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Pulse width modulating motor speed control

2015-03-01 00:13  
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Pulse-width modulation is an effective method for adjusting the amount of power delivered to an electrical load. A simple circuit containing an inverter chip, diodes, trimpot, and capacitor creates the variable duty-cycle PWM. A resistor and transistor switch heavier loads than the  74AC14  chip can drive by itself.Speed control is accomplished by pulse width modulating the gates of two MGP20N45 TMOS devices. Therefore, motor speed is proportional to the pulse width of the incoming digital signal, which can be generated by a microprocessor or digital logic. The incoming signal is applied to comparator Ul, then to paralleled inverters U2, U3, and U4 that drive the two TMOS devices, which, in turn, control power applied to the motor armature. Bridge rectifier Dl supplies fullwave power that is filtered by R5 and Cl.To control the speed of a DC. motor we need a variable voltage d.c. power source.

Pwm motor speed control 
 

Free-wheeling diode D3 (MR854) prevents high voltage across Ql and Q2. A back-to-back zener diode, D2, protects against transients and high voltage surges.