Generating a PWM signal from an analog input voltage ranging 0-10V

[dtparekh]

Hello Friends,

Can any one suggest some digital circuit or microcontroller based PWM which takes a control voltage range from 0 to 10 volts and output a digitally controlled PWM signal.

Thanks in Advance

 

[Ahmed Ragab]

implementing pwm pic

Well it means you need an analog to digital converter to read the 0-10 volt range to your microcontroller, and then the digital value would be read into the microcontroller which would change the values of counters accordingly to vary the pulse width.

Which controllers do you use? I worked with the 8051 family before, but some of my friends mentioned that using PIC would be much easier and simpler in such small applications since it's smaller in pinout and instruction set.

What is your application? What is the PWM signal supposed to control?
hope I've helped you by any means,
salam for now.

 

[dtparekh]

eoc signal adc

 PWM will be a building block in my power supply project.
I have 400Vdc , 250Wpower as input
i want to vary this DC voltage from 100VDC to 300VDC
with coressponding analog contol input from 0 to 10V(source input current 50mA) i.e 0v-to 100v and so on.
for this i need pwm so how to i do it?
use a analog IC or use some digital IC such as microcontrollers?


thanks

 

[Ahmed Ragab]

pwm 10 volts

Well I don't know what kind of analog IC can generate a PWM signal from an analog input voltage ranging 0-10V. Never occurred to have worked with any.

But considering microcontrollers, I have done a circuit with almost the same functionality, I was controlling DC motors using a PWM signal.

So back to your application, you may use the ADC0808 shown in figure:
**broken link removed**

Normally analogue-to-digital con-verter (ADC) needs interfacing through a microprocessor to convert analogue data into digital format. This requires hardware and necessary software, resulting in increased complexity and hence the total cost.

The circuit of A-to-D converter shown here is configured around ADC 0808, avoiding the use of a microprocessor. The ADC 0808 is an 8-bit A-to-D converter, having data lines D0-D7. It works on the principle of successive approximation. It has a total of eight analogue input channels, out of which any one can be selected using address lines A, B and C. Here, in this case, input channel IN0 is selected by grounding A, B and C address lines.

Usually the control signals EOC (end of conversion), SC (start conversion), ALE (address latch enable) and OE (output enable) are interfaced by means of a microprocessor or a microcontroller.

However, the circuit shown here is built to operate in its continuous mode without using any microprocessor. Therefore the input control signals ALE and OE, being active-high, are tied to Vcc (+5 volts). The input control signal SC, being active-low, initiates start of conversion at falling edge of the pulse, whereas the output signal EOC becomes high after completion of digitisation. This EOC output is coupled to SC input, where falling edge of EOC output acts as SC input to direct the ADC to start the conversion.

As the conversion starts, EOC signal goes high. At next clock pulse EOC output again goes low, and hence SC is enabled to start the next conversion. Thus, it provides continuous 8-bit digital output corresponding to instantaneous value of analogue input. The maximum level of analogue input voltage should be appropriately scaled down below positive reference (+5V) level.

The ADC 0808 IC requires clock signal of typically 550 kHz, which can be easily derived from an astable multivibrator constructed using 7404 inverter gates. In order to visualise the digital output, the row of eight LEDs (LED1 through LED8) have been used, wherein each LED is connected to respective data lines D0 through D7. Since ADC works in the continuous mode, it displays digital output as soon as analogue input is applied.

For your application, Vref+ can be changed to 10V (check the datasheets first) and you data outputs connected to the microcontroller. You will have to connect the SC and EOC pins to your controller too. SC will let the controller start conversion process in ADC while EOC pin will notify the controller that there is data ready to be exchanged. IN0 will be conected to your input analog voltage.
According to the output in data pins, the controller will intialize it's counters to give the PWM signal.

If this reply has helped in any way, kindly do click on the "helped me" icon.
Waiting to hear your feedback, Salam.

Added after 17 minutes:

You may also consider the ADC0801, only 1 analog input channel which you already need plus being more simple in external circuitry, it already has a clock generator built on chip.

There are also some microcontrollers that include ADC on them, you will have to check with your local stores if such controllers exist at your place or not. Both in the 8051 and PIC families.

Enjoy.