AC current measurement - input protection circuit
For those currents the burden voltage is in the +0.5 to -0.5V range resulting in an input voltage between 1V - 2V. If the current exceeds those limits you want a clamping device with a forward voltage of less than 0.5V, so the 1N4148 wont work. Shottky diodes have a lower forward voltage. Use R4 to limit the current flowing trough the clamping device. Look at the V-I plot of a diode to determine at which current you get the desired forward voltage.