Depletion Mode MOSFET For Overcurrent Protection

Abstract

A circuit for providing overcurrent protection is disclosed herein. The circuit features a depletion mode MOSFET connected to a resistive element, preferably a PTC (Positive Temperature Coefficient) device, and is configured such that the voltage of the PTC device is equal to the gate-source voltage of the MOSFET. The circuit may be further configured using a TVS diode to clamp the drain-source voltage of the MOSFET during an overcurrent event. Heat transfer between the MOSFET and the PTC device facilitates overcurrent protection. A two-terminal device comprising a depletion mode MOSFET, a PTC device, and a TVS diode may provide overcurrent protection to other circuits. A bidirectional circuit c comprising two MOSFETs placed on both sides of the PTC is also considered for AC voltage overcurrent protection.

Description

Technology Field

[65535] The following description concerns a depletion mode MOSFET for overcurrent protection. Background Technology Overcurrent or excess current is a situation where a current larger than intended flows through a circuit. Overcurrents can be inherently constant or transient. Voltage transients and short-duration electrical energy surges are the result of the sudden release of previously stored energy or energy induced by other means, such as heavy inductive loads or lightning. Repeatable transients frequently occur due to the operation of motors or generators, or the switching of reactive circuit components. Random transients can be caused by lightning and electrostatic discharge. Due to component miniaturization, sensitivity to electrical stresses has increased. For example, microprocessors have structures and conductive paths that cannot handle high currents during ESD transients. Since these components operate at very low voltages, high priority is given to controlling voltage disturbances to prevent device interruptions and potential or catastrophic errors. Current improvements may be useful in relation to these and other considerations. means of solving the problem This summary is provided to introduce a selection of concepts in a simplified form, which is further explained in the detailed description below. This summary is not intended to identify the core or essential functions of the claims, nor is it intended to aid in determining the claims. An exemplary embodiment of a circuit for providing overcurrent protection is disclosed. The circuit comprises a metal oxide semiconductor field effect transistor (MOSFET) and a resistive device having two terminals. The first terminal is connected to the source of the MOSFET and the second terminal is connected to the gate of the MOSFET, wherein the MOSFET and the resistive device protect the circuit while an overcurrent occurs. In one embodiment, the resistive device is a Positive Temperature Coefficient (PTC) device. In one embodiment, the MOSFET is a depletion mode MOSFET. In one embodiment, the MOSFET is an N-channel depletion mode MOSFET. In one embodiment, the circuit further includes a diode connected between the second terminal of the resistive device and ground, and the diode clamps the drain-source voltage of the MOSFET during an overcurrent event. In one embodiment, the diode is a transient voltage suppression (TVS) diode. In one embodiment, the MOSFET is thermally connected to the resistive device, and in response to a circuit receiving a surge current, the MOSFET heats up the resistive device. In one embodiment, in response to a circuit receiving a surge current, the drain-source voltage V of the MOSFET DSThe nearly instantaneous increase of corresponds to the nearly instantaneous decrease of the gate-source voltage VGS of the MOSFET. In one embodiment, the PTC clamps down the surge current, and the rise in resistance of the PTC speeds up the blocking capability of the MOSFET. In one embodiment, the MOSFET has a maximum gate-to-source voltage, and the PTC has a maximum operating voltage, and the maximum operating voltage does not exceed the maximum gate-to-source voltage. An exemplary embodiment of a device connected to a circuit to provide overcurrent protection to the circuit is also disclosed. This device includes a depletion mode MOSFET and a resistive device connected between the source of the MOSFET and the gate of the MOSFET. The current passing