The present invention generally relates to an electrical protection circuit. More specifically, the present invention is related to an electrical protection circuit for protecting a reverse polarity protection unit.
BACKGROUND OF THE INVENTION
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also correspond to implementations of the claimed technology.
Reverse voltage protection circuits prevent damage to power supplies and other electronic circuits such as inverter circuits, in the events where batteries connected to such circuits are connected in a reverse mode. Electronic circuits, such as the inverter circuits, are typically equipped with power devices such as Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) and Insulated-Gate Bipolar Transistors (IGBTs). Such power devices include a body diode. But, when the connections are reversed and reverse current flowing from the battery through body diodes which is uncontrolled and could harm the inverter circuit. A power diode connected in series with a battery allows current to flow through the inverter circuit when the battery is connected to the inverter circuit, with correct polarities. Further, the power diode prohibits flow of reverse current, when connections of the battery are reversed, thereby acting as a reverse voltage protection element.
Fig. 1 illustrates a circuit diagram 100 of a battery 102 and an inverter circuit 104 connected with correct polarities for operation, in accordance with prior art. In one implementation, the battery 102 may be a 12-volt battery, and the inverter circuit

104 may be a single phase full bridge inverter. The inverter circuit 104 comprises MOSFETs 106,108,110, and 112. Gate terminals of the MOSFETs 106,108,110, and 112 are connected with Pulse Width Modulation (PWM) circuits, and Alternating Current (A.C.) output is provided at output terminals 116. During operation, when the polarity of the battery 102 connected to the inverter circuit 104 is correct, current I flows in the desired direction through the MOSFETs 106, 108, 110, and 112, i.e. from Drain to Source, to provide an A.C. output at output terminals 116.
Fig. 2 illustrates a circuit diagram 200 of the battery 102 in a reverse connection with the inverter circuit 104, in accordance with prior art. When the battery 102 is connected with the inverter circuit 104 in a reverse configuration, body diodes of the MOSFETs 106, 108, 110, and 112 become forward bias, and a large amount of reverse current I' flows through the body diodes. Such flow of the reverse current I' damages the MOSFETs 106, 108, 110, and 112.
In order to prevent the inverter circuit 104 from flow of the reverse current I' that can damage the MOSFETs 106,108,110, and 112, a protection circuit 302 is used. Fig. 3 illustrates a circuit diagram 300 showing usage of a protection circuit 302 with the inverter circuit 104, in accordance with prior art. Fig. 3 is referenced to explain a situation where the battery 102 is connected with reverse polarities. The protection circuit 302 either uses a relay, a MOSFET, or a diode, which prohibits the reverse current I' from entering into the inverter circuit 104. If a MOSFET is used in the protection circuit 302 when battery is reversed, gate of MOSFET will turn-off, body diode of the MOSFET will get reverse biased, and the MOSFET will block flow of the reverse current I'. When relays are used in the protection circuit 302, current losses are high and the current protection is less reliable. Similarly, upon usage of diodes, losses are very high and only unidirectional current can flow in a circuit. Further, the protection circuit 302 is susceptible to damage by high inrush current, short-circuit current, thermal protection failure, and internal failure

in inverter circuit 104. There does not exist a mechanism for protecting the protection circuit 302 from electrical damages.
OBJECTS OF THE INVENTION
A general objective of the invention is to provide an electrical protection circuit for protecting an electronic circuit from electrical damages.
Another objective of the invention is to provide an electrical protection circuit for protecting a reverse current protection circuit of an electronic circuit.
Yet another objective of the invention is to provide a controlling circuitry for controlling operation of the reverse current protection circuit.
SUMMARY OF THE INVENTION
This summary is provided to introduce aspects related to an electrical protection circuit for protecting reverse current protection circuit of an electronic circuit, and the aspects are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.
In one embodiment, an electrical protection circuit for protecting reverse current protection circuit of an electronic circuit is disclosed. The electrical protection circuit may comprise a second MOSFET connected in series with a first MOSFET of the reverse current protection circuit in an opposite direction. The second MOSFET prevents damage of the first MOSFET from adverse current. The first MOSFET and the second MOSFET are connected between a battery and the electronic circuit.

The electrical protection circuit also comprises a controlling circuitry connected with gate terminals of the first MOSFET and the second MOSFET. The control circuitry controls operation of at least one of the first MOSFET and the second MOSFET, in a pulsed mode. The first MOSFET and the second MOSFET gets switched OFF when a voltage drop across them exceeds beyond a predefined threshold voltage. Such quick operation of the first MOSFET and the second MOSFET prevents them from being damaged by adverse current.
In an aspect, the adverse current may comprise at least one of inrush current, short circuit current, and any uncontrolled current. The electronic circuit may be an inverter circuit. The controlling circuitry may further comprise a microcontroller to activate the MOSFETs. The controlling circuitry may further comprise a control element for boosting current of output provided by the microcontroller at the gate terminals of the first MOSFET and the second MOSFET. The controlling circuitry may further comprise a control element for boosting voltage of output provided by the microcontroller at the gate terminals of the first MOSFET and the second MOSFET.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings constitute a part of the description and are used to provide a further understanding of the present invention.
Fig. 1 illustrates a circuit diagram of a battery and an inverter circuit connected with correct polarities for operation, in accordance with prior art.
Fig. 2 illustrates a circuit diagram of the battery in a reverse connection with the inverter circuit, in accordance with prior art.

