FR2498807A1 - Low power consumption monostable relay - has ON=OFF switch coupled to bistable relay by capacitor connected transistor pulse generator - Google Patents

Abstract

The relay has an on/off switch (30) connecting a battery (20) to a pulse generator (31) in turn coupled to a bistable relay (32). The pulse generator has a transistor (T) whose base is biassed by a two resistor chain (33,34) and whose collector has a collector resistor (35) and is connected to the gate of a thyristor (TH) connected across the supply lines to the transistor. A diode (D) is connected in one line between the bias chain and collector resistor while a capacitor is series connected in the generator output. The closing and opening of the switch triggers first and second opposite polarity control pulses from the generator by the charging and discharging of the capacitor to switch the relay between its two states.

Description

LOW CONSUMPTION MONOSTABLE RELAY
The present invention relates to electro-mechanical relays known as "monostable". It relates more particularly to low-consumption monostable relays, provided with two input terminals (5, 6) for the application of a direct control voltage and two output terminals (41, 42) intended to be connected to the operating circuit.

 In this type of relay, a moving part, responsible for establishing contacts, can switch around an axis, under the influence of an electromagnet, in a first so-called working position, under the influence of a return spring in a second so-called rest position. This type of relay is advantageous by the simplicity of its control mode, of the "all" or "nothing" type, corresponding to the presence or absence of current; but it has the drawback of consuming electrical energy during the entire period of operation in the "work" position.

 Furthermore, another type of relay is known of which each flip-flop of the moving part is obtained under the action of a control pulse. This type of so-called bistable relay is advantageous by its very low consumption, which is limited in time to that of the pulse, but has the drawback of requiring a complicated control mode, linked to the desired direction of tilting. This type of relay requires two pulse generators of opposite signs or two separate electromagnet coils, operating in opposite directions under the action of a single type of pulse.

 The present invention makes it possible to avoid these drawbacks. To this end, the relay according to the invention is characterized in that it comprises a two-position switch, a voltage pulse generator, and a bistable relay, the closing of the switch causing the generator to trip. '' a control pulse of a first sign which switches the bistable relay in a first position while the opening of said switch causes the generator to trigger a control pulse of a second sign which switches the relay bistable in a second position.

 The relay according to the invention is therefore indeed a monostable type relay, that is to say that maintaining it in the working position requires maintaining the closing of said switch. However, it has the enormous advantage of using a bistable relay which therefore consumes energy only when switching from the open position to the closed position or vice versa of the switch. Since it is easy to produce devices in accordance with the invention in the form of small integrated circuits or hybrid circuits, all of the components of the relay, that is to say the pulse generator, the relay bistable as well as of course its electro-magnetic control coil, can be housed together in the same housing usually used in this type of relay. Therefore, for the user, the relay according to the invention which uses a bistable relay is seen by it as a monostable relay.

 According to a preferred embodiment, the pulses of the first sign and the second sign are caused by the charging and discharging of a capacitor whose output is connected to the input of said bistable relay.

 Indeed, in principle, .'invention simply uses the phenomenon of charging and discharging a capacitor. When the switch is closed, a direct voltage is applied across the capacitor and the charging current of the latter decreases rapidly, taking the form of a pulse of a first sign through the coil of the relay. Conversely, when the switch is opened, the voltage source is suddenly disconnected from the corresponding armature of the capacitor, and according to the invention, this is set to the same potential as the other armature. Consequently, a discharge current from the capacitor occurs through the relay control coil which decreases rapidly in exponential form, thus creating a second current pulse of opposite sign to the previous one. When said capacitor is connected to the terminals of the bistable relay, we thus created a very simple control system for this allowing it to operate as a monostable relay.

 According to a preferred embodiment, the invention uses a pulse generator circuit which can be controlled by any type of electronic or mechanical switch having a low or a high impedance on opening. Indeed, very often, monostable relays are used in electronic circuits and the switch which controls the relay is in this case a controlled electronic switch, of the type well known to those skilled in the art.

When the supply voltage of the capacitor is zero, this corresponds to a conductive or saturated collector-emitter junction of a transistor and there is therefore a switch circuit, of practically zero impedance at that time. The pulse generator according to the invention is insensitive to the impedance of the control switch and operates as explained below in all cases.

The invention will be better understood using the following embodiments, given without limitation, together with the figures which represent
FIG. 1, in a diagrammatic view, a known monostable type relay,
FIG. 2, according to an explanatory diagram as a function of time, the variations in voltage and current implemented in the control of a monostable relay of known type,
FIG. 3, in a diagrammatic view, a monostable relay according to the invention,
- Figure 4, according to an explanatory diagram as a function of time, the voltage and current variations used in the control of a monostable relay of the invention.

