DC / DC converter with safety device

Description

[0001] The present invention relates to the field of electrical converters, in particular DC / DC voltage converters used in the automotive field.

[0002] DC / DC voltage converters used in the automotive industry can, for example, if one of their power components fails and is mounted on a circuit board, create short circuits that generate very high currents, such as several hundred amperes. These short circuits can irreversibly damage not only the voltage converter itself but also the equipment to which it is connected.

[0003] It is therefore necessary to detect such high-amplitude currents and, if necessary, to put the voltage converter into safe mode. For this purpose, a DC / DC voltage converter such as the one shown in Figure 1 Such a 100V voltage converter includes:a. A main input terminal HV intended to be connected to a first DC voltage source 6, for example to a 48V battery; b. A main output terminal LV intended to be connected to a second DC voltage source 7, for example to a 12V battery, said second voltage source delivering a voltage lower than that delivered by said first source; c. A voltage conversion cell 5 or a plurality of conversion cells arranged in parallel, each cell comprising: i. a buck converter 9 comprising an input terminal BE and an output terminal BS, said input terminal of said buck converter being connected to said main input terminal; ii.a safety device 2 comprising an input terminal D and an output terminal S, said safety device comprising a first T1 and a second transistor T2, each of said transistors comprising a current input terminal, a current output terminal and a control terminal, the input terminals or the output terminals of the first and second transistors being respectively connected to the input and output terminals of said safety device, the input terminal of the safety device being connected to the output terminal of the buck converter, the output terminal of the safety device being connected to the main output terminal, said safety device further comprising a control input G intended to receive an inhibit command and being designed on receipt of said inhibit command to open at least one of the first and second transistors d.a supervisory device 80 designed to send an inhibition signal to said safety device when the current arriving at the main output terminal of the voltage converter exceeds a threshold.

[0004] The DC / DC converter 100 monitoring device is generally designed to measure the current delivered by the first power supply 7 through a measuring resistance Rs (in English "shunt resistor"), placed between the safety device and the second DC voltage source and to send an inhibition signal to said safety device in case of a short circuit when the voltage across the measuring resistance is greater than a threshold.

[0005] Thus, in prior art voltage converters: a. A measuring resistor is used to detect the presence of a high current within the voltage converter, particularly at its output terminal when the main input and output terminals are respectively connected to the first and second voltage sources, and when a high current is detected, a safety device is activated to isolate the main output terminal from the other components of the voltage converter.

[0006] However, using a measuring resistor presents the problem of power consumption due to Joule heating when the DC / DC converter is operating normally. Furthermore, its placement within the converter requires significant space on the circuit board.

[0007] US7405495B2 and EP3048712A2 disclose a DC / DC converter, each including a chopper and a protection transistor in series in the power path.

[0008] The invention aims to alleviate, at least in part, the aforementioned problems.

[0009] To this end, a DC / DC voltage converter of the aforementioned type is proposed, characterized in that the monitoring device is designed to, when for a given conversion cell the first and second transistors are in their conducting state and the voltage difference between the main output terminal and the input terminal of the safety device is less than a detection threshold, generate the inhibition command to the safety device of the given conversion cell.

[0010] Thus the use of a measuring resistor is no longer necessary, which eliminates Joule losses related to the measuring resistor and reduces the size of the voltage converter.

[0011] In a particular embodiment of the invention, the safety device is further designed to, upon receiving said inhibition command, open the first and second transistors. Thus, when the first and second transistors are open, the first and second voltage sources are isolated from each other.

[0012] In a particular embodiment of the invention, at least one conversion cell of the DC voltage converter comprises a plurality of step-down choppers in parallel.

[0013] In a particular embodiment of the invention, the monitoring device is active only when the first and second transistors of each cell are in their conducting state.

[0014] In a particular embodiment of the invention, the supervisory device is further designed to generate the inhibition command for the safety devices of each conversion cell.

