Fast relay turn on circuit with low holding current

Claim 1

A drive circuit responsive to an applied electrical signal for controlling the actuation of a relay having an energizing coil with a first and a second end arranged across an output stage of the circuit, said circuit being adapted to be energized by a D.C. voltage present between a positive and a negative potential, said circuit comprising; a charging circuit comprising a serially-arranged first resistor, a capacitor, and a first diode, said first resistor having a first end connected to said positive potential, said first diode having its cathode connected to said negative potential, a second and a third diode, said second and third diodes each having their cathodes connected together at a first end, said second diode having its anode connected to a second end of said first resistor and to a first end of said capacitor, said third diode ectrode being connected to said negative potential, said second electrode being adapted to receive said electrical applied signal, and said third electrode being coupled to the connected cathodes of said second and third diodes, said first switching means being arranged so that (i) when in its nonconductive state it allows said capacitor to be charged to a voltage substantially equal to said D.C. voltage and (ii) upon the occurrence of said applied electrical signal it is rendered conductive and supplies a path to forward-bias said second diode and initiate a discharge of said capacitor; a second switching means having first, second and third electrodes, said first electrode being connected to a second end of said capacitor, said second electrode being coupled by a second resistor to said negative said energizing coil for dissipating inductive stored energy; said charging circuit, said second and third diodes, and said first and second switching means being arranged so that upon the occurrence of said applied electrical signal, both of said first and second switching means are rendered conductive and an initial voltage equal to the sum of the charged potential of said capacitor and said D.C. voltage is applied across said energizing coil to actuate said relay.