I am working on a non-inverting opamp amplifier, using OPA2134, to amplify the 150mV peak signal (1 kHz sine wave playbacked) from a phone audio jack to ~4V peak sine wave, that drives a LED using a N-channel MOSFET. My goal is to turn on the LED by playing music from the phone.
I have biased the non-inverting input of the opamp to 2.5V using a simple voltage divider from 5V. I want the opamp to work with a single supply (+5V).
List of signals:
- OPA2134 V+ - +5V
- OPA2134 V- - 0V (GND)
- Input Vin- 150mV peak, 1kHz sine wave.
- Desired output - ~4V peak, 1kHz sine wave.
- Bias voltage - 2.5V
The input is ac-coupled, gain is set to unity at dc, and the output is also ac-coupled. I am currently not concerned with the noise from bias divider.
If the input is not connected to the phone audio jack, the inpt is floating, and the non-inverting input of the opamp is at 2.5V, the output of the opamp is also at 2.5V and the output after the output capacitor is 0V.
If however i connect the input to the audio jack the bias voltage at the non-inverting input drops to 0V. If then i play audio from the phone, the noninverting input has a signal of 1kHz 150mV peak wave instead of 2.35V to 2.65V and there is nothing at the output, since the opamp can not work with an input signal so close to it's rail.
Here is my circuit, that simulated in falstad operates as desired. For simplicity I marked the opamp max voltage to 5V and min voltage to 0V in falstad. I know that in real life, the OPA2134 can not operate rail-to-rail. The signal on the left is the input (-150mV to 150mV), signal on the right is the output (0V - 5V)