Help Me With The Big Picture Re: Drivers

[pminmo]

I =E/R Ohms law. The absolutley most used formula in electronics, Kirkoff's Laws being second.

Assuming the current sense resistor is in the leg of the FET to ground, each volt dropped across it means you have to raise the gate drive voltage a volt also. The higher the voltage the more power dissipated for no real usefull purpose. As you go lower though, physical circuit layout becomes much more important, because wire, lands and solder joints do have a resistance, small, but needs to be understood. Also, as the sense voltage goes lower, noise becomes a factor as well.

Phil

[mannster]

Thanks Pminmo for your info ! It is really helping !

I am now curious about something else. Since a chopper circuit keeps the current at your desired limit, wouldn't it be possible to use a simple transistor such as a TIP120 since it can handle the voltage, and the current

EX: 1.5- 2 amps and 5 -7 volts for the motors

*TIP120 can handle 5 amps and about 60 volts

Do mosfets and Jfets switch faster ???
Mouser does not carry the IRLZ44 but they offer P/N: FQP50N06 made by Fairchild. It handles 60 Volts and 50Amps and has a gate threshold of 2 volts... seems like it would work ?

Sorry for the trouble ummm...any other electronics guru can answer too...

[pminmo]

I wouldn't sub the FQP for the IRLZ unless your driving it with something more than 5V. Min is 2 V max is 4V, and looking at the transfer characteristics, looks more like 4.
You can use a TIP120, but for each amp switched rule of thumb will be one watt dissipated.

Phil

[mannster]

Thanks ! You have really helped me understand the technical aspects of building a driver. Now I feel better about that part of the project. I don't like to work on something if I really don't understand it.

[mannster]

I have seen the resonance issue brought up many times, and I have read that many stepper motors have this problem at certain frequencies.

I am experience this problem myself, I built a simple driver circuit based on the ST L6506 PWM CHIP I am using a circuit for unipolar motors (not shown in that PDF)

It seems to work and keeps the current at the level I expect. I am using Turbocnc to test it out. It works fine below 150mhz and 200 up to 1000mhz

The motor actually acts kinda crazy at around 150 - 160mhz (SHOCKING)

What can I do about this ???? I stepped up the acceleration rate and don't notice any jerkiness, but I don't know if it is still missing a step when it ramps up past 150mhz.

Does any electronics guru know what I can do alleviate this ?????

***UPDATE:

I was doing these tests without the motor attached to anything. This magnifies the resonance problem. I will have to do more tests.

I found this on the net which includes some info: Jones on Stepping Physics

[H500]

The problem is easy to fix by using a microstepping controller.