pulse width modulation DC motor driver circuit - Electronic Circuits Projects Diagrams Free

eightwgt · 20th April 2004, 03:34 PM

Hey guys.....
I am in the process of building an automated Mirror grinder for telescope primary mirrors....I have a DC motor I need a control for.
I found a couple of PWM circuits online but my problem is I have a 120 vdc 2.25 php motor and the circuit I found is not sufficiant. I found a kit thats rated to 100 volts ..........and may use it as a starting point unless someone here knows a better schematic - I need the PWM to maintain torque at lower RPM's
Any suggestions - I am not the electronics guru - (thats why I allways come here for help !)
here is a link to it :
http://www.circuitspecialists.com/prod.itml/icOid/3349

Thanks guys ! 8)

bmcculla · 20th April 2004, 07:37 PM

Take a look at Digikey.com and find a MOSFET in a package with a tab mounting (like a TO-220). Look for Suitable Vds (300V to be safe) and low Rds on. Buy a big heat sink for it. Calculate the heating for full on; if its higher than 5-10W you might want to find a lower Rds on FET. Find a MOSFET driver to drive the gate. The driver chip makes the FET switch quickly reducing heating. Make sure you drive the gate with at least 12V. Find a high current diode with a fast switching time; I'm not a motor drive expert but one of my coworkers who is says that switching speed on a diode can often be more important than low voltage drop.

If you really want to have high torque at low speed you can make or buy a PID controller. Good motor control will let you have low speed but still have al the available torque when nessesary.

Hope this gives you some ideas to get you started.

Brent

eightwgt · 20th April 2004, 08:46 PM

Quote:

Take a look at Digikey.com and find a MOSFET in a package with a tab mounting (like a TO-220). Look for Suitable Vds (300V to be safe) and low Rds on. Buy a big heat sink for it. Calculate the heating for full on; if its higher than 5-10W you might want to find a lower Rds on FET. Find a MOSFET driver to drive the gate. The driver chip makes the FET switch quickly reducing heating. Make sure you drive the gate with at least 12V. Find a high current diode with a fast switching time; I'm not a motor drive expert but one of my coworkers who is says that switching speed on a diode can often be more important than low voltage drop.

Ill look into this but not being an electronic wizard.... its going to be tricky at best for me to figure this out without help :?

Quote:

If you really want to have high torque at low speed you can make or buy a PID controller."

Whats a PID controller ??

THANKS for your valuable input - I appreciate it........

eightwgt · 20th April 2004, 10:16 PM

I thought Id touch back on my application....

I do not need positioning feedback
I do not need speed (RPM) feedback

115 VAC input-convert to DC with full bridge rectifier ? I get 108 volts DC output for the motor (I already have a few rectifiers from Radio Shack)

Ok.... So now I have to send this voltage in 'pulses' to the DC motor to keep torque and get a smaller duty load right ?

Now - Im trying to understand the MOSFET, and how I use it with other items to accomplish this.......

Hmm............. HELP guys !

eightwgt · 20th April 2004, 10:22 PM

Im reading a really good explanation of the application of MOSFETS and choosing them - Thought Id share the link with everyone

http://homepages.which.net/~paul.hil...l/Mosfets.html :wink:

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20th April 2004, 03:34 PM	(permalink)
eightwgt	pulse width modulation DC motor driver circuit Hey guys..... I am in the process of building an automated Mirror grinder for telescope primary mirrors....I have a DC motor I need a control for. I found a couple of PWM circuits online but my problem is I have a 120 vdc 2.25 php motor and the circuit I found is not sufficiant. I found a kit thats rated to 100 volts ..........and may use it as a starting point unless someone here knows a better schematic - I need the PWM to maintain torque at lower RPM's Any suggestions - I am not the electronics guru - (thats why I allways come here for help !) here is a link to it : http://www.circuitspecialists.com/prod.itml/icOid/3349 Thanks guys ! 8)

20th April 2004, 07:37 PM	(permalink)
bmcculla	Take a look at Digikey.com and find a MOSFET in a package with a tab mounting (like a TO-220). Look for Suitable Vds (300V to be safe) and low Rds on. Buy a big heat sink for it. Calculate the heating for full on; if its higher than 5-10W you might want to find a lower Rds on FET. Find a MOSFET driver to drive the gate. The driver chip makes the FET switch quickly reducing heating. Make sure you drive the gate with at least 12V. Find a high current diode with a fast switching time; I'm not a motor drive expert but one of my coworkers who is says that switching speed on a diode can often be more important than low voltage drop. If you really want to have high torque at low speed you can make or buy a PID controller. Good motor control will let you have low speed but still have al the available torque when nessesary. Hope this gives you some ideas to get you started. Brent

20th April 2004, 10:16 PM	(permalink)
eightwgt	I thought Id touch back on my application.... I do not need positioning feedback I do not need speed (RPM) feedback 115 VAC input-convert to DC with full bridge rectifier ? I get 108 volts DC output for the motor (I already have a few rectifiers from Radio Shack) Ok.... So now I have to send this voltage in 'pulses' to the DC motor to keep torque and get a smaller duty load right ? Now - Im trying to understand the MOSFET, and how I use it with other items to accomplish this....... Hmm............. HELP guys !

20th April 2004, 10:22 PM	(permalink)
eightwgt	Im reading a really good explanation of the application of MOSFETS and choosing them - Thought Id share the link with everyone http://homepages.which.net/~paul.hil...l/Mosfets.html :wink: