FR2703858A1 - Device for protection against overcurrents for a regulator - Google Patents

Abstract

A device (3) for protection against overcurrents, such as short circuits or overloads, for a regulator (2) fed by a rectifier (1) linked to an alternating voltage source (TA) comprises a switch (S) in the form of a field-effect transistor and turn-on and turn-off circuits controlling the switch. The turn-on circuit (35) controls the turning-on of the switch when the rectifier (1) is feeding the regulator (2). The turn-off circuit (36) controls the turning-off of the switch in response to an overcurrent. The protection device can be rearmed automatically.

Description

Overcurrent protection device
for a regulator
The present invention relates generally to voltage or current regulators and pre-regulators, and more particularly to a device for protection against overcurrents due to short circuits and overloads for a regulator supplied by a rectifier connected to a source. of alternating voltage.

 According to the prior art, a rectifier, for example single-phase full-wave bridge, is supplied by a single-phase alternating voltage source. The rectifier supplies a regulator, of the booster type (BOOST), comprising a power circuit, capable of delivering a regulated voltage as an output to an electrical appliance, and a control circuit, for controlling the power circuit, so the absorbed current is sinusoidal.

 In the event of an output overload, or in the event of a short circuit, such a circuit does not include any means of protection. A current greater than the current tolerated by the various components of the circuit flows through the circuit, causing the destruction of the components. A fuse constitutes a means of protection particularly against short-circuits. When the fuse, included in series in the circuit, is crossed by a current greater than a predetermined value, it blows to cause the opening of the circuit and the disappearance of the short-circuit or of the overload. The fuse is a very common safety element in electrical installations; however it is not resettable and its change is necessary after its operation.

 The present invention aims to provide a device for protecting a voltage or current regulator against short circuits or overloads, which can be reset automatically.

 To this end, an overcurrent protection device for a regulator connected to a load and supplied by an alternating voltage rectifier, comprises an interruption means interconnected between an output terminal of the rectifier and an input terminal of the regulator having the same polarity, a closing means for controlling the closing of the interrupting means when the rectifier supplies the regulator, and an opening means for controlling the opening of the interrupting means in response to an overcurrent in the load.

 Advantageously, the switching means is a field effect transistor, or an isolated gate transistor, for example IGBT, or MCT or other.

 The closing means closes the interrupting means when the device is powered up, then keeps the interrupting means closed as long as an overcurrent is not detected.

These two functions are accomplished by means for charging a capacitor with voltage taken from the output of the rectifier in order to close said interruption means, and means coupled to the input of the regulator for keeping said capacitor charged.

Preferably, the closure means comprises,
a resistor and a diode connected in series between said rectifier output terminal and an electrode for controlling the interrupting means,
- a capacitor and a Zener diode connected in parallel between the input terminal of the regulator and the control electrode, and
- an auxiliary inductor coupled to an inductor of the regulator, and at least one diode connected in series between the input terminal of the regulator and the control electrode.

 According to another characteristic, the opening means comprises a first means for detecting an overcurrent, a second means for detecting a voltage at the input terminals of the regulator and means controlled by the first and second means for detecting for opening the means of 'interruption.

 Advantageously, the means for detecting an overcurrent comprises a timer means for delaying the opening of the interrupting means in response to an overcurrent. This prevents the opening control from oscillating too quickly in the event of permanent overload.

 According to a preferred embodiment, the regulator is a switching regulator comprising an adjustment member, of the transistor type, either located after an input terminal of the protection device, or interconnected between the input terminals of the protection device through an inductor of head. The protection device then comprises a means controlling the adjustment member and generating pulses; stopping the pulses is interpreted as signaling an overcurrent by the means for detecting in order to open the interrupting means.

 The opening means comprises a flow diode, which allows automatic resetting of the protection device between input terminals of the regulator.

