DESC:TECHNIAL FIELD

[001] The present subject matter described herein, in general, relates to voltage clamping circuit and more particularly to an improved system and method for clamping of high input voltage for a three phase switch mode power supply (SMPS).

BACKGROUND

[002] An electrical switching device may be defined as a unit designed to connect, carry and disconnect electrical supply so as to protect the equipments connected in the electrical circuit from damage caused by overload, under-voltage or short circuit etc. Circuit breakers are well-known electrical switching devices, used to provide automatic circuit interruption or tripping of the circuit breaker, when circuit fault conditions occur. Conventionally, the circuit breaker uses current transformer for powering up the trip unit and also as a means for sensing the phase current. The circuit breaker includes additional earth leakage module to provide low-level ground fault sensing and relaying functions so as to protect equipment, reducing downtime from damage due to ground faults.

[003] The earth leakage module for circuit breaker takes power directly from mains voltage. The mains voltage may be a single phase voltage (starting from 85 Volts to 265Volts) or three phase voltage which may be of the value 690 Volts (V) or higher. For single phase voltage application, that may be operation within the voltage range of 85V to 265V, alternating current (AC) offline converters are used. This AC offline converter is switched mode power supply working directly with mains voltage and enables conversion of high voltage to a low voltage for powering a unit.

[004] The AC offline converters may either be isolated or non-isolated. In certain devices where mechanical isolation protect the user and service personnel from contact with hazardous voltages and which require very lower power to operate(<2W) non –isolated devices are preferred. For non-isolated power supply, buck and buck –boost regulators are used since such regulators uses less printed circuit board (PCB) area and involves a cost effective design than conventionally used fly-back regulators.

[005] However, when the AC offline convertors are not functional when used with three phase voltages which may be of the value 415 V or high. The problem with the AC offline converters is that, maximum operating voltage range that the devices is enabled to withstand is around 600 to 700V. When three phase voltage is applied directly to the AC offline converters, the input voltage accelerates than the required voltage for the offline convertors. Thus there is a need for a clamping device so as to limit the voltage to safe working levels for offline converters specifically, in three phase star and delta circuits.

[006] Also, for three phase power supply if power required for electronic circuit is large then fly-back topology is normally a preferred choice. But in application where the required power is very small (<2W), then non-isolated topology is used. In case of fly-back topology, if a switcher integrated circuit (IC) is used then stack field effect transistor (FET) technique is used which protect the switcher IC from getting damaged. But this technique does not work in case of non-isolated topologies. So when non-isolated topologies are used for three phase power supply, an improved voltage clamping circuit is required to clamp the input voltage higher than 360V.

[007] The prior art document, US20130321055A1 discloses a voltage clamp circuit wherein an output voltage equals an input voltage for at least a portion of a first range of input voltages, and where the output voltage is less than the input voltage for at least a portion of a second range of input voltages.

[008] The prior art document, US5943200A discloses a peak voltage clamping circuit for high frequency boost converter and method of operation thereof for use in a boost converter having a main boost switch, a boost inductor, a boost diode coupled to the boost inductor and the main boost switch and a resonant, passive snubber coupled to the boost inductor and the main boost switch that limits reverse recovery currents in the boost diode during a turn-on of the main boost switch, a peak voltage clamping circuit for, and method of, reducing voltage stress on the main boost switch caused by operation of the snubber. In one embodiment, the circuit includes a blocking switch and a zener diode, coupled in series between the main boost switch and the boost diode, that cooperate to provide a conductive path from the main boost switch to an output of the boost converter for electrical currents that exceed a predetermined peak voltage value thereby to reduce the voltage stress on the main boost switch.

[009] Conventionally, the voltage clamping circuit with three phase voltage that works on the principle of charging the capacitor up to a certain threshold voltage and then limiting that voltage by opening the current path to charge the capacitor by using a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET). As illustrated in figure 1, for all the input voltages less than the threshold level MOSFET (M1) is turned ON. But current only flows when the input voltage is greater than the capacitor voltage. The resistors (R1 and R2) decide the peak threshold level of voltage that the capacitor can hold. In an event when the input voltage is greater than the threshold level, a transistor (Q1) turns ON, which enables the gate to source voltage of (M1) to be zero thereby turning off the MOSFET. As the MOSFET is open or turned off, the current path required by the capacitor to charge is open and thus the capacitor stops charging. However, such principle works well in case of single phase applications where the input voltage returns to zero after every half cycle in case of a bridge rectifier. If this same circuit is powered from 3 phase star or delta power supply, the output of bridge rectifier does not return to zero since in one complete cycle, all the six diodes will turn ON at certain periodic levels. As illustrated in figure 2, the 1st waveform shows that gate to source is almost zero. So the MOSFET is open or turned off and thus entire input voltage is dropped across the MOSFET as illustrated in the second waveform. Thus, since the current path is open, the capacitor is also not charged as illustrated in the third waveform.

[0010] Thus, in view the hitherto drawbacks of the existing voltage clamping circuit with three phase input voltage, three exists a dire need for an improved voltage clamping circuit that enables efficient clamping of higher input voltages in non-isolated three phase voltage supply.

