What diodes (4 pieces not 1) to use for AC/DC for such device ?

Tonyr1084

Joined Sep 24, 2015
6,452
Use a single Quad diode. More commonly known as a Bridge Rectifier. It consists of four diodes.

If my answer is not what you're looking for - perhaps you might be a little clearer about what you need. Your picture doesn't tell us anything useful in answering your question. Here's a drawing of a bridge rectifier:
1624981747801.png

AC in on the left, DC out on the right. Note: The DC filtered by C1 will have a 1.414 times multiplication factor over the AC voltage. If you're putting 12 VAC in then you get 16.97VDC (minus the forward voltage of two of the four diodes in a bridge rectifier). Typically the Vf is 0.6 per active diode. Since during any portion of the AC sine wave only two of the diodes are active, you would typically subtract 1.2 volts from the calculated output. This case, 15.77VDC filtered.

If you want to build your own bridge rectifier you can simply use four 1N4002 diodes in the same exact configuration shown above. If you're working with higher voltages you'll want a higher 400x number. As the "x" goes up so does its voltage rating. I'd suggest 1 1/2 times higher rating than what you expect to work with. Two times is also a common factor. To find the information you'll need the data sheet will be most useful.
 

LesJones

Joined Jan 8, 2017
3,570
I think I can see locations where 4 diodes have been removed. From where they are located on the board I think they just rectify the mains input. (The voltage will depend on where you are located.) I think 1N4007s will be a suitable replacement. It is quite possible that some other components have failed and they were the cause of the diodes failing. I think even if your mains voltage is only 110 volts that the PIV rating of 1N4002s will be too low. There is very little difference in the cost between 1N4002s and 1N4007s

Les.
 
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