Voltage gate driver for a semiconductor-based transistor, power switching device, and corresponding method

Abstract

A voltage gate driver for a semiconductor-based transistor, the voltage gate driver comprising: a voltage generator circuit arranged to receive a drive voltage, the voltage generator circuit including a capacitor connected in series with a Zener diode, wherein a cathode of the Zener diode is arranged to be connected to a gate of the semiconductor-based transistor; a bias current circuit connected in parallel across the capacitor, wherein the bias current circuit includes a switch and is arranged to provide a bias current to the cathode of the Zener diode based on a state of the switch, wherein the bias current circuit is arranged to provide the bias current to the cathode of the Zener diode when the switch is in a closed state and is arranged to prevent the provision of the bias current to the cathode of the Zener diode when the switch is in an open state.

Description

Technical Field

[0001] The present invention generally relates to gate drivers for semiconductor-based transistors, and more particularly, to increasing the effective threshold voltage of semiconductor-based transistors. Background Art

[0002] Some semiconductor-based transistors have an intrinsic property, that is, their threshold voltage is relatively low compared to, for example, silicon-based metal-oxide-semiconductor field-effect transistors (MOSFETs). This is especially true for enhancement-mode gallium nitride high electron mobility transistors (GaN HEMTs) and silicon carbide MOSFETs. For example, when a conductive channel is formed between the source and drain of a transistor, the threshold voltage can be considered as the voltage at the gate of the transistor.

[0003] The voltage applied between the gate terminal and the source terminal of a semiconductor-based transistor controls the resistance of the conductive channel between the source terminal and the drain terminal of the transistor. If the gate-source terminal of the HEMT is approximately zero, the HEMT is turned off and the resistance of the conductive channel is very high. If the gate-source terminal of the HEMT is higher than its rated threshold voltage, the HEMT is turned on and the resistance of the conductive channel is very low, typically in the mΩ range.

[0004] Therefore, the HEMT can exhibit almost ideal controlled-switching characteristics. Thus, the HEMT has wide applicability as a power switch in a switched-mode power supply. Generally, these HEMTs and other semiconductor-based transistors have the characteristic that their threshold voltage is much lower, and the prior art has not found a way to significantly increase it.

[0005] A typical high-voltage HEMT has a threshold voltage in the range of 1V to 1.5V, while a corresponding silicon-based MOSFET can be designed to have a threshold voltage of 4V or even greater. This low threshold voltage can be disadvantageous, especially for high-power, high-voltage offline AC-DC (alternating current-direct current) and other high-voltage switched-mode power supplies, because these may generate a large amount of switching noise, which may couple into the gate-source circuit of the HEMT and may cause false turn-on and turn-off of the HEMT.

[0006] The present disclosure provides a solution to the above problems. Summary of the Invention

[0007] An overview of aspects of certain examples disclosed herein is presented below. It should be understood that these aspects are presented only to provide a brief overview of these particular embodiments to the reader and are not intended to limit the scope of the present disclosure. Indeed, the present disclosure may cover various aspects and / or combinations of aspects that may not be set forth.

[0008] The object of the present disclosure is to provide a voltage gate driver for a semiconductor-based transistor that is capable of offsetting the turn-off state voltage of a HEMT, thereby effectively increasing the gate-source voltage such that it is less susceptible to noise. Another object of the present disclosure is to provide a corresponding power switching device and related method.

[0009] In a first aspect, there is provided a voltage gate driver for a semiconductor-based transistor, the voltage gate driver comprising:

[0010] A voltage generator circuit arranged to receive a drive voltage, the voltage generator circuit comprising a capacitor connected in series with a Zener diode, wherein the cathode of the Zener diode is arranged to be connected to the gate of the semiconductor-based transistor;

[0011] A bias current circuit connected in parallel across the capacitor, wherein the bias current circuit comprises a switch and is arranged to provide a bias current to the cathode of the Zener diode based on the state of the switch, wherein the bias current circuit is arranged to provide the bias current to the cathode of the Zener diode when the switch is in the closed state and is arranged to prevent the provision of the bias current to the cathode of the Zener diode when the switch is in the open state.

