System and Method for Driving a Transistor

The present disclosure relates generally to an electronic component and particularly to a system and a method of driving a transistor.

High voltage switching transistors such as power MOSFETs, JFETs (Junction Field Effect Transistor) and gallium nitride high-electron-mobility transistor (GaN HEMT) are commonly and as a semiconductor switch in the high-voltage and high-power components, such as switched-mode power converters, motor controllers, and high-voltage high performance circuits used. Some of these components such as the GaN-HEMT, having the ability to operate at very high voltages, without the device fails or is damaged.

Some devices such as the JFET and the GaN HEMT may be produced such that they have a negative threshold voltage, thereby causing that the device is conductive if a voltage of zero at the gate electrode and the source electrode of these transistors is applied. Such components are referred to accordingly as "self-routing" devices or transistors, because these components are effective under conditions with a zero bias voltage. When such self-conducting components are used, are generally taken precautions to ensure that a voltage is generated to ensure that the self-conducting component can be turned off. For example, a negative voltage is in a driving circuit used in a switched-mode power conversion generated or provided, having a voltage which is sufficiently below the threshold voltage of normally-on device, to ensure that the device is actually switched off as intended.

According to one embodiment comprises a circuit for driving a control terminal of a switching transistor: a driver having an output, which is adapted to be coupled to a control terminal of the switching transistor, a first power supply terminal is configured to coupled to the first terminal of a floating power supply to be a second power supply terminal which is adapted to be coupled to a second terminal of the floating power supply, and a switching input terminal adapted to receive a switching signal. The circuit further comprises a bias circuit having an output terminal which is adapted to be coupled to a common mode control terminal of the floating power supply, wherein the bias circuit is adapted to provide a time dependent voltage.

For a more complete understanding of the present invention and its advantages, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

<figref>1a</figref>c illustrate a conventional Schalteransteuersystem;

<figref>2</figref> illustrate a Schalteransteuersystem according to an embodiment;

<figref>3</figref> a Schalteransteuersystem according to another embodiment illustrated;

<figref>4</figref> a Schalteransteuersystem according to another embodiment illustrated;

<figref>5</figref> an embodiment of a transistor copy circuit illustrated; and

<figref>6</figref> illustrates a flow chart of a method according to an embodiment.

Corresponding numerals and symbols in different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to illustrate the relevant aspects of the preferred embodiments clearly, and they are not necessarily drawn to scale.

The making and using of the presently preferred embodiments are discussed in detail below. It is understood, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention and do not limit the scope of the invention.

The present invention will be described with respect to preferred embodiments in a specific context, a system and method for driving a self-conducting switching transistor. Embodiments of the present invention can be applied to various systems using the self-conducting transistors, such as clocked power converters, motor controllers and other circuits. Embodiments may also affect the driving of normally-off transistors.

In one embodiment of the present invention to a circuit is formed, to drive a control terminal of a switching transistor. This switching transistor may have a negative threshold voltage, such as a JFET, a gallium nitride HEMT (GaN-HEMT), a depletion-mode MOSFET or other transistor having a negative threshold voltage, or it may have a positive threshold voltage, such as an enhancement mode MOSFET , The driver comprises power supply terminals, which are coupled to a floating power supply. The floating power supply may generate a positive voltage and a negative voltage, which are coupled to the power supply terminals of the driver. During operation, the driver applies the positive voltage of the floating power supply on to turn on the switching transistor, and applies the negative voltage of the floating power supply on to turn off the switching transistor. A common-mode bias circuit is also provided to bias the common-mode or average voltage of the floating power supply. In some embodiments, this common-mode voltage may produce a time-dependent voltage, which can depend on various parameters.

In a specific example, this common mode voltage may depend on the threshold voltage of the driven transistor or a copy component thereof. In such an embodiment, the common mode voltage is set at or approximately at the threshold voltage of the switching transistor. Embodiments of the present invention can be applied to the driving of the switching transistors, which have negative threshold voltages, positive threshold voltages and / or threshold voltages of zero.

