- #1
John Raines
I'm a mechanical engineer by trade, but I am working on developing a testing apparatus that oscillates a neodymium magnet between two solenoids offset by by a 180 degree phase shift. Basically, one solenoid pushes, the other pulls. To get this, current is essential. I need each solenoid to get a minimum of 750mA. The problem is, the old function generator has a safety feature to shut off current if it exceeds around 500mA.
To get around this, I've set up an inverting op-amp circuit using a 741 op-amp. This kills my current output, but let's me stack energy in voltage. My plan is to push this voltage through a step-down transformer to convert my volts to amps. My understanding is that it's akin to gear ratios: low speed/high torque gets converted to high speed/low torque on a step-down. So I'm wanting high voltage/low current to step down to low voltage/high current. I've crunched the numbers, and my step doesn't seem unreasonable: 70:1. However, when I run the simulations in PSPICE, it shows my circuit only outputting a total of 400mA to my solenoids. Is there something fundamental that I am missing? All I am trying to do is to put a 10Hz AC signal with a current magnitude of 1.5A sent to 2 parallel solenoids.
Also, PSPICE is predicting that this set up leads to a large current coming out of the op-amp. I thought this was impossible? I thought op-amps bump voltage, but kill current? Was I told wrongly on this? Because it would be delightfully simple to just run the output of the op-amp to the solenoids.
Thanks for the help!
-John
To get around this, I've set up an inverting op-amp circuit using a 741 op-amp. This kills my current output, but let's me stack energy in voltage. My plan is to push this voltage through a step-down transformer to convert my volts to amps. My understanding is that it's akin to gear ratios: low speed/high torque gets converted to high speed/low torque on a step-down. So I'm wanting high voltage/low current to step down to low voltage/high current. I've crunched the numbers, and my step doesn't seem unreasonable: 70:1. However, when I run the simulations in PSPICE, it shows my circuit only outputting a total of 400mA to my solenoids. Is there something fundamental that I am missing? All I am trying to do is to put a 10Hz AC signal with a current magnitude of 1.5A sent to 2 parallel solenoids.
Also, PSPICE is predicting that this set up leads to a large current coming out of the op-amp. I thought this was impossible? I thought op-amps bump voltage, but kill current? Was I told wrongly on this? Because it would be delightfully simple to just run the output of the op-amp to the solenoids.
Thanks for the help!
-John