Fig. 3 illustrates a circuit diagram showing usage of a protection circuit with the inverter circuit, in accordance with prior art.
Fig. 4 illustrates a circuit diagram showing an electrical protection circuit for protecting a reverse current protection circuit of an electronic circuit, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. Each embodiment described in this disclosure is provided merely as an example or illustration of the present invention, and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.
The present invention pertains to an electrical protection circuit for protecting an electronic circuit from damages by reverse current. Specifically, the present invention is related to an electrical protection circuit for protecting a reverse current protection circuitry connected to an electronic circuit. Specific details related to implementation and functioning of the invention are now described with reference to Fig. 4.
Fig. 4 illustrates a circuit diagram 400 showing an electrical protection circuit 402 for protecting a reverse current protection circuit of an electronic circuit 404. A battery 406 is shown to be connected with correct polarities so that suitable operation of the electrical protection circuit 402 could be described. Although an inverter circuit is illustrated and described to be the electronic circuit 404; however,

other electronic circuits such as Uninterruptible Power Supply (UPS) and high DC current apparatus could be protected using the electrical protection circuit 402. The inverter circuit comprises MOSFETs 408, 410, 412, and 414. Gate terminals of the MOSFETs 408, 410, 412, and 414 are connected with Pulse Width Modulation (PWM) circuits, and Alternating Current (A.C.) output is provided at output terminals 416.
The electrical protection circuit 402 comprises a second MOSFET 422 connected in series with a first MOSFET 420 of the reverse current protection circuit. In an aspect, the first MOSFET 420 and the second MOSFET 422 may be N-channel MOSFETs. The second MOSFET 422 is connected with the first MOSFET 420 in an opposite direction. The first MOSFET 420 and the second MOSFET 422 are connected between a battery 406 and the inverter circuit.
In case of a reverse polarity connection of the battery 406, reverse current F flows towards the inverter circuit. The first MOSFET 420, of the reverse current protection circuit, will remain in off condition and will protect the inverter circuit from the reverse current I'. The first MOSFET 420 may fail while the battery 406 is connected with right polarities and an adverse current flows towards the first MOSFET 420. Such adverse current may damage the first MOSFET 420. For such situations, the second MOSFET 422 of the electrical protection circuit 402 is provided, to protect the first MOSFET 420 from damage by adverse current, when polarity connections of the battery 406 are correct. Further description is provided with reference to Fig. 4 considering the situation when polarity of the battery 406 is correct. The adverse current may include inrush current, short circuit current, and any uncontrolled current due to protection failure in inverter. Present invention also addresses temperature rise of the first MOSFET 420 and the second MOSFET 422, as temperature impacts RDS(on) of a MOSFET and the current flowing through the MOSFET. Over temperature condition generally arises due to loose connection of an electronic element in an electronic circuit, or loose connection with heat sink, or electronic circuit running at overload.

The electrical protection circuit 402 may also comprise a controlling circuitry 424 connected with gate terminals of the first MOSFET 420 and the second MOSFET 422. The controlling circuitry 424 may control operation of simultaneously of the first MOSFET 420 and the second MOSFET 422 in a pulsed mode. When adverse current arrives towards the electrical protection circuit 402, voltage drop across the first MOSFET 420 and the second MOSFET 422 may exceed beyond a predefined threshold voltage. Such voltage drop would cause the first MOSFET 420 and the second MOSFET 422 to get switched OFF. The controlling circuitry 424 of the electrical protection circuit 402 therefore prevents the both MOSFETs 420, and 422 from damage by adverse current.
In an embodiment, a microcontroller (MC) may be connected to the gate of the first MOSFET 420 and the second MOSFET 422 for providing a reset signal to reset operation of the first MOSFET 420 and the second MOSFET 422. In one case, diode Dll may be connected between the microcontroller (MC) and the source terminal (CS+) of the second MOSFET 422 to prevent flow of current towards the microcontroller (MC) that may damage the microcontroller (MC).
Drain terminals of first MOSFET 420 and the second MOSFET 422 may be connected together. Source terminal (CS+) of the second MOSFET 422 may be connected to the battery 406 and drain terminal of the second MOSFET 422 may be connected with the drain terminal of the first MOSFET 420. If the voltage drop across the first MOSFET 420 and the second MOSFET 422 exceeds beyond a predefined threshold voltage, a transistor Q19 may get activated. Activation of the transistor Q19 may turn off transistors Q20 and Q21, which in turn leads to a low signal at the gate terminals of the first MOSFET 420 and the second MOSFET 422, thereby turning off the first MOSFET 420 and the second MOSFET 422.
In one embodiment, the microcontroller (MC) may send a signal (5V) to the transistor Q19, through resistors R71 and R69. This high signal may also charge