Other characteristics and advantages of the present invention will appear more clearly on reading the following description of several preferred embodiments of the invention, with reference to the corresponding appended drawings in which
- Figure 1 shows in detail a pre-regulator of the decoupage type with sinusoidal current absorption associated with a rectifier according to the prior art;
- Figure 2 shows in detail a preregulator associated with a rectifier and provided with a protection device according to a first embodiment of the invention; and
- Figure 3 shows in detail a preregulator associated with a rectifier and provided with a protection device according to a second embodiment of the invention.

 With reference to FIG. 1, a single-phase alternating voltage source TA formed by the sector at 230 V and 50 Hz is connected to input terminals 11 and 12 of a rectifier 1. Output terminals 13 and 14 of the rectifier are connected respectively to input terminals 23 and 24 of a switching pre-regulator 2, comprising a power circuit 21 and a control circuit 22.

 An electrical appliance, as a CH load, is connected to output terminals 27 and 28 of the pre-regulator and is supplied by the regulated output voltage of the pre-regulator.

 Rectifier 1 is a single-phase full-wave bridge rectifier. Between the two input terminals 11 and 12 and the two output terminals 13 and 14, the rectifier 1 comprises four diodes D1 to D4 arranged in a known manner: the anode of the diode D1 and the cathode of the diode D3 are connected at terminal 11, and the anode of diode D2 and the cathode of diode D4 are connected to terminal 12; and the cathodes of diodes D1 and D2 are connected to terminal 13, and the anodes of diodes D3 and D4 are connected to terminal 14.

 A sinusoidal voltage supplied by the voltage source TA becomes at output 13-14 of the rectifier I a rectified sinusoidal voltage formed by successive sinusoid arches.

The input terminal 23 of the pre-regulator 2 is merged with the positive output terminal 13 of the rectifier. Between the negative output terminal 14 of the rectifier and the terminal 24 which coincides with the output terminal 28, is a shunt resistor
RS used for a measurement of current drawn.

 Terminals 23 and 24 are the input terminals of the power circuit 21 of the pre-regulator. From the positive terminal 23 an inductor L1 is connected to a terminal 25 and a freewheeling diode D5 is connected passing from terminal 25 to the output terminal 27. Between the output terminals 27 and 28 is connected a capacitor filtering Cl. A regulating member of the pre-regulator, in the form of a field effect transistor Q, is connected between the terminals 25 and 28, that is to say in parallel with the diode D5 and the capacitor C1.

 The drain DQ, the source SQ and the gate GQ of the transistor Q are respectively connected to the terminals 25 and 28, and to an output terminal 29 of the control circuit 22 of the preregulator.

The control circuit 22 includes a feedback loop connected to the positive output terminal 27 of the preregulator. Starting from terminal 27, the feedback loop includes a resistive bridge constituted by resistors RA and RB connected in series. To a common terminal of resistances
RA and RB is connected an inverting input of an error amplifier AS through a resistor
RF. A reaction resistor RE connects the inverting input (-) and the output of the amplifier AS.

A VREF reference voltage source is connected to a direct input (+) of the AS amplifier. The output of the amplifier AS is connected to a first input of a multiplier circuit CM.

 On the other hand, a rectified voltage sampling loop is connected to terminal 13 of the rectifier. This loop includes a resistive bridge made up of RC and RD resistors connected in series. The midpoint of this resistive bridge is connected to a second input of the multiplier circuit CM. The output of the multiplier circuit CM is connected to a direct input (+) of a comparator CP. An inverting input (-) of the comparator CP is connected to the output terminal 14 of the rectifier to measure the current drawn with the resistor RS. Finally, the output 29 of the comparator CP is connected to the gate GQ of the switching transistor Q.

 The pre-regulator 2 works as follows.

The rectified voltage supplied by the rectifier 1 is integrated by the low-pass filtering means composed by the inductor Ll and the capacitor C1 included in the pre-regulator, into an output voltage VS between the terminals 27 and 28 of the capacitor.
THIS. A fraction of the output voltage VS is taken by the resistor bridge RA and RB and is subtracted from the reference voltage VREF by the amplifier-subtractor AS. The difference between these two voltages is an error signal, which is transmitted to the first input of the multiplier circuit CM.

