IE53935B1 - Battery-driven ignition circuit for an explosive or an explosive device - Google Patents

Description

This invention relates to electrical circuits for firing explosives and, in particular, to a new and improved oscillator circuit for generating an electric spark between spaced electrodes for igniting a solid explosive, such as would be used in a firearm for propelling a projectile.

Battery-powered oscillator circuits have been utilized for producing electric arcs between electrodes for igniting a fluid fuel in a turbine engine, as shown in U.S. patents 3,671,805 and 3,731,144. Also, oscillator circuits have been utilized for energizing heating elements for setting off explosives, as shown in U.S. patent 4,141,297. However, it is an object of the present invention to provide a new and improved ignition circuit providing an electric spark between electrodes for igniting a solid explosive of the type used in firearms and the like.

The ignition circuit for a firearm should provide a hot, blue spark for igniting the solid explosive. Also, the ignition circuit should provide repeated firing capabilit20 with a minimum recovery time, so that the circuit can be used with automatic weapons. Another requirement is that the circuit have a minimum battery drain, so that the overall circuit including battery can be made quite small.

These requirements are diverse in nature, and it is an object of the present invention to provide a new and improved ignition circuit having optimum performance characteristics .

It is a particular object of the invention to provide a new and improved ignition circuit which will produce the desired spark for the repeated firing of solid propellant explosives while operating with a small battery and having substantial operating life. A further object is to provide such a circuit which can be a solid state device without having any mechanical or moving parts other than the firing switch, and which can be made quite small, inexpensive, and reliable and of a configuration readily incorporated into a firearm.

A further object of the invention is to provide such an ignition circuit incorporating provisions for control of operating frequency and duty cycle along with current load so that the circuit can be modified for various end uses. Other objects, advantages, features, and results will more fully appear in the course of the following description.

S3& 3 3 According to the invention there is provided a battery-driven ignition circuit for an explosive or an explosive device, for generating a sequence of electrical ignition spark impulses between electrodes disposed in spaced-apart relationship, said ignition circuit comprising a normally non-magnetized step-up transformer having a primary winding and a secondary winding on a ferrite core, a direct connection of the secondary winding with the spaced-apart electrodes, a transistor with base, emitter and collector electrodes, a circuit arrangement for direct connection of the electrodes of the transistor, the primary winding and an on-off switch .in series with the battery, a free running multivibrator with integrated circuit, which comprises a first control voltage and reset input, a second trigger and threshold input, a circuit ground, a third discharge input and an output, the 'switch connecting the first input to one terminal of the battery Sn4 the circuit ground being connected to the other terminal of the battery, a first capacitor which is connected between the said other terminal ό£ the battery and the- second input, first and second resistors connected in series between said first and second inputs and connected with the third input, a third resistor connected between the output and the transistor base, and closure of the circuit between the battery and the multivibrator when the switch is actuated, to apply an alternating signal to the transistor base, the battery being repeatedly connected by the switch and transistor to the primary winding, so that a seguence of voltage pulses is generated at the spaced-apart electrodes.

The ignition circuit provides an electric spark between spaced electrodes for igniting an explosive. The circuit includes a step-up transformer having a primary winding and a secondary winding on a ferrite core, with the secondary winding adapted for directly connecting to the spaced electrodes. This circuit also includes a transistor with base and emitter and collector electrodes, a battery with positive and negative terminals, an on-off switch, and circuitry connecting the transistor electrodes, transformer primary winding and switch in series across the battery. The ignition circuit also includes an integrated circuit free running multi-vibrator with the on-off switch connecting one terminal of the battery to control voltage and reset inputs and with the other terminal of the battery connected to circuit ground of the multi-vibrator. A capacitor is connected between the other battery terminal and trigger and threshold input of the multi-vibrator, and resistors are connected in series between this capacitor and the switch, with the series junction of the resistors connected to the discharge input of the multi-vibrator.

Another resistor is connected between the output of the multivibrator and the transistor base. With this configuration, a substantially square wave output is provided to the transistor base whenever the on-off switch is closed to turn the circuit on. Turning the transistor on provides a current pulse in the transformer primary and the step-up winding ratio provides a substantially higher voltage pulse at the transformer secondary and the spaced electrodes. The frequency of the multi-vibrator operation and the duty cycle may be varied by adding a capacitor across the series resistors and by having a capacitor in the circuit between the multi-vibrator output and the transistor base.

In the accompanying drawing: Fig. 1 is an electric circuit diagram of an ignition circuit incorporating the presently preferred embodiment of the invention; and Fig. 2 is a diagram of the integrated circuit chip of Fig. 1.

The ignition circuit of Fig. 1 includes a battery 11, 25 a transistor Ql, a transformer TI, a push-button switch 12, and a safety switch 13, with the transistor, transformer primary winding NI, and the two switches connected in series with the battery. The secondary winding N2 of the transformer is connected directly across spaced electrodes 16, 17.

