[Moved]: How to Convert Analog Voltage to PWM

[farhang_760]

Hi guys ,

1) I produce variable PWM signal with NE555 By potentiometer (50K Ohm) , I wanna change this potentiometer to Analog voltage (0 - 10v) ,
Is there any way or IC to do this ?:?::bang:

(Ne555 )

2) Is there any idea to get Analog voltage and generate PWM signal ? like any IC or any Circuit and etc.

 

[betwixt]

Re: How to Convert Analog Voltage to PWM

The classic method is to generate a triangle shaped waveform and feed it to one input of a comparator. Feed the analog voltage to the other input. The output will tell which is higher so raising the analog voltage makes the output appear closer to the 'peaks' of the triangle and lowering it makes it nearer to the valleys in the triangle. The result is a waveform with pulse width proportional to the voltage which is essentially PWM.

Brian.

 

[farhang_760]

Re: How to Convert Analog Voltage to PWM

The classic method is to generate a triangle shaped waveform and feed it to one input of a comparator. Feed the analog voltage to the other input. The output will tell which is higher so raising the analog voltage makes the output appear closer to the 'peaks' of the triangle and lowering it makes it nearer to the valleys in the triangle. The result is a waveform with pulse width proportional to the voltage which is essentially PWM.

Brian.

Hi Brian,
thank you for your fast reply.
but how to generate a triangle shaped waveform?

 

[BradtheRad]

Re: How to Convert Analog Voltage to PWM

The 555 has an easy way to vary duty cycle, by changing voltage at the 'ctl' pin.
Response may or may not be linear.

 

[crutschow]

What frequency PMW and what is the lowest and highest modulation frequency?

 

[Warpspeed]

Its pretty easy to do with a potentiometer:
**broken link removed**

A 555 all by itself is not really suitable for doing it with a voltage. Its possible, but it will be very non linear and nort work well at the extremes of duty cycle.

Much better to use a proper PWM chip which generates a fixed frequency linear ramp, and it will have its own voltage comparator.
The results will be much better.

 

[schmitt trigger]

Re: How to Convert Analog Voltage to PWM

Hi Brian,
thank you for your fast reply.
but how to generate a triangle shaped waveform?

You can do it with an unijuction transistor, a low IDSS n-chan JFET, one resistor and a capacitor.
Actually a sawtooth, but it also works to generate the PWM