 A fraction of the rectified voltage is measured via the resistor bridge RC and RD and is multiplied by the error signal in the circuit CM.

 A signal proportional to the current drawn, measured using the shunt resistor RS, is compared to the result of the previous multiplication in the comparator CP to form control pulses of the transistor Q applied to the gate of the latter.

 The pre-regulator control circuit 22 thus regulates the output voltage around a desired value, defined by the reference voltage VREF. The control circuit also enslaves the shape of the sampled current, measured by the resistor RS, on the shape of the sampled voltage, that is to say that the sampled current has a shape of sinusoid arches. The pre-regulator is thus sinusoidal current absorption. In the event of an overload or short circuit at the output of the pre-regulator, the control circuit 22 no longer delivers a pulse to the gate of the transistor.

The transistor Q is protected by blocking, but the current at the output of the pre-regulator is not interrupted, and reaches either a short-circuit current depending on the impedance of the pre-regulator and the impedance of the load, in the event of a short circuit. , i.e. an intensity lower than the short-circuit intensity, but greater than a nominal operating value of the pre-regulator, in the event of overload.

Either of these overcurrents causes components in the preregulator to deteriorate.

 With reference to FIG. 2, a controlled protection device 3 according to the invention is interconnected between the rectifier 1 and the pre-regulator 2. The pre-regulator and the rectifier are similar to those described with reference to FIG. 1.

 The protective device 3 is analogous to a quadrupole having a control terminal. The output terminals 13 and 14 of positive and negative polarities of the rectifier are connected respectively to input terminals 31 and 32 of positive and negative polarities of the protection device 3. The input terminals 23 and 24 of the power circuit 21 of the pre-regulator 2 are connected to the output terminals 33 and 34 of the protection device 3. The resistor for measuring the tapped current RS still connects the rectifier terminal 14 to the earth terminal 28 of the load CH which is coincident with the terminals 32, 34 and 24. The control circuit 22 of the pre-regulator is connected to the terminals 13, 14 and 27 and to the gate of the transistor Q, in a similar manner to FIG. 1.

 Between the positive polarity terminals 31 and 33 of the protection device 3 is connected in series an overcurrent interrupting means, in the form of a field effect transistor with NS channel, or with isolated gate, of IGBT type, MCT or other. The drain DS of the transistor S is connected to the input terminal 31, the source SS is connected to the output terminal 33, and the gate GS is connected to a control means for controlling the transistor S.

 This control means comprises on the one hand a closing circuit 35 for closing the protection device 3, by passing the transistor S for normal operation of the load CH, and on the other hand an opening circuit 36 for opening the device 3 in response to an overcurrent.

In the closing circuit 35, a resistor R1 and a diode D6 are connected in series between the terminal 31 and the gate GS, the diode D6 passing from the terminal 31 towards the gate GS. Between the output terminal 33 and the gate GS of the transistor S, a capacitor C2 and a Zener diode D7 are connected in parallel, the anode of the diode D7 being connected to the terminal 33. An auxiliary inductance L2 is coupled to the inductance L1 of the pre-regulator. The terminals of the inductance L2 are respectively connected to the output terminal 33 and to the gate GS of the transistor S through a resistor R8 and a diode
D8 connected in series, the diode D8 passing from the resistor R8 to the gate GS.

 The closing circuit 35 operates in the following manner. For the rectified voltage at the output of rectifier 1 to reach the pre-regulator 2, the transistor S must be on, and therefore the gate GS must be at a potential greater than the potential of its source SS. When the rectifier 1 is energized, the rectified voltage charges an energy reservoir constituted by the capacitor C2, via the resistor R1 and the diode D6, to a value limited by the Zener diode D7. This necessary power draw "at start-up? 1 is carried out with a low efficiency, and the resistor R1 dissipates energy in the form of heat. After power-up, a current flows through the inductance L1, and therefore also l inductance L2 which is coupled to it The current supplied by inductance L2 and rectified by diode D8 then maintains the gate potential.

This constitutes a "maintenance" supply which replaces the "start-up" withdrawal.

