Isolated DC-DC converter, electrical equipment and starting method thereof

Abstract

The present invention relates to an isolated DC-DC converter, an electrical device and a startup method thereof, comprising: a first circuit, comprising at least one induction coil (L1, L2); a second circuit, comprising at least one induction coil (L3, L4), the second circuit further comprising at least one switch arm (Q3, Q4) connected between a terminal of the induction coil (L3, L4) of the second circuit and electrical ground, the switch arm (Q3, Q4) having a conductive state and a non-conductive state; an energy recovery circuit, connected at a connection point of the second circuit, the connection point being connected to the terminal of the induction coil (L3, L4) of the second circuit, the energy recovery circuit comprising a damping capacitor (Cs), when the switch arm (Q3, Q4) is switched to a non-conductive state, the damping capacitor (Cs) can store energy present in the second circuit via the connection point so as to power additional electronic components.

Description

Technical Field

[0001] The invention relates to an isolated DC-DC converter, an electrical device and a method for starting the same. The invention relates in particular to the field of electric or hybrid vehicles. More precisely, the invention relates to an isolated DC-DC converter, in particular arranged between an on-board high-voltage network and an on-board low-voltage network, the converter comprising specific components arranged to recover energy from voltage surges generated during switching of switches belonging to a secondary circuit of the converter, the recovered energy being able to (in particular allowing to) power a control unit of the converter. Background Art

[0002] As is well known, an electric or hybrid vehicle comprises an electric motor system powered by a high voltage power supply battery via an onboard high voltage power grid, and a plurality of electrical equipment auxiliary items powered by a low voltage power supply battery via an onboard low voltage power grid. Therefore, the high voltage power supply battery ensures the function of supplying energy that allows the vehicle to propel to the electric motor system. The low voltage power supply battery supplies power to electrical equipment auxiliary items such as an onboard computer, a window winder motor, a multimedia system, etc. The high voltage power supply battery usually delivers a voltage between 100 volts and 900 volts, preferably between 100 volts and 500 volts, while the low voltage power supply battery usually delivers a voltage of about 12 volts, 24 volts or 48 volts. These two high voltage power supply batteries and low voltage power supply batteries must be able to be charged.

[0003] Recharging the high voltage supply battery with electrical energy may be carried out in a known manner by connecting the high voltage supply battery to an external grid, such as a domestic AC grid, via the vehicle's high voltage DC grid.

[0004] It is also known to charge a low-voltage battery directly with a high-voltage battery. For this purpose, the high-voltage battery is connected to the low-voltage battery via a galvanically isolated direct current-to-direct current converter (commonly referred to as a DC-DC converter).

[0005] Figure 1 Functional block diagram representing a prior art on-board electrical system. This system comprises an electric charger OBC designed to supply a high voltage supply battery HB typically dedicated to the propulsion of an electric or hybrid vehicle, and further comprises a low voltage battery LB ensuring the supply of electrical equipment items of said vehicle.

[0006] In order to control the electric engine ENG driving the wheels of the vehicle, it is known to use an inverter INV making it possible to convert the direct current supplied by the high voltage supply battery HB into one or more alternating control currents (for example sine waves).

[0007] Still refer to Figure 1In order to supply the vehicle's high voltage supply network, which in particular allows charging of the high voltage supply battery HB, the electric charger OBC receives current from an external AC grid G1, such as a household AC grid, to supply the high voltage supply battery HB.

[0008] Finally, still refer to Figure 1 , charging of the low voltage battery LB is carried out in a known manner via the high voltage supply battery HB, for which purpose the system comprises an isolated DC-DC converter DCDC connected between the high voltage supply battery HB and the low voltage battery LB.

[0009] As is known, a DC-DC converter conventionally comprises a transformer consisting of at least one induction coil belonging to a primary circuit coupled to at least one induction coil belonging to a secondary circuit. The primary circuit is a resonant circuit, for example controlled by a half-H bridge, in particular of LLC type. The secondary circuit comprises, for example, a synchronous rectifier circuit.

[0010] The synchronous rectifier circuit includes at least one switch (eg, of the MOSFET type) to rectify current from the at least one inductive coil located in the secondary circuit.

[0011] Described below Figure 2 denoted by an isolated DC-DC converter.

