Simple DC motor PWN speed controls


Posted on Feb 6, 2014

The 555 Ic is wired as an astable and the frequency is constant and independent of the duty cycle, as the total resistance (R charge + R discharge, notice the diode) is constant and equal to 22Kohm (givin a frequency of about 1Khz, notice the hum). When the potentiomenter is all up, the Rcharge resistance is 1, 0 Kohm (the diode prevents the capaci


Simple DC motor PWN speed controls
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tor to charge through the second potentiometer section and the other 1, 0 Kohm resistor), and Rdischarge is 21 Kohm, giving a 5% on duty cycle and a 1Khz frequency. When the potentiomenter is all down, the Rcharge resistance is 21, 0 Kohm (the diode prevents the capacitor to charge through the second potentiometer section and the other 1, 0 Kohm resistor), and Rdischarge is 1 Kohm, giving a 95% on duty cycle and a 1Khz frequency. When the potentiomenter is at 50%, the Rcharge resistance is 11, 0 Kohm (the diode prevents the capacitor to charge through the second potentiometer section and the other 1, 0 Kohm resistor), and Rdischarge is 11 Kohm, giving a 50% on duty cycle and a 1Khz frequency. If you are disgusted by the 1Khz hum of the motor try to rise the frequency out of the audible range (replacing the potenziometer), but rembember that at higher frequency inductive reactance of motor rises so the the efficiency would drop. Obviously the mosfet (or bipolar) must have enough current capability to drive the motor, so the drain (or collector) current must be equal to maximum motor current (at power supply voltage, when it is blocked). The snubber diode too, because it shorts the motor on the off cycle. Both mosfet (or bipolar) and diode have to be hooked (if you don`t want them cooked ;-) ) to a heatsink if the max motor current is more than 100 or 200mA. I suggest to not stress to much the motor with too much work because...




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