FR2785735A1 - Non inductive low power electrical supply device, has storage capacitor charged from alternating rectified supply, via switching device - Google Patents

Abstract

The supply comprises a storage capacitor which is charged by a rectified alternating supply, via a switching device. The device is designed to supply a load with a direct current voltage (Vout) from a storage capacitor (12) fed from an rectified alternating high voltage source (Vin). The capacitor (12) receives the rectified voltage (Vin) via a switch (18), without the imposition of an inductive circuit. The switch (18) is controlled by a bi-stable device (24) connected to a opening unit (26), so as to open the switch (18) when the capacitor output voltage (Vout) exceeds a pre-determined level (V1). A closing unit (28), also connected to the bi-stable device (24), closes the switch (18) when the rectified voltage (Vin) exceeds a second pre-determined level (V2). An internal supply unit (22) is fed from the potential difference between the rectified voltage (Vin) and the output voltage (Vout). The bi-stable device (24) and the opening unit (26) are fed from the potential difference (VC1) between the voltage from the unit (22) and the output voltage (Vout). The closing unit (28) is fed from the voltage produced by the internal unit (22).

Description

LOW POWER WITHOUT INDUCTANCE

  The present invention relates to the field of conver-

  Power weavers of the switching power supply type which use a switch to cut a rectified alternating voltage in order to charge a storage capacitor supplying a direct voltage. The invention relates more particularly to non-isolated power converters, step-downs

  voltage and applies to a supply circuit under a voltage

  low voltage in front of the rectified alternating voltage of a load

of low power.

  FIG. 1 represents a classic example of a switching power supply circuit 2. This circuit comprises, in series between two terminals subjected to a rectified alternating voltage, a

  switch 5, an inductor 7 and a storage capacitor 4.

  The control terminal of switch 5 receives a signal produced by a control circuit 6 whose role is to regulate, by

  pulse width modulation (PWM) for switching closure

  tor 5, the value of the output voltage Vout so that it corresponds to a predetermined value. A freewheeling diode 8 is connected in parallel with the capacitor 4 and the inductor 7, to suppress the appearance of overvoltages in the inductor 7 during switching operations. The structure and operation of circuit 2 are well known and they will not be detailed further.

  The disadvantage of such a circuit is that it cannot

  be integrated easily, for example on a silicon chip, due to the presence of an inductor, all the more

  more than the rectified voltage is most often from the sec-

  (220 or 110 volts), which requires the use of a

  high value inductance (of the order of 1 mH).

  An object of the present invention is to provide a switching type supply circuit which is easy to

  integrate, even if it must receive a rectified alternating voltage

high.

  One solution would be to remove the inductor 7 and the freewheeling diode 8. This solution is, in practice, not possible in a circuit as shown in FIG. 1. Indeed, it would lead to significant overcurrents during closings. multiples (frequency of several kHz) of the switch at each half-wave, due to the large difference in amplitude between the desired voltage Vout (generally less than 50 volts) and the rectified voltage (generally 110 to 220 volts). The role of inductance 7 is precisely to suppress the appearance of

  overcurrents in capacitor 5 during switching.

  The invention aims to propose a new solution which

overcomes this drawback.

  Thus, an object of the present invention is to provide

  ser a switching type supply circuit which does not include any inductive element while minimizing overcurrents in

the storage capacitor.

  The invention aims, in particular, to provide a solution

  tion that is suitable for operation on the sector.

  The invention also aims to propose a supply circuit

  statement providing, at the terminals of a storage capacitor,

  a DC voltage at a load consuming a low power-

sance.

  To achieve these objects, the present invention pre-

  sees a circuit for supplying a load with a direct voltage supplied by a storage capacitor from a rectified alternating voltage of high amplitude in front of the desired value for said direct voltage, which comprises means for charging the capacitor to the more once alternately at

  neighborhood of the beginning of the alternation.

  According to an embodiment of the present invention, the capacitor receives the rectified voltage via

  of a switch, without interposition of inductive element.

  According to an embodiment of the present invention,

  the switch is controlled by a bistable.

  According to an embodiment of the present invention, the supply circuit comprises an opening block connected to the bistable to open the switch when the voltage at

  capacitor terminals exceeds a first predeter-

  undermined. According to an embodiment of the present invention, the supply circuit includes a connected closure block

  at the bistable to close the switch when the voltage

  sée exceeds by a second predetermined voltage the voltage at

capacitor terminals.

