BACKGROUND OF THE INVENTION Flash devices are used in cameras to create a bright"flash"of lights when taking a picture under conditions of insufficient lighting. To generate an intense pulse of light sufficient to create an ideal environment for picture taking, special flash tubes which are capable of generating such intense light are used. Such flash tubes contain gas inside an enclosed glass envelope which must first be ionized before the flash tube can flash. To ionize the gas, a voltage of sufficient level must first be delivered to the surface of the glass envelope. Once the gas is adequately ionized, a capacitor discharge is induced through the flash tube to cause a release of a brilliant"flash".

The trigger voltage required to cause ionization of the gas inside the flash tube is typically around 4 KV. The voltage required to drive the discharge through the flash tube is typically around 300 to 400 Volts. Both of these voltage levels are much higher than what a typical portable DC voltage <BR> <BR> source, e. g. , battery, can deliver. Therefore, proper circuits are needed to convert the battery voltage to those levels which are needed to operate the flash device.

A flash device typically requires four main components which are a flash unit, converter circuit, driver circuit, and a trigger circuit. In general, a

flash unit comprises a flash tube and a flash capacitor. The converter circuit converts a relatively small DC voltage, e. g. , 1.5 to 6 Volts, to a higher oscillating voltage of about 300 to 400 Volts (called converter voltage) for charging the flash capacitor in the flash unit. The trigger circuit transforms the converter voltage from the converter circuit to a much higher trigger <BR> <BR> voltage, e. g. , 4 KV. The driver circuit initiates the trigger circuit to provide the trigger voltage needed for ionizing the gas in the flash tube. The general function of these elements as described herein is generally well known to those skilled in the art.

Improvements in circuit design have resulted in electronic flash circuitry with improved performance and lower costs. Many of such improvements have resulted in circuitry having less components and thus having a more compact design. Some of the larger components in an electronic flash circuit reside in the converter circuit and the trigger circuit.

These components are the converter transformers and trigger coil or trigger transformers.

The configuration of a trigger circuit used in flash devices can come in many forms. However, the general function of the trigger circuit remains the same; which is to transform the converter voltage to a much higher trigger voltage needed for ionizing the gas in the flash tube. However, a typical electronic flash device would then require at least two transformers in the circuitry. At least one transformer in the converter circuit and at least one other transformer in the trigger circuit. These transformers not only add to the space constraints of the flash device, they also add to substantial costs.

SUMMARY OF THE INVENTION A converter circuit for a flash device, the converter circuit having a trigger capacitor, the flash device having a flash capacitor and a flash tube, the converter circuit comprising: a switching means; a transformer, coupled to the switching means to convert a voltage from a DC voltage source into a high oscillating voltage for charging the trigger capacitor and the flash capacitor, the transformer having a primary coil and a secondary coil, the secondary coil comprising a main winding and a feedback winding; a switch, coupled to the trigger capacitor and connecting the primary coil to the secondary coil, for enabling a voltage peak at the secondary coil upon a discharge of the trigger capacitor and thereby provide a trigger voltage for ionizing a gas in the flash tube; and a trigger contact, connected to the secondary coil, for delivering the trigger voltage.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a schematic diagram of an embodiment of the present invention which is incorporated into a schematic diagram of an electric flash device.

FIG. 2 illustrates a schematic diagram of another embodiment of the present invention which is incorporated into the schematic diagram of an electric flash device.

FIG. 3 illustrate a schematic diagram of another embodiment of the present invention which is incorporated into the schematic diagram of an electric flash device.

FIG. 4 illustrates a schematic diagram of another embodiment of the present invention which is incorporated into the schematic diagram of an electric flash device.

FIG. 5 illustrates a schematic diagram of another embodiment of the present invention which is incorporated into the schematic diagram of an electric flash device.

FIG. 6 illustrates a schematic diagram of another embodiment of the present invention which is incorporated into the schematic diagram of an electric flash device.

FIG. 7 illustrates a schematic diagram of another embodiment of the present invention which is incorporated into the schematic diagram of an electric flash device.

