Hi all.
I'm strugling with PWM to voltage converter. PWM duty 0-100%, ampl. 5V, freq.300Hz-3kHz. PWM signal is produced as High Side Driver (pull down resistor at converter's side). Current capability up to 2mA .
Please help me to debug the following circuit which is supposed to convert PWM to voltage (there can be also 0-5V voltage at the input to the circuit- in this case the circuit must serve as voltage follower ).
The circuit should be working well (tested by a friend of mine) with Opamp LMC662CN used with unipolar supply (http://uk.rs-online.com/web/p/op-amp/5344232/). Anyway, I'm not able to make a test as I dont have this OpAmp.
I was forced to used OpAmp TLC271, supplied with unipolar 12V. This is not a rail2rail kind but should it mind when high Vdd used?!
In simulation works quite fine.
Reality differs. The voltage following is ok.
PWM to voltage conversion is NOK. the difference is huge (50%PWM is not 2.5V but about 2.63V, 10% PWM is about 0.7V and not the expected half volt). Vcc always 5V+/- 0.002V.
I'm already desperate and dont understand why there is the offset. ANy thoughts why LMC662 works and TLC271 doesn't? Any important parameter I overlooked? Please could any of you propose an alternative OpAmp which would work and explain why.
Thanks a lot.
I'm strugling with PWM to voltage converter. PWM duty 0-100%, ampl. 5V, freq.300Hz-3kHz. PWM signal is produced as High Side Driver (pull down resistor at converter's side). Current capability up to 2mA .
Please help me to debug the following circuit which is supposed to convert PWM to voltage (there can be also 0-5V voltage at the input to the circuit- in this case the circuit must serve as voltage follower ).
The circuit should be working well (tested by a friend of mine) with Opamp LMC662CN used with unipolar supply (http://uk.rs-online.com/web/p/op-amp/5344232/). Anyway, I'm not able to make a test as I dont have this OpAmp.
I was forced to used OpAmp TLC271, supplied with unipolar 12V. This is not a rail2rail kind but should it mind when high Vdd used?!
In simulation works quite fine.
Reality differs. The voltage following is ok.
PWM to voltage conversion is NOK. the difference is huge (50%PWM is not 2.5V but about 2.63V, 10% PWM is about 0.7V and not the expected half volt). Vcc always 5V+/- 0.002V.
I'm already desperate and dont understand why there is the offset. ANy thoughts why LMC662 works and TLC271 doesn't? Any important parameter I overlooked? Please could any of you propose an alternative OpAmp which would work and explain why.
Thanks a lot.
