Driving circuit for magnetic clutches for use with refrigerant compressors

A driving circuit for a magnetic clutch adapted for use with a refrigerant compressor, the magnetic clutch being of the type including a clutch plate arranged close to a driving member and fixed to a main shaft provided in said refrigerant compressor, and a magnetic coil operable upon energization thereof to cause frictional engagement of said clutch plate with said driving member, said driving circuit comprising:

• a starting switch connected to a power source;
• a first series circuit comprising a first resistance and a capacitor and having a predetermined time constant, said first resistance and capacitor being arranged to be energized upon closing of said starting switch;
• a first transistor having a base thereof connected to the junction of said first resistance with said capacitor, for conduction responsive to an output from said first series circuit;
• a second series circuit arranged in parallel with said first series circuit, said second series circuit comprising a second resistance and a third resistance, said first transistor having a collector and emitter thereof connected in series with said second resistance and third resistance for causing a change in voltage at the junction of said second resistance with said third resistance in response to the conduction state thereof;
• and a second transistor having a base thereof connected to the junction of said second resistance with said third resistance of said second series circuit and a collector and emitter thereof in series with said magnetic coil, respectively, and operable to energize said magnetic coil;
• wherein said magnetic coil is excited to an extent sufficient to cause engagement of said magnetic clutch during charging of said capacitor of said first series circuit after closing of said starting switch, and is excited to a lesser extent but sufficient to maintain the engagement of said magnetic clutch after saturation of said capacitor.

A driving circuit for a magnetic clutch adapted for use with a refrigerant compressor, the magnetic clutch being of the type including a clutch plate arranged close to a driving member and fixed to a main shaft provided in said refrigerant compressor, and a magnetic coil operable upon energization thereof to cause said frictional engagement of said clutch plate with said driving member, said driving circuit comprising:

• a starting switch connected to a power source;
• a series circuit comprising a first resistance and a capacitor and having a predetermined time constant, said first resistance and capacitor being arranged to be energized upon closing of said starting switch;
• a first transistor having a base thereof connected to the junction of said first resistance with said capacitor, for conduction responsive to an output from said series circuit;
• a second transistor having a collector and emitter thereof connected in series with said magnetic coil for energizing same;
• an oscillator having an output terminal thereof connected to the base of said second transistor and adapted to produce pulses with a predetermined pulses duty factor;
• and a second resistance connected to the junction of said second transistor with said oscillator;
• said first transistor having a collector and emitter thereof connected in series with said second resistance for causing a change in voltage at the base of said second transistor in response to the conduction state thereof;
• wherein said magnetic coil is excited to an extent sufficient to cause engagement of said magnetic clutch during charging of said capacitor of said series circuit after closing of said starting switch, and is excited to a lesser extent but sufficient to maintain the engagement of said magnetic clutch after saturation of said capacitor.