seek suggestions on voltage follower

[WeiC]

I am using an Op-Amp voltage follower coupled to a potentiometer in order to provide a variable voltage for my sensor

(a photodiode purchased together with its own pre-Amp).  When the sensor is not hooked up with the voltage follower, I can

get very decent varying voltage outputs simply by swiping the potentiometer, which means that the voltage follower works in

this case.  However, when the sensor is hooked up with the follower, the output voltage from the follower is invariant, regardless

how I swipe the potentiometer, which basically tells me that the follower does not work in this case.

I have tried several different Op-Amps, they all give me the same results. 

Any suggestions?  How can I get the voltage follower to work? 

[OStep]

WeiC,

Your voltage follower is only a voltage follower if you operate the op-amp within its limits. It may very well be that your sensor load is too high, sinking more current from the op-amp than the it allows (all real op-amps and most of their SPICE models have a current limiting functionality to prevent damage to internal circuitry). In that case, you don't want to use a plain op-amp to buffer(or power) your sensor.

Perhaps that answers your question

[WeiC]

Max,

thanks for your suggestions but it occurs strange to me that my sensor only pulls ~15 mA current when it works normally.

It is hard for me to think this 15 mA is beyond the limit of the Op-Amp, among the Op-Amp I tried, they are LM324AN,

LF347N, LM348N, LT1014ACJ.

Wei

[OStep]

attach your circuit please

[WeiC]

Max,

Here is the circuit schematic attached.  The sensor is a position-sensitive photo detector with its own pre-Amp

voltage follower is used to provide a biasing voltage for the diode sensor.  There are additional pinouts from the

sensor, among which I only draw the pinout connection with +15V power supply and the voltage follower.

Wei

[OStep]

I dont know anything about your load and exactly which op-amp model you're using (there are several model for LM324AN). You must attached your .ms10 file

[WeiC]

Hi Max,

here you can find a block diagram for the sensor circuit.  Any suggestions?