Negative voltage protection system for reducing an intensity of negative voltage

1. Field of the Invention

The present invention illustrates a negative voltage protection system, and more particularly, the negative voltage protection system for reducing an intensity of negative voltage by using a comparison circuit.

2. Description of the Prior Art

With the advancement of techniques, various electrical devices with high operational performance are widely adopted. Nowadays, most electrical devices are required to perform high processing speed and low response time in conjunction with a high-level processor integrated to a micro volume circuit. Thus, the electrical devices can be operated by users at any time and in any place. For example, the specification of iPhone 5s states that an A7-typed processor is used. The specification of iPhone 6 Plus states that an A8-typed processor is used. Another example is that the central processing unit (CPU) of the personal computer is upgraded from Intel® Core™ i5 to Intel® Core™ i7. Specifically, power consumption and heat generation of the electrical device are increased since the clock frequency of the processor is increased. Thus, the performance of heat dissipation components such as heat dissipation fans, a water cooling system, thermally conductive adhesive, and a heat sink attracts more attention. Among these heat dissipation devices, a water cooling system has the best heat dissipation performance yet has a large circuit volume, high cost, and high noise. Thermally conductive adhesives and heat sinks have smaller volume with inferior heat dissipation performance since they only use a medium for conducting heat. As a result, heat dissipation fans become the most popular devices for dissipating heat in general electric devices.

Specifically, in a half-bridge circuit based fan motor circuit, when the fan motor performs a phase alternation process, an effect of negative transient voltage is occurred due to Lenz's law. Unfortunately, when the negative transient voltage exceeds a tolerant voltage, a driving stage of the fan motor circuit suffers a latch-up effect. As known, the latch-up effect can interfere with all operations of fan motor circuit, such as interferences of a driving circuit and a clock circuit. Further, when the fan motor circuit is operated under a short state, an overloading state, or an automatic shut-down state, an effect of the negative transient voltage becomes severe.

To avoid the effect of the negative transient voltage, a limiter is introduced to a level shift driving circuit of the fan motor circuit. By using the limiter, the negative transient voltage and an intensity of an electrostatic discharge can be mitigated. However, practicability of aforementioned method is limited in practice. For example, when a distance between a controller and the fan motor circuit with a large capacitor is very long, the negative transient voltage generated from the fan motor circuit may exceed an amplitude of 100 volts (for example, the negative transient voltage is −120 volts). Thus, the limiter may lose a capability of protecting the fan motor circuit from the effect of the negative transient voltage.

In an embodiment of the present invention, a negative voltage protection system is disclosed. The negative voltage protection includes a negative voltage comparison circuit, a signal processing circuit, a driving circuit, driving output circuit, a power device, and a coil module. The negative voltage comparison circuit is configured to detect a negative voltage and output a comparison signal. The signal processing circuit is coupled to the negative voltage comparison circuit and configured to generate a control signal according to the comparison signal. The driving circuit is coupled to the signal processing circuit and configured to generate at least one driving signal according to the control signal. The driving output circuit is coupled to the driving circuit and configured to generate at least one power signal according to the at least one driving signal. The power device is coupled to the driving output circuit and configured to generate a driving voltage according to the at least one power signal. The coil module is coupled to the power device and operated according to the driving voltage. When the coil module generates a back electromotive force, the coil module outputs the negative voltage. When an intensity of the negative voltage detected by the negative voltage comparison circuit is greater than a predetermined value, the signal processing circuit generates the control signal to the driving circuit. The driving circuit controls the driving output circuit and the power device to reduce the intensity of the negative voltage according to the control signal.

In another embodiment of the present invention, a negative voltage protection system is disclosed. The negative voltage protection system includes a negative voltage comparison circuit, a signal processing circuit, a driving circuit, a driving output circuit, a power device, and a coil module. The negative voltage comparison circuit is configured to detect a first negative voltage or a second negative voltage and output a plurality of comparison signals. The signal processing circuit is coupled to the negative voltage comparison circuit and configured to generate a plurality of control signals according to the plurality of comparison signals. The driving circuit is coupled to the signal processing circuit and configured to generate a plurality of driving signals according to the plurality of control signals. The driving output circuit is coupled to the driving circuit and configured to generate a plurality of power signals according to the plurality of driving signals. The power device is coupled to the driving output circuit and configured to generate a plurality of driving voltages according to the plurality of power signals. The coil module is coupled to the power device and operated according to the plurality of driving voltages. When the coil module generates a back electromotive force, the coil module outputs the first negative voltage or the second negative voltage. When an intensity of the first negative voltage or the second negative voltage detected by the negative voltage comparison circuit is greater than a predetermined value, the signal processing circuit generates the plurality of control signals to the driving circuit. The driving circuit controls the driving output circuit and the power device to reduce the intensity of the first negative voltage or the second negative voltage according to the plurality of control signals.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

