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gev 2nd January 2007 03:08 PM

12v=19v 4,7A dcdc
Transformer EI33 --10x0.5mm prallel 20 tour
PCB view and print program

PCB SCHDownload

N-Channel 3rd January 2007 04:38 PM


Looks great. Some questions:
Is this a flyback or c.t. push-pull?
Is it isolated or non-isolated?
What is your application?
Powering a laptop from the car?
Xfmr core/bobbin look familiar: are these from an old AT/ATX psu?
Also, the yellow transformer tape looks familiar. Did you re-use the tape from the old xfmr or buy new tape. I have been looking for this tape, but can't find it anywhere. If you bought it, please say where. Thanks!

BTW, I have built many laptop DC-DC converters using just an LM2587 5 Amp SimpleSwitcher IC. Recently learned to synchronize two of them for increased current output.


gev 3rd January 2007 06:53 PM

sory my bad english:) lamb and notebook test ok no problem

N-Channel 3rd January 2007 07:52 PM

I ask these questions, because I have contemplated doing a DC-DC Boost converter using discrete components rather than an IC swtiching chip. Have lots of experience with those, and I wanted to expand my horizons a bit. I am glad to see someone has successfully done it, and wish to compliment your work.

Couple more questions:

1) Which controller chip? UC384X? Voltage-mode? Current-mode?
2) What is its switching frequency?
3) Have you tested it for EMI/RFI?

I am very curious on your results. Again, Nice work.


luka 3rd January 2007 08:26 PM

I think I can help you with that

This is a CBooste converter as you can see.It uses UC3843 because this chip starts at ~8v and it is voltage mode.

Freq is around 130-170kHz, I cant tell you for because it has about 6% or more dead time.

gev 4th January 2007 10:01 AM

Thanks luka :)

N-Channel 4th January 2007 07:43 PM


Thanks. I suspected a '3843 because of the 12V operation. 130-170kHz, huh? I would be curious to see the switching losses at that frequency range. I was planning a more modest 50-100kHz. Voltage-mode? I thought the UC384X series were current-mode controllers. How did you get it to operate in voltage-mode?

I just finished troubleshooting a 2-F interleaved DC-DC Uppie from 12V to 19-20V using an SG3525, two MTP75N06s switching a T-80-26 (yellow-white) core (24T+24T) into an MBR2545CT at 100kHz. I will post pics & schemo later today. Basically, I gutted a Dell AC-DC Laptop converter, salvaged the Nichicon 470mF 105C caps, heatsinks, and the green LED for the new circuit.

I got the idea for a 2-F interleaved topology from an article in the NOV 2004 QST. It had a 13.8V voltage booster for transmitting full power (100W) on battery for radios whose input voltage range is very picky, and cannot go below 12V.

Input is good down to 8V (the '3525's UVLO threshhold is 6-8V), and the current should be limited by only the guage of the wire, the diode rating, and the Drain current of the two MOSFETs. I haven't tested it on a load greater than 1 Amp because my lab benchtop PSU is good for only 1.5A per channel before current-limiting sets in. I plan on testing it with my big 30A PSU later this week.


I like the test stand you made (swtiches & lights on a perfboard). I think I will construct something similar so I can get a visual effect on the switcher's performance.

luka 4th January 2007 10:24 PM

I only think it is voltage mode, since it doesn't measures any voltage on resistor after fet.There is non.

Can't wait for that shema.
Did you ever made buck converter?

jamesrnz 5th January 2007 04:42 PM

i saw that article in qst also. thought is was interesting,.

i have built a little twelve volt generator out of a 3.5 hp briggs engine and an 10si 105 amp gm alternator. puts out about 75 amps at 13v.

cheap and easy, starts every time a later cs alternator or larger si alternator will make more current, but the si are cheap, i have time in it not a cent.

even new the alternators are around 45 bucks. a horz or vert shaft motor works.


DigitalJunkie 5th January 2007 05:42 PM

I'm (slowly) working on one of those too.. :D

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