Circuitry For Connecting And Disconnecting A Load

Abstract

Electronic circuitry for a so-called automatic staircase time switch for lighting and extinguishing several parallel-connected incandescent lamps, wherein a blocking circuit responding to a predetermined ambient light intensity is blocking actuation of a switch circuit by a manually operable lighting circuit and an extinguishing circuit automatically disconnects the lamps from their current source after a predetermined connecting period.

Description

This invention relates to a circuitry for connecting and disconnecting a load which is connected to a current source via a switch circuit and consists of an incandescent lamp or several parallel-connected incandescent lamps, said circuitry being specifically but not exclusively useful as a so-called automatic staircase time switch which is employed for timed lighting of mostly several light sources (incandescent lamps) in public premises that require but a temporary lighting while persons are passing through said premises.

All previously known automatic staircase time switches are of the electromechanical type and suffer from the inconvenience and drawbacks associated therewith. One of the main drawbacks inherent in prior art automatic staircase switches is that they can be caused to connect the load thereof irrespective of whether ambient light conditions make such a connection unnecessary. In other words, the prior art time switches permit lighting of the light sources even if the prevailing light conditions are fully sufficient.

These drawbacks are overcome by the present invention in the circuitry outlined in the foregoing in that the switch circuit is connected to a manually operable connecting circuit and a blocking circuit which is adapted, in response to a predetermined ambient light intensity, to block actuation of the switch circuit by means of the manually operable connecting circuit, and in that the switch circuit is connected to a disconnecting or extinguishing circuit which is adapted automatically to disconnect the load after a predetermined connecting period.

The invention will be more fully described in the following with reference to the accompanying drawings in which:

FIG. 1 shows a wiring diagram of a circuitry according to the present invention;

FIG. 2 shows a wiring diagram of another embodiment of the circuitry.

The circuitry illustrated in FIG. 1 has a pair of input terminals A, B-- terminal B also serves as an output terminal or connection for a neutral conductor-- and a pair of output terminals C, D. A source of current having a voltage of preferably 220 v. and a frequency of 50 cycles is connected to the input terminals A, B. A load which in the present instance comprises a number of parallel-connected incandescent lamps L (only one being shown in the drawings) in a staircase lighting system, is connected to the output terminals B, C. A manually operable switch circuit which in the present instance comprises a number of parallel-connected pushbutton switches S (again only one of which is shown), is connected to the output terminals B, D. Built into each of said switches S is a glowlamp G and in series with it a resistor SR. A capacitor C6 which serves as an interference eliminator is connected across the input terminals A, B.

The circuitry illustrated in FIG. 1 includes a section which serves to feed the electronic low-current portion of the circuitry and comprises a resistor R1, a diode D2, a capacitor C1, a resistor R2 and a Zener diode D3. The resistor R1 is connected between the input terminal B and the diode D2 which is of opposite polarity compared to the resistor R1. The capacitor C1 is connected between the side of the diode D2 facing away from the resistor R1 and the input terminal A. The resistor R2 is connected to the side of the diode D2 facing away from the resistor R1 and the opposite end of the resistor R2 is connected to the input end of the Zener diode D3, while the output end of said diode is connected to the input terminal A.

The high-current circuit for the connection and disconnection of the load or in the present instance the lighting and extinguishing of the lamps L includes a triac D1 and a control circuit which is intended for said triac and has a unijunction transistor T3. The triac D1 is connected between the input terminal A and the output terminal C and its gate is connected to the input terminal A via a resistor R17 and to the gate of the unijunction transistor T3 via a capacitor C5. The unijunction transistor T3 is connected to the input terminal A via a resistor R16 and to one output from the feed circuit. Thus the unijunction transistor T3 and the resistor R16 can be considered connected over the outputs of the feed circuit, one of which corresponds to the input connection A and the other to the connection between the diode D3 and the resistor R2. The input connection A is connected to the gate of the unijunction transistor T3 via a resistor R15 and a resistor R18. A further unijunction transistor T2 is connected between the connection between the resistors R15 and R18 and the connection between the diode D3 to the resistor R2, while the gate of said unijunction transistor T2 is connected to one terminal for a resistor R9, the other terminal of which is connected to a diode D8 connected in parallel with a resistor R8. The diode D8 is of opposed polarity compared to the resistor R9 and the connection between the diode D8 and the resistor R8 is connected to the input terminal A via a variable resistor R13 and to the connection between the diode D3 and the resistor R2 via a diode D6 and a capacitor C3 connected in series with said diode. The diode D6 is of opposed polarity compared to the capacitor C3 and the connection between the diode D6 and the capacitor C3 is connected to the input for a thyristor D5 via a resistor R7. The output of the thyristor D5 is connected to the connection between the diode D3 and the resistor R2, while the gate of the thyristor D5 is connected to the connection between the diode D3 and the resistor R2 via a resistor R6 and to the output from a diode D4 via a resistor R5. The connection between the resistor R5 and the diode D4 is connected to the connection between the diode D3 and the resistor R2 via a capacitor C2. The input to the diode D4 is connected to the connection between the diode D3 and the resistor R2 via a resistor R4, and to the output terminal D via a resistor R3 or the conductor called lighting conductor.

