LM324: Differential Amplifier

Dheeraj yadav

Part Number: LM324
Other Parts Discussed in Thread: , INA333

I tried to use differential amplifier configuration of LM-324N Opamp but at the time of simulation of circuit in TINA i found some result which i don't able to found how will they came.

1) All 4 resistance in Wheatstsone is 100Ohm, and Amplifier Gain is R3/R1=10 So Opamp result should be o volt but i got 69.19mV and also LM324 input offset voltage is 3mV at Vcc=5V.

2) when my one of resistance is 138.5Ohm then differential input is 383.92mV so Opamp Output must be 3.83V after amplification but it is 3.47Volt.

Both the circuti image attached below.

over 5 years ago

0 Ron Michallick over 5 years ago

TI__Guru**** 151036 points

Hello Dheeray,

The voltage in the first example is high because the feedback resistor requires the op amp to sink current. If output was 0V, the sink current needed would be 227uA ( 2.5V/11k). I would expect closer to 600mV due to the output stage in LM324. See figure 1 in data sheet.

The voltage in the second example is low because the VOH (voltage output high) is about VCC -1.2V (with feedback load), see figure 2 in data sheet. The model is more pessimistic.

Try the LM324LV instead. Its output is rail to rail. Also increase the resistances in the diff amp because they are a load for the bridge.

See application note for LM324 here http://www.ti.com/lit/pdf/SLOA277?jktype=tech_docs, this application note does not apply to LM324LV.