Thanks for the info. Its the heat that I am most concern with. I have different color LED's in the fixture - for example one color (I think its red) has a forward voltage of like 2.1 volts vs the white has a voltage of 3.8. Have a 27 volt input (24volt powersupply turned up all the way). Works great for the White, but the red only needs a little over 12 volt, so that a pretty big difference (27 - 13volt). I know the CAT4101 driver gets too hot, been using the MAX 16820 chip, and that works but just looking at other options.
Tom
You need a switching regulator. No linear reg will handle a drop like that. I'd suggest the LM3409 we've been talking about for the last several pages.
hey, probably a stupid question, but how does one properly solder a CAT4101 chip to the PCB without burning the thing out?
Very carefully?
IMHO forget about the hot air part of the station you just got. I posted this a while back, but this is what I do:
1) Tin the ground pad on the PCB.
2) Place the part and solder a single pin to hold it in place.
3) This part will depend on the shape of the tip you're using, but crank the heat and position the tip along the top of the exposed part of the ground pad on the IC such that your iron is touching the exposed metal AND the pad on the PCB. Hold it for several seconds. As soon as it's hot enough, introduce solder. Use more solder than you think, you want to get it to wick all the way under the entire ground pad on the part.
4) Pull the solder wire away but leave the iron there. Have a tool handy - tweezers, chopstick, whatever. Grab it quick and push down a bit on the chip to ensure good contact with the PCB. Pull the iron off and you're done with the ground pad.
5) Solder the other pins on the chip as usual. They're pretty big and far apart so it is easy. If you make any solder bridges, clean them up with wick and you're done.
I just tried replacing some on a pre-built driver I ordered, and either fried them from overheating the chip, or from static caused by my sliding the PCB a few inches on my kitchen table.
My guess would be accidental solder bridges or a short somewhere else on the board. The chips are pretty durable.
I originally used a cheap stick soldering iron, and tested the chip after soldering it on and it was good, then a few minutes later, tested it again and found it to be faulty
Faulty as in it didn't work? IME these chips don't just stop working when they die, they go up in smoke. If it's simply stopped working, check for bad solder joints, a dead LED, or other conditions. Make sure the whole circuit is appropriate for your design, i.e. voltage drop is in a reasonable range, and so on.
If I have 6 parallel strings, does each string require a 1uf cap from +24v to ground, or just a single cap per string? Right now It's back up and running (I smartly bought spare LEDs
) with just a single cap.
Call the manufacturer and ask. It's an interesting question. I asked waaaaaaay earlier in this thread and we didn't really come to an obvious consensus so I designed it the way I did, with a cap on "each" string of LEDs even though they're effectively in parallel.
Putting caps in parallel does in theory sum their capacitance, but (one of the EEs can correct me if I'm wrong here) that doesn't tell the whole story since different caps will react in different ways. So it may not exactly be the 1uF capacitance we're looking for, but some other property common to caps around that size.
Hey guys I have had a bunch of parts sitting around for a few years. I fired up my CAT4101s, they work, they dim and I'm happy.
But for the PSU, can I use a typical wallwart? For voltage, I knowunderload voltage can shift for unregulated PSUs. Can I somehow size them properly?
Or am I better off buying a regulated PSU(what voltage for 4 White XPG and 5 Royal Blue XPE?) at 2 amps?
You can always try it and see. With the CAT4101 design the biggest enemy is difference between input and output voltage. It might not be an issue that the supply is unregulated but it may be an issue that it's not adjustable, allowing for fine-tuning. Measure what voltage it puts out under load and then design an LED string with enough LEDs to get as close to that voltage as you can while staying at least half a volt under it.
And don't count on the wall warts lasting if you load them more than about 50 - 60% of their capacity...
I have just finished building my LEDs and i have noticed that the heatsinks get to around 50 to 53C and the enclosure where the drivers are is sitting at 45 - 50C. Is this temperature OK for the components?
Thanks
The LED heatsinks are at 50C or the driver heatsinks? Which driver design are you using? Is the enclosure air tight?
If you're using the CAT4101 it'll go into thermal shutdown if it gets too hot (the LEDs will start to blink on and off every few seconds as it heats up and cools down).