[0012] The inventors have found that it may be useful to provide an offset voltage to the gate of a HEMT whenever the gate of the HEMT is not being driven. This is particularly useful in the case where the HEMT is used as a switch, where a drive voltage turns the switch on or off. Thus, it has been found that an offset voltage can be provided to the gate of the HEMT when the drive voltage causes the switch to be turned off.

[0013] The above is achieved by a voltage generator circuit. The voltage generator circuit is arranged to receive a drive voltage and comprises a capacitor connected in series with a Zener diode, the output of the Zener diode being arranged to be connected to the gate of a semiconductor-based transistor (i.e., the switch).

[0014] The Zener diode can be selected such that its breakdown voltage plus any forward voltage of the diode connected in series with the Zener diode is approximately equal to the on-state voltage of the semiconductor-based transistor. For a HEMT, this can typically be 5V to 6V.

[0015] What is effectively achieved above is that the voltage across the capacitor is equal to the drive voltage minus the on-state voltage of the semiconductor-based transistor. However, whenever the drive voltage becomes zero, the capacitor will retain its charge, and the corresponding voltage will appear across the gate of the HEMT with the opposite polarity. Thus, this effectively establishes an offset voltage at the gate of the semiconductor-based transistor.

[0016] The inventors have found that the above solution may have drawbacks. The main drawback is that a typical Zener diode used for this purpose can be very inaccurate. The breakdown voltage of the Zener diode strongly depends on the current flowing through the Zener diode. Essentially, as soon as the gate capacitance of the semiconductor-based transistor is charged, the output voltage at the cathode of the Zener diode drops to a very low value. As a result, the semiconductor-based transistor may not be able to remain properly on.

[0017] It has been found that introducing a bias current circuit may be beneficial. The bias current circuit is arranged to supply a bias current to the Zener diode to mitigate the above drawbacks. The bias current can be connected in parallel with the capacitor such that the capacitor discharges slowly to the Zener diode through the bias current circuit.

[0018] In addition to the above, the inventors have found that whenever the drive voltage drops to zero, the capacitor can discharge completely or nearly completely across the bias current circuit. This is disadvantageous because it will reduce the offset voltage at the gate of the semiconductor-based transistor. This problem may become worse for reducing the operating frequency and duty cycle.

[0019] Therefore, the inventors have found that introducing a switch in the bias current circuit, where the bias current circuit is arranged to supply the bias current to the cathode of the Zener diode when the switch is in the closed state, and is arranged to prevent the supply of the bias current to the cathode of the Zener diode when the switch is in the open state.

[0020] The main benefit is that during the off-state of the semiconductor-based transistor, no bias current needs to flow through the Zener diode, enabling the bias current circuit to be disabled overall. This is achieved by the switch of the bias current circuit, and this ensures that the offset voltage does not decrease slowly because the capacitor does not discharge slowly across the bias current circuit.

[0021] The accuracy of the Zener diode is required during the on-state of the semiconductor-based transistor, such that it is beneficial if a bias current is supplied to the Zener diode during the on-state. In this way, the switch of the bias current circuit will close to ensure that the bias current is supplied to the Zener diode.

[0022] The advantages of the above - proposed solution are: 1) enabling a bias current to be available to the Zener diode during the on - state of the semiconductor - based transistor, thereby making the Zener diode more accurate, and 2) enabling a bias current to be available to the node during the off - state of the semiconductor - based transistor, i.e., the capacitor does not discharge, thereby ensuring a stable offset voltage during the entire off - state period of the semiconductor - based transistor.

[0023] In one example, the gate of the switch is arranged to receive the drive voltage.