through this device generates a voltage in the resistive device equal to the gate-to-source voltage, causing the MOSFET and the resistive device to protect the circuit during an overcurrent event. In one embodiment, the device also includes a first terminal for connecting to a voltage source of the circuit and a second terminal for connecting to a part of the circuit to be protected from an overcurrent event. In one embodiment, the resistive device is a PTC device. In one embodiment, the device has a MOSFET drain-source voltage V during overcurrent protection. DSIt includes a diode for clamping. In one embodiment, the MOSFET has a maximum gate-source voltage, and the PTC device has a maximum operating voltage, and the maximum operating voltage does not exceed the maximum gate-source voltage. In one embodiment, the voltage across the resistance of the PTC is equal to the gate-source voltage VGS of the MOSFET. An exemplary embodiment of another circuit for providing overcurrent protection is also disclosed. The circuit includes a MOSFET, a resistive device having two terminals, the first terminal being connected to the source of the MOSFET and the second terminal being connected to the gate of the MOSFET, and a second MOSFET connected to the resistive device, the gate being connected to the first terminal and the source being connected to the second terminal. In one embodiment, the resistive device is a PTC device. In one embodiment, the circuit has a drain-source voltage V across the second MOSFET. DS It further includes a clamping diode for clamping. In one embodiment, the circuit also includes an AC voltage source. In one embodiment, each MOSFET of the circuit includes an internal diode, so that one of the MOSFETs conducts to each internal diode in reverse mode. In one embodiment, the MOSFET and the second MOSFET are n-channel depletion mode MOSFETs. Brief explanation of the drawing FIG. 1 is a diagram illustrating a circuit for providing overcurrent protection according to exemplary embodiments. FIG. 2 is a diagram illustrating a circuit for providing overcurrent protection according to exemplary embodiments. FIGS. 3, 4, and 5 are waveforms of test results performed in the circuits of FIGS. 1 and FIG. 2 according to exemplary embodiments. FIG. 6 is a diagram illustrating a circuit for providing overcurrent protection according to exemplary embodiments. FIG. 7 is a diagram illustrating a circuit for providing overcurrent protection according to exemplary embodiments. FIG. 8 features two tables of test results performed on the circuit of FIG. 7 according to exemplary embodiments. FIG. 9 and FIG. 10 are waveforms of test results performed on the circuits of FIG. 6 and FIG. 7 according to exemplary embodiments. FIG. 11 and FIG. 12 are waveforms of test results performed on the circuits of FIG. 6 and FIG. 7 according to exemplary embodiments. FIG. 13 is a diagram illustrating a two-terminal device for providing overcurrent protection according to exemplary embodiments. FIG. 14 is a diagram illustrating a bidirectional MOSFET circuit arrangement for providing overcurrent protection according to exemplary embodiments. FIG. 15 is a diagram showing waveforms of test results performed on the circuit of FIG. 14 according to exemplary embodiments. Specific details for implementing the invention Several circuits for providing overcurrent protection are disclosed herein. These circuits feature a depletion-mode MOSFET connected to a resistive element including a Positive Temperature Coefficient (PTC) device, configured such that the voltage of the PTC device is equal to the gate-source voltage of the MOSFET. The circuit may be further configured using a Transient Voltage Suppression (TVS) diode to clamp the drain-source voltage of the MOSFET during an overcurrent event. Heat transfer between the MOSFET and the PTC device facilitates overcurrent protection. A two-terminal device comprising a depletion-mode MOSFET, a PTC device, and a TVS diode may provide overcurrent protection to other circuits. A bidirectional circuit comprising two MOSFETs placed on both sides of the PTC is also considered for AC voltage overcurrent protection. In an exemplary embodiment, a combination of a PTC and a depletion mode MOSFET is included in the circuit to protect each other as a current clamper-then stopper. A metal oxide semiconductor