# US 4,398,129 A · Active lamp pulse driver circuit

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- Number: US 4,398,129 A
- Document ID: US4398129A
- Status: Granted
- Kind: A
- Application number: 06/276,748
- Filed: 1981-06-24
- Granted: 1983-08-09
- Earliest claimed: 1981-06-24
- Assignees: The United States of America as represented by the Administrator of the National Aeronautics and Space Administration
- Inventors: Kenyon E. Logan
- Web page: https://patentgrep.com/patent/US4398129A

## CPC

- H05B 41/30: in which the lamp is fed by pulses, e.g. flash lamp
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL

## Abstract

A flashlamp drive circuit 10 using an unsaturated transistor Q1 as a current mode switch to periodically subject a partially ionized gaseous laser excitation flashlamp 20 to a stable, rectangular pulse of current from an incomplete discharge of an energy storage capacitor C1. A monostable multivibrator MV1 sets the pulse interval, initiating the pulse in response to a flash command by providing a reference voltage to a non-inverting terminal of a base drive amplifier AV1; a tap on an emitter resistor R2 provides a feedback signal sensitive to the current amplitude to an inverting terminal of amplifier AV1, thereby controlling the pulse amplitude. The circuit drives flashlamp 20 to provide a square-wave current flashlamp discharge.

## Claims

### Claim 1

A circuit for driving a gaseous flashlamp, comprising:
circuit switching means;
means generating an output for varying said circuit switching means between two operation modes;
means for applying a potential impulse to a first terminal connectable to one electrode of the flashlamp to initiate ionization thereof;
energy supply means for applying a first potential continuously and directly to a second terminal connectable to a second electrode of the flashlamp, said first potential having sufficient magnitude to maintain partial ionization in the flashlamp when said circuit switching means is in one of its operational modes;
energy storage means exhibiting a single and capacitive reactive impedance component chargeable by said energy supply means for applying a second potential directly to said second terminal of a magnitude sufficient to effect complete ionization of the flashlamp when said circuit switching means is in the other of its operational modes; and
means for providing a signal to said varying means proportional to the amplitude of current flowing through said flashlamp during said other operational mode in response to reception of said signal, whereby said circuit switching means controls the amplitude of electrical current flowing through said second electrode caused by potential applied by said energy storage means to said second terminal during the period of said other mode.

### Claim 2 (depends on 1)

The circuit of claim 1 wherein said circuit switching means and said signal providing means furnish a path for discharge of said energy storage means only while said circuit switching means is in the other of its operational modes.

### Claim 3 (depends on 2)

The circuit of claim 2 wherein said magnitude of said second potential is a function of said energy storage means exhibiting a capacitive impedance component.

### Claim 4 (depends on 3)

The circuit of claim 3 wherein said signal providing means comprises a first resistive impedance component coupled to receive discharge of said energy storage means through said flashlamp during said other operational mode.

### Claim 5 (depends on 4)

The circuit of claim 4 further comprising a resistive impedance component coupled to receive current flowing through said flashlamp during said one operational mode.

### Claim 6 (depends on 5)

The circuit of claim 5, further comprising means for electrically isolating said circuit switching means from said flashlamp during said one operational mode.

### Claim 7 (depends on 6)

The circuit of claim 6 further comprising means susceptible to an ambient condition and connected to said varying means for modifying the amplitude of said signal in response to change in the ambient environment of the flashlamp.

