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Need help to understand circuit!!!

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danishsury

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Hi everyone

This following schematic is of a 24V DC motor speed control circuit required to handle current upto 15A.

Could anyone help me in the basic understanding of this circuit, how it works and what do the main components do.

It'll be a big help.

If you need anything else please let me know.

PS: In the schematic IC = lm324, R5 = 5.6K and R6 = 4.7K and THR- THR+ and THR S make up a potentiometer of 10K, Mosfet = IRF3205R5.

R4 = 5K and not 3.5K
 

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The first Op-amp works as square wave generator and second Op-amp as level shifter based on pot setting. the two transistors drives the mosfet.
 

My explanation:

The first op-amp produces a crude triangle wave, the second op-amp works as a comparator with it's reference taken from the slider of a potentiometer wired between the 'twr' points. The comparator output is a variable width pulse which is used to turn the MOSFET on and allow current through the motor. As the pulse width is changed, the average motor power is controlled.


Brian.
 

Better working circuit based on same principle.

25_1318757430.jpg


Main pwm function is achieved by comparing triangle wave against voltage set by potentiometer. Triangle wave is used because it has slope against time, so on time and off time is easily controlled.
A capacitor is charged and discharged with constant current to produce triangle wave.

A full project with pcb for 12 or 24 volts, see this link.
PWM Motor Speed Controller / DC Light Dimmer
 
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