field effect transistor (MOSFET), known as a MOSFET, is a semiconductor device used to switch and amplify electronic signals in electronic devices. By adjusting the voltage at the gate, the width of the channel placed between the source and drain of the MOSFET is changed. MOSFETs are provided in various configurations depending on whether they are P-channel devices built on an N-type substrate, N-channel devices built on a P-type substrate, vertically positioned semiconductors, laterally positioned semiconductors, and depletion mode or enhancement mode. Unlike enhancement mode MOSFETs, which are turned on by applying voltage to the gate, depletion mode MOSFETs have the gate terminal at 0V (V GSIt is known as a "generally turned on" device when at (V = 0V). In addition to having a thin gate oxide layer between the source and drain regions, a conductive channel is formed beneath the gate oxide layer and between the source and drain regions using ion implantation. The active dopant concentration relative to the substrate versus the channel region is the threshold voltage (V) of the MOSFET. THIt is used to adjust the value to a desired level. Despite the name, many modern MOSFETs can be manufactured with a polysilicon gate rather than a metal gate on an insulating gate oxide. Positive Temperature Coefficient (PTC) devices are made of materials with initial resistance that responds to temperature. As the temperature of the PTC device increases, its resistance also increases. If the current passing through the PTC element increases beyond a predefined limit, the PTC element heats up, increasing its resistance and potentially dramatically reducing or blocking the current flow through the protection device. Otherwise, damage caused by unrelieved fault currents flowing through the circuit is prevented. The PTC returns to a low resistance state once the fault current subsides. Therefore, PTC devices are also called resettable fuses. Polymeric PTC devices are a specific type of device made using polymers. Both Transient Voltage Suppressors (TVS) and Zener diodes are used to absorb excess energy when the voltage level spikes above the device's clamping voltage. While Zener diodes are designed to maintain voltage more stably, TVS diodes prevent high voltage transients such as surges and ESD events. TVS diodes have faster response times than Zener diodes at the nanosecond level and can absorb higher surge currents. Protecting a circuit using TVS diodes locks transient voltages to a fixed value so that high peak voltages do not damage downstream components of the circuit. The exemplary embodiments described herein are considered with these three devices, MOSFETs, PTCs, and diodes, in mind. A circuit with a resistor connected between the gate and source of a MOSFET FIGS. 6 and 7 are representative drawings of circuits (600, 700) for providing overcurrent protection according to exemplary embodiments. Circuit (600) is identical to circuit (100) (Fig. 1), except that the resistor (108) is replaced by a positive temperature coefficient (PTC) device (608). Similarly, circuit (700) is identical to circuit (200) (Fig. 2), except that the resistor (108) is replaced by a PTC device (608). Again, one side (terminal) of the PTC device (608) is connected to the source of a MOSFET (606), and the other side (terminal) of the PTC device is connected to the gate of the MOSFET. In an exemplary embodiment, the PTC device (608) is a polymer PTC (PPTC) device. As in circuits (100 and 200), when a surge current is applied to circuit (600 or 700), the MOSFET (606) will heat up rapidly. Similarly, the PTC device (608) is designed to increase its resistance when heated. Depending on the current passing through the PTC device (608), the temperature of the PTC device increases above a predefined limit known as a trip point or trip state. This dramatically increases the resistance of the PTC device (608), thereby reducing or stopping the flow of current through the PTC. Additionally, placing the MOSFET (606) and the PTC device (608) side by side means that when receiving a surge current, the MOSFET heats up, causing the PTC device to heat up faster than in the case where the MOSFET is not present. Accordingly, in some embodiments, heat transfer from the MOSFET (606) to the PTC device (608) is present to accelerate the response of both devices