Pulsewidth modulated pressure control system for chemical vapor deposition apparatus

A pressure control system utilized, for example, in connection with chemical vapor deposition apparatus, comprising in combination:

• a reduced pressure chamber;
• an exhaust pump coupled to said pressure chamber;
• an electric motor coupled to said exhaust pump for powering said pump;
• controller means operable in response to the difference between the actual pressure within the pressure chamber and the desired pressure therein and generating a pulsewidth modulated pulse train whose pulsewidth varies in accordance with said difference;
• pulsewidth modulation to DC converter means responsive to said pulsewidth modulated pulse train and being operable to generate a control signal whose amplitude varies in accordance with said pulsewidth;
• and
• motor control means coupled to said electric motor and being responsive to said control signal and operable to vary the speed of said motor thereby powering said exhaust system to control the pressure within said pressure chamber.