem so much, it is not a matter of handicap but the number of read notes and application notes (there are also such "how to read datasheets"), which you can easily make up for.

It seems that with the present state of semiconductor technology, the production of repeating diodes and transistors should not cause major problems, but the production to some extent will always be influenced by various factors, aging machines, human errors, quality of materials or ordinary statistical dispersion of parameters, so it is difficult expect all LEDs to be the same.

In most cases, the typical data from the chart carry much more information, but when we want to design a reliable device, we have to rely on the limit values, the data sheet shows that there may be a diode with a reverse current 10x greater than the typical one. The same applies to checking - such a diode checked in the factory will be classified as good and can be delivered to the customer.