FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
The patent Rule, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
“A DC-DC BUCK CONVERTER WITH AN OVERVOLTAGE PROTECTION CIRCUIT AND A METHOD THEREOF”
MINDA CORPORATION LIMITED, of E-5/2, Chakan Industrial Area, Phase-III, M.I.D.C., Nanekarwadi,Tal- Khed, Dist.Pune-410 501, India
The following specification particularly describes the invention and the manner in which it is to be performed.

“A DC-DC BUCK CONVERTER WITH AN OVERVOLTAGE PROTECTION CIRCUIT AND A METHOD THEREOF”
TECHNICAL FIELD [0001] The present disclosure generally relates to DC-DC buck converters. Particularly, the present disclosure relates to a DC-DC buck converter with an overvoltage protection circuit.
BACKGROUND
[0002] DC-DC converters are widely used to efficiently produce a regulated voltage. The DC-DC converters are high-frequency power conversion circuits that use high-frequency switching, inductors, and capacitors to smooth out switching noise to produce regulated DC voltage. The DC-DC converters maintain constant voltage output even when changing input voltages. At 90% efficiency, the DC-DC converters are generally much more efficient than linear regulators. The DC-DC converters come in non-isolated and isolated varieties. Isolation is determined by whether or not an input ground is connected to an output ground. Four most common topologies for DC-DC converters are: buck converters, boost converters, buck-boost converters, and SEPIC converters. A buck converter steps a voltage down producing a voltage lower than the input voltage. A boost converter steps a voltage up producing a voltage higher than the input voltage. A buck-boost converter steps a voltage up or down, producing a voltage equal to or higher or lower than the input voltage. A SEPIC converter also steps a voltage up or down, producing a voltage equal to or higher or lower than the input voltage.
[0003] Restricting the scope to buck converter, there are two types of DC-DC buck converters available in the market. The first type of the DC-DC converter is asynchronous DC-DC buck converter, and the second type of the DC-DC converter is synchronous DC-DC buck converter. The synchronous architecture takes the non-synchronous architecture one step into the future as it enhances several key characteristics of the buck converter and makes it more efficient and easier to implement. Thus, synchronous DC-DC buck converter is widely used in the vehicle and other industrial applications.

[0004] In the electric vehicles, a synchronous DC-DC buck converter (herein after referred as ‘DC-DC buck converter’ or ‘buck converter’) is widely used to convert the traction battery voltage (input voltage) to 12V output voltage for driving connected devices/loads, such as digital cluster, head lamp, tail lamp, electronic control unit, and communication modules. It is very important to isolate the connected devices/loads in electrical vehicles from the traction battery voltage during failure of the buck converter, to protect them from the failures caused due to overvoltage.
[0005] The common failure modes or faults generally observed in the DC –DC buck converters are as follows:
(1) Input short circuit fault
(2) Output short circuit fault
(3) Input to output short circuit faults
[0006] From the above listed faults, faults from the input to output side are considered as the serious ones. Such faults may occur when the input to output circuit is short circuited. These faults may also be regarded as output over voltage faults. When such fault occurs, the traction battery voltage that appears at an input of the buck converter inadvertently get applied as it is to as all the connected devices (i.e., loads) through the faulty buck converter. The connected devices are generally rated for 12V and if the voltage exceeds the rated voltage, then there is a chance of the devices being damaged, which at times proves to be very expensive.
[0007] The output over voltage faults may be observed mainly due to high voltage transients and top side switch failure of the buck converters. When the top side switch fails, the input to output circuit acts as a closed circuit and the input voltage appears as it is at the output of the buck converter, which may damage the connected devices. Hence, it becomes very essential to address such type of faults to protect the connected devices from getting damaged due to the overvoltage signals appearing at the output of the buck converter.

[0008] In some conventional solutions, a buck converter uses Silicon Controlled Rectifiers (SCR) based latches for protection against output over voltage faults. The SCR based solutions do one of the below actions:
• Blowing of the input fuse of the buck converter, or
• Disconnecting the series pass element (MOSFET or relay) between input and output of the buck converter.
[0009] During the input to output short circuit failure of the buck converter, which uses SCR based latches, the SCR is activated to create short circuit condition at the input of the buck converter so that input fuse blows. However, the input fuse needs a replacement before the electronic system is restored to its former condition once the fault is rectified. It is also observed that while replacing the input fuse, a user may replace an incorrect rated fuse or insert a wire instead of a fuse. The SCRs are also prone to nuisance tripping (i.e., unwanted blowing of the input fuse) due to stray transients encountered in power and signal lines of electric vehicle subsystems. This nuisance tripping causes the blow of the input fuse due to occurrence of stray transients which might occur every often. Hence, the SCR based input fuse blowing solution is not a practical solution and suffers following major drawbacks:
• It is not user friendly since it blows the input fuse which needs to be manually replaced by the user.
• It is prone to nuisance tripping, leading to undesired tripping of the SCR, in presence of transient faults, even when the whole system maintains healthy condition.
[0010] In other conventional solutions, to prevent the blowing of fuse, a complex arrangement has been proposed which uses extra power switching device(s) (e.g., power MOSFETS) to disconnect the input from the output of the buck converter. In one such solution, an extra power switch is connected in series with top switch of the buck converter and the extra power switch becomes OFF in presence of output over voltage fault. However, the drawback associated with such solution is that the power switching

