Hi,
I am trying to make a circuit that would convert a pwm signal (0-5v) to a 12v to -12v analog signal. Schematic and the layout is attached. There have been several changes made to the initial circuit, and the changes are marked in the diagrams.
The circuit consists of a differential amplifier and a Sallen Key filter that suppose to get two pwm signals with complement duty cycles and output analog voltage. Dual channel LT1678 opamps are used for both Diff.amp and Sallen Key.
Issue.
We powered up the board, without any PWM inputs to the board we checked all the rails; voltage levels are fine. But when we touched the opamp it is pretty damn hot. Also theoretically when 0V(no pwm) is given into both inputs, the output should be 0v. But we are measuring output voltage around -13.5v, this is strange.
I double checked the circuit, there's nothing wrong with soldering and no short circuits. I'm not sure what's wrong here. I have another spare opamp, but before I swap it and test, i want to double check it.
I would really appreciate if someone could help me debug this.
Thanks in advance.
I am trying to make a circuit that would convert a pwm signal (0-5v) to a 12v to -12v analog signal. Schematic and the layout is attached. There have been several changes made to the initial circuit, and the changes are marked in the diagrams.
The circuit consists of a differential amplifier and a Sallen Key filter that suppose to get two pwm signals with complement duty cycles and output analog voltage. Dual channel LT1678 opamps are used for both Diff.amp and Sallen Key.
Issue.
We powered up the board, without any PWM inputs to the board we checked all the rails; voltage levels are fine. But when we touched the opamp it is pretty damn hot. Also theoretically when 0V(no pwm) is given into both inputs, the output should be 0v. But we are measuring output voltage around -13.5v, this is strange.
I double checked the circuit, there's nothing wrong with soldering and no short circuits. I'm not sure what's wrong here. I have another spare opamp, but before I swap it and test, i want to double check it.
I would really appreciate if someone could help me debug this.
Thanks in advance.
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