[0024] The advantage of this example is that no additional control circuit is required, which is arranged to activate the switch during the expected on - state of the semiconductor - based transistor and to deactivate the switch during the expected off - state of the semiconductor - based transistor. This drive voltage can be used for this specific purpose.

[0025] The switch of the bias current circuit can be, for example, a metal - oxide - semiconductor field - effect transistor MOSFET.

[0026] The MOSFET can be self - biased such that when driven by the drive voltage, it automatically turns on and off at the correct time. Generally, a P - channel MOSFET will be preferably used for this purpose.

[0027] A MOSFET is generally an insulated - gate field - effect transistor made of a semiconductor material (such as silicon or silicon carbide material). The voltage at the gate terminal determines the conductivity of the device. The MOSFET of the bias current circuit can be used as a switch such that the conductivity of the device is either fully conductive or fully resistive.

[0028] In another example, the bias current circuit includes a resistor connected in series with the switch.

[0029] The bias current circuit is connected in parallel with the capacitor of the voltage generator circuit. This means that the capacitor can discharge through the resistor, thereby providing a bias current to the Zener diode. Then, the switch is deactivated to ensure that no bias current flows to the Zener diode whenever the drive voltage intends to turn off the semiconductor - based transistor.

[0030] In one example, the voltage gate driver is arranged to drive a gallium nitride high - electron - mobility transistor GaN HEMT.

[0031] Generally, during the off - state of the GaN HEMT, a negative offset voltage is provided to the gate of the GaN HEMT.

[0032] In another example, the voltage driver further includes:

[0033] A rise and fall time control circuit, which is arranged to receive the drive voltage and to reduce the rise and / or fall time of the received drive voltage.

[0034] In another example, the anode of the Zener diode is grounded. The voltage driver may further include a diode, wherein the anode of the Zener diode is grounded via the diode.

[0035] Note that according to the present disclosure, wherever it is mentioned that a component is connected to a second component, it does not mean that these components need to be directly connected to each other. According to common practice, these components are connected to each other directly or indirectly such that other components can be placed between the connected components.

[0036] In a second aspect of the present disclosure, there is provided a power switching device, such as a switched-mode power supply SMPS, which includes a semiconductor-based transistor and a voltage driver according to any of the previous examples.

[0037] Note that the advantages explained with reference to the first aspect of the present disclosure (i.e., the voltage gate driver) also apply to the second aspect of the present disclosure (i.e., the power switching device).

[0038] In one example, the semiconductor-based transistor of the power switching device is a gallium nitride high electron mobility transistor GaN HEMT.

[0039] There are different types of switched-mode power supplies applicable according to the present disclosure, namely buck converters, boost converters, buck-boost converters, flyback converters, forward converters, etc. The switched-mode power supply may or may not have an isolation topology including a transformer.

[0040] In a third aspect of the present disclosure, there is provided a method of operating a voltage driver according to any of the previous examples, wherein the method includes the following steps:

[0041] When the switch is in the closed state, providing the bias current to the cathode of the Zener diode through the bias current circuit, and

[0042] When the switch is in the open state, preventing the bias current from being provided to the cathode of the Zener diode through the bias current circuit.

[0043] Note that the advantages explained with reference to the first aspect of the present disclosure (i.e., the voltage gate driver) also apply to the second aspect of the present disclosure (i.e., the method of operating the voltage driver).

[0044] Although the technical solution is described herein with reference to an n-channel device that is turned on by a positive gate voltage, it is also applicable to p-channel devices in which all voltages are inverted. For example, it can be applied to a p-channel MOSFET, where the normal zero to negative gate drive voltage can be shifted above zero during the off-time of the device to make it positive, and increase the effective threshold voltage of the MOSFET.

[0045] The present disclosure is described in conjunction with the accompanying drawings. It should be emphasized that, in accordance with standard practice in the industry, the various features are not drawn to scale. In fact, for clarity of discussion, the dimensions of the various features may be arbitrarily increased or decreased.

