"VOLTAGE SHUNT REGULATOR FOR THE PROTECTION OF AN ELECTRICAL LOAD FROM OVERVOLTAGES AND VOLTAGE

TRANSIENTS"

TECHNOLOGICAL BACKGROUND OF THE INVENTION

Field of application

The present invention generally relates to the circuits for protecting electrical loads from overvoltages generated in electrical lines. In particular, the invention relates to a voltage shunt regulator for the protection of an electrical load from overvoltages and voltage transients.

Prior art

In an electrical line, it is known to use voltage regulators to protect an electrical load connected to the line from overvoltages.

Among the voltage regulators that can be used for these purposes, linear regulators comprise a regulation device connectable between the supply voltage source and the load to be protected, i.e. such regulators are installed in series to the electrical line. Commercially available linear regulators comprise, for example, regulators of the semiconductor, ferroresonant or switching type.

Such known linear regulators have considerable limitations .

Firstly, since all the electric power passes through the linear regulator to reach the load, such regulators installed in series to the electrical line have efficiency loss and aging phenomena due to Joule heating .

Secondly, such linear voltage regulators are not able to protect the load from voltage transients.

Thirdly, such linear voltage regulators are characterized by considerable costs, dimensions and weights .

SUMMARY OF THE INVENTION

It is the object of the present invention to devise and provide a voltage regulator, in particular a voltage shunt regulator to protect an electrical load from overvoltages and voltage transients generated in electrical lines, which allows to overcome the above limits which are typical of known voltage regulators.

Such an object is achieved by a voltage shunt regulator for the protection of an electrical load from overvoltages and voltage transients according to claim 1.

In particular, it is an object of the invention to provide a voltage regulator for the protection of an electrical load from overvoltages and voltage transients which is substantially free of distortions caused by parasitic effects and which ensures adequate protection to the electrical load both from the slow fluctuations of the line voltage and from fast voltage transients.

Preferred embodiments of such a voltage shunt regulator are described in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the voltage shunt regulator for the protection of an electrical load in an electrical line of the invention will become apparent from the following description of a preferred embodiment thereof, made by way of non- limiting example, with reference to the accompanying drawings, in which:

- figure 1 shows a block diagram of a voltage shunt regulator for the protection of an electrical load connected to an electrical line according to the present invention;

- figure 2 shows a first embodiment of some blocks of the voltage shunt regulator in figure 1;

- figures 3A—3E show, as a function of time, voltage waveforms applied to the voltage shunt regulator in figure 2; - figure 4 shows a second embodiment of some blocks of the voltage shunt regulator in figure 1.

In the above figures, elements which are equivalent or similar will be indicated by the same reference numerals.

DETAILED DESCRIPTION

With reference to figures 1, 2 and 4, a voltage shunt regulator for the protection of an electrical load LD from overvoltages or voltage transients present on an electrical line according to the invention is indicated as a whole with the reference numeral 1000.

In the following description, the voltage shunt regulator 1000 of the invention will also be referred to as a shunt regulator or simply regulator.

It is noted that the electrical load mentioned above represents a generic load connectable to a supply voltage source Vin by means of an electrical line which includes a first LI and a second L2 conductive line. For example, the supply voltage source Vin is the 230 V mains voltage.

In the present description, the term "overvoltage" is used to indicate slow voltage fluctuations present in the line (or Voltage Swell) . Such voltage fluctuations are, for example, caused by ON/OFF switching of a load and are of the order of milliseconds or seconds.

In the case of slow voltage fluctuations present on the line, the currents associated with these fluctuations, which can cross the regulator 1000, are of the order of hundreds of Amperes.

In the present description, the term "voltage transient" is used to indicate fast voltage variations, among which:

- line voltage spikes, either positive or negative, for example caused by lightning strikes;

- fast voltage oscillatory surges for example caused by relay switches present in the line;

- positive voltage notches, for example caused by switching of thyristors.

All of these voltage transients are of the order of microseconds .

It is noted that the currents associated with lightning strikes that the regulator 1000 can withstand are of the order of tens of thousands of Amperes. The currents associated with fast oscillatory surges and notches that can cross regulator 1000 are of the order of hundreds or even thousands of Amperes .

The voltage shunt regulator 1000 of the invention comprises a power circuit block or final power block 200 connectable between the first LI and the second L2 conductive lines of the electrical line. Therefore, in operating conditions, the power circuit block 200 of the regulator is connected in a shunt to the electrical line, i.e. it is connected in parallel to load LD .

