DIY LED driver for reef lighting
- Thread starter der_wille_zur_macht
- Start date
der_wille_zur_macht
Team RC
That DX driver looks like a very good deal if you can live with the compromises in the design. I see them as:
1) 25v rated input cap. Maybe not the end of the world, but it would have cost them two cents to put a 50v cap on there instead, which would have given us a little more of a safety buffer in setups we're likely to encounter on reef tanks (that is, trying to drive more than 3 or 4 LEDs).
2) It has a bridge rectifier built in to the PCB. Most of us are used to supplying DC so this is not really required - but it could make for an interesting ultra-budget app if you wanted to just run it on an AC transformer as someone else mentioned above.
3) The product photos clearly show two different products, and some of the specs in DX's product listing don't match the chip's datasheet (input voltage range, etc.) which makes me nervous.
4) The DIM connection isn't brought out in an easy to use manner.
Also, some thoughts about the chip itself:
1) Dimming looks iffy low in it's range. People complain about the "shoulder" low down in the range of dimmable Meanwell ELNs all the time - this product looks like it would have the same issues.
2) It's not the most stable thing in the world, but again this probably isn't a big deal.
It would be neat to play with this chip "from scratch" and the SOT89-5 package is probably not bad to solder by hand (the other package has a pad on the bottom that's not exposed, so without reflowing, you'd need to use conductive epoxy to glue it on then solder the actual pins). But by the time you designed and built a driver, I dunno if it would be that much cheaper/better than what we've got in this thread so far - the DX version is more or less cheaper than a hobbyist could expect to DIY it from what I can tell (though I can't find a single vendor that carries the bare chip, so who knows). The only real advantage is that this is a switching reg, not a linear like the CAT4101, so you have a little more freedom in terms of differences in input/output voltage.
1) 25v rated input cap. Maybe not the end of the world, but it would have cost them two cents to put a 50v cap on there instead, which would have given us a little more of a safety buffer in setups we're likely to encounter on reef tanks (that is, trying to drive more than 3 or 4 LEDs).
2) It has a bridge rectifier built in to the PCB. Most of us are used to supplying DC so this is not really required - but it could make for an interesting ultra-budget app if you wanted to just run it on an AC transformer as someone else mentioned above.
3) The product photos clearly show two different products, and some of the specs in DX's product listing don't match the chip's datasheet (input voltage range, etc.) which makes me nervous.
4) The DIM connection isn't brought out in an easy to use manner.
Also, some thoughts about the chip itself:
1) Dimming looks iffy low in it's range. People complain about the "shoulder" low down in the range of dimmable Meanwell ELNs all the time - this product looks like it would have the same issues.
2) It's not the most stable thing in the world, but again this probably isn't a big deal.
It would be neat to play with this chip "from scratch" and the SOT89-5 package is probably not bad to solder by hand (the other package has a pad on the bottom that's not exposed, so without reflowing, you'd need to use conductive epoxy to glue it on then solder the actual pins). But by the time you designed and built a driver, I dunno if it would be that much cheaper/better than what we've got in this thread so far - the DX version is more or less cheaper than a hobbyist could expect to DIY it from what I can tell (though I can't find a single vendor that carries the bare chip, so who knows). The only real advantage is that this is a switching reg, not a linear like the CAT4101, so you have a little more freedom in terms of differences in input/output voltage.
My first mods will be to replace the 25v cap with a 50v cap, remove the bridge rectifier, and switch the inductor and current sense resistor to 1.2A specs.
On the DX forums there are some posts where some people have gotten an EQB8L chip which is supposed to be the same as the PT4115E except it quite a bit smaller and accepts 3v minimum instead of 8v minimum.
On the DX forums there are some posts where some people have gotten an EQB8L chip which is supposed to be the same as the PT4115E except it quite a bit smaller and accepts 3v minimum instead of 8v minimum.
I'm curious about the dimming too as you can dim it by providing voltage between 0.5v and 2.5v or PWM 2.5V. The PWM dimming should give the best results.
mprygh
New member
Can you post a link to which PT4115 based one you ordered?
I am not really sure which one it is.
mprygh
New member
Sweet!!
Looks very easy to mod.
Remove the rectifier, add a better cap.
It even looks like the DIM pin is on the outside edge, easy to get to.
Probably low quality components, but cheap enough to buy a few extra.
I guess we are getting off the thread topic though - not so DIY if
you just buy the thing. :-(
I'm thinking of making my own driver, and don't know where to start. I was hoping to go with the CAT4101 design, but the actual CAT4101 chip is around $3.50. After some more reading I ran into NCP3066, PT4115, and LM3404... I'm leaning for a design with the NCP3066 but after looking at the datasheet for LM3404, this looks like a good candidate too. Then again I know close to nothing about this, and am just learning.
TheFishMan65
New member
The CAT4101 price depends on where you get it. Check Future since they seem to have the best prices IMHO.
der_wille_zur_macht
Team RC
Also, consider pricing for the entire driver circuit, not just the IC. Even if you buy at the $3.50 price, the CAT4101 will be a few cents per LED cheaper than the other designs we fully fleshed out in this thread (i.e. the NCP3066). Plus, consider functionality differences. The CAT4101 responds better to dimming and is actually a little more stable than the NCP3066.