SUMMARY OF THE INVENTION

[0011] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[0012] The main object of the present invention is to provide an improved system for voltage clamping and a method thereof that obviates the above mentioned drawback of the voltage clamping circuit.

[0013] Another object of the present invention is to provide an improved voltage clamping circuit that efficiently limits the input voltage of a three phase power supply, below a threshold value thus making a path for a current to flow for charging a capacitor

[0014] In one implementation, the present invention provides a clamping circuit specifically for non-isolated power supplies powered from three phase voltages. This circuit operates after a threshold is reached by charging a capacitor up to certain threshold value and the output voltage is clamped to that voltage level even if the input voltage is increased.

[0015] In one implementation, the present invention provides an improved voltage clamping circuit specifically for non-isolated power supplies powered from three phase voltages. This circuit operates after a threshold is reached and the output voltage is clamped to that voltage level even if the input voltage is increased. This threshold can be set according to the switcher IC safe operating voltage levels.

[0016] In one implementation, the present invention provides an improved voltage clamping circuit wherein the input voltage is clamped below a threshold voltage so as to turn ON a MOSFET thus making a path for a current to flow for charging a capacitor.
[0017] Accordingly, in one implementation, a voltage clamping circuit for limiting a voltage passing through an electric circuit is disclosed. The voltage clamping circuit comprises at least one bridge rectifier comprising at least one diode connected to at least one voltage source, wherein if an input voltage value detected by at least one resistors exceeds a pre-defined threshold voltage value at least one mosfet is adapted to turns ON thereby making a path for a current to flow for charging at least one capacitor and limiting the voltage passing through the electric circuit.

[0018] In one implementation, a voltage clamping circuit for limiting a voltage passing through an electric circuit is disclosed. The voltage clamping circuit comprises at least one bridge rectifier having at least one first set of diodes (D1, D2, D5, D6) connected to a first set of voltage sources (V1, V2), and at least one second set of diodes (D3, D4, D7, D8) connected to a second set of voltage sources (V3, GND).The voltage clamping circuit achieves technical advancement by enabling the circuit if V1, V2 and V3 voltages are phase shifted by 120 for a particular amount of pre-defined time period only D1 and D2 are adapted to turn ON from OFF state, thereby clamping an output voltage to a pre-defined threshold voltage decided by at least one set of resistors R1 , R2 ,R3 and R4.

[0019] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0020] Figure 1 illustrates a circuit diagram of conventionally used voltage clamping circuit with 3 phase input voltage, in accordance with an embodiment of the present subject matter.

[0021] Figure 2 illustrates a different waveform obtained by using conventional voltage clamping circuit, in accordance with an embodiment of the present subject matter.

[0022] Figure 3 illustrates an improved circuit diagram of a voltage clamping circuit with 3 phase input voltage, in accordance with an embodiment of the present subject matter.

[0023] Figure 4 illustrates different waveforms obtained by using an improved voltage clamping circuit, in accordance with an embodiment of the present subject matter.

[0024] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0025] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0026] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0027] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0028] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0029] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0030] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0031] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0032] Referring now to figure 1, a conventionally used voltage clamping circuit with three phase voltage is illustrated. In one implementation the voltages clamping circuit works on the principle of charging the capacitor up to a certain threshold voltage and then limiting that voltage by opening the current path to charge the capacitor by using a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET). As illustrated in figure 1, for all the input voltages less than the threshold level MOSFET (M1) is turned ON. But current only flows when the input voltage is greater than the capacitor voltage. The resistors (R1 and R2) decide the peak threshold level of voltage that the capacitor can hold. In an event when the input voltage is greater than the threshold level, a transistor (Q1) turns ON, which enables the gate to source voltage of (M1) to be zero thereby turning off the MOSFET. As the MOSFET is open or turned off, the current path required by the capacitor to charge is open and thus the capacitor stops charging. However, such principle works well in case of single phase applications where the input voltage returns to zero after every half cycle in case of a bridge rectifier. If this same circuit is powered from 3 phase star or delta power supply, the output of bridge rectifier does not return to zero since in one complete cycle, all the six diodes will turn ON at certain periodic levels.

[0033] Referring now to figure 2, different waveform obtained by using conventional voltage clamping circuit is illustrated. In one implementation, the 1st waveform illustrates a gate to source voltage across MOSFET (M1) is almost zero indicating M1 open or turned off when a transistor (Q1) is turned ON. So when the MOSFET is open or turned off and thus entire input voltage is dropped across the MOSFET as illustrated in the 2nd waveform. Thus, since the current path is open, the capacitor is also not charged as illustrated in the 3rd waveform.

[0034] Referring now to figure 3, an improved voltage clamping circuit with three phase input voltage is illustrated.

[0035] In one implementation, the voltage clamping circuit is divided into 2 portions. In one portion a bridge rectifier comprising of diodes D1, D2, D5, D6 connected to voltages V1 and V2, and the second portion comprising a bridge rectifier comprising of diode D3, D4, D7, D8 connected to voltages V3 and GND. As V1, V2 and V3 are phase shifted by 1200 for certain period enabling D1 and D2 to be turned ON and for the rest of the cycle D1 and D2 remains turned OFF.

