Robust switcher for P7/MCE 3.5A 5-20V

[LED Boatguy]

Hey there:

I modded a 2D LiIon Mag with a warm white MCE and loved it, so I thought I'd do a 3C and take a stab at making the driver myself, based on the LM3401. Well, it came out great--rugged as hell. It only has one setting, and you can set it up to 3.5 amps. It regulates from 4.7-20 volts, and so far I have not overheated anything on it even though there are no heatsinks or thermal vias on the board.

http://i474.photobucket.com/albums/rr105/Fishnut609/p7driver.jpg

There is no low voltage cutoff, though I am making a daughter card that will blink the light at a given cutoff voltage since my C LiIons are not protected. The low voltage blinking circuitry MAY fit on a D-size driver board.

Is anyone interested in one of these? This isn't a money making venture--just thought I'd share.

 

[Norm]

Very neat.

 

[LED Boatguy]

Very neat.

Thanks, though my stuff generally looks better than that. The big ol capacitor is there because I don't have the correct SMD type here with a small enough footprint. Man, a lot of planning has to go into the layout of these switchers, or their EMI will drive them (and things nearby) nuts. The D board was easy but the C board was a challenge. Oh and the caps--values and ESR are EVERYTHING.

Here's the companion LVC chip. It will blink the flashilght at .5 Hz at any user-set voltage. For my use, it's best to blink rather than totally go out as we camp in bear country. I have two more comparators available. I suppose I could make it switch off completely at some lower voltage.

Anyways, thanks again.

 

[HarryN]

Hi, nice project. A few questions if you don't mind:

- Did you isolation mill that board? Do you have this capability at home?

- What did you end up using for the switching mosfet ?

Thanks

Harry

 

[LED Boatguy]

Hi, nice project. A few questions if you don't mind:

- Did you isolation mill that board? Do you have this capability at home?

- What did you end up using for the switching mosfet ?

Thanks

Harry

No milling here--just toner transfer and that damn, stain everything, Ferric Chloride. I've just switched to 1 part pool acid to 2 parts 3% Hydrogen Peroxide for etching and like it much better, though it's WAY more dangerous.

Q1 is a 20V, 4A 25mOhm PFET #Si3493BDV in the SO-6 package.

Regards,

PS I had National's WEBENCH program kick out some REALLY WEIRD designs with this chip that didn't jive with the datasheet at all. I've used WEBENCH to design things before with other chips and had no problems, but I had to bag attempts with the 3401. Computers...

 

[HarryN]

Thanks for the info. I have been toying with ways to do some proto boards, and your experience is in line with what I have seen - perhaps better quality.

I was trained as a Chemical Engineer, so HCl + H2O2 in those dilutions is not a big deal for me. You might like it better if you dilute it even more and use a sprayer to just sort of mist it on and let it drain off during the etch process. I am not entirely sure that the H2O2 is even needed, but probably speeds things up a bit.

Have you tried using shielded inductors? I am wondering if they will help with EMI. I am just playing in the dark here, just tried National's web bench for the first time last month. (see thread about hobby voltage regulator in this section). A lot to learn on my side, but a good expansion on the flashlight hobby.

I would really like to find some thicker copper blank boards, but that is really challenging, esp. since I don't do the ebay thing.

 

[LED Boatguy]

Thanks for the info. I have been toying with ways to do some proto boards, and your experience is in line with what I have seen - perhaps better quality.

I would really like to find some thicker copper blank boards, but that is really challenging, esp. since I don't do the ebay thing.

I use this ABC Fab guy on Ebay for my boards. His stuff is great. Here are some small 2/2 boards. 2 oz--while tougher to etch--is great for amp loads, spreading heat and high freq switchers.

Snip

...This is a 12 sheet lot.....Material is FR-4, .060 Thick, 2 oz. copper, both sides.......Size, 4 x 6 3/4................Etches very nicely and evenly..This is very good PC Board material.....Shipping $5.95........Priority Mail........Can combine shipping cost for 2 lots (24 sheets) of these boards for $6.95...........Paypal preferred, Money orders and checks accepted. Checks will have to clear before shipping.

/Snip

They're only $6.00/lot. Want me to buy 2 lots and forward one to you? Do You have Paypal? I use UPS ground and shipping to the Bay Area would be like $7 to a business and $9 to a residence.

Re: the chemical etchant: I have a respirator with organic filters. I was just too lazy to wear it. Won't make that mistake again when mixing up a batch. I got a whiff of something I don't ever want to smell again both times. Some of the webistes say not to store the mixture, but I don't see why. Do you think it's OK to store the mix in a stout plastic container with a tight-fitting lid?

PS Here's the next project, though the larger die LEDs are obviating the need for these:

http://s474.photobucket.com/albums/rr105/Fishnut609/?action=view&current=LT3755.jpg

 

[HarryN]

Hi, that is a serious boost circuit - 45 V or so Vf at 1 amp. Looks like a lot of fun.

If it is for household AC use, then it might be easier to start high and buck it down. You probably already know this, but somewhere in the 42 - 48 volt range is the top for intrinsically safe / low voltage ratings. If you get much higher, and something goes wrong, your insurance company might not pay.

As far as etching with HCl / H2O2, an organic respirator will not help much, or at least that is not what is normally recommended for that kind of chemistry. Your best bet is a fan blowing the fumes away and to replace the respirator filters with rags soaked in plain water or better yet, a baking soda or baking powder solution. You are doing this outside - right?

BTW- HCl fumes will eventually permeate through most plastics that resist direct chemical attack.

The challenges you are describing are the same ones that are driving people toward milling PCB protos.

I will send a PM re: the board blanks - sounds interesting. With that driver setup, you will need every bit of 2 oz. I am even toying with the idea of making my own 4 or 10 oz double sided boards, as they are really hard to come by.

Take care,

Harry