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Description  |
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BACKGROUND OF INVENTION
Prior art applications of controlling the energization of a load have
included a triac or bilateral triode switch device which can be made to
conduct on both alternations of an AC voltage. In such applications,
trigger circuits are provided for the triac which must be triggered into
conduction. As an example, in U.S. Pat. No. 3,665,219, there is described
an AC semiconductor switch for controlling the energization of a load from
a relatively high voltage source which is controlled by signal pulses
supplied to the semiconductor from a circuit connected to a relatively low
voltage source. Such teachings, however, have the disadvantage that a
separate DC voltage source must be provided to the signal producing
circuit. This additional DC voltage source tends to degrade the power
control due to the cost, reliability and weight associated therewith.
In addition to the above-described disadvantages of the prior art, circuits
have been developed to control the energization of a load using techniques
such as optical isolation of the trigger signal and the concept of
zerocross triggering to improve radiated noise and reduce surge current,
for an example, as the circuit described in U.S. Pat. No. 3,723,769. Here
again, external DC sources have been utilized.
SUMMARY OF INVENTION
Accordingly, the present invention is directed to an electrical switch
which can be remotely conditioned to an ON or OFF state for controlling
the energization of a load and which does not require additional external
sources of power. More specifically, the circuit provides not only the
activation of power to a load but, in addition, provides isolation of the
line and activator, switching that is logic compatible, and reduced turn
on power surge and yet requires no power from the input activator.
It is therefore an object of the present invention to provide an electrical
switch which overcomes the disadvantages of the prior art.
It is another object of the present invention to provide a circuit for the
activation of power to a load which provides isolation of the power source
and activator, switching that is logic compatable, and reduced turn on
power surge without requiring power from the input activator.
It is yet another object of the present invention to provide an electric
switch which is remotely operated.
The foregoing and numerous other objects, advantages, and inherent
functions of the present invention will become apparent as the same is
more fully understood from the following description and single drawing
which describes one preferred embodiment of the invention; it is to be
understood, however, that the embodiment is not intended to be exhausting
nor limiting of the invention but is given for purposes of illustration in
order that others skilled in the art may fully understand the invention
and principles thereof and the method of applying it in practical use so
that they may modify it in various forms, each as may best be suited to
the conditions of the particular use.
DESCRIPTION OF DRAWINGS
The single FIGURE of the drawing is a schematic diagram of an electrical
switch in accordance with one preferred embodiment of the present
invention.
DESCRIPTION OF INVENTION
Referring to the single FIGURE, it is seen that the switch according to the
present invention includes a transformer 10, such transformer being
utilized to provide operating power to a control source ordinarily
requiring a separate source of power, as well as isolating such control
source from a source of electrical energy applied to the switch via input
terminals 12 and 14. This electrical energy is coupled to a first winding
16 of transformer 10 via a series connected resistor 18. Resistor 18 can,
of course, be of such value to enable, for example, a conventional 115
volt, 60 Hertz waveform to be the source of electrical energy, or it may
be of different value to enable a conventional 230 volt, 60 Hertz waveform
to be the source of electrical energy. Disposed in parallel with first
winding 16 and the limiting resistor 18 is a load 20 and series connected
TRIAC 22. It is the load 20 that the electrical switch according to the
present invention is remotely conditioned to control. This load may be,
for example, a variety of electronic or electric equipment which requires
energization from an AC voltage waveform of the power lines.
The TRIAC 22, which is a conventional three terminal switch that can be
triggered with either positive or negative gate pulses when the anode
potentials are positive or negative, respectively (see "Integrated
Electronics: Analog and Digital Circuits and Systems" by J. Millman and C.
Halkias, copyright 1972 by McGraw-Hill, Inc.), has its gate terminal
coupled to a second winding 24 of transformer 10 via a plurality of diode
pairs 26-28 and 30-32. It should be mentioned that the diodes 26, 28, 30
and 32 are utilized to insure the gate characteristics of the TRIAC are
fully anticipated, and could be eliminated entirely or require additional
ones depending upon the voltage turn on (activation) specification of the
selected TRIAC.
Before continuing, it should be mentioned that transformer 10 is
preferrably a transformer having a second winding 24 with fewer turns that
the first winding 16 to provide a current-step-up for driving the TRIAC
gate. In addition, transformer 10 preferrably provides the dielectric
withstand as required by IEC and UL ratings for line isolation between
primary and secondary.
A third winding 34 of transformer 10 is provided for delivering to the
control source the energy transferred across the transformer. Such energy
is firstly applied to a plurality of diodes 36, 38, 40 and 42. These
diodes are conventionally connected so as to treat the energy transferred
across the transformer to the advantages of full wave rectification.
Coupled between the diodes 36, 40 and 38, 42 is a series connected circuit
comprising a resistor 44, a resistor 52, the base-emitter junction of a
first transistor 50 which is preferrably on the NPN type, and a diode 56.