FIG. 8 illustrates a schematic diagram of another embodiment of the present invention which is incorporated into the schematic diagram of an electric flash device.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIG. 1, the present invention is a converter circuit, which is particularly adapted for use in an electronic flash device 101. The converter circuit 105 differs from conventional flash circuits in that it does not require the use of a separate trigger coil or trigger transformer. This converter circuit 105 serves to perform the functions of converting a relatively small voltage to a higher oscillating voltage, for charging flash and trigger capacitors, and further providing a trigger voltage for ionizing a gas in a flash tube 182.

In general, the electronic flash device 101 can be broken down into: the converter circuit 105 and the flash unit 109.

The flash unit 109 comprises a flash tube 182, a flash capacitor 180 and a trigger contact 184. The converter circuit 105 comprising of a transformer 120 and a switching means 139, converts a relatively small DC voltage of about 1.5 to 3 volts, to a higher oscillating voltage of about 300 to 400 volts commonly referred to as the converter voltage for charging the flash capacitor 180. The converter voltage is then transformed to a much higher trigger voltage of about 4000 volts. This trigger voltage is used to ionize the gas in the flash tube 182. Once the flash tube 182 is sufficiently ionized, a 'brilliant flash'occurs and the flash capacitor 180 discharges the stored energy through the flash tube 182. The general function of these elements described are generally well known to those skilled in the art.

Now to describe the converter circuit 105 in greater detail, the converter circuit 105 comprises of the transformer 120 having a primary coil 122, and a secondary coil 124 and the switching means 139 comprises of a transistor 140. The secondary coil 124 has a feedback lead 132 connected to the secondary coil 124 that divides the secondary coil 124 into a main winding 125 and a feedback winding 127. The feedback lead 132 is also connected to a base 144 of the transistor 140. A first end lead 134 of the secondary coil 124 is connected to a rectifier diode 152, and a second end lead 130 of the secondary coil 124 is connected to a first resistor 156 and a trigger capacitor 150. The trigger capacitor 150 is also connected to a charging resistor 154, which is also connected to the rectifier diode 152. A switch 107 connects the trigger capacitor 150 to the second end lead 128 of the primary coil 122 and a first resistor 156. The first end lead 126 of the primary coil 122 is connected to a collector 142 of the transistor 140, and the second end lead 128 of the primary coil 122 is connected to a positive side of a DC voltage source 110.

An emitter 146 of the transistor 140 is connected to the negative side of the DC voltage source 110.

A current flows from the DC voltage source 110 over the first resistor 156 through the feedback winding 127 and the feedback lead 132 of the secondary coil 124 to the base 144 of the transistor 140. The transistor 140 now opens or switches ON and allows current to flow from the DC voltage source 110 through the primary coil 122, through the transistor 140 and to ground. This induces a positive voltage on the feedback winding 127 and the feedback lead 132 of the secondary coil 124, which drives the transistor 140 into saturation. Saturation of the transistor 140 causes more current to flow through the primary coil 122 and to the transistor 140 driving the transformer 120 into saturation as well. When the transformer 120 reaches saturation the voltage induction at the feedback winding 127 of the secondary coil 124 decreases. The lowering of the induced voltage causes the transistor 140 to be less open and consequently a change in the polarity of the magnetic field in the primary coil 122. A negative voltage is thus induced on the feedback winding 127 and the feedback lead 132 of the secondary coil 124 which causes a negative voltage to be at the base 144 of the transistor 140 turning the transistor 140 OFF. This results in the stopping of current flow through the primary coil 122. As the energy in the transformer 120 drops to zero, the current from the DC voltage source 110 again flows over the first resistor 156 and the sequence repeats itself. The voltage on the main winding 125 of the secondary coil 124 corresponds in polarity and frequency to the feedback winding 127 of the secondary coil 124. It is this voltage of about 300 to 400 volts on the main winding that charges the flash capacitor 180 over the rectifier diode 152.

The voltages induced in the secondary coil 124 charges up both the flash capacitor 180 and the trigger capacitor 150. When the switch 170 is closed, the negative voltage of the trigger capacitor 150 is connected to the second end lead 128 of the primary coil 122 of the transformer 120, and the positive voltage of the trigger capacitor 150 is connected to the second end lead 130 of the secondary coil 124. The primary coil 122 and the feedback

winding 127 of the secondary coil 124 are now in series over the collector 142 and base 144 of the transistor 140. The trigger capacitor 150 is in parallel with the primary coil 122 and the feedback winding 127.

