DC Motor Speed Controller Using 555
To control the speed of dc
motor using 555 timer & MOSFET To Drive The Motor.
Basically, 555 timer is
an 8-pin integrated chip which is capable of producing accurate time delays or
oscillation. By connecting different values of resistor and capacitor to a 555
timer we can use it for counter less application.
In simple, it has
operating in 3 different modes
·
Astable
·
Monostable
·
Bistable
Aim of our project is to
control the speed of the dc motor using 555. To implement that we need to go with Astable mode
of operation.
Astable state
“ here the output pulse
is continuously switched between two states(high – low). “
Once we power up the
circuit, there is no stable state in the output. Means, it will oscillate at a
particular frequency depending upon the RC (resistor – capacitor) values
connected with the 555 timer.
Either we can increase
or decrease the frequency by changing RC values.
The below formula helps
us to select the suitable values for RESISTOR and CAPACITOR for square wave
generation.
NOTE : Resistor in ohms
Capacitor in farads
The formulas used are
ON time (secs) = 0.693 *
(R1 + R2) * C
OFF time (secs) = 0.693
* R2 * C
Frequency = 1.44 / ((R1
+ R2 + R2) * C)
Duty Cycle % = (ON / (ON
+ OFF)) * 100
Example
R1= 1K
R2= 330 ohms
C= 1000 uf
ON time (sec) = 0.693 *
((1×1000)+330) * (1000 X 10 e -6))
= 0.693 * 1330 * 0.001
= 0.92 seconds
OFF time (secs) = 0.693
* 330 * 0.001
= 0.22 seconds
frequency = 1.44 / ((1000
+ 330 +330) * 0.001)
= 0.869 Hz
Duty Cycle % = (0.92 /
(0.92 + 0.22)) * 100
= 80 %
Depending upon the Duty
cycle the speed of the motor will vary
If duty cycle is more,
then the speed of the motor will be high, if it is less , the speed of the
motor will be low.
Circuit Diagram:-
The above circuit
diagram shows the speed controller using 555 with slight modification of our
basic astable circuit.
Working
When we power up the
circuit, consider that output is LOW. Thus capacitor C4 is discharging through
D2 via100k Preset.
Once the capacitor
charge is less than 1/3 voltage of Vcc, the TRIGGER (pin 2) will makes the
OUTPUT (pin 3) to HIGH. Now the capacitor will charge via 100k Preset through
D3.
Once the capacitor’s
charge is greater than 2/3 voltage of Vcc. The THRESHOLD (pin 6) will makes the
OUTPUT to LOW. This process is continues.
According to the
internal connection of the 555, DISCHARGE (pin 6) is like an open collector in
a transistor. When we provide the base current to the transistor the DISCHARGE
pin will become LOW.
here the base current is
provided by OUTPUT (pin 3) internally. This is the reason, when the output
becomes HIGH correspondingly the DISCHARGE (pin 7) will become LOW.
In our circuit we
connected a pull-up resistor to the DISCHARGE (pin 7).
When the DISCHARGE (pin
7) become LOW the current from the pull-up resistor will flow the ground and no
current will flow to the gate of the MOSFET. Which makes the MOSFET to TURN OFF
If the DISCHARGE (pin 7)
becomes OPEN then the current will flow to the gate of the MOSFET. Which makes
the MOSFET to TURN ON
In our circuit diagram
the left part of the pot acts as R1 and right part as R2 and the series
capacitor as c1.
To find the output
frequency,
frequency
= 1.44 / (Preset 100k * C1 )
Click Here to Download Data Of DC Motor Speed Controller Using 555 System Project
