The AOD FET does not work as a drop in replacement for the Vishay 70N02 with the R3 and R4 values currently used for the 70N02. A new board should not be needed, the current boards allow for all necessary components.
I am operating under the assumption that the AOD will function with different resistor values, but that could definitely be a wrong assumption. Regardless of whether the AOD works, I expect weâll continue to use the BLF17DD for whatever setup does work.
Ok, Iâll edit the op to try and reflect this.
wight, can you (if you haven't already) check the datasheets and see if anything jumps out that might explain what's up with the two FETs?
Comfy, I looked over them in detail earlier. I looked at things in general plus things I didnât think of that Microa (and maybe others) brought up. Based on the very very little I know and the things other people brought up it AOD510 looked fine to me.
Right now I donât need to order any other parts, and I donât even normally order from Digikey (I use Mouser - they donât seem to carry the AOD510 
). So unfortunately I donât think Iâll have a chance to play with AOD510 very soon.
And a general Oshpark question: am I missing something or do they really not have a 'shopping cart' to do more than one project per order/payment? What is this, 1996?
You noticed that too huh
Youâre not missing anything. The site is super basic. It annoys me a little bit because I think Laen has indicated in the past that the site would be upgraded but nothing ever seems to happen. There are several useful things missing, such as an order-history/re-order function.
Back on the FET thing⌠now that I think about it, the ATtiny13A datasheet shows it dropping quite a bit of voltage on the outputs. For the PWM pins itâs something in the range of 0.7-1.0v below VCC. If a protection diode is in place VCC is already lower than battery voltage, I forget how much. At least 0.2v lower I think. I posted combined graphs in post #844 showing that while the turn-on for AOD510 is much steeper (good), it also Crap. Nevermind, I was comparing it to the red line, the 70N03. I still see no problem with using the AOD510! Hopefully resistor value tweaks will help.
Well, way back when before we added the gate/pulldown resistors, one thing I found was that bypassing the diode made the FET behave correctly.
edit: this was with the Vishay 70N02, which has issues (on the 17DD/20DD boards only) without the resistors.
Is there a pot that could help find a usable R3 value?
Does that put a slightly higher voltage on the gate?
I assume so. But what keeps defying logic is that you can build a 17DD without the resistors, test it and find it does the crazy mode changing thing, strip all the parts off the PCB and stick them on a SRK-DD board, still without the resistors, and it works perfectly.
Which is another reason I wanna see what happens when you take a 17DD and put the MCU & FET on opposite sides of the PCB.
As I think youâve speculated before, the discrepancy between SRK-DD and BLF17DD builds is probably a trace length thing. Maybe resistance or inductance changes enough with the trace length or trace layout.
My assumption is that the FET does âsomething badâ on the gate pin. The AOD510 being a more powerful one may be doing more of that bad thing, so my gut (yeah, thatâs what guides my decisions on thisâŚ) is saying a higher value resistor. I can only think of 2 âbad thingsâ the FET could do: draw a lot of current (specs says it wonât) or cause a voltage spike. Since the diode suppresses current flowing in reverse, maybe this is whatâs happening: The FET causes spikes on the gate pin and without the diode this flows back towards the battery - with the diode in place voltage on the ATtinyâs PWM output pin spikes. The gate resistor could tame that behavior. Thatâs 100% wild guess.
RBD, I donât see why you couldnât use a pot for that.
But if it's that sensitive to the trace length, the number you read from measuring the temporary pot won't be the same as what it would need once it's replaced with a fixed resistor. :~
Maybe so, maybe not. Itâs a place to start. That or random value resistors from the bin until one works. Not sure if trace length of highly conductive copper acts the same as highly resistive pot wire.
RBD, comfy was probably pointing out that if you use a pot youâre using hookup wire of some kind to tie it into the circuit in place of a 0805 or 0603 resistor. All that hookup wire could have an effect on inductance, capacitance, and/or resistanceâŚ
I was thinking of one of those smallish smd types they use on the charge boards but heâs certainly got a point. I just figure youâve got to start somewhere. Maybe test it first on an SRK DD where the traces are longer and more similar to the wire length and the board is easier to work on.
This most likely wonât become a shared project, itâs to specific / not enough demand and right now it needs a few tweaks, I got it working but itâs no where near âready to goâ so really Iâm just showing off.
This is a set of S->P carrier conversion plates for an olight SR51 WarHawk made for me, he made them perfectly to my specâs but unfortunately my measurements were a little off on the post hole alignment.
It works well enough for me by if I ever do someone else SR51 Iâll need Brian to make a couple tweaks, Iâll also use soldered in place brass rods instead of the stock aluminum rods.
Note in stock setup the rods donât carry any current. The top post is +, two outter ones are ground. Running a 17dd driver in my SR51
Design process
AOD510 works beautifully on the SRK-DD with no resistors whatsoever, so unfortunately that's not gonna tell you much.
The way I came up with the 70N02/17DD's 130R resistor was by just trying the common values from 10 ohms up to 200 ohms.
Iâd say it tells us plenty! I donât think you mentioned before that AOD510 worked in the SRK-DD. To me that definitely makes it sound like more of the same problem, which is encouraging.