[0012] It is well known that voltage surges occur in the secondary during the switching of such a switch. Specifically, when the switch arm of the secondary circuit switches to the off state, the energy present in the secondary circuit causes a voltage surge when opening the switch arm that potentially damages the electronic components of the DC-DC converter.

[0013] In order to overcome this drawback, it is known from the prior art to implement a set of electronic components (generally named with the acronym RCD) comprising a resistor, a capacitor and a diode, the resistor and the capacitor being named "damping" or, according to the terminology of those skilled in the art, respectively "snubber resistor" and "snubber capacitor".

[0014] The diode allows the current caused by the voltage surge to pass through to charge the snubber capacitor. The snubber capacitor stores the energy of the voltage surge and dissipates the energy into a snubber resistor connected in parallel with the snubber capacitor.

[0015] The disadvantage is the energy loss caused thereby. In fact, the energy dissipated in the snubber resistor is lost and adversely affects the efficiency of the corresponding electrical system. In addition, the resistor value is difficult to adjust and requires significant time during the design of the corresponding electrical system.

[0016] In order to at least partially solve this technical problem, the present invention is directed to an isolated DC-DC converter in which the so-called "voltage surge" energy present in the secondary circuit during switching to the off-state of an induction coil connected to the secondary circuit is reused (for example, in particular) to power a control unit of the DC-DC converter. Summary of the invention

[0017] To this end, the invention relates more precisely to an isolated DC-DC converter, in particular for use in a motor vehicle, comprising:

[0018] - a first interface terminal configured to be connected to a first electrical network,

[0019] - a second interface terminal configured to be connected to a second electrical grid,

[0020] - a first circuit connected to the first interface terminal, the first circuit comprising at least one induction coil,

[0021] - a second circuit comprising at least one induction coil, said second circuit further comprising at least one switch arm connected between a terminal of said at least one induction coil of said second circuit and electrical ground, said switch arm having an on state and an off state,

[0022] an energy recovery circuit connected at a connection point of the second electrical circuit, the connection point being connected to the terminals of the at least one inductive coil of the second electrical circuit and to the at least one switching arm, the energy recovery circuit comprising a buffer capacitor capable of storing energy present in the second electrical circuit between its upper terminal and its lower terminal connected to the electrical ground via the connection point when the switching arm is switched to the off state, in such a way as to power electronic components through the third interface terminal of the isolated DC-DC converter.

[0023] By means of the invention, the recovered energy makes it possible to power electronic components. For example, a control unit of an isolated DC-DC converter can be supplied with energy via a DC-DC converter circuit of an energy recovery circuit thereby ensuring an auxiliary power supply function.

[0024] Therefore, the isolated DC-DC converter according to the present invention has improved efficiency in terms of energy consumption.

[0025] The isolated DC-DC converter according to the invention makes it possible to dissipate the voltage surges present in the secondary without resorting to one or more snubber resistors, or to reduce the dimensioning of said voltage surges. An attendant advantage is the possibility of using switches (e.g. MOSFETs) with reduced breakdown voltage, since the voltage surge peaks are absorbed.

[0026] According to an embodiment, the isolated DC-DC converter comprises a preferably isolated DC-DC converter circuit configured to recover energy stored in the buffer capacitor, the DC-DC converter circuit being connected between the upper terminal of the buffer capacitor of the energy recovery circuit and the third interface terminal.

[0027] According to an embodiment, the DC-DC converter circuit ensures an auxiliary power supply function configured to supply power to the electronic component via the third interface terminal.

[0028] According to a preferred embodiment, the DC-DC converter circuit ensures an auxiliary power supply function configured to supply power to a control unit of the isolated DC-DC converter via the third interface terminal.

[0029] According to an embodiment, the energy recovery circuit further includes a switch located between the upper terminal of the buffer capacitor of the energy recovery circuit and the third interface terminal, the switch having a terminal connected to the third interface terminal and capable of switching between a first position in which the third interface terminal is configured to be connected to a terminal of a power supply circuit and a second position in which the third interface terminal is connected to the upper terminal of the buffer capacitor of the energy recovery circuit, so that when the switch is in the second position, the third interface terminal delivers energy stored in the buffer capacitor of the energy recovery circuit.