The circuitry described in the foregoing also includes a blocking circuit comprising a transistor T1 and a resistance network. The collector of the transistor T1 is connected to the input terminal A via a resistor R14, the emitter of the transistor T1 is connected to the connection between the diode D3 and the resistor R2 via a capacitor C4, and the base of the transistor T1 is connected to the sliding contact of a potentiometer R11 via a diode D7 which is of opposed polarity compared to the base of the transistor T1. The connection between the emitter of the transistor T1 and the capacitor C4 is connected to the connection between the gate of the unijunction transistor T2 and the resistor R9. The connection between the base of the transistor T1 and the diode D7 is connected to the side of the resistor R9 facing away from the gate of the transistor T2.

In addition to the above-mentioned potentiometer R11, the resistance network includes a resistor R10 and a further resistance R12. The potentiometer R11 and the resistors R10 and R12 are connected in series with each other, and this series circuit is connected between the input terminal A and the connection between the diode D3 and the resistor R2. The resistor R12 of this series circuit is a light-sensitive resistor.

The function of the circuitry outlined in the foregoing will be more fully described in the following.

The unijunction transistor T3 of the high-current circuit-- after the following detailed conditions have been satisfied-- will operate as an oscillator and feed pulses via the capacitor C5 to the triac D1 which will thus become conductive and in turn connect the load L.

Upon depression of the pushbutton switch 5 the thyristor D5 is caused to ignite via the resistors R3 and R5 and the diode D4. When the thyristor D5 ignites, the capacitor C3 will be discharged via the resistor R7 and a current will begin to flow through the resistor R13 and the diode D6 whereby the capacitor C3 is again charged. During the charge of the capacitor C3 the transistor T1 and the unijunction transistor T2 will obviously be nonconductive whereby a current will flow through the resistors R15 and R18, which will cause oscillation of the unijunction transistor T3, which oscillation causes the triac D1 to ignite and to connect the load. When the capacitor C3 has been charged to a certain level the unijunction transistor T2 will become conductive whereupon the current flowing through the resistor R13 will pass through the resistors R8 and R9 and the diode D8. Thus also the transistor T1 will become conductive, whereby a new path of current is opened via the resistor R14 and the transistor T1 to the unijunction transistor T2. Because both the transistor T1 and the unijunction transistor T2 are conductive the current to the resistor R18 ceases, and the unijunction transistor T3 stops oscillating and feeding pulses to D1. Thus, the load is disconnected or the lamps L are extinguished. The resistor R13 and the capacitor C3 will determine the period of time for which the triac D1 remains connected and as a consequence the load. To make lighting of the system or the lamps unnecessary when this is not required for lighting technical reasons, use is made of the light-sensitive resistor R12 which senses the prevailing light intensity and in response thereto blocks or makes it impossible to cause the transistor T1 to become conductive. Thus, said transistor T1 remains conductive as long as it is not necessary to light the lamps L. The light value at which it shall be possible to light the lamps L is set by means of the potentiometer R11. The resistor R13 being variable, the lighting or connecting period can also be adjusted.

Another embodiment of the present invention is illustrated in FIG. 2. This embodiment agrees in principle both in design and function with that illustrated in FIG. 1. Identical components in the two figures carry the same reference numerals. It should be observed, however, that the component values may differ slightly. In the embodiment shown in FIG. 2 the diode D4 has been dispensed with and the resistor R4 in FIG. 1 has been replaced by a capacitor C7 feeding alternating voltage to a glowlamp G when the pushbutton is not depressed. Moreover, the diode D6 in FIG. 1 has been replaced by a transistor T4 which serves to make the charging of the capacitor C3 as linear as possible whereby said capacitor can be given a smaller size and a smaller leakage current is obtained in it, which involves a saving of cost. Further, a resistor R26 is connected between the variable resistor R13 and the input terminal A. Certain changes have also been made in the blocking circuit. The light-sensitive resistor R12 has been parallel connected with a resistor R7 for better matching of the light-sensitive resistor R12 to the circuit. In addition, the resistors R11 and R10 have changed places. Still another change in the blocking circuit is that the collector of the transistor T1 is coupled to the base of the transistor T4 and to the side of the diode D2 facing away from the resistor R1, via a resistor R25.

The most important difference between the two embodiments resides in the switch circuit. The only remaining components are the resistors R15 and R18. The connection between the resistor R15 and the resistor R18 is connected to the gate of a unijunction transistor P1 of a type that can be programmed and the collector of which is connected to the emitter of the transistor T1, while the emitter thereof is connected to the end of the diode D2 facing away from the resistor R1. The switch circuit further includes two complementarily connected transistors T5 and T6 the emitters of which are connected to the end of the resistor R18 facing away from the resistor R15, said end of the resistor R18 being also connected to the base of a further transistor T7. The base of the transistor T5 is connected to the emitter of the unijunction transistor P1 via a resistor R19, while the emitters of the transistors T5, T6 and T7, are connected directly to the emitter of the unijunction transistor P1. Furthermore, the base of the transistor T5 and the base of the transistor T6 are connected to the output terminal B each via a resistor R20 and R22, respectively. The base of the transistor T6 is connected to the collector of the transistor via a resistor R21. The collector of the transistor T7 is connected to the gate of the triac D1 via a resistor R23.