Moreover, as will be better explained hereinafter, the power circuit block 200 of the voltage shunt regulator 1000 can be activated to limit the voltage applied to the electrical load LD, in case of overvoltages and voltage transients of the supply voltage, to a safety voltage V _LD . Such a power circuit block 200 comprises, in general, a switch circuit SW1 with threshold trigger connected in series to a voltage limiting circuit VL between the first LI and the second L2 conductive lines of the electrical line. In particular, such a switch circuit is a power switching device SW1 with threshold trigger, such a limiting circuit is a voltage limiting device VL.

Advantageously, the voltage shunt regulator 1000 of the invention comprises a circuit block 100 for detecting the supply voltage and driving the above power circuit block 200. In particular, such a detection and driving circuit block 100 is connectable to the electrical line between the supply voltage source Vin and the power circuit block 200.

The above supply voltage detection and driving circuit block 100 is configured to activate the power circuit block 200 upon the detection of a crossing of a preset voltage threshold VT by the supply voltage. In particular, with reference to figure 3A, such a crossing of the voltage threshold VT, configured to activate the power circuit block 200, corresponds to a variation in the supply voltage Vin from a first voltage level V having an absolute value lower than the absolute value of threshold VT to a second voltage level V ' having an absolute value greater than the absolute value of threshold VT .

Conversely, a crossing of the voltage threshold VT by the supply voltage Vin, from a voltage level having an absolute value greater than the absolute value of threshold VT to a voltage level having an absolute value lower than the absolute value of said threshold VT is configured to deactivate the power circuit block 200 of regulator 1000.

With reference to figure 1, the supply voltage detection and driving circuit block 100 of the voltage regulator 1000 comprises a circuit block 10 for detecting the supply voltage connectable to the first LI and to the second L2 conductive lines of the electrical line through a first 1 and a second 2 detection terminal, respectively.

Moreover, the detection and driving circuit block 100 comprises a command terminal 3 configured to connect the detection circuit block 10 to the power circuit block 200 of the shunt regulator 1000.

In addition, with reference to figure 2, the detection and driving circuit block 100 comprises a driving circuit block 30 connected to the command terminal 3. Such a driving block 30 is connectable to the second L2 conductive line of the electrical line through a third terminal 4 of the detection and driving circuit block 100.

In particular, such a driving circuit block 30 is configured to activate the power circuit block 200 upon the detection of the crossing of a preset voltage threshold VT by the supply voltage, as noted above.

As shown in figures 1, 2 and 4, the regulator 1000 of the invention, which comprises as a whole the circuit block 100 for detecting the supply voltage and driving the power circuit block 200, is connected in a shunt to the electrical line.

In one embodiment of the invention, the driving circuit block 30 comprises at least one threshold switching device XI having its own triggering voltage or a first triggering voltage V _TH related to the above- mentioned preset voltage threshold VT of the voltage regulator 1000. Advantageously, such a threshold switching device XI is of bidirectional type, i.e. adapted to be activated at the threshold for both positive values of the voltage applied thereto and for negative values of such a voltage.

In a more particular embodiment, such at least one threshold switching device XI comprises the above- mentioned third terminal 4 connectable to the second conductive line L2 of the electrical line and a switching device terminal 5 operatively connected to the command terminal 3. Such a threshold switching device XI is configured to be activated, i.e. to switch from a high impedance state (in which the device is substantially equivalent to an open circuit) to a low impedance state (in which such a device is substantially equivalent to a short-circuit) , when the absolute value of the voltage applied between the third terminal 4 and the switching device terminal 5 is greater than the triggering voltage V _TH .

It is noted that the number of threshold switching devices XI usable in the driving circuit block 30 depends on the line voltage. For example, for lines with a 230V voltage, the driving circuit block 30 comprises two threshold switching devices connected in series to each other.

For example, the threshold switching device XI of regulator 1000 is selected from the group consisting of:

- DIAC (Diode for Alternating Current),

- TRISIL,

- any bidirectional switching circuit made using discrete components.

With reference to figure 2, the driving circuit block 30 of the power circuit block 200 further comprises a first capacitor CI connected between the command terminal 3 and the terminal 5 of the threshold switching device XI . The capacity of the first capacitor CI is, for example, of the order of 10 nF and such a capacitor is configured to facilitate the activation of the power circuit block 200 upon the activation of the threshold switching device XI.

With reference again to figure 2, the circuit block for detecting the supply voltage 10 of the shunt regulator 1000 includes a compensated voltage divider. Such a compensated divider 10 comprises:

- a first impedance Zl connected between the first detection terminal 1 and the command terminal 3;

- a second impedance Z2 connected between the command terminal 3 and a first node Nl of the compensated divider;

- a third impedance Z3 connected between such a first node Nl and the second detection terminal 2.

Such a compensated divider 10 is configured to implement a proper division of the line voltage supplied by the supply source Vin also in the presence of transient phenomena, avoiding distortion caused by parasitic capacitances.

