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Controlling for DC motor

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civictypeR

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Hey guys . asking you for options , i have a 12 V motor which need to be controlled only speed using PIC. dont care about the direction . I do not plan to use the H bridge circuit to control the speed , i am using darlington array to control an array of high powered resistors , 10W but the darlington array can go to the max 500 mA . i not so sure of the output 500 mA given in the data sheet , means it can support 500mA from the external circuit or it can produce the most 500 mA . My maximum current rating for my motor is 1.5 A , Is there any alternative such as PWM to control the speed of the motor. Thanks guys the model of my darlington array is uln2803A .

CIVIC type R
 
Still working on your final year project?
The ULN2803 will only drive 500mA, try using a TIP120 or similar to drive your motor. And yes PWM is a very good way to drive a DC motor.
PS an H-bridge is designed to control direction, some have enable inputs for PWM to control the speed.
 
Mohammad Rammal

Hello
I have a projet when i used 2 dc motor
but i have from you if you want a circuit diagram for the control of dc motor with automatic break if i cut the power from the motor.
thank you
 
You can get by with a PWM made from only 3 op-amps on a quad general purpose Jfet op-amp,( comparable to a TL-084 from Texas Instruments), for only $1.50 or so from Radio Shack plus the resistors and capacitors needed.They also have a little engineer's handbook on op-amp circuits that show you how to make the circuits.You will get more duty cycle from an op-amp based PWM,(0-to 100%), instead of using a 555 timer based PWM,(30 to 90%),and it is a simpler configuration than using counters and weighted voltage summators for a very precise staircase wave generator for the comparator.PWM's get even more sophisticated with micro-processor based systems where the counters are programmable. The first op-amp will produce a square wave,the second op-amp will produce a sawtooth wave,and the third op-amp is a positive ongoing comparator.By adjusting the DC reference voltage going into the comparator,the output goes high to +VC when the sawtooth wave equals the reference voltage and stays there until the sawtooth wave goes down to the reference voltage,giving you a nice square wave of varying width.For DC motor control it is best to go with a set 20khz oscillator frequency depending on the RC time constant to get fine control of the duty cycle and to avoid audio noise from the motor.This PWM works good for uni-directional DC motor control where the PWM goes into one gate driver for your IGBT or MOSFET. As you stated,bi-directional motor control incorporates an "H" bridge configuration and 2 gate drivers where one gate driver turns on 2 diagonally positioned MOSFETS and the other gate driver turns on the other two MOSFETS..You can use one PWM with a 3 contact switch where the center connection is common to both gate drivers.This way you cannot turn on both MOSFETS at the same time,as this produces a dead short, roasting your MOSFETS. I hope this helps you!ammoniaman.
 
Only two op-amps are required to make a PWM controller.

Here's a simulation of a PWM circuit with the output set to three different duty cycles.
pwm-sim-gif.13173
 
There are many ways to get to the same result,555 timers,etc.That was just one way.I'm working on inverter circuits now and they are not simple at all if you don't want to roast the output transistors.I was trying to be helpful.Please appreciate that!
 
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