Abstract
A device may be for protection against overvoltages in a power supply line. The device may include a breakover diode, an avalanche diode coupled in series with the breakover diode, and a switch coupled in parallel with the breakover diode and the avalanche diode. The device may also include a circuit coupled across the avalanche diode and configured to control the switch.
Claims
1. A device for protection against overvoltages in a power supply line, the device comprising: a branch comprising a breakover diode, and an avalanche diode coupled in series with the breakover diode; a switch coupled in parallel with the branch; and a circuit coupled across the avalanche diode and configured to control the switch.
2. The device of claim 1 wherein the avalanche diode has a breakdown voltage at least ten times smaller than a breakdown voltage of the breakover diode.
3. The device of claim 2 wherein the breakdown voltage of the breakover diode is between 20 V and 1,500 V.
4. The device of claim 1 wherein the switch comprises at least one of a transistor and an insulated-gate bipolar transistor.
5. The device of claim 1 wherein the circuit comprises a first resistor coupled in parallel with the avalanche diode; and wherein a first end of the first resistor is coupled to a midpoint of the branch and a control node of the switch.
6. The device of claim 5 wherein the circuit comprises a second resistor coupled between the first end of the first resistor and the control node of the switch.
7. The device of claim 5 wherein the circuit comprises a capacitor coupled between the control node of the switch and a second end of the first resistor.
8. The device of claim 6 wherein the circuit comprises a diode coupled in parallel with the second resistor.
9. A device for protection against overvoltages in a power supply line, the device comprising: a breakover diode; an avalanche diode coupled in series with the breakover diode; a switch coupled in parallel with the breakover diode and the avalanche diode; and a circuit coupled across the avalanche diode and configured to control the switch.
10. The device of claim 9 wherein the avalanche diode has a breakdown voltage at least ten times smaller than a breakdown voltage of the breakover diode.
11. The device of claim 9 wherein the switch comprises at least one of a transistor and an insulated-gate bipolar transistor.
12. The device of claim 9 wherein the circuit comprises a first resistor coupled in parallel with the avalanche diode; and wherein a first end of the first resistor is coupled to a node between the breakover diode and the avalanche diode, and a control node of the switch.
13. The device of claim 12 wherein the circuit comprises a second resistor coupled between the first end of the first resistor and the control node of the switch.
14. The device of claim 12 wherein the circuit comprises a capacitor coupled between the control node of the switch and a second end of the first resistor.
15. A method for making a device for protection against overvoltages in a power supply line, the method comprising: coupling an avalanche diode in series with a breakover diode; coupling a switch in parallel with the breakover diode and the avalanche diode; and coupling a circuit across the avalanche diode and for controlling the switch.
16. The method of claim 15 wherein the avalanche diode has a breakdown voltage at least ten times smaller than a breakdown voltage of the breakover diode.
17. The method of claim 15 wherein the switch comprises at least one of a transistor and an insulated-gate bipolar transistor.
18. The method of claim 15 wherein the circuit comprises a first resistor coupled in parallel with the avalanche diode; and wherein a first end of the first resistor is coupled to a node between the breakover diode and the avalanche diode, and a control node of the switch.
19. The method of claim 18 wherein the circuit comprises a second resistor coupled between the first end of the first resistor and the control node of the switch.
20. The method of claim 18 wherein the circuit comprises a capacitor coupled between the control node of the switch and a second end of the first resistor.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 shows the current-voltage characteristic of a protection device of the avalanche diode type, according to the prior art.
(2) FIG. 2 shows the current-voltage characteristic of a protection device of the breakover type, according to the prior art.
(3) FIG. 3 shows a protection diode of the breakover type connected to a DC power supply line, according to the prior art.
(4) FIG. 4A shows an equivalent diagram of the assembly of FIG. 3 in a short-circuit state, according to the prior art.
(5) FIG. 4B shows the characteristic of a breakover device in the case of FIG. 4A.
(6) FIG. 5 shows an example of an overvoltage protection device, according to the prior art.
(7) FIG. 6 shows a variation of the protection device of FIG. 5.
(8) FIG. 7 shows an embodiment of an overvoltage protection device, according to the present disclosure.
(9) FIG. 8 shows an example of the device of FIG. 7, according to the present disclosure.
(10) FIG. 9 shows another embodiment of the device of FIG. 7, according to the present disclosure.
(11) FIG. 10 shows another embodiment of the device of FIG. 7, according to the present disclosure.
DETAILED DESCRIPTION
(12) The same elements have been designated with the same reference numerals in the different drawings. Further, in the present description, term connected is used to designate a direct electric connection, with no intermediate electronic component, for example, by way of one or a plurality of conductive tracks, and term coupled or term linked is used to designate either a direct electric connection (then meaning connected) or a connection via one or a plurality of intermediate components (resistor, capacitor, etc.). The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings
(13) Generally speaking, an embodiment provides a method of protection against overvoltages capable of protecting a power supply line, comprising a first branch comprising a breakover diode in series with an avalanche diode, a switch controlled in parallel with the first branch, and a circuit for controlling the switch connected across the avalanche diode. The breakdown voltage of the avalanche diode is at least ten times smaller than the breakdown voltage of the breakover diode.