It is noted that the first node Nl of the compensated voltage divider 10 is directly connected to terminal 5 of the threshold switching device XI, i.e. such a threshold switching device XI is connected in parallel to the above-mentioned third impedance Z3 of the compensated divider 10.

With reference to figure 4, relating to a preferred embodiment of the voltage regulator 1000 of the invention, the compensated divider 10 is a resistive divider including a compensating capacity. In particular, the first impedance Zl of the compensated voltage divider 10 includes a first resistor R3 connected in parallel to a second capacitor C2.

Such a second capacitor C2 is selected according to the power switching device SW1 with threshold trigger of the power block 200 to be driven. Such a second capacitor C2 has a capacity from about 2 nF to 50 nF, for example.

Moreover, the second impedance Z2 of the compensated voltage divider 10 includes a second resistor Rl and the third impedance Z3 of the compensated voltage divider 10 includes a third resistor R2.

It is noted that the embodiment of regulator 1000 in figure 4 is particularly advantageous to protect load LD from overvoltages associated also with a direct component of the supply voltage of the electrical line.

With reference to any of one of figures 1, 2 and 4, the power switching device SW1 with threshold trigger of the power circuit block 200 of regulator 1000 is of bidirectional type. In particular, such a power switching device SW1 is selected, for example, from the group consisting of:

- a gas discharge tube or GDT,

- TRISIL,

- SIDAC (Silicon Diode for Alternating Current) .

With reference to the same figures, the voltage limiting device VL of the power circuit block 200 of regulator 1000 is selected, for example, from the group consisting of: - varistor or Voltage Dependent Resistor (VDR) ,

- Zener diode,

- TRANSIL.

The above-mentioned power circuit block 200 comprises a first power block terminal 6 connectable to the first conductive line LI, a second power block terminal 7 connectable to the second conductive line L2, and a third power block terminal connected to the command terminal 3.

In particular, the power switching device SW1 with threshold trigger is connected between the first power block terminal 6 and the third power block terminal 3. The voltage limiting device VL is connected between the third power block terminal 3 and the second power block terminal 7.

With reference to figures 3A-3E, an operating mode of the voltage shunt regulator 1000 of the invention will be described.

Such figures 3A-3E show, as a function of time, waveforms of voltages applied to the voltage regulator 1000, for example the regulator in figure 2, when the supply voltage supplied by source Vin to the electrical line is sinusoidal with constant frequency.

The above figures 3A-3E, for simplicity, only show the positive half-waves of the waveforms of the voltages applied to regulator 1000, but similar considerations also apply to negative half-waves.

In particular:

- figure 3A shows the waveform of the sinusoidal supply voltage Vin applied to the electrical line;

- figure 3B shows the waveform of voltage V ₅ _ ₄ applied to the threshold switching device XI, between terminals 5 and 4. V _TH is the own triggering voltage associated with the threshold switching device XI;

- figure 3C shows the waveform of voltage V ₆ _ ₃ applied to the power switching device SW1 with threshold trigger, between terminals 6 and 3. V' _TH is indicative of the respective triggering voltage or second triggering voltage of such a power switching device SW1;

- figure 3D shows the waveform of voltage V ₃ - ₇ applied to the voltage limiting device VL, between terminals 3 and 7;

- figure 3E shows the waveform of the above mentioned safety voltage V _LD applied to the electrical load LD when the regulator 1000 of the invention is active .

In addition, figure 3A shows the preset voltage threshold VT of regulator 1000 that is representative of the maximum voltage not to be applied to the electrical load LD .

Moreover, again with reference to figure 3A, a second voltage threshold or clamping voltage V _CL is representative of the maximum value of voltage V _LD applied to the electrical load LD through the regulator 1000 of the invention, as shown in figure 3E . It is noted that, in general, the above clamping voltage V _CL is lower than or at most equal to the preset voltage threshold VT .

Moreover, once the voltage threshold VT has been set, the triggering voltage V _TH associated with the threshold switching device XI can be expressed as a function of the preset threshold voltage VT by the formula :

V _TH (xl) = ¾ VT (1)

Z _j Z ₂ z^

In general, the values of the first Zl, second Z2 and third Z3 impedances of the detection circuit block 10 of the supply voltage are selected so that:

the voltage value between the command terminal 3 and the first node Nl, i.e. the voltage drop on the second impedance Z2, is about 1/10 of the voltage drop on the third impedance Z3, i.e. about 1/10 of the voltage value between the first node Nl and the second detection terminal 2; the voltage value between the first node Nl and the second detection terminal 2, i.e. the voltage drop on the third impedance Z3, is about equal to the voltage drop on the first impedance Zl, i.e. to the voltage value between the first detection terminal 1 and the command terminal 3.