[0015] In a particular embodiment of the invention, the monitoring device comprises: a. An input stage comprising: i. a first and a second voltage divider bridge, ii. a current source or a voltage source, iii. as many diodes as there are conversion cells, the anodes of the input stage diodes being connected together and connected to the current source or the voltage source, each conversion cell being connected via the input terminal of its safety device to the cathode of only one of said diodes, iv. a voltage-shifting diode whose cathode is connected to the main output terminal and whose anode is connected to said voltage or current source, a voltage comparator whose non-inverting terminal is connected via the first voltage divider bridge to the anodes of the input stage diodes and whose inverting terminal is connected via the second voltage divider bridge to the anode of the voltage-shifting diode

[0016] Optionally, the voltage converter also includes a third resistor connected between the output and the non-inverting input of said voltage comparator.

[0017] Optionally, the output of the voltage comparator is also connected to the cathode of a trigger diode, and the anode of the trigger diode is connected to the control inputs of the safety devices of the conversion cells, each of said control inputs of the safety devices being connected directly or through a resistor to the control terminal of the first transistor and / or the second transistor.

[0018] It is also possible to consider, in other embodiments, that the voltage converter has in combination all or part of the aforementioned characteristics. There [ Figure 1 ] represents a DC / DC voltage converter according to the prior art. The [ Figure 2 ] represents a DC / DC voltage converter implementing the invention in a first embodiment of the invention. The [ Figure 3 ] represents a monitoring device for a DC / DC voltage converter implementing the invention in a first embodiment of the invention. The [ Figure 4 ] represents a DC / DC voltage converter implementing the invention according to a second embodiment of the invention. The [ Figure 5 ] represents a monitoring device for a DC / DC voltage converter implementing the invention in a second embodiment of the invention.

[0019] With reference to the [ Figure 2 [ ], a DC / DC voltage converter 1 implementing the invention will now be described. The DC / DC voltage converter 1 is used, for example, in a motor vehicle. For the sake of simplicity, identical references are given in this figure to the common elements of the voltage converter according to the prior art shown in the [ Figure 1 ].

[0020] The DC / DC voltage converter 1 includes: a. a main input terminal HV connected to a first DC voltage source 6, for example a 48V battery, b. a main output terminal LV connected to a second DC voltage source 7, for example a 12V battery, delivering a voltage lower than that of the first voltage source 6 c. a conversion cell 5 comprising: i. an input terminal BE connected to the main input terminal HV, ii. an output terminal BS, iii. a buck converter 9 comprising an inductor L, a transistor T3 whose drain is connected to the input terminal BE and its source to one end of the inductor, and a transistor T4 whose drain is connected between ground and the first end of the inductor L. The combination of the inductor L and the two transistors T3 and T4 constitutes a buck converter of the type "Buck" whose operation is well known to those skilled in the art, iv.a safety device 2 comprising an input terminal D1 connected to the second end of the inductance, an output terminal S1 connected to the main output terminal LV and a control terminal G1. v. a supervisory device 8, and vi. a control device (not shown on the [. Figure 2 ]).

[0021] The safety device 2 comprises a first transistor T1 and a second transistor T2 connected in reverse parallel. In the example described here, the first transistor T1 and the second transistor T2 are N-doped MOSFETs. The drain of the first transistor T1 is connected to the input terminal D1 of the safety device 2, and the drain of the second transistor T2 is connected to the output terminal S1 of the safety device 2. The first transistor T1 and the second transistor T2 are connected via their respective sources such that the intrinsic diodes of these transistors are connected via their anodes. In other words, the cathode of the intrinsic diode of the second transistor T2 is connected to the main output terminal of the voltage converter 1, and the cathode of the first transistor T1 is connected to the input terminal of the safety device 2.In this way, when the first transistor T1 and the first transistor T2 are open, no current can flow between the input terminal D1 and the output terminal S1 of the safety device 2. The control terminals of the first T1 and second transistor T2 are also connected to the control terminal G1 of the safety device 2. Thus, receiving an inhibit command on the control terminal G1 of the safety device 2 triggers the opening of transistors T1 and T2, and therefore interrupts all current flow in both directions between the input terminal D1 and the output terminal S1 of the safety device 2.