[0046] In the drawings, like components and / or features may have the same reference numerals. Additionally, various components of the same type may be distinguished by following the reference numeral with a dash and a second numeral that differentiates the similar components. If only the first reference numeral is used in the specification, the description applies to any of the similar components having the same first reference numeral, regardless of the second reference numeral.

[0047] The above and other aspects of the present disclosure will be apparent and will be elucidated with reference to the examples described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Examples of semiconductor-based transistors and their gate voltage definitions are disclosed;

[0049] Figure 2 A conceptual diagram of a voltage gate driver according to the present disclosure is disclosed;

[0050] Figure 3 A voltage gate driver according to the prior art is disclosed;

[0051] Figure 4 Examples of voltage gate drivers according to the present disclosure are disclosed;

[0052] Figure 5 Voltage diagrams of a voltage gate driver according to the prior art and a voltage gate driver according to the present disclosure are disclosed. DETAILED DESCRIPTION

[0053] Note that in the description of the drawings, like reference numerals represent the same or similar components performing the same or substantially similar functions.

[0054] A more detailed description is provided with reference to specific examples, some of which are illustrated in the accompanying drawings, so that the features of the present disclosure can be understood in more detail. Note that the accompanying drawings only show typical examples and should not be considered as limiting the scope of the subject matter of the claims. The accompanying drawings are incorporated to facilitate understanding of the present disclosure and are not necessarily drawn to scale. After reading the specification in conjunction with the accompanying drawings, the advantages of the claimed subject matter will become apparent to those skilled in the art.

[0055] The following description only provides preferred exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the present disclosure. On the contrary, the following description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing the preferred exemplary embodiments of the present disclosure. It should be understood that various changes can be made to the functions and arrangements of the elements (including combinations of features from different embodiments) without departing from the scope of the present disclosure.

[0056] Unless the context clearly requires otherwise, throughout the specification and claims, the words "comprise", "comprising", etc. shall be construed in an inclusive sense rather than an exclusive or exhaustive sense; that is, in the sense of "including but not limited to". As used herein, the term "connected", "coupled" or any variation thereof means any direct or indirect connection or coupling between two or more elements; the coupling or connection between elements can be physical, logical, electromagnetic, or a combination thereof. Additionally, the words "herein", "above", "below", and words of similar import when used in this application refer to the entire application rather than any particular part of the application. Where the context permits, the use of singular or plural words in the detailed description may also respectively include the plural or singular. The word "or" with respect to a list of two or more items covers all of the following interpretations of that word: any item in the list, all items in the list, and any combination of items in the list.

[0057] These and other changes to the technology can be made in light of the following detailed description. Although this specification describes certain examples of the technology and describes the best mode contemplated, no matter how detailed this specification may appear, the technology can be practiced in many ways. The details of the system can vary considerably in its specific implementation while still being encompassed by the technology disclosed herein. As noted above, the specific terms used when describing certain features or aspects of the technology should not be taken to imply that the term is re - defined herein to be limited to any specific characteristic, feature, or aspect of the technology with which the term is associated. In general, the terms used in the appended claims should not be construed to limit the technology to the specific examples disclosed in the specification unless the detailed description section explicitly defines such terms. Thus, the actual scope of the technology includes not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

[0058] Figure 1 Examples of semiconductor - based transistors and their gate voltage definitions are disclosed.

[0059] The transistor shown on the left can be any one of a HEM, MOSFET, or any other type of transistor. The transistor includes a gate “Gate”, a source “Source”, and a drain “Drain”.

[0060] According to the present disclosure, the transistor can be turned on or off based on the gate - source voltage “Vgs”. Then, the transistor will operate essentially as a switch, where the drain - source connection is low - ohmic (on), or the drain - source connection is high - ohmic (off).

