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Description  |
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This invention is directed to an improved voltage regulator circuit and,
more specifically, to a voltage regulator including both overvoltage and
under frequency protective features.
A voltage regulator circuit which not only maintains alternator output
voltage constant at the desired frequency but also ramps the output
voltage down linearly with decreases of output voltage frequency and
removes the alternator field excitation with sustained overvoltage
conditions is desirable.
It is, therefore, an object of this invention to provide an improved
alternating current alternator voltage regulator circuit.
It is another object of this invention to provide an improved alternating
current alternator voltage regulator circuit which automatically reduces
the alternator output voltage along a substantially linear ramp with
conditions of reduced output voltage frequency.
It is a further object of this invention to provide an improved alternating
current alternator voltage regulator circuit which automatically
interrupts the alternator field excitation with sustained overvoltage
conditions.
The alternating current alternator voltage regulator circuit of this
invention maintains the alternator output voltage substantially constant
within a desired frequency range and is compatible with both 60 cycle and
50 cycle applications. The circuit of this invention automatically reduces
the alternator output potential level along a linear ramp with output
potential frequencies less than the desired frequency and automatically
interrupts the alternator field winding excitation with sustained
overvoltage conditions which last for a period of time that may be
damaging to the alternator.
In accordance with this invention, a voltage regulator circuit for use with
alternating current alternators is provided wherein the alternator field
winding is electrically energized by circuitry responsive to an electrical
signal produced when the potential level of a ramp potential signal
produced in synchronism with each half cycle of the alternator output
potential rises to a value equal to a direct current reference potential
signal of a potential level inversely proportional to alternator connected
load and, additionally, includes circuitry for ramping the output voltage
down linearly with low output voltage frequency conditions and for
automatically interrupting the alternator field excitation with sustained
overvoltage conditions.
For a better understanding of the present invention, together with
additional objects, advantages and features thereof, reference is made to
the following description and accompanying drawing in which:
FIG. 1 is a schematic representation of a portion of the voltage regulator
circuit of this invention.
FIG. 2 is a schematic representation of the remaining portion of the
voltage regulator circuit of this invention,
FIG. 3 is a set of curves useful in understanding the operation of the
circuitry of FIGS. 1 and 2, and
FIGS. 4a and 4b are diagrams of a program board through which 50 cycle or
60 cycle operation may be selected.
As point of reference or ground potential is the same point electrically
throughout the system, it has been represented by the accepted schematic
symbol in FIGS. 1 and 2 and referenced by the numeral 3.
Referring to FIG. 1 of the drawing, the alternating current alternator is
schematically represented and referenced by the numeral 5 and is shown to
include three output coils 5A, 5B and 5C; a field winding 6 and a separate
exciter 7 having a field winding 8. Diode 9 is a free feeling diode for
dissipating the potential induced in exciter field winding 8 upon the
interruption of energization in a manner well known in the art.
One of the output phases of alternator 5, in FIG. 1 the phase comprising
output coils 5A and 5B, is connected across the primary winding 11 of a
transformer 10 having a center-tapped secondary winding 12 and another
secondary winding 13.
The center-tap of secondary winding 12 is connected to the ungrounded side
of the exciter field winding 8 through the normally closed contacts,
movable contact 16 and stationary contact 17, of an electrical relay 15
having an operating coil 18. The purpose of relay 15, as will be later
brought out in this specification, is to interrupt the exciter field
winding 8 energizing circuit with sustained alternator output voltage
overvoltage conditions. Electrical relay 15, therefore, may be replaced by
a conventional commerically available circuit breaker of the type
electrically operable to the electrical circuit open condition or by a
conventional commercially available circuit breaker of the type both
electrically and thermally operable to the electrical circuit open
condition.
Secondary winding 13 of transformer 10 is connected across the alternating
current input terminals of a full wave diode bridge rectifier circuit 20,
FIG. 2, through leads 28 (1) and 29 (1) of FIG. 1 and 28 (2) and 29 (2) of
FIG. 2. Diode bridge rectifier circuit 20 includes two positive polarity
diodes 21 and 23, two negative polarity bank diodes 22 and 24, a positive
polarity output terminal 25, a negative polarity output terminal 26
connected to point of reference or ground potential 3 and a load resistor
27.