[0030] According to an embodiment, the energy recovery circuit includes an additional capacitor located between the terminal of the switch connected to the third interface terminal and the electrical ground, and the additional capacitor is configured to be charged and configured to deliver energy to the third interface terminal during switching of the switch from the first position to the second position.

[0031] The DC-DC converter circuit is, for example, a step-down type.

[0032] Advantageously, the energy recovery circuit comprises at least one diode upstream of the buffer capacitor, the cathode of the at least one diode being connected to the upper terminal of the buffer capacitor.

[0033] According to an embodiment, the second circuit comprises two induction coils and two switch arms, the switch arms being configured to rectify currents respectively coming from each of the induction coils, the energy recovery circuit comprising a diode per switch arm, the diode being located upstream of the buffer capacitor, the cathode of each diode being connected to the upper terminal of the buffer capacitor.

[0034] According to an embodiment, the energy recovery circuit further comprises a snubber resistor configured to dissipate unconsumed voltage surge energy via the third interface terminal, the snubber resistor being connected in parallel with the snubber capacitor.

[0035] The invention also targets an electrical device comprising an isolated DC-DC converter such as briefly described above and a control unit of components of said isolated DC-DC converter, said control unit being connected to a third interface terminal and being supplied with electrical energy at least partly via an energy recovery circuit.

[0036] The invention further relates to an electric or hybrid vehicle comprising such an electrical device.

[0037] The invention also has as its object a method for starting an electrical device comprising a DC-DC converter such as that briefly described previously, said starting method comprising the following steps:

[0038] - verifying that the switch is in the first position and that said switch is switched to this position if necessary,

[0039] - verifying the presence and value of a voltage at a third interface terminal configured to power a control unit of the isolated DC-DC voltage converter,

[0040] - starting the isolated DC-DC converter with its function of converting a DC voltage, the third interface terminal being connected to a power supply circuit connected to the switch when the switch is in the first position,

[0041] - measuring the voltage at the connection point corresponding to the second position of said switch,

[0042] If the voltage complies with the requirement for a predefined duration, for example equal to 100 microseconds, the switch switches to the second position so that the third electrical terminal delivers the energy stored in the buffer capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The invention will be better understood by reading the following description given only as an example and by referring to the accompanying drawings given as non-limiting examples, in which like references are given to similar objects and in which:

[0044] - Figure 1 (Described) shows a functional block diagram of a known electrical system onboard an electric or hybrid vehicle.

[0045] - Figure 2 An isolated DC-DC converter according to the present invention is shown which recovers electric energy corresponding to the loss caused by the voltage surge in the secondary.

[0046] - Figure 3 A method according to the invention for starting and shutting down such an isolated DC-DC converter is shown.

[0047] - Figure 4 Graph resulting from a simulation showing the damping relative to the secondary losses of an isolated DC-DC converter not comprising any means for recovering voltage surge energy in the secondary or comprising an RCD type snubber circuit or recovery device according to the invention.

[0048] It should be noted that the figures illustrate the invention in a detailed manner for implementing the invention, which figures will obviously enable better definition of the invention when necessary. DETAILED DESCRIPTION

[0049] In the description that will be given below, the implementation of the present invention in an electric or hybrid vehicle will be discussed. However, this should not be interpreted in a limiting manner, and the present invention can be implemented in any type of vehicle or other application.

[0050] The embodiments described below are particularly suitable for electric or hybrid vehicles, which include a high-voltage power supply battery, an electric power system, an on-board high-voltage power grid, a low-voltage power supply battery, an on-board low-voltage power grid, and multiple electrical equipment auxiliary items.

[0051] The on-board high-voltage power grid connects the high-voltage power supply battery and the electric-motor system so that the high-voltage power supply battery ensures the function of supplying the electric-motor system with energy that allows the vehicle to propel. As previously described, the high-voltage power supply battery typically delivers a voltage between 100 volts and 900 volts, preferably between 100 volts and 500 volts.

[0052] The vehicle low voltage grid connects the low voltage power supply battery and a plurality of electrical equipment auxiliary items so that the low voltage power supply battery supplies power to the electrical equipment auxiliary items such as the vehicle computer, the window motor, the multimedia system, etc. As is known to all, the low voltage power supply battery generally delivers a voltage of about 12 volts, 24 volts or 48 volts.

