Possible to use just PWM circuit on AMC7135 driver?

[wildstar87]

So I have a few projects that are direct drive setups, I know there are other drivers (taskled comes to mind), but since I'm looking for these in a P60 drop-in, size is a limitation.

I know that that I have seen people disable the PWM circuit on the boards to use just the AMC7135 portion of the drivers, but has anyone just used the PWM circuit by itself, removing the AMC7135 chips, and using it a direct drive setup, basically like a poorman's D2Dim/D2Flex?

It "seems" possible, but I can't say for sure. Anyone have any ideas? I did do a search on the forum, but didn't come up with anything.

 

[uk_caver]

I think that PWM with a 7135 is generally done by driving the 7135 Vdd pin , so it should be possible to use that same signal to drive one or more low-threshold FETs.

In fact, there may not be any need to take the 7135s out of the circuit - just connecting a FET in parallel with them might well work, and should be easy to try out for a quick test of operation and maximum current flow. I guess it depends what effect the 7135s would have on the clean-ness of the PWM signal.

I'd assume that the PWM high level is pretty much the same as the input voltage, but that should eb easy to check by setting a driver to full-on and measuring the Vdd voltage at the 7135s.

 

[wildstar87]

Can you give me a bit more information, forgive me I'm not an EE. Not sure what a FET does, and do you have a suggestion on a part?

I'm guessing I can't just attach the load to the Vdd?

 

[VidPro]

did you know that Kai already sells a "poor mans Dim2dim" ? they have a board that only does PWM with (i think) 5 levels, it has just the microcontroller chip and the mosfet which does the switching.
it is good for the ~3amp (supposedly) just like the dim2dim.

myself i was going to do the exact Opposite putting in the AMC driver thing, then the PWM controller , because the limitations of the max power of Either mosfet is for 3amps switching.
so if you DD and your dd ends up pushing out 4 amps, the PWM controller will fail, because its over the spec of the little parts.
I had a dim2dim for the longest time, and i keep scratching my head as to how i am going to use it without it eventually burning out, yet still being efficient and as direct drive as possible, i wanted to have major overdrive, but its not made for that. like mabey putting a full sized mosfet on it, instead of the teeney one, something i dont know how to do.

 

[wildstar87]

No I wasn't aware that KD was selling something like this, do you have a link?

I'm actually putting almost 4A through an AMC7135 1A multi-mode + two 1.4A drivers, and haven't had any issues. The only problem seems to be heat probably, after running for a while it doesn't want to switch out, but if I turn it off, leave it for awhile, then turn on again, it switches just fine.

Not sure how much life I'm gonna get out of it, but it was an experiment in a 4D mag anyway, it's working just fine.

Wouldn't the MOSFET be taking the load, and the PWM controller just be turning the MOSFET on and on real quick? I'm guessing it's kinda working like a relay?

 

[VidPro]

no i dont have the link just one of the boards.

yes, not the controller, just the mosfet takes the heat, and i have seen them turned into charred ruin more than once, but not from high amperage , from being partly switched, when they are not fully switched they become a most horrible resister that takes a lot of heat to itself and turns it into a pile of carbonised crud this has happened in mass marketed products driven properly :-( and it ticks me off that they cant put a big fat part in, when there is the room for it.
as long as the mosfet is either on or off, then it only has to deal with the power of its own on resistance , the .0whatever ohms.

i was wondering often if the heat can be fully removed from the part, that it could handle more, as if it is all about the packaging, with much better heat removal even on high resitance the internal gate items might survive better. like potting it?