Squib control circuit

Claim 2

In a squib control circuit comprising a number of branch circuits connected in parallel across a pair of voltage input points, each branch circuit including a squib element which, when a given current is fed therethrough for a given duration, heats and blows to trigger a given operation and open the branch circuit involved, and energizing circuit means for providing successive squib-blowing initiating voltage pulses each of which initiates the flow of said given current for at least said given duration to effect the blowing of a squib element in a different branch circuit when there is a low resistance path presenting a low resistance between said input points and the squib element involved, the improvement comprising: a separate self-resetting, solid state threshold level responsive switch device connected in series with the squib element of each branch circuit, each of said threshold level responsive switch devices having a pair of terminals across which the device normally presents a resistance many orders greater than said low resistance to provide a blocking condition for substantially blocking current through the associated squib element, and wherein said high resistance in response to a voltage applied across said pair of terminals thereof above a given threshold voltage value for a given period substantially instantaneously decreases to said low resistance to provide a conducting condition for substantially conducting current therethrough, which low resistance condition persists until the current flowing therethrough drops below a given holding current level, each squib-blowing initiating voltage pulse having a magnitude above said given threshold voltage value of the threshold level responsive switch device associated with the squib element to be blown thereby and effecting the application of a voltage pulse across the terminals of said threshold level responsive switch device whose magnitude is above the threshold voltage value thereof, and each of said threshold level responsive switch devices being responsive to the flow therethrough of a squib-blowing current for a substantially greater period than said given duration by destroying itself to open the circuit to the associated squib element should the latter fail to blow, so subsequent squib-blowing voltage pulses can trigger the other threshold switch devices in succession.

Claim 3

The squib control circuit of claim 1 wherein each of said threshold level responsive switch devices is located in the branch circuit with the associated squib element, wherein each voltage pulse applied across said input points is similarly applied across the switch devices of the branch circuits associated with still unblown squib elements and exceeds the threshold voltage values thereof, the voltage response characteristics of the various threshold switch devices being nonidentical wherein one will be triggered into its low resistance state before the others, such triggering instantaneously reducing the voltage applied across any other such device below the threshold voltage value thereof, so only one threshold switch device can be triggered by a given pulse.

Claim 4

The squib control of claim 1 wherein each of said threshold level responsive switch device is located in the branch circuit with the associated squib element, wherein each voltage pulse applied across said input points is similarly applied across the switch devices of the branch circuits associated and Still unblown squib elements, the voltage response of the various threshold switch devices being nonidentical wherein one will be triggered into its low resistance state before the others, the voltage pulse occurring across said input points and the voltage characteristics of said threshold level responsive switch devices permitting only one threshold switch device to be triggered by a given pulse.

Claim 5

In a squib control circuit comprising a number of branch circuits connected in parallels across a pair of voltage input points, each branch circuit including a squib element which, when given current is fed therethrough for a given duration, heats and blows to trigger a given operation and opens the branch circuit involved, an energizing circuit means for providing successive squib-blowing initiating voltage pulses each of which initiates the flow of said given current for at least a given duration to effect the blowing of a squib element in a different branch circuit when there is a path of low resistance between said input points and the squib element involved, the improvement comprising: a separate, self-resetting, solid state, threshold level responsive device connected in each of said branch circuits in series with the associated squib element, wherein each voltage pulse appearing across said input points is similarly applied across each branch circuit, each of said threshold level responsive switch devices having a pair of terminals across which the device normally presents a high resistance many orders greater than said low resistance to provide a blocking condition for substantially blocking current through the associated squib device and wherein said high resistance in response to a voltage applied across said terminals thereof above a given threshold value for a given period substantially instantaneously decreases to said low resistance to provide a conducting condition for substantially conducting current therethrough which low resistance condition persists until the current flowing therethrough drops below a given holding current level, each squib-blowing initiating voltage pulse having a magnitude above said given threshold voltage value of the threshold voltage value of the threshold switch device associated with the squib element to be blown thereby and effecting the application of a voltage pulse across the terminals of said threshold switch device whose magnitude is above said threshold voltage value thereof, the voltage response characteristics of the various threshold level responsive switch devices in said branch circuits being nonidentical, wherein one will be triggered into its low resistance conducting condition before the other untriggered devices and none of the other untriggered devices will be triggered into its low resistance conducting condition until the application of the next voltage pulse across said input points.

