[WIP] 10mm DD-only LFPAK33 driver

I thought that I’d already made one of these, but apparently I did not. Oops. I ran around in some PMs telling one or two folks to ‘go find it’… I felt bad about that so I went and made one this morning. :frowning: :wink:

  • ~1mm physical keepout around the edges on top and bottom IIRC. Electrical & exposed copper keepout is a bit less.
  • B+ strap required as usual on this type of thing
  • Some vias under components, boo-hoo. The only thing that is truly sacred here is the gate pin on the LFPAK33, you really, really shouldn’t place a via under there - so I didn’t.
  • 0.7mm exposed copper on GND rings
  • 0805 sized passive components but using the small rounded pads.
  • LFPAK33 or similar MOSFET. See my other 15mm or less driver threads for any discussion on which MOSFET to use.

A10DD-33 v003

Reserved.

Hmm…. I have a BLFTINY10DD already assembled on my desk, but this looks much simpler to attach the strap to. I still haven’t figured out that bit….

It looks good to me right now, but I make no promises. :wink:

v001 had a minor design rule violation (OSH Park would have successfully built it anyway)
v002 and v001 were missing GND ring vias
v003… who knows?

:stuck_out_tongue:

I’ll find out as soon as they get em shipped. This tiny, they ought to fit in almost anywhere! lol

I have seen 3.2A before, but the 10440 I just tested in direct drive with nothing but 2 wires and a cell showed 2.74A. So the cell will have to be a new one, and there’s just not much to be gained at 3A or so. The smaller FET can be used for space savings and it still does well. The Vishay Si2312CDS is a new SOT-23 format that might offer the most out of the package, either way though the cell is at the top of it’s game.

Gaining efficiency with the FET+1 layout is a critical gain, making that a no-brainer in a very tiny light that is capacity compromised.

Edit: Just tested another that charged up to 4.19V and delivered 3.16A directly wired to an XP-L V6 3D on a 20mm Noctigon. Ceiling is pretty much capped.

DBCstm, do you use a reverse polarity protection diode on that light?

And yes, it’s there, as prescribed on all our drivers. And yes, it might gain a wee bit to bypass that, redundant though with a 3.2A draw on a 350mAh cell.

Might let me see 1000 lumens though… hmmmmmmm………

D1 doesn’t drop voltage to the emitter but only to the mcu. Different current path. BatteryLED>LED~~FET (Drain>Source)>Battery~~ . D1 is in the path that powers the gate.

If it’s not about the voltage, what then? It’s not really necessary to have in this light as I’M not gonna put the cell in backwards. And it’s around my neck 24/7/365. (virtually)

Just saying that the diode drop doesn’t affect lumens. Any reduction in current draw to the mcu path(s) would help a tiny amount reducing sag but not sure if it would be measurable since it’s such a tiny fraction of another tiny fraction of DD draw.

Edit- what was I thinking? As Crux reminded me below while the diode isn’t in the led current path it certainly does affect the maximum voltage on the Gate which directly affects FET resistance.

Given that these cells are flat tops it’s a bit easier to mess up and drop one in backwards and this is about as “free” as anything gets.

Thanks Alex, it’s mind boggling how much time you have put into contributing to a worldwide shared resource.

This may not mean anything to anyone else but the main reason the components on the side opposite the attiny were crowded to the center was the narrow neck of a Mag Solitaire. I have plenty of the tiny10’s I can drop a 2502 on so that’s not an issue and this layout has a lot more room to work with along with a stronger B+ idea.

I've been thinking about the diode too. While it does not carry the LED current it does drop the voltage available to drive the FET, so depending on the FET and the battery voltage, the ON resistance may be higher than normal. (but maybe not enough to matter)

Aside from protecting the processor IC from reverse battery, it also isolates the power from the IC while programming it. (assuming the programmer supplies power to the chip)

What this means is without the diode the whole driver will be powered during programming, and because the PWM pin is one of the pins used during programming, the LED may follow the data on the that line. The blinking LED isn't necessarily a problem unless the power source can't handle the power draw and sags. This sag could corrupt the program process. This may all depend on the type of driver.

I'm not sure about this as I've not done any testing, but it seems reasonable to me.

Anyone have any insight on this?

Part of me wants this for the giggle factor (3 amps off of a cell that is likely good for .250 AH means that all you can do is giggle during the 5 min runtime) part of me wants to figure out a way to get a linear regulator into the mix too.

I used that java circuit sim I did the SOS disable circuit in and it looks like that capacitor that is across the LED + pad and ground helps efficiency significantly at low duty cycles. With a 47 microF capacitor and 1% duty cycle, I’m getting a peak of ~160mA and a minimum of 20mA once I add some resistor to simulate real life circuit resistances. At .5% duty cycle, I’m getting a peak of 54mA and a min of 14mA.

You’re right Crux, that part slipped my mind. It depends on how close to the elbow in the R vs Vg we’re operating since mV do count here. Not so much with purely 7135 based drivers. All the more reason to use the best FET.

Dale go ahead and try it with a jumper instead of the diode. As Crux points out it could very well change the resistance of the FET enough to result in higher amps.

Can’t get any higher than a direct connection to a cell, and that nets 3.16A, which is about where I’m at in the light. So the little Efest IMR10440 has hit the ceiling. Is there a fet out there that’s gonna boost the cell?

Think I’m just gonna stick a Luminus SBT-70 in it and run it as a mule. :stuck_out_tongue:

I’m going to mention this now so you have someone to blame if it ever comes into existence: XPH70 penlight. 2xIMR10400 and a reflector slightly taller than the LED.

I also released one of those today: [WIP] 10mm DD+single-7135 driver: double sided 10440 torture for Dual-PWM