(14) Also, the breakdown voltage of the breakover diode may be in the range from 20 to 1,500 V. The switch may be a MOS transistor or an insulated-gate bipolar transistor. The control circuit may comprise a first resistor connected in parallel with the avalanche diode, the end of the first resistor connected to the midpoint of the first branch being further connected to a control node of the switch.
(15) Moreover, the end of the first resistor may be connected to the midpoint of the first branch is connected to the control node of the switch. The end of the first resistor connected to the midpoint of the first branch may be connected to the control node of the switch via a second resistor. Additionally, the control node of the switch may be connected to the other end of the first resistor via a capacitor. A diode may be connected in parallel with the second resistor.
(16) In the devices of FIGS. 5 and 6, the control circuit CONTROL of switch SW is connected, on the one hand, to terminals A and B of the branch comprising breakover diode D and, on the other hand, to a control node or terminal of switch SW. The control circuit controls switch SW according to the voltage between nodes A and B. The control circuit may comprise a processor or another logic circuit or programmer. Thus, the control circuit should comprise a high-voltage interface to withstand the line power supply voltage. Further, the control circuit should comprise a power storage capacitor to supply the logic circuits with a DC power supply voltage having a level lower than the line power supply voltage. In certain applications, for example, in a solar power plant, the line power supply voltage may be particularly high, typically in the order of several hundred volts. As a result, the circuit CONTROL for controlling switch SW is relatively expensive and bulky.
(17) FIG. 7 shows an embodiment of an overvoltage protection device. The device comprises, as in the example of FIG. 6, between two terminals A and B, the parallel assembly of a first branch comprising a breakover type protection diode D in series with an avalanche diode d, and a switch SW. Avalanche diode d has a breakdown voltage Vbr smaller than breakdown voltage VBR of breakover diode D. Preferably, the breakdown voltage Vbr of avalanche diode d is much lower, for example, at least ten times lower, than breakdown voltage VBR of the breakover diode. In the shown example, the breakover diode D has its anode connected to terminal A and its cathode connected to a node or a terminal C of the first branch. Avalanche diode d has its cathode connected to node C and its anode connected to terminal B. As an example, the breakover diode D has a breakdown voltage in the range from 20 to 1,500 V.
(18) The switch SW, for example is, a metal-oxide semiconductor (MOS) transistor or an Insulated Gate Bipolar Transistor (IGBT). As an example, the switch SW is a PNP-type IGBT having its collector connected to terminal A and having its emitter connected to terminal B.
(19) The protection device of FIG. 7 differs from the device of FIG. 6 in that the control circuit CONTROL of the device of FIG. 6, connected between terminals A and B in the example of FIG. 6, is replaced with a circuit 70 connected on the one hand across avalanche diode d (that is, to nodes C and B in this example), and on the other hand to a terminal or to a control node of switch SW. Thus, in the embodiment of FIG. 7, the control circuit 70 of switch SW is not connected to terminals A and B of connection of the protection device to the power supply line.
(20) The operation of the protection device of FIG. 7 is similar to that of the device of FIG. 6, with the difference that instead of controlling switch SW according to the voltage between terminals A and B, control circuit 70 controls switch SW according to the voltage across avalanche diode d. An advantage of the embodiment of FIG. 7 is that the control circuit can be considerably simplified as compared with the control circuit of the devices of FIGS. 5 and 6.
(21) FIG. 8 shows an embodiment of control circuit 70 of the protection device of FIG. 7. In the example of FIG. 8, the circuit 70 is reduced to a resistor R1 connected between nodes C and B, in parallel with avalanche diode d. The end of resistor R1 connected to node C in the first branch and to the control gate of switch SW. Thus, in this example, the voltage across avalanche diode d is directly used to control switch SW. Resistance R1 is preferably much greater than the on-state resistance of avalanche diode d. As an example, the value of resistance R1 is in the range from 1 to 100 k.
(22) Protection device of FIG. 8 operates as follows. As long as the voltage between terminals A and B remains smaller than the breakdown voltage of breakover diode D, the protection device is non-conductive. Resistor R1 enables to take the potential of node C substantially to the potential of node B (for example, grounded), so that switch SW is off. When an overvoltage appears, breakover diode D and avalanche diode d become conductive and the power supply connected between terminals A and B is shorted. The voltage across avalanche diode d then switches from a zero value to a value substantially equal to Vbr, which turns on switch SW. Thus, switch SW turns on at the same time or almost at the same time as diodes D and d. The current associated with the overvoltage is shared between switch SW and the branch comprising diodes D and d. Switch SW absorbs what current it can absorb until it saturates, the rest (in practice, most of the current) being absorbed by diodes D and d. Once the overvoltage is over, the current flowing through the protection device decreases and becomes equal to short-circuit current ISC of the power supply. Switch SW is sized to be able to absorb all or the most part of this current, so that breakover diode D blocks. The potential of node C is then substantially taken to the potential of node B via resistor R1, and switches SW turns off. In practice, the switch SW may slightly turn off after breakover diode D due to the stray capacitance between its control gate and terminal B, which forms a circuit RC parallel to resistor R1.