[0022] The control device allows transistors T3 and T4 to be switched on or off in order to operate the buck converter in switching mode. In addition, the control device also allows transistors T1 and T2 of the safety device 2 to be switched on or off. To do this, the control device supplies the voltage required to activate transistors T1, T2, T3, and T4 at their respective control terminals.

[0023] The supervisory device 8 is further designed to generate the inhibition command for the safety device 2 of the conversion cell 5 when the first T1 and the second transistor T2 are in their conducting state and when the voltage difference between the input terminal D1 of the safety device 2 and the main output terminal LV is less than a detection threshold VThreshold.

[0024] Furthermore, the threshold voltage Vseuil is equal to the voltage difference Vb-Va which is equal to the sum of the drain-source resistances of transistors T1 and T2 in their on-state multiplied by the current through these transistors as defined in equation [Math.1]. Vseuil = Rds T 1 + Rds T 2 . I

[0025] In the example described here, the threshold voltage Vs is equal to -0.3V.

[0026] The monitoring device 8 is shown on the [ Figure 3 and includes: a. A measuring circuit 3 comprising: i. A voltage comparator 12 including an inverting terminal, a non-inverting terminal, and an output terminal whose output potential VS is positive when the voltage at the positive inverting terminal is greater than the voltage at the non-inverting terminal of the voltage comparator 12, and whose output potential VS is negative otherwise; ii. An input stage comprising a current source SC1 supplied by a voltage Vin. The current source SC1 is connected in series with an on / off switch Ta. The current source SC1 supplies a first and a second electrical branch. The on / off switch Ta has a control terminal connected, for example, to a microcontroller. Thus, via this on / off switch Ta, it is possible to activate (switch Ta closed) or deactivate (switch Ta open) the monitoring device 8 from the microcontroller.Thus, the monitoring device can be activated only when a current actually flows through the safety device 2. In the following description, we will assume that the monitoring device 8 is activated. The first electrical branch has a diode D3 whose cathode is connected to the main output terminal LV, and the second electrical branch has a diode D2 with the same threshold voltage as diode D3 and whose cathode is connected to the input terminal D1 of the safety device 2. iii. A first voltage divider bridge consisting of a resistor R3 and a resistor R1, connected to the non-inverting terminal of the voltage comparator 12. Resistor R3 is connected between the non-inverting terminal and the anode of diode D2, and resistor R1 is connected between the non-inverting terminal and ground. iv.A second voltage divider bridge with resistors R5 and R6 connected to the inverting terminal of the voltage comparator 12. Resistor R5 is connected between the inverting terminal of the voltage comparator 12 and the anode of diode D3, and resistor R6 is connected between the inverting terminal and ground. The value of resistor R5 (respectively, resistor R6) is equal to the value of resistor R3 (respectively, resistor R1). b. A control circuit 4 comprising: i. a diode D5 whose anode is connected to the control terminal G1 of the safety device, and whose cathode is connected to the output Vs of the voltage comparator 12.

[0027] The combination of resistors R1, R3, R4, R5, and R6 and the voltage comparator 12 compares the voltages present at the anodes of diodes D3 and D2. The voltage V2 present at the anode of diode D3 is equal to the voltage present at the main output terminal, offset by the threshold voltage of diode D3. The voltage V1 present at the anode of diode D2 is equal to the voltage present at the input terminal of the safety device 2, offset by the threshold voltage of diode D2. In other words, up to the threshold voltages of diodes D3 and D2, the voltage comparator 12 compares the voltage present at the input terminal of the safety device 2 to the voltage present at the main output terminal.

