Schematic Review - Page 1
Forum section: electronics / projects

author: PCB101
author_rank: Newbie
timestamp: June 17, 2025, 07:25:48 pm
content: [ Specified attachment is not available ]Hi all,I'm working on my first full PCB design and would really appreciate any feedback or suggestions you might have.The board is intended to drive and control multiple lasers and fans. I've attached images of the schematics, which are split into different sections based on function (e.g., laser drivers, fan control, microcontroller interface, etc.).If anything stands out—whether it's a potential design issue, layout improvement, or just a best-practice tip—I'd love to hear it. Constructive criticism is welcome!Also, the schematics are updated so that they are easier to read. I hope this helps.Thanks in advance!

author: Benta
author_rank: Super Contributor
timestamp: June 17, 2025, 09:03:21 pm
content: So where's the schematic?You've presented a collection of Lego blocks with labels.A list of the involved data sheets would bring the same.Do you expect us to build a spreadsheet listing the labels and their relations?Sorry, no time.

author: PGPG
author_rank: Frequent Contributor
timestamp: June 17, 2025, 11:20:16 pm
content: You used the way of drawing schematic that is:- easy to understand by its author,- easy to analyse by computer,- hard to analyse by human.So ask computer and not human for opinion.

author: Benta
author_rank: Super Contributor
timestamp: June 17, 2025, 11:41:44 pm
content: Quote from: PGPG on June 17, 2025, 11:20:16 pmYour point one is time dependent. In two years, it will have moved to point three.

author: PCB101
author_rank: Newbie
timestamp: June 18, 2025, 04:31:13 pm
content: I updated the schematics so that they are neater and easier to read.I was hoping to get feedback on the design decisions that I made and the components/values I picked.

author: floobydust
author_rank: Super Contributor
timestamp: June 18, 2025, 06:51:15 pm
content: Your part numbers are missing or incomplete.U13 LDO requires an output capacitor, but your new schematic lost the part number. I forgot what it was yesterday.AP1503A5A buck is obsolete. It has no pin 6, tab is heatsink and GND. There is a 12V part AP1501A-12, or you seem to be using the AP1501A-ADJ. Seems to be similar to LM2596 or XL4005/4015 etc. You are missing the output Schottky diode.U9LM61480min. Vout is 12V with pin 5 VBIAS tied to GND. I don't know your laser diode typical voltage.You might consider adding a voltage limiter because an open/disconnected laser will make the output V go up there C40/C53 might pop. It's a bit ambitious a 2.2MHz switcher PCB layout for a first time and if it doesn't work it will roast your lasers. Follow the EVAL board layout at the very least.If the 3.3V rail is late coming up/first coming down, U10 will not do much so careful there. Yesterday you showed the second op-amp pins 5,6 all floating but now it's not even on the schematic.TLV9002.C46/C59 seems big 1uF is 20msec time constant so the CC might be too slow? Why no LED's to show this thing is on?I don't know how many (laser) dollars are at stake here but you might want to first do a smaller scale of this project if you don't have the experience or attention to detail that you need for success.

author: ledtester
author_rank: Super Contributor
timestamp: June 18, 2025, 07:19:06 pm
content: In your previous schematics U13 was labeled as a TPS709 voltage regulator.The capacitor from Vin to EN looks wrong. The TPS709 datasheet shows a recommended capacitor from Vin to GND. EN should be either left floating or driven low.

author: floobydust
author_rank: Super Contributor
timestamp: June 18, 2025, 09:28:14 pm
content: TPS70933in a SOT-23 will cook and overheat with 24V in and a few 10's mA load.

author: Benta
author_rank: Super Contributor
timestamp: June 18, 2025, 11:33:29 pm
content: Quote from: PCB101 on June 18, 2025, 04:31:13 pmThey're not.But your thinking is upside-down. If you want us to evaluate your component choices, the circuit needs to be understandable.If this is your first design, you've not done badly. But why not use wires instead of text labels? Anyone can follow a line and understand the connection. And it even makes multiple connections understandable. Searching for labels does not.Labels all over the place is just too much effort for reviewers.