FIG. 1 illustrates a circuit structure of a negative voltage protection system according to a first embodiment of the present invention.

FIG. 2 illustrates a circuit structure of a negative voltage protection system according to a second embodiment of the present invention.

FIG. 1 illustrates a circuit structure of a negative voltage protection system 100 . The negative voltage protection system 100 includes a negative voltage comparison circuit 10 , a signal processing circuit 11 , a driving circuit 12 , a driving output circuit 13 , a power device 14 , and a coil module 15 . The negative voltage comparison circuit 10 includes a first resistor R 1 , a second resistor R 2 , a third resistor R 3 , a fourth resistor R 4 , and a comparator CMP 1 . The first resistor R 1 includes a first terminal configured to receive a reference voltage Vref, and a second terminal. The second resistor R 2 includes a first terminal configured to receive a negative voltage, and a second terminal coupled to the second terminal of the first resistor R 1 . The third resistor R 3 includes a first terminal coupled to the first terminal of the first resistor R 1 , and a second terminal. The fourth resistor R 4 includes a first terminal coupled to the second terminal of the third resistor R 3 , and a second terminal coupled to a ground terminal GND. The comparator CMP 1 includes a first input terminal coupled to the second terminal of the second resistor R 2 , a second input terminal coupled to the first terminal of the fourth resistor R 4 , and an output terminal coupled to the signal processing circuit 11 and configured to output a comparison signal SS 1 to the signal processing circuit 11 . An operation mode of the negative voltage comparison circuit 10 is illustrated below. The first terminal of the second resistor R 2 receives the negative voltage (i.e., the negative voltage is illustrated later). Thus, a voltage of a node NQ can be regarded as a partitioned voltage between the negative voltage and the reference voltage Vref. Similarly, a voltage of a node GQ can be regarded as a partitioned voltage between a voltage of the ground terminal GND and the reference voltage Vref. In the negative voltage protection system 100 , when an intensity of the negative voltage is greater than a predetermined value, the comparator CMP 1 outputs a comparison signal SS 1 with a first voltage level. Contrarily, when the intensity of the negative voltage is smaller than the predetermined value, the comparator CMP 1 outputs the comparison signal SS 1 with a second voltage level. Here, the intensity of the negative voltage can be defined as an absolute value of the negative voltage. For example, an intensity of −7 volts is greater than an intensity of −1 volt. The comparison signal SS 1 with the first voltage level or the second voltage level is transmitted to the signal processing circuit 11 . In the negative voltage protection system 100 , the signal processing circuit 11 can modulate the comparison signal SS 1 . For example, the signal processing circuit 11 can modulate the comparison signal SS 1 to an ON-OFF signal, a bipolar signal, or a unipolar signal. The modulated comparison signal can be regarded as a control signal. The control signal is transmitted from the signal processing circuit 11 to the driving circuit 12 .

