convert 0..+3.3V to a range of -5V..+5V

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robz

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Got a question about converting voltages.

i've got a +3.3V pwm signal out of my CPLD, convert it with a RC network to a maximum analog voltage of +3.3V (duty cycle 100%).

Now i'am going to use the signal for creating an offset signal after a DAC circuit.

This offset must be about -5V or +5V.. it also may be a little bit lower (4V should also work).

so i want to convert the analog voltage of the RC network (0..+3.3V) to a range of -5V..+5V.

Somebody got an idea how to do it? thank you...
 
Do you have +/- supplies? You will need at least +/- 5V. +/-7V or higher will give you a wider choice of op amps. I'll try to post a schematic after you answer.
 
yep, i've got +/- 5V supply on my board. Because of the losses i think a range of +4..-4V must be possible to make.
 
This circuit's output will swing within millivolts of the supply rails. The input impedance is very high, so your input can come directly from your PWM filter.
If your +5V supply is accurate and stable, you can use the bottom circuit, instead of requiring the LM336.
You can use a different op amp, so long as its output can swing rail-to-rail and it can handle +/-5V supplies.
 

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thank you very much! this is what i needed! i've got a stable 5V supply but i prefer a LM336.
 
You could convert the 0 - 3.3 V PWM signal to +/- 5 V while it is still a digital signal, before the RC network.

That can easily be done with a MAX3232 or similar, and you don't need to mess around with an op-amp.
 
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