Oshpark Projects

Your talking about what is R3 on a 17DD here? What were the reasons you say you needed it when using this baby FET? I’m running a Tiny10 with one of those FET’s and it’s got some quirks, it works but I’m wondering of this could be the answer.

So do you guys recommend that this have a gate resistor?

I will go ahead and put one in when I get home…so consider the first release “beta”

I will also create a separate thread as to not clutter this one

Perhaps it’s working in my Texas Poker because it uses the 10440 cell and doesn’t provide over 3A? But work, it does! Loving it! Thanks again Scott, Matt, my family, the fans that supported me, Country music radio and my agent and the mailman and….oh, sorry.

Um, I see where the positive via could go straight through but isn’t the negative via going to cause direct drive only? Shouldn’t the negative on the FET side of the board be the ground ring and the negative on the MCU side be LED only?

And if the FET can be moved around easily, why not go ahead and put a center contact pad for a battery?

Nevermind, the FET has to feed the negative from the LED through the board. It needs to be known though that the “-” sign is not for battery use but LED use only, that could get confusing to someone that isn’t electronics saavy, like me.

But, isn’t the schematic on the FET backwards to what’s on the board? Isn’t “G” going to pin 6? And “S” going to ground? I’m confused.

K I will put LED - to clarify

Discussion moved here BLF Tiny 10DD and Tiny12DD

Just an FYI the 70N02 FET’s are no longer listed on ebay, the link under the BLF17DD is dead. I cant find any on ebay anymore but I can find lots of 70N03’s and 80Nxx’s. would those be as good or should I go with the digikey option?

That seller seems to have disappeared entirely. Maybe later those will show back up along with their other items?

As to your question - It looks to me that the 70N03 is not as good as the 70N02. 0.0081 Ohms at VGS = 4.5v is not as good as 0.0053 Ohms at VGS = 4.5 V. The Digikey link seems to be better than the 70N02 though, it has 0.0032 Ohms at VGS = 4.5v. I think all of those values are acceptable though, really.

The method for rating continuous drain current for the datasheets I looked at (“NTB75N03R, NTP75N03R” vs “SUD70N02-03P”) seemed to be different. To me it seems that continuous drain current is close enough. Voltages look OK. As I said, RDS (on) seems higher but acceptable. I don’t see a problem with using the 70N03.

0.0081 Ohms at VGS = 4.5v is not as good as 0.0053 Ohms at VGS = 4.5 V…That’s almost inconsequential (I believe…heck that .003 ohm might cause it to heat up 2x as fast for all I know)…sure it’s more but it’s a “viable” replacement until the 70N02 come out…as long as everything else is the same

That’s mostly what I was getting at.

I suppose between the 70N03 and 70N02 is a difference of like 0.02 vDrop at 8 Amps. 8 Amps is a drive level I arbitrarily chose, vDrop will be lower at lower current levels. Since it’s direct drive, vDrop in the entire power supply chain (everything, springs, body tube, driver, etc) has an effect on the Vf available at the emitter. The lower the voltage you can supply to the LED the lower the current you can supply to the LED.

8 A x 0.0081 Ohms = 0.0648 volts
8 A x 0.0053 Ohms = 0.0424 volts
8 A x 0.0032 Ohms = 0.0256 volts

At 4 amps the difference is about half of that. This is not a big deal, but will have a measurable effect. You should end up seeing a difference of 0.01-0.1A between the 70N02 and 70N03 depending on what you are doing with them.

Heck, the wrong gauge wire can cause more volts loss in just a few inches…

This is why I run 22Ga silicon wire now…my lights seem to reaaaly like the bigger gauge wire

I don’t disagree. Clearly for direct drive lights all resistance including wire, spring, body, cell contact area, etc is important. For current regulated lights resistance is not as big a deal in terms of maximum brightness, but still affects other performance aspects.

OTOH the AOD510 are better than either of the others and cost about the same. Why not use them?

Just did a search and the 70n02 still shows up but from a different seller. Until I use them up I’ll stick with the Lfpak56 since it fits more easily on a 105c than the vishay. I don’t do nearly as many mods as others so they should last awhile.

I have a question in my mind that when you guys are finding the low Ron FET, did you consider the low on Vgs of the FET is also a very important criteria for a single li-ion cell driver?

Microa, I'm comparing the RDS(on) at the lowest specified VGS. Is there something else I should be considering such as the "Gate Threshold Voltage"?

Most of the high power FETs show their Ron at 4.5Vgs and 10Vgs. I am not sure how many Vgs the attiny13A can provide to the FET but obviously under 4.5V. I doubt that the FET can be fully turned on. Low Vgs FET can be fully turned on at 2.5V or even 1.8V.

I’ve eyeballed the datasheets some more. See below for what I’m currently looking at.

That’s fine. Both 70N02 and 70N03 can go through 20A under 3Vgs.

I haven't caught up yet with the last 100(!) or so posts, but I tried the AOD510 and... the other one, both of them were flaky changing modes using the same known good gate&pulldown resistors as with the Vishay 70N02, so I didn't bother trying to get any current measurements for comparison.

Huh. Well that’s definitely the most valuable info at this moment.

I wonder where the hangup is. Come to think of it… can you precisely describe the flaky mode changes again?

It (both of them, really) acted the same as the early 70N02/17DD weirdness before the gate/pulldown resistors were added. It might just need different values there, but I didn't have time (and, I have like 150 of the 70N02s).