to a surge event. When the PTC device (608) heats up, the resistance increases. The PTC device (608) has a holding current I H and trip current I TThere are two parameters. Unless the current flowing through the PTC device (608) exceeds the holding current, it does not enter a tripped state (where the resistance rises dramatically). However, if the current flowing through the PTC device (608) exceeds the tripped current value, the resistance of the PTC device (608) rises rapidly to block more current until it reaches a normal state, with a very small current flowing to maintain the tripped state of the PTC. The PTC is reset to a low resistance state only after the fault current is removed. FIG. 8 includes two tables (800 and 850) used to describe the results of a test performed on the circuit (700) (Fig. 7) according to an exemplary embodiment. In this example, the circuit (700) includes a PTC device (708) connected between the source and gate of a MOSFET (706) and a TVS diode (710). Both tables provide parameters for two conditions. 1) The PTC 708 is a Littelfuse ® It is an RXEF375 PTC device manufactured by (Condition 1); and 2) the PTC (708) is removed from the circuit (700) (Condition 2). This is equivalent to replacing the PTC (708) with a 0-ohm resistor. In other words, Condition 2 is simply removing the PTC (708) and connecting the source of the MOSFET (706) to the gate. In this embodiment, the MOSFET (706) is an IXTH16N10D2 D-MOSFET and the TVS diode (710) is a 30KPA30A TVS diode, both of which are Littelfuse ® It was manufactured in. Also, the circuit (700) has an input voltage V of 130V with a 1.2 / 50μs surge. in It receives. Looking at the datasheet for the IXTH16N10D2 MOSFET, V DS and V DG The maximum rated voltage for is 100V, and the maximum rating for voltage is V GSv is + / - 20V. Therefore, with a transient waveform of 1.2 / 50μs at a peak voltage value of 130V, the MOSFET absorbs surge energy and allows some let-through voltage. A TVS diode is required to further suppress surge energy. Table 800 shows the drain-source voltage V of the TVS diode (710) under PTC and non-PTC conditions. DS , gate-source voltage V GS , surge current I S and maximum clamping voltage V C Table 850 shows the drain-source voltage V for both PTC and non-PTC conditions. DS , surge current I S and MOSFET power are indicated. Tables 800 and 850 show that for surge tests, a PTC (708) connected in series with the MOSFET (706) and a PTC connected between the source and gate of the MOSFET clamp the surge level and reduce surge power loss to the MOSFET compared to when the gate is directly connected to the source of the MOSFET (Condition 2). Thus, the PTC helps clamp part of the surge level through heat dissipation, and the negative gate-source voltage (V) further blocks current passing through the depletion mode MOSFET. GS It generates (= -0.5V). The result in FIG. 8 provides data on the operation of the circuit (700) when an overvoltage is applied. In an exemplary embodiment, the circuit (700) of FIG. 1 is also used to test a constant overcurrent. Tables 800 and 850 show that placing a PTC device (608) to replace the 0-ohm resistor helps to lower the clamping voltage level VC of the TVS diode (710). Also, the PTC device (608), V GS and I S V depending on the existence of DSWhile the value increases, the MOSFET power consumed decreases. This is a promising result when providing transient or continuous overcurrent protection. The results of additional experimental tests performed on circuits (600 and 700) using different PTC devices are provided as dual waveforms in FIGS. 9 and FIGS. 10, respectively, according to exemplary embodiments. Each circuit (600 and 700) has an input voltage V of 130 V with a 1.2 / 50 μs surge in It receives. The waveform (900) shows the result of applying a surge transient to the circuit (600). Here, the PTC device (608) is a Littelfuse ® This is an RXEF375 PTC device manufactured by. The trip current I of the RXEF375 device. T is 7.50A, minimum resistance R MIN 0.03 ohms, maximum resistance R MAX Ω is 0.05 ohms. As before, the voltage V between the drain and source is DS While the gate-source voltage V immediately increases to heat the MOSFET (606), the gate-source voltage V GS The voltage drops. In this example, the surge current lasts for about 50 μs. Waveform (950) shows the result of a