I'm trying to find which diode in a charger is bad. I took the 1N5819 diode out of the electronics board and tested it with my multi-meter set to "diode".
What I got was 0000 in both directions. Shouldn't this diode (or any diode for that matter) only give a reading in one direction?
Does getting 0000 reading mean that this diode is bad?
What should the reading be?
Electronic – 1N5819 diode reading
diodes
Related Solutions
A 1N5819 is a 40V 1A Schottky diode.
Any Schottky diode with a similar rating will be acceptable (see below)
BUT in fact a 1N5817 or equivalent would be slightly superior here. The difference is small but there is no point in throwing away efficiency for no resultant benefit. The 1N5817 has a SLIGHTLY lower forward voltage drop when conducting so cause very slightly less losses overall. You may get a percent or two extra efficiency by using it.
1N5817 - 20 V 450 mV drop at 1A
1N5818 - 30 V 550 mV drop at 1A
1N5819 - 40 V 600 mV drop at 1A
For 5V output (5 + .450) / (5 + .6) = 0.973
ie notionally at 1A you need to make about 2% more voltage at thesame current with the higher voltage diode.
1N5817, 1N5818, 1N5819 data sheet
The output voltage is 5V so a diode of 10V and above rating will be notionally OK for D3.
A 20V rating will be very safe.
Looking through tables and checking forward voltage drops would allow you to select a Schottky diode that was best suited, but most of similar ratings will be OK.
1N5819 is axial leaded through hole mount - but you could easily solder an SMD part on the board bottom if one had especially good specs. One does, if you can get it - see below.
You don't say where you are and that affects availability somewhat, but using memory & digikey as a guide:
Generic SMD: SS12 = 20V, SS14 = 40V
ST STPS1L20MF 1A 20V 430 mV at 1A
Microsemi LSM115JE3/TR13 15V 1A 220 mV at 1A !!!!!!!!!! Datasheet
Digikey's component database selector guide is a powerful design aid.
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Best Answer
Usually, the multimeter will give you a reading in only one direction: the forward biased direction. Some expensive meters can do reverse biased voltages, i.e. zener diodes, but most multimeters will only do one direction. So, you'd have to connect the positive lead to the anode and the negative lead to the cathode. Then the meter will give you the forward voltage drop of the diode.
If your meter is giving you '0000' both directions, it could mean one of two things: -- The diode is definitely busted. -- The meter is not functioning correctly.
Is it possible for you to test the diode function on your multimeter using a known, good diode? That way you can verify at least the meter is working as expected. You don't have to unsolder or take the diode out of the good test board to do this.