### Claim 8

A circuit for optically pumping a laser medium comprising:
a partially evacuated flashlamp tube exhibiting a negative resistance characteristic with a longitudinal bore containing an ionizable gas between an anode oppositely positioned at one end of said tube from a cathode electrode;
a storage capacitor coupled to discharge directly through said anode;
an ignition voltage source coupled to a third electrode of said flashlamp, for applying a voltage spike to said third electrode with sufficient magnitude to create an arc of partial ionization of gas within said bore;
a direct current power supply directly coupled to said anode and continuously providing energy to said anode for maintaining said arc of partial ionization of said gas while cyclically charging said storage capacitor to a potential of sufficient magnitude to fill said bore with a plasma of said gas;
a transistor with an emitter, connected in a common emitter configuration with the collector operatively coupled to said cathode electrode;
bias means coupled to the base of said transistor to hold a junction between said emitter and collector in a reverse bias condition;
a multivibrator cyclically generating a reference voltage pulse of predetermined duration;
an operational amplifier coupled between said transistor and said multivibrator and being receptive to the reference voltage pulse to provide a drive signal to said base of sufficient magnitude to forwardly bias said junction between said base and said collector during reception of said reference voltage pulse;
a reference potential source having a lower voltage than the potential of said power supply; and
an impedance coupled between said emitter and said reference potential, having a tap coupled to said operational amplifier thereby providing said operational amplifier with a sense signal proportional in magnitude to the amplitude of electrical current through said emitter.

### Claim 9 (depends on 8)

The circuit of claim 8, wherein said:
impedance includes an adjustable tap; and
said operational amplifier is receptive to the reference voltage pulse and to a voltage at said adjustable tap, on different of a non-inverting terminal and an inverting terminal.

### Claim 10 (depends on 8)

The circuit of claim 8, further comprising a diode interconnecting said cathode electrode and said collector.

### Claim 11 (depends on 8)

The circuit of claim 8, further comprising:
a resistive impedance coupled between the cathode electrode and a ground potential for establishing the level of electrical current between said anode and cathode during partial ionization of said gas; and
a capacitor coupled between the collector and a ground potential, for suppression of electrical current caused by application of said voltage spike to said third electrode.

### Claim 12 (depends on 8)

The circuit of claim 8 further comprising means susceptible to an ambient condition for modifying the amplitude of said sense signal in inverse proportion to change in the ambient environment of the flashlamp.

### Claim 13

A circuit for generating optical energy, comprising:
a partially evacuated tube with a bore containing an ionizable gas between an anode electrode disposed apart from a cathode electrode, exhibiting a negative resistance characteristic during a first operational condition occurring in response to application of a voltage to said anode electrode with sufficient magnitude for maintaining a minor electrical current through an arc of partial ionization of said gas, a change from said first condition to a second operational condition occurring upon an increase in said minor current to a major current with sufficient magnitude for causing a plasma of said gas to fill said bore, and a change from said second condition to said first condition occurring in response to a decrease in said major current to the level of said minor current;
energy storage means exhibiting a single and capacitive reactive impedance component for supplying said major electrical current to said electrodes during said second operational condition;
energy supply means for applying said voltage directly and continuously to said anode electrode and providing energy during said first operational condition directly to said energy storage means;
circuit switching means for providing a variable internal impedance for discharge of said energy storage means through said tube during said second operational condition;
amplification means for periodically shifting said tube between said first and second operational conditions by varying said internal impedance of said circuit switching means between a non-conducting mode and a linearly responsive conducting mode; and
sensing means responsive to the amplitude of said electrical currents, providing a first signal to said amplification means whereby said internal impedance is varied by said operational means linearly in dependence upon amplitude of said electrical currents.

### Claim 14 (depends on 13)

The circuit of claim 13 further comprising:
biasing means for holding said internal impedance of said circuit switching means at a higher impedance during said first operational condition; and
resistive means for providing an intermediate level of impedance between said cathode and a ground potential during said first operational condition.

### Claim 15 (depends on 13)

The circuit of claim 13 wherein said circuit switching means further comprises a transistor arranged in a common emitter configuration.

### Claim 16 (depends on 15)

The circuit of claim 15 wherein said amplification means further comprises an active device providing a second signal to the base of said transistor dependent in magnitude upon a difference between the level of a logic state and said first signal.

### Claim 17 (depends on 13)

The circuit of claim 13 further comprising means susceptible to an ambient condition for modifying the amplitude of said first signal in inverse proportion to change in the ambient environment of said partially evacuated tube.