devices or the power switches are very costly. Moreover, such systems are complex compared to other traditional solutions. Further, these solutions do not discuss any special technique for nuisance tripping due to transients.
[0011] There is no cost efficient and convenient solution for preventing nuisance tripping due to stray transients encountered in the conventional buck converters. Thus, there exists a need for the technology to solve above-mentioned problems and overcome the disadvantages or difficulties of the conventional buck converters used in the automotive applications.
[0012] The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
SUMMARY
[0013] One or more shortcomings discussed above are overcome, and additional advantages are provided by the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the disclosure.
[0014] An object of the present disclosure is to provide a synchronous DC-DC buck converter with an over voltage protection circuit to protect connected devices from getting damaged due to overvoltage signals appearing at an output of the buck converter.
[0015] Another object of the present disclosure is to provide an improved buck converter having inbuilt safety mechanisms to enable safety against output overvoltage signals appearing at the output of the buck converter.

[0016] Yet another object of the present disclosure is to provide cost effective and simple solutions to prevent blowing of input fuse of a buck converter due to stray transient voltage.
[0017] The above stated objects as well as other objects, features, and advantages of the present disclosure will become clear to those skilled in the art upon review of the following description, the attached drawings, and the appended claims.
[0018] According to an aspect of the present disclosure, a DC-DC buck converter with an overvoltage protection circuit and corresponding method are provided.
[0019] In a non-limiting embodiment of the present disclosure, the present application discloses a DC-DC buck converter with an overvoltage protection circuit. The buck converter comprising an input fuse configured to receive an input voltage from a power source. The buck converter further comprises a first switch connected between the input fuse and an input of a filter circuit and configured to receive the input voltage through the input fuse, where the first switch comprises a control terminal. The buck converter further comprises a second switch connected between an input of the filter circuit and a ground terminal of the filter circuit, where the second switch also comprises a control terminal. The buck converter further comprises an output configured to provide an output voltage at an output of the filter circuit and a switching circuit operable to control switching operations of the first switch and the second switch by alternatively driving the control terminals of the first switch and the second switch to maintain a constant desired level of the output voltage. The buck converter further comprises the overvoltage protection circuit connected between the control terminal of the second switch and the output of the filter circuit. The overvoltage protection circuit is configured to override the switching circuit in controlling the switching operations of the second switch and control the switching operations of the second switch by toggling the second switch to an ON state without blowing the input fuse when the output voltage reaches or exceeds a threshold limit due to an overvoltage transient pulse appearing at the output of the filter circuit. The switching circuit is configured to take back the control of the switching operations of the second

switch and alternatively drive the control terminals of the first and second switches when the output voltage reaches below the threshold limit due to disappearance of the overvoltage transient pulse at the output of the filter circuit.
[0020] In a non-limiting embodiment of the present disclosure, the present application discloses an overvoltage protection method for a DC-DC buck converter, the DC-DC buck converter comprising: an input fuse connected at an output of a power source; a first switch connected between the input fuse and an input of a filter circuit, the first switch comprising a control terminal; a second switch connected between an input of the filter circuit and a ground terminal of the filter circuit, the second switch comprising a control terminal; a switching circuit connected with the control terminals of first switch and the second switch; and an overvoltage protection circuit connected between the control terminal of the second switch and the output of the filter circuit. The method comprising controlling, by the switching circuit, switching operations of the first switch and the second switch by alternatively driving the control terminals of the first switch and the second switch to maintain a constant desired level of the output voltage. The method further comprising overriding, by the overvoltage protection circuit, the switching circuit in controlling switching operation of the second switch by toggling the second switch to an ON state without blowing the input fuse, when the output voltage reaches or exceeds a threshold limit due to an overvoltage transient pulse appearing at the output of the filter circuit. The method comprising taking back, by the switching circuit, the control of switching operations of the second switch and alternatively driving the control terminals of the first and second switches when the output voltage reaches below the threshold limit due to disappearance of the overvoltage transient pulse at the output of the filter circuit.
[0021] The present disclosure provides a cost effective, efficient, and simple solution to protect devices connected at the output of a buck converter from output over voltages. The present disclosure discloses an improved buck converter with inbuilt safety mechanism which enables safety against the output overvoltage signals during the permanent fault as well as transient spurious fault. The proposed buck converter does not blow the fuse if the output overvoltage condition is caused by a transient pulse. Thus, the present disclosure

protects the buck converter and the devices connected to it during a stray transient voltage without blowing the fuse. Further, the proposed buck converter requires no additional power components to blow fuse thereby achieving the cost effectiveness.
[0022] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BREIF DESCRIPTION OF DRAWINGS
[0023] Further aspects and advantages of the present disclosure will be readily understood from the following detailed description with reference to the accompanying drawings. Reference numerals have been used to refer to identical or functionally similar elements. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure wherein:
[0024] Figure 1 illustrates a functional block diagram 100 of the proposed DC-DC buck converter, according to an exemplary embodiment of the present disclosure.
[0025] Figure 2 illustrates an electrical circuit diagram 200 of the proposed buck converter described in Figure 1, according to an exemplary embodiment of the present disclosure.
[0026] Figure 3 illustrates a flow diagram representing an exemplary overvoltage protection method 300 for the DC-DC buck converter, according to an exemplary embodiment of the present disclosure.
[0027] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state

transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0028] In the present document, the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or implementation of the present disclosure described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.
[0029] While the disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will be described in detail below. It should be understood, however, that it is not intended to limit the disclosure to the particular form disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and the scope of the disclosure.
[0030] The terms “comprise(s)”, “comprising”, “include(s)”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device, apparatus, system, or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or apparatus or system or method. In other words, one or more elements in a device or system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system.
[0031] The terms like “buck converter”, “DC-DC buck converter”, “synchronous DC-DC buck converter” may be used interchangeably throughout the description. The terms like “transient pulse”, “transient voltage”, “transient fault”, “momentary overvoltage transient pulse” may be used interchangeably throughout the description.

[0032] In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration of specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense. In the following description, well known functions or constructions are not described in detail since they would obscure the description with unnecessary detail.
[0033] The present disclosure provides techniques for protecting the devices (i.e., loads) connected with a buck converter from overvoltage signals appearing at the output of the buck converter.
[0034] Referring now to Figure 1, which illustrates a functional block diagram 100 of a proposed DC-DC buck converter 190, in accordance with some embodiments of the present disclosure. It may be worth noting here that for the sake of simplicity and explanation, the entire block diagram 100 of Figure 1 is considered as the block diagram of the proposed buck converter 190 comprising a normal buck converter, an overvoltage protection circuit, and an input fuse. In one non-limiting embodiment of the present disclosure, the input fuse may be external to the proposed buck converter 190 (i.e., the input fuse may not be part of the buck converter 190). It may be noted here that the buck converter described in the present disclosure is a synchronous DC-DC buck converter.
[0035] The buck converter 190 of the present disclosure may comprise an input 170 for receiving input voltage from an external power source (not shown) and an output 180 for providing an output voltage to one or more devices/loads (not shown) connected at the output 180 of the buck converter 100. The buck converter 190 may further comprise an input fuse 110, a switching circuit 120, a filter circuit 130, a first switch 140, a second switch 150, and an overvoltage protection circuit 160.

[0036] Now the connections of the various components of the buck converter 190 and their working is described in detail with the help of Figure 2, which illustrates an electrical circuit diagram 200 of the buck converter 190.
[0037] In one non-limiting embodiment of the present disclosure, the input 170 may receive the input voltage from the power source. An input terminal of the input fuse 110 may be connected with the input 170. The input fuse 110 may be configured to receive the input voltage from the power source via the input 170. The input fuse 110 is used to protect the devices connected to the buck converter from getting damaged due to any fault/failure in the buck converter 190. The input fuse 110 may have predefined fuse rating. Fuse rating may be defined as the maximum value of safe current allowed to flow through a fuse before it melts/blows. The melting point of a fuse may be calculated using below equation:
M=I2t (1)
The melting point may indicate thermal energy resulting from current flow. The thermal energy created across the input fuse 110 during a failure can melt the fuse thereby preventing the buck converter 190 and the connected devices from getting damaged.
[0038] In one non-limiting embodiment of the present disclosure, the first switch 140 may comprise three terminals: an input terminal, an output terminal, and a control terminal. Further, the second switch 150 may also comprise three terminals: an input terminal, an output terminal, and a control terminal. The overvoltage protection circuit 160 may comprise a Zener diode Z1 (herein after referred as a first Zener diode Z1), a first resister R1, an optocoupler U1, a diode D1 (herein after referred as a first diode D1), a regulator circuit, and a second resister R2. The optocoupler U1 may comprise an input circuit having terminals 1, 2 and an output circuit having terminals 3, 4. The regulator circuit may comprise a Zener diode Z2 (herein after referred as a second Zener diode Z2), a capacitive element C1 (herein after referred as a first capacitive element C1). The filter circuit 130 may be made up of an inductive element L1 and a capacitive element C2 (herein after

referred as a second capacitive element C2). Each of the inductive element L1 and the second capacitive element C2 may comprise a first terminal and a second terminal.
[0039] In one non-limiting embodiment, the input terminal of the first switch 140 may be connected with the output terminal of the input fuse 110. The control terminal of the first switch 140 may be connected with the switching circuit 120 and the output terminal of the first switch 140 may be connected with the first terminal of the inductive element L1 via a node N1.
[0040] In one non-limiting embodiment, the input terminal of the second switch 150 may be connected between the output terminal of the first switch 140 and the first terminal of the inductive element L1 (i.e., the input terminal of the second switch 150 may be connected at the node N1). The control terminal of the second switch 150 may be connected with the switching circuit 120 via a diode D2 (herein after referred as a second diode D2) such that the anode of the second diode D2 is connected with the control terminal of the second switch 150 via a node N3 and the cathode of the diode D2 is connected with the switching circuit 120. The output terminal of the second switch 150 may be connected with a ground terminal G1.
[0041] The switching circuit 120 may be an integrated circuit package having a plurality of conducting pins. One pin of the switching circuit 120 may be connected at the output terminal of the input fuse 110 via a very high resistance R3 (herein after referred as third resistance R3). The purpose of this connection is to provide the initial power to the switching circuit 120 and the purpose of adding the third resistor R3 is to limit the amount of current provided to the switching circuit 120.
[0042] As mentioned earlier, the first terminal of the inductive element L1 may be connected with the output terminal of the first switch 140 and the input terminal of the second switch 150. The second terminal of the inductive element L1 may be connected with the output 180 via nodes N2 and N4. The first terminal of the second capacitive element C2 may be connected with the second terminal of the inducive element L1 at