A negative voltage peak at the second end lead 128 of the primary coil 122 induces a high positive voltage at the first end lead 134 of the secondary coil 124. This high positive voltage in the converter circuit 105 is the trigger voltage, which is blocked by the rectifier diode 152. The trigger voltage via contact of a trigger contact 184 to the surface of the flash tube 182 ionizes the gas in the flash tube 182. Once the gas in the flash tube 182 is sufficiently ionized, the flash capacitor 180 discharges the stored energy through the flash tube 182 and a'brilliant flash'occurs.

The present invention of the converter circuit eliminates the use of an additional trigger coil or trigger transformer. In the present invention, the transformer 120 having the feedback winding 127 is used to also act as a trigger transformer in addition to providing an oscillating voltage for charging of capacitors. When both the flash capacitor 180 and the trigger capacitor 150 are charged, closing the switch 170 results in the trigger capacitor 150 being connected in parallel to the primary coil 122 and the feedback winding 127 which are connected in series when the switch 170 is closed. This results in a very high voltage on the secondary side of the transformer, which is directed to a trigger contact 184 by the rectifier diode 152, which prevents the positive voltage from shorting over the flash capacitor 180 to ground. This description also applies directly to the circuits as shown in FIG. 2 to FIG. 6.

Conventional transformers for such converter circuit applications operate usually at about 40KHz and do not have the necessary permeability at this frequency to replace a trigger transformer directly. Trigger transformers are required to operate at frequency levels achieved only by conventional trigger transformers operating at about 1 MHz. Conventional transformers may have a turn ratio of about 200, which would produce a

theoretical voltage in excess of 50kV at the secondary coil 124 when a voltage of 270V is applied from the trigger capacitor 150. However, Conventional transformers practically would only give a voltage of about 1000V with the same applied voltage of 270V.

By connecting the primary coil 122 and the feedback winding 127 of the secondary coil 124 in the present invention in series, the turn ratio of the transformer 120 with the feedback winding in series with the primary coil 122 is brought down to about 98. The increased number of windings from the connection of the primary coil 122 and the feedback winding 127 in series increases the inductance and correspondingly reduces the operating frequency as well. Theoretically, the transformer 120 with the feedback winding connected in series with the primary coil 122 having a turn ratio of about 98 would give a voltage in excess of 25kV. Practically, a voltage of about 4kV is produced. This description also applies to the other circuits as shown in FIG. 2 to FIG. 6.

Referring to FIG. 2, a variation of the circuit of FIG. 1. The flash unit 109 remains the same. Several components in this converter circuit 205 are the same as those in FIG. 1, such as the transformer 120, the transistor 140 and the trigger capacitor 150.

In this circuit, the trigger capacitor 150 is now connected directly to the first end lead 126 of the primary coil 122 and to the collector 142 of the transistor 140. When the switch 170 is closed, the negative voltage of the trigger capacitor 150 is connected to the feedback lead 132 of the secondary coil 124, and the positive voltage is connected to the first end lead 126 of the primary coil 122. The primary coil 122 and the feedback winding 127 of the secondary coil 124 are now directly in series as opposed to the converter circuit 105 in FIG. 1 where they are in circuit over the collector-base of the transistor 140. The trigger capacitor 150 is in parallel with the primary coil 122 and the feedback winding 127 of the secondary coil 124. A high trigger

voltage is similarly induced as the circuit in FIG. 1 at the first end lead 134 of the secondary coil 124 which ionizes the gas in the flash tube 182. This converter circuit 205 can further be provided with a"READY"to flash indication in the form of an LED (Light Emitting Diode) 260. When the flash capacitor 180 is fully charged, the LED 260 lights up. The LED 260 is connected in parallel with a first resistor 258 and then in series with a second resistor 256. The parallel circuit is further connected to the base 144 of the transistor 140, while the second resistor 256 is connected to the feedback lead 132 of the secondary coil 124 and the switch 170 which is connected to the charging resistor 154.

Referring to FIG. 3, a variation of circuit shown in FIG. 1 and FIG. 2.