As already mentioned, the function of the circuitry illustrated in FIG. 2 in principle agrees with that of the circuitry in FIG. 1. For elucidatory purposes, the function of the circuitry illustrated in FIG. 2 will, however, be described more in detail in the following. The capacitor C2 serves as an interference filter and prevents ignition of the thyristor D5 by means of transients via the resistors R3 and R5. The igniting pulse from the pushbutton 5 travels via the resistors R3 and R5 to the gate of the thyristor D5 whereby the latter is ignited. Upon ignition the thyristor D5 will discharge the capacitor C3 via the resistor R7 and short circuit the current flowing via the resistors R26 and R13 and the transistor T4 to minus. Thus no voltage drop arises over the resistor R9, for which reason also the transistor T1 will become nonconductive, which implies that also the unijunction transistor P1 will become nonconductive. Thus also the gate of the transistor P1 becomes nonconductive, for which reason the voltage from the resistor R15 will travel via the resistor R18 and block out the transistor T7. Thus the triac D1 will be ignited and the charge connected. After recharge of the capacitor C3, which takes place via the resistors R26 and R13, the transistor T4 will cause the unijunction transistor P1 to become conductive. As a result a current occurs via the resistors R8 and R9 which causes a voltage drop via the resistor R9 and makes the transistor T1 conductive. Current will therefore flow via the resistor R14 and the transistor T1 to the collector of the unijunction transistor P1. When the collector of said transistor is conductive, also the gate thereof will be conductive, whereby the voltage via the resistors R15 and R18 will be short circuited to minus. The base of the transistor T7 thus receives no control current and pulses are not either fed to the triac D1 for which reason the load is disconnected. Like in the circuit illustrated in FIG. 1, the light-sensitive resistor R12 produces a certain current when it is exposed to light of a given predetermined intensity. This current flows through parts of the resistor R11 and the diode D7 and will thus keep the transistor T1 conductive. Even if the pushbutton S is depressed, which results in ignition of the thyristor D5 and discharge of the capacitor C3, the unijunction transistor P1 will not be devoid of current because the transistor T1 is conductive. Thus the gate of the transistor P1 will not be nonconductive, for which reason the voltage via the resistor R15 will not be short circuited to minus and the load remains disconnected. After release of the pushbutton S the capacitor C3 will again be charged, whereupon the charging current again takes over the holding current to the transistor P1 while the load remains disconnected. If the light intensity should fall below a given predetermined value the transistor T1 will not have sufficient current when the capacitor C3 is discharged, whereby the transistor P1 ceases to be conductive and the load is connected.

Claims

What I claim and desire to secure by Letters Patent is:

1. A circuit device for connecting and disconnecting a load in the form of several parallel-connected incandescent lamps, comprising means for feeding a current to said load, means for switching said load to or from said current feeding means, means for manually actuating said switching means, means for blocking in response to a predetermined ambient light intensity actuation of said switching means by said manual actuation means, and means for automatically disconnecting said load after a predetermined connecting period, and switching means including a first unijunction transistor operating as an oscillator, a triac the gate of which is connected to the gate of the unijunction transistor via a capacitor, and a second unijunction transistor which when caused to become nonconductive is adapted to cause the triac to connect said load.

2. A circuit device for connecting and disconnecting a load in the form of several parallel-connected incandescent lamps, comprising means for feeding a current to said load, means for switching said load to or from said current feeding means, means for manually actuating said switching means, means for blocking in response to a predetermined ambient light intensity actuation of said switching means by said manual actuation means, and means for automatically disconnecting said load after a predetermined connecting period, said blocking means including a transistor which when nonconductive is adapted to permit connection of said load via said switching means, a resistor network the base of said transistor is connected to said resistor network, said network determining the voltage at which the transistor is caused to become nonconductive and which includes a potentiometer the sliding contact of which is connected to the base of said transistor and a light-sensitive resistor.

3. A circuit device for connecting and disconnecting a load in the form of several parallel-connected incandescent lamps, comprising means for feeding a current to said load, means for switching said load to or from said current feeding means, means for manually actuating said switching means, means for blocking in response to a predetermined ambient light intensity actuation of said switching means by said manual actuation means, and means for automatically disconnecting said load after a predetermined connecting period, said switching means including a triac, a unijunction transistor of a type that can be programmed, a complementary transistor pair and a further transistor, the collector of the unijunction transistor being connected to said blocking means, the gate of the unijunction transistor being connected to the emitters of said complementary transistors and to the base of said further transistor via a resistor, and the collector of said further transistor being connected to the gate of said triac.

4. A circuit device as claimed in claim 1, wherein a capacitor is adapted, during charging, to keep said transistor and said second unijunction transistor nonconductive whereby said triac will maintain the load connected during charging of the capacitor.