Hiyee,
was looking through the LM2674 from national and wanted to make a simple 12V-5V converter for my Gameboy to be used in a car...so I was wondering how to make the PSU always on as the chip has an on-off function with a -0.1V to 6V limit...help me out plase...not sure where else to ask this question...
http://www.national.com/ds/LM/LM2674.pdf
was looking through the LM2674 from national and wanted to make a simple 12V-5V converter for my Gameboy to be used in a car...so I was wondering how to make the PSU always on as the chip has an on-off function with a -0.1V to 6V limit...help me out plase...not sure where else to ask this question...
http://www.national.com/ds/LM/LM2674.pdf
I can't open the datasheet 'cause acrobat reader is crashing on my PC, but I think it's simple: use a voltage divider on the 12V side with two 1k resistors.
Meaning i will have to put in arund 6V...using the voltage divider...hmm seems like a good one...anyone else??
ground the on-off pin, it needs a TTL Logic High to disable the device.
a switcher is a better idea than a resistive voltage divider -- the output is regulated so the device will work over a range of load conditions -- Nat Semi has the software for component values right on their website.
Nat Semi has provided a layout for a PCB -- switchers should always be built on a PCB with short, fat traces where the manufacturer recommends.
a switcher is a better idea than a resistive voltage divider -- the output is regulated so the device will work over a range of load conditions -- Nat Semi has the software for component values right on their website.
Nat Semi has provided a layout for a PCB -- switchers should always be built on a PCB with short, fat traces where the manufacturer recommends.
So I just ground this thing and it will stay off?? Oh yeah...I was thinking of copying the same design...shouldn't be too difficult...just a penknife and a scapel plus a magnifying glass would be ok...and then a check with a dmm...SMD protyping...but I wun be using SMD caps...just the IC itself...or should I go with the LM2575-5.0 which can carry up to an Ampere...hmmm...spoilt for choices here...
you can actually get an LM317 -- which everyone has in their junkbox -- to oscillate and use as a switcher. I have used the LM2574-5 -- one of the first "simple-switcher" chips from National in flyback converters. How much current does a Gameboy draw anyway? I have some of the LM2574's just sitting around collecting dust, so let me know...
it's a gameboy light...draws arund 500mA...so an ampere will be a good one...will stick to the above mention parts...anyways I just got some from national as samples...
sheesh....the 7805 can pass 1A I know that...but efficiency sucks big time...and since the gameboy is not an "audio" device...it wouldn't care about all the stuff hat is exiting from the power lead...so I wanna try a SMPSU....I am currently still waiting for the parts to arrive...as soon as I'm done maybe I can post a few pics here...
Well how much current does it pull? If it burned an entire ampere it would last all of one or two hours on batteries. Besides, as long as the car's running you have essentially as much power at hand as the cigarette lighter is fused for.
Tim
Tim
heat's the problem...I dun wanna use heatsinks...that's my aim for now anyways...droppping 12V to 5V is like burning an entire 7V...quite ineffiecient if you ask me...
But at 100mA it's all of 700mW, which won't even need a heatsink. And building an SMPS for that low level really would be rather wasteful.
Tim
Tim
it's just a little project...and I wanna have a bit of fun..so nobodies gonna stop me...HAHAHAHAHAHA...I'm bad (this was just an odd sense of humor)...just need to ground the pin eh....I'm going in...
- Status
- Not open for further replies.