[0053] Recharging the high voltage supply battery with electrical energy may be performed by connecting the high voltage supply battery to an external grid, such as a domestic AC grid, via the vehicle's high voltage DC grid.

[0054] Recharging the low voltage battery is performed directly with the high voltage battery. For this purpose, the high voltage battery is connected to the low voltage battery via an isolated DC-DC converter.

[0055] As explained previously, the isolated DC-DC converter DCDC has the function of converting a high DC voltage into a low DC voltage (possibly reversibly). A high voltage, typically between 100 and 500 volts, is delivered to or derived from the terminals of the onboard high voltage network HV. A low voltage, typically equal to about 12 volts, 24 volts or 48 volts, is delivered to or derived from the terminals of the onboard low voltage network LV.

[0056] For this purpose, a conversion ratio is configured between the input voltage and the output voltage of a transformer integrated in the isolated DC-DC converter.

[0057] Voltage surges may occur during the switching of the switch, so that electrical energy is stored in the secondary circuit. Such voltage surges may damage the switch, since the latter can only withstand a predetermined maximum voltage at its terminals.

[0058] Figure 2 An isolated DC-DC converter DCDC configured to be located between a first interface terminal X connected to a high voltage network and a second interface terminal Y configured to be connected to a low voltage network is shown. The isolated DC-DC converter DCDC comprises a half H-bridge marked H, which comprises two switches Q1, Q2 controlling energy circulating in induction coils L1, L2 in a primary circuit of the DC-DC converter DCDC.

[0059] In the secondary circuit, the induction coils L3 and L4 transfer energy to a charger connected between the second interface terminal Y and the electrical ground via switches Q3 and Q4, which rectify the current from the induction coils L3 and L4 in a synchronous manner. Therefore, the switches Q3 and Q4 of the secondary circuit form a synchronous rectifier circuit.

[0060] therefore, Figure 2 The isolated DC-DC converter DCDC represented in FIG. 1 has synchronous rectification. The converter DCDC is particularly configured to be connected between a high voltage network and a low voltage network on board an electric or hybrid vehicle.

[0061] The induction coils L1 , L2 , L3 , and L4 may form an LLC type resonant circuit; however, the DC-DC converter DCDC may be another type of isolated DC-DC converter.

[0062] Preferably, the switches Q1 and Q2 are MOSFETs that can be operated in a soft switching mode (or named Zero Voltage Switching (ZVS)), that is, they can be switched at zero voltage. The switches Q3 and Q4 are also MOSFETs, but they are not operated in the soft switching mode, in which a voltage surge is generated during the switching of the switches Q3 and Q4 in the secondary circuit.

[0063] In the secondary circuit, the switches Q3 and Q4 have in practice intrinsic diodes which cause voltage surges during switching, as explained previously. According to the present invention, in order to overcome this drawback, the DC-DC converter DCDC comprises an energy recovery circuit configured to recover voltage surge energy in order to power a user electrical device (in particular a control unit of the DC-DC converter DCDC).

[0064] More precisely, the energy recovery circuit configured to recover the energy of voltage surges in the manner of an RCD circuit comprises a snubber capacitor Cs between the terminals of the induction coil L3 (respectively, the induction coil L4) and electrical ground, said snubber capacitor Cs being configured (according to the invention) to “dampen” the energy caused by these voltage surges by charging.

[0065] Unlike the RCD circuit, in order to consume the energy stored in the buffer capacitor, the energy recovery circuit of the isolated DC-DC converter DCDC according to the present invention includes a DC-DC converter circuit FB, thereby forming an auxiliary device for recovering the energy stored in the buffer capacitor Cs. In other words, according to the present invention, a connection is provided between the buffer capacitor Cs and the auxiliary power supply constituted by the converter circuit FB.

[0066] Typically, the auxiliary power supply formed by the DC-DC circuit converter FB imparts electrical energy which is transmitted by the buffer capacitor Cs to the control unit of the isolated DC-DC converter DCDC.

[0067] according to Figure 2 In the embodiment shown in , a switch R with two positions is provided. The switch R is, for example, a low-current relay. The switch R can in particular be a transistor.

