Electricity: power supply or regulation systems – In shunt with source or load – Using diode
Reexamination Certificate
2000-01-21
2001-04-24
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using diode
Reexamination Certificate
active
06222350
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
This invention relates to generally to the field of discrete component shunt voltage regulator circuits. More specifically, it relates to a shunt voltage regulator circuit suitable for high voltage, low current applications, especially in high temperature environments.
Shunt voltage regulators are components or circuits that are usually connected in parallel with a particular electronic device, or across the input or output terminals of a circuit, to limit the voltage that can be applied across the device or between the terminals. The shunt regulator performs this function by conducting very little current until a preset voltage is reached, at which point the regulator becomes a very low resistance device that conducts a high current.
A well-known type of shunt voltage regulator is the zener diode. A zener diode exhibits a very high resistance, and thus allows the passage of very small currents, until a predefined reverse threshold voltage (or “zener” voltage) is applied across it. When the zener voltage is reached or exceeded, the zener diode becomes conductive with a variable current at the zener voltage. Zener diodes are commonly available with zener voltages of about 2 volts to about 400 volts. A problem with zener diodes is that those with zener voltages above about 5 or 6 volts exhibit large positive temperature coefficients (expressed in V/° C.), as shown in the graph of FIG.
1
. Thus, high voltage zener diodes are not suitable in many applications in which high ambient temperatures may be experienced. Of course, a large number of low voltage zener diodes may be connected in series to provide a high voltage regulator that is relative temperature-stable, but this is usually impractical in terms of cost and space considerations.
U.S. Pat. No. 5,949,122—Scaccianoce discloses an integrated circuit that provides thermal compensation for a series string of zener diodes, in which several bipolar transistors are connected as V
BE
multipliers. While this circuit provides temperature-stable high voltage regulation, it may not work well at very low collector currents. This is because the bipolar transistors are connected in a common emitter configuration, in which the collector current (I
C
) in each transistor is equal to the base current (I
B
) multiplied by the common emitter gain (H
FE
) of the transistor. The value of H
FE
for a typical bipolar transistor is in the range of about 10 to about 200. Since the collector current in the Scaccianoce device is the shunt regulation current, the base current would be between 0.5% and 10% of the shunt regulation current. Thus, at low shunt regulation currents (i.e., about 25 &mgr;amps to about 500 &mgr;amps), the base current would be at or near the value of the collector cutoff current (the collector-to-base leakage current, or I
CBO
) for typical bipolar transistors. There are bipolar transistors with values of I
CBO
low enough to allow the Scaccianoce device to work at low shunt regulation currents, but the value of I
CBO
exhibits a large positive temperature coefficient, especially at temperatures above about 100° C. Thus, as a practical matter, a device constructed in accordance with the Scaccianoce disclosure to operate at low shunt regulation currents would be limited to operation in temperatures below about 125° C.
The prior art also includes a gas discharge tube device that operates in the corona mode of discharge. This device operates as a high voltage equivalent of a zener diode, and it functions well with low shunt regulation currents and at high temperatures (100° C. to 200° C.). These devices are fragile, however, and expensive, and they require a radioactive component (a beta emitter), which may present a health concern in some contexts.
There is thus a need for a high voltage regulation device that can operate with low shunt regulation currents in high temperature environments. There is a further need for a device that meets these operational criteria, and that may also be realized in a space-efficient and shock-resistant package.
SUMMARY OF THE INVENTION
Broadly, the present invention is a high voltage shunt regulator circuit comprising a high voltage device with a predetermined reverse-conduction threshold connected in series with a thermal compensation device comprising a plurality of gate threshold amplifiers connected in series with one another. The high voltage device comprises a plurality of zener diodes connected in series. Each of the gate threshold amplifiers comprises a resistive voltage divider and a voltage-controlled resistive device, preferably a MOSFET. Specifically, the voltage divider comprises first and second resistors connected in series between first and second terminals of the gate threshold amplifier, with a MOSFET having its drain connected to the first terminal, its source connected to the second terminal, and its gate connected to an intermediate tap of the voltage divider.
The zener diodes provide high voltage regulation (up to at least about 1600V), while the thermal compensation device exhibits a negative temperature coefficient that substantially offsets the positive temperature coefficient of the zener diodes. This allows efficient operation at temperatures at least as high as about 200° C. The gate threshold amplifiers, each including a voltage-controlled resistive device, allow operation at low shunt regulation currents, i.e., on the order of about 25 &mgr;amps to about 500 &mgr;amps.
The present invention is preferably realized with discrete components, thereby minimizing costs. Because only a few components are needed, even for the regulation of high voltages in relatively high temperature environments, efficient use of space is achieved. Furthermore, the use of solid state components provides a high degree of resistance to mechanical shocks and vibrations. These and other advantages of the present invention will be better appreciated from the detailed description that follows.
REFERENCES:
patent: 5204612 (1993-04-01), Lingstaedt
patent: 5519313 (1996-05-01), Wong et al.
patent: 5585949 (1996-12-01), Yamazaki et al.
patent: 5621307 (1997-04-01), Beggs
patent: 5949122 (1999-09-01), Scaccianoce
Klein & Szekeres LLP
Nguyen Matthew
Titan Specialties, Ltd.
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