Using laptop power supply as supply for supermate dc6? (19v vs 18v) - Page 1
Forum section: electronics / beginners

author: micnolmad
author_rank: Newbie
timestamp: February 17, 2016, 10:24:04 am
content: So before I go crazy with providing images of the charger board and power supply stickers to save me doing a hole lot that right of the bat is just plain impossible, I would like to ask if it even worth trying?I have this "supermate dc6" battery charger I bought at a RC store, but I cannot verify if it is a real or fake supermate, nor do I know if it even matters, since it all comes from china, right?Anyway it states on it Input: DC11~18V. Max charge rate is 5A.Power supply is a 19V, 4.74A output (90W).My thought was either use the power supply directly because the circuit could handle the 1V extra or add something to the power supply to lower the voltage out be 1.So where do I go from here? Is it worth it?Thank you for your time/michael

author: prawncrackers
author_rank: Contributor
timestamp: February 17, 2016, 10:51:24 am
content: initially id try out two series silicon diodes (ordinary ones 5A) to drop the voltage by 1.2-1.4V... i know that will work.then ill try to break open the thing and look at the front end of the circuit. usually it will have an input cap and i guess it should make sense if it is rated at >25Vthen check other parts of the circuit particularly the semiconductors if they can handle 19V. their spec sheets should be on the interwebs.i have an old linksys router rated at 12v but when i opened it up the front end had a 25V cap and an LM2675 DC-DC converter with max input of 40V per its spec sheet.so i had no problem working my wireless router from a 15v smps wallwart. of course this will not guarantee the longevity of the product but it should work for most cases.

author: amyk
author_rank: Super Contributor
timestamp: February 17, 2016, 11:03:17 am
content: As above poster said, open it up and see the ratings on the input components. An extra 5% is usually no problem for laptops, but given that it does say 11~18V there might be something that's already being run near its upper limit at 18V.If it has a SMPS on its input the higher voltage means lower current, which could be better since there's less I^2R losses.

author: micnolmad
author_rank: Newbie
timestamp: February 19, 2016, 01:13:37 am
content: Thanks for the input. I have taken some pictures of the circuit input side and found what I hope are the correct spec sheets. Could someone confirm? I think it's the 4425 chip that handles this input voltage but I am not sure. The cap is 25V so that should be fine?https://goo.gl/photos/K1FbtD9P18gUPrLF8IRhttps://drive.google.com/file/d/0B-CH4AR_3OIkQ3pCZi1vZUx6NVk/view?usp=docslist_apiIChttps://drive.google.com/file/d/0B-CH4AR_3OIkSFEtckNmY1RxYTA/view?usp=docslist_apiPrawn, I am very new to the world of diodes. In Every circuit, a diodes has four parameters, but non of them are amps. What an I missing?

author: prawncrackers
author_rank: Contributor
timestamp: February 19, 2016, 01:43:54 am
content: sorry i didnt go and did a lot to imagine a schematic for this but theres an (IR)F7413 MOSFET it MAY be driven by the 4423 MOSFET driver. the 4423 driver has an absolute max of 22v but the safe operating area is up to 18v only, so if it was me i wouldnt drive it with 19v.there could be many ways to make this powered from 19v but the easiest one would be the series diode i said, its not efficient but it will work.diodes have 4 parameters? the most important ones for your application would just be(1) amp/current rating - at least 6a(2) reverse voltage - 50V or higher(3) forward voltage drop - around 0.6-0.7V should be finetwo 6A05 should work fine, theyre common garden variety rectifier diodes.http://www.diodes.com/_files/datasheets/ds28009.pdf(1)Max RMS Voltage - 50v(2)Maximum Average Forward Rectified Current - 6.0A(3)Maximum Instantaneous Forward Voltage at 6.0A DC - 0.9V

author: amyk
author_rank: Super Contributor
timestamp: February 19, 2016, 11:14:29 am
content: That's where the 18V upper voltage limit comes from, as the datasheet for the 4423 specifies it.

author: micnolmad
author_rank: Newbie
timestamp: February 19, 2016, 04:27:38 pm
content: I have added a picture of the diode properties in Every circuit in my photo folder.Prawn: How did you figure that diode would work? I mean would I find a specific diode in the future? I can't run to you every time I guess!Amyk: Yea I'm not too hot on pushing that Chinese part any harder then it already is.