smps board problem - Page 1
Forum section: electronics / beginners

author: 5282
author_rank: Regular Contributor
timestamp: January 21, 2016, 01:45:24 pm
content: hiiii use ic 3842 as smps controllerbut i try about 30 days and i can't solve problem :sad:the problem is the power transistor driver is always burn and i try every thing and it's burn in less than 1second.

author: SebG
author_rank: Regular Contributor
timestamp: January 21, 2016, 03:59:18 pm
content: HiPlease provide more information. What is your circuit. Is it the power transistor that is burned or the on chip driver. What transistor, current sense resistor are you using?

author: wraper
author_rank: Unknown
timestamp: January 21, 2016, 04:01:43 pm
content: Without a schematic, your question is useless.

author: 5282
author_rank: Regular Contributor
timestamp: January 24, 2016, 01:53:30 pm
content: thank to all i burn about 16 transistor and 6 mosfetthe transistor is burn in less than 1 second when i test it with 220v." i use 40w 220v lamp as current protective resistor"but the circuit work well when i work only with 24v . and with 220v it make short circuit

author: bitshift
author_rank: Regular Contributor
timestamp: January 24, 2016, 03:11:39 pm
content: Holy %!#@Take out life insurance NOW!

author: wraper
author_rank: Unknown
timestamp: January 24, 2016, 03:59:41 pm
content: Driving bipolar transistor from UC3842 through 1k resistor, just wow. Why did you think you can do this? And BTW you cannot use UC3842 without a feedback as it does not have any duty cycle limitation at all, unlike UC3844.What I see, you are completely clueless, therefore advise to stop doing this before you killed yourself.QuoteTrust me, it does not.

author: 5282
author_rank: Regular Contributor
timestamp: January 24, 2016, 05:41:35 pm
content: thank you for helping me it's duty cycle problem.but i put 40watt lamp as protective resistor dummy load so the transistor must be heated first and then burn . the transistor burn in less on secondQuotei'm phd in electrical engineering and bs in electronic engineering and phd in computer science and asic design O0 but i haven't phd in 3842

author: wraper
author_rank: Unknown
timestamp: January 24, 2016, 06:23:29 pm
content: Quote from: 5282 on January 24, 2016, 05:41:35 pmThis is not about particularly 3842. What do you think will happen with half open transistor (have you heard about BJT current gain? 1k base resistor) and how big power will be dissipated in BJT at this voltage? BTW MJE13007 has too low VCEOto work in flyback circuit where mains voltage is 220-240V, though this is not the reason of the particular failure. Moreover UC3842 is not supposed to drive the BJT at all. Every time you blow up a transistor, UC3842 should fail in most cases too (maybe insanely high 1k resistance will save it). Lamp will not protect anything because of the way how you made the circuit, and the current through the cold incandescent lamp is much higher than nominal.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 24, 2016, 09:08:29 pm
content: a phds that burnt 16 transistor and 6 mosfet and never learnt how ironic

author: EPTech
author_rank: Regular Contributor
timestamp: January 25, 2016, 08:26:23 am
content: Hi There,My advice to you is to go on manufacturers websites, like national semi, TI, power integrations and search for some reference designs to get you started. An open-loop SMPS is doable but will not give you any stable output. I have seen them in action and they use some kind of power measurement of the primary but it is still a feed back.You can do some experiments on the primary but you need to use an oscillator or function generator to drive a HV (400V at least) MOSFET and use the lowest duty cycle possible to start with.BE CAREFULL: use an isolation transformer to supply the primary.Still I do not see any practical use for a setup like that unless you want to do some quantitative measurements on the transformer.

author: homebrew
author_rank: Frequent Contributor
timestamp: January 25, 2016, 09:03:19 am
content: Quote from: AcHmed99 on January 24, 2016, 05:56:37 pmWell, don't be too harsh on him. That's pretty normal in academia. Once people are specialized to a very very very narrow area of knowledge, a lot of them often loose the connection to practical work altogether (or never had it in the beginning).I've seen 5 doctoral students (very bright people indeed) standing around a computer not figuring out why it randomly froze. They even went so far to open the case. However, just sticking their hands in the machine to figure out the CPU cooler was dislocated and loose was out of range :-)As for the topic: There are sooo many SMPS-Designs out there! Just gohttps://www.google.ch/search?q=smps+uc3842and you will find a lot of schematics that look far better suited than the simplistic design presented.As mentioned by many others: Be careful!

author: AlxDroidDev
author_rank: Frequent Contributor
timestamp: January 25, 2016, 09:17:30 am
content: Quote from: 5282Cool! I'm a bullshitter in electronics engineering too! I can read datasheets, 'though.