 FIG. 1 represents an example of a monostable relay of known type.

 It comprises a coil 1, provided with a ferromagnetic core 2, and a pivoting movable contact 3, brought into a fixed angular position by a spring 4. In operation, a voltage is applied to the terminals of the coil 5 and 6 by a contactor 7 or by any other device (electronic or other) arranged in series with a continuous source 8. The magnetic field created in the coil attracts the movable contact, which bears on the fixed contact 9, and thus closes the controlled circuit, not shown, connected to output terminals 10 and 11 of the monostable relay.

 FIG. 2 represents, according to an explanatory diagram as a function of time, the variations of the control voltage VC in (a), and of the intensity Ig in (b) brought into play in the operation of the known monostable relay.

 The voltage being applied throughout the duration TC of the working phase of the relay, the current Ig passing through the coil is maintained at its operating value throughout the duration Tc.

The energy consumption is therefore high if TC has a long duration.

 Figure 3 shows, in a schematic view a monostable relay according to the invention.

 It consists of a combination between a bistable relay (32) of known simple type, a pulse generator (31), these pulses being able to take two opposite polarities, from a simple control signal generated by the switch. (29) of the type described above for the monostable relay. The polarities of the pulses are inverted by a capacitor (C), and corresponds to the charge and discharge phases of this.

The switch 29 consists of a voltage source 20 whose negative pole is connected to the ground of the circuit, and whose positive pole is connected to the contactor 30. The output 5 of this is connected on the one hand to the anode of diode D and on the other hand to resistor 34 which forms with resistor 33, the other end of which is grounded, a divider bridge whose midpoint is connected to the base of the transistor
T. The collector thereof is connected on the one hand to the trigger of the thyristor Th and on the other hand to the resistor 35 itself connected at its other end on the one hand to the cathode of the diode D and on the other leaves at the anode of thyrystor Th. The cathode of this thyristor Th is connected to ground as well as the emitter of transistor T. The anode of transistor
Th is connected to the capacitor C, the other end of which is connected at point 37 to the input of the bistable 32, the other input 45 of which is grounded. Between points 37 and 45 is connected the control coil 38 of the bistable relay, the moving assembly of which is represented by 39. The movable blade 44 can take two positions 46 or 40, the latter being connected to the output 41 of the monostable relay according to the invention, while the blade 44 is connected to the second output 42 of said relay.

 The operation of this circuit will be better understood using FIG. 4 which represents three curves, respectively in FIG. 4a the variation of the voltage across the terminals of the capacitor as a function of time, in FIG. 4b the variation of the current passing through the capacitor as a function of time, in FIG. 4c the variation of the current passing through the control coil of the bistable relay as a function of time. The contactor 30 is normally open, as shown in FIG. 3, which corresponds to a position of the strip 44 in electrical contact with the contact 46, not connected to the outside of the circuit. However, it should be noted that this could also be used. When the contactor 30 closes, the circuit 31 is therefore energized. The capacitor C charges through the diode D. The contactor 30 was closed at the instant tl (see FIG. 4), which results in the passage of the voltage across the terminals of the capacitor C at the value + V corresponding to the supply voltage of the source 20, charged to said capacitor by a current lC which decreases exponentially from the instant tl and which therefore creates in the coil of relay 38 a current Ig also varying in the same way.

This current pulse Ig causes the tongue 44 to switch over on the contact 40, thus putting the terminals 41 and 42 in electrical contact. During the entire time interval when the contact 30 is closed, nothing then happens at the level of circuit 32, this of course consuming no current since the current Ig in the coil is zero as shown in FIG. 4.

When the contact 30 is opened again, the voltage at the common point of the capacitor C and the anode of the thyristor Th decreases suddenly. In fact, the capacitor C being charged, there is a potential difference across its terminals. One of its armatures, connected to point 37 is grounded via the coil 38. Furthermore, the voltage existing on the other armature of the capacitor C causes the collector of the transistor to be biased.
T, the voltage of which becomes substantially equal to the voltage existing at the terminals of the capacitor, since the resistors 34, 33 not being supplied due to the presence of the diode D connected in reverse, the transistor T is blocked. The high voltage on the collector of transistor T therefore causes a high voltage on the trigger of thyristor Th which therefore becomes conductive. As the cathode of this is ground, its anode is also suddenly grounded, which causes the discharge of the capacitor C. The discharge current of the capacitor having the opposite direction to the charging current thereof, a pulse of opposite sign to that of the pulse resulting from the charge is caused in the coil 38 of the relay. This negative pulse (see Figure 4, curve Ig as a function of t) therefore causes the return of the tongue 44 on the contact 46. The circuit is then ready to operate again.