The junctions formed by the connection of the resistors 44, 52 and the
connection of the diode 56 to diodes 38, 42 respectively, are provided
with terminals 54 and 58 with polarity as shown. These terminals are
provided as logic compatible inputs for logical circuits such as TTL, RTL,
DTL, MOS, CMOS, Reed Relays, switches, Optoisolators, etc. and will be
discussed elsewhere in the description.
The circuit additionally consists of a second transistor 48 which is
preferrably of the PNP type, having its emitter-collector junction
disposed between the diodes 36, 40 and the junction formed by the
connection of the resistor 52 and the base of first transistor 50. The
base of this second transistor 48 is directly coupled to the collector of
first transistor 50 and also coupled to the diodes 36, 40 via a
base-emitter resistor 46. Although not shown in the drawings, each
transistor may have a capacitor disposed across its base-emitter for noise
suppression purposes.
Before considering the operation of the switch, while applicants do not
wish to be limited to any particular set of values, the following values
for the components have proved useful in one embodiment of the described
invention:
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Resistor 18 10K.OMEGA., 3 Watt at 110V; 20K.OMEGA. 6 Watt at 230V
Resistor 44 100K.OMEGA., 1/2 Watt
Resistor 46 4.7K.OMEGA., 1/2 Watt
Resistor 52 6.2K.OMEGA., 1/2 Watt
TRIAC 22 General Electric SC141D
Diodes 26,28,30,32,56
1N4152
Diodes 36,38,40,42
1N4610
Transistor 48 2N3906
Transistor 50 2N3904
Transformer 10
Winding 16 - 3000 turns #42
Winding 24 - 300 turns #33
Winding 34 - 3000 turns #42
Core - EI-25
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Operation of the circuit will now be considered. Assuming that terminals 54
and 58 are as shown in the drawings and that an AC source of power is
instantaneously applied between the pair of power terminals 12, 14, there
will exist the beginning of a pulsating of half-sinusoid at the output of
the bridge rectifier comprising the already mentioned diodes 36, 38, 40
and 42. This causes a current to flow via resistor 44, resistor 52, and
the base-emitter junction of transistor 50 which is returned to the bridge
via the diode 56. Transistor 50 is therefore biased into conduction which,
in turn, turns on transistor 48. With transistors 48 and 50 both
conducting, the voltage across winding 34 is clamped. Due to transformer
action, the winding 24 is also clamped but the level of clamping is not
sufficient (voltage) to activate TRIAC 22 into conduction. Consequently,
the load 20 is not energized.
In this mode of operation, auxilary features of the present invention
exist. As has been previously stated, the voltage across terminals 54, 58
is logic compatible with TTL, RTL, DTL, MOS, CMOS, Reed Relay, Switch,
Optoisolators, and is available since the diode 56 is a level shifting
diode to make the control voltage logic compatable. This diode could be
eliminated for some logic types.
Continuing, assume now that some means were provided whereby the terminals
54 and 58 would be remotely controlled, say, by a simple mechanical switch
coupled between the terminals and manually switched to short the
terminals. Another example would be a computer or the like, so that
terminals 54 and 58 become electrically connected together. This could be
a normally non-conductive transistor whose collector-emitter junctions
were appropriately disposed between the subject terminals and where the
base thereof was controlled by a control voltage obtained from a computer
to render the transistor conductive for certain periods of time to thereby
short the terminals together.
With the terminals 54 and 58 electrically connected together, the
transistors 48 and 50 continue to conduct until the next zero crossing of
the applied AC source of power. With such zero crossing, transistors 48
and 50 lose the necessary substaining current and switch to the
non-conductive state. Instantly, the output of the transformer produces a
normal-sinusoid voltage which is transfered via winding 24 to gate the
control terminal of TRIAC 22 so that TRIAC 22 conducts thereby completing
the series circuit. Consequently, the AC source of power applied across
power terminal 12, 14 now energizes the load. As long as the terminal 54
and 58 remain electrically connected together, the SCR like switch is off
and the load remains energized. In addition, the voltage at the output of
the bridge rectifier could be utilized for power startup or sensing
applications.
Therefore, the present invention provides an electrical switch for
controlling the energization of load 20 which comprises a pair of power
terminals 12, 14 which are connectable to the load for receiving an AC
source of power, a switch 22 connected in series with the load with the
switch having a control terminal which is selectively controlled to cause
the load to be conditioned to either an ON or OFF state, and a control
means which is isolatively coupled to the power terminal and to the TRIAC
22 which includes a means for activating the control means which, in turn,
provides a control signal to control the energization of the load by
controlling the conduction of the TRIAC 22.
While there has been shown and described the preferred embodiment of the
present invention, it will be apparent to those skilled in the art that
changes and modifications may be made without departing from the invention
in its broader aspects. For example, it would be possible to utilize an
activator means so that the winding 34 is directly shorted thereby
eliminating the necessity of the bridge, SCR operated switch, etc.
Therefore, the appended claims are intended to cover all such
modifications that fall within the true spirit and scope of the invention.
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