- #1
Jdo300
- 554
- 5
Hello All,
I have yet another puzzling question for you all. As I am working on the design for this DDS sine wave generator, I am contemplating a means of accurately measuring the amount of current being drawn from the output into the load. For my application, I am mainly going to be dealing with inductive loads so I don't simply want to put a 50Ohm resistor or something on the output, but rather I want to drive a coil directly with the possibility of regulating the current output that comes out. At the moment, I have digital control over the amplitude and offset of the sine wave, which has an max amplitude of 20V pk/pk, with a max short circuit current of 100mA (possably up to 250MmA with a change of op-amp ICs).
My thinking is that if I could somehow accurately measure the magnitude of the current flowing through the load, that I could digitally adjust the amplitude to regulate the current to some desired value. But the challenge here is that the output sine wave has a frequency range of 0.2Hz up to 20MHz! I haven't done much research in depth in current measurement techniques but some that I am familliar with are magnetic hall effect sensors, current shunt measurements, and RMS to DC converter ICs. Each of these solutions seems to have it's pros and cons but I'm wondering if there is a technique which would work across such a large bandwidth?
I have been pondering this problem a bit and so far, my best thought is to use a shunt resistor and op-amp setup to measure the current magnitude and then send it through an adjustable low-pass filter to get a DC value that can be read by the uC ADC. The only problem is that I might end up with a ridiculous filter circuit arrangement with 10 or more switched RC combinations just to get reasonable measurements. Does anyone know of any better (or simpler) way to do something like this?
Thank you,
Jason O
I have yet another puzzling question for you all. As I am working on the design for this DDS sine wave generator, I am contemplating a means of accurately measuring the amount of current being drawn from the output into the load. For my application, I am mainly going to be dealing with inductive loads so I don't simply want to put a 50Ohm resistor or something on the output, but rather I want to drive a coil directly with the possibility of regulating the current output that comes out. At the moment, I have digital control over the amplitude and offset of the sine wave, which has an max amplitude of 20V pk/pk, with a max short circuit current of 100mA (possably up to 250MmA with a change of op-amp ICs).
My thinking is that if I could somehow accurately measure the magnitude of the current flowing through the load, that I could digitally adjust the amplitude to regulate the current to some desired value. But the challenge here is that the output sine wave has a frequency range of 0.2Hz up to 20MHz! I haven't done much research in depth in current measurement techniques but some that I am familliar with are magnetic hall effect sensors, current shunt measurements, and RMS to DC converter ICs. Each of these solutions seems to have it's pros and cons but I'm wondering if there is a technique which would work across such a large bandwidth?
I have been pondering this problem a bit and so far, my best thought is to use a shunt resistor and op-amp setup to measure the current magnitude and then send it through an adjustable low-pass filter to get a DC value that can be read by the uC ADC. The only problem is that I might end up with a ridiculous filter circuit arrangement with 10 or more switched RC combinations just to get reasonable measurements. Does anyone know of any better (or simpler) way to do something like this?
Thank you,
Jason O