Claim 6

In a squib control circuit comprising a number of branch circuits connected in parallels across a pair of voltage input points, each branch circuit including a squib element which, when given current is fed therethrough for a given duration, heats and blows to trigger a given operation and opens the branch circuit involved, an energizing circuit means for providing successive squib-blowing initiating voltage pulses each of which initiates the flow of said given current for at least a given duration to effect the blowing of a squib element in a different branch circuit when there is a path of low resistance between said input points and the squib element involved, the improvement comprising: a separate, self-resetting, solid state, threshold level responsive device connected in each of said branch circuits in series with the associated squib element, wherein each voltage pulse appearing across said input points is similarly applied across each branch circuit, each of said threshold level responsive switch devices having a pair of terminals across which the device normally presents a high resistance many orders greater than said low resistance to provide a blocking condition for substantially blocking current through the associated squib device and wherein said high resistance in response to a voltage applied across said terminals thereof above a given threshold value for a given period substantially instantaneously decreases to said low resistance to provide a conducting condition for substantially conducting current therethrough which low resistance condition persists until the current flowing therethrough drops below a given holding current level, each squib-blowing initiating voltage pulse having a magnitude above said given threshold voltage value of the threshold voltage value of the threshold switch device associated with the squib element to be blown thereby and effecting the application of a voltage pulse across the terminals of said threshold switch device whose magnitude is above said threshold voltage value thereof, the voltage response characteristics of the various threshold level responsive switch devices in said branch circuits being nonidentical, wherein one will be triggered into its low resistance conducting condition before the other untriggered devices and none of the other untriggered devices will be triggered into its low resistance conducting condition until the application of the next voltage pulse across said input points.

Claim 7

The squib control circuit of claim 4 wherein each voltage pulse applied across said input points exceeds the threshold voltage values of all the threshold level responsive switch devices, but only one will be triggered into its low resistance state before the other devices still in a high resistance blocking condition, such triggering instantaneously reducing the voltage applied across any other such device below the threshold voltage value thereof before it is triggered into such condition, so only one threshold switch device can be triggered by a given pulse.

Claim 8

The squib control circuit of claim 4 where there is provided a test circuit for testing the operation of said threshold level responsive switch devices in the squib control circuit, said test circuit including a series of test fuse elements which will blow if substituted for said squib element in said branch circuits under the aforesaid voltage and current conditions, and switch means for selectively connecting said squib elements or said test fuse elements into said branch circuits.

Claim 9

The squib control circuit of claim 4 wherein said energizing circuIt means includes a source of DC voltage for supplying the current to blow said squib elements, the output of said source of DC voltage being substantially less than said threshold voltage values of said threshold switch devices, rectifier means, means connecting said source of DC voltage and said rectifier means in series across said input points, a source of voltage pulses which at least when added to the output of said source of DC voltage produces a resultant voltage which will apply across at least one threshold level responsive switch device in series with an unblown squib element a voltage which exceeds said threshold voltage value thereof for a period to trigger the same, a capacitor, means connecting said source of voltage pulses and said capacitor in series between said input points so said capacitor will charge to the output of said source of DC voltage between successive pulses and will relatively quickly charge up to the value of the applied pulses when a threshold level responsive switch device in a branch circuit is initially triggered to its low resistance condition prior to the blowing of the associated squib element, so the voltage across said input points drops below the value which will trigger the other threshold level responsive switch devices as soon as the first device triggered by a given pulse into its low resistance condition is so triggered.

Claim 10

The squib control circuit of claim 5 wherein the threshold switch devices in all of the branch circuits have approximately the same threshold voltage values, the time it takes for each threshold switch device to begin response to a squib-blowing initiating pulse, namely the delay time thereof, being different for the various devices, and the time it takes each threshold switch device to switch from its high to its low resistance condition once it begins to respond to a squib-blowing initiating pulse being many orders faster than said delay time thereof.