Help! Why is this MC34063 INV dose not work properly? - Page 1
Forum section: electronics / beginners

author: ali6x944
author_rank: Frequent Contributor
timestamp: June 19, 2016, 11:29:31 pm
content: Hi everyone,I made this switching INV with MC34063, and it is not operating properly...It should output -15v but it is outputting -5v pluse the cap dose not make any oscillations like it should be considering the fact that I changed the dameged chip I made sure of all connections and thay all seem ok...Photors:https://drive.google.com/folderview?id=0B5vW-k7HbsL4UkxvYU1hM3QtMTQ

author: ali6x944
author_rank: Frequent Contributor
timestamp: June 20, 2016, 12:48:15 am
content: List of parts:3 one ohm resistors2 one k resistors1 10k resistor4.7k resistor smd 1208100uh inductor1nf cap470uf 25v capSS34 smd shottky barrier diode3mm red ledMC34063A SOIC-8Calculations:R1=1kR2=11kVin=3vVout=-15vIout=100mAVsat=0.7 -I picked the worst case scenario-Vf=0.4 -see instantaneous forward current to voltage drop graphfFout=32kVripple(pk-pk)=0.1mVton/toff=6.695652174(ton+toff)=3.125*10^-5toff=4.060734463*10^-6ton=2.718926554*10^-5Ct=1nfIpk(switch)=~1.5Rsc=~0.3L(min)=~42uHCo=470uF -its kinda over kill-

author: JoeO
author_rank: Frequent Contributor
timestamp: June 20, 2016, 01:20:41 am
content: Schematic?

author: ali6x944
author_rank: Frequent Contributor
timestamp: June 20, 2016, 09:49:07 am
content: Oh.... I forgot I will post it in a second

author: ali6x944
author_rank: Frequent Contributor
timestamp: June 20, 2016, 05:02:33 pm
content: Its here:https://drive.google.com/folderview?id=0B5vW-k7HbsL4UkxvYU1hM3QtMTQ

author: ali6x944
author_rank: Frequent Contributor
timestamp: June 20, 2016, 07:00:58 pm
content: Now did u see it the pdf

author: bktemp
author_rank: Super Contributor
timestamp: June 20, 2016, 07:48:20 pm
content: Connection between pin 7+8 and input capacitor are missing in your circuit.

author: ali6x944
author_rank: Frequent Contributor
timestamp: June 20, 2016, 09:52:08 pm
content: Input capacitor is not necessaryI fixed it and still not working properly....High output voltage of -5v instead of -15v and no oscillations on pin 3

author: JoeO
author_rank: Frequent Contributor
timestamp: June 20, 2016, 10:00:49 pm
content: There are many differences between your schematic and the schematic from the spec sheet.

author: ali6x944
author_rank: Frequent Contributor
timestamp: June 20, 2016, 10:39:55 pm
content: Mine is a mirror image so it is flipped...Don't forget the connection between pin 8,7 and I mistakenAnd drawn the feedback resistor connections.

author: ali6x944
author_rank: Frequent Contributor
timestamp: June 21, 2016, 10:59:48 am
content: I'm not quite sure but if the output cap or timing cap is shorted or damegd it will give a similar behavior so I will check...

author: Ravenghost
author_rank: Contributor
timestamp: June 21, 2016, 07:03:24 pm
content: Could it be that you connected a load which resistance is too small and it goes into current limit(i believe yours is limited to 0.5-0.7A) and therefore output voltage goes down?

author: ali6x944
author_rank: Frequent Contributor
timestamp: June 21, 2016, 11:42:20 pm
content: I don't think so, because I designed it for an output current of 100mA and and the led with the resistor I chose would give a current draw of around 3 mA, but I will remove the led and see what will happen

author: JoeO
author_rank: Frequent Contributor
timestamp: June 22, 2016, 01:11:19 am
content: Your schematic and the sample schematic are different in many ways.Your schematic is WRONG!

author: Skimask
author_rank: Super Contributor
timestamp: June 22, 2016, 01:25:06 am
content: Quote from: ali6x944 on June 21, 2016, 11:42:20 pmYou designed it?How?Did you consult the datasheet?Or just throw random marks on a piece of paper somewhat resembling a schematic, collect more random parts that looked fairly similar to the things on that piece of paper, and start soldering random stuff to other random stuff?QuoteYa that'll fix everything!!!Uhh...No...

author: ali6x944
author_rank: Frequent Contributor
timestamp: June 22, 2016, 11:18:28 am
content: I removed the led and nothing happened...Also I redrawn the schematic to make it clear because I missed some connections on the board, sorry if I intimidated some of you by not updating the schematic when I modified the circuit on the board so please forgive me for what happened.

author: ali6x944
author_rank: Frequent Contributor
timestamp: June 29, 2016, 02:45:20 am
content: So what shall I do??