The second lead 128 of the primary coil 122 of the transformer 120 is now connected to the collector 142 of the transistor 140, while the second end lead 130 of the secondary coil 124 is connected to the base 144 of the transistor 140. The first end lead 126 of the primary coil 122 is connected to the positive side of the DC voltage source 110 and also to the trigger capacitor 150. The feedback lead 132 of the secondary coil 124 is now connected to the switch 170, which is also connected to the trigger capacitor 150. A"READY"to flash indication is also provided by a LED 360 connected to the feedback lead 132 of the secondary coil 124, an input resistor 362 in series with a capacitor 364 connects the LED 360 to the emitter 146 of the transistor 140 and to the negative side of the DC voltage source 110. When the switch 170 is closed after both the flash capacitor 180 and the trigger capacitor 150 are fully charged, a negative voltage peak at the first lead 126 of the primary coil 122 of the transformer 120 induces a negative trigger voltage at the first end lead 134 of the secondary coil 125 which ionizes the gas in the flash tube 182. The feedback winding 127 of the secondary coil 124 is in series with the primary coil 122 over the collector-base junction of the transistor 140 when the switch 170 is closed. This is similar to the converter circuit 105 in FIG. 1. Note that in the present converter circuit 305, the rectifier

diode 152 and the flash capacitor have their polarities reversed as compared to the circuits in FIG. 1 and FIG. 2.

Referring to FIG. 4, a variation of the circuits in FIG. 3. The feedback lead 132 of the secondary coil 124 is connected directly to the first end lead 126 of the primary coil 122 and the positive side of the DC voltage source 110. The trigger capacitor 150 is connected directly to the second lead 130 of the secondary coil 124. The trigger capacitor 150 is also connected to the second end lead 128 of the primary coil 122 via the switch 170. When the switch 170 is closed, a positive peak voltage from the trigger capacitor 150 at the second lead 128 of the primary coil 122 induces a negative trigger voltage at the first end lead 134 of the secondary coil 124. The gas in the flash tube 182 is then ionized via contact with a trigger contact 184. The series connection of the primary coil 122 with the feedback winding 127 of the secondary coil 124 is direct and there are no losses as compared to a series connection via the collector-base of the transistor 140. The"READY" indicator is via an LED 460 connected in parallel with a first resistor 456 and to an input resistor 462 connected to the base 144 of the transistor 140. A damping capacitor 464 might be needed to protect the transistor 140 from a voltage peak at the collector 142 when the switch 170 is closed. This circuit can further be modified by using a transformer with an air gap and by switching the polarities of the rectifier diode 152. A capacitor can replace the LED 460 and the first resistor 456 can be replaced by a diode. This will convert the converter circuit 405 to a Flyback circuit, which advantageously has a faster charging time. This can similarly be done in the circuits shown in FIG. 1 to FIG. 3 and FIG. 5 as well.

Referring to FIG. 5, a variation of circuit in FIG. 4. The converter circuit 505 shown here is similar to the circuit shown in FIG. 4. The differences lie in that the components of the flash unit 109 are not connected directly to ground. In this circuit, the flash tube 182 and flash capacitor 180 are connected directly to the base of the transistor.

Referring to FIG. 6, a variation of circuit in FIG. 5. The circuit shown here is similar to the circuit shown in FIG. 5. The difference lies in the use of a PNP transistor 640 instead of a NPN transistor 140 as in Fig 1 to FIG. 5. As such, some of the components would have their connections changed to reflect a change in polarity. The rectifier diode 152 connected to the first end lead 134 of the secondary coil 120 and the flash capacitor 180 would have their polarities reversed. The positive side of the DC voltage source 110 is connected directly to the emitter 642 of the transistor 640. This can similarly be done in the circuits shown in the other circuits as well.

