EP0972335A2 - Thermal power converter for supplying electricity to an autonomous apparatus with low consumption from a very slight difference in temperature - Google Patents

Abstract

The invention concerns an energy converting circuit, boosting the voltage supplied by a low direct voltage source (1), comprising a self-oscillating circuit, operating at very low voltage, using a voltage boosting transformer (3, 4, 6, 6', 7) generating the control signals of two chopper-boosters (11-14) operating alternately, comprising an enhancement-type field effect transistor (11, 12) used in synchronous switching with the self-oscillating circuit, which is in serial connection with an inductive resistor (13, 14) to the terminals of said source (1) and which is connected to a user circuit via a diode (15, 16). The invention also concerns a device for supplying electricity to appliances using such a supply device. The invention further concerns the production of thermal converters for the utilisation of low-voltage thermoelectricity, and a method for the manufacture of thermal converters on an industrial scale.

Description

 Thermal power converter for supplying electricity to an autonomous device with reduced consumption from a very small temperature difference.

The present invention relates to an energy converter for supplying an autonomous device with reduced consumption from thermocouples subjected to a small temperature difference constituting a source of very low voltage and of low but non-zero internal resistance, the production of thermocouples , as well as an industrial manufacturing process for thermocouples.

Many devices must operate independently, that is, they have their own power supply. This is the case with portable devices such as watches or ear amplifiers which cannot be permanently connected to a power supply network. This is also the case for devices placed in places that are difficult to access, such as intrusion detectors used in alarm systems; they are arranged for example in openings such as windows where it is difficult and expensive to bring a power cable.

These autonomous devices of reduced consumption are currently powered by batteries or rechargeable cells whose lifetime or discharge is limited, which results in relatively frequent replacement or recharging operations and obliges to keep spare batteries or accumulators for avoid interruption of operation.

It has already been envisaged to exploit very low voltage sources by using converters providing an output voltage of the order of a few volts to power devices of reduced consumption without any interruption in operation by using a self-oscillating circuit comprising a step-up transformer and a field effect transistor whose drain-source path is plugged into the transformer primary.

These known converters are designed to oscillate so as to increase the voltage and they have a mediocre efficiency which does not make it possible to extract, from very low voltage sources, the power necessary for the operation of a watch or of a device. auditory. Furthermore, the operation of these oscillators is greatly disturbed when the load becomes large; they may stop oscillating or even fail to start.

We are familiar with the documents: 1 (PETER WILSON “V

Switching Mode Power Supplies ”), 2 (DE 14 37 235 A -Philips), 3 (US 3 679 918 A KEIZI), 4 (F.BUTLER“ Transistor Inverter Frequency Stabilized Circuit

Suitable for Running a Tape Recorder ”, 5 (Patent Abstracts of JAPAN vol 5, n ° 78 (E-058)), 7 (FR 1 162 168 A - Company general equipment for the automobile, aerial locomotion). These documents all include oscillator circuits, the diagrams described in documents 3 and 7 are the closest to the invention, however none of them is able to oscillate spontaneously when the circuit is supplied by a DC voltage also weak than 10 to 200 millivolt. This is due to the threshold effect presented by the Base-Emitter junction of the oscillator transistor (of the order of 0.5 volts). A bipolar transistor must be polarized to be able to be used in a self-oscillating circuit. This is not the case of the JFET junction field effect transistor used in the present invention, it has a variable resistance when the gate-source voltage Vgs fluctuates around zero volts.

Document 1 as well as document 6 (US 3,913,000 A - GILBERT, CARDWELL) present converter circuits using the load of an inductor to convert a voltage, the process is known as well specified in document 6, FIG. 1. What is new in the context of the present invention is the combination of the self-oscillating circuit and the switching converter optimized for very low powers (10 microWatt to 10 milliWatt), with no other energy source to make operate the converter.

The problem underlying the invention is to provide an energy converter having a yield making it possible to extract the desired power and voltage from very low voltage electrical energy sources and the operation of which is ensured even for a significant charge.

To this end, the subject of the invention is an energy converter circuit, booster of the voltage supplied by a low continuous voltage source with non-zero internal resistance, comprising a self-oscillating circuit, operating at very low voltage, using a step-up transformer generating the control signals of two chopper boosters in alternating operation, of the type comprising an enhancement field effect transistor which is used as a synchronous switch with the self-oscillating circuit, which is connected in series with an inductor across said source and which is connected to the user circuit through a diode.

The use of chopper-booster circuits makes it possible to extract approximately 50% of the power available in the source. Devices can be supplied with a voltage of a few volts from a source whose voltage is of the order of a few tens of millivolts. In addition, operation is ensured for large loads.

Advantageously, a voltage clipping diode and a large capacity capacitor or an accumulator are connected in parallel to the output terminals.

In this way, the output voltage is fixed at the desired value.

The invention also relates to a reversible converter circuit, characterized in that it comprises two converter circuits connected in antiparallel to the source and connected to the output terminals by means of four switches controlled in pairs by two additional windings of the transformer of the active converter and in that each converter has a blocking device blocking the other converter when it is active.

Such a circuit makes it possible to extract the energy supplied by a source whose polarity is variable. The two converters operate alternately depending on the polarity of the source, the active converter blocking the other converter to avoid any loss of power in the non-active converter.

Advantageously, the blocking device comprises a third additional winding of the transformer at the terminals of which is connected a rectification circuit generating a direct voltage blocking the self-oscillating circuit of the non-active converter.

The invention also relates to a device for supplying an autonomous portable device from a thermal system comprising a hot source and a cold source having a small temperature difference between them, such as the epidermis of a human being and the ambient atmosphere, characterized in that it consists of a converter circuit in which the electrical source consists of a set of Seebeck effect detectors connected between the two thermal sources. This converter is also suitable for extracting power from a photovoltaic source.