Based on such a selection, the triggering voltage V _TH of the threshold switching device XI generally is in the range of 0.3VT - 0.5VT .

It is further noted that, by indicating with Vin _MA x the maximum voltage present on the line supplied by the supply voltage source Vin (which includes both the rated voltage of the line and any line tolerances), the voltage regulator 1000 is configured to satisfy the following relationship:

VinMAX < V' _TH (SWI) < VT (2) where V' _TH (SW1) indicates the above-mentioned triggering voltage of the power switching device SW1 included in the power circuit block 200.

From an operational point of view, in the presence of an overvoltage, the supply voltage Vin crosses the preset voltage threshold VT in the regulator 1000 from the first voltage level V lower than threshold VT to the second voltage level V ' greater than threshold VT, as shown in figure 3A. On the basis of the above equation (1) and as shown in figure 3B, such a crossing of the voltage threshold VT corresponds to exceeding the triggering voltage V _TH of the threshold switching device XI by voltage V ₅ - ₄ applied to such a device at a first instant t 1.

In such a case, the threshold switching device XI, which under normal conditions is in the high impedance state, switches to the low impedance state. Therefore, the voltage V ₅ _ ₄ applied to the threshold switching device XI between terminals 5 and 4 substantially instantly takes the value of zero and the third impedance Z3 of the compensated divider 10 is short- circuited .

At such an event at the first instant tl, as shown in figure 3C, voltage V ₆ -3 applied to the power switching device SW1 undergoes an increase which leads it to exceed the respective triggering voltage V' _TH of the power switching device SW1. The triggering or activation of the power switching device SW1 is facilitated by the first capacitor CI.

Once activated, the power switching device SW1 is configured to directly connect the first conductive line LI of the electrical line to the command terminal 3 of regulator 1000, i.e. to the voltage limiting device VL. In other words, assuming that the voltage drop on the power switching device SW1 is negligible in the active state, the line voltage Vin including the overvoltage is applied to the ends of the voltage limiting device VL, i.e. the supply voltage source Vin is connected in parallel to the voltage limiting device VL. To this ends, see the waveform of voltage V3-7 applied to the voltage limiting device VL, between terminals 3 and 7 (figure 3D) .

Thereafter, the voltage limiting device VL is configured to release the excess energy associated with the overvoltage on the electrical line itself, limiting the safety voltage V _LD applied to load LD to the clamping voltage value V _CL as shown in figure 3E . Thereby, the regulator 1000 of the invention protects the electrical load LD from overvoltage.

At the end of the overvoltage on the line, i.e. when the supply voltage Vin crosses the preset voltage threshold VT at a second instant t2, the threshold switching device XI is deactivated, returning to the high impedance state. The deactivation of the power switching device SW1, which returns to the high impedance state to decouple the first conductive line LI from the voltage limiting device VL occurs when the supply voltage supplied by source Vin crosses the clamping voltage threshold V _C L at the third instant t3. Thereby, the whole voltage regulator 1000 is deactivated.

While the above operating example makes explicit reference to an overvoltage, the regulator 1000 of the invention allows to protect the electrical load LD from voltage transients in a totally similar manner.

As can be seen, the object of the present invention is fully achieved by the voltage shunt regulator 1000 for the protection of an electrical load LD from overvoltages and voltage transients described above in its structural and functional features .

In particular, since the voltage regulator 1000 of the invention is connected in a shunt to the electrical line, such a regulator 1000 is substantially immune from aging and efficiency loss phenomena due to heating by Joule effect which affect the known regulators installed in series to the electrical line.

Moreover, it is noted that since the threshold switching device XI is bidirectional, the regulator 1000 of the invention is adapted to operate both for positive polarity of the supply voltage Vin and for negative polarity of such a voltage. In addition, through the circuit block 10 for detecting the line supply voltage, the regulator 1000 of the invention is adapted to substantially continuously monitoring voltage Vin on the line, reducing the activation time of the threshold switching device XI. This ensures adequate protection to the electrical load LD from both slow line voltage fluctuations and from fast voltage transients.

Since the voltage regulator 1000 of the invention is configured to activate only at overvoltages and voltage transients on the line, such a regulator 1000 has no insertion losses that serial type regulators instead have. In other words, the regulator 1000 of the invention allows to preserve the efficiency of the supply chain of load LD .

Finally, compared to known regulators, the regulator of the invention ensures reduced weights, dimensions and costs.

Those skilled in the art can make several changes, adaptations and replacements of elements with others which are functionally equivalent to the embodiments of the above-described voltage shunt regulator for the protection of an electrical load from overvoltages and voltage transients, in order to meet contingent needs, without departing from the scope of the following claims.

Each of the features described as belonging to a possible embodiment can be obtained independently of the other embodiments described.