  According to an embodiment of the present invention, the supply circuit includes an internal supply unit

  powered by the potential difference between the alternating voltage

  rectified voltage and the output voltage, said bistable and said opening block being supplied by the potential difference between the voltage produced by the internal power supply and the output voltage, and said closing block being supplied

  by the voltage produced by the internal power supply.

  According to an embodiment of the present invention, the supply circuit comprises a starting block supplied by said potential difference between the voltage produced by the internal supply block and the output voltage, and connected to the bistable to open the switch when said potential difference between the voltage produced by the internal power supply unit and the output voltage is less than

  a third predetermined voltage.

  According to an embodiment of the present invention, the supply circuit comprises a first protection block, connected in parallel with a measurement resistor situated between the switch and the capacitor, and connected to the bistable for

  open the switch when the voltage across the resistor

  measurement tance is greater than a fourth voltage

predetermined.

  According to an embodiment of the present invention, the supply circuit includes a second protection block, connected to the terminals of the capacitor to limit the voltage of

  output at a fifth predetermined voltage.

  According to an embodiment of the present invention, the supply circuit comprises an RC filter connected to the

switch control terminal.

  These and other objects, features and advantages of the present invention will be discussed in detail in

  the following description of particular embodiments

  made without implied limitation in relation to the attached figures among which: FIG. 1 described previously is intended to expose the state of the art and the problem posed; Figure 2 is a block diagram of a first mode of

  realization of a supply circuit according to the present invention

  tion; FIG. 3 illustrates, in the form of chronograms, the operation of the circuit of FIG. 2; Figure 4 is a block diagram of a second mode of

  realization of a supply circuit according to the present invention

  tion; FIG. 5 represents a detailed electrical diagram of an embodiment of the circuit of FIG. 4; and FIG. 6 illustrates, in the form of chronograms, the

  operation of the circuit of figure 5.

  In FIGS. 1 to 6, the same references designate the

same elements.

  A characteristic of the present invention is to provide a circuit for supplying a load with a direct voltage supplied across the terminals of a storage capacitor which does not include an inductive element. To avoid the problems of overcurrent and overvoltage, means are provided to limit the voltage at which the charging of the storage capacitor begins. According to the invention, these means have the characteristic of not introducing a dissipative element (as would be the case of a resistor inserted in series with the capacitor). A characteristic of the invention is to organize the charge of the storage capacitor at the start of each alternation of the

  supply voltage rectified and only once per alter-

  nance. FIG. 2 schematically represents, in the form of blocks, a first embodiment of a supply circuit according to the present invention intended to supply a load (not shown) by a voltage Vout taken from the terminals of a

storage capacitor 12.

  The capacitor 12 is connected in series with a conmmu-

  tator 18, between a positive terminal 14 and a reference terminal 16 for applying a rectified alternating voltage Vin. If necessary, a protective resistor 20 is inserted upstream of

  the positive terminal 14. A power supply unit (POW) 22 of a circuit

  the control circuit 10 of the switch 18 is supplied between the first terminal 14 and the midpoint of the series association of the switch 18 and of the capacitor 12, constituting a terminal

  output 23 delivering the voltage Vout.

  The circuit 10 includes a bistable circuit 24, supplied between an internal supply terminal 25 at the output of the block 22 and the output terminal 23. The role of the circuit 24 is to close and

  open switch 18 when it is, for example,

  active and inactive. An opening block 26, supplied between terminal 25 and terminal 16, is connected to bistable 24 to deactivate it when the voltage Vout exceeds a first predetermined voltage Vi. A closing block (CL) 28, supplied between terminal 25 and terminal 23, is connected to the bistable 24 to activate it as soon as the voltage Vin exceeds the voltage Vout by one second

predetermined voltage V2.

  FIG. 3 illustrates, in the form of timing diagrams, the operation of the circuit of FIG. 2. These timing diagrams respectively represent the rectified alternating voltage Vin supplied between terminals 14 and 16, the current I passing through the

  switch 18 and the voltage Vout across the capacitor 12.

  The voltage Vin represented here is a rectified voltage in

double alternation.

