Toroids and MOSFETs and firmware, oh my! (aka:'Tiny13+N-FET=???')

OK smart guys, I'm in over my head here. Is this even possible, do I need something else in the middle? Or just a different FET (this one (38N03) sucks anyway, just trying it as-is to see what happens)? What happens is, not much. Very erratic. Sometimes it comes on bright, then turns itself off after a few seconds, and no longer responds to switch inputs, power has to be cycled before it'll do anything again. Sometimes it'll change modes 2-3 times (but the levels are not what they should be), then lock up again, but the LED stays lit. Sometimes it does nothing.

The firmware is Werner's beta, it does work properly on a plain 105c using the 7135s. Just not driving the FET.

I've removed the 10k resistor after the gate since photos were taken, it did make some difference - before it would rarely work at all, now it's reliably erratic. (lol, I know...)



Can’t help though. :slight_smile:

HA! HA HA! But this works flawlessly...

Old-style SRK drivers have 3 PWM-out pins on the MCU (#s 5, 6, & 7), only piggybacked onto one of them here, and using the corresponding L2 channel, testing with just a single LED for now. The mode spacing needs fixin' but it ramps up and down and turns on/off like it should.

I didn't even disable anything on the original driver - if there were two switches connected, you could choose whether you wanted the stock SRK UI, or the one in the 105c....

OK, similar issue when it's tied to all 3 PWM lines at the same time - doesn't work. It has enough grunt to run one channel at a time, but not two or more. Using the stock MCU it works fine with the 3 PWM pins bridged so that's not the issue, and it's not a firmware issue.

Hi comfy, have you tried driving the three pwm inputs from the output of the 105 board with just one 7135?

It might give it enough omph to work…

The gate on the single FET driver (or the PWM pads on the SRK driver) needs a positive signal, 7135 works backwards. Or is there another way to wire it up?

I'm assuming it needs a P-channel somethingorother that can be driven by the tiny13, is fast enough for the modes to work properly, and that can then drive the FET's gate with higher current.

Back to the single FET board for just a sec...

Does the resistor at R13 help or hinder in this setup? I've removed it and tied straight onto the gate, never tried it with the resistor in place. Is it worth trying different FETs from the junk box? It'll need a different one anyway, not sure if anything I have here would be better.

Tried something called 'APM3055L' from the junk box, the Tiny13 drives it just fine. Off to try a few others...

Aaaaaand... the FETs that work great stop working when they're soldered to the driver. Wired up with alligator clip test leads and hanging in midair they work. I even lifted the gate pin and soldered the PWM out from the 105c straight to the pin, still doesn't work.

I need a 'gate driver', right? (whatever that is...) Mainly for the old-style SRK drivers (since it works driving only one channel, but gives up when trying to drive all 3). The single-FET drivers can probably work as-is, with the right FET (which I don't have and don't know how to tell the ones that'll work from the ones that won't).

Not only do the FETs from the junk box work off the board and not work on it, they stop working when the wires are soldered to the pins instead of using alligator clip leads. What does that mean? Does the ATTiny require some resistance in the circuit? Are low resistance connections overloading the MCU, causing it to shut down/lock up?

I'm trying to search and find stuff that might be relevant, but that's probably not a good idea since I don't understand nearly all of it... :~

If you have a multimeter at hand, can you measure any voltate at the L- pad?
For the fun of it, you could disconnect the gate from the Attiny and turn the FET on directly by connecting the gate to a battery or something.
If it doesn’t turn on the LED then, there can’t be to much reasons why.

(Resistance in the gate path is usually there to limit the gate charge/discharge current, manipulate turn on/off time or suppress ringing at faster switching speeds. But it shouldn’t be important for this problem )

I thought that when I returned from work you would have this working by now! Sorry you’re still having probs :frowning:

The resistor R13 is to stop the gate sucking more current than the mcu can deliver. Maybe the croc clips are providing just enough resistance for it to work?

Im not an electronics expert though!

Oh, yeah, it works when jumped, either gate to BAT+ or LED- to GND. The FET part itself is reliable, just not when it's being driven directly by the ATTiny. When it stops responding there's still power to the ATTiny (it's hardwired, after all) and there's nothing present at the gate/105c's output, appears to be exactly the same as when the 105c is switched off (it doesn't really have an 'off', just a mode that's 0%).

Sometimes it locks up and no number of button presses will make it do anything at all, while the LED is stuck on at whatever level it was when it froze. Sometimes it shuts off right after changing modes and never comes back until after a hard reset (I have a clicky switch on the side of my battery box).

That same 105c when piggybacked onto only one of the 3 channels on the old SRK driver works perfectly - never locks up, modes always change, it turns on/off every time like it should. But connect the 105c's PWM-out to two or more channels, and it does nothing, ever. And it works on any of the 3 channels, but just one at a time.

I even added that resistor back, didn't change it. Tried with all combinations of both resistors, too (the other one, 10K, over at the right going from gate to GND, but I don't think that one's needed, the ATTiny has an internal drain to take care of any leftovers on the gate when the output's switched off).

But like I said, I'm pretty sure the single-FET drivers will work fine, if I can nail down which FET will work with this combo.

Curious. Have you tried removing the 10k R14? If not, maybe you can try that, or at least change to something higher e.g 50k or so. Seems like the board itself is sinking some of the signal current.

Yup, tried with & without both resistors, the one inline with the gate and the one from gate to ground. Haven't tried a different value resistor at R13 yet and I'm pretty sure R14 isn't needed.

How many amps do you need? And how many outputs? 1 output or 3 separately controlled outputs?

As noted, why not use a 7135 or something else, don’t you have those tiny mosfets to use as gate drivers for this big beast?

What about the inline resistor to the gate?

The original driver has some different kinds of security aspects.
gate pulldown
Controller to gate resistor
Capacitor between GND and VCC
Diode between VCC and controllerVCC
Resistor between VCC and controllerVCC
Capacitor against GND on Controller VCC

I know it’s too late but maybe you should have just removed the Stock controller and wire the tiny 13 on its place with all the features the stock driver came with…

Try some bigger cap between GND and VCC first, I had this issue before on my 15mm driver.

Doesn't the 105c host board have all the parts the attiny needs?

I think I read somewhere that it doesn't need a pulldown resistor on the gate, 'cause the attiny handles that internally - could be totally wrong though. Either way with resistor/without resistor it still didn't work.

What's weird is that the setup that did work with the FET not mounted, was just the PWM wire from the 105c soldered to the gate pin, BAT+ to the 105c & LED+, GND to 105c & FET's source (with an alligator clip), and LED- to FET's drain (again with alligator clip). No resistors anywhere. But solder the FET to the board, and solder the GND & LED- connections, and it goes back to being erratic and locking up/shutting down. There's no other components on the original board, and I've verified none of the PCB traces is funky. Everything's isolated like it should be.