VOLTAGE AND CURRENT LIMITER

Abstract

The invention relates to a voltage and / or current limiting device (10) for a low-voltage DC network, comprising: - voltage and / or current limiting means (20); - voltage measurement means (30) and first means (MA6) for comparing a measured voltage with a first reference value (33), providing an output voltage proportional to this comparison; - current measurement means (40) and second means (MA4) for comparing a measured current with a second reference value (43), providing an output voltage proportional to this comparison; - a control circuit (50) for the voltage and / or current limiting means (20) based on the first output voltage provided by the first comparison means (MA6) and the second output voltage provided by the second comparison means (MA4). Figure for the abstract: 3

Description

Title of the invention: VOLTAGE AND CURRENT LIMITER

[0001] TECHNICAL FIELD AND PRIOR TECHNOLOGY

[0002] The invention relates to the field of electronic equipment, particularly for aeronautics, which is powered by a DC voltage network of nominal value, for example 28V DC, but whose voltage value can fluctuate.

[0003] In order to optimize the sizing of voltage-controlled electronic equipment, a stage designed to limit overvoltages can be added to the input of such equipment.

[0004] Similarly, a stage designed to limit the current drawn to a predefined maximum value can also be added to the input of such equipment. This protects electronic equipment against overcurrents in its input current that may occur during startup (inrush current) or in the event of a downstream fault. This current limitation also optimizes the sizing of this equipment because it is no longer necessary to oversize the conductors or components through which this current flows.

[0005] Figure 1 shows a diagram of a device 110 known for current and voltage limiting. This example of a prior art device includes, among other things, a series limiter 112 whose input and output have the same voltage reference, conventionally ground, generally designated GND. This device further includes means 114 for measuring and controlling the voltage, and means 116 for measuring and controlling the current.

[0006] The operation of the series limiter depends on commands sent by the voltage measurement and control means 114 and commands sent by the current measurement and control means 116. Depending on the commands received, the series limiter 112 can absorb a portion of the series voltage, thus limiting the voltage, or oppose the flow of current, thus limiting the current.

[0007] In the absence of overvoltage or overcurrent, the series limiter 112 behaves like a conducting switch.

[0008] However, implementing this type of device implies several constraints on the integration environment:

[0009] - when current or voltage limiting is activated, voltage stability is not always obtained, which implies transients or oscillations which must be taken into account in the design of the series limiter, downstream of it; in this type of assembly stability, particularly in temperature, is not always controlled;

[0010] - the current limitation is very imprecise; this is, for example, linked to the base-emitter voltage of a transistor; however, this voltage can vary.

[0011] - the imprecision regarding the current limitation necessitates an oversizing of the fuse and cable placed upstream of this assembly;

[0012] - the limiting current values ​​are reduced to the shunt resistance values chosen;

[0013] - the limiting voltage values ​​are reduced to the values ​​of the chosen diode; however, of the same as for resistors, the voltage values ​​offered by manufacturers are limited (E12 series).

[0014] The input stages which are known as series limiters are therefore not sufficiently precise, which results in the need to oversize both in voltage and current the electronic equipment powered downstream.

[0015] The problem therefore arises of finding a new circuit and a new method which make it possible to obtain limiting values ​​which are more stable and more precise, both for voltage and for current. Description of the invention

[0016] The invention aims to provide better accuracy on the current and voltage limitations of electronic equipment powered by a DC voltage network.

[0017] The invention presents a series limiter intended to supply equipment with low voltage direct current supply, and incorporating a precise current and voltage limiting solution.

[0018] The invention relates in particular to a voltage and / or current limiting device for a low-voltage direct current network, comprising:

[0019] - means for regulating or limiting (or limiting) the voltage and / or the fluent ;

[0020] - means for measuring voltage and initial means for comparing a voltage measured with a first reference value, providing a first output voltage, proportional to this comparison;

[0021] - means for measuring the current and second means for comparing a current measured with a second reference value, providing a second output voltage, proportional to this comparison;

[0022] - a control circuit controlling the regulating or limiting means of the voltage and / or current as a function of the first output voltage supplied by the first comparison means and the second output voltage supplied by the second comparison means.