Such a feeding device can be integrated into a watch or a hearing aid. It can also be used to recharge a rechargeable element. Other characteristics and advantages of the invention will emerge from the description which follows, given by way of illustration and in no way limiting, with reference to the attached drawings in which: FIG. 1 is the diagram of a converter circuit according to the invention; FIG. 2 is the diagram of a reversible converter circuit according to the invention; Figures 3a to 3f are diagrams of operation of the converter circuit of Figure 1; FIG. 4 represents a device for supplying from a source of energy of thermal origin; FIG. 5 illustrates the use of a device for supplying from a source of energy of thermal origin disposed on a partition; FIG. 6 illustrates the use of a device for feeding from a source of energy of thermal origin placed on the ground; FIG. 7 illustrates the use of a device for feeding from a source of energy of thermal origin placed on a window; FIG. 8 represents a power supply device according to the invention used to replace the battery of a watch; FIG. 9 shows another watch originally fitted with a power supply device according to the invention; FIG. 10 represents yet another embodiment of a watch according to the invention; Figure 1 1 is the electrical diagram of the watch of Figure 10

; and FIG. 12 represents a shoe fitted with a supply device according to the invention.

FIG. 1 is the diagram of a converter circuit intended to extract the electrical energy supplied by a source 1 of very low voltage, for example from 10 to 200 mV, which has a non-zero internal resistance shown diagrammatically at 2 by supplying a voltage much higher output, for example a voltage of 2 V for an electronic device. The electrical source 1 is connected to the primary 3 of a step-up transformer 4 via the source-drain path of a N-channel junction field effect transistor (JFET). The transistor

JFET 5 is of the pinch type, that is to say that for a zero gate voltage, its drain-source resistance is not infinite but of the order of a few ohms and it is clamped when the gate voltage becomes negative.

The secondary of the transformer 4 has two similar windings 6 and 6 'connected by a middle point 7 connected to ground. The gate of the JFET transistor 5 is connected to ground by a resistor 8 and to the secondary 6 'by a capacitor 9. When the gate voltage varies, this causes a variation in the drain-source resistance and, consequently, a variation in the current in the primary 3 which creates a high voltage in the secondary 6 'of the transformer 4. The frequency of this oscillation depends on the inductance of the transformer 4, the distributed capacitance of the secondary 6 and 6 'and the gate-source capacitance of the JFET transistor 5. The capacitor 9 forms a galvanic decoupling of the gate and allows the oscillator, thanks to the junction PN grid-source, to consume very little energy. In accordance with the invention, a circuit of the chopper-booster type comprising a transistor 11, respectively 12, of MOS-FET type with N channel and enhancement whose gate-source voltage of threshold is low (for example, 1 to 3 V), an inductor 13, respectively 14, and a Schottky diode 15, respectively 16. Each MOS-FET transistor 11, respectively 12, is connected in series with the inductor 13, respectively 14, and their gates are controlled by the secondary 6 ′, respectively 6 of the transformer 4, the outputs of which are crossed so that the gate voltages of the two MOS-FET transistors 11 and 12 are in phase opposition.

The Schottky diodes 15 and 16 are each connected between the drain of the MOS-FET transistor and the positive output pole. A capacitor 17 of very high capacity and a voltage clipping diode 18 are in parallel on the output terminals of the converter. These two elements are used to set the value of the output voltage; they can be replaced by a rechargeable element.

The operation of this converter circuit is illustrated by the diagrams of FIGS. 3a to 3f which respectively represent the voltages of the secondary 6 and 6 ′, the current in one of the inductors, the drain-source voltage of one of the transistors, the current crossing the other inductor, the drain-source voltage of the other transistor and the voltage of the source 1. When the gate voltage of the transistor 12 is positive and greater than the threshold, Vs, this transistor is conductive, the inductor 14 accumulates energy as the current flowing through it increases, while the voltage across the source 1 decreases in an almost linear fashion. When the gate voltage falls below the threshold, the transistor 12 is blocked and the energy stored in the inductance 14 is transferred to the positive output terminal by the Schottky diode 16. For the following alternation, it is the transistor 11 which charges the inductor 13 which then discharges at the output.

The advantage of using the two boosters is that the auto-oscillator is, from an energy point of view, used in its only oscillator function and we use the alternating voltage available only to drive the chopper-boosters.

FIG. 2 represents a reversible converter which can extract the energy supplied by a source 21 of very low voltage whose polarity varies. Two converter circuits are connected in antiparallel to this source so as to operate alternately depending on the polarity of the source 21. Each of these circuits includes a JFET transistor 22, respectively 22 ', a primary 23, respectively 23', a secondary with double winding 20-24, respectively 20'-24 ', two MOS-FET transistors 25 and 26, respectively 25' and 26 ', two inductors 27 and 28, respectively 27' and 28 ', and two Schottky diodes 29 and 31, respectively 29' and 31 'which are connected to the output 32 by means of switches which will be described below. The transformer of each converter has an additional winding 33, respectively 33 ', whose voltage is sent to a rectifier circuit consisting of two diodes 34, respectively 34', associated with a capacitor 35, respectively 35 ', and whose DC voltage output is applied between the source and the gate of the JFET transistor 22 ', respectively 22 of the self-oscillating circuit of the other converter so as to ensure the blocking of the second converter while the first is active and vice versa.

The output voltage of each chopper is sent to the output terminals, U + and U-, via four switches 39, 41, 38 and 37, of the MOS-FET transistors, which are connected in bridge and are each controlled by the voltage from the additional windings 42 and 43, respectively 42 'and 43', of the transformer of each converter which is rectified by diodes 44 and 45, respectively 44 'and 45', and filtered by capacitors.

