Electronic gurus: Where to get a 12volt switching voltage regulator?

[nobb]

I'm looking for a 12 volt, 1 amp switching regulator to power a video surveillance camera in my car. Anyone have any idea where I can get one locally for cheap, or maybe a simple schematic to build my own from a chip? Or maybe someone has one laying around...

Specifically looking for a switching type for high efficiency, since the system is running from battery.

[revelations]

within Calgary, try
MRO
ACTIVE
B&E

[punky]

definitely go talk to the guys at Active electronics, most of them come in single IC chips now, just learning how to use them might be a little bit different. I'd be careful running 24/7 surveillance that on your battery, even 1A could drain your battery pretty quickly.

[nobb]

I did check the Active website, I just couldnt find anything that is a switching regulator. I previously built a linear regulator and just today I realized how hot it runs, so I am looking to redesign it.

Ive already taken ìnto account the power drain. I have a deep cycle battery in the back, and the whole system only draws about 3 watts.

[punky]

active definitely doesnt have anything.
http://ca.mouser.com/Search/ProductDetail.aspx?qs=2OtswVQKCOHn%252b8eUfCg6Yw%3d%3d
have a look at those, they look pretty flexible, they're really cheap too.

[nobb]

That chip looks exactly like what I want it to do. The datasheet is a bit complex though:

http://www.onsemi.com/pub_link/Collateral/LM2575-D.PDF

On page 2, I am guessing the capacitors Cin and Cout are just for smoothing, so the value isn't too critical. What about the inductor labeled L1? Since it's placed in series to the output, is it only for smoothing as well, or is the value critical? aka. just slap on any old inductor pulled from a broken circuit board.

[Alterac]

stick with what it says on pg 10/11 regarding your cin/cout and l.

[punky]

definitely have a good look at page 10/11 for good understanding of each of those component's purpose, but from skimming through the datasheet, the circuit you're most interested in is in page 22 figure 33. Are you planning to make this yourself? the initial investment might be costly compared to buying a prebuilt one, you'll need all the edging materials, not to mention its difficult to test without function generator and oscilloscope.

[punky]

also check these guys out, they specialize in all sort of regulator.
http://www.aimtec.com/

[nobb]

Fig 33 is for an adjustable version, I thought Fig 1 (12v fixed output chip) was what I was going for. Dont really plan on doing any circuit board etching. It looks simple enough to just solder everything together, slap on some electrical tape, and put it in a plastic box. Not sure what the purpose of a function generator and oscilloscope would be...as long as the output voltage is fixed at ~12v then it should be fine.

Of course if I can find a prebuilt one, that would be even better.

[punky]

the added flexibility of the voltage adjustment is very nice to have, especially when you have to add very little to the circuit (1pot?). it's probably important to test the transient state of the regulator, because when your car crank, and the voltage dips hard, your system may shutdown that's why u need a scope and function gen. to test, but i guess you could technically just plug and test. Make sure you clarifies whether is your system is 1A X 12V = 12W or 3W as you stated that's a huge difference in power.

OR go to futureshop/bestbuy or whetever, and buy one of these: http://shop.ebay.com/?_from=R40&_trksid=p3907.m38.l1313&_nkw=auto+laptop+adapter&_sacat=See-All-Categories
plug it in, see if your system survive cranking, if it does you're golden. Unfortunately they never tell you the efficiency on these things, but you can always put an amp meter while its operating to measure the current, and see how much power its using.

[nobb]

The current drain of the DVR + camera is about 0.25 amps, so roughly 3 watts. Or round up and say 4-5 watts just to be certain. Regardless, I have been running this setup using an inefficient linear regulator just fine since September.

I'm not really worried about transients, since the device is hooked up to an auxiliary deep cycle battery in the trunk which is isolated from the main battery with a diode battery isolator. Current can only flow from the alternator to charge up the deep cycle, but current cannot go from the deep cycle to the starter motor. Therefore, no need to worry about crank and voltage drop.

Anyways, I'm going to order the parts and see how it goes :thumbsup:

[punky]

oh you got a 2 battery setup, if the old setup was working fine, why change it at all?

[Alterac]

Effeciency, and longevity.

The secondary battery will only last so long. I think he is going for 48hours of recording before the 2nd battery dies?

[nobb]

The old linear regulator was a fire hazard. Even though I stuck it on a heatsink, it got hot enough that when you touch it with your finger, you can hear a sizzle from the sweat evaporating :(

Although I did the calculations to design the regulator to output 12v, in reality, the output was more like 7v. :dunno: I dont think linear regulators work well when the input voltage is only a few volts above the output voltage.

The system can theoretically run off battery for a whole week, maybe more if I got something more efficient to regulate the voltage.

[UndrgroundRider]

You've done something wrong with the voltage regulator you currently have. If it's reading 7v at the output terminal then either you have a 7v regulator, or its damaged. In any case, a switching regulator for that kind of current is expensive, and also not what you're looking for.


I would suggest running the camera at 10v. If it's running on 7v already, obviously it has an internal power supply and will run just fine on 10v. Here's a 10v linear regulator http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=BAJ0BC0T-ND. $1.38.

[Zero102]

If the linear regulator is not running anywhere near its current limit (i.e. 1A regulator at 0.25A) then it should not be getting noticeably hot, especially not with a heat sink attached. While I follow you on your quest for efficiency here, have you directly measured the efficiency of your existing system?

[punky]

Here is a good alternative:
http://store.mp3car.com/ProductDetails.asp?ProductCode=PWR-022&Show=ExtInfo
if you look at the spec sheet, you can select the output voltage (5/9/12V). only thing is, when the input is =< output voltage, then the output voltage = input voltage - 1V (you set vout = 12, if your battery gives exactly 12V then you have 11V regulated output, but your battery is usually 12V+) and plus if you say its working fine at 7V, running even at 11V should be ok. also its >90% efficiency.