[0023] Current measurement means, which can allow the current in the network to be measured, may include at least one of the following characteristics:

[0024] - an operational amplifier with open collector output;

[0025] - and / or means for fixing a bias voltage at a constant value used for current measurement;

[0026] - and / or means for fixing a current limiting value;

[0027] - and / or means of compensating and controlling the dynamics of the current.

[0028] The means for measuring voltage may include at least one of the following characteristics:

[0029] - an operational amplifier with open collector output;

[0030] - means for fixing a voltage limiting value;

[0031] - means for compensating and controlling the voltage dynamics.

[0032] The control circuit can control said voltage and / or current limiting means as a function of the smallest voltage between the first output voltage supplied by the first comparison means and the second output voltage supplied by the second comparison means, for example when the current measuring means include an operational amplifier with collector output and the voltage measuring means include an operational amplifier with open collector output.

[0033] The invention also relates to a low voltage direct current network, for example comprising voltage supply means, for example at 28 V, and a limiting device according to the invention.

[0034] The invention also relates to a method of limiting voltage and / or current in a low voltage direct current network implementing a device according to the invention, as described above or in the continuation of this description.

[0035] The invention also relates to a method for limiting voltage and / or current in a low-voltage direct current network, comprising:

[0036] - a measurement of the voltage and a comparison of the measured voltage with a first reference value, providing a first output voltage proportional to this comparison;

[0037] - a measurement of the current in the network and a comparison of the measured current with a second reference value, providing a second output voltage proportional to this comparison;

[0038] - a proportional regulation of voltage and / or current limiting means based on, or depending on, the first output voltage and the second output voltage, provided by said comparisons.

[0039] In a particular embodiment, the proportional regulation of voltage and / or current limiting means is carried out as a function of the smallest voltage between the first output voltage and the second output voltage.

[0040] The invention relates to a new voltage and / or current limiting device, and / or a new voltage and / or current limiting method which allows:

[0041] - to implement a limitation in both current and / or voltage, which is precise and easily adjustable;

[0042] - the use of an adjustable compensation, which allows the tension to be controlled supplied to downstream equipment, as well as inrush currents.

[0043] The invention proposes in particular an input stage solution and / or a method performing and / or implementing the two functions of voltage limiting and current limiting, and providing several advantages over existing solutions, in particular the following advantages: - One or more easily adjustable limit value(s); - Stability of the supplied voltage during the limiting phases; - A reduction in the size of upstream wiring, as well as the size of fuses and circuit breakers, with a positive impact on weight; - A regulated voltage is supplied during the activation phases, which allows for the most accurate voltage sizing of downstream components, thus resulting in gains in mass, volume, and cost.

[0044] A device or method according to the invention allows, in particular: • to better protect against overvoltages the electronics downstream of the device or means implemented within the framework of a process according to the invention; • to limit the size of the cable supplying the equipment through precise current limiting. Brief description of the drawings

[0045] Fig. 1 represents a device of a known type;

[0046] Figure [Fig. 2] represents an example of an embodiment of a device according to the invention;

[0047] Figure 3 represents a detailed embodiment of a device according to the invention.

[0048] Fig. 4A and Fig. 4B represent the evolution of the output voltage as a function of the input voltage (Fig. 4A) and as a function of time (Fig. 4B).

[0049] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0050] An example of an embodiment of a device 10 according to the invention is illustrated in [Fig.2].

[0051] It comprises:

[0052] - means 20 forming a limiter arranged in series on a supply line 11 voltage between an input, to which a continuous power supply is provided, and low voltage (for example, less than 100W of power), and a load (not shown in [Fig.2]), for example an electronic device, connected to the output of the device; the term "series limiter" is used to refer to these means 20;

[0053] - means 30 for detecting (or measuring) the value of the output voltage of the limiter; these means may for example include an R61, R44 divider bridge;

[0054] - means 32 which make it possible to provide the difference between a voltage value measured and a reference value of 33;

[0055] - means 40 for detecting (or measuring) the value of the current at the output of the limiter; these means may for example include a voltage divider R72, R74;

[0056] - means 42 which make it possible to supply a voltage which corresponds to the difference between a measured current value and a reference value 43;

[0057] - means 50 whose output provides the means 20 with the minimum voltage between the outputs of devices 42 and 32:

[0058] *if the output voltage of means 42 is lower than the output voltage of means 32, the output of means 42 is supplied to the output of means 50;

[0059] * if the output voltage of the means 32 is lower than the output voltage of the means 42, the output voltage of means 32 is supplied at the output of means 50.