When the voltage delivered by the source 21 is positive, it is the self-oscillating circuit built around the JFET transistor 22 which oscillates. In doing so, it delivers a direct voltage which ensures the conduction of the MOS-FET transistor switches 41 and 39. The positive terminal of the chopper-booster (cathode of diodes 29 and 31) is thus switched via the drain-source path of the MOS transistor. -FET 41 on the U + output. The negative output of the chopper-booster (sources of the transistors 22, 25 and 26) is thus switched via the source-drain path of the MOS-FET transistor 39 on the output U-. Furthermore, the winding 33 delivers a voltage which, once rectified by the diodes 34 and filtered by the capacitor 35, will block the JFET transistor 22 'of the non-active self-oscillating circuit but whose drain-source resistance was previously low.

When the voltage delivered by the source 21 is negative, it is the self-oscillating circuit built around the JFET transistor 22 'which oscillates. The operation is identical to the operation described above. The MOS-FET transistor switch 38 will switch the positive output of the booster chopper (cathode of the diodes 29 'and 31') to the output U +. The MOS-FET transistor switch 37 will switch the negative output of the chopper-booster (sources of the transistors 22 ', 25' and 26 ') to the output U-.

Likewise, a negative voltage resulting from the rectification of the voltage of the secondary 33 ′ will block the JFET transistor 22.

The winding 20, respectively 20 ′, constitutes a variant of the winding 6 ′ of the assembly of FIG. 1. It makes it possible to operate the self-oscillating circuit with the correct transformation ratio and it makes it possible to increase the tension of control the MOS-FET transistors of the chopper-booster so as to obtain more frank switching.

According to one embodiment of the invention, the low voltage energy source is constituted by a set of Seebeck effect detectors placed between a hot thermal source and a cold thermal source whose temperature difference is small, for example a few degrees. These two sources can be formed by the epidermis of the person using an autonomous device and the surrounding environment.

FIG. 4 illustrates the principle of such a feeding device using heat of animal origin. It comprises a substrate 51 of thermally insulating material in which are placed Seebeck effect detectors 52, in the form of small bars, that is to say kinds of thermocouples. Given the low value of the voltage delivered by such detectors, namely 0.2 mV per degree Celsius (Seebeck coefficient), they are connected in series to obtain a voltage of 10 to 200 mV. All the bars are placed between a collecting plate 56 disposed on the skin 53 of the user and a heat exchanger 54 exchanging the heat with the ambient air. Two electrodes 55 provide the low voltage output for the converter.

FIG. 5 illustrates the use of a source of thermal origin between the two sides of a wall 61. The Seebeck detectors are arranged between a radiator 62 disposed inside the room and constituting a heat exchanger with the air and exchanger 63 with the outside air which comprises an upright 64 passing through the wall 61 in a section 65 of thermally insulating material.

FIG. 6 illustrates the case where the temperature difference is used with the ground 71. A thermally insulating support 72 is placed in the ground and it comprises at its upper part a surface heat exchanger 73. The Seebeck detectors are arranged between the lower face of this heat exchanger 73 and the upper face of a pile 74 thermal collector planted in the ground.

This supply device uses a reversible converter because the temperature difference between the ground and the ambient air is reversed between day and night. This supply device can for example be used in the field of road traffic signs. In particular, it can be used to power a light device 75 such as a light-emitting diode and produce a marked white strip. FIG. 7 represents the use of the temperature difference between the two faces of a window 81. A heat exchanger 82 is used, arranged on the outside wall of the window in contact with the outside air, a collecting plate 83 placed on the inside of the glass and a heat exchanger 85 placed inside on a thermally insulating support 84 placed on the inside of the glass and receiving the collecting plate 83. Seebeck detectors are arranged between the collecting plate 83 and the heat exchanger 85.

The power supply device of Figures 5 and 7 can for example be used to power an intrusion detector disposed at an opening of a room, such as a window and operating independently.

Figure 8 is a sectional view of a watch 91 which comprises, in the bottom of its case, a battery compartment 92. A power supply according to the invention is interposed between the skin of the user and the bottom of the case instead of the original closing cover of the watch. It comprises a heat collecting bottom 93 on which the Seebeck detectors 94 are arranged in a circle being embedded in a thermally insulating material 95. A receptacle 96 having the shape of a battery includes the electronic circuits and is placed in the housing 92.

FIG. 9 shows a watch in which the supply device is integrated in the housing. In this case also, the Seebeck detectors 101 are arranged in a crown and the electronic circuits contained in the body 102 of the watch and embedded in a thermally insulating material 103. FIG. 10 represents an embodiment of a watch where, to increase the exchange surface and, consequently, the power of the source, the Seebeck detectors are placed in the watch strap which is made up of articulated links in which are placed Seebeck detectors. In this case, we added a photovoltaic generator 111 on one of the links; it can be directly paralleled to the output of the supply device according to the invention or also include a converter circuit. Figure 11 shows the electrical diagram of the assembly, the sources constituted by each link being connected in series to constitute the electrical source connected to the converter.

Figure 12 shows the integration of a supply device according to the invention in a footwear element such as a shoe. In this case, the Seebeck detectors 121 are housed in the sole 122 of the shoe and use the temperature difference between the user's foot and the ground. There is then provided a plate 123 for evacuating the heat from the feet which is in contact with Seebeck detectors as well as a plate 126 for collecting the heat from the feet. The electronic circuits 124 are also housed in the soleplate 122. The power supply device can be used to power security elements such as light-emitting diodes 125.

In the case of a ski boot, the power supply device can operate a transmitter or a transponder making it possible to find the user in the event of an accident such as an avalanche or to power the electronic device for triggering the contact by contact security of fixings.

