Using PCA9685 to drive MOSFET IRFZ44N - Page 1
Forum section: electronics / projects

author: Velth
author_rank: Contributor
timestamp: May 19, 2023, 06:12:41 pm
content: Hello I want to know if it'll be any problem with de follow schematic that I madeI want to use this system to control a DC motorThe signal PWM_OUT1 will come from PCA9685 in 5VI want to drive 12 Motors like this, but I'm afraid of the current drained of PCA it will be enough.

author: DavidAlfa
author_rank: Super Contributor
timestamp: May 19, 2023, 08:30:45 pm
content: That FET is pretty old, less sensitive to gate voltage, I would use a newer one, Rds on will be much better @ 5V.

author: Benta
author_rank: Super Contributor
timestamp: May 19, 2023, 09:36:24 pm
content: If you want to PWM the motor, the 10 uF cap will defeat that purpose completely. Why is it there?

author: Velth
author_rank: Contributor
timestamp: May 19, 2023, 10:47:07 pm
content: I want to use in 100hz, I thought to put a cap there maybe 0.1uf just to clean the signalWhat other FET would you recomend to me ?

author: Benta
author_rank: Super Contributor
timestamp: May 19, 2023, 11:10:37 pm
content: Quote from: Velth on May 19, 2023, 10:47:07 pmExtremely goofy idea.Look for a logic-level MOSFET, 5 V insn't really enough for driving the IRFZ44.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 19, 2023, 11:21:05 pm
content: At what frequency?IRFZ44N at 5V is hopeless, but there is a logic-level IRLZ44N that would do.With those values, running above 10kHz or so is unlikely to be fruitful. I guess from the diode, it's not much current anyway, and maybe a '3055 would do for example. Like uh, RFD3055LESM9A let's say.Remember to place the FET, diode and a bypass capacitor (100uF+ electrolytic would be enough here?) very close together. It's the transistor that causes the motor to flyback, not the motor doing it by itself: don't put the diode at the motor. So the clamp diode also goes at the transistor.Tim

author: PCB.Wiz
author_rank: Super Contributor
timestamp: May 20, 2023, 12:05:02 am
content: Quote from: Velth on May 19, 2023, 10:47:07 pmThe SCH says 10uF and you say 0.1uf, both are too large for PWM.A modest cap is not a bad idea to slow down the FET edges a little, but keep in mind slower edges mean more heat loss.You can get a similar effect with the inherent FET capacitance and a higher gate drive R.You could try something like 470~1k ohms series R.Quote from: Velth on May 19, 2023, 10:47:07 pmWhat package and what current ?There are shiploads of Logic level MOSFETS out there, search by package and voltage and RDS at 4.5Vgseg Digikey hasGT088N06T TO-220 N-Channel 60 V < 13 mΩ at 4.5 VgsMCP90N06Y-BP N-Channel 60 V TO-220AB < 10 mΩ at 4.5V Vgsor, you may like insulated TAB TO220TK4R3A06PL,S4X MOSFET N-CH 60V TO220SIS < 7.2 mΩ at 4.5V Vgs

author: Velth
author_rank: Contributor
timestamp: May 20, 2023, 12:34:06 am
content: I thought that 5V would be more than necessary , that I need to change de 100 resistor to lower this voltageMy load is a 12/24V motor that can consume almost 2A with 100hz pwmThe bypass capacitor that TIM said 100uf but I presume that I need i lower capacitor, gonna put it on gate right ?The package to me is irrelevant I want something cheap and that won't disappear in a few months or years.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: May 20, 2023, 01:32:43 am
content: Quote from: Velth on May 20, 2023, 12:34:06 amI would omit gate C entirely, initially, and increase the 10k to 100k, it is only there to keep the gate OFF with no drive.The 100R can increase to 470~1k fine for 100Hz PWM.Quote from: Velth on May 20, 2023, 12:34:06 amYou may need to check the inrush current,Quote from: Velth on May 20, 2023, 12:34:06 amMost designs have some dictates around package, as that is determined by how you want to mount it. Are you doing a PCB design for this ? Will you get it assembled ?Common packages are TO-220, TO-220F, TO-263/D2PAK (the SMD version of TO-220) and DPAK, the smaller SMD brother.Also common in SMD are SO-8 and compatible footprints.If you are doing 12 channels, and making volume production, PCB size and time matter, so you might look at Dual Mosfets in SO-8 and compatible flat-pack variants.eg Diodes inc have DMTH6016LSD variants, in stock at Digikey and Mouser SO-8 < 24mOhm at 4.5Vgs, 60V Dual

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 20, 2023, 03:20:28 am
content: Quote from: Velth on May 19, 2023, 10:47:07 pmExcept that even if the PWM frequency is very low, you still want as short edges as possible to avoid keeping the MOSFET in its linear region for too long.Otherwise it's going to have huge losses and dissipate all that as heat.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 20, 2023, 08:53:52 am
content: No capacitor on the gate. The capacitor goes between +24V and GND.Tim