On BILLO's circuit. According to the Fairchild datasheet for a 2n2222a, Vce(sat) is 1V for "large" currents. That means that a maximum of 1V will be dropped by the transistor and a minimum of 4V will be dropped by the resistor. That puts the max collector current at 4V / 10R = 400mA. That means the resistor will be dissipating 4V * 400mA = 1.6W which will exceed the resistors max dissipation. The 2n2222a will be dissipating 1V * 400mA = 400mW which will exceed the derated maximum dissipation for the transistor as it heats up. Tell me where I got it wrong please.