problem with mc34063 - Page 1
Forum section: electronics / projects

author: Armin
author_rank: Newbie
timestamp: October 26, 2013, 09:38:41 pm
content: hi guyswell i have voltage drop problem with mc34063i wanna convert 3-5 v to 12 volt 800mA, i made a circuit using "mc34063 universal calculator" software but i have very huge voltage drop, it drops from 12v to 4v under 20mA load!!i watched the video on YouTube (just loved it it was awesome) there were an example of 5 to 15 volt 100mA and it was working grate on video, i made the same circuit for myself and again i have huge voltage drop even in Proteus! it drops to 7.7v under 20mA!!pls help mebtw sorry for bad english

author: Mad_Hank
author_rank: Contributor
timestamp: October 26, 2013, 10:06:47 pm
content: I hope you didn't use one of the resistor like inductors?

author: c4757p
author_rank: Super Contributor
timestamp: October 26, 2013, 10:15:08 pm
content: Quote from: Armin on October 26, 2013, 09:38:41 pmAre you sure you actually built it in real life? It might not work in Proteus, but it works quite nicely in LTspice... Methinks Proteus is at fault.

author: Armin
author_rank: Newbie
timestamp: October 26, 2013, 10:23:53 pm
content: Quote from: c4757p on October 26, 2013, 10:15:08 pmyes i did and it didn't work,voltage drop is hugethe only new experience is ic heats up and gets out of order!!

author: Armin
author_rank: Newbie
timestamp: October 26, 2013, 10:26:08 pm
content: Quote from: Mad_Hank on October 26, 2013, 10:06:47 pmi did just like schematic and the inductor is 3amps (doesn't look like a resistor)

author: fcb
author_rank: Super Contributor
timestamp: October 26, 2013, 10:33:46 pm
content: Did you get the ic round the right way - the schematic shows the l-r reversed.

author: Armin
author_rank: Newbie
timestamp: October 27, 2013, 09:25:04 am
content: Quote from: fcb on October 26, 2013, 10:33:46 pmyes i didthis is the example given in datasheet, i made it and it works nice under 170mA and there is no voltage drop!!idk y my circuit doesn't work

author: Mad_Hank
author_rank: Contributor
timestamp: October 27, 2013, 10:23:42 am
content: What (I think) he means is that in your images pin 8 is in the left top corner, on your IC the left top corner is pin 1

author: mariush
author_rank: Super Contributor
timestamp: October 27, 2013, 10:36:26 am
content: I don't think the MC34063 can actually DO 800mA at 12v.Do the formulas and you'll see you have peak currents that exceed 1.5A (which is the output switch current limit) and you also need an inductor with peak currents capability of about 10-12 amps. Are you sure you have the proper inductor?Also, the online calculators I use :http://ukpyr.narod.ru/calc_mc34063.htmhttp://dics.voicecontrol.ro/tutorials/mc34063/say you need about 6-10uH inductor for step up configuration, while your picture shows 33uH inductor... the 33uH may be too big and make the IC overheat.

author: minime72706
author_rank: Frequent Contributor
timestamp: October 27, 2013, 04:47:23 pm
content: A lot of people on this forum will tell you of their inherent distrust of that chip. I had one detonate like a grenade and nearly blind my friend --- presumably because the oscillator failed to start up and the output switch was on, causing 35V to short to ground across the chip's innards ...

author: Armin
author_rank: Newbie
timestamp: October 27, 2013, 06:33:18 pm
content: Quote from: AcHmed99 on October 27, 2013, 12:18:38 pmwell i got the values from mc34063 calculator softwarshow much should that 0.4r be?this ic is just a bad ic!Quote from: minime72706 on October 27, 2013, 04:47:23 pmhah i have many experiences exploding componenti always wear safety glasses

author: free_electron
author_rank: Super Contributor
timestamp: October 27, 2013, 06:33:50 pm
content: Quote from: minime72706 on October 27, 2013, 04:47:23 pmYou betcha ! It is the GARBAGE of smps chips.They have piss poor performance, no protection , use bipolar transistors as switch element , run at very low frequency and the regulation loop is so unstable it commits suicide if a flea takes a leak on the other side of the continent it is run on.Grind them back to the sand they came from.There are far better converters than that miserable pile of refined sand and epoxy...

author: Armin
author_rank: Newbie
timestamp: October 27, 2013, 06:35:24 pm
content: Quote from: mariush on October 27, 2013, 10:36:26 amno my inductor is 3 amps!ill be also happy with 400mA, but idk y its so hard to make this ic work

author: Armin
author_rank: Newbie
timestamp: October 27, 2013, 06:38:12 pm
content: could any one pls do the calculations with softwares and give me the value of components and ill try with them, maybe i make calculation wrong

author: free_electron
author_rank: Super Contributor
timestamp: October 27, 2013, 07:04:30 pm
content: Quote from: Armin on October 27, 2013, 06:35:24 pmthat doesnt mean anything !there is only so much current the chip can pump into the current.you have to realise that switchers are POWER converters.power = voltage * currentso if you want 15 volt 1 ampere out that is 15 watt. you will need to send 15 watt IN . starting from 5 volts that would be 3 ampere !if the chip can only handle 1.5 , or if you set the current control resistor to 50 milliampere it simply will not work !

author: Mad_Hank
author_rank: Contributor
timestamp: October 27, 2013, 10:11:43 pm
content: Because the 34063 is notorious, what IC actually is recommended? My only experience is with the 555 and for my VFD project I'm going to use the uC to do the dirty work. Another chip that I know of is the MAX1771 but as far as I know component layour is somewhat critical with that one.

author: minime72706
author_rank: Frequent Contributor
timestamp: October 27, 2013, 10:16:04 pm
content: Quote from: Mad_Hank on October 27, 2013, 10:11:43 pmWhat's the goal? A boost converter with an output of about an amp?

author: mariush
author_rank: Super Contributor
timestamp: October 27, 2013, 10:34:08 pm
content: What springs to mind, would be LT1170 , LT1172 (dip version of LT1170) , LT1370 ..http://www.linear.com/product/LT1170http://www.linear.com/product/LT1172http://www.linear.com/product/LT1370You have the models in LTSpice so you can easily reproduce the typical application circuit from the datasheet by just dumping the ready made component in LTSpice and adding the passive parts, then you can play with different values.Linear Technology parts aren't cheap though, but you can request a couple of chips as samples and you'd get them in a couple of weeks.

author: poorchava
author_rank: Super Contributor
timestamp: October 28, 2013, 09:02:46 am
content: Simulating MC34063 is a bad idea for two reasons: different models and different vendors. There are 5 or more spice models for that chip, and probably like 50+ vendors selling it all over the world. I've tried simulating that chip many times in PSpice, LTSpice and TINA-TI and they all gave different results, yet none consistent with real measured values.

author: DutchGert
author_rank: Frequent Contributor
timestamp: October 28, 2013, 09:40:01 am
content: Quote from: Mad_Hank on October 27, 2013, 10:11:43 pmSIMPLE SWITCHERS from Ti work a treat.Some older versions had a duty cycle bug of some sort but i think they fixed it by now