The unfiltered direct current output potential of rectifier circuit 20 is
applied across a shunt linear voltage regulator circuit 30, FIG. 1,
through current limiting resistor 31, blocking diode 32 and lead 33 (2) of
FIG. 2 and lead 33 (1) of FIG. 1 and through point of reference or ground
potential 3. This rectifier circuit 20 output potential is filtered, a
filter network comprised of resistor 34 and parallel capacitors 35 and 36.
The potential appearing across positive polarity lead 40 and point of
reference or ground potential 3 is applied across the series combination
of the Zener diode 41, the parallel combination of diode 42 and resistor
43 which provide temperature compensation and resistor 44 and across the
end terminals of a potentiometer 45 having a movable contact 46. Junction
47 between the diode 42 and resistor 43 parallel combination and resistor
44 is connected to the non-inverting input terminal of a comparator
circuit 50 and the movable contact 46 of potentiometer 45 is connected to
the inverting input terminal of comparator circuit 50. In the preferred
embodiment, comparator circuit 50 is a commercially available comparator
circuit marketed by the National Semiconductor Corporation under the
designation LM2901. The output of the LM2901 comparator is the uncommitted
collector electrode of a grounded emitter NPN output transistor which is
conductive while more current is flowing out of the non-inverting input
terminal than is flowing out of the inverting input terminal and is not
conductive while more current is flowing out of the inverting input
terminal than is flowing into the non-inverting input terminal. With a
pull-up resistor 51 connected across positive polarity lead 40 and the
output terminal of comparator 50, therefore, while more current is flowing
out of the inverting input terminal than is flowing out of the
non-inverting input terminal the signal upon the output terminal of
comparator 50 is of a positive polarity and while more current is flowing
out of the non-inverting input terminal than is flowing out of the
inverting input terminal, the signal upon the output terminal 50 is
substantially ground. Capacitor 52 is a closed loop compensation capacitor
for comparator 50. The magnitude of the desired regulated output potential
across positive polarity lead 40 and point of reference or ground
potential 3 is selected by adjusting movable contact 46 of potentiometer
45. With movable contact 46 set at the point at which the shunt linear
regulator circuit 30 produces the desired regulated output potential, as
the potential across positive polarity lead 40 and point of reference or
ground potential 3 tends to increase, the potential drop across resistor
44 also increases, a condition which causes the output signal of
comparator circuit 50 to rise. The rise of the output signal of comparator
circuit 50 increases the base drive current to NPN transistor 54 through
current limiting resistor 53, a condition which increases the
collector-emitter conduction therethrough. The increased collector-emitter
conduction through NPN transistor 54 produces an increased potential drop
across resistors 31 of FIG. 2 and 34 of FIG. 1, thereby maintaining the
potential across positive polarity lead 40 and point of reference or
ground potential 3 substantially constant. The regulated output potential
of voltage regulator circuit 30 is applied to all points labeled V+ of the
circuit of FIG. 2.
The unfiltered output potential of rectifier circuit 20, curve A of FIG. 3,
is applied across the series combination of resistor 55, resistor 56,
automatic voltage control rheostat 57 and resistor 58 for 50 cycle
applications and is also applied across an R-C time constant network
consisting of resistor 59 and capacitor 60. Resistor 58 is shorted out of
the series combination for 60 cycle applications in a manner to be later
explained. The output voltage level may be selected by adjusting rheostat
57. The regulated output potential of shunt linear regulator circuit 30 is
applied across the series combination of resistors 61 and 62. The
potential across capacitor 60, which appears across junction 63 and point
of reference or ground potential 3 as a direct current output voltage
sensing potential signal of a potential level proportional to the
alternator output voltage level, is applied to the non-inverting input
terminal of an operational amplifier 65 and the potential upon junction 64
across resistor 62 is applied to the inverting input terminal of
operational amplifier 65. In the preferred embodiment, operational
amplifier 65 is a commercially available device marketed by the National
Semiconductor Corporation under the designation LM2902. With more current
flowing out of the inverting input terminal than is flowing out of the
non-inverting input terminal, the signal upon the output terminal of
operational amplifier 65 is of a positive polarity potential and with more
current flowing out of the non-inverting input terminal than is flowing
out of the inverting input terminal, the signal upon the output terminal
of operational amplifier 65 is of a substantially ground potential.