The above description of exemplary embodiments of the invention has been provided for illustration only and is in no way limitative and modifications or variants may be made without departing from the scope of the present invention. In particular, it is possible to use other sources of very low voltage or to use several of them in combination.

The reversible converter of FIG. 2 can be used in the case of heat exchanges with the ambient air, for example in the case of FIGS. 5 to 7. This reversible converter makes it possible to supply power when the temperature difference, for example example between the earth and the ambient air, reverses between day and night. We recover all possible energy by using the ebb and flow of heat exchanges.

In addition, an ear amplifier can be produced powered by a power supply device using the difference of temperature between the skin and the ambient air and placed in or around the ear.

Such an energy converter effectively exploits the very low voltages generated at low impedance by a thermoelectric module using the Seebeck effect, when the latter is subjected to a small temperature difference.

It also effectively exploits the very low voltages generated at low impedance by a thermoelectric module using the Seebeck effect comprising only a few pairs, when the latter is subjected to a large temperature difference.

Such a thermocouple for example made of FeSi2 doped N and P supports temperature differences of about 700 ° C, a single pair then generates between 100 mV and 1V.

For example, a single pair can help power a thermometer to measure high temperatures with a stand-alone sensor. The action of the converter at the thermocouple output regulates the supply voltage of the thermometer, the thermometer can for example use the voltage of the thermocouple to measure the temperature.

A first embodiment of an iron disilicide thermocouple relates to the measurement of the temperature of a food container, a saucepan, a pressure cooker or a pan for example. Energy generation is achieved by the FeSi2 element inserted between the wall of the container heated during cooking, and the handle, which acts as a radiator. The converter connected to the thermocouple output generates the operating voltage of the thermometer.

This first example can also be carried out with a thermocouple module based on bismuth tellurium as described in the second part of the text, in place of the element in FeSi2, as soon as the hot temperature does not exceed 250 ° C. .

A second embodiment relates to the safety of gas stoves, the accidental self-extinction of which is the basis of many accidents.

A piezoelectric ignition device is intended to automatically relight the accidentally blown flame. A FeSi2 couple with one junction in the flame and the other at temperature water from the inlet pipe is a great way to power the ignition system. The converter circuit secures its operation and simplifies installation.

A third application example concerns the electrical generation of a car.

Traditionally provided by an alternator, recharging the battery and supplying electrical power takes place at the expense of propulsion. However, the heat engine dissipates a lot of waste heat in the environment.

This heat can be converted by a thermoelectric process into 12V live current. A FeSI2 thermocouple in contact with the exhaust gas and in contact with the water circuit observes a temperature difference between its faces which can reach 700 ° C. A couple is enough to generate a voltage which can be used by the converter circuit described above. A high power version of this circuit would be recommended.

The fuel saving resulting from such a process can reach 20%.

An embodiment of a thermocouple module used for small temperature differences, based on bismuth tellurium, is described below.

The so-called Peltier or Seebeck effect thermocouples are commonly used in industry for cooling.

Passed by a supply current, the thermocouple absorbs heat on one of its faces and rejects it on the other.

Operating as a heat pump with no moving parts, this device is remarkable for its integration and reliability more than for its energy efficiency and manufacturing cost.

Subject to a temperature difference between its collecting faces, and traversed by a thermal flux, the thermocouple acts as an electrical generator with low impedance, it transforms part of the thermal flux into usable electrical power. There too, the generator is remarkable for its simplicity but deplores a mediocre yield and questionable economic profitability. Thermoelectric modules are traditionally made up of an electrical circuit putting in series semiconductor bars alternately doped N and P, these bars are subjected in parallel to the thermal flux passing through the module. Traditionally, these vertical bars are aligned in tight rows on a horizontal plane, and sandwiched between two insulating ceramic plates provided with a screen-printed electrical circuit.

- A general characteristic of this type of embodiment is the low electrical impedance of the module, a direct consequence of the limited number of bars of low electrical resistance. This results in either the need for a low voltage supply for the generation of cold, or the use of a step-up converter at the output of the generator thermocouple.

- A second characteristic concerns the difficulty of integration or assembly of this module in a thermal system: the heat flow does not cross the interstices, the module must be glued or compressed or welded to its thermal drains, this requires precision and knowledge do, and this results in yield losses. The modules are generally made of ceramic, to guarantee the electrical insulation of the circuit and the good conduction of the heat flow, and to avoid the rupture caused by the expansions associated with the temperature differences between the faces. It is not possible to weld these modules, bonding is delicate and compression requires heatsink assemblies. In addition, the thermal drains to which the modules are related must have high conductivities or significant dissipation due to the intensity of the flux which crosses the module.

- A third characteristic of the modules concerns their sensitivity to corrosion. In fact, the semiconductor bars are generally assembled without protection, in order to limit thermal losses, they are then exposed to corrosion.

- Finally, the critical characteristic of these modules is their cost.

The cost factors are successively: the price of the thermoelectric raw material, the cost of transformation, the cost of cutting into elements, the handling of miniature elements, the cost of ceramic, its cutting, its screen printing and soldering and finally the cost of assembling the pressing and cooking of the module. The invention presents a thermoelectric module which improves the four general characteristics, a method for producing such modules as well as some examples of applications.

According to the invention, the thermocouples are produced from semiconductor materials with carriers of type N and P, connected in series electrically and in parallel thermally.

P-type materials are for example made from an alloy containing a composition of 77.5% of Sb2Te3 in 22.5% of Bi2Te3, N-type materials are made from an alloy containing 5% of Bi2Se3 in 95% of Bi2Te3.

