Note: Descriptions are shown in the official language in which they were submitted.
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MOTOR STARTI~G CIRCUIT
.
This invention relates generally to any single
phase AC motors and more particularly to capacitor start AC
motors and electronic motor starting circuit means therefor.
In general, single phase AC motors employ a start
winding and a main runnlng winding. The current in the start
winding i~5 phase shifted relative to the main winding current
in order to provide starting torque during the normal motor
start up periods; the start winding usually being deenergized
prior to the motor reaching operating speed~ In normal
course, deenergization of the start windings is carried out
by speed responsive switch or timed means, such as a
centrifugal swltch and actuator or electromagnetic switch,
operable at a preselected motor speed, to deenergize the
start winding circuit. Employment of such an actuator-switch
generates typical disadvantages such as corrosion, adjustment
or breakage of mechanical parts, sparking, contact wear, etc.
In other instances electronic switching circuits have been
substituted for the speed responsive switch means. However,
due to relative high cost such developments have encountered
limited acceptance and use.
In addition to the speed responsive switch means
noted above, the typical single phase AC motor also employs
an AC starting capacitor which is relatively cumbersome, and
is limited in its cyclic capability of energizing the start
winding.
Brief Summary~ of the Invention
The present invention is directed to novel
electronic circuit means or starting single phase powered AC
motors which avoids the above noted difficulties attendant to
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the use of AC starting capacitors and speed responsive switch
means by eliminating such elements in the motor starting
means of this invention.
In brief this invention comprises all electronic,
sparkless, starting and control circuitry for single phase
powered AC motors wherein phase displaced current is provided
to excite the motor start windings~ Uniquely the pulse width
of such starting current signals is gradually reduced to zero
to deenergize the start winding. To accomplish this the
basic circuitry of this invention includes a single phase AC
power source, the main motor windings, first rectifier means
for producing a series of rectified pulses from the
sinusoidal AC input, zero crossing detector means for
detecting and providing an output signal each time the
sinusoidal ~C wave form goes through zero, and integrated
signal manager means for accepting the output of the zero
crossing detector along with other signals, conditioning the
signal information and providing an output pulse rate to
electronic switch means which cooperate with second rectifier
means to control energization of the start windings of the
motor. Timin~ circuit means operate in conjunction with the
signal manager to condition the output signals of the latter
to progressively decreasing pulse width or time duration
whereby to bring about the ultimate deenergization of -the
motor start winding. The two rectifier means are arranged to
provide a compact dual power supply, which eliminates the
need for a cumbersome line isolation transformer or the like
while presenting low current power for the logic circuitry
and high current power to the motor start winding.
A principle object of this invention is to provide
0 a novel all electronic starting circuit for AC motors
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utilizing a single phase power source.
Another important object of this invention is toprovide a single phase AC motor starting circuit as aforesaid
which is sparkless and safe to operate in potentially
hazardous atmospheres.
Another object of this invention is to provide a
phase displaced current in the start windings of a single
phase AC motor without the use of an AC start capacitor.
Still another object of the invention is to provide
means for interrupting starting current in single phase
powered AC motor start windings without the use of mechanlcal
or other speed responsive switch means.
A further object of this invention is to provide
means for exciting the start winding of a single phase
powered AC motor for a controlled time period.
Still another important object of this invention is
to provide a novel bridge rectifier power supply arrangement
capable of providing high and low current without the use of
isolation transformers.
A urther important object of this invention is to
provide an electronic starting circuit for AC motors
embodying timing means for continuously reducing the time
interval for start winding excitation and operable to reduce
magnetic noise when the start winding is deenergized.
Still another important object of this invention is
to provide improved starting and control circuit means for
single phase AC motors which is compact, substantially
maintenance free and lends itself to economies of production.
Having described this invention the above and
further objects, features and advantages thereof will appear
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from time to time from the following description of a
preferred embodiment thereof illustrated in the accompanying
drawings and representing the best mode presently
contemplated for enabling those with skill in the art to
practice this invention.
Fig. 1 is a schematic circuit diagram of the basic
motor starting and control circuit of this invention;
Fig. 2 is a chart showing electrical wave forms at
various points in the circuit of Fig. 1; and
Fig. 3 is a schematic diagram illustrating the dual
power supply incorporated in the starting and control circuit
of Fig. 1.
Description of the Preferred Embodiment
Turning now to the detail features of the preferred
embodiment shown in the drawings~illustrative of the basic
features of the motor starting circuit means according to
this lnvention, reference is made to Fi~ures 1 and 2.