<figref>1a</figref> illustrates a conventional Schalteransteuersystem <figref>100</figref> a voltage source <figref>106</figref>, A driving circuit <figref>104</figref> and a self-blocking transistor <figref>102</figref>, As shown, the driver is<figref>104</figref> with a fixed voltage VP of the voltage source <figref>106</figref> supplied to the source potential S of the transistor <figref>102</figref> is related. The threshold voltage Vth of the transistor<figref>102</figref> is the gate-source voltage level which defines the transition between the states "on" and "off". In the case of a "normally-off" in the transistor<figref>102</figref> existing positive threshold voltage Vth uses the power scheme represented a single positive voltage source <figref>106</figref>, During operation of system<figref>100</figref> , the driver <figref>104</figref> the voltage VP at the gate electrode G of the normally-off transistor <figref>102</figref> at. If the voltage V P is greater than the threshold voltage Vth of the normally-off transistor<figref>102</figref>, The normally-off transistor <figref>102</figref> switched on. If both the voltage at the negative terminal of the voltage source<figref>106</figref> at the gate electrode G of the normally-off transistor <figref>102</figref> is applied, the normally-off transistor is turned off.

<figref>1b</figref> illustrates a conventional Schalteransteuersystem <figref>120</figref> a voltage source <figref>126</figref>, A driving circuit <figref>124</figref> and a normally-on transistor <figref>122</figref>, As shown, the driver circuit<figref>124</figref> with a fixed voltage VN by the voltage source <figref>126</figref> supplied to the source potential S of the transistor <figref>122</figref> is related. Similar to the in<figref>1b</figref> normally-off transistor shown <figref>102</figref> is the threshold voltage Vth of the transistor <figref>122</figref> the gate-source voltage level which defines the transition between the states "on" and "off". In the case of the normally-on transistor<figref>122</figref> however, this threshold voltage Vth is a negative voltage, which means that the voltage of the gate electrode G of the self-conductive transistor <figref>122</figref> is brought to a voltage potential which is lower than the voltage of the source node S to the self-conducting transistor <figref>122</figref> off. If the voltage potential Vn of the voltage source<figref>126</figref> the negative threshold voltage Vth of the self-conducting transistor <figref>122</figref> exceeds, may accordingly the self-conducting transistor is turned off by applying a voltage to the negative terminal of the voltage source <figref>126</figref>, However, if the gate-source voltage of the self-conductive transistor<figref>122</figref> a voltage of zero, the self-conducting transistor is <figref>122</figref> conductive.

In cases where the threshold voltage Vth of the driven transistor is a low positive or a low negative voltage close to ground, a bipolar driving scheme can be used to ensure that the transistor is turned on and off. <figref>1c</figref> illustrates a conventional bipolar Schalteransteuersystem <figref>130</figref> with a positive voltage source <figref>134</figref>, A negative voltage source <figref>136</figref>, A driving circuit <figref>138</figref> and a transistor <figref>132</figref>, When the transistor<figref>132</figref> is turned on, the positive voltage source by the <figref>134</figref> generated voltage VP to the gate terminal G of the transistor <figref>132</figref> applied. Similarly, when the transistor<figref>132</figref> is turned off by the negative voltage source <figref>136</figref> VN generated voltage to the gate terminal G of the transistor <figref>132</figref> applied. The use of such a bipolar Ansteuerschemas can improve switching performance when the threshold voltage Vth is a low voltage, and can provide a margin to ensure that the transistor<figref>132</figref> properly switched. For example, if the threshold voltage Vth of the transistor<figref>132</figref> about 1 V, the driving of the transistor can <figref>132</figref> providing an asymmetrical drive voltage having a positive power supply of 12 V. In suchCases helps using a negative voltage source <figref>136</figref> ensure that the transistor <figref>132</figref> off with sufficient overdrive.

