# explaining circuit

Discussion in 'General Electronics Chat' started by Bill David, Oct 23, 2012.

1. ### Bill David Thread Starter New Member

Oct 23, 2012
5
0
Hi all

the attached picture shows the internal circuit of an operational amplifier LM324.

it actually measures the difference of voltage between 2 inputs.

can anyone of you help me with explaining how does the process of measuring this difference take place ?

Thank you

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Sep 20, 2005
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Sep 19, 2012
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4. ### ScottWang Moderator

Aug 23, 2012
4,925
777
The theory similar like Seesaw.

You can measure the V,I of the circuit.

Rc1,Rc2 use 10K. (Rc1-Q1,Rc2-Q2)
Re1,Re2 use 100Ω. (Re1-Q1,Re2-Q2)
R1=1K
Input1 → 22K → VR1M1 → +Vcc
Input2 → 22K → VR1M2 → +Vcc
+Vcc → +5V
-Vee → GND
VR1M1,VR1M2 - Variable resistor.

You could adjust the VR1M1, not adjust VR1M2, and measure the following Voltage, and calculating the current.
Adjust VR1M2, not Adjust VRM1, and measure the following Voltage, and calculating the current.

Vc2_Q2=
V_Rc1=
V_Rc2=
V_Re1=
V_Re2=
V_R1=

I_Rc1=V_Rc1/10K=
I_Rc2=V_Rc2/10K=
I_Re1=V_Re1/100Ω=
I_Re2=V_Re2/100Ω=
I_R1=V_R1/1K=

You can also change the resistors to the other values, and then adjust VR1M1,VR1M2, and do the measuring as above.

If you want to measure more value, then you can change +Vcc to 9V,12V,15V...30V

Last edited: Oct 24, 2012
5. ### ramancini8 Member

Jul 18, 2012
447
119
The schematic is not for a lm324 because the transistors are NPN.

6. ### kubeek AAC Fanatic!

Sep 20, 2005
4,688
806
The original schematic is not for anyhting because no opamp is that simple.