US20060220698A1 - Drive circuit for a switching element - Google Patents

Drive circuit for a switching element Download PDF

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US20060220698A1
US20060220698A1 US10/907,397 US90739705A US2006220698A1 US 20060220698 A1 US20060220698 A1 US 20060220698A1 US 90739705 A US90739705 A US 90739705A US 2006220698 A1 US2006220698 A1 US 2006220698A1
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low
drive
current
drive current
circuit
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US7123060B1 (en
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Tien-Tzu Chen
Chia-Hung TSEN
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Global Mixed Mode Technology Inc
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Aimtron Technology Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/04—Modifications for accelerating switching
    • H03K17/041—Modifications for accelerating switching without feedback from the output circuit to the control circuit
    • H03K17/0412—Modifications for accelerating switching without feedback from the output circuit to the control circuit by measures taken in the control circuit
    • H03K17/04123—Modifications for accelerating switching without feedback from the output circuit to the control circuit by measures taken in the control circuit in field-effect transistor switches
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
    • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
    • H03K17/687—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors
    • H03K17/6877—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors the control circuit comprising active elements different from those used in the output circuit

Definitions

  • the present invention relates to a drive circuit and, more particularly, to a high-speed and high-efficiency drive circuit for driving a switching element.
  • FIG. 1 is a detailed circuit diagram showing a conventional drive circuit 10 for a switching element.
  • the drive circuit 10 applies a drive voltage V O through an output terminal OUT to a switching element (not shown) to be driven.
  • the switching element may be implemented by an NMOS transistor or a PMOS transistor.
  • a transistor Q 1 when a control voltage VIN is at a low level state, a transistor Q 1 is turned on and then supplies a current to a base electrode of a transistor Q 3 .
  • the drive voltage V O is pulled up to become approximately equal to a supply voltage source V CC minus a collector-emitter saturation voltage V CE, sat(Q3) of the transistor Q 3 , i.e., V CC -V CE, sat(Q3) . If at this moment the drive voltage V O is applied to a gate electrode of an NMOS switching element, then the NMOS switching element can be turned on.
  • a transistor Q 2 When the control voltage V IN is at a high level state, a transistor Q 2 is turned on and then supplies a current to a base electrode of a transistor Q 4 . As a result, the drive voltage V O is pushed down to become approximately equal to a collector-emitter saturation voltage V CE, sat(Q4) of the transistor Q 4 . If at this moment the drive voltage V O is applied to a gate electrode of an NMOS switching element, then the NMOS switching element can be turned off.
  • An object of the present invention is to provide a drive circuit for a switching element, capable of achieving a high-speed driving operation.
  • Another object of the present invention is to provide a drive circuit for a switching element, capable of achieving a high-efficiency driving operation.
  • a drive circuit for applying a drive voltage through an output terminal to a switching element.
  • the drive circuit has a high-side drive unit and a low-side drive unit.
  • the high-side drive unit applies a high-side drive current to the output terminal for increasing the drive voltage.
  • the low-side drive unit applies a low-side drive current to the output terminal for decreasing the drive voltage.
  • the high-side drive unit has a high-side supplying circuit, a high-side amplifying circuit, a high-side detecting circuit, and a high-side adjusting circuit.
  • the high-side supplying circuit generates a first high-side drive current in response to the high-side control signal.
  • the high-side amplifying circuit generates a second high-side drive current based on the first high-side drive current and applies the second high-side drive current to the output terminal for increasing the drive voltage.
  • the second high-side drive current is larger than the first high-side drive current.
  • the high-side detecting circuit is coupled to the output terminal for generating a high-side detection signal representative of the high-side drive voltage.
  • the high-side adjusting circuit is implemented by a high-side differential comparator for dynamically adjusting the first high-side drive current based on a comparison of the high-side detection signal and a predetermined high-side threshold voltage.
  • the low-side drive unit has a low-side supplying circuit, a low-side amplifying circuit, a low-side detecting circuit, and a low-side adjusting circuit.
  • the low-side supplying circuit generates a first low-side drive current in response to the low-side control signal.
  • the low-side amplifying circuit generates a second low-side drive current based on the first low-side drive current and applies the second low-side drive current to the output terminal for decreasing the drive voltage.
  • the second low-side drive current is larger than the first low-side drive current.
  • the low-side detecting circuit is coupled to the output terminal for generating a low-side detection signal representative of the low-side drive voltage.
  • the low-side adjusting circuit is implemented by a low-side differential comparator for dynamically adjusting the first low-side drive current based on a comparison of the low-side detection signal and a predetermined low-side threshold voltage.
  • FIG. 1 is a detailed circuit diagram showing a conventional drive circuit for a switching element
  • FIG. 2 is a circuit block diagram showing a drive circuit for a switching element according to the present invention
  • FIG. 3 is a waveform timing chart showing an operation of a drive circuit for a switching element according to the present invention
  • FIG. 4 is a detailed circuit diagram showing one example of a high-side drive unit according to the present invention.