transient surge in circuit (700) where the PTC (708) is an RXEF375 PTC and a 30KPA30CA TVS diode (710) is used. Again, the duration of the surge current is about 50 μs, and as expected, the drain-source voltage V of the MOSFET channel DSIt is clamped by a TVS diode (710). With the help of an RXEF375 PTC (708), the current is fixed at approximately 13.57 A. The surge waveform is characterized as a 1.2 / 50 μs wave with a peak voltage of 130 V and a peak current of 130 V / 2 ohms = 65 A (2 ohms is the virtual impedance of the surge generator network for the 1.2 / 50 μs waveform). With the help of an RXE375 PTC (708), the current is fixed at approximately 13.75 A. As before, the thermal effect between the MOSFET and each PTC in the two circuits helps the circuit to respond more to the surge current. In FIG. 10, waveform (1000) shows the result of applying a surge transient to the circuit (600) with the PTC device (608) removed (R = 0 ohms). The voltage V between the drain and source. DS increases immediately, and the gate-source voltage V GS is not changed. Surge current I S It lasts for about 40 μs. Waveform (1050) shows the result of a transient surge in a circuit (700) where the PTC (708) is removed and a 30KPA30CA TVS diode (710) is used. Surge current I S The duration is maintained at approximately 40μs, and the MOSFET channel V DS The drain-source voltage of is clamped. The gate-source voltage V of the MOSFET (706). GS When short-circuited, the current is clamped at approximately 26.36 A, which is greater than that of a PTC connected in series between the gate and source (Fig. 9). Therefore, there are two effects on the PTC. The first is an increase in resistance in response to the surge, and the second is the gate-source voltage V GSThe purpose is to increase the resistance of the MOSFET to a more negative level. This demonstrates the advantage of using a PTC between the gate and source of the MOSFET, rather than simply connecting the gate and source terminals. Again, the thermal effect between the MOSFET and the PTC is observed in both circuits (600 and 700). The above circuits can be tested with different input voltages, MOSFETs, PTC devices, and TVS diodes. The results of experimental tests performed on the circuits (600 and 700) according to one embodiment are provided as the dual waveforms of FIGS. 11 and FIGS. 12, respectively. In each dual waveform, the gate-source voltage (V) of the MOSFET (606) GS ), MOSFET drain-source voltage (V DS ), surge current I S The three parameters of the input voltage V in It is characterized by. In other words, the voltage (V) across the MOSFET (606). DS ), surge current I S The voltage (V) across the PTC device (608) generated at GS ) is measured. The two circuits (600) and (700) receive an input voltage V of 100V at a surge of 1.2 / 50μs. In FIG. 11, the waveform (1100) is the PTC device (608) Littelfuse ® This shows the result of applying a transient surge to the circuit (600) (Fig. 6), which is an RXEF030 PTC device manufactured by [company name]. The trip current I of the RXEF030 device. T is 0.60A, minimum resistance R MIN 0.88 ohms, maximum resistance R MAX is 1.33 ohms. The circuit (600) has a surge current I at the trigger point T (0μs). S It undergoes. The voltage V between the drain and the source. DS increases immediately and then decreases for more than about 60μs. Meanwhile, the gate-source voltage V GSIt drops very rapidly to about 20V. Surge current I in waveform (1100) S It lasts for about 67 μs, which is significantly less than waveforms (300), (400), and (500). The second waveform (1150) in FIG. 11 shows the result of applying a surge transient to circuit (700) (Fig. 7), where the PTC (708) is an RXEF030 PTC device and the TVS diode (710) is a 30KPA30CA diode. Here, the TVS diode (710) is the MOSFET channel V DS Clamp the voltage through to less than 40V. Surge current I S The duration of is about 65 μs, which is slightly shorter than in waveform (1100). Therefore, V DS In addition to clamping, the TVS diode (612) also clamps the surge current I compared to what is shown in the waveform (1100). S It has a positive effect by lowering the duration of. At waveforms (1100 and 1150), V DS The voltage across the MOSFET (606) given by is the surge current I S It is rapidly increasing when receiving (despite the voltage being clamped by the TVS diode (708) in waveform (1150)). The nearly instantaneous voltage increase between the drain and source means that the MOSFET (606) is heating up. Meanwhile, V GS The voltage across the PTC device (608) given by is decreasing. However, as the current surge ends, the PTC device (608) heats up as shown in the waveform. Therefore, the MOSFET (606) has a thermal effect on the PTC device (608), which allows the circuit (600) to respond more quickly to the surge current. Continuing in FIG. 12, the waveform (1200) shows the result of applying a surge transient to the circuit (600). Here, the PTC device (608) is a Littelfuse ®It is also an RXEF065 PTC device manufactured by. The trip current I of the RXEF065 device T is 1.30A, minimum resistance R MIN Ω is 0.31 ohms, maximum resistance R MAX is 0.48 ohms. As before, the voltage V between the drain and source is DS immediately increases, and the gate-source voltage V GS It drops. Surge current I S It lasts for about 65 μs. Waveform (1150) shows the result of a transient surge in a circuit (700) where the PTC (708) is an RXEF065 PTC and a 30KPA30CA TVS diode (710) is used. In this case, the surge current I S The duration is approximately 65μs and the MOSFET channel V DS The drain-source voltage is clamped by the TVS diode (710). As with circuit (600), waveforms (1200 and 1250) show the MOSFET (706) in circuit (700) experiencing a nearly instantaneous voltage increase V DS Indicates that it is heating up due to. Although the PTC (708) was not heated initially, the surge current I S V as decreases GS The increase shows that the PTC (708) is being heated by a thermal effect close to the MOSFET (706). This thermal effect makes the circuit (700) more responsive to surge current in some embodiments. 2-Terminal Device Application FIG. 13 illustrates a representative diagram of a circuit (1300) for providing overcurrent protection according to exemplary embodiments. The circuit (1300) features a depletion mode MOSFET (1304), a positive temperature coefficient (PTC) device (1308), and a TVS diode (1312). Similar to the PTC devices (608 and 708) in the circuits (600 and 700) above, the PTC device (1308) is connected in series with the MOSFET (1304) between the source and the gate. Thus, the voltage across the PTC device is the gate-source voltage V of the MOSFET (1304). GS It is identical to. In one embodiment, the MOSFET (1304) is an n-channel depletion mode MOSFET. In an exemplary embodiment, the PTC device (1308) is a polymer PTC (PPTC) device. Because it is a depletion mode device, the MOSFET (1304) has a negative threshold voltage V TH It has. In the case of a depletion mode MOSFET, the channel is completely conductive and the gate terminal is 0V (V GS When = 0), a strong current flows between the drain and the source. As increasingly negative bias occurs at the gate of an N-channel MOSFET, channel conduction decreases, and finally -V GS (Off) Device threshold voltage V TH It reaches and conduction through the MOSFET stops. These two hours (V GS = 0 V and V GS = -V THBetween (when), the resistance across the channel of the MOSFET (1304) will increase. Therefore, when a surge current is applied to the circuit (1300), the MOSFET (1304) will heat up rapidly. Similarly, the PTC device (1308) is designed to increase its resistance when heated. Depending on the current passing through the PTC device (1308), the temperature of the PTC device increases above a predefined limit known as a breakpoint. This dramatically increases the resistance of the PTC device (1308), reducing or stopping the flow of current through the PTC. Additionally, placing the MOSFET (1304) and the PTC device (1308) side by side means that when a surge current is received, the MOSFET (1304) will heat up, causing the PTC device (1308) to heat up faster than in the case where the MOSFET is not present. Therefore, in some embodiments, heat transfer from the MOSFET (1304) to the PTC (1308) is present to accelerate the response of both devices to a surge event. When the PTC (1308) heats up, the resistance increases. A voltage is generated across the PTC (1308), which eventually reaches the threshold voltage (V) of the MOSFET (1304). TH The MOSFET is turned off beyond a certain limit. Since the gate is connected to one side of the PTC (1308), there is no need to apply a separate voltage to the gate. In an exemplary