 The opening circuit 36 of the protection device 3 detects a short circuit or an overload and blocks the transistor S in response to a detected short circuit or a detected overload. Circuit 3 essentially comprises an open collector threshold comparator CCO, a timing filter R7-D9-C4 and a transistor T.

 An inverting input EI of the comparator CCO is connected to the output terminal 29 of the pre-regulator control circuit 22, via the timing filter.

The time delay filter comprises a resistor R7 and a diode D9 connected in parallel, the diode D9 passing from terminal 29 to the inverting input EI, as well as a capacitor C4 connected between the inverting input and the ground corresponding to the charging station 28.

 A resistive bridge is connected between the output terminals 33 and 34 of the protection device 3. This bridge is formed by resistors R2 and R3 and a filtering capacitor C3 which is connected in parallel with the resistor R3 to terminal 34. The terminal common to resistors R2 and R3 is connected to one of the terminals of a second bridge of resistors R5 and R6, the other terminal of which is brought to an adjustment voltage VR.

The terminal common to resistors R5 and R6 is connected to the direct input ED of the threshold comparator CCO.

 The drain DT and the source ST of the field effect transistor T are respectively connected to the gate GS of the transistor S and to the negative terminals 3234. The gate GT of the transistor T is connected on the one hand to the output of the threshold comparator CCO and on the other hand at the midpoint of the R2-R3 bridge, via a R4 counter-reaction resistor. Finally, a flow diode D10 is connected passing from terminal 34 to terminal 33.

 As has already been specified, on power-up, the rectifier 1 delivers a voltage in the form of sinusoid arches and the transistor S becomes conducting under the action of the closing circuit 35 of the protection device 3. The rectified voltage reaches the power circuit 21 of the pre-regulator, which delivers a regulated voltage thanks to pulses supplied by the control circuit 22 to the transistor Q.

 As regards the opening circuit 36 of the protection device 3, the pulses charge the capacitor C4 via the diode D9, which has the effect of bringing the potential of the inverting input EI of the comparator CCO to a value greater than that of direct ED input. The output of the comparator CCO is then zero and the transistor T is blocked. As long as there is neither overload nor short-circuit, the opening circuit blocks the transistor T and consequently the transistor S remains on.

In the event of an overcurrent due to an overload or a short circuit, as has already been said, the control circuit 22 blocks the transistor Q and no longer delivers a pulse. In the time delay filter, the capacitor C4 discharges and the voltage at the inverting input EI of the comparator CCO decreases, with a time constant depending on the product of the ohmic value of the resistance R7 and the capacitance of the capacitor C4. The time delay filter thus delays the instant when the voltage at the inverting input EI becomes lower than the voltage at the direct input.
ED, defined by the ohmic values of the bridge resistors R2, R3, R5 and R6 and by the value of the adjustment voltage VR, that is to say the instant when the threshold comparator CCO switches. The comparator output voltage is no longer zero; it is then equal to a value defined by the bridge R2-R3 and the resistor R4, that is to say to a value proportional to the rectified and filtered voltage.

This voltage value is applied to the gate of transistor T; if it is non-zero, it causes the passage to the passing state of the transistor T, and causes the potential of the gate GS of the transistor to drop
S, and thus its passage to the blocked state. As long as the transistor S remains in the off state, the protection device 3 is open between the terminals 31 and 33 and the current no longer flows from the rectifier 1 to the preregulator 2, which eliminates the short-circuit current or overload and protects the pre-regulator.

As long as the circuit is open between terminals 31 and 33, the energy accumulated in the inductor L1 decreases while a current flows through the inductor L1, the output terminals 27 and 28 connected for example by a short circuit, and the flow diode D10. Consequently, the voltage across the diode D10 and therefore of the resistance bridge
R2 and R3 decrease, until a value which will block transistor T again. The circuit then returns to a state similar to the power-on previously exposed. The flow diode D10 allows automatic resetting of the protection device.

 The switchover of the CCO comparator in the event of an overload takes place after a delay dependent on the resistive and capacitive components R7 and C4 in the delay filter and on the adjustment voltage VR. This time delay is chosen as a function of the rate of rise of the current in the inductor L1 and to avoid too rapid oscillation of the opening command in the event of permanent overload.