(23) FIG. 9 shows another embodiment of control circuit 70 of the protection device of FIG. 7. In the example of FIG. 9, the circuit 70 comprises the same resistor R1 as in the example of FIG. 8, and further comprises a circuit RC comprising a resistor R2 connecting the end of resistor R1 connected to node C to the control gate of switch SW, and a capacitor C1 connecting the control gate of switch SW to terminal B.
(24) The operation of the device of FIG. 9 is similar to that of the device of FIG. 8, but differs from the operation described in relation with FIG. 8 in that, when an overvoltage appears, the switch is turned on with a delay relative to the turning-on of diodes D and d, such a delay being set by the RC circuit formed by resistor R2 and capacitor C1. Thus, at least part of the overvoltage may be removed by diodes D and d before switch SW is turned on. Once the overvoltage has passed and diode D is blocked, the switch SW turns off with a delay set by circuit RC.
(25) Thus, the circuit of FIG. 9 enables to set a desired delay between the triggering of diodes D and d and the turning-on of switch SW, and between the blocking of diodes D and d and the turning-off of switch SW. As an example, the values of capacitance C1 and of resistance R2 are selected to obtain a time constant, and thus a delay between the triggering of the protection and the turning-on of switch SW, in the range from 5 to 100 s, for example, approximately 20 ms. The capacitance of capacitor C1 is for example in the range from 20 nF to 2 F, and resistance R2 for example has a value in the range from 10 to 1 k.
(26) As a variation, the capacitor C1 may be omitted. The delay between the triggering of the protection and the turning-on of switch SW is then set by circuit RC formed by resistor R2 and the intrinsic capacitance of switch SW between its control node and terminal B (for example, the gate-source capacitance in the case of a MOS transistor, or the gate-emitter capacitance in the case of an IGBT).
(27) FIG. 10 shows another embodiment of control circuit 70 of the protection device of FIG. 7. In the example of FIG. 10, the circuit 70 comprises the same elements as in the example of FIG. 9, and further comprises, in parallel with resistor R2, a diode D1 having its anode connected to node C and having its cathode connected to the control gate of switch SW.
(28) The operation of the device of FIG. 10 is similar to that of the device of FIG. 9, but for the fact that, due to the presence of diode D1, the switch turns on substantially at the same time as diodes D and d when an overvoltage occurs. Thus, circuit RC delays the turning back off of switch SW at the end of an overvoltage, but does not delay its turning on at the beginning of an overvoltage.
(29) Protection devices of the type described in relation with FIGS. 7 to 10 have the similar advantages to those of the devices of FIGS. 5 and 6. In particular, they enable to use a breakover diode having a relatively small surface area, for example, 50 mm.sup.2, while, as indicated previously, for protection voltages greater than from approximately 50 to 1,000 volts, protection avalanche diodes should have surface areas approximately ranging from 1 to 10 cm.sup.2. The assembly of switching device SW, for example, a MOS or IGBT transistor, and of the control circuit will, for example, have a surface area in the range from 10 to 15 mm.sup.2 only. Thus, the total surface area of the protection device is smaller than 65 mm.sup.2, while fulfilling the function of an avalanche protection component having a surface area in the range from 1 to 10 cm.sup.2.
(30) An additional advantage of the embodiments described in relation with FIGS. 7 to 10 is that due to the connection of control circuit 70 across avalanche diode d, the architecture of the control circuit may be considerably simplified with respect to the examples of FIGS. 5 and 6. In particular, a control circuit with no logic circuits, no programmer or processor, and with no supply power storage capacitor may be formed. Further, the described embodiments do not require accurately measuring the voltage or the current in the branch comprising diodes D and d.
(31) Specific embodiments have been described. Various alterations, modifications, and improvements will readily occur to those skilled in the art. In particular, the described embodiments are not limited to the embodiments of control circuit 70 described in relation with FIGS. 8, 9, and 10. It will be within the abilities of those skilled in the art to adapt the described examples according to the targeted application, particularly to make tradeoffs in terms of sizing of switch SW, of breakover diode D, and of avalanche diode d. In particular, although examples of circuits 70 only formed of passive components have been described, active components such as transistors may be added to the control circuit of switch SW, particularly to more accurately control the turn-on and turn-off times of switch SW. Further, only one-way protection diodes have been described and shown in the drawings. Of course, bidirectional protection diodes (having their characteristics illustrated in FIGS. 1 and 2, although they have not been described) may also be provided.
(32) Further, the use of the protection component in association with a line biased to a DC voltage only has been described. This component may also be used in the case where the line is an alternating current (AC) power supply line, for example, at 50 or 60 Hz. Indeed, if the overvoltage occurs at the beginning of a half wave, it may be desired for the protection diode to stop being conductive rapidly after the occurrence of an overvoltage without waiting for the end of a half wave, the duration of a half wave being 10 ms in the case of a power supply at 50 Hz.
(33) Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.