 The monostable relay as described above has an important advantage of low consumption compared to the monostable relay of known type. By way of nonlimiting example, a monostable relay as described in FIG. 1 supplied with a direct voltage of 12 volts and a current of 40 milliamps, will consume if it is made to function due to a closing of the contactor 7 per second with a duty ratio of 1 to 1 (i.e. 0.5 seconds of opening and 0.5 seconds of closing of the contactor), the consumption of this will be approximately 900 joules.

 In comparison, if a relay according to the invention with a similar electrical characteristic (12 volts, 40 milliamps of control current) is used, the pulse generator circuit comprising a capacity of 15 microfarads, the consumption will be under the same conditions as above 18 joules for the pulse generator part to which must be added the consumption of the resistance bridge 33, 34 which is typically of the order of 18 joules also for one hour (total value of the resistors 33 and 34 of 12kn >.

 The total consumption of the relay according to the invention will therefore be established at a value of the order of 36 joules, which corresponds to a consumption 25 times lower than for a relay of the known art. It is understood that the more the operating frequency of this relay increases the more the consumption ratio between the monostable relays of the prior art and those of the invention also increases.

 The exemplary embodiment described in FIG. 4 made use in particular of a mechanical contactor 30. It is understood that this can advantageously be replaced by an electronic switch controlled by a clock or any other suitable type of control. The relay according to the invention is particularly advantageous in this case since it makes it possible to connect at 5 and 6 in FIG. 3 a switch circuit 29 having any output impedance, whether that is high or low. This also constitutes another important advantage of the invention since the control switch circuits are not limited to a circuit having a very high impedance when the switch is open.

 For clarity in the description, there is shown diagrammatically in FIG. 5 an exemplary embodiment of a controlled electronic switch which can replace the assembly 29 of FIG. 3. A train of clock pulses 62 is sent to base 60 of transistor T ', whose emitter is grounded and whose collector is connected to the positive voltage + V via R. The output voltage is produced between 5 and 6.

At each pulse 63, 64, ... clock, positive, the transistor
T 'becomes conductive and the voltage VcE thereof becomes substantially zero. Therefore, 5 is at the same potential as 6 (mass).

The capacitor C discharges and generates a pulse such as 52 (Figure 4). Conversely, when the clock signal becomes zero, or preferably negative, the transistor T 'is blocked and 5 is brought substantially to the potential + V (depending on the value of R and of the current output). The capacitor C is charged and a pulse such as 51 is generated in the coil of the relay.

 The example of an electronic switch above has been given without limitation. In practice, this is often replaced by a logic control (gate), the output level of which goes, depending on the case, from the "high" level to the "low" level and vice versa ensuring the switch function.

 In the case of the switch described in FIG. 5, it is indeed possible to limit the circuit 31 to the sole presence of the capacitor C.

Claims (6)

1. Low consumption monostable relay provided with two input terminals (5, 6) for the application of a direct control voltage and two two output terminals (41, 42) intended to be connected to the use circuit , characterized in that it comprises a switch (30) with two positions, a voltage pulse generator (31) and a bistable relay (32), the closing of the switch causing the generator to trigger a control pulse of a first sign which switches the bistable relay in a first position while the opening of said switch causes the generator to trigger a control pulse of a second sign which switches the bistable relay in a second position.  2. monostable relay according to claim 1, characterized in that the pulses of the first sign and the second sign are caused by the charging and discharging of a capacitor (C) whose output is connected to the input (37) of the bistable relay (32).  3. monostable relay according to claim 2, characterized in that the pulse generator consists of a transistor T whose base is biased by a divider bridge consisting of a first and a second resistor (33, 34) , the end of the first resistor (33) being connected to one of the ends of the voltage source as well as to the emitter of transistor T, while the end of the second resistor (34) is connected by via the switch (30) and, via a diode (D), on the one hand to a third resistor connected to the connector of the transistor (T) and on the other hand to the capacitor (C) as well as a first electrode of a thyristor (Th) whose second electrode is connected to the emitter of the transistor (T) and whose trigger is connected to the connector of said transistor (T), the direction of conductor of said diode, of the transistor and of the thyristor being such that when the switch (30) is closed, a charge occurs capacitor (C) through the diode (D) while at the opening of this there occurs a discharge of said capacitor through the thyristor (Th).  4. Monostable relay according to one of claims 1 to 3, characterized in that the switch with two positions is of the mechanical type, ensuring a very low electrical resistance on closing and very high on opening.  5. Monostable relay according to one of claims 1 to 3, characterized in that the switch has two positions and of the electronic type having any output impedance.  6. Monostable relay according to one of claims 1 to 5, characterized in that the different elements are combined inside the same housing.