According to the invention, each material is subjected to vacuum annealing at a temperature of 650 ° C. for a period of approximately 12 hours, under a quartz bulb, then to crystallization at controlled temperature according to the method known as THM (Traveling Heater Method), generating a bar of diameter of the order of 30 mm in diameter at the speed of about 20 mm per day. By this method, polycrystalline materials of high thermoelectric quality are obtained, whose coefficient of merit Z of the order of 3 10 ³ K ^"1 exceeds that of the materials marketed to date (Z = 2.5 10 ^{" 3} K ^"1 Such a material increases the coefficient of performance of a cooling device by about 30% compared to the materials used to date. It has an axis of better efficiency A, in the axis of the bar, as shown in figure 13.

According to the invention, the materials are cut into bars, assembled, and wrapped.

According to a preferred but not exclusive embodiment, the elementary thermocouple consists of the same number of N-doped bars and P-doped bars aligned and intercalated. These bars are of equal dimensions, basic for example square of width L between 0.45 x 0.45 and 1 x 1 mm and of height H between 1 and 3 mm. The number of bars will vary depending on the applications between 20 and 400 approximately. Figure 14

According to the invention the bars aligned alternately N

(221) and P (222) are glued to each other by the opposite sides. Such bonding will be carried out for example by insertion between each bar of a membrane 223 prepreg, heat-bondable, the adhesion of which is ensured during a hot compression cycle.

A thin kapton film: approximately 25 microns, prepreg on a total thickness of 75 microns achieves a solid and durable bond between each bar, ensuring electrical insulation between them. The kapton, with a thermal conductivity 10 times lower than the thermoelectric material causes only a very weak thermal bridge between the bars, its influence on the performances is negligible.

In addition, kapton is a reinforced material, compatible with epoxy bonding. M consolidates the structure by protecting the bars.

An epoxy prepreg fiberglass membrane is also suitable.

According to the invention, the aligned bars are wrapped on the sides by a thin membrane 224. This is glued to the sides, adheres to the bars and the intermediate membranes.

These membranes finish consolidating the alignment, protecting each bar of which only the sections 225 remain visible.

Such a membrane is for example made from a fiberglass weave prepreg of epoxy resin or from a kapton film prepreg in an epoxy resin.

The kapton has the advantage of pre-gluing on a single side only. Pressure fusing consolidates and stiffens the structure.

Epoxy glass will be preferred to allow the element to be shaped before thermosetting. It seems possible to flex the element and give it the curvature essential for certain assemblies. Such a shape shown in top view in Figure 16 will be imposed before cooking, which will freeze it definitively.

According to the invention, the bars are electrically connected in series, the junctions N P between two successive bars being produced on the upper sections, the junctions P N on the lower sections.

According to a first embodiment of the invention, the junctions are made directly on the section of the bars, by nickel tracks 231 in FIG. 15 with a thickness of the order of approximately 50 microns. Each junction element has a length slightly less than 2xL and a width of L, it ensures the junction by completely covering the section surface of two successive bars. According to several exemplary embodiments which will be detailed in the description of the manufacturing process, the section is either covered with a layer of chemical nickel with a thickness of 50 microns, sectioned at the appropriate places, or covered with a bonding layer. ultra thin in nickel, on which the nickel track is soldered with tin bismuth 232, or else the section is etched with acid which preserves only bismuth, which is brazed with bismuth with the nickel track. By this first embodiment, the nickel electrical circuit is deposited directly on the sections, which contributes to the protection of the material because nickel constitutes an excellent chemical barrier and oxidizes only slightly. In this first embodiment, the bar will preferably be glued to the thermal drains 251 in FIG. 17 during assembly, according to the usual electronic methods aimed at dissipating the heat of the components towards the circuit on which they rest.

Such bonding provides electrical insulation between the component and the support, for example metallic and electrical conductor, this quality is essential so that the nickel tracks are not short-circuited. Such bonding ensures good heat conduction to the support due to the intrinsic thermal conductivity of the resin 252 optimized for this application. A good resin has a conductivity equivalent to that of the thermoelectric material. Finally, the mechanical strength of such a bonding can be optimized by a fiberglass reinforcement in the resin, guaranteeing a secure recovery of effort. An epoxy adhesive loaded with a conductive ceramic impregnating a fine weaving of fiber optimizes the mechanical strength. Such bonding carried out hot under pressure fixes the bar on the support with a robust anchoring. The epoxy of the thermal glue fusing with the epoxy of the membranes, the structure is reinforced and the bars are then completely wrapped. According to a second embodiment in FIG. 18, the sections of the bars are covered with a very thin layer of nickel forming a diffusion barrier. The strip is soldered with tin bismuth 263 on a printed circuit 261 which carries out the inter-bar junctions, by contiguous parallel tracks 262 isolated between them spaced at a pitch of 2L and of a width slightly less than 2L. These rectangular tracks 262 have a length of a few millimeters, they are made of nickel-plated copper. In this second embodiment, the printed circuit is made from a thin membrane 264 of the “flex type” constituted by a fiberglass weave impregnated with an epoxy resin loaded with heat conducting elements, such as than a ceramic powder, covered with a sheet of copper 262 of conventional thickness, 35 or 70 microns. Care will be taken to etch the copper circuit, then deposit nickel as a diffusion barrier, and finally pre-tinning with bismuth. An exemplary embodiment uses an epoxy glass prelaminate loaded with boron nitride bonded to a copper strip. The serigraphy and copper engraving define the circuit, it is then brazed after nickel plating on the bars.

In this second embodiment, the printed circuit is glued against the metal parts making heat sink 265, in aluminum, copper, tin, sheet metal, nickel steel, Invar or stainless steel depending on the application, or else the circuit is integrated, a conventional circuit with copper dissipators and for example copper bushings for heat transfer.