Operational amplifier 65 with feedback capacitor 66 and feedback resistor
67 operates as a direct current reference and summing amplifier circuit in
a manner well known in the art. The unfiltered output potential of
rectifier circuit 20 is also applied across the combination of resistor 68
connected in series with the parallel combination of capacitor 69 and
resistor 70. The potential upon junction 63 is a sensing potential, in the
preferred embodiment 6 volts DC, which the voltage regulator circuit of
this invention tends to maintain at a constant direct current potential
level. The unfiltered output potential of rectifier circuit 20 charges
capacitor 69 through resistor 68 to produce a direct current potential
ramp signal across capacitor 69 as shown in curve B of FIG. 3. When the
unfiltered output potential of rectifier circuit 20 returns to zero,
capacitor 69 discharges through diode 71 to reset capacitor 69 preparatory
to the next rise of the unfiltered output potential of rectifier circuit
20. That is, the combination of resistors 68 and 70, capacitor 69 and
diode 71 produce a direct current ramp potential signal in synchronism
with each half cycle of the alternator output potential which increases in
magnitude within a predetermined range during each half cycle. The output
signal of operational amplifier 65 is a direct current reference potential
signal of a potential level inversely proportional to alternator connected
load and is applied to the non-inverting input terminal of comparator
circuit 75. The direct current ramp potential signal appearing across
capacitor 69 is applied to the inverting input terminal of comparator
circuit 75. In the preferred embodiment, comparator circuit 75 is a
National Semiconductor type LM2901 comparator circuit as described with
regard to the shunt linear regulator circuit 30. Resistor 76 is a pull up
resistor connected to the output terminal of comparator circuit 75 and
resistor 77 is a bias resistor. The center-tapped secondary winding 12 of
transformer 10, FIG. 1, is connected across the junctions 78 and 79
between diode 80 and silicon controlled rectifier 81 and diode 82 and
silicon controlled rectifier 83, respectively, through lead 84 (1) of FIG.
1 and 84 (2) of FIG. 2 and lead 85 (1) of FIG. 1 and 85 (2) of FIG. 2. The
potential induced in center-tapped secondary winding 12, therefore, is
full wave rectified by diodes 80 and 82 and appears as a direct current
potential across lead 74 and point of reference or ground potential 3.
While NPN transistor 86 is not conductive through the collector-emitter
electrodes thereof, the potential appearing across lead 74 and point of
reference or ground potential 3 triggers silicon controlled rectifier 87
conductive to supply gate current to both silicon controlled rectifiers 81
and 83 through respective blocking diodes 88 and 89. Resistors 90 and 91
are gate electrodes stabilizing resistors for respective silicon
controlled rectifiers 81 and 83. Capacitor 92 is a filter capacitor and
resistor 93 is a current limiter.