  • FIG. 5 is a detailed circuit diagram showing one example of a low-side drive unit according to the present invention.
  • FIG. 2 is a circuit block diagram showing a drive circuit 20 for a switching element SW according to the present invention.
  • FIG. 3 is a waveform timing chart showing an operation of a drive circuit 20 for a switching element SW according to the present invention.
  • the drive circuit 20 according to the present invention is a combination of a high-side drive unit 20 H and a low-side drive unit 20 L.
  • the high-side drive unit 20 H is activated to apply a high-level drive voltage V O through an output terminal OUT to the switching element SW.
  • the switching element SW is implemented by an NMOS transistor
  • the high-level drive voltage V O is applied to turn on the switching element SW.
  • the low-side drive unit 20 L is activated to apply a low-level drive voltage V O through the output terminal OUT to the switching element SW.
  • the switching element SW is implemented by an NMOS transistor
  • the low-level drive voltage V O is applied to turn off the switching element SW.
  • the activation of the high-side drive unit 20 H by the high-side control signal INH should not be overlapped in time with the activation of the low-side drive unit 20 L by the low-side control signal INL. Therefore, the control signals INH and INL effectively turn on/off the switching element SW through the drive circuit 20 .
  • the high-side drive unit 20 H has a high-side supplying circuit 21 H, a high-side amplifying circuit 22 H, a high-side detecting circuit 23 H, and a high-side adjusting circuit 24 H.
  • the high-side control signal INH activates the high-side supplying circuit 21 H to supply a high-side drive current IH a .
  • the high-side amplifying circuit 22 H Based on the high-side drive current IH a , the high-side amplifying circuit 22 H generates a magnified high-side drive current IH b to be applied to the output terminal OUT.
  • the magnified high-side drive current IH b causes the drive voltage V O to rise more rapidly and thus shortens the transient time of the switching element SW from off to on.
  • the high-side detecting circuit 23 H is coupled to the output terminal OUT for generating a high-side detection signal VH representative of the drive voltage V O .
  • the high-side adjusting circuit 24 H controls the high-side applying circuit 21 H for dynamically adjusting the magnitude of the high-side drive current IH a . More specifically, it is necessary for a relatively large drive current to speed up the rising rate of the drive voltage V O at the beginning when the switching element SW starts approaching conductive from nonconductive. Under such circumstance, the high-side adjusting circuit 24 H allows the high-side supplying circuit 21 H to supply as much the high-side drive current IH a as possible.
  • the high-side adjusting circuit 24 H prevents the high-side supplying circuit 21 H from supplying any of the high-side drive current IH a to the high-side amplifying circuit 22 H, thereby stopping the generation of the high-side drive current IH b . Therefore, the high-side adjusting circuit 24 H effectively saves the current consumption of the high-side drive unit 20 H, achieving a high-efficiency driving operation.
  • the low-side drive unit 20 L has a low-side supplying circuit 21 L, a low-side amplifying circuit 22 L, a low-side detecting circuit 23 L, and a low-side adjusting circuit 24 L.
  • the low-side control signal INL activates the low-side supplying circuit 21 L to supply a low-side drive current IL a .
  • the low-side amplifying circuit 22 L Based on the low-side drive current IL a , the low-side amplifying circuit 22 L generates a magnified low-side drive current IL b to be applied to the output terminal OUT.
  • the magnified low-side drive current IL b causes the drive voltage V O to fall more rapidly and thus shortens the transient time of the switching element SW from on to off.
  • the low-side detecting circuit 23 L is coupled to the output terminal OUT for generating a low-side detection signal VL representative of the drive voltage V O .
  • the low-side adjusting circuit 24 L controls the low-side applying circuit 21 L for dynamically adjusting the magnitude of the low-side drive current IL a . More specifically, it is necessary for a relatively large drive current to speed up the falling rate of the drive voltage V O at the beginning when the switching element SW starts approaching nonconductive from conductive. Under such circumstance, the low-side adjusting circuit 24 L allows the low-side supplying circuit 21 L to supply as much the low-side drive current IL a as possible.
  • the low-side adjusting circuit 24 L prevents the low-side supplying circuit 21 L from supplying any of the low-side drive current IL a to the low-side amplifying circuit 22 L, thereby stopping the generation of the low-side drive current IL b . Therefore, the low-side adjusting circuit 24 L effectively saves the current consumption of the low-side drive unit 20 L, achieving a high-efficiency driving operation.
  • FIG. 4 is a detailed circuit diagram showing one example of a high-side drive unit 20 H according to the present invention.
  • a transistor H 1 When the high-side control signal INH is at the low level state, a transistor H 1 is turned off such that a current source I 1 supplies a high-side drive current IH a through a transistor H 2 to a base electrode of a transistor H 3 .
  • the high-side drive current IH a is magnified with a factor of P through the transistor H 3 and then supplied to a base electrode of a transistor H 4 to be magnified once again with another factor of ⁇ . Consequently, a magnified high-side drive current IH b supplied from a collector electrode of the transistor H 4 is approximately equal to ⁇ 2 times the original high-side drive current IH a .
  • the magnified high-side drive current IH b causes the drive voltage V O to rise more rapidly and thus shortens the transient time of the switching element SW from off to on.
  • a transistor H 5 and a current source 12 are coupled to form a level shifter.
  • the transistor H 5 has a base electrode connected to the output terminal OUT for detecting the drive voltage V O , and an emitter electrode for generating a high-side detection signal VH. Therefore, the high-side detection signal VH is equal to the drive voltage V O minus a base-emitter voltage V BE(H5) of the transistor H 5 .