capacitor C24, and through resistors R69 and R72 the value of (R69+R72)*C24 must be more than turn on time of the MOSFETs 420 and 422.
The controlling circuitry 424 also comprise control elements for boosting voltage of output provided by the microcontroller (MC) at the gate terminals of the first MOSFET 420 and the second MOSFET 422. Transistors Q20 and Q21 may shift voltage level of the signal provided by the microcontroller MC to about 12V to properly activate the first MOSFET 420 and the second MOSFET 422. In another aspect, the controlling circuitry 424 may also comprise control elements for boosting current level of the signal provided by the microcontroller (MC) at the gate terminals of the first MOSFET 420 and the second MOSFET 422. Transistors Q23 and Q24 may be utilized as control elements for boosting current signal of the microcontroller (MC).
In an aspect, the transistor Q19 may be present in OFF-condition during turn on period of the first MOSFET 420 and the second MOSFET 422. A resistor R73 is used as pull down resistor for false trigger prevention of the transistor Q19 due to noise or float condition.
In an aspect, the controlling circuit 424 may comprise resistors R74 and R75 for biasing a transistor Q20. So, the transistor Q20 may get turned OFF when the transistor Q19 is ON, and vice versa. Upon turning ON the transistors Q20, Q21, and Q23, gate signal for each of the first MOSFET 420 and second MOSFET 422 will be high. The high gate signal will turn ON both the first MOSFET 420 and second MOSFET 422.
In an advantageous aspect, the controlling circuitry 424 may implement a pulse by pulse operation with a circuit response time of around 5 microseconds to activate and deactivate the first MOSFET 420 and second MOSFET 422. Therefore, in case of high inrush current, or short circuit, or over temperature, the voltage drop across the first MOSFET 420 and second MOSFET 422 will increase. The increased

voltage drop is detected by the controlling circuitry 424 and the first MOSFET 420 and second MOSFET 422 are shut down. The first MOSFET 420 and second MOSFET 422 can be turned ON again by a reset signal from the microcontroller (MC).
Although implementations of electrical protection circuit for protecting an electronic circuit have been described in language specific to structural features and/or methods, it is to be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features and circuits are disclosed as examples of electrical protection circuit for protecting an electronic circuit. Further, circuit elements used herein are merely exemplary, and other elements performing similar functions could be utilized.

We Claim:

1. An electrical protection circuit (402) for protecting a reverse current protection circuit of an electronic circuit (404), the electrical protection circuit (402) comprising:
a second MOSFET (422) connected in series with a first MOSFET (420) of the reverse current protection circuit in an opposite direction, to prevent damage of the first MOSFET (420) from adverse current, wherein the first MOSFET (420) and the second MOSFET (422) are connected between a battery (406) and the electronic circuit (404); and
a controlling circuitry (424) connected with gate terminals of the first MOSFET (420) and the second MOSFET (422), for controlling operation of both the first MOSFET (420) and the second MOSFET (422) in a pulsed mode, wherein the first MOSFET (420) and the second MOSFET (422) gets switched OFF when a voltage drop across them exceeds beyond a predefined threshold voltage, thereby preventing the first MOSFET (420) and the second MOSFET (422) from damage by the adverse current.
2. The electrical protection circuit (402) as claimed in claim 1, wherein the adverse current comprises at least one of inrush current, short circuit current, and over temperature condition.
3. The electrical protection circuit (402) as claimed in claim 1, wherein the electronic circuit (404) is an inverter circuit.
4. The electrical protection circuit (402) as claimed in claim 1, wherein the controlling circuitry (424) further comprising a microcontroller (MC) to reset operation of the first MOSFET (420) and the second MOSFET (422).
5. The electrical protection circuit (402) as claimed in claim 1 or 4, wherein the controlling circuitry (424) further comprises control elements (Q23, Q24) for

boosting current of output provided by the microcontroller (MC) to the gate terminals of the first MOSFET (420) and the second MOSFET (422).
6. The electrical protection circuit (402) as claimed in claim 1 or 4, wherein the controlling circuitry (424) further comprises control elements (Q20, Q21) for boosting voltage of output provided by the microcontroller (MC) to the gate terminals of the first MOSFET (420) and the second MOSFET (422).
7. The electrical protection circuit (402) as claimed in claim 1 or 4, wherein the controlling circuit further comprises a diode (Dl 1) for blocking flow of current from source of the first MOSFET (420) to the microcontroller (MC).