[0028] With reference to the [ Figure 3 and in accordance with equations [Math. 2] and [Math. 3], the voltages of the non-inverting terminal V+ and of the inverting terminal V- are expressed as a function of the voltages V1, V2 and the output voltage Vs of the voltage comparator 12. V + = R 3 . R 4 R 3 + R 4 R 1 + R 4 . R 3 R 4 + R 3 . V 1 + R 1 . R 3 R 1 + R 3 R 4 + R 1 . R 3 R 1 + R 3 . Vs

[0029] Assuming that resistance R3 is equal to resistance R5, and that resistance R1 is equal to resistance R6. V − = R 5 R 5 + R 6 . V 2 = R 3 R 1 + R 3 . V 2

[0030] According to equation [Math. 2], when resistance R4 is chosen to be much greater than resistance R3, for example ten times greater, equation [Math. 2] is equivalent to equation [Math. 4]. V + = R 3 R 1 + R 3 . V 1 + R 1 . R 3 R 1 + R 3 R 4 + R 1 . R 3 R 1 + R 3 . Vs

[0031] The output voltage of voltage comparator 12 switches from +Vsat to -Vsat when the voltage V+ becomes less than the voltage V-. In other words, the switchover occurs when the condition in equation [Math. 5] is met. V + − V − = V 1 − V 2 R 3 R 1 + R 3 + R 1 . R 3 R 1 + R 3 R 4 + R 1 . R 3 R 1 + R 3 . Vs < 0

[0032] According to equation [Math. 5], when the voltage V1-V2 becomes less than a switching threshold SB (given by equation [Math. 6]), the output voltage VS of the voltage comparator changes from its positive saturation value +Vsat to its negative saturation value -Vsat. V 1 − V 2 < − R 1 R 4 + R 1 . R 3 R 1 + R 3 . Vs = SB

[0033] By choosing appropriately the values ​​of the resistances R1, R3, R4, R5 (equal to R3) and R6 (equal to R1) according to the saturation voltage Vsat we obtain a switching threshold SB equal to the voltage Vseuil.

[0034] Thus, when the voltage V1-V2 is less than the voltage Vseuil, the output voltage of the voltage comparator 12 goes to its negative saturation value - Vsat.

[0035] Thus, during a malfunction of the DC / DC converter 1 for example when the transistor T4 is short-circuited, the current through the two transistors T1 and T2 increases until a potential drop appears at the input terminal of the safety device, said potential drop being detected by the flip-flop of the voltage comparator 12.

[0036] When the voltage Vs is equal to the negative saturation value -Vsat, the potential -Vsat is applied to the control terminal G1.

[0037] When the voltage Vs is equal to the negative voltage -Vsat the diode D5 allows to cancel / short circuit the voltage supplied by the control device on the control terminal of switches T1 and T2 the opening of these.

[0038] In other words, when the output voltage Vs is equal to the negative saturation value -Vsat, the safety device 2 receives an inhibition command on its control terminal G1.

[0039] In a variant of the first embodiment, the DC / DC converter 1 has a plurality of buck converters 9, each of which has an input terminal BE and an output terminal BS. The plurality of buck converters are connected in parallel, with the BE terminals connected together and the BS terminals connected together. The plurality of buck converters are connected in parallel so as to convert a larger current.

[0040] With reference to figures 4 And 5 , a second embodiment of the invention will now be described. The elements identical to the first embodiment of the [ Figure 2 ] and the [ Figure 3 ] retain the same references and will not be described again.

[0041] In this second embodiment, the DC / DC voltage converter 1' shown in the [ Figure 4 ] includes a second conversion cell 5' connected in parallel with the first conversion cell 5.

[0042] The 5' conversion cell includes: a. an input terminal BE' connected to the main input terminal HV, b. a buck converter 9' comprising an inductor L', a transistor T3' whose drain is connected to the input terminal BE' and its source to one end of the inductor, and a transistor T4' whose drain is connected between ground and the first end of the inductor L'. The combination of the inductor L' and the two transistors T3' and T4' constitutes a buck converter of the type "Buck" whose operation is well known to those skilled in the art, c. a safety device 2' comprising an input terminal D1' connected to the second end of the inductor, an output terminal S1' connected to the main output terminal LV and a control terminal G1'.

