I'm looking to build a PWM motor controller (single direction) and came across this MOSFET on Adafruit, https://www.adafruit.com/product/355 and also this simple schematic. I'm going to bench test it soon, as it's all PTH components.
I'm planning to use 2 or maybe even 3 of these in parallel, for heat distribution. Each MOSFET will have it's own pull-down resistor, and also the 150 ohm resistor to the arduino. I guess I can use one arduino pin for all three MOSFETS. I will be PWMing it at 20Khz.
The 10k pull down resistor is there for the Arduino pin, not for the mosfet, so you only need one. Wise to have a gate resistor for each fet though.
Leo..
That technic is used in professional drivers. They might delivere 400 Amps.
Important is to buy transistors coming from the same batch. Then they more likely share the load, the current, well.
If just heat is the problem, use a heatsink, maybe a little fan too.
Have a look at the datasheet and find out that this FET is specified best at 10Vgs. Add a MOSFET driver and be happy with one such MOSFET .for up to 60A. Power dissipation then will be as low as 250mW at 30A.
I’ve made a dozen or so custom PCBs for different motor projects, usually using the VNH5019 or the VNH2SP30.
But neither will do for 30Amp
I’d be happy to try a mosfet driver if that is much superior to just driving it from an arduino pin. But I don’t know much about them and there’s so many attributes that I’m not sure what I would need if you had a suggestion for one I’m welcome to it
The BTS7960 is Not Recommended for New Designs but you can find lots of carrier boards populated with them (or clones!). There are also newer replacements.
I haven't tried it at the limits, but I think it claims 30A continuous and PWM to 25kHz.
You cannot drive a power mosfet at 20Khz with your circuit. The switching times will be much too slow. You will need a lot more current into the gate (but only during switching). Also you will need more than 5V into the gate.
I would suggest a MosFet Driver IC.
AND the flyback diode must be a high speed device. A typical 1N4004 will be much too slow and actually allow current backward through the diode when switching the MosFet ON.
Thanks. I'm learning about and hoping to use the IR2110 MOSFET driver, and going to use just one MOSFET. This newer IRFB7440PBF MOSFET
I found this diode at DigiKey which has a forward current of 40A, more than the max stall current of my motor (30A).
Here is a photo of my schematic I've come up with. I'm uncertain as to the correct values of R1 & R2, and the function of D1
Paralleling power metal-oxide semiconductor fieldeffect transistors (MOSFETs) is a common way to reduce conduction losses and spread power dissipation over multiple devices to limit the maximum junction temperature. This application brief shares best practices and examples of paralleling power MOSFETs in various applications.
R1 is there to limit the fet gate current when turning on. The gate to source has a fairly high capacitance. The faster you charge that up by putting current in the faster the fet turns on. R1 at 10R will limit the initial input current to about 1 amp. Once the gate capacitance is charged the gate current goes to zero. Maybe lower than 10R if the driver can supply the current. D1 is to discharge the gate voltage quickly to turn off the fet. R2 10K is not really essential as R1 and D1 do the work of turning the fet on and off but I usually have R2 right at the pins of the fet just in case anything in the driver get open circuited. R2 then in that case keeps the fet turned off
Thanks so much! I understand all that. It's nice to know how things work. This is my first experience with using a driver IC, rather than just the arduino pin.
If this really truly CAN handle 15 A continuous current I'll be amazed. I'm used to stuff from amazon/china that says 45amp, that has traces and block connectors built for 3amps.
I'm prepared to add good heatsink and hefty short traces/terminals to my finished PCB. I'll going to bench test it all first next week.
thanks.
I should likely at a 1000uF cap on the 12VDC line so the motor doesn't suck the voltage down. It's running from a large lithium battery that can output 30A continuous or 80A for 30 seconds, but a large cap close to my circuitry is probably a good idea? I've always seen that done, and done it myself on other motor drivers like the VNH5019 or VNH2SP30's.
Thanks! Something I've never done before, and am googling now. This would be the voltage across drain to source. Would I measure this with it just "ON", or in PWM state with a certain PWM %? I assume just a steady on state from the driver chip.
Looking at the data sheet, figure 3, and figure 10 both have info on Vds. So when it fully open, Vds should be pretty close to, if not 0 volts?
When operating MOSFETs in parallel, it is important to carefully consider how the devices share the load to ensure that each one stays within its safe operating limits. Major factors include gate circuitry, layout design, current imbalance, and temperature imbalance.
Since MOSFETs have a positive temperature coefficient, as one device heats up, it will conduct less current, allowing the other MOSFETs to take on the additional load. A common heatsink is the easiest and generally most cost-effective way to manage this thermal distribution.
In my experience, it is best to place the MOSFETs on a shared heatsink and use at least a 20-ohm resistor in each gate circuit. Failing to do this can lead to poor load sharing and potential device failure.
It’s also important to recognize that some losses are inevitable due to variations in the electrical characteristics of different devices. To account for this, I typically apply a 25% current de-rating to ensure reliability.
Using separate modules will significantly exacerbate the balancing problem and is not recommended, especially for those without extensive experience in this area.
Yes, if you only have a voltmeter this will at least tell you, at steady state, what the ON voltage is.
If you know the current flowing, you can calculate the ON resistance to see if it is within range.
Ideally, an oscilloscope would be used to check the PWM waveform for proper switching, good rise time, and observe ringing if any.