node N2 and the second terminal of the second capacitive element C2 may be connected with the output terminal of the second switch 150. The second terminal of the second capacitive element C2 and the output terminal of the second switch 150 may be connected to the ground terminal G1.
[0043] In one non-limiting embodiment, the over voltage protection circuit 160 may be connected between the node N4 and the node N3. In other words, an input terminal of the over voltage protection circuit 160 may be connected between the second terminal of the inductive element L1 and the output 180 (i.e., at node N4). Further, an output terminal of the over voltage protection circuit 160 may be connected between the second diode D3 and the control terminal of the second switch 150 (i.e., at node N3).
[0044] In one non-limiting embodiment, the first Zener diode Z1 may be connected between the node N4 and the input circuit of the optocoupler U1 via the first resistor R1 such that the anode of the first Zener diode Z1 is connected with the node N4 and the cathode of the first Zener diode Z1 is connected with the input circuit of the optocoupler U1. Specifically, the first Zener diode Z1 may be connected with the terminal 1 of the input circuit of the optocoupler U1 via the first resistor R1. The terminal 2 of the input circuit of the optocoupler U1 may be connected with a ground terminal G2. The first diode D1 may be connected between the output circuit of the optocoupler U1 and the node N3 such that the anode of the first diode D1 is connected with the node N3 and the cathode of the first diode D1 is connected with the output circuit of the optocoupler U1. Specifically, the first diode D1 may be connected with the terminal 3 of the output circuit of the optocoupler U1. Terminal 4 of the optocoupler may be connected with the output terminal of the input fuse 110 via the second resister R2. The input circuit of the optocoupler U1 may comprise a diode (such as a light emitting diode (LED)) and the output circuit of the optocoupler U1 may comprise a photo sensitive device (such as a phototransistor).
[0045] As described above, the output circuit of optocoupler U1 is connected to the regulator circuit comprising the second Zener diode Z2 and the first capacitive element C1. The first capacitive element C1 and the second Zener diode Z2 may be connected in

parallel. A first terminal of the regulator circuit may be connected at the terminal 3 of the optocoupler U1. The second terminal of the regulator circuit may be connected to the ground terminal G2. The purpose of the regulator circuit is to adjust clamping level of voltage applied to the control terminal of the second switch 150.
[0046] In one non-limiting embodiment of the present disclosure, each of the first switch 140 and the second switch 150 may be a metal–oxide–semiconductor field-effect transistor (MOSFET). The first switch may also be named as a high side MOSFET or a top MOSFET and the second switch may be named as low side MOSFET or a bottom MOSFET. In another non-limiting embodiment, the first switch 140 and the second switch 150 may be a Bipolar Junction Transistor (BJT).
[0047] In general, a buck converter is a DC-to-DC power converter which steps down voltage from its input to its output. It may be noted here that the buck converter described in the present disclosure is a synchronous DC-DC buck converter. The basic operation of the buck converter includes controlling the current in the inductive element using two switches. A synchronous DC-DC buck converter produces a regulated voltage that is lower than its input voltage and can deliver high currents while minimizing power loss. The synchronous DC-DC buck converter consumes minimal power across the switches as both switches are synchronously operated by the switching circuit.
[0048] The switching circuit 120 may comprise at least one processor, a memory, a pulse width modulation (PWM) controller and other active and passive components. The at least one processor, the memory, and the PWM controller may be operatively connected to each other. The memory may be configured to store one or more instructions. The at least one processor and the PWM controller may be configured to execute the one or more instructions stored in the memory. The memory may include a Random- Access Memory (RAM) unit and/or a non-volatile memory unit such as a Read Only Memory (ROM), optical disc drive, magnetic disc drive, flash memory, Electrically Erasable Read Only Memory (EEPROM), a memory space on a server or cloud and so forth.

[0049] Example of the at least one processor may include, but not restricted to, a general-purpose processor, a Field Programmable Gate Array (FPGA), an Application Specific Integrated Circuit (ASIC), a Digital Signal Processor (DSP), microprocessors, microcomputers, micro- controllers, digital signal processors, central processing units, state machines, logic circuitries, and/or any devices that manipulate signals based on operational instructions.
[0050] The PWM controller may control the switching operations of the first switch 140 and the second switch 140. During a normal operation of the buck converter, the PWM controller alternatively drives the control terminals of the first and second switches to maintain a regulated desired level of output voltage at an output of the filter circuit 130 (or at output 180). The PWM controller alternatively toggles the first and second switches to ON/OFF states such that both switches are not ON simultaneously to prevent unnecessary short circuit in the buck converter.
[0051] When the PWM controller turns ON the first switch 140, current is supplied to the output 180 through the first switch 140. During this time, the second switch 150 is OFF and the current through the inductive element L1 increases and thereby voltage across the second capacitive element C2 also increases, which lead to charging of the second capacitive element C2. When the PWM controller turns OFF the first switch 140, immediately the second switch 150 is turned ON by the PWM controller and thus, now the current is supplied to the output 180 through the second switch 150. During this time, the current through the inductive element L1 decreases, thereby discharging the filter circuit 130 leading to decaying of the output voltage to the extent of stabilizing at the stipulated threshold limit.
[0052] By synchronously toggling the first and second switches to ON/OFF states, the DC input is converted into a pulsating signal at the junction of the first switch 140 and the second switch 150 (i.e., at node N1). The filter circuit 130 extracts pure DC signals from the pulsating signal and suppresses and bypasses AC signals, thereby producing a smooth DC at the output 180 with reduced magnitude.