[0060] The means 32, respectively 42, can be realized in the form of an operational amplifier with open collector output MA6, respectively MA4, incorporating the reference value 33, respectively 43.

[0061] This example implements 2 nested control loops:

[0062] - a regulation loop, comprising means 20, on the maximum voltage of output (means 30, 32);

[0063] - and another control loop, also comprising means 20, on the maximum current (means 40, 42).

[0064] This architecture allows for precise limitation and controlled behavioral response.

[0065] In a normal operating condition (no overvoltage or overcurrent), neither of these two regulation loops is active. The upstream voltage and current (at input 12 of the equipment) are transmitted in full to the downstream electronics (at output 14 of the equipment).

[0066] In a process implementing such a device or in a process according to the invention:

[0067] - the voltage limiting, using means 32 and 50, is activated in the case of a overvoltage present at input 12;

[0068] - and / or current limiting using means 42 and 50, is activated in the case of an overcurrent demanded by the downstream electronics 14.

[0069] In the case where both limitations are activated at the same time, the regulation that prevails over the other is the one requiring the strongest command, therefore the strongest value between the output Vout 4 2 and the output Vout 3 2 of the means 32:

[0070] - the output Vout 4 2 of the means 42 corresponds to the difference between the reference 43 and the output of device 40 (Vout 4 2 = Vref 4 3 - VmesUre_ COurant4 o); for example, if the output of 40 is low compared to the reference 43, the output voltage of the means 42 is high;

[0071] - the output Vout 3 2 of the means 32 corresponds to the difference between the reference 33 and the output of device 30 (Vout 3 2 = Vref 3 3 - VmesUre_ voltages o), for example, if the output of 30 is low compared to the reference 33, the output voltage of means 32 is high.

[0072] The invention allows the limitations to be adjusted to the exact value desired, the limitation values ​​being adjusted for example by means of the means 30 and / or 40, for example of the voltage divider bridges R61, R44 and / or R72, R74, implemented for the measurement of voltage and / or current.

[0073] Fig. 3 is a detailed representation of an implementation of a limiting circuit according to the invention.

[0074] In this figure, examples of the realization of different blocks 52, 54, 56 are shown, which are means 52 for controlling the series limiter, means 54 for controlling the voltage limiter, means 56 for controlling the current limiter.

[0075] The means 52 include a transistor Q5, for example a bipolar or MOS transistor, whose operation remains the same in both cases (voltage limitation, or current limitation).

[0076] At the input of the current limiter control means 56, the assembly comprising resistor R71 and diode CR15 (which functions identically to a Zener diode) generates a fixed voltage V_P5V_FILT, for example, 5V, which is independent of any variation. This allows a constant voltage offset to be added to the current measurement signal. This offset provides component MA6 (described below) with an "offset" that allows it to assimilate the current signal: this voltage allows the current limiting value to be adjusted and / or the bias point of the measurement and current limiting to be fixed. Indeed, the internal reference 43 is fixed and inaccessible. When the current limiting is activated, the output of device 40 is, for example, approximately 2.5V. If this voltage were supplied only across R63, too much power would be dissipated in it.Components R71 and CR15 prevent this situation by adding a voltage offset to the current measurement.

[0077] Resistors R72, R74, and R63 allow for precise current measurement and also for setting the current limiting value: R72 and R74, which determine the gain of the control loop in which they are arranged, form a divider between the value V fixed by means R71 and CR15 and the ground GND, R63 performing the current measurement.

[0078] The MA6 component generates the current control for the limiter Q5; this MA6 component is, for example, an open-collector operational amplifier with two distinctive features: it is powered by its output and an integrated voltage reference 33 ([Fig. 2]). The output of MA6 is corrected by a compensator assembly (C67, C68, R73), thus forming the V_FB_Prot voltage, which can vary, for example, from 3V to 36V, depending on the regulation setpoint. The circuit operates at least partially in linear mode: the output of MA6 is proportional to the correction applied. In other words, the invention provides a gradual response that avoids instabilities.

[0079] An open-collector output operational amplifier such as MA6 (but also MA4, see below) is powered by its output, therefore it does not need a dedicated power supply - thus limiting the number of components - and is capable of operating over wide voltage ranges.