[0068] In the second position B, the switch R connects the input terminals of a DC-DC converter circuit FB, for example, for powering a control unit of an isolated DC-DC converter DCDC, to the terminals of a buffer capacitor Cs. In the first position A, the switch R connects the input terminals of a converter circuit FB, for powering a control unit of an isolated DC-DC converter DCDC, to the terminals of a boost converter circuit PSU, which is capable of configuring the voltage at a connection point A of the switch R in the first position at a value substantially equal to the value of the voltage delivered by the buffer capacitor Cs to the connection point A of the switch R in the first position.

[0069] In fact, the DC-DC converter circuit FB is powered at startup via a power supply circuit supplied with electric energy through the battery LB, thereby powering the control unit of the isolated DC-DC converter DCDC according to the embodiment, while there is no electric energy in the isolated DC-DC converter DCDC and the converter has not yet started.

[0070] At start-up, the switch R is therefore in the first position A so that the control unit of the isolated DC-DC converter DCDC is powered via the connection point A powered by the boost converter circuit PSU receiving electrical energy originating from the battery LB.

[0071] The presence of a step-up converter circuit PSU for stepping up the voltage delivered by the battery LB makes it possible to bring the corresponding connection point A to a potential similar to the potential of the connection point B corresponding to the second position of the switch R.

[0072] In practice, the respective connection points A, B of the switch R in the first position and the second position must have similar voltage potentials.

[0073] The isolating transformer T of the DC-DC converter DCDC has a transformation ratio configured in a conventional manner to deliver a voltage having a value corresponding to twice the voltage delivered by the low voltage battery. Therefore, the boost converter circuit PSU is configured to deliver a voltage having a value substantially equal to twice the voltage delivered by the battery LB to the connection point A corresponding to the first position of the switch R.

[0074] For example, in case the low voltage battery LB delivers a voltage between 8 and 16 volts, the DC-DC converter circuit FB or any suitable auxiliary power supply implemented is selected to have an operating range of voltage supplied to its input connection terminals between 16 and 32 volts.

[0075] Figure 4Simulation results are shown which make it possible to compare the effects obtained with a conventional RCD snubber circuit as previously described with the effects obtained with a device according to the invention in which the voltage surge energy in the secondary circuit RD is dissipated via the DC-DC converter circuit FB, for example for powering a control unit of the DC-DC converter DCDC, instead of being dissipated by the snubber resistor of the conventional RCD snubber circuit. Figure 4 The simplified diagram shows the evolution of the voltage V in the secondary as a function of the time t.

[0076] Figure 4 The simulation shows equivalent limitation of voltage peaks when an RCD circuit (curve 2) or a device according to the invention (curve 3) has been implemented. By comparison, in the absence of a snubber device, the voltage at point B is represented by curve 1 showing the presence of a significant voltage surge in the secondary.

[0077] In the automotive case, a DC-DC converter circuit FB of the type supplying a control unit of a DC-DC converter DCDC consumes approximately 10 to 14 Watts, roughly corresponding to the energy dissipated as losses in the snubber resistor of an RCD type snubber circuit according to the prior art.

[0078] In the embodiment shown, the DC-DC circuit converter FB, in which the electric energy stored in the buffer capacitor Cs is recovered (in particular, corresponding to the voltage surge energy generated in the secondary circuit RD during the off state of the switches Q3, Q4 through the induction coil controlling the secondary RD), ensures an auxiliary power supply function for supplying power to the control unit of the DC-DC converter DCDC to which the secondary circuit RD belongs, it is necessary that the circuit DC-DC converter FB is initially supplied by the battery LB.

[0079] For this purpose, as explained previously, reference is made to Figure 2 , the switch R is in position A when activated, which corresponds to the first position of the switch.

[0080] If necessary, the voltage at the connection point A is brought to the desired value at the point B, which varies as a function of the dimensioning of the DC-DC converter DCDC, by means of a suitable circuit converter, for example of the step-up type.

[0081] When startup is completed, the switch R switches to position B corresponding to the second position of the switch R, in which the terminal of the DC-DC converter circuit FB is connected to a point of the secondary circuit of the DC-DC converter DCDC where voltage surge energy is recovered via the snubber capacitor Cs.

[0082] During the stop of the DC-DC converter DCDC, the switch R switches back to position A.

[0083] according to Figure 2 In the embodiment represented in , the energy recovery circuit further comprises a capacitor CF between a connection terminal of the converter circuit FB and electrical ground, the capacitor CF being configured to be charged and configured to deliver energy to the converter circuit FB during switching of the switch R from the first position A to the second position B.