  During the first alternation shown, we consider

  dere that one is at the start of the circuit and that the capacitor 12 is not charged (Vout = 0). When the voltage Vin exceeds the voltage Vout by a voltage V2 (instant t2), the closing circuit 28 controls the bistable 24 to close the switch 18. For reasons of simplification, we choose

  here a voltage V2 equal to 0 volts, which constitutes an optimal case

  wrong. The capacitor 12 charges until the voltage Vout

  reaches the voltage V1 (instant tl). So the opening circuit

  ture 26 controls the bistable 24 to open the switch 18, and

  the capacitor 12 discharges through the charge which it supplies

lie.

  The current I passing through the switch 18 increases suddenly-

  only when the switch is closed, then decreases when the capacitor 12 is charged and is canceled when the switch is open. It should be noted, however, that the sudden growth of the current when the switch is closed does not constitute an annoying overcurrent due to the low voltage Vin at this instant. In addition, the resistor 20 contributes to limiting the current flowing in the switch 18. Unlike the closings of a conventional switching power supply which take place over the entire alternation, therefore under high voltage, the closure (single by alternation ) of the invention is carried out as close as possible to the start of the alternation (ideally as soon as the voltage Vin exceeds

the voltage Vout).

  The charge of the circuit consuming a low power, the capacitor 12 does not discharge completely and at the start of the second half-wave of the voltage Vin, the voltage Vout is not

not zero.

  During the second half-cycle, the charge of the condensa-

  tor 12, triggered by the closing circuit 28 when the voltage Vin exceeds the value Vout + V2, begins later than during the first half-wave. The charge continues until the voltage Vout exceeds the voltage V1. The capacitor 12 then discharges until the switch 18 is again

  closed, at the start of the next alternation, and so on.

  In the example shown, the power consumption of the circuit load is such that the voltage Vout across the capacitor changes between a maximum value Vl and a minimum value from the third half-wave. The voltage V1 is chosen to be relatively low in order to optimize the regulation of the voltage Vout at the desired value. The voltage V2 is chosen to be as low as possible, not only for the regulating objective, but above all to minimize the voltage Vin on closing, therefore

  the peak currents of each half-wave. During each alter-

  nance, the capacitor 12 is charged for a very short time relative to the duration of an alternation, therefore relative to the

  time during which it discharges in the charge which it

  lie. Thus, the present invention is more particularly intended to supply loads consuming a low power at a low voltage. The scales of the curves have not been respected for reasons of clarity, and the difference between the maximum and minimum values of the voltage Vout is small before

the voltage Vl.

  FIG. 4 represents, in the form of blocks, a second embodiment of a supply circuit according to the present invention. This embodiment incorporates the elements of the circuit of FIG. 2 and also includes security functions.

  A starter block (LP) 36, powered by the diff

  potential reference between the internal supply terminal 25 and the output terminal 23, is connected to the bistable 24 to force the opening of the switch 18 when its supply voltage

  Vin drops below a third predetermined voltage V3.

  A first protection block (SC) 38 is connected in

  parallel with a measuring resistor 40 placed between the commu-

  tator 18 and the capacitor 12. The protection block 38 is connected to the bistable 24 to force the opening of the switch 18 if the voltage across the measurement resistor 40 exceeds

  a fourth predetermined voltage V4.

  A second protection block (OV) 42 is connected in parallel with the capacitor 12 to limit the voltage of

  Vout output at a fifth predetermined voltage V5.

  A filter (FIL) 44, connected to the output terminal 23, is connected to the control of the switch 18 to filter possible

  parasites capable of causing unexpected switching

switch 18.

  An emergency resistor 46 is connected between terminals 14 and 16 to create a non-capacitive current loop and eliminate any interference in the circuit when none

  load is only connected across the capacitor 12.

  The bistable 24 is supplied, like block 36, between

  terminals 25 and 23, and the voltage levels of the pro-

  produced by the bistable 24 depend on its supply voltage.

  The predetermined voltage V3 of the block 36 is chosen so that the switch 18 is systematically opened when the supply voltage of the bistable 24 becomes too low. This avoids knowing the switch 18 by signals having low voltage levels and which could lead to undesired operation. For example, if switch 18 is a MOS transistor and it is ordered to close with too high voltage levels

  weak, undesirable linear operation can be obtained.

  The measurement resistance 40 is of very low value, and the predetermined voltage V4 is chosen to correspond to a maximum current in the switch 18 and the capacitor 12. The predetermined voltage V5 is chosen as a function of the maximum voltage that the capacitor can withstand and the

load which it must supply.