embodiment, the circuit (1308) is packaged as a two-terminal device used as overcurrent protection in another circuit. Thus, the first terminal (1314) of the device (1300) is connected to a voltage source of the circuit to be protected, and the second terminal (1316) is connected to a part of the circuit to be protected (e.g., a downstream component of the device). In an exemplary embodiment, the device (1300) protects against both constant overcurrent and transient overcurrent. Bidirectional MOSFET circuit FIG. 14 is a representative diagram of a circuit (1400) comprising a pair of MOSFETs providing bidirectional protection connected to a PTC device positioned between two MOSFETs according to exemplary embodiments. The circuit (1400) includes a voltage input (1402) which is an AC input, a switch (1404), a first depletion mode MOSFET (1406), a PTC device (1408), a second depletion mode MOSFET (1412), and a CKT (1410). In one embodiment, the MOSFETs (1406 and 1412) are n-channel depletion mode MOSFETs connected in a back-to-back configuration. In an exemplary embodiment, the PTC device (1408) is a polymer PTC (PPTC) device. The PTC device (1408) is connected to the source of the MOSFET (1406) at the first end and to the gate of the same MOSFET at the second end, as before. With the introduction of the second MOSFET, the first end is connected to the gate of the MOSFET (1412) and the second end is connected to the source of the second MOSFET. When the circuit (1400) receives an AC voltage input, one of the MOSFETs is configured as an internal diode. When a positive cycle AC current flows into the circuit (1400), the first MOSFET (1406) and the PTC (1408) act together as a current limiter, while the other MOSFET (1412) operates in reverse mode so that only the body diode of the MOSFET (1412) conducts current. This operation is reversed when another cycle of AC current flows. That is, the MOSFET (1412) and the PTC (1408) act together as a current limiter, and only the diode of the MOSFET (1406) conducts current. Thus, this circuit (1400) provides AC current limiting protection. In one embodiment, the CKT (1410) is replaced with a bidirectional diode to clamp the voltage across both the MOSFET (1412) and the MOSFET (1406).In the second embodiment, the diode is a bidirectional TVS diode, so it protects against bidirectional surge current. Also, in one embodiment, Since the RMS voltage multiplied by is the DC peak voltage, the AC RMS voltage is limited to 17V during a long-term overcurrent PTC trip to ensure that the gate-source voltage VGS does not exceed 25V (17V x 1.414 = 24V). The results of experimental tests performed on the circuit (1400) are provided as the dual waveforms of FIG. 15 according to an exemplary embodiment. The circuit (1400) receives an input voltage Vin of 90V at a surge of 1.2 / 50μs. The AC RMS voltage is V during a long-term overcurrent PTC trip. GS The voltage is limited to a maximum of 17V so that it does not exceed 25V. Both MOSFETs (1406) and (1412) are Littelfuse ® It is IXTH16N10D2 manufactured by (V DS = 100V, I D(on) = 16A, R DS(on) = 64 milliohm mounting torque (using TO-247) PTC device (1408) has a maximum resistance R MAX is an RXEF375 of 0.05 milliohm. Waveform 1500 is the gate-source voltage (V) of the MOSFET (1306). GS ), MOSFET drain-source voltage (V DS ), surge current I S The three parameters of are the input voltage, V in It is characterized by. In other words, the voltage (V) across the MOSFET (1406). DS ), surge current I S Voltage across the PTC (1408) (V) caused by GS ) is measured. In waveform (1450), the gate-source voltage (V) of the MOSFET (1412) is measured. GS ), MOSFET drain-source voltage (V DS ) and surge current I S is the input voltage Vin It is due to. In other words, surge current I S The voltage (V) across the MOSFET (1412) generated from DS ), voltage across PTC (1408) (V GS ) is measured. Therefore, the voltage across the PTC (1408) is the gate-source voltage of the two MOSFETs (1406 and 1412). Waveforms (1500) and (1550) are nearly identical. Thus, there is almost symmetry between them. This indicates that the back-to-back MOSFET and PTC configuration of the circuit (1400) provides AC power protection. In some cases, the above embodiment considers specific versions of depletion mode MOSFETs, PTC devices, and TVS diodes. Nevertheless, other devices