[0084] refer to Figure 3 , in a more precise manner, the startup sequence of the DC-DC converter DCDC includes the following steps.

[0085] Upon receipt of the start command (step E0), the battery LB supplies the low-voltage network, the system basis chip (SBC), the microcontroller μC and the boost converter circuit PSU (step E1). Thus, an optional delay step of, for example, 100 milliseconds duration is provided, during which the charging of the components initiated at step E1 is carried out. According to the invention, it is then verified that the switch R is in position A and that it is switched to this position if necessary (step E2). The presence and value of the voltage at the output of the DC-DC converter circuit FB, which is configured to supply a control unit of the isolated DC-DC voltage converter DCDC according to an embodiment, is verified (step E3).

[0086] If the output of the DC-DC converter circuit FB is correct, the isolated DC-DC converter DCDC starts with its voltage conversion function (step E4). The voltage Vrcd is measured at the output of the isolated DC-DC converter DCDC at the connection point B. If the voltage meets the requirements for a predefined duration equal to, for example, 100 microseconds, and is therefore close to the voltage at point A, the switch is switched to position B (step E5).

[0087] The advantage that comes with the invention lies in the fact that the boost converter PSU is not continuously operated in order to allow the control unit of the isolated DC-DC converter DCDC to be powered. Once the startup of said isolated DC-DC converter DCDC is completed, the auxiliary power supply via the DC-DC converter circuit FB actually takes over said powering of the control unit, thereby recovering for this purpose the voltage surge energy present in the secondary circuit RD.

[0088] In an alternative embodiment, it is provided that a snubber resistor is connected in parallel with the snubber capacitor Cs if the energy consumed by the DC-DC converter circuit FB due to switching of the switches Q3, Q4 of the secondary circuit RD is less than the energy stored in the snubber capacitor.

[0089] In this case, the invention is still advantageous in terms of efficiency in terms of energy consumption, still an improvement, since part of the electrical energy caused by the voltage surge is reused, for example to power the control unit of the DC-DC converter DCDC. Furthermore, even if it is necessary to provide a buffer resistor to consume part of the voltage surge energy, this will have reduced dimensions compared to the prior art, thus making the system less expensive and less heated.

[0090] Still refer to Figure 3 , stopping the DC-DC converter DCDC first comprises a step E6 consisting of stopping the voltage conversion function of the isolated DC-DC converter DCDC. The voltage Vrcd is measured at the output at the connection point B of the isolated DC-DC converter DCDC. If the voltage there drops below a predefined low threshold, for example equal to 5 volts, the switch R switches back to point A, in other words in the first position (step E7). A delay of, for example, 100 milliseconds duration is then allowed to pass, during which the switch R switches to the first position, and then the power supply to the SBC, the microcontroller μC and the boost converter circuit PSU is stopped (step E8) to finally completely stop the isolated DC-DC converter DCDC (step E9).

[0091] The invention as previously described by means of the examples given in a graphical manner is specified to be adaptable within the scope of a person skilled in the art. For example, the circuit ensuring the auxiliary power supply function is not necessarily a DC-DC converter circuit for powering the control unit of the DC-DC converter DCDC. Instead, it can be any type of auxiliary power supply for which the energy supplied by the buffer capacitor Cs will be useful, such as a step-up DC-DC converter circuit or a resonant circuit.