[0053] The desired level of voltage at the output 180 may be obtained by controlling a duty cycle of the switching circuit 120. The duty cycle (D) is defined as the ON-time of the first switch 140 divided by the total switching time, as defined in below equation:

where
TFS_ON is the time duration during which the first switch is in ON state;
TFS_OFF is the time duration during which the first switch is in OFF state or the time
duration during which the second switch is in ON state;
VOUT is the output voltage at the output 180; and
VIN is the input voltage at the input 170.
[0054] If the duty cycle of the switching circuit 120 is equal to 1, it means that the first switch is ON 100% of the time and the output voltage is equal to the input voltage. If the duty cycle is equal to 0.50, it means that the first switch is ON 50% of the time, producing an output voltage which is approximately 50% of the input voltage. Thus, by controlling the duty cycle of the switching circuit 120, the desired output voltage may be obtained at the output 180. And the duty cycle (i.e., the ON/OFF time duration of the first switch 140 and the second switch 150) may be controlled by the PWM controller. Thus, by selectively controlling the switching operations of the first and second switches by the PWM controller, the desired level of voltage may be obtained at the output 180.
[0055] In one non-limiting embodiment of the present disclosure, the first Zener diode Z1 is chosen such that when the output voltage at the output of filter circuit 130 exceeds a breakdown voltage of the first Zener diode Z1, the first Zener diode Z1 breaks down and starts conducting. A threshold voltage limit may be defined such that when the output voltage reaches or exceeds the threshold limit, the first Zener diode Z1 breaks down. The output voltage may reach or exceed the threshold limit either because of momentary transients (i.e., overvoltage transient pulses) or because of permanent malfunctioning of the first switch 140.

[0056] The proposed buck converter 190 momentarily switches ON the second switch 150 during a momentary transient and again restores it to an OFF state when the momentary transient disappears, thereby eliminating the input fuse blowing/replacement. The same is described below in details.
[0057] In one non-limiting embodiment of the present disclosure, an overvoltage transient pulse may pass through the filter circuit and may appear at the output of the filter circuit 130. The overvoltage transient pulse may cause the output voltage to reach or exceed the threshold limit. In such scenarios, the first Zener diode Z1 may break down and may start conducting current. The current coming out from the first Zener diode Z1 may reach at the input circuit of the optocoupler U1 via the first resister R1. The input circuit (which comprises the LED) may start emitting light and a photosensitive device in the output circuit of the optocoupler U1 may detects the light emitted by the LED. The output circuit of the optocoupler U1 may start transmitting one or more electrical signals upon detecting the light from the input circuit (i.e., a current may start flowing across the output circuit).
[0058] In one non-limiting embodiment of the present disclosure, the first diode D1 which is connected at the output circuit of the optocoupler U1 may get forward biased and current may pass through it when the one or more electrical signals are detected at the output circuit. The current passing through the first diode D1 may be passed to the second switch 150 via the control terminal, which may toggle the second switch 150 to the ON state. Thus, the second switch 150 is controlled by the over voltage protection circuit 160 when the output voltage reaches or exceeds the threshold limit due to the overvoltage transient pulse appearing at the output of the filter circuit 130.
[0059] It may be noted here that when the first diode D1 is forward biased, the second diode D2 gets reverse biased because the voltage at the anode of second diode D2 is more than the voltage supplied by the switching circuit 150 at the cathode of the second diode D2. Thus, the over voltage protection circuit 160 overrides the switching circuit 120 in controlling the switching operations of the second switch 150 and controls the switching operations of the second switch 150 by toggling the second switch 150 to the ON state

