- #1
Jdo300
- 554
- 5
Hello,
Lately, I have been venturing into the wonderful world of analog circuits and am currently working on debugging a circuit I made which is supposed to convert the current flowing through a very small sense coil I wound, into a voltage signal that I can read with my scope. The circuit consists of a simple Current to Voltage converter op-amp circuit, where, in my case, the Op-amp outputs 1V for every 1mA of current flowing through the input side (See attached circuit).
The circuit consists of a LT1206 current feedback op-amp (I used this because it is the only fast op-amp I happen to have in my collection). To test the circuit out, I used my function generator with a 1k resistor in series so that I could limit the current into the circuit. I then clamped my DC-50MHz current probe on the input so that I could measure the actual input current to the circuit. The voltage output from the op-amp was then shown on the scope also for comparison and I noted that with a sine, triangle and square wave that the circuit worked flawlessly within the bandwidth of 0Hz to 15Mhz before significant attenuation of the output signal occurred.
However, once I attached the small sense coil to the inputs (as shown in the diagram), the op-amp started drawing over 100mA through both the input rails and oscillating randomly at about 47Hz more or less. Thinking that the op-amp didn't like the low resistance of the coil, I added the 10k resistor I used with the function generator and it still did the same thing though the frequency changed. I think took the coil out completely and just put the resistor across the leads. Even in that case, it still was drawing a bunch of current. I'm sure there is probably something silly that I am missing here so I was hoping someone here could give me some insight into what I'm missing here .
Thanks,
Jason O
Lately, I have been venturing into the wonderful world of analog circuits and am currently working on debugging a circuit I made which is supposed to convert the current flowing through a very small sense coil I wound, into a voltage signal that I can read with my scope. The circuit consists of a simple Current to Voltage converter op-amp circuit, where, in my case, the Op-amp outputs 1V for every 1mA of current flowing through the input side (See attached circuit).
The circuit consists of a LT1206 current feedback op-amp (I used this because it is the only fast op-amp I happen to have in my collection). To test the circuit out, I used my function generator with a 1k resistor in series so that I could limit the current into the circuit. I then clamped my DC-50MHz current probe on the input so that I could measure the actual input current to the circuit. The voltage output from the op-amp was then shown on the scope also for comparison and I noted that with a sine, triangle and square wave that the circuit worked flawlessly within the bandwidth of 0Hz to 15Mhz before significant attenuation of the output signal occurred.
However, once I attached the small sense coil to the inputs (as shown in the diagram), the op-amp started drawing over 100mA through both the input rails and oscillating randomly at about 47Hz more or less. Thinking that the op-amp didn't like the low resistance of the coil, I added the 10k resistor I used with the function generator and it still did the same thing though the frequency changed. I think took the coil out completely and just put the resistor across the leads. Even in that case, it still was drawing a bunch of current. I'm sure there is probably something silly that I am missing here so I was hoping someone here could give me some insight into what I'm missing here .
Thanks,
Jason O