Need help to determine MOSFET

[Paddy]

Hello all,

as my HoverMower chassis is almost complete, I need to investigate in electronics. Because I'm not that familiar when it comes to FETs, I hope you can advise me.

So my Mower is equipped with a 10S2P Li-Ion battery ratet with 36V. When fully charged, it has up to 42V. The robot itself gets operated by a NVidia Jetson, which is similar to Raspberry PI when it comes to GPIO. So it provides 3.3V logic level. Beside that, a Arduino Nano gets used as perimeter receiver and for general power management operating with 5V.

Bernard send me a PCB named PowerBoard V1.01, which I want to use to monitor battery, toggle charging contacts on/off and to disconnect entire robot from battery before drawing it to death. This board I want to hook to Arduino Nano. One reason for this is, Jetson will take some time to boot up and I don't want to keep the button pressed that long.

Beside this requirement, I also want to switch some other components directly by Jetson Nano which are:
- LED headlights running at 15V (unknown current consumption as they're taken from HoverBoard and no data sheet is available)
- Lidar running at 5V, normally powered by USB, so it should not be more than 400mA
- Power Switch circuit of Motor driver. Normally a simple switch is used to turn Motor driver PCB on/off. I want to replace it with a FET so I can control it by Jetson. The switch closes the main circuit of board (like PowerBoard will do for entire robot). I measured full voltage through the switch, so the FET should also be able to handle 42V for a short moment

Can someone please help me to find a FET (or multiple different ones) which:
- switch 50V (or more) with only 3.3V gate voltage (high current flow as this is the main FET of robot)
- switch 50V/1 amp with only 3.3V gate voltage for a short period (max. 1 sec.) to turn motor driver on/off
- switch 15V ( or more) with a few 100mA with 3.3V gate voltage (LED headlights)
- switch 5V/400mA with 3.3V gate voltage (Lidar)

Maybe a single FET can cover all of these requirements which eases purchasing for me.
The following FETs I already owned but I'm not sure if they will work properly with 3.3V

- TIP120
- IRF9540N
- IRLIZ44N

I already checked the data sheets but to be onest, I'm simply lost in all these technical details.

BR Patrick

 

[Sascha]

I can't help you directly now, because I always have to search there too
But the TIP120 should be able to do that, maybe this thread is interesting or this example?
Or you look here, especially under MOSFET

 

[Paddy]

Thanks, some of them I already know. Especially mikrocontroller.de is often a waste of time as they start flame wars instead of helping people.
However, I tried to get a feeling of how it is solved in general. From my understanding, it seems to be common to switch high voltages not only by a MOSFET, but also by a transistor which feeds the gate of MOSFET.

I'll check how you solved it for PowerBoard PCB. After looking to Ardumower PCB and the schematics I've found related to hoverboard PCB. it seems they're more or less identically.

So basically, there is a voltage divider connected to BAT+ and source of a transistor. This transistor gets controlled by a MCU with 3.3V. When this Transistor switches, it closes the gate of a MOSFET.


Taken from Hoverboard schematics, MCU controls SUPPLY_EN and switch Q1.s will close circuit of Q2 and connect battery to the rest. Also SUPPLY_EN gets driven by pushbutton via voltage divider.

Do you know a circuit simulator? I wan't to try it in simulation before purchasing lots of parts I don't need. I tried differerent online tools but the free ones wasn't good and the better ones are expensive,

 

[Sascha]

From my understanding, it seems to be common to switch high voltages not only by a MOSFET, but also by a transistor which feeds the gate of MOSFET

Yes you are right. On PowerPCB there are High Side Switch.
The Circut you post, is mostly the same like we use on PowerPCB.

No did not know a Circuit Simulator.
I tried one once, but somehow it didn't work.
I the end up and took breadboard and multimeter to test.
In principle, you should be able to use the PowerPCB with appropriate Mofsets and transistors and the resistors for the battery measurement must probably also be adapted.