Because the threshold voltage can change Vth of a transistor on a temperature variation, process variation, statistical variations, drift effects and other causes of time, such changes are often considered during the design of conventional driver circuits. For example, if the threshold voltage Vth of a self-conductive transistor of a variation between -5 V and -9 V is subjected, provides a negative supply voltage in a conventional system, a negative voltage that is to provide sufficient overdrive to turn off the transistor. In this example, a negative voltage of -11 V provides an override of 2 V to turn off the transistor in the worst-case scenario, if the threshold voltage Vth of the self-conducting transistor is at -9 V.

In one embodiment, power supply voltages are for a gate driver to a gate potential in relationship, which corresponds to a threshold value, for example, VG = VS + Vth. In other words, the drive level to VS + Vth related, rather than directly VS. Thus, a positive Gateansteuerpegel ( "a") than Vth + VP (positive override) can be expressed, and the negative level ( "off") can be used as Vth - VN be expressed. Under real working conditions, however, the current threshold voltage Vth can change the temperature and other drift effects over time due to changes.

<figref>2</figref> illustrates a Schalteransteuersystem <figref>200</figref>That a positive voltage source <figref>206</figref> and a negative voltage source <figref>208</figref>, A drive circuit <figref>204</figref> and a transistor <figref>202</figref> includes. transistor<figref>202</figref> can be implemented using various types of transistors. For example, the transistor including a power MOSFET transistor, a GaN-HEMT, a JFET, an enhancement mode MOSFET, a depletion MOSFET or a Bipolarsperrschichttransistor (BJT) include.

In some embodiments, the combination of positive voltage source <figref>206</figref> and negative voltage source <figref>208</figref> a floating power supply, the common mode voltage by applying a voltage to a common node <figref>220</figref> can be set between the positive voltage source <figref>206</figref> and the negative voltage source <figref>208</figref> coupled. By coupling the voltage source<figref>210</figref> between the common node <figref>220</figref> and the source node S of the transistor <figref>202</figref> The common mode output of the driving circuit <figref>204</figref> corresponding to the time-dependent threshold voltage Vth (t) of the transistor <figref>202</figref> or any other time-dependent voltage can be set. In some embodiments in which the outputs of the voltage source<figref>206</figref> and <figref>208</figref> of the threshold voltage of the transistor <figref>202</figref> chase (Engl .: track), the voltage VP of the positive power source can <figref>206</figref> and the voltage VN of the negative voltage source <figref>208</figref> be selected, without a variation in the threshold voltage of the transistor <figref>202</figref> must be considered. In such embodiments, the minimum values ​​of VP and VN according to a switching dynamics can be selected.

For example, in one embodiment, the voltage sources <figref>206</figref> and <figref>208</figref> each set so that they produce about 3 V, and the voltage source <figref>210</figref> is adapted to deliver a voltage which is the threshold voltage of the transistor <figref>202</figref> approaches. If the approximation of the threshold voltage of the transistor<figref>202</figref> about -5 volts, provides the voltage source <figref>210</figref> thus about -5 V, the positive terminal of the voltage source <figref>206</figref> provides about -2 V and the negative terminal of the voltage source <figref>208</figref> provides about -8 V. In alternative embodiments, other voltage levels may be used depending on the system and determine its specifications.

The voltage sources <figref>206</figref> and <figref>208</figref> can be implemented using methods known in the art power circuits. For example, pulsed power supplies, voltage regulators, batteries and other power supply circuits and systems for implementing the voltage source<figref>206</figref> and <figref>208</figref> be used. For example, the voltage source<figref>210</figref> be implemented using a variety of biasing circuits and / or power supply circuits, which are known in the art. In some embodiments, the voltage source<figref>210</figref> using a copy of the transistor <figref>202</figref> be implemented to generate a voltage which is the threshold voltage Vth of the transistor <figref>202</figref> approaches. The driver circuit<figref>204</figref> can be implemented using techniques known in the art driver circuits, such as a driver from the family of Infineon EiceDRIVER or a driver from the series Texas Instruments UCC27x.

