Electric motor starting circuit

A circuit for controlling the voltage to a motor system including a permanent magnet D.C. moor connected between legs of a full bridge rectifier, said circuit comprising:

• a power supply means for applying power to a first leg of a full bridge rectifier of a motor system, said motor system including a permanent magnet D.C. motor and said full bridge rectifier;
• a first triac means connected to a second leg of the full bridge rectifier;
• a diac means connected to provide a diac output to the triac means;
• a first timing network including a first resistance and a first capacitance, said first timing circuit being connected to the second leg and to the diac means to provide a control voltage to the diac means;
• a second timing circuit including a second capacitance and a second resistance connected to the power supply means for charging the second capacitance responsive to actuation of the power supply means;
• an illumination source connected to the power supply means to receive a firing voltage in response to actuation of the power supply means, said illumination source further being connected in parallel with the second capacitance, thereby to receive said firing voltage only after the charging of the second capacitance;
• a first photocell positioned to receive light from the illumination source and a third resistance, connected in series as a shunt resistance path around said first resistance;
• and
• a means for maintaining the firing voltage across the illumination source, for as long as the power supply means remains actuated after said actuation;
• wherein said first timing network, when the first photocell is not receiving light from the illumination source, has a total resistance determined substantially by the first resistance and provides a first level of said control voltage to the diac means and causes a corresponding first diac output to the first triac means, substantially inhibiting the first triac means from conducting current, to apply a soft start voltage to the motor system;
• and
• wherein said first photocell, when receiving light from the illumination source, shunts current to reduce said total resistance, to provide a second level of said control voltage and a corresponding second diac output to the first triac means, said second diac output being at a higher voltage than said first diac output and enabling the first triac means to conduct current, thereby to apply a full running voltage to the motor system.