[0080] Capacitor C67, in parallel with capacitor C68 and resistor R73, allows adjustment of the compensation of the control signal V_FB_PROT within the current limiting regulation loop. These components C67, C68, and R73 perform a correction function to adjust the control signal, which indirectly adjusts the measurement. A regulation mechanism acts on an actuator, here Q5, which allows adjustment of the desired physical quantity. The means C67, C68, and R73 constitute means for compensating and controlling the current dynamics. Such means contribute to the stability of the device.

[0081] At the input of the voltage limiter control means 54, resistors R61 and R44 form a voltage divider that allows for a precise output voltage measurement and also sets the voltage limiting value and the gain of the feedback loop in which this divider is located. Since reference 33 is not accessible, the limiting voltage is adjusted via the feedback gain, i.e., by resistors R61 and R44, which thus impose a voltage limiting value.

[0082] MA4 is, for voltage limiting, a component of the same type as MA6 for current limiting. It is therefore, for example, an open-collector operational amplifier with two distinctive features: it is powered by the output and a voltage reference 43 ([Fig. 3]) is integrated into it. Here again, the circuit operates at least partially in linear mode: the output of MA4 is proportional to the correction to be applied. Here again, the invention allows for a gradual response that avoids instabilities.

[0083] At the output of MA4, capacitor C38, along with capacitor C41 and resistor R42, which are connected in parallel with C38, perform a voltage feedback control function for the voltage loop to adjust the control signal, which in turn indirectly adjusts the measurement. A regulator acts on an actuator, here Q5, which allows adjustment of the desired physical quantity. The components C38, C41, and R42 constitute means of compensation and control of the voltage dynamics. Again, such means contribute to the stability of the device. Output 80 is common to MA4 and MA6.

[0084] The open-collector outputs of amplifiers MA4 and MA6 can only absorb a current that flows to ground. They are arranged in parallel, which allows the lowest voltage to be selected.

[0085] This minimum value allows the limiter 20 to choose, as appropriate, which action to take: a current or voltage limitation.

[0086] This overall command is transmitted to the voltage limiter Q5, through a control stage 52 comprising components R41, R43, Q6 and R62. These allow for inversion and biasing of the signal compatible with the control of the limiter Q5.

[0087] This limiter Q5 is controlled according to the value of the voltage V_FB_PROT, generated by the voltage limiter or by the current limiter.

[0088] The two control generators 54, 56 are put in parallel, thus they perform a selection of the minimum voltage value (signal V_FB_PROT).

[0089] An open-collector output is a transistor output in which the collector is connected only to the output. The emitter (in the case of an NPN transistor) is internally connected to ground. Thus, the output only forces a current to ground. A pull-up resistor (R60 in the given example) is used in this type of circuit. With this type of output, it is possible to connect several outputs together. This allows for the simultaneous implementation of a minimum value selection function.

[0090] Resistor R60 contributes to the biasing of MA4, MA6, and Q6. Resistor R71 provides the biasing for CR15. A circuit according to the invention allows:

[0091] - to achieve a current limitation that is stable and very precise, which allows:

[0092] * to optimize the size of the fuses on the line;

[0093] * to reduce the size of the cables.

[0094] - to achieve a voltage limitation that is stable and very precise, which allows:

[0095] * to provide during the activation phases (in the case of an upstream overvoltage or a downstream overcurrent) a regulated voltage downstream;

[0096] * a voltage sizing as precisely as possible of the downstream components, therefore of gains in mass, volume and cost.

[0097] Figure 4A shows the evolution of the output voltage as a function of the input voltage Vinput (input voltage of the circuit); depending on whether the latter is lower or If the voltage exceeds the limit defined by the voltage limitation, the voltage limitation is activated, or not.

[0098] Figure 4B illustrates the evolution of the output voltage over time: initially, V_FB_prot and the input voltage Vinput are below the voltage limit defined by the voltage limiter, so the voltage limiter is not activated; subsequently, the input voltage Vinput is above the voltage limit defined by the voltage limiter, so the voltage limiter is activated. There is a gradual adjustment of the control (i.e., V_FB_prot) to allow a fixed output voltage Voutput.

[0099] The invention makes it possible in particular to produce a device which meets voltage resistance requirements.