<figref>3</figref> illustrates a Schalteransteuersystem <figref>300</figref> according to an embodiment of the present invention. As shown, generates the copy-transistor circuit<figref>306</figref> a time-dependent voltage V (t) to the common mode terminal VCM of the floating current source <figref>302</figref> is coupled. In one embodiment, the generatedfloating power supply <figref>302</figref> a voltage at the terminal VP, which lies at a voltage potential that is greater than the VCM voltage at the terminal, and generates a voltage at the terminal VN, which is on a voltage potential below the voltage at the terminal VCM. Effectively monitor the voltages at the terminals VP and VN by the transistor copy circuit<figref>306</figref> generated voltage V (t).

In one embodiment, the transistor circuit generates copy- <figref>306</figref> a voltage V (t) extending in the threshold voltage of the transistor <figref>202</figref> approaches and / or is at her in relationship by a transistor having a similar structure and / or a similar device geometry as transistor <figref>202</figref> is used. The voltage V (t) can vary over time to track changes relative to the threshold voltage temperature drift effects, and changes in other parameters which the threshold voltage of the transistor and the copy component in the transistor circuit copy<figref>306</figref> can influence. In alternative embodiments, the voltage V (t) may in addition to the copy transistor circuit<figref>306</figref> be generated by other types of circuitry.

The driver circuit <figref>304</figref> has supply connections to the terminals VP and VN of the floating power supply <figref>302</figref> are coupled.

In one embodiment, the driver circuit applies the alternating voltages at the terminals VP and VN of the floating power supply <figref>302</figref> according to a switching signal VSW at the input of the driver circuit <figref>304</figref> to the gate terminal G of the transistor <figref>202</figref> at. For example, sets, in one embodiment, the driver circuit<figref>304</figref> the voltage at the terminal VP of the floating power supply <figref>302</figref> to when the signal at the input VSW is a logic H, and sets the voltage at the terminal VN of the floating power supply <figref>302</figref> to when the signal at the input VSW is a logic L. Alternatively, the relationship between the logical sense of the input VSW and to the gate electrode of the transistor<figref>202</figref> applied voltage be reversed. In some embodiments, the output of the driver circuit<figref>304</figref> introduce a voltage drop between its power supply connections and the output terminal.

<figref>4</figref> illustrates a Schalteransteuersystem <figref>400</figref> According to a further embodiment of the present invention wherein the floating power supply using windings <figref>416</figref> and <figref>418</figref> the transformer <figref>414</figref> is implemented with center tap. In one embodiment, the windings may<figref>416</figref> and <figref>418</figref> be secondary and / or auxiliary windings of a transformer of a switching mode power converter such as a flyback converter. In some embodiments, the transformer<figref>414</figref> a primary winding <figref>430</figref> included, which is coupled to a primary-side switching power supply circuitry is not shown for ease of illustration. The realization and the operation of such a primary-side switching mode power supply circuit can be carried out using methods known in the art circuits and methods.

The Schalteransteuersystem <figref>400</figref> includes the transistor <figref>202</figref> and the drive circuit <figref>402</figref>Which is adapted to a switching signal VSW to the gate electrode of the transistor <figref>202</figref> to apply. transistor<figref>202</figref> can be any type of transistor, for example, has a positive threshold voltage or a negative threshold voltage. The positive power supply terminal<figref>422</figref> the driver circuit <figref>402</figref> is through a diode <figref>410</figref> to the winding <figref>416</figref> the transformer <figref>414</figref> coupled and the negative power supply terminal <figref>424</figref> the driver circuit <figref>402</figref> is via the diode <figref>412</figref> to the winding <figref>418</figref> the transformer <figref>414</figref> coupled. diodes<figref>410</figref> and <figref>412</figref> direct the current in the windings <figref>416</figref> and <figref>418</figref> the transformer <figref>414</figref> equal. In some embodiments, the diodes can<figref>410</figref> and <figref>412</figref> be implemented using switching transistors which are operated as a synchronous rectifier. The to the diodes<figref>410</figref> and <figref>412</figref> coupled capacitors <figref>406</figref> and <figref>408</figref> provide filtering and dampen the supply ripple.

