# Output of op-amp getting as a constant voltage of 500 mV in PROTEUS

Earlier i tried generating a +5V to -5V square wave using an op-amp as an astable multivibrator . The wave had a frequency of 1 kHz. The op-amp was given +Vcc of 5.5V and -VCC of -5.5V. I got the desired square wave at the output. Now i want to generate 0 to 5V square wave using the same circuit. However when I tried simulating the circuit taking -Vcc as 0V im getting a constant voltage of 500mV. Can you please help me to troubleshoot the circuit. The op-amp I have used is an LM324.

• Your opamp is trying its hardest to swing low, but the lowest it can go is 500mV (a little above the negative rail). At that point the junction of R1/R2 is about 250mV, so the opamp neg input is still higher than its pos input so the opamp is forever stuck low. In your original design the opamp was free to swing all the way down to -4.5V, and R1/R2 would then set the pos input to about -2.2V, allowing the opamp to flip when C1 voltage reached -2.2V. Commented Aug 27, 2020 at 0:06
• Can you suggest a circuit employing op-amp i can use to get a 0 to +5V pulsating DC waveform at 1KHz? if not, please suggest me the sources which i could use to figure out the connections for op-amp. Commented Aug 27, 2020 at 7:36