Printed circuits of the copper on aluminum laminate type are particularly suitable for application, after nickel plating of copper.

In this embodiment, the bar is sandwiched between two such circuits and hot pressed in order to consolidate both the solder and the epoxy adhesive.

Two embodiments of the elementary thermocouple have been described in the form of a bar consisting of an alignment of bars of alternately N and P doped material. In one case, the electrical circuit is made of nickel on the bar provided with connector at the ends , in the other case the circuit is produced on the support, in the form of a printed circuit, on which the strip is soldered.

In both cases, the bar is hot pressed preferably between the support making the lower thermal drain and the upper thermal drain. Cold pressing with a polymerizable thermal glue is also possible.

Another embodiment of the module is made up of multiple bars attached to form a block whose dimensions are of the order of 10 × ¹⁰ × 2 mm ³ . Its constitution is similar, its characteristics similar.

According to the invention, the elementary component has elementary characteristics of electrical, thermal impedance, cold power, as well as a useful section corresponding to the section of its base.

The assembly methods of these elementary thermocouple bars make it easy to integrate them into thermoelectric cooling systems or thermoelectric generators, because it makes it possible to adapt the density and the number of elementary modules to the electrical and thermal characteristics of the interfaces.

In particular, a conventional thermocouple has a high thermal conductivity, and potentially a large flux, sometimes causing the need to dissipate heat and cold by large fin radiators and in forced mode.

A lower density of thermoelectric material makes it possible, for example, at lower cost to spread the thermocouples over a large surface, and therefore to have greater exchange surfaces without ventilation or bulky fins. This simplifies the transport of heat. By this process, the cold and hot faces can be only simple very discreet aluminum plates insulated from each other by a self-adhesive foam placed around the components. In thermogeneration, the temperature differences are reduced, the dissipated powers are low, the strip densities also.

According to the invention, we describe a first embodiment of a cooling device for example intended for a mini-refrigerator.

Such a device has an interior, cold face, an exterior, hot face, and optionally a heat exchanger.

Depending on the performance, the external hot face dissipates approximately twice the heat taken from the cold part. Provision will therefore sometimes be made for forced ventilation, the principle of which is described below.

The cold face 271 in FIG. 19 constitutes the structure of the cooling system. It is produced from a printed circuit laminated copper nickel-plated on aluminum. On the aluminum is laminated a sandwich consisting of a layer of fiberglass prepreg with thermal conductive resin, and a layer of copper representing the desired electrical circuit 272.

The electrical circuit is divided into two zones: A first zone where the supply and regulation device is installed, a second zone representing the thermoelectric circuit.

The supply and regulation circuit is made from surface mount components, located in the first zone. It consists of a simple diode rectifier, a capacitor 274 and a multiple relay 275 controlled by the integrated thermostat 276.

The 277 thermocouple bars are welded with tin bismuth and installed in the area of the thermoelectric circuit, according to a series-parallel scheme. The mounting process conforms to the standards of the CMS components.

A layer of adherent thermal insulating foam 278 fills all the residual volume between the components, over a height of the order of L. Finally, a mosaic of heat sinks 279 covers the area of the thermocouple strips, each heat sink provided with a circuit statified copper tin is welded on between 2 and 4 bars, and for example consolidated in its center by a stainless steel rivet.

These heatsinks 279 are for example made of extruded aluminum.

According to a non-exclusive embodiment of the invention, an optional fan 701 performs forced dissipation in a tunnel 702 around the blades of the dissipators. This fan is triggered in parallel with the thermocouples, under the thermostat setpoint. Associated with the ventilation tunnel and the fan, two valves 703 close under the effect of their mass the entrances and exits of the tunnel, in order to minimize the effect of insulation losses when the relay is open, consequence of the conductivity thermal cells. These valves open when the fan and thermocouples are started.

An insulating wall 702 and 278 contributes to reinforcing the insulation, in particular around the ventilation tunnel.

Such a process can be used for mini-refrigerators, for mini-air-conditioning, for cooling systems for industrial or food liquids, (in this particular case, the cold wall 271 is in contact with a fluid circulation exchanger), for butcher's stalls, etc.

This device optimizes the size and efficiency of the cooling, as well as the insulation. Indeed: it has a large exchange surface for the cold side, so it allows only convective exchange without fan and without bulk, it moderately concentrates the flow on the hot side, and it is possible to condition the operation of thermocouples l heat exchange with the outside by forced ventilation. In addition, the supply circuit is located in a lost area for cooling at no additional cost.

For an application of this type, square modules of approximately 10 × 10 mm ^{2 will} be preferred, made up of adjoining strips, each pumping approximately 1 watt over a surface of 10 cm ² .

According to the invention, we describe in Figure 20 an example of an electric microgenerator device, a bracelet link:

The heat collector is made of aluminum copper laminate 281, the copper 282 of which is nickel-plated or on a printed circuit. The heatsink is made of aluminum copper laminate 283 of which copper 284 is nickel-plated. This dissipator represents the upper face of the bracelet and has small fins 285.

On either side of the link, as well as on the central zone, strips of approximately 10 mm in length are brazed between the collector and the dissipator. At each end of the link, a nickel-plated pivot 287 is brazed on the internal face of the dissipator, or else on the internal face of the collector, it ensures electrical continuity from link to link thanks to a conductive axis.

A rivet or a stainless steel screw helps to consolidate the link by exerting pressure on the solder.

A foam (not shown) provides protection and cleanliness of the link, as well as insulation between the two faces.

On the wrist, the temperature difference between the collector and the dissipator induces a heat flux converted into electromotive force collected between the pivots.

