Hi, I am building a 4.2V @ 6A
stepper motor (6 wires - unipolar) driver, using the IRL530N or IRLZ24 power N
FET. I actually using
the Alegro 2398 (twin bridge bipolar driver) dedicated chip for small
motors, that chip doesn't stand such 6A current.
As a protection scheme, I am
designing a feedback current limit for the FETs, so it won't fry the stepper in
case of a mechanical lock or even during steady holding current. The main
idea is to measure a 0.05 ohm resistor small voltage drop, connecting FETs drain
to ground. The small vdrop is to be compared with an adjusted trimpot
voltage at a LM339 comparator. The comparator will cut off the respective
FET that had overcurrent. This approach is being used with the 2398, since it
has an enable/disable input per side of each bridge.
I already came up with
several possibilities, using opto-couplers, or PNP or P Channel (BS110)
small switching transistor to fire the FETs, everything under control of an AVR
of course, but also with the current limit control by the LM339 and additional
circuitry.
Then I thought about the
possibility to use some already small dedicated chip for the job of firing the
external FET. Something that has current limit sensing, that I can connect
to the FET drain resistors, and will cut me some slack in the board and make
things better.
Perhaps some stepper motor
driver, or a multiple solenoid or small motor driver, enough to have the output
as open collector or floating emitter, enough to deal with a pull-up or
pull-down resistor at the gate of the IRL530N.
Of course that those small
dedicated chips that has "step forward, backward, etc" do not serve, since all
the control is being done already by the AVR. All I need is something that
can deal with higher voltage at output (20V) and has voltage sensing comparator
for current limiting.
I always have the other
solutions, using LM339, etc, but why not try something ready...?
+AVRDrive +5V +12V
+5V
-------. |
| |
| ; |
| |
R10k | R1k
COIL
| |¯¯¯¯¯|
| |
300mV
o-----(+)| | | |--'
IRF530
| | LM |---o---|--. IRL530N
R620 |
339 | |<-| IRLZ24
| .-(-)|
| | w/clamp
diode
_|_ |
|_____| |
|
|
'---------------------o
300mV |
R0.05
|
_|_
R620 could be a trimpot
adjusting full span current of 6A over R0.05.
One LM339 houses 4
comparators, so one chip per unipolar motor (4 phases & FETs).
Any known dedicated IC to
substitute the LM339 with advantages?
Thanks.
Wagner.