 On the other hand, the transition to the on state of the transistor T, and consequently the blocking of the transistor S, occurs after switching of the comparator CCO, on the condition that a non-zero voltage exists between the terminals 33 and 34. This allows the pre-controller to be started or restarted.

 In FIG. 3, a controlled protection device 3 ′ according to a second embodiment of the invention replaces the device 3 compared to FIG. 2, and is therefore interconnected between the rectifier 1 and the pre-regulator 2. The device 3 ′ is also a controlled quadrupole having input terminals 31 'and 32' connected respectively to the output terminals 13 and 14 of the rectifier, and output terminals 33 'and 34' connected respectively to the input terminals 23 and 24 of the preregulator.

 However, in the protection device 3 ′, the input and output terminals of positive polarity 31 ′ and 33 ′ are combined, and an interruption means is connected between the terminals of negative polarity 32 ′ and 34 ′. This interruption means consists of a P-channel field effect transistor S '. The drain DS 'of the transistor S' is connected to the terminal 32 ', the source SS' is connected to the terminal 34 'and the gate GS' is connected to a means for controlling the transistor S '.

 This control means comprises on the one hand a closing circuit 35 'for closing the protection device 3' by turning on the transistor S 'for normal operation of the load, and on the other hand an opening circuit 36' to open the device 3 'in response to an overcurrent.

 The closing circuit 35 ′ is produced in a similar manner to that shown in FIG. 2.

A resistor R1 'and a diode D6' are connected in series between terminal 32 'and the gate GS', the diode
D6 'passing from grid GS' to terminal 32 '. Between terminal 34 'and gate GS' of transistor S ', a capacitor C2' and a diode of
Zener D7 'are connected in parallel, the anode of diode D7' being connected to the grid GS '. An auxiliary inductor L2 'coupled to the inductor L1 of the pre-regulator has a terminal connected to the gate GS', and another terminal looped back to terminal 34 'through a resistor R8' in series with a diode
D8 'which passes from the gate GS' towards the terminal 34 '.

 The closing circuit 35 'operates in a similar way to that shown in FIG. 2.

For the rectified voltage at the output of rectifier 1 to reach the pre-regulator 2, the transistor S 'must be on. When the rectifier 1 is energized, the rectified voltage charges the capacitor C2 'via the resistor R1' and the diode
D6 'to a value limited by the Zener diode D7'.

After power-up, when a current crosses the inductor L1, the coupled inductor L2 'supplies a current which is rectified by the diode D8' and which maintains the potential of the gate GS '. So there is still a "starting power" draw and a "maintenance" supply.

 The opening circuit 36 'of the protection device 3' detects a short circuit or an overload and blocks the transistor S 'in response to a detected short circuit or a detected overload.

The opening circuit 36 ′ comprises, as in the circuit 36 shown in FIG. 2, a threshold comparator with an open collector CCO ′, of which an inverting input EI ′ is connected to the output terminal 29 of the preregulator control circuit 22, through a timing filter constituted by a resistor
R7 ', a diode D9' and a capacitor C4 '. The direct input ED 'receives by a resistance bridge R2' and
R3 ', a fraction of the pre-regulator input voltage, filtered by a capacity C3' and referenced by a voltage VR 'through a resistor bridge R6'-R5'.

The output of the threshold comparator CCO 'is connected to the gate GT' of a field effect transistor T 'and to the midpoint of the resistance bridge R2' and R3 'through a feedback resistance
R4 '. The source ST 'of the transistor T' is connected to the terminal 34 '.

 The components designated by accentuated references, set out above and included in the opening circuit 36 ′ are thus arranged with one another in the same way as the corresponding elements included in the opening circuit 36 and designated by non-accentuated references. .