With around 20 NP pairs per link, and a temperature difference of around 10 ° C between the faces, each link with a surface area of 2 cm ² generates a potential difference of around 20 mV, under a 2.4 ohm impedance, or about 40 microwatts maximum delivered.

This constitutes a non-exclusive example of the use of an optimized thermogenerator. The output voltage is proportional to the temperature difference between the collecting and dissipating faces and to the number of couples NP, and moreover, the electric power delivered is maximum when the thermal resistance of the bars is equivalent to that of the dissipator, the total section of authorized thermoelectric material is therefore frozen. The maximum tension is obtained for bars whose H / L ² ratio is maximum. With a small cross-section and long length, the bars are fragile, and the reinforcement by membranes contributes to making possible the optimization of the factor H / L ² .

These two implementations of elementary modules in a strip are non-limiting and the examples given highlight their simplicity.

According to the invention, we describe a method for producing a module strip.

Each strip contains an alternation of P and N doped thermoelectric materials. These materials are subject to crystal growth and have an anisotropy axis A in Figure 13 of thermal conductivity and merit factor. According to the invention, the starting ingots N and P are rectangular, elongated along the anisotropic axis.

The ingots are then cut according to parallel slices containing the anisotropic axis, of thickness close to L. Such a cutting is for example carried out with a multi-wire saw or else with a disc saw.

The sections 291, 292 in FIG. 21 are then alternated P and N while keeping the parallel axes, superimposed, by inserting in each section a heat-bondable membrane 293 of small thickness.

This membrane is for example a 25 micron Kapton comprising on both sides 25 microns of epoxy resin, or else an epoxy glass.

The reconstituted ingot is therefore a composite consisting of alternating electrically insulated N P wafers.

A first firing ensures partial polymerization, under pressure, at a temperature close to 130 ° C. After treatment, the new ingot is then cut again into slices of thickness L approximately, according to planes containing the anisotropy axis and perpendicular to the previous slices.

Each slice 2101 in FIG. 22 containing rectangular rods of section L ² alternately of material N and P is then covered on either side by two kapton membranes 2102, 2103 pre-glued on one side only. The slices are then superimposed and the ingot reconstituted. Bars are thus produced, because the slices are not glued together. It is also possible to cover the slices of epoxy glass, and to separate them by a release membrane in pacothane. The latter will allow the separation of the bars.

Finally, to make block modules, a single kapton membrane pre-glued on both sides or an epoxy glass membrane will be inserted between the slices. We will take care to alternate the bars N and P to achieve a checkerboard distribution.

A pressure cooking cycle completes the polymerization of the slices.

The ingot is then cut along the plane perpendicular to the anisotropy axis in slices of thickness H, 2111, 2112, FIG. 23, each slice revealing the sections of the bars.

Each section contains the elementary bars N P, the bars are juxtaposed and are linked by the residual adhesion. A shear dissociates them. The modules remain in block.

The wafer has the vivid sections of the thermoelements, which is protected by a deposit of nickel, either electrolytic or chemical, in a bath. Nickel acts as a diffusion barrier and bonding interface for the solder. Several alternatives appear:

- The layer of nickel deposited is very thick, around 0.1 mm and it ensures continuous covering of the wafer, with robust attachment to the bars. Then, by cutting or selective chemical attack, it is possible to make the connections between the bars directly, then to separate the bars provided with their own electrical circuit. A flash by sputering contributes to trigger the attachment before chemical deposition. The strip is intended to be glued with thermal glue.

- The nickel layer is thin. The edge is nickel-plated on the section of the bars exclusively. So we come to braze in a hot press a flexible copper circuit pre-tinned with tin bismuth 2121, figure 24 on an epoxy glass membrane loaded with boron nitride. A brazing temperature pressing phase of the wafer welds the junctions. The circuit will have been previously engraved by screen printing on copper bonded to a transparent adhesive sheet 2122 in charged epoxy glass. Each bar produced by this process has two weldable tabs, the bars are separated by cutting out the charged epoxy glass membrane.

- The nickel layer is thin, the strip is intended to be soldered on a printed circuit which ensures the inter- elements. The printed circuit is made of nickel-plated copper and tinned with bismuth. Aluminum nickel-plated copper laminate is the best technical alternative.

A thermoelectric module has been described in the form of a multi-element strip, assembly versions of this strip either by bonding or by soldering, the integration of this strip in an electrical and thermal circuit, two examples of setting work of such elements for a refrigeration device and for a microgenerator, and finally, a process for producing such bars minimizing the cutting and handling operations.

An assembly of bars constitutes a block whose applications are similar.

The bar presents as announced: - an optimization of the electrical impedance, consequence of the optimization of H / L ² and the number of bars.

- optimization of the thermal impedance: The bar has an elementary thermal conductivity, the very simple association of the bars in series electrically and in thermal parallel allows the adaptation of the thermal resistance of the bars to that of the drains and heat sink associated preexisting .

- improved mechanical resistance due to the composite structure. - improved corrosion resistance by the fact that each element is completely coated with either resin or nickel.

- a simplification of the assembly, by the implementation of techniques similar to those used in CMS.

The production process is optimized in terms of cost by the fact that it eliminates the following elements:

- individual cutting of the bars

- handling of individual bars

- brazing on ceramic support

The assembly is less costly, since it is limited to hot bonding or else to soldering on a printed circuit with dissipative support.

Claims

1. Energy converter circuit, booster of the voltage supplied by a source (1; 21) with low continuous voltage of internal resistance (2) not zero, comprising a self-oscillating circuit, operating at very low voltage, using a transformer voltage booster (3, 4, 6, 6 ', 7; 20, 23, 24, 20', 23 ', 24') generating the control signals of two chopper boosters (11-14; 25-28, 25 '-28 ") in alternating operation, of the type comprising an enriched field effect transistor (11, 12; 25, 26, 25', 26 ') which is used as a synchronous switch with the self-oscillating circuit, which is connected in series with an inductor (13, 14; 27, 28, 27 ', 28 ") at the terminals of said source (1; 21) and which is connected to the user circuit through a diode (15, 16; 29, 31 , 29 ', 31').

