I bought these a little while ago (MP1584 step down modules). The issue I had with these is they are extremely sensitive and also have a horrible voltage range (it goes sort of 1V, 2V, 3, 4, 4.5, 15V... as you turn the potentiometer.. and guess what voltage I needed - 5!). Anyway I dealt with it for a while until I blew my up micro-controller because I must have jogged the board and the potentiometer moved.
So obviously, the next best thing would be to get a constant 5V output board instead. While looking for one, I noticed the circuits are almost identical with just different values of resistors (and probably caps) and a different value inductor. That then got me thinking surely I can just replace the potentiometer with 2 resistors to get a fixed output. So that is what I did: (excuse the drawing)
I did exactly as shown and put two 2.7K resistors across the two pins (NOTE: I have two of these boards - this is not the one I put the resistors on - the other one has the pot removed)
Unfortunately, I still got 23V on the output (max output = input - 1V). I would think this should be working because of diagrams like this:
The next thing I noticed was that the pin with the green arrow pointing at it doesn't seem to be connected to anything:
If it was connected there should at least be some vias directly in line with the '+' (the board is flipped so the pot is on the left side now)
The pin may well be connected to ground but it just doesn't seem to be.
What am I doing wrong here? - maybe I have the resistors the wrong value but they should still at least affect the output a bit right?
Thanks,
Bod
EDIT: I just had a look over the board again. The left pin (green arrow) is indeed connected to ground. There's a trace hidden underneath pot that seems to got to one (if not both) of the vias on the underside, connected to ground (the ones between the 'U' and 'T' in 'OUT')
So obviously, the next best thing would be to get a constant 5V output board instead. While looking for one, I noticed the circuits are almost identical with just different values of resistors (and probably caps) and a different value inductor. That then got me thinking surely I can just replace the potentiometer with 2 resistors to get a fixed output. So that is what I did: (excuse the drawing)
I did exactly as shown and put two 2.7K resistors across the two pins (NOTE: I have two of these boards - this is not the one I put the resistors on - the other one has the pot removed)
Unfortunately, I still got 23V on the output (max output = input - 1V). I would think this should be working because of diagrams like this:
The next thing I noticed was that the pin with the green arrow pointing at it doesn't seem to be connected to anything:
If it was connected there should at least be some vias directly in line with the '+' (the board is flipped so the pot is on the left side now)
The pin may well be connected to ground but it just doesn't seem to be.
What am I doing wrong here? - maybe I have the resistors the wrong value but they should still at least affect the output a bit right?
Thanks,
Bod
EDIT: I just had a look over the board again. The left pin (green arrow) is indeed connected to ground. There's a trace hidden underneath pot that seems to got to one (if not both) of the vias on the underside, connected to ground (the ones between the 'U' and 'T' in 'OUT')
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