The ignition circuit of Fig. 1 also includes an integrated circuit IC which is a free-running multi-vibrator having terminals 1-8, The multi-vibrator IC is show in greater detail in Fig, 2 and typically may be a Texas Instruments NE 555 or a Motorola C6130P or a J4-1555 timeroscillator chip.

The multi-vibrator terminals 4 and 8 are connected together and to the positive battery terminal through the switches 12, 13. The multi-vibrator terminal 1 serves as circuit ground and is connected to the negative terminal of the battery. The output terminal 3 of the multi-vibrator is connected to the base of the transistor Ql through resistor R3. In the preferred embodiment, a capacitor C3 is connected across the resistor R3. A diode DI is connected between the transistor base and circuit ground, to prevent high negative voltages on the transistor base.

Multi-vibrator terminals 2 and 6 are connected together and to the negative terminal of the battery through a capacitor C2. Resistors Rl, R2 are connected in series between terminals 2 and 6 at one end and terminals 4 and 8 at the other end. The junction between the two resistors is connected to multi-vibrator terminal 7. Also in the preferred enbodiment, capacitor Cl is connected across the resistors Rl, R2.

In the preferred embodiment illustrated, the transformer has a 1 to 400 step-up ratio,and the battery is a 12 volt battery rated at 1.5 ampere hours. The values for the other components are set out in Table 1.

Table 1 Rl 8.2 kohms Cl 1 mf R2 2.2 kohms C2 .01 mf R3 2.2 kohms C3 5 mf Ql 2N-3055 TI Time-Magn.1002 DI IN-3600 In operation, the safety switch 13 is closed, and the ignition circuit is ready for use. When it is desired to ignite an explosive, the push button 12 is depressed, providing battery voltage across the emitter and collector of the transistor through the primary winding NI, and also providing battery voltage to the multi-vibrator at pins 1 and 8. This produces oscillation of tbe multi-vibrator and provides the substantially square wave output at terminal 3, cyclically switching the transistor into and out of conduction and providing a series of current pulses in the transformer primary. The voltage of these pulses is increased by the step-up ratio of the windings, providing a high voltage pulse train across the electrodes 16, 17.

The frequency of the multi-vibrator output is controlled by the selection of resistors Rl and R2 and capacitors Cl and C2, as follows: „ 1 1.44 1 t ” (Rl + 2R2) x (Cl + C2)_ With capacitor Cl omitted, the frequency is about khz. With Cl included at the value stated, the frequency is reduced to about 1 khz. This also reduces the current drain from the battery from about 2.5 amperes to about 250 milliamperes. With the capacitor C3 omitted, the duty cycle for the transistor Ql is about 60 7«, on and 40% off. With capacitor C3 added at the value indicated above, tbe duty cycle is about 80% on and 207° off.

This ignition circuit provides a number of advantages. The emitter of Ql and transformer Tl may be connected directly across the battery. The ignition circuit does not require any storage capacitor in the secondary winding, and by providing for control of frequency and duty cycle, the desirable clean, blue spark can be achieved with a minimum of current drain. Such a spark is especially suited for igniting solid propellants of the type used in firearms.

Claims (6)

CLAIMS:
1. I.A battery-driven ignition circuit for an explosive or an explosive device, for generating a sequence of electrical ignition spark impulses between electrodes disposed in spaced-apart relationship, said ignition circuit comprising a normally non-magnetized step-up transformer having a primary winding and a secondary winding on a ferrite core, a direct connection of the secondary winding with the spaced-apart electrodes, a transistor with base, emitter and collector electrodes, a circuit arrangement for direct connection of the electrodes of the transistor, the primary winding and an on-off switch in series with the battery, a free running multivibrator with integrated circuit, which comprises a first control voltage and reset input, a second trigger and threshold input, a circuit ground, a third discharge input and an output, the switch connecting the first input to one terminal of the battery and the circuit ground being connected to the other terminal of the battery, a first capacitor which is connected between the said other terminal of the battery and the second input, first and second resistors connected in series between said first and second inputs and connected with the third input, a third resistor connected between the output and the transistor base, and closure of the circuit between the battery and the multivibrator when the switch is actuated, to apply an alternating signal to the transistor base, the battery being repeatedly connected by the switch and transistor to the primary winding, so that a sequence of voltage pulses is generated, at the spaced-apart electrodes.
2. 2. An'ignition circuit according to claim 1, wherein a second capacitor is connected in parallel with the resistors to reduce the frequency of the multivibrator·
3. 3. An ignition circuit according to claim 2, wherein a third capacitor is connected- in parallel with the third resistor, in order to alter the duty cycle of the multivibrator by increasing the on time.
4. 4. An ignition circuit according to claim 3, wherein a diode is connected between the transistor base and the circuit ground.
5. 5. An ignition circuit according to claim 1, wherein a further capacitor is connected to the third resistor, in order to alter the duty cycle of the multivibrator by increasing the on time.
6. 6. An ignition circuit claimed in any of claims 1-5, substantially as hereinbefore described and with reference to and as illustrated in the accompanying drawing.