2. Circuit according to claim 1, characterized in that a voltage clipping device and a large capacity capacitor or an accumulator are connected in parallel to the output terminals.

(18).

3. Reversible converter circuit, characterized in that it comprises two converter circuits (20, 22-29, 31; 20 ', 22'-29', 31 ') according to claim 1 connected in antiparallel to the source (21) and connected to the output terminals (U +, U-) via four switches (37-39, 41) controlled two by two by two additional windings (42, 43, 42 ', 43') of the transformer of the active converter and in that each converter has a blocking device (33-35, 33'-35 ') blocking the other converter.

4. Circuit according to claim 3, characterized in that the blocking device comprises a third additional winding (33, 33 ") of the transformer at the terminals of which is connected a rectification circuit (34, 34 ') generating a direct voltage blocking the self-oscillating converter circuit not active.

5. Device for supplying an autonomous portable device from a thermal system comprising a hot source and a cold source having a small temperature difference between them, such as the epidermis of a human being and the atmosphere room, characterized in that it consists of a converter circuit according to claim 1, 2, 3 or 4 in which the electrical source consists of a set of Seebeck effect detectors (52; 94; 101) connected between the two thermal sources.

6. Device for supplying an autonomous portable device characterized in that it consists of a converter circuit according to claim 1, 2, 3 or 4 in which the electrical source is constituted by a photovoltaic cell (111).

7. Wrist watch (91) characterized in that it comprises a supply device (94; 101) according to at least one of claims 5 or 6 placed under its case in place of the battery (92) or integrated in the housing.

8. Watch strap consisting of articulated links, characterized in that it comprises a supply device according to at least one of claims 5 or 6, in that the links each include Seebeck detectors, the sources constituted by each link being connected in series to constitute the electrical source connected to the converter.

9. Road signaling device on the ground, characterized in that it comprises a supply device according to claim 5 using the temperature difference between the ambient air and the road supplying a light device.

10. Intrusion detector characterized in that it comprises a supply device according to claim 5 or 6 disposed between the inside and the outside of the monitored room.

11. Shoe characterized in that it comprises a supply device (121, 124) according to claim 5 disposed between the inside and the outside of the shoe and supplying a safety device (125) carried by the shoe.

12. Thermoelectric component comprising bismuth tellurium doped with antimony and bismuth tellurium doped with selenium, characterized in that its structure is of a composite nature, consisting of parallelepiped bars of joined thermoelectric material (221, 222), coated on the facing faces of an electrical and thermal insulating membrane (223), mechanically reinforced on the sides by an electrical and thermal insulating membrane (224), covered on the visible faces (225) of a thin electrical circuit, ensuring the setting electric bars series.

13. elementary component according to claim 12 characterized in that it consists, according to a bar structure, of an alignment of bars alternately doped P and N, bonded to each other by the opposite faces by a heat-sealable membrane, coated with a reinforced lateral membrane, nickel-plated on the visible edges of the bars, then brazed to an elementary thin circuit ensuring the junctions from one bar to the next.

14. parrallélépipédique module according to claim 12 characterized in that it consists of the juxtaposition of several elementary components according to claim 13 connected in series electrically and crossed in parallel by the heat flow.

15. Component according to claims 13 and 14 characterized in that the thin electrical circuit (261) is made from a thin membrane of epoxy glass charged with boron nitride (264), support for an etched nickel-plated copper (262 ) and pre-tinned with bismuth (263), and in that this membrane is brazed and heat-sealed in the press to said component.

16. Component according to claims 13 and 14 characterized in that the electrical circuit is produced on a rigid support and thermal conductor (251, 265) covered with an electrically insulating and thermal conductive membrane (252,264), by an etched copper, nickel-plated and tinned with bismuth.

17. Cold generator characterized in that it operates components according to claims 12 to 16 and in that it consists of an aluminum plate covered with a thin electrical circuit ensuring the connection between the components, in that that the components are heat-bonded to the plate or brazed, in that the components are covered by several dissipators under an air flow driven by a fan.

18. Thermoelectric generator characterized in that it comprises components according to claims 12 to 16 each interposed between a collector at a temperature (281) and a dissipator at a different temperature (285), and an electrical connection circuit between the components (282).

19. A method of producing the component according to claims 12 to 16 characterized in that the starting materials, in the form of two bars, one doped with selenium, the other with antimony, undergoes a first cutting cycle in slices, then a reconstitution of the bar with the interposition of heat-sealable membranes, with alternating materials from one slice to another, then a hardening of the reconstituted bar, then a slice cut in a perpendicular plane, then a reconstruction with interposition of membrane , and hardening, and finally a third cutting cycle in the axis perpendicular to that of the bars, producing the components without an electrical circuit.

20. Voltage generator for supplying a thermometer for measuring the temperature of a culinary container, characterized in that it comprises at least one thermoelectric couple in iron disilicide or indeed a thermocouple module according to claim 12, one or the other interposed between the handle and the container, and connected to a converter circuit according to claim 1.

21. Voltage generator for supplying a safety circuit for a gas water heater characterized in that it comprises an iron disilicide thermocouple in contact with the flame and with the water circuit connected to a converter circuit according to claim 1.

22. Generator for a motor vehicle characterized in that it comprises an iron disilicide thermocouple in contact with the exhaust and the cooling circuit connected to a converter circuit according to claim 1.