  FIG. 5 represents a diagram of an embodiment

  tion of the circuit of FIG. 4. The internal power supply unit 22 comprises, in series between the output terminal 23 and the terminal 14, a resistor 223 and a capacitor 221, a Zener diode 222 being connected in parallel to the capacitor 221 The Zener diode fixes a value VCI of internal supply voltage supplied by the capacitor 221. The resistor 223 serves to limit

  the charging current of capacitor 221 and absorb the diff-

  potential reference between terminals 14 and 25.

  The bistable 24 is, for example, an RS flip-flop formed by a first NAND gate 241 whose output is connected to a first input of a second NAND gate 242. The output of

  door 242 is connected to a first input of door 241.

  The second entrances to doors 241 and 242 respectively constitute

  The inputs S and R of the RS flip-flop 24. The output of gate 241 constitutes the output Q of the flip-flop. The doors 241 and 242 are supplied by the voltage VCI and are therefore referenced to the voltage Vout. Thus, when the flip-flop 24 is deactivated, the

  terminal Q will be at voltage Vout and when the rocker will be activated

  terminal, terminal Q will be at a voltage Vout + VCI.

  The opening block 26 preferably comprises a non-inverting amplifier 261 (for example made up of two NAND gates in series), connected in series with a resistor 264 between the cathode of a diode 263 and the midpoint a resistive divider bridge 265, 265 ', connected between terminal 25 and, via a potentiometer 266, terminal 16. The anode of

  diode 263 is connected to input R of bistable 24 and a resistor

  tance 262 is placed in parallel on the amplifier 261.

  The amplifier is supplied by the VCI voltage and referenced to the

  Vout tension. Thus, a low logic state at the output of the amplifier

  cator 261 corresponds to a voltage Vout and a high logic state at the output of amplifier 261 corresponds to a voltage Vout + VCI. The closing block 28 preferably comprises a bipolar transistor 281 of the NPN type, the emitter of which is connected to the output terminal 23 and the collector of which is connected to the

  terminal 25 via a resistor 282. A condensa-

  tor 283 also connects the collector of transistor 281 to terminal S of the bistable and a resistor 284 connects this terminal S to terminal 25. The base of bipolar transistor 281 is connected to the midpoint of a resistive divider bridge 285, 285 'connected Between

terminal 23 and terminal 14.

  The starting block 36 includes two bipolar transistors

  NPN 361 and 362 type laires whose respective transmitters are

  connected to the output terminal 23 and whose collectors respect

  tifs are connected to the internal supply terminal 25 via resistors 363 and 364 respectively. The base

  of transistor 361 is connected, via a resistor

  tance 365, at the midpoint of a series association of a Zener diode 366 and a resistor 365 ′, connected between terminal 23 and terminal 25, the cathode of diode 366 being connected to terminal 25. L the anode of a diode 367, the cathode of which is connected to the base of transistor 362, is connected to the collector of transistor 361. A resistor 368 connects the base of transistor 362 to the

output terminal 23.

  The first protective block 38 includes a dividing bridge

  resistive sor 381, 381 ′ connected in parallel with the measurement resistor 40. The anode of a diode 382, the cathode of which is connected to the base of transistor 362, is connected to the midpoint of this

divider bridge.

  il The protective block 42 comprises a Zener diode 42 whose anode is connected to terminal 16 and whose cathode is

connected to the output terminal 23.

  The filter 44 includes a resistor 441 connected between the output of the bistable 24 and the control terminal of the switch 18 (the gate of the MOS transistor), a capacitor 442 being connected between this control terminal and the terminal of

exit 23.

  FIG. 6 illustrates the operation of the circuit of the

  figure 5. It represents, in the form of chronograms, an example

  ple of current I281 and voltage V281 of transistor 281, and of the respective voltages V286, VQ, VA and VB at node 286,

  at the output Q of the bistable 24 and at nodes A and B, for two alter-

  nances of the rectified alternating voltage Vin applied between terminals 14 and 16. When this rectified voltage exceeds by a value V2 the voltage Vout (instants t2), the divider bridge 285, 285 ′ sees a voltage V2. The values of the resistances of the bridge 285, 285 ′ are chosen for, when it is subjected to a

  voltage higher than V2, put transistor 281 in conduction.