[0061] The illustration on the right shows the threshold voltage of the transistor “V_threshold” and the drive signal on the gate of the transistor. The transistor can be driven with a high voltage (i.e., “V_high”), which is much higher than the threshold voltage, to achieve the conduction of the transistor. The transistor can be driven with a low voltage (i.e., zero voltage “0”), which is lower than the threshold voltage, to achieve the turn - off of the transistor. The above cases are visually represented in Figure 1 Intuitively represented.

[0062] Figure 2 A conceptual diagram of a voltage gate driver according to the present disclosure is disclosed.

[0063] The inventors have found that for certain semiconductor - based transistors, such as HEMT, the threshold voltage can be relatively low. This is also visually shown in Figure 1 One of the disadvantages is that any noise introduced may cause the gate - source voltage Vgs to inadvertently rise above the threshold voltage, thus turning on the semiconductor - based transistor. This is undesirable.

[0064] In this way, a solution is found in which a voltage generator circuit is introduced between the generated drive voltage and the gate of a semiconductor-based transistor. In Figure 2 the illustrated embodiment, whenever the drive voltage is low, the voltage generator circuit effectively reduces the voltage at the gate of the semiconductor-based transistor. This is denoted by the reference symbol "-Vneg".

[0065] The voltage generator circuit may include a capacitor connected in series with a Zener diode, wherein the cathode of the Zener diode is arranged to be connected to the gate of the semiconductor-based transistor. This circuit can be considered a voltage divider such that the drive voltage is divided across the capacitor and the Zener diode. Thus, the drive voltage is equal to "Vgate + Vneg", while the voltage at the gate is "Vgate", which is equal to the voltage across the Zener diode. The voltage across the capacitor is equal to "Vneg".

[0066] During the off state, i.e., when the drive voltage is zero, the polarity of the voltage across the capacitor flips such that a negative voltage "-Vneg" is provided to the gate of the semiconductor-based transistor.

[0067] The voltage gate driver may further include a rise and fall time control circuit arranged to receive the drive voltage and to reduce the rise and / or fall time of the received drive voltage.

[0068] Figure 3 A voltage gate driver according to the prior art is disclosed.

[0069] The rise and fall time control circuit can be represented by components with reference numerals R1, R2, and D1. They ensure that the slope of the drive voltage is reduced.

[0070] A voltage generator circuit is provided, which is composed of a capacitor C1, a Zener diode D6, and an additional diode D5. The voltage across the series-connected Zener diode D6 and another diode D5 is provided to the gate of the semiconductor-based transistor. The capacitance of the gate is visually represented by a capacitor C2.

[0071] There is a bias current circuit, which is formed by a resistor R4 placed in parallel with the capacitor C1. The implementation of the bias current lies in the discharge of the capacitor C1 across R4, and this discharge current is provided to the Zener diode. Note that the gate of the semiconductor-based transistor is considered to have a very high impedance such that this bias current will flow through the Zener diode.

[0072] Figure 4 An example of a voltage gate driver according to the present disclosure is disclosed.

[0073] One disadvantage of the bias current as described above is that whenever the drive voltage is low, the capacitor C1 will be discharged. This has an effect on the voltage supplied to the gate of the semiconductor-based transistor. The effect is that whenever the capacitor is fully discharged, there is no longer an offset voltage (i.e., a negative voltage).

[0074] For a drive voltage with a low frequency, this disadvantage is particularly evident because it can lead to the following situation: the capacitor is fully discharged on R4 during a relatively long off-state of the transistor.

[0075] The present inventors have found a beneficial way to overcome the above-mentioned drawbacks, that is, to provide a switch M1 in series with the resistor R4, where during the on-state, i.e., whenever the drive voltage is high, the switch is activated so that the bias current is supplied to the Zener diode, and during the off-state, i.e., whenever the drive voltage is low, the switch is deactivated so that no bias current is supplied to the Zener diode. Then, during the off-state, the capacitor will not be able to discharge through the resistor R4, so that the offset voltage at the gate of the semiconductor-based transistor can be maintained for a longer time period.

