A gas generator for a protective airbag includes at least one pressurized gas chamber, a first actuator arranged so as to open the pressurized gas chamber, and a diffusion chamber including at least one diffusion hole defining a communication surface. Outside the diffusion chamber, the gas generator includes an obturator having a second actuator. The obturator is arranged in a first position in which it defines a first diffusion surface. The second actuator is arranged so as to allow it to go into a second position in which it defines a second diffusion surface.