Hi,

I am using an Arduino Uno to output a PWM signal. In order to amplify this signal I am using an operational amplifier OPA541AP. I've attached the circuit design.

The problem is that the output of the op amp seems to controlled by the power supply and not the input from the arduino. I've connected 10V to +Vs and 0V to -Vs. The output pin of the op amp has 6.9V no matter the input from the arduino. Even when I ground the input pin the output pin has 6.9V.

I've set the gain of the op amp to 5 so I'm using a 20k and a 5k resistor.

Could you tell me where I'm going wrong?

Thank you.

 

Nice diagram. But it doesn’t show what the connections actually are. Can you draw a schematic with the op amp connections labeled?

 

PWM is a digital signal, so it generally doesn't work well to amplify it with an analog op amp due to its limited frequency response.
What is the PWM frequency and what output voltage do you want?

 

I also connected a RC filter to the PWM output but the input still does not influence with the output. The PWM is connected to pin 3 of the arduino so it's about 980 Hz. The output voltage I need is in the range of 5V - 15V.

 

Just to check I also sent a 3.3V dc output from the arduino power pin instead of a PWM signal. Still no change in the op amp response.

 

Still no change in the op amp response.

Then you apparently have a wiring error.
Post a schematic.

 

Hello,

You have not used the current limiting input of the OPA:



I would also connect pin 3 and 4 to V- and pin 10 and 11 to V+ as decribed in the datasheet.
The pins 5 and 7 should also be connected together.

Bertus

 

What are you going to do with OpAmp output ?

Keep in mind an OpAmp, unless it is high speed, will slow down the Tr and Tf
of the amplified output. In this case 10V / uS for the 541 worst case.

If your G is 5, your Arduino is running on 5V, then you have to slew 25 volts, or
2.5 uS will be your Tr, Tf.



Regards, Dana.

 

I second bertus’ comment. Per the data sheet, pins (3,4) should be connected together as well as pins (5,7) and (10,11). If you aren’t wiring per the datasheet, no one can guarantee how the op amp will behave.

I think that’s your problem. Your feedback resistor may only be connected to part of the op amp internal circuit. And likewise, your input is only connected to part of the circuit.

Additionally, what are you trying to amplify? The PWM signal? Assuming that, then “WIREPAD2.54/(unintelligible)” must be ground. Correct?

I don’t know how anyone can help, when the device is midwifed IMHO