  When the transistor 281 goes into conduction, the voltage across the capacitor 283 is zero and the point 286 is brought to

  the reference voltage of transistor 281, i.e. the voltage

  Zout Vout. This activates the bistable 24 which was previously inactive. The output voltage VQ of the bistable 24 goes high (Vout + VCI). The transistor 281 being always activated, the capacitor 283 charges through the resistor 284 until the voltage across its terminals is equal to the voltage VCI. As the capacitor 283 charges, the voltage of the node 286 increases from the voltage Vout to the voltage Vout +

  VCI (instants t3), then stabilizes. When, at the end of the alter-

  nance, the rectified voltage Vin drops below the voltage Vout + V2 (instants t4), the transistor 281 is blocked and the capacitor 283 is discharged through the resistors 282 and 284. The discharge of the capacitor 283 through the resistor 284 creates an overvoltage on node 286, the voltage of which returns to the value Vout + VCI when the capacitor 283 discharges (instants t5). The value of this overvoltage is limited, by

  example, by a diode protection device (not shown

  sensed) conventionally connected to terminal S of bistable 24.

  The voltage between the divider bridge 265, 265 'and the potentiometer 266 is equal to 1 / 2VCI + Vout. When the voltage Vout increases, the voltage across each of the resistors of the bridge 265, 265 'and of the potentiometer 266 increases. The voltage VA decreases when the voltage increases across the resistors of the divider bridge 265, 265 '. The amplifier 261 is supplied by the voltage VCI (therefore referenced on the voltage Vout), and it is designed to provide a high or low output depending on whether its input terminal is subjected to a voltage higher or lower than VCI / 2. The divider bridge 265, 265 ′ and the potentiometer 266 are provided so that the voltage VA becomes lower than Vout + VCI / 2 when the voltage Vout exceeds the predetermined voltage V1 (instant tl). In this case, the amplifier 261 provides a low output, that is to say equal to Vout. A current then flows to

  across resistor 262 and the voltage VA is lowered suddenly-

  below the value Vout + VCI / 2. This voltage drop creates a hysteresis on the input of amplifier 261 and prevents its output from oscillating. When the output of the amplifier 261 is brought to the voltage Vout, the bistable 24 is inactive, and the voltage VQ becomes again equal to Vout. The switch 18 is then open, the capacitor 12 begins to discharge and the voltage Vout begins to decrease, as does the voltage across the resistors of the divider bridge 265. The decrease in this latter voltage increases the voltage VA . When the voltage VA reaches the value Vout + VCI / 2, the amplifier 261 outputs a high voltage, equal to Vout + VCi. It will be noted that when the voltage VA is equal to the value Vout + VCi / 2, the voltage of the midpoint of the divider bridge 265, 265 ′ has a value equal to Vout + VCi / 2 increased by the voltage due to the

  current which then flows through resistor 264. When the amplifier

  cator supplies a high voltage, the current changes direction in the resistor 262 and the voltage VA increases suddenly (instants t6). This increase in voltage creates hysteresis and prevents the output of amplifier 261 from oscillating. VA voltage

  then increases as the capacitor 12 discharges.

  The potentiometer 266 makes it possible to adjust the value of V1. It will be noted that the curves of FIG. 6 represent a constant voltage Vout whereas we have seen in relation to FIG. 2B that the voltage Vout oscillates between a minimum value and the value V1. For reasons of clarity, the scales have not been respected, in particular for the variations of the voltage VA which are proportional to the variations of the voltage Vout.

  The starting block 36 operates as follows:

  boast. The Zener diode 366 and the resistor 365 'are subjected to the

  VCI voltage. The Zener diode 366 is chosen to be in conduct-

  tion as long as the voltage VCI is greater than a predetermined voltage V3. If the VCI voltage drops below V3, the

  Zener 366 diode is blocked and the current is canceled in the resistors

  tances 365 and 365 '. The base of the bipolar transistor 361 is then brought to the voltage Vout, which constitutes its reference voltage, and the transistor 361 is open. A current then flows through the resistors 363 and 368 through the diode 367, the base-emitter voltage of the bipolar transistor 362 increases and the transistor 362 enters into conduction, which activates the terminal R of the bistable 24. Thus, the device 36 controls the bistable 24 to open the switch 18 when the voltage VCi

  drops below a predetermined voltage V3.

  The operation of the protective block 38 is as follows

  boast. The values of the resistors 381 and 381 ′ are chosen so as to close the transistor 362 by means of the diode 382 when the voltage across the terminals of the measurement resistance 40 exceeds a predetermined value V4. Thus, the block 38 makes it possible to control the bistable 24 to open the switch 18

  when a too strong current crosses it.

