Adjustable active clamp circuit for high speed solenoid operation

Claim 2

A solenoid system having an adjustable clamp circuit for maximizing the repetition rate of a solenoid which comprises; a source of supply voltage connected to said solenoid; a driver transistor having a collector connected in series with said solenoid and supply voltage for driving said solenoid; a Darlington switching pair of transistors having an input terminal connected in circuit with said solenoid and the collector of said driver transistor; and a clamp circuit voltage divider connected between said input terminal and said switching transistors for biasing the transistors, said switching transistors being turned off during saturation of said solenoid driver transistor; said voltage divider being effective upon turn off of said driver transistor to clamp the resultant rising voltage at said input terminal and to forward bias said switching transistors on and provide a path for current in said solenoid to decay.

Claim 3

A solenoid system as defined in claim 1 wherein the voltage at said input terminal will be clamped at a level which is approximately the breakdown level of said driver transistor.

Claim 4

A solenoid system as defined in claim 1 wherein said voltage divider includes adjustable means for varying the clamp level of the voltage at said input terminal.

Claim 5

A solenoid system having an adjustable clamp circuit for maximizing the repetition rate of a solenoid which comprises; a source of supply voltage connected to said solenoid; a driver transistor having a collector connected in series with said solenoid and supply voltage for driving said solenoid; first and second switching transistors each having A base, emitter and collector, with the emitter of said first transistor being connected to the base of said second transistor; an input terminal for said switching transistors connected in circuit with said solenoid and the collector of said driver transistor, the collectors of said switching transistors being connected to said input terminal; and a clamp circuit voltage divider connected between said input terminal and the emitters of said switching transistors for biasing the transistors, said switching transistors being turned off during saturation of said solenoid driver transistor; said voltage divider being effective upon turn off of said driver transistor to clamp the resultant rising voltage at said input terminal at a level which is approximately the breakdown level of said driver transistor and to forward bias said switching transistors on and provide a path for current in said solenoid to decay.

Claim 6

A solenoid system having an adjustable clamp circuit for maximizing the repetition rate of a solenoid which comprises; a source of supply voltage connected to said solenoid; a driver transistor having a collector connected in series with said solenoid and supply voltage for driving said solenoid; first and second switching transistors each having A base, emitter and collector, with the emitter of said first transistor being connected to the base of said second transistor; an input terminal for said switching transistors connected in circuit with said solenoid and the collector of said driver transistor, the collectors of said switching transistors being connected to said input terminal; and a clamp circuit voltage divider connected between said input terminal and the emitters of said switching transistors for biasing the transistors, said switching transistors being turned off during saturation of said solenoid driver transistor; said voltage divider being effective upon turn off of said driver transistor to clamp the resultant rising voltage at said input terminal at a level which is approximately the breakdown level of said driver transistor and to forward bias said switching transistors on and provide a path for current in said solenoid to decay.

Claim 7

A solenoid system having an adjustable clamp circuit for maximizing the repetition rate of a solenoid which comprises; a source of supply voltage connected to said solenoid; a driver transistor having a collector connected in series with said solenoid and supply voltage for driving said solenoid; first and second switching transistors each having a base, emitter and collector, with the emitter of said first transistor being connected to the base of said second transistor; an input terminal for said switching transistors connected in circuit with said solenoid and the collector of said driver transistor, the collectors of said switching transistors being connected to said input terminal; and a clamp circuit voltage divider comprising a resistor, a diode and an adjustable potentiometer connected in series between said input terminal and the emitters of said switching transistors and also having a connection to the base of said first switching transistor for biasing the transistors, said switching transistors being turned off during saturation of said solenoid driver transistor; said voltage divider being effective upon turn off of said driver transistor to clamp the resultant rising voltage at said input terminal at a level which is approximately the breakdown level of said driver transistor, and also effective when the voltage across said diode and potentiometer exceeds the cut-in voltage of the junctions of said switching transistors to forward bias the switching transistors on and provide a path for current in said solenoid to decay.

Claim 8

A solenoid system having an adjustable clamp circuit for maximizing the repetition rate of a solenoid which comprises; a source of supply voltage connected to said solenoid; a driver transistor having a collector connected in series with said solenoid and supply voltage for driving said solenoid; first and second switching transistors each having a base, emitter and collector, with the emitter of said first transistor being connected to the base of said second transistor; an input terminal for said switching transistors connected in circuit with said solenoid and the collector of said driver transistor, the collectors of said switching transistors being connected to said input terminal; and a clamp circuit voltage divider comprising a resistor, a diode and an adjustable potentiometer connected in series between said input terminal and the emitters of said switching transistors and also having a connection to the base of said first switching transistor for biasing the transistors, said switching transistors being turned off during saturation of said solenoid driver transistor; said voltage divider being effective upon turn off of said driver transistor to clamp the resultant rising voltage at said input terminal at a level which is approximately the breakdown level of said driver transistor, and also effective when the voltage across said diode and potentiometer exceeds the cut-in voltage of the junctions of said switching transistors to forward bias the switching transistors on and provide a path for current in said solenoid to decay.

Claim 9

A solenoid system as defined in claim 5 and including means for blocking any current flow from said supply voltage back through said voltage divider when the driver transistor is on to protect the base-emitter junctions of said switching transistors from breakdown.

Claim 10

A solenoid system as defined in claim 5 wherein the rising voltage at said input terminal is clamped at a level dependent on the setting of said clamp circuit voltage divider.