Op Am Gain Max400

[Mike Blankenship]

I have a 2 stage circuit. The 1st stage is a basic Voltage follower that
works good. It out puts
100mv. My problem is with the second stage which I am trying to gain by 10

Stage 1 >>>> 100mv
Stage 2 MAX400

Pin1 Vos Trim Not used
Pin2 -IN
Pin3 +IN
Pin4 V- (GND)
Pin5 NC
Pin6 Vout
Pin7 V+ (5V)
Pin 8 Vos Trim Not used

Pin 6 (vout) is connect to Pin2 (-IN) with a 100K resistor. Pin2 (-IN) is
connected
to ground via a 10K resistor. This should give me a gain of 10 and I should
see a
Voltage of 1Volt at the put put Pin6 (Vout)

I have a clean signal going into Pin3 (+IN) of 100mv .. ~5mv noise. The
output always reads ~
4.85 volts. Any insight would be appreciated.

Thanks

mike

 

[kansas_ray]

I have a 2 stage circuit. The 1st stage is a basic Voltage follower that
works good. It out puts
100mv. My problem is with the second stage which I am trying to gain by 10

Stage 1 >>>> 100mv
Stage 2 MAX400

Pin1 Vos Trim Not used
Pin2 -IN
Pin3 +IN
Pin4 V- (GND)
Pin5 NC
Pin6 Vout
Pin7 V+ (5V)
Pin 8 Vos Trim Not used

Pin 6 (vout) is connect to Pin2 (-IN) with a 100K resistor. Pin2 (-IN) is
connected
to ground via a 10K resistor. This should give me a gain of 10 and I should
see a
Voltage of 1Volt at the put put Pin6 (Vout)

I have a clean signal going into Pin3 (+IN) of 100mv .. ~5mv noise. The
output always reads ~
4.85 volts. Any insight would be appreciated.

Thanks

mike

The gain is actually 11 (1+100K/10K) but this is not your problem.

The MAX400 is only rated down to +/- 3V on its supplies. You are trying to
run it on a single +5V supply and ground.

If you have a -5V supply, connect it to pin 4 (after removing ground) and
see what happens.

Regards,
Ray

 

[Mike Blankenship]

I was using an OP-Amp whic did not have rail to Rail Inputs. I was tring to
measure 200mv
But the Common mode range was above 1 Volt on the lower end.

Thanks
all for the input