in one or more of the aforementioned circuits may be used to provide overcurrent protection for various other applications. In some embodiments, the parameter V DSX = 100V, I D(on) ≥ 16A, and R DS(on) An N-channel depletion mode MOSFET IXTT16N10D2 or IXTH16N10D2 having ≤ 64 milliohms is used for the MOSFET. In some embodiments, an N-channel depletion mode MOSFET IXTY08N50D2, IXTA08N50D2 or IXTP08N50D2 (parameter V DSX 500V, I D (on) ≥ 800mA and R DS(on) Littelfuse having (≤4.6 ohms) ® A MOSFET manufactured in is used. In some embodiments, parameter V DSX 500V, I D (on) ≥ 16A and R DS(on) An N-channel depletion mode MOSFET IXTH16N50D2 or IXTT16N50D2 having ≤ 300 milliohm is used for the MOSFET. Additionally, in some embodiments, a Littelfuse ® Poly-Fuse of the 72R series manufactured by® A radial lead resettable PTC is used in the PTC device. In some embodiments, Littelfuse ® Polyswitch of the RXEF series manufactured by ® A radial lead resettable PPPT is used in a PTC device. In some embodiments, a Littelfuse ® The 30KPA series axial lead transient voltage suppression diode manufactured by is used in the TVS diode. Littelfuse ® Alternatively, the use of other devices manufactured by other device manufacturers may be considered without departing from the concept of the present disclosure. In an exemplary embodiment, with the introduction of a PTC device, a depletion mode MOSFET connected to the PTC device is shown to operate together to limit overcurrent under both transient and continuous conditions. In one embodiment, the combination of a MOSFET and a PTC in the circuit is such that the maximum gate-source voltage V of the MOSFET GSAnd it operates at less than 30V because it is lower than the maximum PTC operating voltage. In another embodiment, to prevent damage to the depletion mode MOSFET, the input voltage range is limited to between 5 and 24V, which are functional operating voltage levels. In another embodiment, adding a heat sink to the depletion mode MOSFET can extend the thermal performance of the MOSFET because the presence of the heat sink improves the overall thermal impedance. As used herein, elements or steps referred to in the singular and proceeding with the word "a" or "an" should be understood as not excluding elements or steps in the plural unless such exclusion is explicitly stated. Furthermore, references to "one embodiment" in this disclosure are not intended to be interpreted as excluding the existence of additional embodiments including the cited features. While this disclosure refers to specific embodiments, various modifications, changes, and alterations to the described embodiments are possible without departing from the scope and range of this disclosure, as defined in the appended claim(s). Accordingly, the present disclosure is not limited to the described embodiments and is intended to have the full scope defined by the language of the following claims and their equivalents.

Claims

Claim 1 A circuit capable of operating to provide overcurrent protection, comprising: a first MOSFET; a resistive device having two terminals, the first terminal being connected to the source of the first MOSFET and the second terminal being connected to the gate of the first MOSFET; a second MOSFET connected to the resistive device; and a drain-source voltage V across the first MOSFET and the second MOSFET. DS A circuit comprising a bidirectional diode that clamps down, wherein the gate of the second MOSFET is connected to the first terminal and the source of the second MOSFET is connected to the second terminal, and the resistive device comprises a positive temperature coefficient (PTC) device. Claim 2 In claim 1, the circuit further comprises a voltage source, and the voltage source is an AC voltage source. Claim 3 In paragraph 2, each MOSFET further comprises an internal diode, and the first MOSFET or the second MOSFET conducts to each internal diode in reverse mode, circuit. Claim 4 In claim 1, the circuit wherein the first MOSFET and the second MOSFET are n-channel depletion mode MOSFETs. Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 delete Claim 9 delete Claim 10 delete Claim 11 delete Claim 12 delete Claim 13 delete Claim 14 delete Claim 15 delete Claim 16 delete Claim 17 delete Claim 18 delete Claim 19 delete Claim 20 delete

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