  The filter 44 makes it possible to suppress the voltage peaks which could be generated on the control of the switch 18, for example by voltage peaks introduced by noise on the rectified alternating voltage or by the overvoltages of the closing block 28, as has was previously described. The circuit of Figure 5 is particularly suitable

  to be integrated, but it can also be made as a component

  discrete health, depending on the technologies available and the power that you want to provide to the load. If we consider an embodiment in discrete components, doors 241 and 242

  of the bistable 24 as well as the non-inverting amplifier 261 may

  can be obtained by connecting the elements of a circuit, for example an SGS-Thomson HCF40M, comprising four NAND gates. Amplifier 261 will then be produced by connecting two NAND gates in series, the inputs of which are connected together, including

this is shown in Figure 5.

  As a particular embodiment, a circuit

  cooked as described in connection with FIG. 6, intended to be supplied by the 220-volt sector and to supply a voltage

  Vout between 0 and 25 volts, can be achieved using the following values for the various components:

368: 1 MQ

  282: 150 kQ 12: 1000 Of 16 volts 221: 47 Of 16 volts 283, 442: 1 nf: 22 223: 68 k.2 285: 560 kQ 285 ', 284, 265, 365, 365', 441: 47 kQ

381: 150 Q

381 ': 220 Q

  363, 364, 46: 150 k 2 264: 4.7 kQ 265, 265 ': 10 kQ

262: 1M

1 Q

  366: 8.2 volts 266: 47 kf 222: 10 volts Of course, the present invention is susceptible of various variants and modifications which will appear to the person skilled in the art.

  job. Thus, the preceding descriptions correspond to a

  supply circuit which receives a rectified alternating voltage

  seated in double alternation, but those skilled in the art will easily adapt them to a voltage rectified in single alternation. Of

  even, the bistable 24 and the amplifier 261 may have no

  carries what equivalent operating structure.

Claims (10)

  1. Circuit for supplying a load with a direct voltage (Vout) supplied by a storage capacitor (12) from a rectified alternating voltage (Vin) of high amplitude in front of the desired value for said direct voltage, characterized in that it includes means (22, 24, 26, 28, 18) for charging the capacitor at most once alternately at   neighborhood of the beginning of the alternation.   2. Supply circuit according to claim 1, characterized in that the capacitor (12) receives the rectified voltage (Vin) via a switch (18), without interposition of inductive element.   3. Supply circuit according to claim 2, characterized in that the switch (18) is controlled by a bistable (24).   4. Supply circuit according to claim 3, characterized in that it comprises an opening block (26)   connected to the bistable (24), to open the switch (18) when   that the voltage (Vout) across the capacitor (12) exceeds one   first predetermined voltage (Vl).   5. Supply circuit according to claim 3 or 4, characterized in that it comprises a closing block (28) connected to the bistable (24) to close the switch (18) when   the rectified voltage (Vin) exceeds by a second predefined voltage   completed (V2) the voltage (Vout) across the capacitor (12).   6. Supply circuit according to claims 3 to   , characterized in that it comprises an internal power supply unit (22) supplied by the potential difference between the rectified alternating voltage (Vin) and the output voltage (Vout), said bistable (24) and said power unit opening (26) being supplied by the potential difference (VCI) between the voltage produced by the internal power supply (22) and the output voltage,   said closure block (28) being supplied by the tension   ion produced by the internal power supply.   7. Supply circuit according to claim 6, characterized in that it comprises a starting block (36) supplied by said potential difference (Vci) between the voltage produced by the internal supply block (22) and the output voltage (Vout), and connected to the bistable (24) to open the switch (18) when said potential difference between the voltage produced by the internal power supply and the output voltage is less than a third voltage predetermined (V3).   8. Supply circuit according to claim 6 or 7, characterized in that it comprises a first protective block (38), connected in parallel with a measurement resistor (40) located between the switch (18) and the capacitor (12), and connected to the bistable (24) to open the connector when the voltage across the measurement resistance is greater than   a fourth predetermined voltage (V4).   9. Supply circuit according to any one of   Claims 6 to 8, characterized in that it comprises a second   protection block (42), connected to the terminals of the capacitor (12), to limit the output voltage (Vout) to one fifth predetermined voltage (V5).   10. Supply circuit according to any one of   Claims 6 to 9, characterized in that it comprises a filter   RC (44) connected to the switch control terminal (18).