A BJT is wired to the output of a variable duty cycle oscillator In Figure 1. The oscillator turns the BJT on and off at a constant frequency. This results in a square-wave voltage that can be applied to the connected load. The average voltage applied to the load would depend on the pulse duration. When the BJT is on, its resistance will be zero and it won't generate any power. The load was tested to have a no-load current of 70 mA