With the alternator operating under conditions of no connected electrical
load with 50 cycle applications, the potential induced in secondary
winding 13 of transformer 10, FIG. 1, is full wave rectified by rectifier
circuit 20 and attenuated to a level suitable as an input signal to
operational amplifier 65 by the voltage divider network comprised of
series resistors 55 and 56, rheostat 57 and resistor 58. Resistor 58 is
included in this network for 50 cycle applications but is shorted out for
60 cycle application in a manner to be later explained. With this
condition of operation, the direct current reference potential signal
produced by operational amplifier 65 of the reference and summing
amplifier circuit is of a maximum direct current potential level as
determined by the potentials upon junctions 63 and 64, as indicated by
reference A of curve B of FIG. 3. At the beginning of each half cycle of
the alternator output potential, the ramp potential signal level is less
than that of the reference potential signal, consequently, the signal
present upon the output terminal of comparator circuit 75 is of a positive
polarity. This positive polarity signal supplies base-emitter drive
current to NPN transistor 86 to trigger this device conductive through the
collector-emitter electrodes thereof. Conducting NPN transistor 86 shunts
gate current from silicon controlled rectifier 87 to point of reference or
ground potential 3 through current limiting resistor 94, consequently,
silicon controlled rectifier 87 is not triggered conductive. While silicon
controlled rectifier 87 is not conductive, gate current is not supplied to
either of silicon controlled rectifiers 81 and 83, consequently, these
devices remain not conductive to interrupt the energizing circuit, to be
later described, for exciter field winding 8. When the potential level of
the ramp potential signal has reached the potential level of the reference
potential signal, for example at 120 electrical degrees of each alternator
output potential half cycle, comparator circuit 75 switches and the signal
appearing upon the output terminal thereof is of substantially ground
potential, being above ground by the drop across the conducting output NPN
transistor. The substantially ground potential signal upon the output
terminal of comparator circuit 75 extinguishes NPN transistor 86. When NPN
transistor 86 extinguishes, gate current is supplied through resistor 94
to silicon controlled rectifier 87 to trigger this device conductive
through the anode-cathode electrodes thereof. Conducting silicon rectifier
87 supplies gate current to silicon controlled rectifiers 81 and 83
through respective blocking diodes 88 and 89. Therefore, the one of
silicon controlled rectifiers 81 and 83 which is forward biased at the
time silicon controlled rectifier 87 is triggered conductive is triggered
conductive thereby to complete an energizing circuit for exicter field
winding 8. Assuming that terminal end 12a of center-tapped secondary
winding 12 of transformer 10, FIG. 1, is of a positive polarity with
respect to the center-tap, the exciter field winding 8 energizing circuit
may be traced from terminal end 12a of center-tapped secondary winding 12,
through lead 85 (1) of FIG. 1, lead 85 (2) of FIG 2, conducting silicon
controlled rectifier 83, the one of the silicon controlled rectifier 81-83
pair forward biased at this time, point of reference or ground potential
3, exciter field winding 8, FIG. 1, the normally closed contacts 16 and 17
of electrical relay 15 to the center-tap of secondary winding 12.
Consequently, exciter field winding 8 is energized during the last 60
electrical degrees of each cycle of the alternator output potential, curve
C of FIG. 3.
Should the alternator output potential level fall as a result of a
connected load or some other reason, the potential level upon junction 63,
FIG. 2, tends to reduce. A reduction of potential upon junction 63 results
in a decrease of the potential level of the reference potential signal
produced by operational amplifier 65 of the reference and summing
amplifier circuit, as indicated by reference level B of curve B of FIG. 3.
At the beginning of each half cycle of the alternator output potential,
the ramp potential signal level is less than that of the reference
potential signal, consequently, the signal present upon the output
terminal of comparator circuit 75 is of a positive polarity. Therefore,
silicon controlled rectifier 87, FIG. 2 is not conductive for reasons
hereinbefore described. When the potential level of the ramp potential
signal has reached the potential level of the reference potential signal,
for example at 40 electrical degrees of each alternator output potential
half cycle, comparator circuit 75 switches and the signal appearing upon
the output terminal thereof is of substantially ground potential. The
substantially ground potential signal upon the output terminal of
comparator circuit 75 extinguishes NPN transistor 86. When NPN transistor
86 extinguishes, gate current is supplied to silicon controlled rectifier
87 to trigger this device conductive through the anode-cathode electrode
thereof. Conducting silicon-controlled rectifier 87 supplies gate current
to silicon controlled rectifiers 81 and 83 through respective blocking
diodes 88 and 89. Therefore, the one of silicon controlled rectifiers 81
or 83 which is forward biased is triggered conductive to complete the
exciter field winding 8 energizing circuit previously described.
Consequently, exciter field winding 8 is energized during the last 140
electrical degrees of each half cycle of the alternator output potential,
curve D of FIG. 3. As a result of the exciter field winding 8 being
energized for a longer period of time during each half cycle of the
alternator 5 output potential, the alternator field winding 6 is energized
for a longer period of time, a condition which increases the level of the
alternator output potential in a manner well known in the art.
From this description, it is apparent that the voltage regulator circuit of
this invention controls the electrical energization of the field winding 6
of alternating current alternator 5 in a manner to maintain the alternator
alternating current output potential substantially constant by tending to
maintain the potential across capacitor 60 substantially constant, the
energization of the alternator field winding 6 being adjusted in a
direction to maintain a substantially constant potential across capacitor
60.