[0100] Equipment is subject to standards and other requirements; for example, for a 28V network, there may be a maximum voltage of 80V. The same applies to the input current. Standards specify a starting current limit for the device to meet this type of requirement in order to limit stress on upstream or downstream components.

[0101] A circuit according to the invention makes it possible, in particular, to prevent the input current value from exceeding a value close to the maximum permissible current, the current limitation being precise and easily adjustable. When the current or voltage limitation is not activated, the input voltage is fully transmitted to the output. The same applies to the current. When neither the voltage nor the current limitation is activated, the current consumed by the equipment comes directly from input 12 (see [Fig. 3]).

[0102] The invention can be very advantageously used with any type of direct current (DC) power supply, batteries, DC generator, etc. For example, it can be used with a 28V DC power supply intended to power electronic equipment in the aeronautical field.

[0103] A circuit according to the invention can be made entirely of analog components. In particular, the use of resistors allows for high accuracy, since these components have very low drift with, for example, temperature. This gain in accuracy allows the use of smaller cables upstream and downstream of the device.

[0104] Conventionally, current measurement and limitation can be implemented using a resistor. However, in a standard series of resistors (for example, the E12 or E24 series...), the standardized values ​​are very limited, and therefore the limiting currents obtained are also very limited. These standardized series are standard for resistor manufacturers who do not offer other values. The limiting output current is then generally defined by the following formula: Iiiit=Vbe / R; the value of Vbe being fixed, the current limit value is directly related to the value of resistance R.

[0105] The limiting values ​​(current, voltage) of a device according to the invention are defined or fixed by the internal reference of the MA4 and MA6 integrated circuits and by the resistance tolerances; we therefore have a precision of the order of 1 or 2% (conventional thin-film resistors have a precision of the order of 25 ppm / million (in other words, for 1° of AT, we have a variation of 2571 million); we therefore have limiting values ​​which are much more stable, especially in temperature, than a VBE (base-emitter voltage) of a transistor which can vary from one to two.

[0106] The same applies to the reference value 33, 43, integrated into each component MA4, MA6: it varies by only a few tens of ppm / °C, which ensures high stability.

Claims

Demands

1. A voltage and / or current limiting device (10) for a low-voltage DC network, comprising: - voltage and / or current limiting means (20); - voltage measurement means (30) and first means (MA6) for comparing a measured voltage with a first reference value (33), providing a first output voltage, proportional to this comparison; - current measurement means (40) and second means (MA4) for comparing a measured current with a second reference value (43), providing a second output voltage, proportional to this comparison; - a control circuit (50) controlling the voltage and / or current limiting means (20) as a function of the first output voltage provided by the first comparison means (MA6) and the second output voltage provided by the second comparison means (MA4).

2. Device according to claim 1, current measurement means (40) and / or voltage measurement means (30) comprising an open-collector output operational amplifier (MA6, MA4).

3. Device according to claim 1 or 2, the current measurement means (40) comprising means (R71, CR15) for fixing, at a constant value, a bias voltage used for current measurement.

4. Device according to any one of claims 1 to 3, the current measurement means (40) comprising means (R72, R74) for fixing a current limiting value.

5. Device according to any one of claims 1 to 4, the current measurement means (40) comprising means (C67, C68, R73) for compensating and controlling current dynamics.

6. Device according to any one of claims 1 to 5, the control circuit controlling said voltage and / or current limiting means as a function of the smallest voltage between the first output voltage supplied by the first (MA6) comparison means and the second output voltage supplied by the second (MA4) comparison means.

7. Device according to any one of claims 1 to 6, voltage measurement means (30) comprising means (R61, R44) for fixing a voltage limiting value.

8. Device according to any one of claims 1 to 7, voltage measurement means (30) comprising means (C38, C41, R42) for compensation and control of voltage dynamics.

9. A low-voltage direct current network, comprising voltage supply means and a limiting device according to any one of claims 1 to Q

10. O. A method for limiting voltage and / or current in a low voltage DC network, comprising: - a measurement of the voltage and a comparison of the measured voltage with a first reference value (33) providing a first output voltage proportional to this comparison; - a measurement of the current in the network and a comparison of the measured current with a second reference value (43), providing a second output voltage proportional to this comparison; - a proportional regulation of voltage and / or current limiting means (20) as a function of the first output voltage and the second output voltage, provided by said comparisons.