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IC555 - control pin

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giovannithex

New Member
Hello everyone.

I'm wondering if (how) could i make it possible;

I have simple circuit from two parts: one stands as PWM oscilator (555 timer) and that timer drives the transistor (npn, let us forget about efficiency for now)
On the CE line of transistor i have connected a DC motor of which speed i control via changing the pulse width.
When the motor is on full throttle, it gives away all the torque it has. But when lower the speed, the story is different.

My question follows - how could i get"fairly good" torque out of motor even spinning in lower speed?
I heard that there is possibility of using pin 5 on 555 timer. When the motor got loaded "too much", the voltage (of yet unknown circuit) tells the IC555 to increase the pwm signal to acheive the "same" speed of motor rotation, and when there is no / less load on motor, the pwm decrease and still keeps the "same" speed of motor.
But how should i take current from the mains of the motor and somehow make connection to control pin? Can anyone explain me that principle of the control pin?

thanks.
john
 

ci139

Active Member
i'm quite sure there is a technique to achieve what you aim but let us consider the odds here
the motor has physical momentum that is a way more difficult to regulate than the (average) output voltage of your pwm -- which means the circuit may be quite complex one e.g. you have to overdrive your motor for it to respond fast - which in turn means if your motor is jammed it'd take the pulse of near infinite energy to "keep it up to a specified speed" -- there are more aspects like this resolving of which adds up to the complexity of your drive circuitry . . .
-- that thing suppose to have efficieny optimized control -- e.g. -- what you ask has been compacted inside there
about pin-5 (though it's from datasheet)
 
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alec_t

Well-Known Member
Most Helpful Member
I heard that there is possibility of using pin 5 on 555 timer. When the motor got loaded "too much", the voltage (of yet unknown circuit) tells the IC555 to increase the pwm
That's one way. Fig 18 of the 555 datasheet shows how pin 5 can be used for PWM. You would need to find a way of providing a pin 5 control voltage which varies with motor rpm.
 

AnalogKid

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The speed-power-torque characteristics of a motor are set by the motor's design and construction. Without feedback from a tachometer, current sensor, or some other method of determining how the motor is responding to its load, I don't see any way to regulate torque at low speed. Generally speaking, when you reduce the total energy to the motor, either through a linear regulator or PWM, you get less torque.

ak
 

audioguru

Well-Known Member
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I think at a very low speed, the full power pulses of PWM produces much better speed regulation of a DC motor than simply reducing its DC voltage but probably with a lot of vibration.
 

dr pepper

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I adapted the above to work in machine code for the pic, it works well, really well.
 

dr pepper

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Yes assembly, much quicker than higher level languages, for this particular job it works better.
As soon as things get more complex though I switch to C.
 

atferrari

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