An important feature of the voltage regulator circuit of this invention is
the automatic interruption of the exciter field winding 8 energizing
circuit with sustained overvoltage conditions above any selected voltage
level of a selected percentage, in the preferred embodiment 10 percent. As
the voltage regulator circuit of this invention operates to maintain a
substantially constant potential across capacitor 60, in the preferred
embodiment 6 volts DC, the ohmic value of resistors 100 and 101 connected
as a voltage divider network across positive polarity lead 40 and point of
reference or ground potential 3, FIG. 1, are so selected that the
potential upon junction 102 is 10 percent greater than the selected
potential across capacitor 60 of FIG. 2, in the preferred embodiment 6.6
volts DC. The potential upon junction 102 is applied to the inverting
input terminal of comparator circuit 105 which may also be a National
Semiconductor type LM2901 comparator circuit as previously described with
regard to the shunt linear voltage regulator circuit 30. The potential
upon junction 63, the potential appearing across capacitor 60 of FIG. 2,
is applied to the non-inverting input terminal of comparator circuit 105
through lead 106 (2) of FIG. 2 and lead 106 (1) of FIG. 1. So long as the
potential upon junction 102 is greater than the potential upon junction
63, the signal present upon the output terminal of comparator circuit 105
is substantially ground potential. In the event the potential upon
junction 63 rises to a value equal to or greater than that upon junction
102, comparator circuit 105 switches and the signal present upon the
output terminal thereof is of a positive polarity. This positive polarity
signal is applied through a bilateral switch 107 to the gate electrode of
a silicon controlled rectifier 108. Upon the application of a gate signal
to silicon controlled rectifier 108, this device is triggered conductive
through the anode-cathode electrodes thereof to complete an energizing
circuit for operating coil 18 of electrical relay 15. This energizing
circuit may be traced from terminal end 13b of secondary winding 13
through diode 109, operating coil 18 of electrical relay 15, conducting
silicon controlled rectifier 108, point of reference or ground potential
3, diode 22 of rectifier circuit 20 of FIG. 2, lead 28 (2) of FIG. 2 and
lead 28 (1) of FIG. 1 to terminal end 13a of secondary winding 13. Upon
the energization of operating coil 18 of electrical relay 15, movable
contact 16 thereof is operated out of electrical circuit engagement with
stationary contact 17 to interrupt the energizing circuit previously
described for exciter field winding 8. Upon the interruption of the
energizing circuit for exciter field winding 8, the alternator field
winding 6 is no longer energized and the alternator output potential
reduces to a value determined by the magnetic flux produced by the
residual magnetism in the alternator iron. Capacitor 110 is a filter
capacitor. Resistor 111 is a pullup resistor for comparator 105, resistor
112 is a current limiting resistor and capacitor 113 provides a delay
feature which prevents the operation of electrical relay 15 with
alternator output potential over-voltage conditions of short duration.
Bilateral switch 107 may be any of the commercially available potential
threshold sensitive switching devices such as a type 2N4992 marketed by
General Electric or a type MPS4992 marketed by Motorola.
Another important feature of the voltage regulator circuit of this
invention is the automatic reduction of alternator output voltage level at
frequencies less than the desired frequency. Comparator 115, FIG. 2, and
operational amplifier 116 and the associated circuitry operate as a
monostable multivibrator circuit. Comparator circuit 115 may also be a
National Semiconductor type LM2901, previously described with regard to
the shunt linear regulator circuit, and operational amplifier 116 may be a
National Semiconductor type LM2902, as previously described in regard to
the reference and summing amplifier circuit. The potential appearing upon
junction 64 is applied as a bias potential to the inverting input terminal
of comparator 115 and the potential across movable contact 119 of
potentiometer 120 and point of reference or ground potential 3 is applied
as a bias potential to the non-inverting input terminal of operational
amplifier 116. This bias condition results in a signal upon the output
terminal of operational amplifier 116 of a positive polarity and a signal
upon the output terminal of comparator 115 of a substantially ground
potential which holds capacitor 121 discharged. Capacitor 122 is charged
by the positive polarity signal upon the output terminal of operational
amplifier 116 through diode 123 and resistor 124 and the charge
thereacross is applied to the non-inverting input terminal of comparator
circuit 115. When the charge potential across capacitor 122 has risen to a
value equal to the reference potential applied to the inverting input
terminal of comparator circuit 115, comparator circuit switches. At this
time, capacitor 121 begins to charge through diode 125 and resistor 126.
