A drive unit has a control power supply, a power source (1) producing direct current to one or more inverters (2), an energy storage (C) arranged at the power source (1) output, and a discharge circuit (8,10) for discharging the energy stored in the energy storage (C) and including a power resistor (8). Switches (5, 6) are arranged between the power source (1) and energy storage (C) and in default position when there is no control power in the drive unit. The power source (1) is disconnected and the energy storage (C) discharged through the power resistor (8) when the switches (5, 6) are in default position.