Hmmm then that means I might have a little problem... I was planning on using one power supply (MeanWell SP200-24 24V@8.4A) to run 24 CW XPG at 1A and 24 XPEROY at 0.7A using a CAT4101 driving 6 leds per string. But I ran into a problem, the power supply specs said the adjustment range for voltage was 22.8~26.4V, so if I ran 6 XPG's at 1A that would average out at 19.8V per string (6x3.3v). 3V would have to be dissipated by the driver. Bad right?
Maybe ill just settle for a MeanWell SP240-24 24V@10A it has an adjustment range of 20~28V.
Also I'm still debating on the colors to use for my 55 gallon. Ive been reading LED Color Aesthetics: The Emperor’s got no clothes. Or does he? and am waiting for the final product of this non-standard build Yet Another DIY LED Build Thread.
Maybe ill just settle for a MeanWell SP240-24 24V@10A it has an adjustment range of 20~28V.
Also I'm still debating on the colors to use for my 55 gallon. Ive been reading LED Color Aesthetics: The Emperor’s got no clothes. Or does he? and am waiting for the final product of this non-standard build Yet Another DIY LED Build Thread.
der_wille_zur_macht
Team RC
It's common that the real adjustment range for those power supplies is a little larger than the spec, but of course it would be "dangerous" to count on that. That said, you could always add another XP-G to get the total Vf up into an appropriate range - as long as it doesn't exceed 25v you're fine with the CAT4101.
The Meanwell SP are nice supplies but you might be able to find similar products more cheaply. Check out mpja.com for lots of inexpensive supplies.
The Meanwell SP are nice supplies but you might be able to find similar products more cheaply. Check out mpja.com for lots of inexpensive supplies.
Yeah you're right I can always add another one, but I'm a little picky about how I want the lights set up. I have a 48"X12"X19" aquarium and wanted to use two 48" aluminum c-channels (1/4" thickness, maybe even 1/2") to hold 24 lights each over the length of the aquarium (alternating blue and white). If I add one more led per strings that'll push it to 28 leds in a row (not something I want
)I checked mpja.com before (and just now) but couldn't find anything with adjustable voltage. I'd like to have less bulk, and use one power supply to power it all that's why I decided to stick with the higher cost meanwell. I think the meanwell will work well with the CAT4101's to power 6xpg at 19.8v and 6xpes at 20.4v if i drop the voltage down to 20.5 or so. What do you think?
der_wille_zur_macht
Team RC
Many of the supplies listed on mpja are adjustable. This one is commonly used:
http://www.mpja.com/prodinfo.asp?number=16854+PS
Keep in mind that the CAT4101 needs a half a volt of overhead. So if your LED string needs 20v, you must keep the DC power supply above 20.5v. The optimal solution would be exactly 20.5v, as anything above that is waste (since it's a linear regulator).
Keep in mind also that if you do a 1:1 ratio of cool white XP-G and royal blue XP-E, the rig is going to be very white. Most people who use XP-G and XP-E end up using fewer XP-Gs to keep the balance a little towards the blue spectrum.
http://www.mpja.com/prodinfo.asp?number=16854+PS
Keep in mind that the CAT4101 needs a half a volt of overhead. So if your LED string needs 20v, you must keep the DC power supply above 20.5v. The optimal solution would be exactly 20.5v, as anything above that is waste (since it's a linear regulator).
Keep in mind also that if you do a 1:1 ratio of cool white XP-G and royal blue XP-E, the rig is going to be very white. Most people who use XP-G and XP-E end up using fewer XP-Gs to keep the balance a little towards the blue spectrum.
der_wille_zur_macht
Team RC
Also keep in mind that the voltage drop specs published for the LEDs are not exact - I've seen strings vary by a few tenths of a volt from spec. So while doing the math will get you in the neighborhood, it's not set in stone.
der_wille_zur_macht
Team RC
It totally depends on the power requirements for whatever your dimming controller is. Did you have something specific in mind? In general though, there's nothing wrong with sharing the DC power supply with other devices.
DustinB
New member
According to the datasheet here: http://www.onsemi.com/pub_link/Collateral/CAT4101-D.PDF
You can apply 3-25v to VCC. You only need to apply a half a volt or so more than your string of LEDs require. The best solution is to get another power supply at or close the the required voltage. If you can only get a few volts above you can use a voltage regulator to step the voltage down, but anything not used is dissipated as heat. Stepping down from 24v to 6v is going to create a lot of wasted energy/heat.
Keep in mind the power supply you choose has to be voltage regulated as this driver will only regulate current.
EDIT: Just noticed you were looking at powering the dimming boards. Your best option is probably to use another power supply as you have to power the driver board with a 5v source as well. You could get a 9v wall wart and a 7805 regulator to power all your boards that require 5v, depending on the current required of course.
You can apply 3-25v to VCC. You only need to apply a half a volt or so more than your string of LEDs require. The best solution is to get another power supply at or close the the required voltage. If you can only get a few volts above you can use a voltage regulator to step the voltage down, but anything not used is dissipated as heat. Stepping down from 24v to 6v is going to create a lot of wasted energy/heat.
Keep in mind the power supply you choose has to be voltage regulated as this driver will only regulate current.
EDIT: Just noticed you were looking at powering the dimming boards. Your best option is probably to use another power supply as you have to power the driver board with a 5v source as well. You could get a 9v wall wart and a 7805 regulator to power all your boards that require 5v, depending on the current required of course.
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