A buffer amplifier <figref>404</figref> with a gain of one (germ .: unity gain buffer amplifier) ​​is adapted to the voltage V (t) to the center tap <figref>432</figref> the transformer <figref>414</figref> buffering. The voltage V (t) may represent, for example, a voltage which is the threshold voltage of the transistor<figref>202</figref> approaches. Alternatively, the voltage V (t) can be any time-dependent voltage. In many embodiments, the temporal variation of V (t) is slow compared to the switching transients. Then, the capacitor C, between the source node S of the transistor blocks<figref>202</figref> and the output of buffer amplifier <figref>404</figref> is coupled to a gain of unity, the common mode supply component V (t), but provides a low impedance path for fast switching transients.

The amplifier <figref>404</figref>Shown in a feedback configuration with unity gain (Engl .: unity gain feedback configuration), can be realized using a transconductance amplifier, an operational amplifier or other means known in the art of amplifier. In alternative embodiments,, other amplifier configurations are used in addition to a one-configuration. For example, an amplifier with a power factor be used less than one or greater than one. In some embodiments, the amplifier<figref>404</figref> . omitted It is understood that the system<figref>400</figref> only one of many embodiments that can be used to an embodiment of Transistoransteuerschaltungen and - to implement systems. In alternative embodiments, other circuit architectures and topologies can be used.

<figref>5</figref> illustrates an embodiment of a circuit with which a time-dependent voltage V (t) is generated based on a copy of the to be controlled switching transistor. As shown, the copy transistor<figref>508</figref> connected as a diode, its drain electrode coupled to its gate electrode. The voltage source<figref>506</figref> may be between the drain electrode and the gate electrode of the transistor copy <figref>508</figref> be coupled to account for negative threshold voltages for self-conducting components. The power source<figref>504</figref> is to copy transistor <figref>508</figref> coupled and provides a bias current. According to various embodiments, the source node S of the transistor copy<figref>508</figref> coupled to the same node as the source electrode of the switching transistor, which is controlled (for example, transistor <figref>202</figref> in <figref>3</figref> and <figref>4</figref>), Or is coupled to a node having a same or similar voltage as the source electrode of the switching transistor.

In one embodiment, the copy has transistor <figref>508</figref> a structure similar to the activated switching transistor. For example, if the switching transistor is a GaN HEMT transistor is also the copy<figref>508</figref> a GaN-HEMT. In some embodiments, the geometry of the transistor copy the geometry of the switching transistor may correspond. For example, the switching transistor using n unit devices can be constructed, while the copy transistor can be realized by using one or two of the unit component. In such embodiments, the current of the current source must<figref>504</figref> / N of the current of the switching transistor are only in the order of 1, so that V (t) can track the threshold voltage of the switching transistor. In some embodiments, the unit elements of the copy of the transistor can<figref>508</figref> are located at the same place as the switching transistor in order to improve an adapted power. By arranging the copy transistor<figref>508</figref> the same place as the main switching transistor changes in temperature the switching transistor on the copy transistor <figref>508</figref> applied.

It is understood that the circuit of <figref>5</figref> is merely one of many examples of circuits that can be used to generate an approximation of a threshold voltage of a switching transistor. In alternative embodiments, circuits and systems, which are described in co-pending US Application Serial Number 14 / 473.377.

<figref>6</figref> illustrates a flow diagram of one embodiment of a method <figref>6:00 am</figref> for driving a switching transistor. This method can be used for example in conjunction with various embodiments disclosed herein illustrated examples. In one embodiment, a common mode control terminal of a floating power supply with a based on a threshold voltage of the switching transistor voltage in step<figref>602</figref> biased. In step<figref>604</figref> of the switching transistor is turned on by driving a control terminal of the switching transistor to a first voltage of the floating power supply and, in step <figref>606</figref> of the switching transistor is turned off by driving the control terminal of the switching transistor to a second voltage of the floating power supply.

