N-mosfet as an external switch for mc34063 - Page 1
Forum section: electronics / beginners

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 26, 2016, 06:43:28 pm
content: hello everybody,I'm working in a switching transformer less power supply based on the great mc34063 ic.I want a fare current capability and a duel output voltage supply that could reach 0v, so i will put it like this:220/110v ac,60hz-------> -15v -0- +15v @ 3A, because I'm using a switching supply we would have some voltage ripple,i could deal with 100mv pk-pk .after somework i got these measurements -raw rectified dc-:@ 220v AC, i got 306.6v dc and a max current of around 325mA,@ 110v AC, i got 152.2v dc or so, and a max current of around 175mA,so the first problem is the big voltage drop that should be present to run the mc34063 and the second problem is the the output current capability, the third is efficiency related problems.oh! by the way, I'm using a capacitor based transformer less design, I already dealt with inrush current problems, so u don't need to worry about that.please help!thanks .

author: c4757p
author_rank: Super Contributor
timestamp: January 26, 2016, 06:45:20 pm
content: Quote from: ali6x944 on January 26, 2016, 06:43:28 pmActually, I'm terrified...

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 26, 2016, 06:53:43 pm
content: why???

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 26, 2016, 07:48:09 pm
content: it works nicely, but it is not isolated that's all

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 26, 2016, 08:39:33 pm
content: so what to do now?

author: cpt.charlie
author_rank: Contributor
timestamp: January 29, 2016, 10:20:42 pm
content: Quote from: ali6x944 on January 26, 2016, 06:53:43 pmBecause it's quite dangerous! by the way those voltages exceed the operational voltages of the mc34063 you need to decrease the input voltage at 40v max.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 29, 2016, 11:26:10 pm
content: The MC34063 is not that great to drive a MOSFET or use high voltages. There are better chips for this purpose. A UC384x might be a better alternative here.A non isolated design also has only limited applications, like powering lights inside an enclosure. At higher frequencies the transformer for a flyback version is not that large anymore.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 30, 2016, 02:20:54 am
content: I'm not sure which one this thread needs more, holy water or gasoline...

author: c4757p
author_rank: Super Contributor
timestamp: January 30, 2016, 02:24:03 am
content: Gasoline, I think it's less conductive...

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 30, 2016, 01:52:24 pm
content: but seriously speaking, i did some simulation in ltspice and in real life...when i operated the 34063 at output ratings 15v-/+@0.5A current draw -external supply not the transformerless one-, and i got this:a current draw of 100mA. so i installed a 0.1A constant load at the output of the rectifier and i got this:https://drive.google.com/file/d/0B5vW-k7HbsL4d1JZUVpFUVhpVkk/view?usp=sharing