when the output voltage reaches or exceeds the threshold limit due to the overvoltage transient pulse appearing at the output of the filter circuit 130. The overvoltage transient pulse may disappear after a short duration of time.
[0060] In one non-limiting embodiment of the present invention, when the second switch 150 is turned ON, the excess voltage due to the overvoltage transient pulse may start discharging to ground terminal G1 via the filter circuit 130 and the second switch 150 and the output voltage may again start decaying. Once the output voltage goes below the threshold limit, the first Zener diode Z1 may stop conducting and the over voltage protection circuit 160 may get disabled. Now, the switching circuit 120 may again take back the control of the switching operations of the second switch 150 from the over voltage protection circuit 160. Thus, the switching circuit 120 may alternatively drive the control terminals of the first and second switches when the output voltage reaches below the threshold limit due to disappearance of the overvoltage transient pulse at the output of the filter circuit 130.
[0061] Thus, it is clear from above explanation that in the event of a momentary overvoltage transient pulse, the second switch 150 is turned OFF automatically as the first Zener diode Z1 employed in the over voltage protection circuit 160 again enters OFF region upon restoration of the output voltage (before the input fuse 110 can blow), post disappearance of the overvoltage transient pulse. The switching circuit 120 may enter into a fault recovery mode where the switching circuit 120 may alternatively turn OFF and ON the first switch 140 for a predefined number of times in a rapid succession to sense if the momentary overvoltage transient voltage has disappeared or not. The switching circuit 120 may recovers its normal operation in response to determining that the overvoltage transient pulse has disappeared, without blowing the fuse. Thus, the techniques of the proposed solution do not blow the input fuse 110 if the overvoltage condition is caused by an overvoltage transient pulse.
[0062] In the event of a permanent fault the output voltage permanently reaches or exceeds the threshold limit. The permanent fault may occur when the first switch 140 is

ON permanently (i.e., the first switch acts as a conducting wire). Due to the permanent overvoltage, the second switch 150 may also stay ON permanently (until the fault is rectified by a technician) due to the turning ON of the overvoltage protection circuit 160 which will override the control on the second switch 150 over the switching circuit 120 and the buck converter may draw a very high current from the power source via the input fuse 110 because the current may discharge directly to ground via a low resistance path comprising input fuse 110, the first switch 140, the node N1, the second switch 150, and ground terminal G1. This continuous current incoming from the power source may heat up the input fuse 110 according to equation (1) and eventually the input fuse 110 may blow up to protect the connected devices. Thus, the power source gets disconnected from the buck converter due to blowing the input fuse 110 when the output voltage permanently reaches or exceeds the threshold limit.
[0063] Therefore, the present disclosure does not blow the input fuse 110 if the over voltage condition is caused by an overvoltage transient pulse. However, when the switching circuit 120 using the overvoltage protection 160 circuit determines that the momentary fault condition is not disappeared over a predetermined duration (i.e., the overvoltage pulse is due to permanent fault), the input fuse is blown up. Thus, the present disclosure enables blowing of the input fuse only during the permanent fault condition and not during transient conditions. Hence, the present disclosure provides a safety mechanism which provides safety to device connected at the output of the buck converter during the permanent faults as well as transient spurious faults.
[0064] Referring now to Figure 3, which depicts a flowchart illustrating an overvoltage protection method 300 for a DC-DC buck converter, in accordance with some embodiments of the present disclosure. The buck converter may comprise an input fuse 110 configured to receive an input voltage from a power source and a first switch 140 connected between the input fuse 110 and an input of a filter circuit 130 and configured to receive the input voltage through the input fuse 110, the first switch 140 may comprise a control terminal. The buck converter may further comprise a second switch 150 connected between an input of the filter circuit 130 and a ground terminal G1 of the filter circuit 130,

the second switch 150 may comprise a control terminal. The buck converter may further comprise an output 180 configured to provide an output voltage at an output of the filter circuit 130. The buck converter may further comprise a switching circuit 120 operable to control switching operations of the first switch 140 and the second switch 150 by alternatively driving the control terminals of the first switch 140 and the second switch 150 to maintain a constant desired level of the output voltage. The buck converter may further comprise an overvoltage protection circuit 160 connected between the control terminal of the second switch 150 and the output of the filter circuit 130.
[0065] As illustrated in Figure 3, the method 300 includes one or more blocks illustrating the overvoltage protection method 300 for the DC-DC buck converter.
[0066] The method 300 may include, at block 302, controlling switching operations of the first switch 140 and the second switch 150 by alternatively driving the control terminals of the first switch 140 and the second switch 150 to maintain a constant desired level of the output voltage. For example, the switching circuit 120 may be configured to control the switching operations of the first switch 140 and the second switch 150 by alternatively driving the control terminals of the first switch 140 and the second switch 150 to maintain the constant desired level of the output voltage.
[0067] At block 304, the method may include overriding the switching circuit 120 in controlling switching operation of the second switch 150 by toggling the second switch 150 to an ON state without blowing the input fuse 110, when the output voltage reaches or exceeds a threshold limit due to an overvoltage transient pulse appearing at the output of the filter circuit 130. For example, the overvoltage protection circuit 160 may be configured to control the switching operation of the second switch 150 by toggling the second switch 150 to the ON state without blowing the input fuse 110, when the output voltage reaches or exceeds the threshold limit due to the overvoltage transient pulse appearing at the output of the filter circuit 130.

