MOSFET issue with LED's - Page 1
Forum section: electronics / beginners

author: d4v1dcn
author_rank: Contributor
timestamp: March 31, 2025, 01:53:48 pm
content: Hi guys!I have a "strange problem" with section 6 'front lights' of this circuit. LED's 61-63 are always on and i don't know why. If i measure between GND and anode of D61 or D62 i got 0v, but if i measure between GND and mosfet's gate or drain, i got around 4v. I'm using IRLR024N mosfet. Maybe the mosfet is damaged or there is any problem in the circuit design?Schematic is attached.Thanks in advance!

author: PGPG
author_rank: Frequent Contributor
timestamp: March 31, 2025, 02:26:07 pm
content: Quote from: d4v1dcn on March 31, 2025, 01:53:48 pmAnodes are connected to +5V so getting 0V is surprising.Quote from: d4v1dcn on March 31, 2025, 01:53:48 pmWith 4V at gate MOSFET should be conducting so getting at the same time 4V at drain is surprising.

author: squadchannel
author_rank: Frequent Contributor
timestamp: March 31, 2025, 02:30:41 pm
content: Can you also show us the board design? it could be that the footprint and symbol assignments are incorrect.It is a working circuit as far as i see. it does not take into account chattering of the switches, though.

author: madires
author_rank: Super Contributor
timestamp: March 31, 2025, 02:33:59 pm
content: Yep, the voltage between Gnd and the anodes of the LEDs should be 5V. Could you please measure the voltages at the anodes of D61 and D62?

author: d4v1dcn
author_rank: Contributor
timestamp: March 31, 2025, 03:45:23 pm
content: Quote from: squadchannel on March 31, 2025, 02:30:41 pmYes, pcb footprint is attached.Thanks!

author: d4v1dcn
author_rank: Contributor
timestamp: March 31, 2025, 03:46:49 pm
content: Quote from: madires on March 31, 2025, 02:33:59 pmThe measurement is between GND and D61 or D62 and there should be no voltage unless SW1 or SW2 is pressedThanks!

author: squadchannel
author_rank: Frequent Contributor
timestamp: March 31, 2025, 04:48:39 pm
content: first, I have many questions about your board design and component selection.1) 9V boost section is terrible.look at the datasheets of the various switching controller ICs and learn about their designs. I can't even begin to explain it.routing is too thin, bulk capacitors are too far away from the IC, you run the motor, is that routing width ok?it is a boost converter, boosting to 9V will approximately double amps the 5V side, but it does not work that way, so you need to design with the expectation that 3-4 times the current will flow.2) D61 and D62 are too big, big.don't need SMA package for MOSFET gate driving. need to use a small diodes, not a big one. for small signals, use SOD-323.3) Q61 MOSFET is also too big.Do you want to use LEDs that burn your eyes out?The title of the board is "screwdriver", so it's just to light up the tip of the drill, right? AO3401A is sufficient, right?4) thermal pad on the U11 makes no sense at all. The only way for heat to escape is the 10mil GND trace that leads only slightly.also, U41.The list of questions is endless. reason why it is not working is probably in the board design: the GND plane is broken and the air wire is present.With this board design, it is impossible(or lucky) to run a motor, and connect a load to it, it will magic smokes all over the board.mod:BMS section of the schematic, power symbols leading to EP and BAT in U11, draw the schematic so that the top ispositiveand the bottom isnegative(or gnd).IMPORTANT!

author: d4v1dcn
author_rank: Contributor
timestamp: March 31, 2025, 06:32:14 pm
content: Quote from: squadchannel on March 31, 2025, 04:48:39 pmHi,Thank you very much for your comments. This is my first PCB design (and I see you’ve noticed,).I had to replace the AO3400 MOSFET with the LR024N because the units I bought on AliExpress all turned out to be defective… and I had several LR024Ns at home that I wanted to reuse. Why do you suggest using an AO3401 instead of the AO3400?Right now, the PCB is working—at least the motor spins in both directions when I press SW1 or SW2. Luck? Probably, haha.Any other feedback that can help me improve this PCB design is more than welcome.Thanks again for your help!

