delabs Circuits

Thursday, May 05, 2016

Long Duration Linear Sweep or Ramp Generator

I hope you can help me with a circuit. Its a voltage sweep circuit that will sweep from 0v to10v in a 45 min time period, I'm using it for an input on a signal generator to control the output frequency.

I have tried a constant current source charging a capacitor but it just didn't seem to be solid. If It can be done digitally would be great! I have been struggling to do this and its the last part of the piece for my project.

Mail from CB in NA

I have once answered a similar question. Ramp Generator Elex Quna.

You need clock pulses driving a counter, which operate a digital potentiometer. Or any D-A convector - or R-2R circuit. Say you need 1-10V in 45 mts. You first figure how fine the ramp needs to be, like resolution of 100mV?

The constant current may not work as the capacitor may leak and it may not be a perfect ramp. The cc ramp is good for 1 second or less.

A staircase ladder ramp is best for you, define every step of ladder as say 10 or 100mV. A clock of 1 Sec is given to a counter, binary counts, and the digital output of counter goes to D/A Convertor.

Another here with LTspice, install and launch  LTC6993-2 Demo Circuit to try.

 Pulse Staircase Ramp Generator
"This design highlights the use of the LTC6993-2 and LT1490 to generate a pulse staircase ramp that is re-triggerable. "

Pulse Staircase Ramp Generator

If you wish to use a PIC, AVR or 8051 uC, then use it to time and control a built in D-A convertor or PWM. This is done in the code or firmware.

So .... clock >> counter >> digital to analog >> Ramp = you got it. You can implement in both software or hardware, it is your choice.