The 555 timer is one of the most popular and
versatile integrated circuits ever produced. Depending on the manufacturer,
it includes over 20 transistors, 2 diodes and 15 resistors on a silicon chip
installed in an 8-pin mini dual-in-line package (DIP-8).
The 555 has three operating modes:
- Monostable mode: in this mode, the 555 functions as a "one-shot".
Applications include timers, missing pulse detection, bouncefree switches,
touch switches, Frequency Divider,Capacitance Measurement, Pulse Width
Modulation (PWM) etc.
- Astable - Free Running mode: the 555 can operate as an oscillator. Uses
include LED and lamp flashers, pulse generation, logic clocks, tone
generation, security alarms, pulse position modulation, etc.
- Bistable mode or Schmitt trigger: the 555 can
operate as a flip-flop, if the DIS pin is not connected and no capacitor is
used. Uses include bounce free latched switches, etc.
Using a CMOS version of the 555 timer, this
circuit can be used to control the speed of a motor by adjusting the duty
cycle of the pulses sent to the motor.
The effective voltage can be varied by inserting
a series resistor or by an electronically controlled switching device made
of thyristors, transistors, or, formerly, mercury arc rectifiers. In a
circuit known as a chopper, the average voltage applied to the motor is
varied by switching the supply voltage very rapidly. As the "on" to "off"
ratio is varied to alter the average applied voltage, the speed of the motor
varies. The percentage "on" time multiplied by the supply voltage gives the
average voltage applied to the motor. Therefore, with a 100 V supply and a
25% "on" time, the average voltage at the motor will be 25 V. During the
"off" time, the armature's inductance causes the current to continue through
a diode called a "flyback diode", in parallel with the motor. At this point
in the cycle, the supply current will be zero, and therefore the average
motor current will always be higher than the supply current unless the
percentage "on" time is 100%. At 100% "on" time, the supply and motor
current are equal. The rapid switching wastes less energy than series
resistors. This method is also called pulse-width modulation (PWM) and is
often controlled by a microprocessor. An output filter is sometimes
installed to smooth the average voltage applied to the motor and reduce
DC Motor Driver Using NE 555
Rangkaian penggerak motor DC ini adalah berdasar pada
pembangkitan sinyal PWM menggunakan menggunakan IC NE555, kecepatan putaran
motor DC ini dipengaruhi oleh lebar pulsa PWM yang dapat diatur dengan
mengubah besarnya VR 500K. Pulsa PWM yang dihasilkan digunakan untuk
mengon-offkan MOSFET, sehingga dapat digunakan untuk motor DC. (daya MOSFET
tersebut adalah 70 watt).
Gambar 1. Rangkaian Driver Motor DC Menggunakan IC NE555.