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# What is wrong with this LM324

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#### rob1310

##### Newbie level 2
Hello..

I am trying to build an Amp crcuit for an input voltage range between 28mV-59mV from a transducer.

I am using the LM324 amp for this purpose. I built the circuit on a PCB later on to bang into a few problems. SO now i am trying to understand the op-amp and itfunctions.

I built a basic amp circuit
Rf = 1000 Ohm;
R1 = 33 Ohm

input is given too 2nd pin of lm324 which has to result in a negative ouput
but the output obtained is show in this link below..

the circuit is show as

Can you please send me ur feedback as to what basic connections have to be done on a LM324..

Why am i not getting a negative voltage output which is designed according to the GAIN.. Av = - Rf / R1..

Added after 17 minutes:

Voltage suply for OP-AMP = 9v

Input voltage to pin 0.15V at pin no 2 .. the inverting input pin of LM324//

It's very simple, you can't get a negative output voltage without a negative respectively bipolar supply.

### rob1310

Points: 2
thank you sir for ur reply.. but what happens to the calculated gain..

Does it mean that the value 0.12v is some scrap value. > ?

The output swing of your amplifier is limited based on loading and rail voltages. You are seeing it swing towards your lower rail but it can't go fully to zero volts because of the nature of the push pull output stage in the amplifier.

You can redesign the amplifier circuit to work in a non-inverting amplifier mode. Note that the resistor ratios may change due to the different closed loop gain. May want to add a resistor in series with the amplifier positive input equal to 33||1000 ohms (or Rfb||Rin) to insure the impedance looking out of the inputs is the same and reduce input offset voltage errors. The LM324 doesnt have input bias current compensation.

### rob1310

Points: 2
i have one doubt on ur setup
where did u connect +Ve input pin???

iam not sure that LM324 supports 1K load.. Please check Voh & Vol of the device for 1K load. the 0.12V which is the output might be equal to Vol for 1K load....

Please understand the question from the OP:
1) The opamp is inverting, its DC input reference voltage is 0V (+ input pin) and its power supply negative supply voltage is also 0V (no negative supply).
2) Its gain is 1000/33= 30.3 times.
3) Its input is +0.15V so why isn't its output -4.5V?

Because it does not have a negative supply!

matrixofdynamism

Points: 2