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In ammeter application, I am using CT for step down current value. primary current range is 150mA to 5A an i get secondary current 60uA to 2mA. what kind of circuitry i have to add for low current measurement before giving it to ADC of microcontroller?
A CT only works for AC. You will need a burden resistor on the secondary. This will generate both positive and negative input voltages for the AD (neg excursions have to be current-limited, clamped, and cannot be measured by the AD).
You will either have to do the peak finding in software, or build a op-amp full-wave rectifier circuit between the burden resistor and the AD input.