Current flow controller for DC Motors

[sayzer]

If your PIC has comparator, then you can use it to detect current as you wish.
The example below shows the use of an external comparator, but if your PIC has an internal one then you are good to go.


<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=2892&d=1223533980" >
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[mikebar]

If your PIC has comparator, then you can use it to detect current as you wish.
The example below shows the use of an external comparator, but if your PIC has an internal one then you are good to go.


<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=2892&d=1223533980" >
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Thank you Sayzer, for the hint.
To be honest, I've not clearly understood if GH1 and GH2 are 2 different pins or whatelse. Any suggestions for the filter capacitanze (R and C values) that goes to the comparator? I think to drive the motor with max 5KHz PWM wave. Voltage 24Volts, maximum allowed current to the motor 5A.
Some suggestions also for a good logic level MOSFET for this kind of motor and the name for a fast recovery diodes?

Thank you a lot.

[sayzer]

mike,

This is for reference.

You can play with the values and come up with the right ones much faster then using formulas.

---------OR------------
You can use analog reading to speed up and down the motor for the time you need.
You need a resistor for detecting motor current anyway.

If your analog reading is high, then slow down the motor, and if low then speed up the motor.
You just do it for 2 seconds as you need.

[mikebar]

mike,

This is for reference.

You can play with the values and come up with the right ones much faster then using formulas.

---------OR------------
You can use analog reading to speed up and down the motor for the time you need.
You need a resistor for detecting motor current anyway.

If your analog reading is high, then slow down the motor, and if low then speed up the motor.
You just do it for 2 seconds as you need.

Thank you for the answer.
Analog reading is what I will do if it is not possible (or reasonable/reliable) to do the same without disturb a PIC chip for this task.
To drive the motor, I have in mind to use the logic type mosfet RFP30N06LE for this kind of application. Do you think it is a good choice?
I thought that a fast recovery diode for this kind of application (if memory is still good) should be a BYV28-200. Do you think is a good choice too or you have some better idea?

Thanks in advance.

[sayzer]

Will the motor run in one direction or you need both directions? CW/CCW

If one direction, then I would use IRFZ44. PIC PWM pin directly goes to the gate with 15K to GND. Easy, reliable, affordable.

If you need both directions then I wish you luck


For the diode, what is your plan to use it? Where, why, idea etc.

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[mikebar]

Will the motor run in one direction or you need both directions? CW/CCW

If one direction, then I would use IRFZ44. PIC PWM pin directly goes to the gate with 15K to GND. Easy, reliable, affordable.

If you need both directions then I wish you luck


For the diode, what is your plan to use it? Where, why, idea etc.

-----------------------

Thank for the suggestions.
Yes, I need just one direction: CW
I think to use the diode in order to protect the MosFET from the back EMF while switching on and off the motor because the PWM (like anode to the side where the motor is connected to the GND through the FET and catode to +24Vcc)
I saw from the datasheet of the mosfet you have suggested that the IRFZ44 has an internal avalanche diode. So my one outside is useless.
But I also saw in the datasheet that there is no mention about IRFZ44 to be a "logic level" mosfet. Since I never used it before, it is really enough to drive a PIC pin directly to the Gate and put in the middle of this path a 15K resistor to the GND?

Thank you in advance.

[sougata]

IRFZ44 has an internal avalanche diode. So my one outside is useless.

The MOSFET body diode is not a soft recovery type. While you can live without an external diode putting one may save trouble. Switch Off ringing + Brush Noise + Reverse Recovery Time may kill your MOSFET.

You can use SG3525 PWM controller that solves your whole purpose.