The charge potential across capacitor 121 is applied to the inverting
input terminal of operational amplifier 116, consequently, when the charge
potential across capacitor 121 rises to a value equal to the reference
potential applied to the non-inverting input terminal thereof, operational
amplifier 116 switches and the signal present upon the output terminal
thereof is of substantially ground potential. Capacitor 121 continues to
charge to the V+ voltage less the drop across diode 125 and capacitor 122
is charged to the V+ voltage less the drop across the output transistor of
operational amplifier 116. Diode 123 blocks the discharge path of
capacitor 122 through resistor 124 and diode 127 is reverse biased. At the
end of each half cycle of the alternator output potential, diode 127
conducts to discharge capacitor 122 through resistor 128. When the charge
potential across capacitor 122 drops below the reference potential applied
to the inverting input terminal of comparator circuit 115, comparator
circuit 115 switches and the cycle repeats. The output signal of
operational amplifier 116 is of a constant pulse width and height and
occurs at twice the alternator output potential frequency because of the
full wave rectification of rectifier circuit 20. Resistor 129 is a load
resistor.
The output signal of the monostable multivibrator circuit just described is
filtered by the resistor 130 and capacitor 131 combination and is applied
to the non-inverting input terminal of operational amplifier 135.
Operational amplifier 135 may be a National Semiconductor type LM2902
previously described. Operational amplifier 135 is employed as an
amplifier circuit wherein resistors 136 and 137 determine the amount of
amplifier feedback which, establishes the amplifier gain. Capacitor 138
provides dynamic feedback for improved amplifier stability and ripple
reduction. The output of operational amplifier 135 is a direct-current
voltage of a level proportional to the frequency of the signals produced
by the previously described monostable multivibrator circuit which, in the
preferred embodiment, was arranged to provide 6 volts at 60 cycles. This
voltage may be brought out through terminal 140 and employed with a
voltmeter or an ammeter to provide an accurate electronic tachometer.
Series resistor 141 protects operational amplifier 135 from short
circuits.
Resistors 143 and 144 form a voltage divider network that establishes a
reference voltage upon the noninverting input terminal of operational
amplifier 145 which may be a National Semiconductor type LM2902. With 50
cycle operation, resistor 142 is parallelled with resistor 144 in a manner
to be later explained. Resistors 146 and 147 cooperate with feedback
resistor 148 to establish the gain of operational amplifier 145 and divide
the pulse averaging potential output of operational amplifier 135 to the
proper voltage level. Capacitor 149 provides dynamic feedback for
operational amplifier 145. While alternator 5 is operating at rated
frequency, the voltage at the inverting input terminal of operational
amplifier 145 is greater than the reference potential upon the
non-inverting terminal thereof, a condition which maintains the output
signal of operational amplifier 145 at substantially ground potential.
When the frequency of the alternator 5 output potential decreases to a
point at which the potential produced by operational amplifier 135 and
applied to the inverting input terminal of operational amplifier 145 is of
a magnitude less than that of the reference potential applied to the
non-inverting input terminal, the output signal of operational amplifier
145 begins to ramp up in a positive direction at a rate inversely
proportional to alternator 5 output voltage frequency. This direct current
frequency error ramp signal is added to the sensing voltage at the summing
point 63 of the reference and summing amplifier circuit previously
described through weighting resistor 150. As has been previously brought
out, the voltage regulator circuit of this invention operates to maintain
the sensing voltage upon junction 63 substantially constant, in the
preferred embodiment 6 volts DC, the voltage upon capacitor 60 must
decrease by the same amount that the voltage added by the output signal of
operational amplifier 145 has increased. Consequently, the remainder of
the voltage regulator circuit of this invention operates to decrease the
alternator 5 output potential with decreasing frequency. As the output
voltage of operational amplifier 145 increases, this voltage supplies gate
current to silicon controlled rectifier 155 through current limiting
resistor 156. This gate current triggers silicon controlled rectifier 155
conductive through the anode-cathode electrodes thereof to establish an
energizing circuit for an electrically energizable indicator device, in
the preferred embodiment a light emitting diode 157, to energize this
device which is a visual indication of alternator 5 output voltage low
frequency. This energizing circuit may be traced from the positive
polarity output terminal 25 of rectifier circuit 20 through lead 158,
current limiting resistor 159, light emitting diode 157, silicon
controlled rectifier 155 and point of reference or ground potential 3 to a
negative polarity terminal 26 of rectifier circuit 20.