In the negative voltage protection system 100 , the driving circuit 12 includes a first driving unit DR 1 and a second driving unit DR 2 . The first driving unit DR 1 includes a first terminal, a second terminal, and a third terminal coupled to the first terminal of the second resistor R 2 . The second driving unit DR 2 includes a first terminal, a second terminal, a third terminal coupled to a ground terminal GND, and fourth terminal coupled to the signal processing circuit 11 and configured to receive the control signal. The driving circuit 12 generates at least one driving signal to the driving output circuit 13 according to the control signal. For example, the first terminal of the first driving unit DR 1 , the second terminal of the first driving unit DR 1 , the first terminal of the second driving unit DR 2 , and the second terminal of the second driving unit DR 2 generate four driving signals to the driving output circuit 13 . The driving output circuit 13 includes a first transistor T 1 , a second transistor T 2 , a third transistor T 3 , and a fourth transistor T 4 . The first transistor T 1 includes a first terminal configured to receive a first circuit voltage, a second terminal, and a control terminal coupled to the first terminal of the first driving unit DR 1 . Specifically, a second circuit voltage VCC becomes the first circuit voltage by passing through a diode D. When the diode D is operated in a forward current state, the first circuit voltage received by the first terminal of the first transistor T 1 is substantially equal to the second circuit voltage VCC. The second transistor T 2 includes a first terminal coupled to the second terminal of the first transistor T 1 , a second terminal coupled to the first terminal of the second resistor R 2 , and a control terminal coupled to the second terminal of the first driving unit DR 1 . The third transistor T 3 includes a first terminal configured to receive a second circuit voltage VCC, a second terminal, and a control terminal coupled to the first terminal of the second driving unit DR 2 . The fourth transistor T 4 includes a first terminal coupled to the second terminal of the third transistor T 3 , a second terminal coupled to the third terminal of the second driving unit DR 2 , and a control terminal coupled to the second terminal of the second driving unit DR 2 . In the driving output circuit 13 , the first terminal of the second transistor T 2 and the first terminal of the fourth transistor T 4 output at least one power signal to the power device 14 . For example, the first terminal of the second transistor T 2 outputs a power signal HS to the power device 14 . The first terminal of the fourth transistor T 4 outputs a power signal LS to the power device 14 . The power device 14 includes a fifth resistor R 5 , a sixth resistor R 6 , a first switch SW 1 , and a second switch SW 2 . The fifth resistor R 5 includes a first terminal coupled to the first terminal of the second transistor T 2 , and a second terminal. The sixth resistor R 6 includes a first terminal coupled to the first terminal of the fourth transistor T 4 , and a second terminal. The first switch SW 1 includes a first terminal configured to receive a bus voltage VBUS, a second terminal coupled to the first terminal of the second resistor R 2 and configured to output the driving voltage to the coil module 15 , and a control terminal coupled to the second terminal of the fifth resistor R 5 . The second switch SW 2 includes a first terminal coupled to the second terminal of the first switch SW 1 , a second terminal coupled to the third terminal of the second driving unit DR 2 , and a control terminal coupled to the second terminal of the sixth resistor R 6 . The coil module 15 can be any typed coil module, such as a coil module of brushless fan. The first switch SW 1 and the second switch SW 2 can be two N-type metal-oxide-semiconductor field-effect transistors. Specifically, two parasitic diodes with respect to the first switch SW 1 and the second switch SW 2 are denoted as a parasitic diode PD 1 and a parasitic diode PD 2 respectively. A method for reducing the intensity of the negative voltage is illustrated below.

For presentation completeness, all operational modes of the coil module 15 at all-time points and the operational method for reducing the intensity of the negative voltage are described. Initially, the first switch SW 1 is operated in short state. The second switch SW 2 is operated in open state. Then, the first switch SW 1 becomes open state. The second switch SW 2 maintains open state. At the moment, the coil module 15 generates a back electromotive force. As a result, a current IL is transmitted from the ground terminal GND to the coil module 15 through the parasitic diode PD 2 . Since the current IL is transmitted from a high voltage terminal to a low voltage terminal inherently, equivalently, when the ground terminal GND is regarded as a terminal with zero voltage, a node O 1 becomes a terminal with a negative voltage. When the negative voltage exceeds a tolerant voltage, all circuit components and driving signals suffer severe interferences or disturbances, leading to a short circuit effect (i.e., large current short circuit). Thus, the coil module 15 may be burned out. To avoid high intensity of the negative voltage, the comparator CMP 1 of the negative voltage comparison circuit 10 may compare a voltage of the node NQ and a voltage of the node GQ. As with the aforementioned illustration, a voltage of the node NQ can be regarded as a partitioned voltage between the negative voltage (i.e., a voltage of the node O 1 ) and the reference voltage Vref. Similarly, a voltage of the node GQ can be regarded as a partitioned voltage between a voltage of the ground terminal GND and the reference voltage Vref. Thus, when the intensity of the negative voltage (i.e., for example, −7 volts) is greater than the predetermined value (i.e., for example, −3 volts), the comparator CMP 1 outputs a comparison signal SS 1 with the first voltage level. Contrarily, when the intensity of the negative voltage (i.e., for example, −0.5 volt) is smaller than the predetermined value (i.e., for example, −3 volts), the comparator CMP 1 outputs the comparison signal SS 1 with a second voltage level. The comparison signal SS 1 is modulated to become a control signal by using the signal processing circuit 11 for controlling the driving circuit 12 . For example, when the intensity of the negative voltage is large, the control signal corresponding to the comparison signal SS 1 with the first voltage level can operate the driving circuit 12 , the driving output circuit 13 , and the power device 14 to control the second switch SW 2 to operate in a short state. When the second switch SW 2 is controlled to operate in the short state, the node O 1 becomes the ground terminal. Thus, the intensity of the negative voltage can be reduced or eliminated. Contrarily, when the intensity of the negative voltage is small, the control signal corresponding to the comparison signal SS 1 with the second voltage level can maintain the second switch SW 2 to operate in an open state.