[0076] Figure 5 Voltage diagrams of a voltage gate driver according to the prior art and a voltage gate driver according to the present disclosure are disclosed.

[0077] On the Figure 5 left side shows the timing diagram of a conventional gate driver, and on the right side shows the voltage gate driver according to the present disclosure.

[0078] On the left side, it is clearly shown that the negative voltage applied to the gate of the semiconductor-based transistor during the off-state of the semiconductor-based transistor cannot be maintained because the voltage gradually returns to zero. This is again caused by the discharge of the capacitor on the resistor.

[0079] On the right side, it is clearly shown that the negative voltage applied to the gate of the semiconductor-based transistor during the off-state of the semiconductor-based transistor can be maintained for a longer time because the capacitor can no longer discharge itself on the resistor R4.

[0080] Above, the present disclosure is explained by taking a semiconductor-based transistor as a HEMT. It should be noted that the present disclosure can be applied to any semiconductor-based transistor having a gate terminal, a source terminal, and a drain terminal.

[0081] To reduce the number of claims, certain aspects of the present technology are presented in the form of certain claims below, but the applicant contemplates various aspects of the present technology in any number of claim forms. For example, while some aspects of the present technology may be described as computer-readable medium claims, other aspects may equally be implemented as computer-readable medium claims, or in other forms, such as apparatus-plus-function claims.

[0082] In the foregoing description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the implementations of the disclosed technology. However, it will be apparent to one of ordinary skill in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

[0083] In practicing the claimed invention, those of ordinary skill in the art can understand and realize other variations of the disclosed embodiments by studying the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting their scope.

Claims

1. A voltage gate driver for a semiconductor-based transistor, the voltage gate driver comprising: A voltage generator circuit including a capacitor connected in series with a Zener diode, wherein the cathode of the Zener diode is arranged to be connected to the gate of the semiconductor-based transistor and the capacitor, and an end of the capacitor not connected to the Zener diode is arranged to receive a drive voltage; A bias current circuit connected in parallel across the capacitor, wherein the bias current circuit includes a switch, the switch being a metal-oxide-semiconductor field-effect transistor (MOSFET), and the bias current circuit is arranged to provide a bias current to the cathode of the Zener diode based on the state of the switch, wherein the bias current circuit is arranged to provide the bias current to the cathode of the Zener diode when the switch is in a closed state and is arranged to prevent the bias current from being provided to the cathode of the Zener diode when the switch is in an open state, and wherein the gate of the switch is arranged to receive the drive voltage.

2. The voltage gate driver according to claim 1, wherein the MOSFET is a P-channel MOSFET.

3. The voltage gate driver according to claim 1, wherein the bias current circuit includes a resistor connected in series with the switch.

4. The voltage gate driver according to any one of claims 1 to 3, wherein the voltage gate driver is arranged to drive a gallium nitride high electron mobility transistor (GaN HEMT).

5. The voltage driver according to any one of claims 1 to 3, wherein, The anode of the Zener diode is grounded.

6. The voltage driver according to claim 5, wherein, The voltage driver further includes a diode, wherein the anode of the Zener diode is grounded via the diode, wherein the anode of the diode is connected to the anode of the Zener diode.

7. A power switch device comprising a semiconductor-based transistor and a voltage driver according to any one of the preceding claims.

8. The power switch device according to claim 7, wherein the semiconductor-based transistor is a gallium nitride high electron mobility transistor (GaN HEMT) or a silicon carbide MOSFET.

9. A method of operating a voltage driver according to any one of claims 1 to 6, wherein the method comprises the steps of: Providing the bias current to the cathode of the Zener diode through the bias current circuit when the switch is in the closed state, and Preventing the bias current from being provided to the cathode of the Zener diode through the bias current circuit when the switch is in the open state.

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