Claims

1. An isolated DC-DC converter, include: a first interface terminal (X) configured to be connected to a first power grid, a second interface terminal (Y), configured to be connected to a second power grid, a first circuit connected to the first interface terminal (X), the first circuit comprising at least one induction coil (L1, L2), a second circuit, comprising at least one induction coil (L3, L4), the second circuit further comprising at least one switch arm (Q3, Q4) connected between a terminal of the induction coil (L3, L4) of the second circuit and electrical ground, the switch arm (Q3, Q4) having an on state and an off state, an energy recovery circuit connected at a connection point of the second circuit, the connection point being connected to the terminals of the induction coil (L3, L4) of the second circuit and to the at least one switching arm (Q3, Q4), the energy recovery circuit comprising a buffer capacitor capable of storing energy present in the second circuit between its upper terminal and its lower terminal connected to the electrical ground via the connection point when the switching arm (Q3, Q4) is switched to the off state, in such a way as to power the electronic components through the third interface terminal (Z) of the isolated DC-DC converter; wherein the energy recovery circuit further comprises a switch (R) located between the upper terminal of the buffer capacitor of the energy recovery circuit and the third interface terminal (Z), the switch (R) having a terminal connected to the third interface terminal (Z) and being switchable between a first position (A) in which the third interface terminal (Z) is configured to be connected to a terminal of a power supply circuit and a second position (B) in which the third interface terminal (Z) is connected to the upper terminal of the buffer capacitor of the energy recovery circuit, such that when the switch (R) is in the second position (B), the third interface terminal (Z) delivers energy stored in the buffer capacitor of the energy recovery circuit; When the voltage at the first position (A) is equal to the voltage at the second position (B) within a predefined duration, the switch (R) switches to position B.

2. The isolated DC-DC converter according to claim 1 comprises an isolated DC-DC converter circuit configured to recover the energy stored in the buffer capacitor, the DC-DC converter circuit being connected between the upper terminal of the buffer capacitor of the energy recovery circuit and the third interface terminal (Z).

3. The isolated DC-DC converter according to claim 2, wherein the DC-DC converter circuit ensures an auxiliary power supply function configured to power the electronic component via the third interface terminal (Z).

4. An isolated DC-DC converter according to claim 2 or 3, wherein the DC-DC converter circuit ensures an auxiliary power supply function configured to power a control unit of the isolated DC-DC converter via the third interface terminal (Z).

5. An isolated DC-DC converter according to claim 1, wherein the energy recovery circuit includes an additional capacitor located between the terminal of the switch (R) connected to the third interface terminal (Z) and the electrical ground, and the additional capacitor is configured to be charged and configured to deliver energy to the third interface terminal (Z) during switching of the switch (R) from the first position (A) to the second position (B).

6. An isolated DC-DC converter according to claim 1, wherein the energy recovery circuit comprises at least one diode (Ds1, Ds2) located upstream of the buffer capacitor, the cathode of the at least one diode (Ds1, Ds2) being connected to the upper terminal of the buffer capacitor.

7. The isolated DC-DC converter according to claim 1, in, The second circuit includes two induction coils (L3, L4) and two switch arms (Q3, Q4), wherein the switch arms (Q3, Q4) are configured to rectify currents respectively coming from each of the induction coils (L3, L4), and the energy recovery circuit includes a diode (Ds1, Ds2) per switch arm (Q3, Q4), wherein the diodes (Ds1, Ds2) are located upstream of the buffer capacitor, and the cathode of each diode (Ds1, Ds2) is connected to the upper terminal of the buffer capacitor.

8. The isolated DC-DC converter according to claim 1, wherein the energy recovery circuit further comprises a snubber resistor configured to dissipate unconsumed electrical energy via the third interface terminal (Z), the snubber resistor being connected in parallel with the snubber capacitor.

9. An electrical device comprising an isolated DC-DC converter according to claim 1 and a control unit of a component of the isolated DC-DC converter, the control unit being connected to the third interface terminal (Z) and being supplied with electrical energy at least partially via the energy recovery circuit.

10. A method for starting a DC-DC converter and an electrical device, the DC-DC converter comprising The isolated DC-DC converter according to claim 1, wherein the electrical device is the electrical device according to claim 9, and the method for starting the DC-DC converter and the electrical device The following steps are involved: verifying that the switch (R) is in the first position (A) and that the switch (R) switches to this position during a stop of the DC-DC converter or when the voltage at the second position (B) drops below a predefined low threshold (step E2), Verify the presence and value of the voltage at the third interface terminal (Z), which is configured to supply power to the control unit of the DC-DC converter (step E3). Start the DC-DC converter with the function of converting the DC voltage of the DC-DC converter (step E4), where the third interface terminal (Z) is connected to the power supply circuit, and the power supply circuit is connected to the switch (R) when the switch (R) is in the first position (A). Measure the voltage at the connection point corresponding to the second position (B) of the switch (R). If the voltage meets the requirements within a predetermined duration, then the switch is switched to the second position (step E5) so that the third electrical terminal delivers the energy stored in the buffer capacitor.

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