DIY LED driver for reef lighting

der_wille_zur_macht said:
Simon,

Value of .18R was calculated from the design spreadsheet tool available on the product page at the manufacturer. What value are you using for ADJ pin voltage? If ADJ is floating (full on signal from PWM) it'll be 1.25v, and .18R gives an average LED current of ~525mA. At the max of 2.5v, your calcs would be correct.
Click to expand...
Hmm. Are you sure ? On page 20 of the datasheet I'm reading:<center><table border=1><tr><th>Rs(ohms)</th><th>Nominal average current (mA)</th></tr>
<tr><td>0.2</td><td>1000</td>
<tr><td>0.27</td><td>740</td>
<tr><td>0.56</td><td>357</td>
</tr></table>
</center>
"The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (=1.25V).Note that RS = 0.2R is the minimum allowed value of sense resistor under these conditions to maintain switch current below the specified maximum value. It is possible to use different values of RS if the ADJ pin is driven from an external voltage. (See next section)."

Perhaps you're doing something with ADJ that I haven't figured out :)

der_wille_zur_macht said:
Stop trying to win me back with your cost analysis. :lol: I need to just make up my mind and go one way or the other here. To top it all off, I just spent my lunch break reading about home-made reflow ovens. :lol: As if I need another way to complicate this!
Click to expand...

It could be worse... I've just had the heating guy in and been told my furnace needs replacing (which is reasonable, it's apparently 35 years old [grin]). Cost will be roughly $3500. NOT having a good day...

Simon
 
Well my mistake - you are correct! The problem is that I was using the design spreadsheet, which has an option for the ZXLD1362 - not the 1366. I assumed that they used the same sense resistor values, but clearly that's not the case - it's off by a factor of two.

Too bad about your furnace. If it makes you feel any better, my "they'll last forever" steel roof and vinyl siding are both going to get replaced as soon as there's a warm spell.
 
SpacedCowboy said:
It could be worse... I've just had the heating guy in and been told my furnace needs replacing (which is reasonable, it's apparently 35 years old [grin]). Cost will be roughly $3500. NOT having a good day...

Simon
Click to expand...

They aren't really hard to replace if you are handy. I installed forced air heating from scratch and had really no issues at all. There is a site that sells Goodman Furnaces that has very good how-to movies that show how to do most of the unfamiliar aspects.

pm me if you want me to find the site.
 
Last edited:
just so happens heating and cooling service is my line of work and kcress is right you can save at least 2000 Goodman is a good brand i never get call backs with that furnace and i have been using them for at least twenty years
 
marspeed said:
just so happens heating and cooling service is my line of work and kcress is right you can save at least 2000 Goodman is a good brand i never get call backs with that furnace and i have been using them for at least twenty years
Click to expand...

Thanks for the info, guys :) but whereas I'm fine with DIY-ing smaller things, I tend to want someone else to do the larger stuff... Plus, I don't really have the tools/skills to take out the old one - it looks like it was put in with the idea that it would outlast the house...

Simon.
 
We went LEDs for efficiency. So SpacedCowboy you are going to have to go geo thermal. They work great. about $.125 a kilowatt and my electric bill for about 8 months is running $100 to maybe $125 a month. According to KiloWatt meter the fish get $30 of that.
 
different chip driver...

different chip driver...

Ok, looking at the datasheet again, it appears my component selection was a bit off - the recommended layout uses an 0603 capacitor and resistor. The 1uF capacitor can be anything I guess (using 1206, here).

So we have:<center><table border=1><tr><th>Part</th><th>Mouser #</th><th>Cost</th></tr><tr><td> CAT4101 </td><td> 698-CAT4101TV-T75 </td><td>$1.90</td></tr><tr><td> 0.1uF capacitor </td><td> C0603C104K5RACTU </td><td>$0.03</td></tr><tr><td>1uF capacitor (*)</td><td> 77-VJ1206V105ZXATBC </td><td>$0.11</td></tr><tr><td>768R resistor</td><td> 71-CRCW0603-768 </td><td>$0.05</td></tr><tr><td colspan=2 align=right>Total component cost:</td><td>$2.09</td></tr></table></center>

(*): Not sure if this is strictly necessary, given two well-regulated power supplies...

These *are* SMT parts, and 0603 is a bit fiddly to hand-solder, but it's still do-able. Blu-tak (or putty) is your friend, hold down one end of the resistor/capacitor with the blu-tak and solder the other. Remove the blue-tak and solder the second end. Takes a little practice, but it's easy after a while...

Simon
 
That chip does look interesting. No efficiency claims, but they state min. dropout of .5v. I'm guessing this thing is a linear regulator since no inductor?

Half a volt dropout at 25v and 700mA is .35w against 17.5w for the LEDs. Rset is 1.2v. Power dissipated by the resistor is going to be really tiny. It's looking very efficient.

Arduino's PWM dimming frequency is right in the middle of the range.
 
marspeed said:
i seen that on page 8 i was thinking about putting more than one chip on a board
Click to expand...

Well, it ought to be just a matter of replicating that layout. The only real thing to take into consideration is the thermal requirements, so using their 2 square inches (and halving that because you have 2 sides), you need 1" square regions of PCB covered in copper, with the chip in the middle of each square.

If you're truly paranoid, you could use some thermal adhesive and put a TO-220 heatsink on top. That'd add another 29 cents per driver, but I don't know if it'd be necessary...

I've ordered the parts. I'll throw together a circuit and see how well it works :)

Simon.
 
That CAT4101 looks very nice at first glance.

When Looking at how simple the circuit is I first thought "Yeah I can do exactly that with an even simpler part - an IRF510 N-channel Power Mosfet"
It can do 100 Volts at 5 Amps!
That is how I made my own - 1 Component - PWM driven LED driver.
You cant get much simpler than that.

However - The nice thing about this driver is that it has the current limit circuitry built in.

So I am guessing that it uses an Op Amp circuit to regulate the FET current by running in the linear region when the PWM = ON.

And the closer you run it to Max voltage, the less the FET wastes running in linear mode.

Nice find! I think we have a winner!

Stu
 
i have to agree with the above, going with a linear is a much better approach, the power dissipation is low enough to do that. very simple N-Channel FET and an op-amp, couple resistors your done, maybe a x-former and a bridge if you want to.

p.s. i'm a EE at a power supply company, www.tdipower.com
 
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