As shown in Fig. 1, an AC voltage source 10,
typically 115/230 volts 60 Hertz, is coupled between main
conductors 11 and 12. This AC power input is applied to the
motor's running or main winding 13 and to a first full wave
bridge rectifier 14, constituting a diode rectifier, coupled
in parallel circuit with windinys 13.
As shown in Fig. 2 of the drawings the uppermost
wave form I demonstrates that the AC input to rectifier 14 is
a sinusoidal wave while the output from rectifier 14,
indicated by wave form II, comprises a series of full wave
rectified pulses.
The rectified pulses developed by bridge rectifier
14 are applied simultaneously to the base circuit of
3~ transistor 15, and to diode 16 to charge a capacitor 17 with
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DC voltage. Such rectified pulses also are applied to diode
18 to charge a second capacitor 19 to a DC level.
Transistor 15 is in circuit with a second
transistor 20 and diode section 21 of an optocoupler 22.
Components 15, 20 & 22 serve as a zero crossing detector for
determining each time the sinusoidal wave form of the AC
power input goes through a zero crossing point. (See wave
form I of Fig. 2). Transistor 15 is a NP~a type and turns on
only in response to positive signals. Therefore the positive
output from bridge rectifier 14 switches transistor 15 to an
"on" state which in turn drives transistor 20 each time the
sinusoidal wave form I in Fig. 2 goes through a zero crossing
point. Conduction of transistor 20 serves to energize the
diode section 21 of optocoupler 22 causing the same to
conduct each time a zero crossing occurs. Conduction of the
diode section 21 causes the conduction of transistor portion
23 thereof. The outpu~ of transistor 20 to the diode portion
21 of optocoupler 22 constitutes a series of positive spike
pulses (wave form III of Fig. 2) with each positive pulse
occuring as the input sinusoidal wave form goes through its
zero crossing point.
Each time the transistor portion 23 of the
optocoupler 21 conducts, the input to trigger signal pin 6 of
an integrated circuit signal manager 30, goes l'low" and is
clamped to reference ground via resistor 31 to produce a
resulting wave form constituting a series of negative pulses
which occur in synchronism with the zero crossing of the
input sine wave, as illustrated by wave form IV in Fig. 2.
Signal manager 30 comprises an integrated micro-
circuit which serves to manage and condition the signal input
and output therefrom by accepting multiple signals,
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conditioning the received signal information and providing an
output signal pulse rate requisite to start and accelerate the
single phase motor, as will appear in greater detail presently.
Dual timing integrated circuits generally identified under
industry standard No. 555-556 capable of providing the functions
of signal manager 30 are commercially available from many
manufacturers.
A low current power supply for the integrated circuit
of signal manager 30 is provided by the diode 18, resistance 32,
capacitor 33 and a zener diode 34 network; the zener diode 34
serving to provide a regulated voltage. In addition to its
signal management functions, the integrated circuit 30 also
importantly serves as a timing device in conjunction with related
timing circuit networks as will be described more fully
hereinafter; -the major thrust of which is to phase out or
regulate the output of the integrated circuit 30 to accordingly
deactivate the start winding of the motor. Thus in accordance
with that objective of this invention the start period for the
motor is time controlled.
On reception of input trigger signals at pin 6, the
integrated signal manager 30 develops a series of positive output
pulses at pin 5 (see wave form V of Fig. 2) which feed a
differentiator network comprising capacitor 40, resistor 41 and
diode 42. The capacitor 40 and resistor 41 serve to
differentiate the positive output signal from pin 5, with the
positive portion of the differentiated wave form VI of Fig. 2
being clamped to reference ground level by diode 42 and the
negative portion of such signal being fed to pin 8 for purposes
of triggering the time at which drive signals at output pin 9
commence or i'start" as will be described presently.
The pulse width or time duration of the output signals
from pin 5 is controlled by a network comprising series related
resistors 43, 44 and capacitor 45. It also is to be noted that
resistor 43 is in parallel with a direction switch means 46 which
is normally closed to bypass or short out resistor 43 providing a
first predetermined time constant for the output pulses of pin 5
over resistor 44 and capacitor 45. In operation the resistor
capacitor network 44, 45 controls the length of ti~le for pin 5 to
be positive by regulating the input to pins 1 and 2 of the signal
manager. When capacitor 45 reaches a threshold voltage dictated
by pin 2 it discharges into pin 1 causing the output at pin 5 of
the signal manager 30 to go "low". Opening of switch 46 places
resistor 43 in the circuit causing a lon~er time constant that
increases the width of pin 5 signals. The width of the pin 5
signals is sufficient to shift over into a phase of opposite
polarity. Thus, the signals received by pin 9 occur during the
time of opposite polarity to start the motor in a reverse
direction, if desired.
