The functional description of how a loadswitch works is as follows: A small input current applied at the base of Transistor Tr2 switches a high output current at the collector of Transistor Tr1. Let’s explain this circuit step by step. A small base current, which is less than 1 milli Amp, drives Transistor Tr2. Transistor Tr2 drives Transistor Tr1. Resistor R3 sets Transistor Tr1’s base current. The higher Transistor Tr1’s base current, the lower the resulting voltage drop, which is VCEsaturation. And the lower the voltage drop, the higher the circuit’s power dissipation. Remember, power dissipation is equal to the input voltage times the base current of Transistor Tr1.