Referring to FIG. 7, this is a circuit using a push-pull converter to implement the charging cycles of the circuit. Now to describe the converter circuit 705 in greater detail, the converter circuit 705 comprises of a transformer 720 having a primary coil 722 and a secondary coil 724, and switching means 139. The switching 139 means in this circuit further comprises a first transistor 740 and a second transistor 750. The primary coil 722 has a middle lead 728 at about the halfway point of the primary coil 722 dividing the primary coil into a first winding 723 and a second winding 725. Likewise, the secondary coil 724 has a middle lead 734 dividing the secondary coil into a first half 727 and a second half 729. The first end lead 726 of the primary coil 722 is connected to the collector 742 of the first transistor 740. The second end lead 730 of the primary coil 722 is connected to the collector 752 of the second transistor 750. The trigger capacitor 150 is also connected to the collector 742 of the first transistor 740 and to the switch 170. The switch 170 in turn is connected to the collector 752 of the second transistor 750. A first resistor 762 is connected between the base 744 of the first transistor 740 and the second end lead of the primary coil. A second resistor 764 is connected between the base 754 of the second transistor 750 and the collector 742 of the first transistor 740. The rectifier diode 152 is connected between the first end lead 736 of the secondary coil 724 and the positive side of the flash capacitor 180 and also to the charging resistor 154.

The charging resistor 154 is further connected to the positive side of the trigger capacitor 150. Another rectifying diode 766 is connected between the second end lead 732 of the secondary coil 724 and the positive side of the flash capacitor 180. The emitters 746,756 of the first and second transistors 740,750 are both connected to ground. The middle end lead 734 of the secondary coil 724 is also connected to ground. The middle lead 728 of the primary coil 722 is connected to the positive side of the DC voltage source 110.

The push-pull converter converts the low voltage from the DC voltage source into a high oscillating voltage to charge both the flash capacitor 180 and the trigger capacitor 150. When both the flash capacitor 180 and the trigger capacitor 150 are fully charged, the switch 170 is closed connecting the first winding 723 and the second winding 725 of the primary coil 722 in series. The trigger capacitor 150 is also now in parallel with the first winding 723 and the second winding 725. A negative peak voltage at the first end lead 726 of the primary coil 722 induces a negative voltage at the first end lead 736 of the secondary coil 724. This voltage is blocked by the rectifier diode 152. The gas in the flash tube 182 is then ionized via contact with the trigger contact 184.

Referring to FIG. 8, another variation of the present invention is shown where a converter circuit 805 comprises a transformer 820 having a primary coil 822 and a secondary coil 824. A primary lead 828 divides the primary coil 822 into a main winding 825 and a feedback winding 823. The primary lead 828 is directly connected to the DC voltage source 110. The feedback lead 826 of the primary coil 822 is connected to an LED 860 connected in parallel to a first resistor 856. A second resistor 862 is connected between the parallel circuit of the LED 860 and the first resistor 856 and to the collector 142 of the transistor 140. The collector 142 is connected to the second end lead 830 of the primary coil 822 and also to a first capacitor 866, which is connected to ground. The emitter 146 of the transistor 140 is

connected directly to ground. The base 144 of the transistor 140 is connected via a third resistor 864 to the primary lead 828 of the transformer 820. The base 144 is also connected to the second end lead 832 of the secondary coil 824 and also to a second capacitor 868, which is connected to ground. A third resistor 864 is connected between the primary lead 828 of the primary coil 822 and the base 144 of the transistor 140. The trigger capacitor 150 is connected between the collector 142 of the transistor 140 and the charging resistor 154. The switch 170 is connected between the feedback lead 826 of the primary coil 822 and the positive side of the trigger capacitor 150. The rectifier diode 152 is connected to the first end lead 836 of the secondary coil 824 and to the trigger contact 184. The rectifier diode 152 and the charging resistor 154 are both connected to the flash unit 109.

After the flash capacitor 180 and the trigger capacitor 150 are charged, the switch 170 is closed, a negative voltage peak from the trigger capacitor 150 is connected to the feedback lead 826 of the primary coil 822 and the positive side of the trigger capacitor 150 is connected to the second end lead 830 of the primary coil 822. The feedback winding 823 and the main winding 825 are in series and together induce a voltage peak at the first end lead 836 of the secondary coil 824. The trigger capacitor 150 is now in parallel with the feedback winding 823 and the main winding 825. The voltage peak at the secondary coil 824 is blocked by the rectifier diode 152. This voltage peak also called the trigger voltage then ionizes the gas in the flash tube 182 via the trigger contact 184. Once the gas in the flash tube 182 is sufficiently ionized, the flash capacitor 180 discharges the stored energy through the flash tube 182 and a'brilliant flash'occurs.