According to one embodiment comprises a circuit for driving a control terminal of a switching transistor: a driver having an output, which is adapted to be coupled to a control terminal of the switching transistor, a first power supply terminal which is adapted to coupled to a first terminal of a floating power supply to be a second power supply terminal which is adapted to be coupled to a second terminal of the floating power supply, and a switching input terminal adapted to receive a switching signal. The circuit further comprises a bias circuit having an output terminal which is adapted to be coupled to a common mode control terminal of the floating power supply, wherein the bias circuit is adapted to provide a time dependent voltage. In some embodiments, the circuit further comprises the floating power supply.

In one embodiment, the floating power supply comprises a first coil, a first diode coupled between the first terminal of the floating power supply and the first coil, a second coil to the first coil of the common mode control terminal and to the second terminal of the floating power supply is coupled, and a second diode connected between the second coil and the second terminal of the floating Power supply is coupled. The second coil is magnetically coupled to the first coil.

In one embodiment, the switching transistor includes a normally-on transistor, which can be part of the circuit. The self-conductive transistor can be implemented using a GaN-HEMT device, and the control terminal of the self-conductive transistor may be a gate electrode of the GaN-HEMT. In some embodiments, the time-dependent voltage is a based on a threshold voltage of the switching transistor voltage. This voltage may be based on the threshold voltage of the switching transistor and can be a voltage which is the threshold voltage of the switching transistor is substantially equal. In one embodiment, the bias circuit possesses a copy of the switching transistor.

In one embodiment, the driver is configured to turn on the switching transistor by coupling a voltage of the first power supply terminal to the control terminal of the transistor, and turn off the switching transistor by coupling a voltage of the second power supply terminal to the control terminal of the switching transistor.

According to a further embodiment includes a method for controlling a switching transistor: turning on the switching transistor by driving a control terminal of the switching transistor with a first voltage of a floating power supply, turning off the switching transistor by driving a control terminal of the switching transistor to a second voltage of the floating power supply, and biasing a common mode control terminal of the floating power supply with a based on a threshold voltage of the switching transistor voltage which can be equal to the threshold voltage of the switching transistor substantially. The biasing of the common mode control terminal of the floating power supply may include providing a threshold voltage of a copy of the switching transistor.

In one embodiment, the steps of turning on and off are performed in accordance with a switching signal. The switching transistor may comprise a self-conducting transistor include, and the switching transistor includes a GaN-HEMT device, so that the control terminal of the switching transistor is a gate electrode of the GaN-HEMT.

According to a further embodiment, a circuit includes a floating power supply having a positive terminal, a negative terminal and a common-mode connection. The circuit further comprises a driver circuit having a first power supply terminal coupled to the positive terminal of the power supply, a second power supply terminal coupled to the negative terminal of the power supply, and an output terminal that is adapted to coupled to a control terminal of a switching transistor to become. The circuit further comprises a common-mode bias circuit having an output coupled to the common-mode terminal of the floating power supply, so that the common mode bias circuit is adapted to a based on a threshold voltage of the switching transistor voltage at the output of the common mode bias provide voltage. In some embodiments, the circuit comprises the switching transistor.

In one embodiment, the switching transistor includes a self-conducting transistor and the self-conductive transistor includes a GaN-HEMT device, so that the control terminal of the switching transistor comprises a gate electrode of the GaN-HEMT. The common-mode bias circuit may include a voltage buffer amplifier having an output which is coupled to the common terminal of the floating power supply.

The switching circuit may include a capacitor coupled between a Lastweganschluss of the switching transistor and the output of the voltage buffer amplifier, and may also contain a copy of transistor, which is coupled to an input of the voltage buffer amplifier. In some embodiments, the floating power supply comprises a transformer, and the common connection of the floating power supply comprises a Mittenabgriffsanschluss the transformer.

To advantages of some embodiments include power savings due to that lower supply voltages are used to provide power to switch drivers. Another advantage includes the ability to track the threshold voltage variation with time and the ability to deliver symmetrical control voltages of switching transistors.

Other advantages of the exemplary embodiments include the ability to vary the Gateansteuerpegel not only with respect to the transistor threshold voltage, but also to take into account other aspects such as the transistor working mode (switch / diode), the load current variation and the switching speed.