[0036] Referring now to figure 4, different waveform obtained by using an improved voltage clamping circuit is illustrated.

[0037] In one implementation, 1st waveform indicates gate to source voltage of MOSFET M1 and M2. In an event when an input voltage in the upper portion of the circuit (V1 and V2) is below the threshold level, MOSFET M1 is turned ON. The MOSFET M2 is turned ON in a similar manner. The 2nd waveform indicates the voltage across MOSFET M1 and M2 drops to zero when MOSFET is turned OFF. Thus because of the arrangement the output voltage across the capacitor is clamped to a preset threshold voltage decided by resistors R1 , R2 ,R3 and R4 as indication in the 3rd waveform.

[0038] In one implementation, the present invention relates to 3 phase voltage power supply only. In single phase voltage of 230V line voltage offline converter IC are readily available. They don’t need voltage clamping circuit at the input as the MOSFET inbuilt are rated for line voltage. Now when we enter into three phase voltage 415V and above the peak voltage of the Line input goes above 700V which exceeds the MOSFET rating. So there is a requirement of clamping circuit. For high power circuit normally Fly back topology is used and to protect the MOSFET rating, the clamping circuit used is a stackfet technique. Now for lower power applications normally buck converter is used but the stack FET technique does not work for buck converters. So we require a clamping circuit to protect the MOSFET rating. The technique used in single phase applications is prior art and known technology but that cannot be used readily in the 3 phase power supply without any modification. This invention is the modification required to make the clamping circuit work for 3 phase power supply for non-isolated application. So a separate path is provided so that voltage in either path is reduced and simultaneously each MOSFET is turned ON as the 3 phase voltage is phase shifted by 120 degree. In many applications of 3 phases the circuit should also work even if one phase of the system is lost. This circuit works well when 1 or 2 phase (3 phase 4 wire systems) is lost and the phases are also interchangeable.

[0039] Some of the important features of the present invention, considered to be noteworthy are mentioned below:
1. The present invention is capable of efficiently clamping an input voltage higher than a threshold level.
2. The present invention gives the additional safety to voltage margin for switcher integrated circuit (IC) operating in non-isolated 3 phase power supplies.
3. The present invention requires less PCB area as low power MOSFET can be used for switching.
4. The present invention can be used as a single power supply from a voltage range of 85 to 690 V or higher.
5. The present invention provides a cost effective design for 3 phase non-isolated power supply operating at voltages greater than 415V.
6. If the power supply is operated from 3 phase, and if 1 phase is lost then the present invention is still configured to work as 1 part of the circuit will be always working.
7. As there are two section (circuit divided in two loops with tow bridge rectifiers), all the 3 phases are interchangeable as 3 phase are phase shifted by 120 Degree.
,CLAIMS:1. A voltage clamping circuit for limiting a voltage passing through an electric circuit, the voltage clamping circuit comprising:
at least one bridge rectifier comprising at least one diode connected to at least one voltage source, wherein if an input voltage value detected by at least one resistors exceeds a pre-defined threshold voltage value at least one mosfet is adapted to turns ON thereby making a path for a current to flow for charging at least one capacitor and limiting the voltage passing through the electric circuit.

2. A voltage clamping circuit for limiting a voltage passing through an electric circuit, the voltage clamping circuit comprising:
at least one bridge rectifier comprising:
at least one first set of diodes (D1, D2, D5, D6) connected to a first set of voltage sources (V1, V2); and
at least one second set of diodes (D3, D4, D7, D8) connected to a second set of voltage sources (V3, GND); WHEREIN
if V1, V2 and V3 voltages are phase shifted by 120 for a particular amount of pre-defined time period only D1 and D2 are adapted to turn ON from OFF state, thereby clamping an output voltage to a pre-defined threshold voltage decided by at least one set of resistors R1 , R2 ,R3 and R4.

3. The voltage clamping circuit as claimed in claim 1 and 2, characterized in that adapted to limit the input voltage below the pre-defined threshold voltage so that the mosfet turns on making the path for the current to flow for charging the capacitor.

4. The voltage clamping device as claimed in claim 1 and 2, is preferably used in circuits powered by a three phase star or a delta power supply.

5. The voltage clamping circuit as claimed in claim 1 and 2, characterized in that adapted to operate after the pre-defined threshold voltage is reached and the output voltage is clamped.

6. The voltage clamping circuit as claimed in claim 1 and 2, comprises two bridge rectifiers, wherein a first bridge rectifier from the two bridge rectifiers include at least one set of diode (D1, D2, D5, D6) connected to the first set of voltage sources (V1, V2), and a second bridge rectifier from the two bridge rectifiers include at least one set of diode (D3, D4, D7, D8) connected to a second set of voltage sources (V3, GND).

7. The voltage clamping circuit as claimed in claim 1 and 2 is connected the power supply operated from 3 phase electric power systems, wherein the 3 phases are interchangeable.

8. The voltage clamping circuit as claimed in claim 1 and 2 is connected the power supply operated from 3 phase electric power systems, wherein said voltage clamping circuit is adapted to work if 1 phase is lost.