  • the high-side adjusting circuit 24 H is implemented by a differential comparator for comparing the high-side detection signal VH and a predetermined high-side threshold voltage VH th . Based on such a comparison, the high-side adjusting circuit 24 H dynamically adjusts the magnitude of the high-side drive current IH a . More specifically, the high-side detection signal VH controls a base electrode of a transistor H 6 while the high-side threshold voltage VH th controls a base electrode of a transistor H 7 . The transistors H 6 and H 7 have their emitter electrodes connected together to a current source I 3 . Following that the high-side detection signal VH becomes larger, the current source I 3 distributes more current components through the current path formed by the transistor H 6 .
  • the current supplied from the current source 13 completely flows through the current path formed by the transistor H 6 . Since a collector electrode of the transistor H 6 is connected to the current source I 1 of the high-side supplying circuit 21 H, such the current sinking through the transistor H 6 causes a drop in the high-side drive current IH a , thereby achieving the dynamical adjustment of the high-side drive current IH a in accordance with the drive voltage V O .
  • the current source I 3 is designed to be larger than or equal to the current source I 1 such that the current supplied from the current source I 1 is completely sunk through the transistor H 6 and no more transferred as the high-side drive current IH a when the high-side detection signal VH goes beyond the high-side threshold voltage VH th . Therefore, the high-side adjusting circuit 24 H effectively saves the supply of the high-side drive current IH a , achieving a high-efficiency driving operation.
  • the high-side threshold voltage VH th is designed to make a collector-emitter voltage V CE(H4) of the transistor H 4 large enough for preventing the transistor H 4 from operating into a deep saturation region, thereby keeping a fast response of the drive voltage V O upon transition.
  • a resistor R 3 provides the transistor H 3 with a discharge path while a resistor R 4 provides the transistor H 4 with another discharge path, thereby ensuring that the high-side amplifying circuit 22 H is shut down.
  • the transistor H 2 is coupled to the transistor H 6 such that a collector-emitter voltage V CE(H6) of the transistor H 6 is set equal to an emitter-base voltage V EB(H2) of the transistor H 2 , thereby ensuring that the transistor H 6 is normally operated before the high-side detection signal VH goes beyond the high-side threshold voltage VH th .
  • FIG. 5 is a detailed circuit diagram showing one example of a low-side drive unit 20 L according to the present invention.
  • a transistor L 1 When the low-side control signal INL is at the low level state, a transistor L 1 is turned off such that a current source 14 supplies a low-side drive current IL a to a base electrode of a transistor L 2 .
  • the low-side drive current IL a is magnified with a factor of ⁇ through the transistor L 2 and then supplied to a base electrode of a transistor L 3 to be magnified once again with another factor of ⁇ . Consequently, a magnified low-side drive current IL b supplied from a collector electrode of the transistor L 3 is approximately equal to ⁇ 2 times the original low-side drive current IL a .
  • the magnified low-side drive current IL b causes the drive voltage V O to fall more rapidly and thus shortens the transient time of the switching element SW from on to off.
  • a transistor L 4 and a current source I 5 are coupled to form a level shifter.
  • the transistor L 4 has a base electrode connected to the output terminal OUT for detecting the drive voltage V O , and an emitter electrode for generating a low-side detection signal VL. Therefore, the low-side detection signal VL is equal to the drive voltage V O plus an emitter-base voltage V EB (L 4 ) of the transistor L 4 .
  • the low-side adjusting circuit 24 L is implemented by a differential comparator for comparing the low-side detection signal VL and a predetermined low-side threshold voltage VL th . Based on such a comparison, the low-side adjusting circuit 24 L dynamically adjusts the magnitude of the low-side drive current IL a . More specifically, the low-side detection signal VL controls a base electrode of a transistor L 5 while the low-side threshold voltage VL th controls a base electrode of a transistor L 6 . Each of transistors L 7 and L 8 is diode-connected and provided as a load at respective collector electrodes of the transistors L 5 and L 6 . The transistors L 5 and L 6 have their emitter electrodes connected together to a current source I 6 .
  • the current source I 6 distributes more current components through the current path formed by the transistor L 5 .
  • the current supplied from the current source 16 completely flows through the current path formed by the transistor L 5 . Since a transistor L 9 forms a current mirror with the transistor L 7 and has a collector electrode connected to the current source 14 of the low-side supplying circuit 21 L, such the current sinking through the transistor L 9 causes a drop in the low-side drive current IL a , thereby achieving the dynamical adjustment of the low-side drive current IL a in accordance with the drive voltage V O .
  • the current source I 6 is designed to be larger than or equal to the current source I 4 such that the current supplied from the current source I 4 is completely sunk through the transistor L 9 and no more transferred as the low-side drive current IL a when the low-side detection signal VL goes below the low-side threshold voltage VL th . Therefore, the low-side adjusting circuit 24 L effectively saves the supply of the low-side drive current IL a , achieving a high-efficiency driving operation.
  • the low-side threshold voltage VL th is designed to make a collector-emitter voltage V CE(L3) of the transistor L 3 large enough for preventing the transistor L 3 from operating into a deep saturation region, thereby keeping a fast response of the drive voltage V O upon transition. After the low-side drive current IL a is stopped, a resistor R 5 provides the transistor L 3 with a discharge path, thereby ensuring that the low-side amplifying circuit 22 L is shut down.

