Maker Pro
Maker Pro

PWM Motor Control Using MOSFETS

G

Gerrard Shaw

Jan 1, 1970
0
In addition to picking a non-existant MOSFET,

Well I can't help it the datasheet was wrong :)
you picked a
nearly unobtainium controller IC. No stock anywhere, and
minimum order of 3000 from one "supplier" with a shipping
delay of who knows how long. And no second sources, natch.
No apparent provision for engineering samples. Sounds like
a non-starter component. Mark that kid down for a "D." :>)

We haven't used any others (unless you count a 4 output IC that
forgets the program when you take the battery out)! That's what an
evaluation is for - to say what you should do in reality but can't
because you don't have the resources / time to. I could always go back
to using a variable resistor with the motor if you like!

Btw is "unobtainium" a new radioactive element - I can't wait to see
Ub-Mh batteries in my next project!

Regards,

Gerrard
 
G

Gerrard Shaw

Jan 1, 1970
0
Hi again,

Guess what? I changed my circuit - again! I think that the PIC chip
isn't really necessary in a mass market power tool and could cause
more trouble than it's worth (and besides it makes the schematic too
difficult to copy neatly by hand). I will be using the "simple
controller" design shown in the datasheet, which it says is suitable
for electrical tools.

Regards,

Gerrard
 
G

Gerrard Shaw

Jan 1, 1970
0
Hi again,

Just a couple of days until the design paper and still for every thing
I find out there's always another question! I took apart a dead DeWalt
drill today and looked at the circuit - there was an IC there and once
I scrubbed off some blue sticky stuff I could see the model number -
NE555! It seems that a £100+ drill has a £1 PCB inside it! There was
also a complex switching block inside - I'm not sure but it seems as
if it's switching the RC network to change the pulses. I have checked
the wiring with a multimeter and the circuit is an astable so I know
it must be PWM.

I have found a circuit that seems a bit similar here: -

http://www.eleinmec.com/article.asp?28

It uses two 555 chips but does a similar job. The main question I have
is to do with the frequency. I thought that the frequency had to be
quite high to make the motor move smoothly but this circuit says it
does up to 30Hz - that doesn't seem a lot considering that the TD340
IC does up to 25kHz?!

There is also a single astable circuit here: -

http://www.nomad.ee/micros/pwm555.html

Does anyone know what would be most suitable to use in a power tool as
the only problem with the TD340 is that you need to mount 4 FETs (each
with equal heatsinking?).

I'd be really grateful for any advice - I think I need it!

Regards,

Gerrard Shaw
 
P

Paul Burke

Jan 1, 1970
0
Gerrard said:
Hi again,

It seems that a £100+ drill has a £1 PCB inside it!

Surprise surprise! A few weeks ago a local hifi shop was showing off an
expensive amplifier with the lid off. Impregnated paper single sided
PCBs, 5% resistors, cheap electrolytics, and a tangle of wire like the
cat's got at granny's knitting again.

Paul Burke
 
Top