Compared to that 36 shown in Figure 2, the opening circuit 36 'has the following differences. The drain DT 'of the transistor T' is connected to the base of a bipolar PNP transistor T1 '. The emitter of transistor T1 'is connected to the midpoint of the resistance bridge R2' and R3 '. The collector of transistor T1 'is connected to the base of a bipolar NPN transistor
T2 'through a resistor R9'. The emitter of transistor T2 'is connected to the base through a resistor R10' and is also connected to the gate
GS 'of transistor S'. Finally, the collector of transistor T2 'is connected to the earth terminal 34'.

 The operation of the protection device 3 ′ according to the second embodiment has the following differences compared to that described with reference to FIG. 2. When there is an overload or short-circuit, the CCO comparator 'switches over, which causes the switch to 'on state of transistors T', T1 'and T2'. When the transistor T2 'is on, the potential of the gate GS' is equal to that of the source SS 'and the transistor S' is blocked, which interrupts the short-circuit or the overload.

 Although the protection device according to the invention has been described with reference to a single-phase electric circuit, such a device can be used in a three-phase network for example. The protection device is adaptable to any type of regulator or pre-regulator, whether it is switching or not, or that it comprises an adjustment member at the head before the inductor L1, or between the inductor L1 and the diode D5 freewheel as shown in Figures 1 to 3.

Claims (9)

 1 - Protection device (3) against overcurrents for a regulator (2) connected to a load (CH) and supplied by an alternating voltage rectifier (1), characterized in that it comprises an interruption means (S ; S ') interconnected between an output terminal (13; 14) of the rectifier (1) and an input terminal (23; 24) of the regulator (2) having the same polarity, a closing means (35; 35' ) for controlling the closing of the interrupting means when the rectifier (1) supplies the regulator (2), and an opening means (36; 36 ') for controlling the opening of the interrupting means (S; S' ) in response to an overcurrent in the load (CH).  2 - Protection device according to claim 1, characterized in that the interrupting means (S; S ') is a field effect transistor or an isolated gate, type IGBT, or MCT.  3 - Protection device according to claim 1 or 2, characterized in that the closing means (35; 35 ') comprises means (Rl, D6; Rl', D6 ') for charging a capacitor (C2; C2' ) by the voltage taken from the output of the rectifier (1) in order to close said interruption means (S; S '), and means (L2; L2') coupled at the input of the regulator (2) to maintain said capacitor charge (C2; C2 ').  4 - Protective device according to claim 1 or 2, characterized in that the closure means (35; 35 ') comprises  - a resistor (Rl; R1 ') and a diode (D6; D6') connected in series between said output terminal (13; 14) of the rectifier (1) and a control electrode (GS; GS ') of the means d 'interruption (S; S'),  - a capacitor (C2; C2 ') and a Zener diode (D7; D7') connected in parallel between the input terminal (23; 24) of the regulator and the control electrode (GS; GS '), and  - an auxiliary inductor (L2; L2 ') coupled to an inductor (L1) of the regulator (2) and at least one diode (D8) connected in series between the input terminal (23; 24) of the regulator and the electrode (GS; GS ').  5 - Protection device according to any one of claims 1 to 4, characterized in that the opening means (36; 36 ') comprises a first means (CCO; CCO') for detecting an overcurrent, a second means (R2, R3, C3; R2 ', R3', C3 ') to detect a voltage at the input terminals (23,24) of the regulator (2), and a means (T; T') controlled by the first and second means for detecting to open the interrupting means (S; S ').  6 - Protection device according to claim 5 characterized in that the means for detecting an overcurrent (CCO; CCO ') comprises a timer means (R7, C4; R7', C4 ') to delay the opening of the means of interruption (S; S ') in response to an overcurrent.  7 - Protection device according to claim 5 or 6, characterized in that the opening means is a field effect transistor (T; T ').  8 - Protection device according to any one of claims 5 to 7, characterized in that the means for detecting an overcurrent (CCO; CCO ') detects a pulse stop at the output of a means (22) included in the regulator (2) for controlling an regulating member (Q) of the regulator, in response to an overcurrent.  9 - Protection device according to any one of claims 1 to 8, characterized in that the opening means (36) comprises a flow diode (D10) between input terminals (23,24) of the regulator.