Current measurement circuit

here is an opamp circuits that can measure current through a load
at output voltage will be equal to the amount of current

Hi Majoka, which current are u measuring in each circuit? (current through which resistor?) Is it possible to use this circuits to measure the current of a uP?

@ MPU_Beginner
microprocessor has too low currents
this circuit has less efficiency at low currents
for that u has to use maxim current measuring chips

Actually I wanted to build my own circuit using a transimpedance amplifier, as suggested above in this thread, which output voltgae is qual to the feedback resistor multiplied by the current to be measured.
Is there any way to apply that to current measurement for uP?
Thx

Sorry Rumman, I did not really figured out what do you mean, it would be really awesome if you can post a diagram and mention exactly how does your circuit looks like...

MPU_Beginner

hey bro here is my circuit ,

I used ,,
Rf = 1 mega ohms
powr supply=+/- 5 volts

and Cf ,, I am still working on to find its exact value for stability

one more change in above circuit that I connected cathode to inverting terminal of op-amp and anoode is grounded ,,so that current flows from right to left in feedback resistor branch and I get a positive output vltg ,,

Thx rumman so much for your postings. I'm convinced that this circuit would not work for measuring currents through uP because, I would connect the supply pin of my uP to Vbias, and the pin which is supposed to be connected to GND, according to ur circuit, has to be connected to (-) IN of the amp, and hence no current can flow through the uP because at (-)IN of the amp we have a virtual gnd and no true ground.
Ur circuits definitely works for diods.

Thx

The transimpedance amp is to be used with current output devices like photo-diodes, photo-transistors,DACs and the sort.Moreover it's prone to instabilities as any stray capcitances at the input would make the opamp oscillate.

For your application the shunt method will have to be used.The only point of concern is the wide dynamic range needed for measuring 1uA-100mA.
A log-amp or some auto range-selection mechanism would have to be looked into.

hi shashi after long time .............

Could you suggest any circuit for me, using a shunt to cover this wide range of current?
I tried this one, using TI shunt monitor, but it doesn't work for currents lower then 1mA :-(
Which caracteristics do i have to take care about while choosing the op amp and the sense amplifier? (apart from the gain)? The problem is, in the data sheets of the sense amplifiers it is mentioned that they support very low sense voltages, but this did not work for me, for currents lower then 1mA
Do you have any suggestion for me?
Thanks

The transimpedance amp is to be used with current output devices like photo-diodes, photo-transistors,DACs and the sort.Moreover it's prone to instabilities as any stray capcitances at the input would make the opamp oscillate.

For your application the shunt method will have to be used.The only point of concern is the wide dynamic range needed for measuring 1uA-100mA.
A log-amp or some auto range-selection mechanism would have to be looked into.

sashijoseph