Made 10Amp PWM, here's the schematic, any problems?

Thread Starter

Hamlet

Joined Jun 10, 2015
327
Just for reference, I'll post thumbnail schematic from "Chemlee" first. This is the one I built first, operated at 12v, and blew the diodes & mosfets.

555 PWM motor control CHEMLEE.jpg

And this is my interpretation:

555 PWM motor control REVISED.jpg

Anyway, I have this operating a 12v, 10 amp grinder. I operated it at 7A to 8A for about an hour, and it held together, mosfets are cold,
freewheel diode warm. Any observations are welcome. I am new to PWM.

In my reading, the freewheel diode, EMI diode, avalanche diode, snubber diode, or whatever it's called,
is essential when switching inductive loads. I have ONE freewheel diode on the motor leads, not the 3 located on the mosfets
as in the first schematic.

My freewheel diode isn't "SOFT RECOVERY", just a fast diode I had in my junk. If anyone can recommend a good, cheap, popular
freewheel soft recovery diode that I can find on ebay, let me know. I want something that will work from 12volts thru 150volt motors. Would a 200v rating be sufficient?

Okay, all for now.
 
Last edited:

Dodgydave

Joined Jun 22, 2012
9,205
Your pot diodes are drawn wrong, that's not a proper pwm circuit. But if you're happy with the design and it's working ok.


Here is the correct way..
pwmfancontrollerwith555_1241855842.jpg
 

JUNELER

Joined Jul 13, 2015
183
Hi,
I think 1pc of IRFZ44 is enough to drive the moto(12v/10a). since IRFZ44(55V/49A drain current.

IF use 3 pcs its tripple the current x 3 which cause the motor get hot causing the mosfet burned.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
327
1) lower the gate resistors;
2) do some calculation to see if your 555 can drive that much capacitance.

Yeah, I was wondering about that. I was looking at the datasheet for the mosfets,
and the capacitance was so small, I figured it wouldn't matter. I don't really understand
ohms law when it comes to filling capacitors. I'm not sure I even need that voltage divider,
& 100 ohm resistors on each gate would probably work. Anyway, the mosfets stay cool,
so either I'm driving them hard enough, or, I'm not asking them to do much work in the
linear region...
 

crutschow

Joined Mar 14, 2008
25,117
IF use 3 pcs its tripple the current x 3 which cause the motor get hot causing the mosfet burned.
Not true.
The MOSFETs should go fully on and off when switching the PWM signal so adding MOSFETs in parallel will not increase the current or power (except for the reduction in ON resistance).
If one MOSFET is not sufficient to carry the current, then that could cause a blown MOSFET.
 

dannyf

Joined Sep 13, 2015
2,197
This is the one I built first, operated at 12v, and blew the diodes & mosfets.
those mosfet should operate at anything above 10v. But running it a little bit higher than that helps in getting the mosfet more fully open, if your 555 drops too much voltage on the output pin.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
327
Not true.
The MOSFETs should go fully on and off when switching the PWM signal so adding MOSFETs in parallel will not increase the current or power (except for the reduction in ON resistance).
If one MOSFET is not sufficient to carry the current, then that could cause a blown MOSFET.
YES! It is only the load that determines the current, ohms law and all that.

Can one use a pass transistor on a 555 for more drive current? I'm guessing it should be rated for the MHz of whatever you are doing...
Any suggestions?
 

dannyf

Joined Sep 13, 2015
2,197
yes, you could add some additional drivers, bjt or even mosfet, at the cost of additional loss of drive voltage - it may not swing as close to rail.

I think you should try to figure out what your problem (or goal) is. if you want to drive it at 12v (if your motor is 12v), you should be focusing on drive voltage -> to make sure that it goes above 10v at least;

if your issue is insufficient drive current, add buffers or dedicated gate drivers.

in either event, figure out the motor you are using and do some math first.
 

dannyf

Joined Sep 13, 2015
2,197
on gate resistor. for digital applications, they are typically 11ohm or lower - i have never seen them above 22ohm;

for analog applications, 47/110 -> 470ohm are common.
 

ronv

Joined Nov 12, 2008
3,770
Just for reference, I'll post thumbnail schematic from "Chemlee" first. This is the one I built first, operated at 12v, and blew the diodes & mosfets.

View attachment 117200

And this is my interpretation:

View attachment 117202

Anyway, I have this operating a 12v, 10 amp grinder. I operated it at 7A to 8A for about an hour, and it held together, mosfets are cold,
freewheel diode warm. Any observations are welcome. I am new to PWM.

In my reading, the freewheel diode, EMI diode, avalanche diode, snubber diode, or whatever it's called,
is essential when switching inductive loads. I have ONE freewheel diode on the motor leads, not the 3 located on the mosfets
as in the first schematic.

My freewheel diode isn't "SOFT RECOVERY", just a fast diode I had in my junk. If anyone can recommend a good, cheap, popular
freewheel soft recovery diode that I can find on ebay, let me know. I want something that will work from 12volts thru 150volt motors. Would a 200v rating be sufficient?

Okay, all for now.
In the first circuit (thumbnail) the diodes are in the wrong place. Yours are correct.
No matter what diode you use it will get warm. A schottky will be cooler, but may be hard to find at 200 volts. You can use a small heatsink.
If you are going to use higher voltages you need to do something different to power the 555 and make sure your FET's are good for it.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
327
yes, you could add some additional drivers, bjt or even mosfet, at the cost of additional loss of drive voltage - it may not swing as close to rail.

I think you should try to figure out what your problem (or goal) is. if you want to drive it at 12v (if your motor is 12v), you should be focusing on drive voltage -> to make sure that it goes above 10v at least;

if your issue is insufficient drive current, add buffers or dedicated gate drivers.

in either event, figure out the motor you are using and do some math first.
With PWM, I am inclined to double the voltage that the motor is rated for, and then
back off the signal a little. So as an example, with a 12v motor, using a PWM with a 20v rail, I will
have enough voltage for the mosfet, and the motor will have better torque at partial
settings, and the opportunity to speed things up if I'm in the mood to over drive my
motor.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
327
then sounds like you are OK, right? the issue of blown diodes / mosfet was just for the 12v version if I read you right.
Yes, the first version I used was only good for resistive loads. When I tried to power inductive loads, it failed.
Then I monkeyed with it, and seems to be working satisfactory.
I'm new to electronics, so I wanted someone to double-check my work,
especially before experiment further.

Do you want kuddos and to close the thread?
 

dannyf

Joined Sep 13, 2015
2,197
Then I monkeyed with it, and seems to be working satisfactory.
I'm new to electronics, so I wanted someone to double-check my work,
you did well, aside from the gate resistors (for such a low frequency, it may not matter that much).

if you were to drive bigger / more mosfets at higher frequencies, buffers or dedicated gate drivers may be needed.

For now, what you have seems to work well for you. job well done.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
327
you did well, aside from the gate resistors (for such a low frequency, it may not matter that much).

if you were to drive bigger / more mosfets at higher frequencies, buffers or dedicated gate drivers may be needed.

For now, what you have seems to work well for you. job well done.

Okay, I'll keep that in mind. I don't know shit about gate-drivers, other than they cost more than the mosfets!
Thanks for all your help, & a big thumbs-up!
 
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