[0043] The DC / DC voltage converter 1' also includes a supervisory device 8' and a driver device (not shown) for the transistors of the DC / DC voltage converter 1'.

[0044] The safety device 2' comprises a first transistor T1' and a second transistor T2' connected in reverse parallel. In the example described here, the first transistor T1' and the second transistor T2' are N-doped MOSFETs. The drain of the first transistor T1' is connected to the input terminal of the safety device 2', and the drain of the second transistor T2' is connected to the output terminal of the safety device 2'. The first transistor T1' and the second transistor T2' are connected via their respective source terminals such that the intrinsic diodes of these transistors are connected via their anodes. In other words, the cathode of the intrinsic diode of the second transistor T2' is connected to the main output terminal of the voltage converter 1', and the cathode of the first transistor T1' is connected to the input terminal of the safety device 2'.In this way, when the first transistor T1' and the first transistor T2' are open, no current can flow between the input terminal D1' and the output terminal S1' of the safety device 2'. The control terminals of the first T1' and second transistor T2' are also connected to the control terminal G1' of the safety device 2'. Thus, receiving an inhibit command at the control terminal G1' of the safety device 2 triggers the opening of transistors T1' and T2'.

[0045] The 8' monitoring device is shown in the [ Figure 5 ] and includes a measurement circuit 3' and a control circuit 4'. It is further designed to generate an inhibition command to the safety device 2' and to the safety device 2 when the first T1, T1' and second T2, T2' transistors are in their conducting state and when one of the voltage difference between the input terminal D1' of the safety device 2' and the main output terminal LV and the voltage difference between the input terminal D1 of the safety device 2 and the main output terminal LV is less than the detection threshold Vthreshold.

[0046] In this second embodiment, the 8' monitoring device differs from the 8 monitoring device in that: a. The measuring circuit 3' further includes a third electrical branch comprising a diode D4 whose cathode is connected to the input terminal D1' of the safety device 2' and whose anode is connected to the anode of diode D2. In other words, diodes D2 and D4 form a diode AND gate. Furthermore, the threshold voltages of diodes D2 and D4 are identical. b. The control circuit 4' further includes a diode D6 whose anode is connected to the control terminal of the safety device 2', and whose cathode is connected to the output terminal Vs of the voltage comparator 12.

[0047] The voltage V1 at the anode of diodes D2 and D4 is equal to the lower of the voltages present at input terminals D1 and D1', shifted by the threshold voltage of diodes D2 and D4. The voltage V2 at the anode of diode D3 is equal to the voltage present at the main output terminal, shifted by the threshold voltage of diode D3. In other words, up to the threshold voltages of diodes D3, D4, and D2, the voltage comparator 12 compares the lower of the voltages present at input terminal D1 and input terminal D1' to the voltage present at the main output terminal.

[0048] Thus, according to equations [Math. 6], when the voltage V1-V2 becomes less than the switching threshold SB, the output voltage VS of the voltage comparator changes from its positive saturation value +Vsat to its negative saturation value -Vsat.

[0049] When the voltage Vs equals the negative voltage -Vsat, diode D5 allows the voltage supplied by the control device to be short-circuited across the control terminals of switches T1 and T2, preventing them from opening. Similarly, when the voltage Vs equals the negative voltage -Vsat, diode D6 allows the voltage supplied by the control device to be short-circuited across the control terminals of switches T1' and T2', preventing them from opening.

[0050] In other words, when the voltage V1-V2 becomes less than the switching threshold SB, the output voltage Vs is equal to -Vsat which causes the opening of transistors T1, T1', T2 and T2'.

[0051] Ainsi,In the event of a malfunction of the DC / DC converter 1', for example when the transistor T4' is short-circuited, the current through the two transistors T1' and T2' increases until a potential drop appears at the input terminal of the safety device 2', said potential drop being detected by the flip-flop of the voltage comparator 12, this flip-flop causing the opening of the transistors T1, T1', T2 and T2' of the safety devices 2 and 2' and the safety shutdown of the DC / DC voltage converter 1'.