author: Benta
author_rank: Super Contributor
timestamp: March 31, 2025, 09:22:33 pm
content: https://www.eevblog.com/forum/chat/please-rate-my-designschematic-ltrantgt/msg5746275/

author: d4v1dcn
author_rank: Contributor
timestamp: April 01, 2025, 08:07:24 am
content: Quote from: Benta on March 31, 2025, 09:22:33 pmHi Benta,Thank you so much for making it clear to everyone that you're an intelligent and knowledgeable person. I'm happy for you.When someone like me (a beginner with little knowledge) asks these kinds of questions, the least they expect is humility and respect in their answers instead of criticism from gifted individuals who are the smartest in the class.If you're not going to help with what they're asking, it's better to stay quiet than to think you're superior to others.I'm sure when you made your first design in college, it was perfect and they put it on an honor roll in the halls, right?

author: PGPG
author_rank: Frequent Contributor
timestamp: April 01, 2025, 08:51:21 am
content: Quote from: d4v1dcn on April 01, 2025, 08:07:24 amthen should be interested to make helpers to help him as easy as possible.You were simply told that your schematic is hard to read for someone who looks at it for the first time. What wrong you see in such information.When you given PCB I noticed there are R64 in paralel to R63 while at schematic not = schematic you gave is not the schematic of this PCB. My decision - it is waste of time until information given will be at least coherent.Quote from: d4v1dcn on April 01, 2025, 08:07:24 amWHAT !?Do there are really people getting interest in electronic so late. I have build my first circuit (detector radio receiver) when I was 10.At college when I got idea to do it I spend one afternoon to build circuit that allowed me to switch my desk (AC220V) lamp by clapping my hands.The whole thing was assembled as a spider on a newspaper (I had only germanium transistors those time and they had about 6cm long legs).

author: davep238
author_rank: Contributor
timestamp: April 01, 2025, 10:32:59 am
content: I didn't see anyone else mention it, but each LED needs its own series resistor. Otherwise, one LED will hog most of the current. And that 33 ohm resistor seems low. Do you really need to drive the LEDs with so much current?

author: d4v1dcn
author_rank: Contributor
timestamp: April 01, 2025, 11:59:07 am
content: Quote from: davep238 on April 01, 2025, 10:32:59 amHi,Yes, the correct way is a resistor for each led but i can't place a series resistor with each led because i don't have enough space to place it. Is a LED ring of 24mm of diameter x 3mm height with 3 SMD 3528 LED's connected between them in parallel with 0.3mm insulated copper cable. With a calculator, connecting them in parallel, requires a single 30 Ohm @ 1/4Watt resitor.Thanks.

author: squadchannel
author_rank: Frequent Contributor
timestamp: April 01, 2025, 12:00:23 pm
content: Quote from: davep238 on April 01, 2025, 10:32:59 amYes, the correct way to do it is to put one resistor on each LED, but I believe the LEDs are probably moduled. This would be the best way.Quote from: PGPG on April 01, 2025, 08:51:21 amIt is certainly not consistent, but the limiting resistor and the pads for connection are the only difference.Please be sure to attach a consistent schematic and board design next time.Quote from: PGPG on April 01, 2025, 08:51:21 amit is never too late to learn. In today's Japanese news, a 90 year old man has obtained licence of electrician. This is wonderful.Quote from: d4v1dcn on March 31, 2025, 06:32:14 pmAO3400 and AO3401 are Nch/Pch complementary pairs. The 3400A/3401Aare newer components. immediately remembered the AO3401.

author: Benta
author_rank: Super Contributor
timestamp: April 01, 2025, 05:04:03 pm
content: Quote from: d4v1dcn on April 01, 2025, 08:07:24 amIt's unfortunate that you regard my post as an attempt to insult you. It was not.The thread it linked to is written provocatively, I agree, but it's not directed at you.Rather, I linked tto itbecauseyou're a beginner. I wanted to save you from galloping into a cul-de-sac and acquiring bad habits. Doing this as early as possible is best.Best Regards.

author: d4v1dcn
author_rank: Contributor
timestamp: April 02, 2025, 08:33:47 am
content: Quote from: Benta on April 01, 2025, 05:04:03 pmHi Benta,Thanks for the clarification. I hope you understand that simply posting a link without further explanation can lead to confusion and misinterpretation of the intentions (that's what happened to me).Best regards.