Simple high side current detector using "simple" parts?

[John B]

I just used a ZXCT1009 in a design, with pretty similar requirements. Between 50-500mA current sensing, doesn't need to be very precise.

It's a SOT23 device which will output a current proportional to the voltage developed across a sense resistor, in this case it will be a 0.1 ohm sense resistor. The benefits of an integrated device are things like bandwidth, linearity and dynamic range.

That output current then develops a voltage across a resistor to ground, in this case you might use it with a comparator with hysteresis to trigger your 100mA threshold