DC Motor Speed Controller

This is the schematic diagram of DC motor speed controller circuit. The circuit applies two oscillators/timers which are connected as a Pulse Width Modulator (PWM). The timer chip which applied in this circuit will be an nmos dual timer/oscillator NE556. This timer IC has two 555 timers in a single 14-pin IC package.

One 555 (IC1:B) is set up as an astable oscillator. The output frequency of the trigger pulses is specified by:

f = 1.44 / ((R3 + 2R4)C2), or about 410Hz.

The time period for the high output is specified by

THIGH = 0.69(R3 + R4)C2 seconds.

And, the low output by T_LOW = 0.69R4C2 seconds. The 2nd 555 (IC1:A) is set up for Pulse Width Modulation. It will be build in monostable mode. It is triggered using the continuous pulse train from the first 555 timer. Nevertheless, by also applying a DC voltage to pin 3, the comparator reference levels are going to be modified from their nominal levels of one-third & two-thirds of the supply voltage. This has the effect of modulating the pulse width as the control voltage varies. The control voltage is supplied via transistor Q1, which is configured as an emitter-follower. This means that the emitter output voltage follows the base input voltage (less 0.6 volt base-emitter drop). This configuration gives us a low output impedance voltage source with which to drive the control input of the timer. This makes the control voltage less susceptible to the loading effect of the timer control input.
The output from the timer is a continuous stream of pulses whose width is controlled by the voltage level used on the control voltage input. This modulated output drives a MOSFET, Q2, that is applied to switch the voltage to the DC motor.
Components List:

R1 = 560R
R2 = 470R
R3 = 33K
R4, R7 = 2K2
R5 = 10K
R6 = 10R
P1 = 500R (501) Koa trimpot
RV1 = 10K potentiometer
D1 = 1N4004
C1 = 10uF/50V
C2, C3, C4, C5, C6, C7 = 100nF
C8 = 100uF/25V
IC1 = Nmos LM/NE556
Q2 = IRF530 mosfet
Q1 = BC547 Transistor

Technical Details:

• Uses NE556 to pulse-width modulate IRF530N MOSFET.
• DC Motor Speed Controlled via a potentiometer.
• Speed control for DC motors up to 100 Volts @ 7.0Amps without sacrificing motor torque.
• This DC Motor controller can handle up to 16 Amps, but PCB trace capacity would have to be beefed up with some hookup wire where DC motor current runs through the Printed Circuit Board.
• Requires operating voltage of 5 – 16 VDC.