In other words, when the intensity of the negative voltage exceeds a predetermined value, the second switch SW 2 is operated in the short state. Thus, since the transmission path of the current IL from the ground terminal GND to the coil module 15 is dissipated, the intensity of the negative voltage can be reduced or eliminated. As a result, since the negative voltage protection system 100 can reduce or eliminate large negative voltage, the negative voltage protection system 100 has a capability of circuit protection.

FIG. 2 illustrates a circuit structure of a negative voltage protection system 200 . The negative voltage protection system 200 includes a negative voltage comparison circuit 10 , a signal processing circuit 11 , a driving circuit 12 , a driving output circuit 13 , a power device 14 , and a coil module 15 . The negative voltage comparison circuit 10 is used for detecting a first negative voltage (i.e., a negative voltage of a node O 1 ) or a second negative voltage (i.e., a negative voltage of a node O 2 ) and outputting a plurality of comparison signals. The signal processing circuit 11 is coupled to the negative voltage comparison circuit 10 for generating a plurality of control signals according to the plurality of comparison signals. The driving circuit 12 is coupled to the signal processing circuit 11 for generating a plurality of driving signals according to the plurality of control signals. The driving output circuit 13 is coupled to the driving circuit 12 for generating a plurality of power signals according to the plurality of driving signals. The power device 14 is coupled to the driving output circuit 13 for generating a plurality of driving voltages according to the plurality of power signals. A coil module 15 is coupled to the power device 14 and operated according to the plurality of driving voltages. In the negative voltage protection system 200 , the negative voltage comparison circuit 10 includes a first resistor R 1 , a second resistor R 2 , a third resistor R 3 , a fourth resistor R 4 , a seventh resistor R 7 , an eighth resistor R 8 , a ninth resistor R 9 , a tenth resistor R 10 , a first comparator CMP 1 , and a second comparator CMP 2 . Here, a circuit structure including the first resistor R 1 , the second resistor R 2 , the third resistor R 3 , the fourth resistor R 4 , and the first comparator CMP 1 is similar to the negative voltage comparison circuit 10 in the negative voltage protection system 100 . Specifically, a first terminal of the second resistor R 2 is coupled to a first terminal of the coil module 15 for receiving the first negative voltage of the node O 1 . An output terminal of the first comparator CMP 1 is used for outputting the first comparison signal SS 1 to a first input terminal of the signal processing circuit 11 . Further, a circuit structure including the seventh resistor R 7 , the eighth resistor R 8 , the ninth resistor R 9 , the tenth resistor R 10 , and the second comparator CMP 2 is similar to the circuit structure including the first resistor R 1 , the second resistor R 2 , the third resistor R 3 , the fourth resistor R 4 , and the first comparator CMP 1 . Specifically, a first terminal of the eighth resistor R 8 is coupled to a second terminal of the coil module 15 for receiving the second negative voltage of the node O 2 . An output terminal of the second comparator CMP 2 is used for outputting the second comparison signal SS 2 to a second input terminal of the signal processing circuit 11 . In the negative voltage protection system 200 , when an intensity of the first negative voltage is greater than a predetermined value, the first comparator CMP 1 outputs the first comparison signal SS 1 with a first voltage level. When the intensity of the first negative voltage is smaller than the predetermined value, the first comparator CMP 1 outputs the first comparison signal SS 1 with a second voltage level. Similarly, when an intensity of the second negative voltage is greater than a predetermined value, the second comparator CMP 2 outputs the second comparison signal SS 2 with a first voltage level. When the intensity of the second negative voltage is smaller than the predetermined value, the second comparator CMP 2 outputs the second comparison signal SS 2 with a second voltage level. Here, the intensity of the negative voltage can be defined as an absolute value of the negative voltage. For example, an intensity of −7 volts is greater than an intensity of −1 volt. The first comparison signal SS 1 and the second comparison signal SS 2 (i.e., with the first voltage level or the second voltage level) are transmitted to the signal processing circuit 11 . In the negative voltage protection system 200 , the signal processing circuit 11 can modulate the first comparison signal SS 1 and the second comparison signal SS 2 . For example, the signal processing circuit 11 can modulate the first comparison signal SS 1 and the second comparison signal SS 2 to two ON-OFF signals, two bipolar signals, or two unipolar signals. The modulated comparison signals can be regarded as two control signals. The control signals are transmitted from the signal processing circuit 11 to the driving circuit 12 .

