Feedback for custom ESP8266 LED controller - Page 1
Forum section: electronics / projects

author: Gearloose
author_rank: Newbie
timestamp: May 16, 2018, 01:46:30 pm
content: Hello,I'm very, very beginner in electronics and I would love some feedback on my design below.I try to design a PCB to control 2 LED strips with ESP8266, one RBG and one White.This is the setup a came up. Do you have any improvements to propose? Best practices etc? (I try to lern in the process of building the controller)MOSFET: IRLML6244TRPBF

author: Tadas
author_rank: Contributor
timestamp: May 16, 2018, 08:27:33 pm
content: I'm also an absolute beginner and actually building something similar right now.Any particular reason you picked LM317 for 3.3v supply?.. I'm thinking of using ZLDO1117G33TA, which is a fixed voltage regulator with input of up to 18v. Less parts, less things to worry about. With 12v supply it does get somewhat hot.:https://uk.rs-online.com/web/p/linear-voltage-regulators/7515183/

author: Gearloose
author_rank: Newbie
timestamp: May 17, 2018, 12:09:27 pm
content: Hi Tadas,to be honest I dint even know the existence of the ZLDO1117G33TAIn the past I have used the LM317 (in bigger package) for a power supply so I knew it as a part (I think it is quite popular).The most important reason though is that the specific design is used in this product:https://www.sparkfun.com/products/13032Also comparing the 2 parts I think they require almost the same setup to work (based on the datasheets at least)best,Nikitas

author: JS
author_rank: Frequent Contributor
timestamp: May 17, 2018, 12:42:31 pm
content: It's quite reasonable, you have to be careful with thermals and current capability of the mosfets. It could be perfectly ok or burn quite fast depending on the strips length. Also, if you modulate the output with pwm the power dissipation on the Mosfet will increase, just be aware of it. Lowering the pwm freq you can improve efficiency but it could start to flicker.JS

author: Gearloose
author_rank: Newbie
timestamp: May 18, 2018, 02:18:10 pm
content: Hello JS,thank you for the feedback!Indeed this is one of my considerations. The specific MOSFET (IRLML6244TRPBF) was used in commercial LED strip drivers without haetsink so I hope it can handle it (I do not know how to read the thermal parameters in the datasheet so I used one other people use)I kept them all in one row, close to each other so I can glue a heatsink if needed. I guess it will be a trial and errorbest,Nikitas

author: JS
author_rank: Frequent Contributor
timestamp: May 20, 2018, 01:46:29 am
content: Quote from: Gearloose on May 18, 2018, 02:18:10 pmThermal math isn't hard at all, you could start with the thermal resistance junction to air, but in this datasheet it includes the maximum power dissipation, at 1.3W@25ºC ambient and 0.8W@70ºC ambient. That's maximum, eep it lower than that.Let's say your product won't be at 70º, more likely 40ºC max so 0.8W might be reasonable.RDS is 0.027Ω max at 2.5V VGS, you are likely to be under 0.025Ω at 3.3V0.8W=I^2*0.025ΩThat's 5.6A maxIf you run your LEDs with a maximum current of 4A you are most likely safe to go, you could strech to 5A and still be reasonably safe but not so reliable for long term. (depending on PWM freq, switching transition is where most power is generated inside the switching element)Note that the things are really small and they don't even specify thermal resistance from junction to case (to then add a heat sink). Of course you could help a bit with a heatsink but not much, and if 4A is not enough you could go for something beefier.If you are doing PWM be sure to drive the mosfet fast (IE no or low gate resistance) so the switching is done fast and you keep efficiency up.JS