[0068] At block 306, the method may include taking back the control of switching operations of the second switch 150 and alternatively driving the control terminals of the first and second switches when the output voltage reaches below the threshold limit due to disappearance of the overvoltage transient pulse at the output of the filter circuit 130. For example, the switching circuit 120 may be configured to take back the control of switching operations of the second switch 150 and alternatively drive the control terminals of the first and second switches when the output voltage reaches below the threshold limit due to disappearance of the overvoltage transient pulse at the output of the filter circuit 130.
[0069] In one non-limiting embodiment of the present disclosure, the method 300 may further comprise disconnecting the power source from the buck converter by blowing the input fuse 110 when the output voltage permanently reaches or exceeds the threshold limit.
[0070] In one non-limiting embodiment of the present disclosure, the method 300 may further comprise discharging the excess output voltage when the output voltage exceeds the desired level of the output voltage. For example, the second switch 150 and the filter circuit 130 may be configured to discharging the excess output voltage when the output voltage exceeds the desired level of the output voltage.
[0071] In one non-limiting embodiment of the present disclosure, each of the first switch 140 and the second switch 150 may be a metal–oxide–semiconductor field-effect transistor (MOSFET) or a Bipolar Junction Transistor (BJT), and the buck converter may be a synchronous DC-DC buck converter.
[0072] In one non-limiting embodiment of the present disclosure, the first switch 140 may comprises an input terminal connected with the input fuse 110 to receive the input voltage and an output terminal connected with the input of the filter circuit (130). In one non-limiting embodiment of the present disclosure, the second switch 150 may also comprise an input terminal connected with the output terminal of the first switch 140 and an output terminal connected with the ground terminal G1 of a capacitive element C2 of the filter

circuit 130 so that the excess output voltage discharges to ground when the second switch 150 is toggled to the ON state by the overvoltage protection circuit 160.
[0073] In one non-limiting embodiment of the present disclosure, the overvoltage protection circuit 160 may comprise a first Zener diode Z1 whose cathode is connected with the output of the filter circuit 130 and the first Zener diode Z1 breaks down when the output voltage reaches or exceeds the threshold limit.
[0074] In one non-limiting embodiment of the present disclosure, the overvoltage protection circuit 160 may further comprise an optocoupler U1 having an input circuit and an output circuit, the input circuit of the optocoupler may be connected with an anode of the first Zener diode Z1 and the output circuit of the optocoupler may be configured to transmit one or more electrical signals when the first Zener diode Z1 breaks down due to the output voltage reaching or exceeding the threshold limit. The overvoltage protection circuit 160 may further comprise a first diode D1 whose anode may be connected with the output circuit of the optocoupler U1 and whose cathode may be connected with the control terminal of the second switch 150, the first diode D1 may be forward biased when the one or more electrical signals are detected at the output circuit of the optocoupler U1. The overvoltage protection circuit 160 may be configured to toggle the second switch 150 to the ON state when the first diode D1 is forward biased.
[0075] In one non-limiting embodiment of the present disclosure, the overvoltage protection circuit 160 may further comprise a regulator circuit comprising a second Zener diode Z2 connected in parallel with a capacitive element C1. The regulator circuit may be configured to adjust a clamping level of a voltage applied to the control terminal of the second switch 150.
[0076] In one non-limiting embodiment of the present disclosure, the DC-DC buck converter may comprise a second diode D2 whose anode may be connected with the switching circuit 120 and whose cathode may be connected with the control terminal of the second switch 150. The second diode D2 may be configured to be forward biased

when the output voltage is less than the threshold limit and may be configured to be reverse biased when the output voltage reaches or exceeds the threshold limit.
[0077] The above method may be described in the general context of computer executable instructions. Generally, computer executable instructions can include routines, programs, objects, components, data structures, procedures, modules, and functions, which perform specific functions or implement specific abstract data types.
[0078] The order in which the various operations of the methods are described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the method. Additionally, individual blocks may be deleted from the methods without departing from the spirit and scope of the subject matter described herein. Furthermore, the methods can be implemented in any suitable hardware, software, firmware, or combination thereof.
[0079] It may be noted here that the subject matter of some or all embodiments described with reference to Figures 1-2 may be relevant for the method and the same is not repeated for the sake of brevity.
[0080] The terms “an embodiment”, “embodiment”, “embodiments”, “the embodiment”, “the embodiments”, “one or more embodiments”, “some embodiments”, and “one embodiment”, “other embodiment”, “yet another embodiment”, “non-limiting embodiment” mean “one or more (but not all) embodiments of the disclosure(s)” unless expressly specified otherwise. Further, the terms “including”, “comprising”, “having” and variations thereof mean “including but not limited to”, unless expressly specified otherwise.
[0081] The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an

application based here on. Accordingly, the embodiments of the present invention are intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the appended claims.

WE CLAIM:
1. A DC-DC buck converter with an overvoltage protection circuit (160), comprising:
an input fuse (110) configured to receive an input voltage from a power source;
a first switch (140) connected between the input fuse (110) and an input of a filter circuit (130) and configured to receive the input voltage through the input fuse (110), wherein the first switch (140) comprises a control terminal;
a second switch (150) connected between an input of the filter circuit (130) and a ground terminal (G1) of the filter circuit (130), wherein the second switch (150) comprises a control terminal;
an output (180) configured to provide an output voltage at an output of the filter circuit (130);
a switching circuit (120) operable to control switching operations of the first switch (140) and the second switch (150) by alternatively driving the control terminals of the first switch (140) and the second switch (150) to maintain a constant desired level of the output voltage; and
the overvoltage protection circuit (160) connected between the control terminal of the second switch (150) and the output of the filter circuit (130),
wherein the overvoltage protection circuit (160) is configured to override the switching circuit (120) in controlling the switching operations of the second switch (150) and control the switching operations of the second switch (150) by toggling the second switch (150) to an ON state without blowing the input fuse (110), when the output voltage reaches or exceeds a threshold limit due to an overvoltage transient pulse appearing at the output of the filter circuit (130), and
wherein the switching circuit (120) is configured to take back the control of the switching operations of the second switch (150) and alternatively drive the control terminals of the first and second switches when the output voltage reaches below the threshold limit due to disappearance of the overvoltage transient pulse at the output of the filter circuit (130).
2. The DC-DC buck converter as claimed in claim 1,

