Nifty Nonsense & Creativity - A show and tell thread. - Page 1
Forum section: electronics / general

author: LEECH666
author_rank: Frequent Contributor
timestamp: February 04, 2011, 08:16:51 pm
content: Ever ordered some parts from a distributor just to test out some cool new circuit you just thought out (or discovered)?I bet you did! And I also bet there was a time when you screwed up your BOM and forgot to order one of the parts needed.The same thing just happend to myself and so instead of driving to the local radio shack I just spend half an hour solderingtogether 20 resisitors to create a 0.5 Ohms resistor that I need to test my MC34063 circuit.I know this is probably not the most impressive hackjob ever done, but anyway I hope it will get the job done.Tell me about your exploits! Tell me how you overcame the final obstacle to a working circuit!I am all ears! ... and who knows maybe your idea might help someone to get rid of exactly the same problem.Go go go.Cheers from Germany,Florian

author: Zero999
author_rank: Super Contributor
timestamp: February 04, 2011, 08:25:11 pm
content: It's very neat job, much better than the sloppy component forming and soldering I see a lot on forums. You might want to consider cleaning the flux off though, not only does it make it look neater but it also reduces corrosion and keeps it cleaner as flux attracts moisture and dirt.

author: LEECH666
author_rank: Frequent Contributor
timestamp: February 04, 2011, 09:19:49 pm
content: Hello again Hero999,yeah I probably should clean of that flux.I went through a few years of electrotechnical training, I sort of know what I am doint when it comes to assembling (mainly soldering). Understanding circuits in detail, however is still a mystery to me. :S

author: mitpatterson
author_rank: Regular Contributor
timestamp: February 04, 2011, 09:58:11 pm
content: Did you actually measure it? did you get the reading you expected? because i'm not sure what all the solder joints does to your resistance there

author: LEECH666
author_rank: Frequent Contributor
timestamp: February 04, 2011, 11:09:31 pm
content: Yes I meassured it, but my crappy DMM (Digital Multi Meter) can only do 000.x ohm, so the meassurement might be a little inaccurate. It's 20 10-ohm (1%) resisitors in prallel, and the reading in my DMM showed 000.5 sometimes jumping to 000.6 ohm, but that might be the fault of the testleads, as they allone (shorted) read 000.1 ohm.I also assembled the circuit I wanted to test on my breadboard. 12Vin (1A) / -12V out (150ma) / 100khz / 10mV ripple.I didn't reach the 10mV ripple I initially aimed for but 50mV is still not too bad ... I guess.I want to use this circuit to power some op-amps in a future active crossover design. Not sure if noise comming from the switch converter might be an issue :S.Cheers from Germany,Florian

author: Zero999
author_rank: Super Contributor
timestamp: February 05, 2011, 10:17:34 am
content: The tolerances will average out so your 0.5R resistor will be better than 1%.It's probably your crappy meter and leads, if you can't zero the meter, always short the leads together and subtract the reading from your results.A breadboard isn't ideal for building an SMPS on, using a proper PCB will give you better performance.Oh and please upload here rather than on some other image hosting site.

author: jahonen
author_rank: Super Contributor
timestamp: February 05, 2011, 10:29:05 am
content: I wouldn't make any conclusions of the ripple of a switch-mode regulator assembled on a breadboard. Parasitic inductance is way too high. BTW, resistors you mentioned can be replaced by a short-circuit for testing purposes, but that of course defeats the overcurrent protection.Anyway, 34063 would be mylastchoice of switch-mode regulator for audio application. Since it does not have any PWM modulator, it creates fair amount of subharmonic noise, which is in the audio band. Instead of trying to filter it, try something like MAX743, if your current requirements are not too steep.This problem can be seen from following test measurements I made some time ago:Ripple:Same but different time scale:It can be seen that due to way 34063 works, the ripple amplitude distribution seems to have sort-of quantization steps. For most of the time, ripple stays quite low, but then it sometimes shoots high amplitude "blips". For regulators with proper error amplifier and PWM modulator, the ripple amplitude stays constant (for constant current load and input voltage) without any high "blips". This randomness can be seen from following measurement of the switch node:Only good thing about 34063 it is that it is a) cheap b) ubiquitous. And of course it does not care if you get the compensation right. Just throw in just about any inductor and output capacitor and it worksCertainly it can be used for powering digital circuits, but it is far from the good. I have sometimes wondered if the bad reputation of switch mode regulators for analog applications is due to the 34063.Regards,Janne

author: Unknown
author_rank: Unknown
timestamp: February 05, 2011, 12:58:32 pm
content: Quote from: Hero999 on February 04, 2011, 08:25:11 pmFlux may also increase leakage, which will be a major issue in this high-impedance circuit.

author: sonicj
author_rank: Frequent Contributor
timestamp: February 05, 2011, 11:33:04 pm
content: Quote from: LEECH666 on February 04, 2011, 08:16:51 pmlol! i have a box of old/dead electronics that i keep on hand for just such occasions. sometimes i can complete a project from junk + parts in my bin, but 9 times out of 10 i'll be missing just one component.btw, the MC34063 is popular in many cellphone car chargers. you get the ic, circuit board and all of the supporting components often in a ready to use form. if you don't have a old one laying around, your local thrift store likely has a box full of them. dollar stores are another potential source. cheers!-sj