Resistor 160 and capacitor 161 form a one pole low pass filter circuit and
resistors 162 and 163 are connected in parallel with resistor 160 to alter
the filter characteristics for various alternator sizes. Resistors 160,
162 and 163 are all connected in parallel for low KW ratings, resistors
160 and 162 are connected in parallel for medium KW ratings and resistors
162 and 163 are left open for high KW ratings. In general, the larger the
alternator, the longer the time constant, therefore, the longer the low
pass time constant and vice versa. The output of the low pass filter is AC
coupled through capacitor 165, resistor 166 and lead 167 (1) of FIG. 1 and
lead 167 (2) and junction 64 of FIG. 2 to the inverting input terminal of
operational amplifier 65 of the reference and summing amplifier. Should
the voltage across the exciter field winding 8 oscillate or hunt, the
frequency thereof is three to seven cycles per second. The low pass filter
passes this low frequency and couples it back to the inverting input
terminal of operational amplifier 65 to stop the oscillation or hunting.
That is, the network just described functions as a low band pass filter at
the hunt frequency of the alternator. Capacitor 173 and resistor 174
provide surge protection.
As the output voltage level with 50 cycle applications is lower than with
60 cycle applications, resistor 58 is shorted out with 60 cycle
applications to provide 60 cycle operation upper and lower output voltage
limits. To maintain a 6 volts DC potential charge upon capacitor 60, a
greater output potential magnitude is required. For 50 cycle operation,
resistors 142 and 144 are paralleled to lower the reference potential upon
the non-inverting input terminal of operational amplifier 145, and
resistor 146 is shorted to increase the operational amplifier 145 gain.
This results in a steeper frequency error ramp signal which begins at
lower frequencies.
To provide dual frequency operation, the points of FIG. 2 labeled T1, T2,
T3, T4 and T5 are brought out to external terminals, FIG. 4. A program
board 170 is provided with corresponding terminals which are of a type
which engage the external terminals in electrical connections. Terminals B
and C and terminals D and E are electrically interconnected by respective
conductors 171 and 172. With program board 170 positioned so that
terminals A, B, C, D, E and F engage respective external terminals T3, T4,
T6, T1, T2 and T5, resistor 58 is shorted to provide 60 cycle operation.
With program board 170 positioned so that terminals A, B, C, D, E and F
engage respective external terminals T1, T2, T5, T3, T4 and T6, resistor
58 is connected in the previously described voltage divider network,
resistor 146 is shorted out and resistor 142 is connected in parallel with
resistor 144 to provide 50 cycle operation. Program board 170, therefore,
provides for the selective conditioning of the voltage regulator circuit
for either of two alternator output voltage frequencies.
From this description, it is apparent that the novel voltage regulator
circuit of this invention controls the electrical energization of the
field winding of an associated alternating current alternator in a manner
to maintain the alternator alternating current output potential
substantially constant and provides the following features:
1. Automatic over-voltage protection a selected percentage above any preset
voltage level.
2. Dual frequency operation.
3. A voltage and frequency program card through which the regulator circuit
may be pre-programmed for two separate operating frequencies.
4. A tachometer output.
5. An under-frequency indicator.
While a preferred embodiment of the present invention has been shown and
described, it will be obvious to those skilled in the art that various
modifications and substitutions may be made without departing from the
spirit of the invention which is to be limited only within the scope of
the appended claims.
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