Variable time ratio control having power switch which does not require current equalizing means

Claim 2

A control for supplying variable time ratio pulses from an electrical source to a load including, in combination, a power switch between said source and said load having a plurality of paralleled power transistors with commoned collectors and commoned emitters, each said power transistor having a forward current transfer ratio characteristic with a portion wherein said ratio decreases abruptly with increase in collector current, a substantially constant current base drive source for said power switch coupled to the base of each of said power transistors and providing substantially constant current output sufficient to cause each of said powEr transistors to operate on said portion of said characteristic wherein said forward current transfer ratio decreases abruptly with increase in collector current, and means for periodically removing said base drive source to selectively vary the time ratio of pulses from said electrical source supplied by said power switch to said load, whereby external current equalization means are not required to balance the collector current levels in said plurality of paralleled power transistors.

Claim 3

A control in accordance with claim 1 wherein each of said power transistors is in a Darlington circuit with a base drive transistor and said base drive source is coupled to the base of said base drive transistor.

Claim 4

A control in accordance with claim 1 and including a plurality of diodes each of which couples said base drive source to the base of one of said power transistors.

Claim 5

A control in accordance with claim 1 wherein each of said power transistors is of the single-diffused silicon type.

Claim 6

A control in accordance with claim 1 wherein each of said power transistors has a characteristic wherein collector-to-emitter saturation voltage increases with increase in collector current.

Claim 7

A control in accordance with claim 1 wherein each of said power transistors has a characteristic wherein base-to-emitter voltage increases with increase in collector current.

Claim 8

A control in accordance with claim 3 wherein each of said power transistors has a characteristic wherein collector-to-emitter saturation voltage increases with increase in collector current and also has a characteristic wherein base-to-emitter voltage increases with increase in collector current.

Claim 9

A control in accordance with claim 1 wherein the emitter-collector circuit of a clamping transistor is in shunt to the output of said base drive source, and said means for periodically removing said base drive source includes means for applying variable time ratio pulses to the base of said clamping transistor to shunt current away from said power transistors and thereby turn them off.

Claim 10

A control in accordance with claim 8 wherein said base drive source includes a plurality of clamping transistors having commoned emitters, commoned bases and commoned collectors connected in shunt to the output of said drive source, said means for applying variable time ratio pulses is coupled to the commoned bases of said plurality of clamping transistors, and said base drive source also includes a transistor switch, a filter choke in a series circuit with said transistor switch and also with said plurality of clamping transistors, means for detecting the magnitude of current flowing in said series circuit, and duty cycle varying means responsive to said current detecting means for controlling said transistor switch to maintain the magnitude of current flowing in said series circuit substantially constant.

Claim 11

A control in accordance with claim 2 wherein each said power transistor is a unitary Darlington device having said base drive transistor integral therewith.

Claim 12

A control in accordance with claim 10 wherein each power transistor is a triple-diffused silicon Darlington power transistor.

Claim 13

A control in accordance with claim 2 wherein each said power transistor has a collector-to-emitter saturation voltage characteristic which increases with increase in collector current and also has a base-to-emitter voltage characteristic which increases with increase in collector current.

Claim 14

A control in accordance with claim 12 and including a plurality of diodes each of which couples said base drive source to the base of one of said base drive transistors.

Claim 15

A control for supplying variable time ratio pulses from an electrical source to a load including, in combination, a power switch between said source and said load having a plurality of paralleled power transistors with commoned collectors and commoned emitters, each said power transistor having a forward current ratio characteristic with a portion whErein said ratio decreases abruptly with increase in collector current, a switching current regulator coupled to the base of each of said power transistors and including a transistor switch, output transistor clamping means, an inductor in a series circuit with said transistor switch and said output transistor clamping means, means for varying the duty cycle of said transistor switch to maintain substantially constant current output from said regulator sufficient to cause each of said power transistors to operate on said portion of said characteristic wherein said ratio decreases abruptly with increase in collector current, and means for periodically applying variable time ratio pulses to the base of said output transistor clamping means to shunt current away from said power switch and thereby turn it off.

Claim 16

A control for supplying variable time ratio pulses from an electrical source to a load including, in combination, a power switch between said source and said load having a plurality of paralleled power transistors with commoned collectors and commoned emitters, each said power transistor having a forward current ratio characteristic with a portion whErein said ratio decreases abruptly with increase in collector current, a switching current regulator coupled to the base of each of said power transistors and including a transistor switch, output transistor clamping means, an inductor in a series circuit with said transistor switch and said output transistor clamping means, means for varying the duty cycle of said transistor switch to maintain substantially constant current output from said regulator sufficient to cause each of said power transistors to operate on said portion of said characteristic wherein said ratio decreases abruptly with increase in collector current, and means for periodically applying variable time ratio pulses to the base of said output transistor clamping means to shunt current away from said power switch and thereby turn it off.

Claim 17

A control in accordance with claim 14 wherein each of said power transistors is in a Darlington circuit with a base drive transistor and said switching current regulator is coupled to the base of said base drive transistor.

Claim 18

A control in accordance with claim 15 wherein each said power transistor is a unitary Darlington device having said base driver transistor integral therewith.

Claim 19

A control in accordance with claim 14 and including a plurality of diodes each of which is connected between said switching current regulator and the base of one of said power transistors.

Claim 20

A control in accordance with claim 14 wherein each of said power transistors is of the single-diffused silicon type which has a collector-to-emitter saturated voltage characteristic that increases with increase in collector current and also has a base-to-emitter voltage characteristic which increases with increase in collector current.

Claim 21

A control in accordance with claim 14 wherein each of said power transistors has a collector-to-emitter saturated voltage characteristic which increases with increase in collector current.

Claim 22

A control in accordance with claim 14 wherein said transistor switch is of the complementary Darlington configuration including a main transistor and a driver transistor and said switching regulator also includes a constant current pre-driver stage coupled to the base of said driver transistor.

Claim 23

A control in accordance with claim 20 wherein said output transistor clamping means includes a plurality of paralleled clamping transistors having commoned bases, commoned collectors and commoned emitters, and wherein said means for varying the duty cycle of said transistor switch includes feedback impedance means in said series circuit for deriving a feedback signal which is a function of the magnitude of current flowing in said series circuit, means for deriving a reference voltage signal, and differential amplifier means responsive to said feedback and reference signals for controlling said pre-driver stage to maintain the magnitude of current flowing in said series circuit substantially constant.