- #1
Kazkek
- 5
- 0
Good afternoon PhysicsForums! I have a design for a voltage controlled current source. I've included the circuit diagram. The basics of the design is that I have an AC voltage and a DC Voltage summed then passed through a 1MOhm resistor to give me a current on the order of 1 microAmp. This of course is determined by the amount of applied DC voltage. The DC voltage is applied via a DAQ board and the MAX4622 analog chip is controlled by the digital DAQ board signals.
My problem with the circuit is that I have built it on a bread board and everything is fine but after I've assembled it on a pcb I am getting an odd voltage drop on the -15V supply to the opamps. If I put the multimeter across the 15V and ground at the power supply, I get 15V but when I do the same at the -15V it reads 1.4V. I am unsure of what component is causing this issue. Removing the components is much harder on the pcb and like I said it works well on the bread board. I've replaced the AD797 opamps and the MAX4622 chips but I still get the same issue. I also have tried different power supplies and the issue is persistent.
Resistors, MAX4622 and LT1990 are surface mount components if that helps any.
I guess what I mostly am looking for are points at where I should try testing the components and what voltages I should expect.
Sorry for the image link instead of uploading. I was having issues re sizing the image file with ability to read the text.
Voltage Controlled Current Source (IMGUR)
My problem with the circuit is that I have built it on a bread board and everything is fine but after I've assembled it on a pcb I am getting an odd voltage drop on the -15V supply to the opamps. If I put the multimeter across the 15V and ground at the power supply, I get 15V but when I do the same at the -15V it reads 1.4V. I am unsure of what component is causing this issue. Removing the components is much harder on the pcb and like I said it works well on the bread board. I've replaced the AD797 opamps and the MAX4622 chips but I still get the same issue. I also have tried different power supplies and the issue is persistent.
Resistors, MAX4622 and LT1990 are surface mount components if that helps any.
I guess what I mostly am looking for are points at where I should try testing the components and what voltages I should expect.
Sorry for the image link instead of uploading. I was having issues re sizing the image file with ability to read the text.
Voltage Controlled Current Source (IMGUR)