In the negative voltage protection system 200 , the driving circuit 12 generates a plurality of driving signals to the driving output circuit 13 according to the control signals. The driving output circuit 13 generates a plurality of power signals to the power device 14 according to the driving signals. For example, the driving output circuit 13 generates four power signals to the nodes A to D. In other words, a first output terminal of the driving output circuit 13 is coupled to the node A. A second output terminal of the driving output circuit 13 is coupled to the node B. A third output terminal of the driving output circuit 13 is coupled to the node C. A fourth output terminal of the driving output circuit 13 is coupled to the node D. The power device 14 includes a fifth transistor T 5 , a sixth transistor T 6 , a seventh transistor T 7 , and an eighth transistor T 8 . The fifth transistor T 5 includes a first terminal configured to receive a circuit voltage VCC, a second terminal configured to receive the first terminal (i.e., node O 1 ) of the second resistor R 2 , and a control terminal coupled to the first output terminal (i.e., node A) of the driving output circuit 13 . The sixth transistor T 6 includes a first terminal coupled to the second terminal of the fifth transistor T 5 , a second terminal coupled to a ground terminal GND, and a control terminal coupled to a second output terminal (i.e., node B) of the driving output circuit 13 . The seventh transistor T 7 includes a first terminal configured to receive the circuit voltage VCC, a second terminal coupled to the first terminal (i.e., node O 2 ) of the eighth resistor R 8 , and a control terminal coupled to a third output terminal (i.e., node C) of the driving output circuit 13 . The eighth transistor T 8 includes a first terminal coupled to the second terminal of the seventh transistor T 7 , a second terminal coupled to the second terminal of the sixth transistor T 6 , and a control terminal coupled to a fourth output terminal (i.e., node D) of the driving output circuit 13 . Particularly, the first terminal of the sixth transistor T 6 and the first terminal of the eighth transistor T 8 are used for outputting driving voltages to the coil module 15 in order to operate the coil module 15 . The coil module 15 can be any typed coil module, such as a coil module of brushless fan. The power device 14 can be abridge circuit-based power device. A parasitic diode PD 3 corresponds to the sixth transistor T 6 . A parasitic diode PD 4 corresponds to the eighth transistor T 8 . A method for reducing the intensity of the negative voltage is illustrated below.

