Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-02-23
2001-11-27
Berhane, Adolf Deneke (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
Reexamination Certificate
active
06323629
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a current regulator and more particularly to a current regulator designed especially for use with a ring laser gyroscope.
BACKGROUND OF INVENTION
Inertial navigational systems generally include gyroscopes, such as ring laser gyroscopes, to sense rotation about different axes. In the ring laser gyroscope, the HeNe glow discharge of the laser tube is controlled by a high voltage power supply operating in conjunction with a current regulator.
As is known in the art, a common cathode of the laser tube operates with two anodes whose current must be regulated to control the glow discharge and to maintain constant tube intensity. The current regulator typically is implemented with an operational amplifier feedback loop and a transistor.
FIG. 1
illustrates a typical current regulator design for use with a gas laser tube. As shown, a power supply
10
generates a high voltage to operate a laser tube
12
. The high voltage is applied to the tube's cathode
12
c.
The tube current is controlled by identical current regulators coupled to the tube's anodes
12
a.
Each current regulator includes a ballast resistor
14
, an operational amplifier
16
, a transistor
18
, a current sense resistor
20
, and a reference voltage Vref
22
. Generally, each transistor
18
is a P-channel fet with a voltage rating of 450 VDC.
During operation, for each current regulator, operational amplifier
16
drives transistor
18
to maintain a constant voltage drop across current sense resistor
20
. The current is controlled to a value of the reference voltage Vref divided by the value of current sense resistor
20
. In a typical operation, transistor
18
is biased to have a 100 to 200 voltage across it, which generally requires that power supply
10
be tightly regulated to account for voltage variations occurring as a function of temperature within laser tube
12
. Voltage variations also occur throughout the natural life of laser tube
12
.
Moreover, to protect each transistor
18
from the high voltages that are required for the anode, each current regulator is provided with protection diodes
24
. Unfortunately, these protection diodes place a severe limitation on the dynamic range of the current regulator, typically limiting operation to approximately 320 VDC.
This limitation, in turn, forces tight regulation requirements on the power supply design, and requires large values for the ballast resistor
14
. Moreover, the design requires that the value of the ballast resistor
14
change for different current levels. These problems are particularly acute due to the substantial difference between the start-up voltage (e.g., 3000 VDC) and the operating-run voltage (e.g., 1000 VDC) applied to the laser tube's cathode required with typical gyroscopes.
It is therefore an object of the present invention to provide a current regulator that has a wide dynamic range and large operating voltage capability, that uses a lower value ballast resistor, and that requires lower power supply voltage regulation.
Various other objects, advantages and features of the present invention will become readily apparent to those of ordinary skill in the art, and the novel features will be particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
In accordance with the present invention, the current regulator includes a current source that achieves a greater operating range than that of existing regulators by utilizing a voltage divider to provide for incremental voltage level drops across multiple transistors placed in series.
In accordance with an embodiment of the present invention, an apparatus for use in a ring laser gyroscope comprises a laser tube having a cathode and at least one anode, a power supply for powering the laser tube, and a current regulator coupled to the anode. The current regulator includes the current source for current flowing from or to the laser tube and the current source is adapted to provide incremental voltage level drops, the current source comprises first and second transistors coupled in series.
As another aspect, the current regulator includes a voltage divider adapted to control the voltage level drop across at least one of the transistors as a function of the voltage potential at the laser tube's anode.
In accordance with another embodiment of the present invention, a current regulator for use in a ring laser gyroscope comprises a ballast resistor coupled to an anode of the gyroscope's laser tube, an output for the current, a current source coupled between the ballast resistor and the output, a control circuit that establishes the amount of current flow through the current regulator, and a voltage divider that senses the voltage across the current source. The current source includes two transistors coupled in series, the first transistor being coupled to the output and the second transistor being coupled to the ballast resistor. The voltage divider generates a divided voltage as a function of the sensed voltage differential and supplies the divided voltage to the second transistor to control the second transistor so that a voltage drop across the second transistor is equal to a voltage drop across the first transistor.
As an aspect of this embodiment, the output for the current source is a current sense resistor that is coupled to ground, and the control circuit controls the voltage across the current sense resistor.
As another aspect, a zener diode is coupled between the second transistor and the voltage divider to protect the second transistor from excessive voltages applied across it.
As a further aspect, the voltage divider is comprised of two equal value resistors coupled in series, and the divided voltage is the voltage level at which the two resistors are coupled.
In accordance with a further embodiment of the present invention, the current regulator comprises the above-mentioned ballast resistor, output, control circuit, current source and voltage divider. However, the current source in this second embodiment includes a first transistor and a plurality of second transistors, all coupled in series, wherein each of the second transistors is controlled by a respective output of the voltage divider to cause the voltage drop across all of the second transistors to be the same as the voltage drop across the first transistor.
REFERENCES:
patent: 4282495 (1981-08-01), Ljung
patent: 4632555 (1986-12-01), Malvern
patent: 4656637 (1987-04-01), McCormick
Dr. James H. Sharp, Laser Gyroscopes, pp. 1-10, Date Unknown.
Scruggs Michael K.
Sozusen Serdar T.
Berhane Adolf Deneke
Honeywell International , Inc.
Yeadon Loria B.
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