I've tried stencils on several different boards and for me I don't really like them--especially on boards like these that have fairly large pads and a small number of pads at that. The setup, cleanup, and mess of using a stencil just isn't worth it IMO.
I use stencils almost exclusively and love how even and precise the amount of solder paste is with em.
Having to do more than one by hand is a PITA, in my opinion… Just built a panel of 20 with no stencils and about went bonkers!
That's why I like this forum: you get a good debate from differing opinions. Dale and I are friends, but anyone who has followed us long enough will notice that we often have opposite opinions about a lot of different things.
A question for the driver gurus;
I'm planning on using four XHP70's for my DIY comp build.
If I were to piggyback 3 or 4 FET's on the same board (Older v1.0 type board, DPAK-2 FET), will the 13a have a strong enough drive signal to operate them all?
Unless you're only planning on a 100% mode level with a big gate resistor, no. We're already pushing the little attiny pretty hard switching one of them at the faster PWM levels. You'll find that the attiny will glitch out big time trying to drive multiples in the middle levels, and even a single FET sometimes.
I think you could get away with a single FET for that build with a little creativity: use a small PFET to power the NFET gate directly from the 8V+ input. It will load the attiny way less and will give the FET access to higher gate voltages, which will decrease the resistance of the FET. You could also easily power more than one FET off the same attiny, if needed. You would need to basically invert the PWM values, since the PFET turns on when the gate is pulled low.
It is a crazy untested idea, but in theory it should work. I don't think you need a dedicated gate driver IC since we're switching relatively slow.
Thanks Richard.
I can see this quickly getting over my head.....
Using the method you described, are you suggesting that all four XHP70's could be powered by a single DPAK-2 FET?
So the flow for the PWM signal would be;
Attiny pwm---->PFET gate, PFET drain----->NFET gate.
Can you point me in the direction of an appropriate PFET for this application?
Hmmm - I'm having difficulty understanding how I'd wire this up.
Am I on the right track here? (I realize it's not the Zener schematic)
Yep. That works. You can use a very small PFET, just use one that has sufficient voltage ratings. You may also need a pull up resistor to keep it off, but you'll have to figure that out in use.
Is there a reason I can't use the LFPAK56 or DPAK-2 in lieu of the PFET in that diagram?
Or even a 7135 ?
Thanks.
Do you understand the difference between a P channel and N channel FET?
I tried reading up on them, but I'll just accept a "no", & move on to locating a suitable P channel.
All I know is that the FET doing the main switching is rather loaded with a lot of current, so the AtTiny is having dramas moving the switch(NFET), so we are using an intermittent switch (PFET) to lend a hand.
I know that's probably the least technical description, & will make someone who knows what they are talking about cringe.... ;)
-- edit --
I now understand enough to see why the N channel would not work.... from a Positive feed.
Will this one do the trick?
Transistor Polarity: P Channel
Continuous Drain Current Id: 11A
Drain Source Voltage Vds: 200V
On Resistance Rds(on): 500mohm
Rds(on) Test Voltage Vgs: -10V
Threshold Voltage Vgs Typ: -4V
Power Dissipation Pd: 125W
Package: TO-220
Pulse Current Idm: 44A
I'd get one with a much lower voltage rating (you'll get better overall specification for your application). I'd look at an SOT-23 package. That 44nC gate charge is really high and you don't need a huge TO-220 package.
Those ought to work well. 
I’ve been hitting a wall. I’m putting together an Triple XP-L for woodfiend, and I have a problem. When I put it together (assemble the light, with driver soldered to the pill) the light loses its ability to change modes. I didn’t notice until I went to do measurements on it, and I’m wondering if it’s not the driver but the LED’s(but I can’t fathom why).
I’m using BLF17DD’s (I’m on the second one, I assumed the first one was bad, but the second is doing the same thing). When I tested it on my PSU before soldering the driver everything worked. Soldered the driver in place, still working. Assemble the light, mode switches 1 time only then not any more. I can program the guppydrv and set mode groups and it will start at whatever the modes first level is, but won’t change.
Do I just need to bite the bullet and start replacing LED’s?
Have you tried longer and shorter switching off and on? Maybe you have a problem with the off time memory capacitor?
It is bizarre that it will go into programming mode but not change modes. What BLF17DD revision are you using? V1.0?
Yes I have. I had the same concerns about the OTC, but considered it unlikely when a second driver with all new components exhibited the same issue once assembled into the light. Not saying it’s completely ruled out, but I’m doubtful at this point that it’s the culprit.
They’re actually MTN17DD’s, I remembered wrong. Version 1.11, you’re special batch of boards with the masked + pad. Using the guppydrv firmware you flashed for me.
This is the 8th or 9th I’ve assembled, and only 1 other had any issues after assembly(I think that one got overheated).