Can not under stand the R11 to R14 Value wattage

[sanjib.s]

can any one help me to understand the values of shunt resistors in the schematics and its wattage, i am using irfz44n mosfets and sanyo 1.8v 3amp stepper motor with l297 and mach3 i am using 12volt power supply.

[PMinMO]

I would use two .5 ohm 1/2w resistors in parallel for an equivalent .25 ohm 1 w value and set vsense to .75 for 3A. Do not use wire wound resistors.

[LevonTecH18]

Slow motion Stepper motor if you used it that kind of motor.

[sanjib.s]

why there is no clamp diode in the circuit? I want to use 1n5822 in series 80volt and 3ams to get rid of reverse voltage spike I am thinking driving the motor with 40 volts and replacing the irfz44n with irf640 to get the speed it is too slow on 12volts. i have burnt 4 irfz44 at 40volt what do you think? thank you.

[PMinMO]

why there is no clamp diode in the circuit? I want to use 1n5822 in series 80volt and 3ams to get rid of reverse voltage spike I am thinking driving the motor with 40 volts and replacing the irfz44n with irf640 to get the speed it is too slow on 12volts. i have burnt 4 irfz44 at 40volt what do you think? thank you.

Clamp diode is built into most mosfets. Unipolar voltage rating on mosfet has to be double ps voltage at a minimum. Since the irf640 isn't a logic level mosfet it's marginal.

[sanjib.s]

Is there any way to use non-logic level mosfet instead of logic level. I have asked for irlz but the shop owner said only irfz are available.

[sanjib.s]

can I use a npn and pnp transistor like darlington to amplify the logic signal or an op-amp to increase the signal.

[sanjib.s]

can op-amp like 741 incorporated to boost the voltage or a totem pole to do so, which one is more preferable. I think 741 with 2x gain will give 10v output that will drive the mosfet.

[PMinMO]

A 741 op amp isn't fast enough. You need both an active pull up driver as well as an active pull down driver so an actual low side mosfet driver like the TC4468 chip is the answer. http://ww1.microchip.com/downloads/en/D ... 21425b.pdf

[sanjib.s]

TC4468 or MIC4468 is not available. can it be possible to use push pule transistors drive the irfz mosfets or any DIY idea for mosfets, I have got a push-pule type idea from net please look at it, it is to drive mosfets, thanks Phil.

mosfet driver

mosfet driver2.gif (13.91 KiB) Viewed 2154 times

[sanjib.s]

can max232 and a or gate could be used as max232 easily available to me. Is it fast enough to do the need? it is a level shifter and it can give 20v+- if some how it is to be incorporated. If i have got the irl series it would be no problem.

[PMinMO]

The discrete component schematics will work.

[sanjib.s]

I have a idea I will test that then I will post again.

[sanjib.s]

I found IRF740 interesting it will open from logic voltage.

[PMinMO]

The IRF740 is your normal N-chn mosfet. Vgs threshold 2 to 4 volts. What that means is it's guaranteed to START to conduct by 4V, but that's not a solution. It needs to be virtually fully on by 4V or less. Some batches that start to conduct at 2V may work but get hot because they are partially on. Some batches that start to conduct at 4V won't work at all. If you look at the transfer characteristics, you will see it isn't fully on till around 7V at 25 C.