Been looking through lots of OLD posts here, but I can't find anything helpful to me.
Anyone have a schematic for a 10A 12V DC motor controller?
I built a controller, and everything works like I want, but the MOSFETs get pretty hot even at 1.5A. I'm using an Arduino outputting a 25Khz PWM signal (for silent operation) to a pair of IRL3705N Logic Level MOSFETs. Also have an MBR2045CT Schottky diode. Motor is a basic brushed DC motor that draws 10.
I've been spending a lot of time studying this so I think I have a good handle on the basics. (gate resistors, flyback diodes, etc) However, I'm not an electrical engineer and I'm not trying to be one. I just want to get this to work properly, so I can move on to other things.
I'm guessing I'll need different MOSFETs, a gate driver, or something other than larger heatsinks. There are a few too many variables here, and the reference material I've found hasn't been very helpful. Would appreciate any advice. Thanks!
Yes but why rule out a larger heatsink? The junction to ambient rating of that package is 60 ˚C per watt, so without a heatsink it is going to get hot anyway.
This will be about the same on any FET with the same package.
The Rds(on) is 0.01R which can be bettered these days but not by much.
How are these wired up, can you post a schematic please?
If they are in a push pull configuration have you ensured a dead zone to make sure that the two can't be turned on at the same time causing heavy spikes of current known as shoot through. This is why @LarryD asked for waveforms.
A FET driver can help with the switching transients which at 25 KHz is quite high. I know why you want it that high, but have to tried it at a lower frequency to see if that helps with the heat problem.
Sorry, no oscilloscope. I haven't graduated to that level yet. I did build a frequency counter to verify my hertz setting. (thanks to learnelectronics on YouTube) Yes, I do have a multimeter.
I don't really have a diagram as such. I don't usually make one if the wiring is so simple that I can keep track of it in my head. The drain and source are wired in parallel. I have a 10k resistor at each gate to ground, and a 220 ohm resistor at each gate to the same pin on the Arduino. No H-bridge or anything fancy.
Oh, I'm not ruling out larger heatsinks. Not having a lot of experience with MOSFETs, I'm not sure what is "normal". I've heard lots of comments about the low ON resistance of MOSFETS, and stuff like not breaking a sweat at 5A. I have my MOSFETS wired in parallel and they're getting quite warm at 1.5A. That doesn't seem right. I addressed how they're wired in another reply.
I do have heatsinks and this motor is for a fan where there will be active cooling. They will sometimes be run at max 6A, but then there's more airflow. None-the-less, I'm not sure how long the MOSFETs will last if they're run like this even with the cooling.
I have not yet tried a lower frequency. 25khz was just what one of those cheap 555-based motor controllers was using, and I was using that for testing. I just want to stay out of the audible range. There was quite a whine at 490hz.
Two in parallel doubles the gate capacitance and that reduces the rise time of the gate voltage. This slower turn on adds to the heat generated as the FET goes through the linearly region slower, before you get to the saturated state with the stated Ron resistance.
No real reason to have 2 MOSFETs. The module I used as a template had 2, and that didn't seem like a bad idea to me. It cuts the load in half (I think), and I have room for 2. I plan to try it with 1, and I may have to drop to 1 anyway if I have to add a gate driver.
The very next sentence after the quote answered that question.
I don't have a scientific reason for having 2 FETs. Just seemed like a good idea. I'm going to do some more testing tomorrow. I want to try a lower frequency and only one FET. Maybe a lower gate resistor and see what happens. Will report back.
But I get it. I'm sure lots of people ask questions here and it's hard to help them without knowing exactly how things are set up. When I posted this, I kinda figured someone would ask for a diagram. Was hoping that listing the exact parts I'm using and 2 sentences describing exactly how they're hooked up would be enough for this very simple circuit.
I was planning to make an actual schematic once I had everything "locked in". But I'll draw up something if that will help. I thought I was close to having this locked in like 3 or 4 times now but something keeps changing. Sheesh.
One of these days I'll have to get some program for drawing circuit diagrams. Haven't graduated to that level, or taken the time to shop around. Recommendations for a free app would be welcome. If I draw a schematic at all, it's pencil and paper and lots of erasing.
I use a general purpose vector drawing package and build up a library of component symbols. It is a payed for application called McDraft (also available for Windows). But I would recommend a free program called InkScape. The only slight problem is that you might be overwhelmed by what it can do, most of which you don't need in order to create a schematic. Just google the name.
