Using SOIC to DIP breakout boards with switching ICs ? - Page 1
Forum section: electronics / beginners

author: Dannyx
author_rank: Regular Contributor
timestamp: March 12, 2025, 09:22:18 pm
content: Good day folks.TL;DR: has anyone ever tried using a SOIC to DIP breakout board likeTHESEwith switching ICs on the HOT side of SMPSs, or can these interfere with the operation of the IC and cause unexpected results ?I'm trying to fix a small SMPS out of a PA amplifier. It's nothing complicated and LOOKED like an easy enough job, but it's turned into a marathon of failures: initially, the bridge rectifier was shorted, so the fuse was also blown. The FET checked out fine on my multimeter, so did all the small components around it, so I replaced just the rectifier and tried it out: still no output. Given there weren't any other components that I could check with my humble DMM, I decided to just replace the switching IC, aLD7575. There was a catch: I couldn't find the DIP package the SMPS came with (pictured), so I had no choice but to go with the SMD version. Initially, I was planning on laying on the back of the board and running wires to each pin, like the "dead-bug" technique, but then I remembered I had these little breakout boards in my parts bin and thought it would make things a lot easier and neater, so I soldered the IC onto it, soldered header pins and inserted it into the original DIP holes.The SMPS STILL didn't fire up. Moreover, the FET AND the IC itself also died now. When I checked them again, the "CS" pin was shorted to GND, despite having a 25w lightbulb in series with the mains, as it's common practice. It glowed faintly upon power-up, which was a sign something was not working as it should, since it should just come on bright for a brief moment as the main cap charges and immediately go out almost entirely. This got me thinking whether the failure was caused by the FET being on its last legs ever since the bridge rectifier shorted out and sent half-wave DC into the circuit, or is it because of that breakout board messing with my IC somehow.....I got replacements for both the IC and the FET ready, but I'm not sure whether I should try again, or just remove the breakout board and do it the slow and tedious way...

author: Buriedcode
author_rank: Super Contributor
timestamp: March 12, 2025, 10:10:09 pm
content: SMD adapters - like those you linked, are less than ideal for high switching frequencies, with their rather thin traces, but given those traces are rather short, its worth a try.I assumed you measured the "shorted CS pin" out of circuit? Because thats going to be the current resistor resistor in circuit and will be a low resistance to ground. Or is it your soldering to the adapter?Note: I have used a set of those adapter and one (SOIC28) had a manufactureres defect where two adjacent pads were shorted - despite visually appearing to be fine (held up to the light, couldn't see any connection, but it measured a dead short without any IC mounted on it).Hows the main capacitor measuring? Given fuses are slow, when something shorts down stream it can cause a fair bit of damage to a lot of components before it opens.Also, what is the wattage rating on this PSU? I've had a few power supplies that wouldn't start up when a single 60W bulb was in series, or 100W - it needed 2x 100W in parallel before it would start up during tests. That was rated for 500W though.

author: David Hess
author_rank: Super Contributor
timestamp: March 13, 2025, 12:50:47 am
content: Since the device already uses a DIP package, a SO to DIP adapter will not be a problem.

author: coppercone2
author_rank: Super Contributor
timestamp: March 13, 2025, 01:00:22 am
content: I ran a very high frequency SOIC or maybe smaller chip on a DIP package with a bunch of through hole capacitors and it worked OK, even though I had through hole ferrite beads instead of the 0402's. Every part was the best quality (i.e. X7R), but through hole, and dead bugged over copper sheet, without any serious guesses on what might be a acceptable substitute value.I think you mileage may vary but it has a decent chance of working. Like I am thinking the square wave is already pretty shit, and they use things like edge blanking or whatever, so your not gonna mess it up too much more easily. Those advanced switching controllers.... I think if the phase is in the ballpark it plays, IF the bulk component of the part is correct. I imagine it might not pass to their compliance limits they advertise, if you take it to a lab.I think its wishful thinking that just the switching controller dies and it does not effect the power part, I think those failures tend to take out a network unless its truely a defect (like a broke bond wire), though I guess the gate driver part of the controller might be being pushed pretty hard, especially if its not speced great.

author: tszaboo
author_rank: Super Contributor
timestamp: March 13, 2025, 12:00:01 pm
content: Quote from: David Hess on March 13, 2025, 12:50:47 amAgreed, the ICs will have the same die, one with bondwires the other with a bit of extra PCB in between.Plus this is some dozen khz SMPS, not a buck converter working at 3MHz.

author: Dannyx
author_rank: Regular Contributor
timestamp: March 13, 2025, 01:52:27 pm
content: Thanks for the replies. I decided to give it one more try with the breakout board, since I quickly realized soldering the SMD IC on the back of the board wasn't going to be as easy as I pictured it in my mind at first. I tried laying the IC on the back of the board, just to get an idea of what it would look like and it became apparent it would be no easy task - running all those small wires from each of the legs without any adjacent ones touching would be tough enough in itself, but as you can see there are also some SMD components directly below the IC, which would make the job even more miserable still, so I dropped the idea.Long story short, it worked this time: replacing both the IC and the FET brought the supply back to life. It's a 24vDC supply, by the way........although I must've been blind or something at first, because if you look closely at the "model", it says so right thereSomeone pointed out the main 450v cap: true, it TOO was dead, reading only a few puFsAlthough I DID replace it just before the FET shorted completely and the first IC also blew, the IC must've already been dead at that point (because I tried running it on the dead cap first), so it made no difference.Here's some more pics of the supply and the IC.