Inasmuch as the integrated circuit 30 not only
conditions the signal information, but provides a regulated pulse
output rate for the starting and acceleration of the single phase
motor and more particularly for controlling energization and
deenergization of the start windings thereof, it is essential
that certain timing functions be performed. This is accomplished
by means of two additional time constant networks which control
the input to threshold voltage pin 12 of the signal manager 30.
The first time constant is determined by the series
resistance capacitor network 51, 52 paralleled by transistors 53,
54, respectively, which cooperate to regulate the pulse width or
duration of the input signals to pin 12.
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The second time constant is provided by the series
resistor-capacitor network 551 56 paralleling the first time
constant network. This second time constant functionally
prevents application of starting current to the single phase AC
motor start winding, when capacitor 56 is fully charged.
Regarding the first time constant, the charge across
capacitor 56 begins to increase as soon as DC voltage is
available from the regulated power supply provided by diode
18, capacitor 19, resi~tor 32, capacitor 33, and ~ener diode
34. As the positive charge across capacitor 56 builds up
transistor 53 begins to conduct. As a consequence ~he
resistance of parallel resistor 51 is modified effecting a
decrease in the first time constant network.
When the charge across capacitor 52 reaches a
threshold level established within IC30 for firing it causes
transistor 54 to conduct which thereby discharges capacitor
52. This action resets the signal manager 30 for the next
incoming zero crossing signal thereby regulating the pulse
width of the output signal from IC30 pin 9 which is
continuously reducing toward zero as shown by wave form VII
of Fig. 2. The time for this pulse width to approach zero is
dependent upon the second time constant of resistahce 55 and
capacitor 56.
When capacitor 56 is fully charged transistor 53 is
driven into saturation, causing its parallel resistor 51 to
react as if it were a short circuit. At this time the pulse
width of the output signal at pin 9 is so small as to effect
deenergization of the motor's start windings.
It will be recalled that the output drive signals
at pin 9 of the signal manager are triggered by the
di~ferentiated start signals from pin 5 by virtue of the
differentiator network 40, 41. Such output drive signals are
Eed over resistor 60 to electronic switch means 61 comprising
a power MOSFET which is connected across the plus and minus
terminals of a second full wave bridge rectifier 62 to
operably switch the load (in this instance the motor starting
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winding 63) "on" and "off" for the controlled starting cycle.
Inasmuch as the output signal from pin 5 gradually approaches
zero pulse width as heretofore noted, so do the MOSFET
driving signals from pin 9. Thus the starting pulse to start
winding 63 also gradually decreases to nearly zero,
deenergizing the start winding according to that objective of
this invention.
It will be noted in Fig. 1, that the MOSFET 61 is
paralleled by a capacitor 65 across the plus and minus
terminals of the second bridge rectifier 62. This capacitor
serves to reduce transients generated when current in the
start winding 63 is interrupt~d. It also aids the phase
displacement of the current through winding 63 to increase
the level of starting torque during the period when such
starting current is active.
As noted heretofore one of the more important
objectives of this invention is the provision of a compact
and dependable dual power supply for providing low current
power to the logic circuits and high current power to the
motor start winding 63 without the need for isolation
transformers. This is accomplished by the novel arrangement
of the two full wave bridge rectiiers 14 and 62 as
illustrated in Fig. 3.
As there shown, bridge rectifier 14 comprises four
diodes Dl-D4 and bridge rectifier 62 comprises four diodes D5-
D8. The supply for powering IC30 (not shown) is taken from
the positive side of rectifier 14 over diode 18, resistance
32, and zener diode 34 to the negative side of bridge
rectifier 62. This arrangement provides positive voltage
from bridge rectifier 14 with respect to the negative
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reference of bridge rectifier 62~ At the same time bridge
rectifier 62 is connected in series with the motor start
winding 63 and across the supply lines 11 and 12 to provide
high current drive pulses to start winding 63 in response to
the time regulated switching activity of the MOSFET 61.
Uniquely, in accordance with~this invention the time duration
of such driving pulses is gradually reduced -to effect
deenergization of the start windings.
From the foregoing it is believed that those
skilled in the art will readily recognize the novel
advancement of the present invention over prior known motor
starting means, and will appreciate that while this invention
has been described in conjunction with a particular preferred
embodiment thereof illustrated in the drawing, the same is
susceptible to variations and substitution of equivalents
without departing from the spirit and scope of the invention
which is to be unlimited by the foregoing except as may
appear in the hereafter appended claims.
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