[0052] In addition, and optionally, the control device can scan the voltage at the output terminal of comparator 12 and when this voltage is equal to -Vsat, the control device opens switches T3, T3', T4 and T4' thus placing the DC / DC voltage converter 1' in a completely safe state.

Claims

1. A DC / DC converter comprising: a. a main input terminal (HV) designed to be connected to a first DC voltage source (6) b. a main output terminal (LV) intended to be connected to a second DC voltage source (7), said second voltage source (7) supplying a voltage lower than that supplied by said first source (6), c. a conversion cell (5) or a plurality of conversion cells (5, 5') arranged in parallel, each cell (5) comprising: i. a step-down chopper (9) comprising an input terminal (BE) and an output terminal (BS), said input terminal of said step-down chopper (9) being connected to said main input terminal, ii. a safety device (2) comprising an input terminal (D1) and an output terminal (S1), said safety device (2) comprising a first (T1) and a second (T2) transistor, each of said transistors (T1, T2) comprising a current input terminal, a current output terminal and a control terminal (G), the input terminals and output terminals of the first (T1) and second (T2) transistors being connected respectively to the input (D1) and output (S1) terminals of said safety device (2), the input terminal (D1) of the safety device (2) being connected to the output terminal (BS) of the step-down chopper (9), the output terminal (S1) of the safety device (2) being connected to the main output terminal (LV), said safety device (2) further comprising a control input (G1) for receiving an inhibit command and being configured, upon receipt of said inhibit command, to turn off at least one of the first (T1) and second (T1) transistors; said DC / DC converter being characterised in that it further comprises a monitoring device (8) designed so that, when, for a given conversion cell (5), the first (T1) and second (T2) transistors are in their on-state and the voltage difference between the main output terminal (LV) and the input terminal (D1) of the safety device (2) is less than a detection threshold, to generate the inhibit command intended for the control device (2) of the specific conversion cell (5).

2. A DC / DC converter according to claim 1, in which at least one conversion cell (5) comprises a plurality of step-down choppers in parallel.

3. A DC / DC converter according to one of the preceding claims, in which the monitoring device (8) is active only when the first (T1) and second (T2) transistors of each cell are in their on-state.

4. A DC / DC converter according to one of the preceding claims, in which the monitoring device (8) is further designed to generate the inhibit signal intended for the safety devices (2, 2') of each conversion cell (5, 5').

5. A DC / DC converter according to one of the preceding claims, in which the monitoring device (8) comprises: a. an input stage comprising: i. a first and a second voltage divider bridge, ii. a current source or a voltage source, iii. as many diodes (D2, D4) as there are conversion cells (5, 5'), the anodes of the diodes in the input stage being connected to one another and to the current source or voltage source, each of the conversion cells (5, 5') being connected via the input terminal (D1, D1') of its safety device (2, 2') to the cathode of only one of the said diodes (D2, D4), iv. a voltage-shifting diode (D3) whose cathode is connected to the main output terminal (LV) and whose anode is connected to the said voltage or current source, b. a voltage comparator (12) whose non-inverting input is connected via the first voltage divider bridge to the anodes of the diodes (D2, D4) of the input stage and whose inverting input is connected via the second voltage divider bridge to the anode of the voltage-shifting diode (D3).

6. A DC / DC converter according to the preceding claim, further comprising a third resistor (R4) connected between the output and the non-inverting input of said voltage comparator.

7. A DC / DC converter according to claim 5 or 6, in which said output of the voltage comparator is further connected to the cathode of a trigger diode (D5, D6), and the anode of the trigger diode is connected to the control inputs (G1, G1') of the safety devices (2, 2') of the conversion cells (5, 5'), each of said control inputs (G1, G1') of the safety devices (2, 2') being connected directly or via a resistor to the control terminal (G) of the first transistor (T1) and / or the second transistor (T2).