current controlled LED circuit...problemz - Page 1
Forum section: electronics / beginners

author: TruyersCas
author_rank: Newbie
timestamp: May 20, 2021, 05:18:31 pm
content: hello all, I'm a first-year electronics student and also new to this forum. I have designed a PCB for a LED driver circuit using the MagI3C Power Module from Würth Elektronik.Today I tested it for the first time and... it doesn't work. The soldering looks good and I checked connections with a multimeter and all is well, as far as my knowledge is concerned.I measure the correct voltage at the input(pin1 and 2), so up to that point everything is fine. But what strikes me and the reason why there is no voltage/current at the load is that the same voltage of the input(pin1 and 2) is also at the output (pin7). And since my load is connected to pin1 and 2 as negative terminal and pin7 as positive terminal there is no voltage difference thus no power.I don't know the details of how this module works and if it is normal to have a voltage and in this case the same voltage on pin7. You can also see on the picture of my power supply that I am only supplying 2mA. The current output can be determined by a resistor on pin5 to the ground and the formula in the datasheet. I did the math and it should provide 220mA. As a load, I used 5 x 220 Ohms resistors in parallel to get a total resistance of 44 Ohms so I don't need a high voltage to supply that current since my power supply can only go up to 18V. (If there is a better load to test the functionality of the board, please let me know!). Maybe the load is just.. idk, bad to test the board and thus not function? With this load, it should only need a voltage of 9.68 which I should be able to provide. (my DMM fuse broke so I can't measure the current directly)I used a reflow oven to solder the module, don't know if it might have broken by the heat? Too bad I didn't look in the datasheet beforehand to look at the reflow info. The thermal sensor was mounted on the PCB and not on the module as advised by the datasheet. Maybe the module gets heated up a lot faster? But I don't think this should be the issue since a good reflow oven was used and the temperature never got above 245 (i think?).I have attached the datasheet, schematics, pcb design and pictures. I tried my best to provide enough information, but if more is needed I will supply it!In the pictures, I'm measuring between pin1-2 to ground and pin7 to ground to show the same voltage level on these pins.Any kind of help is highly appreciated!thanks!Casdatasheet link:https://www.we-online.com/catalog/datasheet/172946001.pdf(also, please excuse my English)

author: TruyersCas
author_rank: Newbie
timestamp: May 20, 2021, 08:05:41 pm
content: I've found something interesting in this videoa wurth Elektronik webinar about this module.At 16:20 minutes they talk about the LED failure protection. When that occurs the Vout (pin7) jumps to Vin (pin1-2). Which is the case here.I guess I'm testing with a bad representation for the load, or my circuitry after the module is wrong...any suggestions?

author: ZedaPeida
author_rank: Newbie
timestamp: May 21, 2021, 11:47:18 am
content: I´m not sure, but I think the 1K to ground on the DIM pin might be too low and it's disabling the driver.Voltage on DIM pin should be higher than 1.25V for enabling.I would try with the DIM pin floating.

author: TruyersCas
author_rank: Newbie
timestamp: May 21, 2021, 12:32:46 pm
content: I just noticed this as well, tried it with a positive voltage on the pin and things are working!thanks for your support!