Power transistor protection detecting circuit

A power transistor protection detecting circuit comprises an output unit, a control unit, a diode, and a detecting module. The power transistor generates a first voltage due to internal resistance, and a second voltage after voltage-drop by crossing the diode. The second voltage will be divided by the voltage dividing circuit of detecting module, and then transmitted to the detecting module. The digital-to-analog converter will convert the second voltage from analog signal to a comparison value of digital signal. When the comparison value is greater than a limitation value, the control unit will cut off the control signal to disable the power transistor, so as to constitute the present invention.