wherein the first switch (140) further comprises an input terminal connected with the input fuse (110) to receive the input voltage and an output terminal connected with the input of the filter circuit (130), and
wherein the second switch (150) further comprises an input terminal connected with the output terminal of the first switch (140) and an output terminal connected with the ground terminal (G1) of a capacitive element (C2) of the filter circuit (130) so that the excess output voltage discharges to ground when the second switch (150) is toggled to the ON state by the overvoltage protection circuit (160).
3. The DC-DC buck converter as claimed in claim 1, further configured to:
disconnect the power source from the DC-DC buck converter by blowing the input
fuse (110) when the output voltage permanently reaches or exceeds the threshold limit.
4. The DC-DC buck converter as claimed in claim 1, further configured to:
discharge the excess output voltage using the filter circuit (130) and the second
switch (150) when the output voltage exceeds the desired level of the output voltage.
5. The DC-DC buck converter as claimed in claim 1,
wherein the overvoltage protection circuit (160) comprises:
a first Zener diode (Z1) whose cathode is connected with the output of the filter circuit (130), wherein the first Zener diode (Z1) breaks down when the output voltage reaches or exceeds the threshold limit;
an optocoupler (U1) having an input circuit and an output circuit, wherein the input circuit of the optocoupler is connected with an anode of the first Zener diode (Z1), and wherein the output circuit of the optocoupler is configured to transmit one or more electrical signals when the first Zener diode (Z1) breaks down due to the output voltage reaching or exceeding the threshold limit;
a first diode (D1) whose anode is connected with the output circuit of the optocoupler (U1) and whose cathode is connected with the control terminal of the second switch (150), wherein the first diode (D1) is forward biased when the one or more electrical signals are detected at the output circuit of the optocoupler (U1),

and wherein the overvoltage protection circuit (160) is configured to toggle the
second switch (150) to the ON state when the first diode (D1) is forward biased;
and
a regulator circuit comprising a second Zener diode (Z2) connected in
parallel with a capacitive element (C1), wherein the regulator circuit is configured
to adjust a clamping level of voltage applied to the control terminal of the second
switch (150), and
wherein the DC-DC buck converter further comprises a second diode (D2) whose anode is connected with the switching circuit (120) and whose cathode is connected with the control terminal of the second switch (150), and wherein the second diode (D2) is configured to be forward biased when the output voltage is less than the threshold limit and is configured to be reverse biased when the output voltage reaches or exceeds the threshold limit.
6. The DC-DC buck converter as claimed in claim 1, wherein each of the first switch (140) and the second switch (150) is a metal–oxide–semiconductor field-effect transistor (MOSFET) or a Bipolar Junction Transistor (BJT), and wherein the DC-DC buck converter is a synchronous DC-DC buck converter.
7. An overvoltage protection method (300) for a DC-DC buck converter, the DC-DC buck converter comprising: an input fuse (110) connected at an output of a power source; a first switch (140) connected between the input fuse (110) and an input of a filter circuit (130), the first switch (140) comprising a control terminal; a second switch (150) connected between an input of the filter circuit (130) and a ground terminal of the filter circuit (130), the second switch (150) comprising a control terminal; a switching circuit (120) connected with the control terminals of first switch (140) and the second switch (150); and an overvoltage protection circuit (160) connected between the control terminal of the second switch (150) and the output of the filter circuit (130), the method (300) comprising:
controlling (310), by the switching circuit (120), switching operations of the first switch (140) and the second switch (150) by alternatively driving the control terminals of

the first switch (140) and the second switch (150) to maintain a constant desired level of the output voltage;
overriding (320), by the overvoltage protection circuit (160), the switching circuit (120) in controlling switching operation of the second switch (150) by toggling the second switch (150) to an ON state without blowing the input fuse (110), when the output voltage reaches or exceeds a threshold limit due to an overvoltage transient pulse appearing at the output of the filter circuit (130); and
taking back (330), by the switching circuit (120), the control of switching operations of the second switch (150) and alternatively driving the control terminals of the first and second switches when the output voltage reaches below the threshold limit due to disappearance of the overvoltage transient pulse at the output of the filter circuit (130).
8. The overvoltage protection method (300) as claimed in claim 7, further comprising disconnecting the power source from the DC-DC buck converter by blowing the input fuse (110) when the output voltage permanently reaches or exceeds the threshold limit.
9. The overvoltage protection method (300) as claimed in claim 7, further comprising discharging the excess output voltage using the filter circuit (130) and the second switch (150) when the output voltage exceeds the desired level of the output voltage.
10. The overvoltage protection method (300) as claimed in claim 7, wherein each of the first switch (140) and the second switch (150) is a metal–oxide–semiconductor field-effect transistor (MOSFET) or a Bipolar Junction Transistor (BJT), and wherein the DC-DC buck converter is a synchronous DC-DC buck converter.