For presentation completeness, all operational modes of the coil module 15 at all-time points and the operational method for reducing the intensity of the negative voltage are described. Initially, the fifth transistor T 5 and the eighth transistor T 8 are operated in a short state. The sixth transistor T 6 and the seventh transistor T 7 are operated in open state. At the moment, a current is transmitted from the fifth transistor T 5 to the eighth transistor T 8 . Then, the fifth transistor T 5 , the sixth transistor T 6 , the seventh transistor T 7 , and the eighth transistor T 8 become an open state. Thus, the coil module 15 generates a back electromotive force. As a result, a current IL is transmitted from the ground terminal GND to the node O 1 of the coil module 15 through the parasitic diode PD 3 . Since the current IL is transmitted from a high voltage terminal to a low voltage terminal inherently, equivalently, when the ground terminal GND is regarded as a terminal with zero voltage, the node O 1 becomes a terminal with a first negative voltage. When the first negative voltage exceeds a tolerant voltage, all circuit components and driving signals suffer severe interferences or disturbances, leading to a short circuit effect (i.e., large current short circuit). Thus, the coil module 15 may be burned out. To avoid high intensity of the first negative voltage, similar to operations of the negative voltage protection system 100 , the first comparator CMP 1 of the negative voltage protection system 200 compares a partitioned voltage between the first negative voltage and a reference voltage Vref, with a partitioned voltage between a voltage of ground terminal GND and the reference voltage Vref. Thus, when the intensity of the first negative voltage (i.e., for example, −7 volts) is greater than the predetermined value (i.e., for example, −3 volts) the first comparator CMP 1 outputs a first comparison signal SS 1 with a first voltage level. Here, when a voltage of the node O 2 is normal, the second comparator CMP 2 outputs a second comparison signal SS 2 with a second voltage level. The first comparison signal SS 1 and the second comparison signal SS 2 are modulated to become two control signals by using the signal processing circuit 11 for controlling the driving circuit 12 . For example, when the intensity of the first negative voltage is large, the control signal corresponding to the first comparison signal SS 1 with the first voltage level can operate the driving circuit 12 , the driving output circuit 13 , and the power device 14 to control the sixth transistor T 6 to operate in a short state. When the sixth transistor T 6 is controlled to operate in the short state, the node O 1 becomes the ground terminal GND. Thus, the intensity of the first negative voltage can be reduced or eliminated. Contrarily, when the intensity of the first negative voltage is small, the control signal corresponding to the first comparison signal SS 1 with the second voltage level maintains the sixth transistor T 6 to operate in an open state.

Afterward (i.e., in next phase), the sixth transistor T 6 and the seventh transistor T 7 become a short state. The fifth transistor T 5 and the eighth transistor T 8 become an open state. At the moment, a current is transmitted from the seventh transistor T 7 to the sixth transistor T 6 . Then, the fifth transistor T 5 , the sixth transistor T 6 , the seventh transistor T 7 , and the eighth transistor T 8 become an open state. Thus, the coil module 15 generates a back electromotive force. As a result, a current IL is transmitted from the ground terminal GND to the node O 2 of the coil module 15 through the parasitic diode PD 4 . Since the current IL is transmitted from a high voltage terminal to a low voltage terminal inherently, equivalently, when the ground terminal GND is regarded as a terminal with zero voltage, the node O 2 becomes a terminal with a second negative voltage. When the second negative voltage exceeds a tolerant voltage (i.e., a predetermined value), the second comparator CMP 2 outputs a second comparison signal SS 2 with a first voltage level. Here, when a voltage of the node O 1 is normal, the first comparator CMP 1 outputs a first comparison signal SS 1 with a second voltage level. The first comparison signal SS 1 and the second comparison signal SS 2 are modulated to become two control signals by using the signal processing circuit 11 for controlling the driving circuit 12 . For example, when the intensity of the second negative voltage is large, the control signal corresponding to the second comparison signal SS 2 with the first voltage level can operate the driving circuit 12 , the driving output circuit 13 , and the power device 14 to control the eighth transistor T 8 to operate in a short state. When the eighth transistor T 8 is controlled to operate in the short state, the node O 2 becomes the ground terminal. Thus, the intensity of the second negative voltage can be reduced or eliminated. Contrarily, when the intensity of the second negative voltage is small, the control signal corresponding to the second comparison signal SS 2 with the second voltage level maintains the eighth transistor T 8 to operate in an open state.

In other words, when the intensity of the first negative voltage or the second negative voltage is greater than a predetermined value, a corresponding transistor is operated in the short state. Thus, since the transmission path of the current IL from the ground terminal GND to the coil module 15 is dissipated, the intensity of the first negative voltage and/or the second negative voltage can be reduced or eliminated. As a result, since the negative voltage protection system 200 can reduce or eliminate large negative voltage, the negative voltage protection system 200 has a capability of circuit protection.

To sum up, the present invention discloses a negative voltage protection system. The method for protecting circuit components from a negative voltage is to detect the negative voltage generated by a current which is transmitted from a ground terminal to a coil module through a parasitic diode. When an intensity of the negative voltage is greater than a predetermined value, the negative voltage protection system controls a corresponding transistor to operate in the short state. Thus, the negative voltage can be reduced or eliminated. As a result, since the negative voltage protection system of the present invention can avoid large negative voltage, the negative voltage protection system has a capability of circuit protection.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.