Abstract

A drive circuit applies a drive voltage through an output terminal to a switching element. The drive circuit includes a supplying circuit, an amplifying circuit, a detecting circuit, and an adjusting circuit. In response to a control signal, the supplying circuit generates a first drive current. The amplifying circuit generates and applies a second drive current, which is larger than the first drive current, to the output terminal for changing the drive voltage. The detecting circuit is coupled to the output terminal for generating a detection signal representative of the drive voltage. Based on the detection signal, the adjusting circuit implemented by a differential comparator dynamically adjusts the first drive current.

Description

    BACKGROUND OF THE INVENTION
  • 1. Field of the Invention
  • The present invention relates to a drive circuit and, more particularly, to a high-speed and high-efficiency drive circuit for driving a switching element.
  • 2. Description of the Related Art
  • FIG. 1 is a detailed circuit diagram showing a conventional drive circuit 10 for a switching element. The drive circuit 10 applies a drive voltage VO through an output terminal OUT to a switching element (not shown) to be driven. For example, the switching element may be implemented by an NMOS transistor or a PMOS transistor.
  • Referring to FIG. 1, when a control voltage VIN is at a low level state, a transistor Q1 is turned on and then supplies a current to a base electrode of a transistor Q3. As a result, the drive voltage VO is pulled up to become approximately equal to a supply voltage source VCC minus a collector-emitter saturation voltage VCE, sat(Q3) of the transistor Q3, i.e., VCC-VCE, sat(Q3). If at this moment the drive voltage VO is applied to a gate electrode of an NMOS switching element, then the NMOS switching element can be turned on. When the control voltage VIN is at a high level state, a transistor Q2 is turned on and then supplies a current to a base electrode of a transistor Q4. As a result, the drive voltage VO is pushed down to become approximately equal to a collector-emitter saturation voltage VCE, sat(Q4) of the transistor Q4. If at this moment the drive voltage VO is applied to a gate electrode of an NMOS switching element, then the NMOS switching element can be turned off.
  • In order to provide a drive circuit with a higher operational speed and a better operational efficiency, a few of techniques and circuitry have already be developed and disclosed, for example, in U.S. Pat. No. 5,939,907 and U.S. Pat. No. 6,130,575, each of which is fully incorporated herein by reference.
    • SUMMARY OF THE INVENTION
  • An object of the present invention is to provide a drive circuit for a switching element, capable of achieving a high-speed driving operation.
  • Another object of the present invention is to provide a drive circuit for a switching element, capable of achieving a high-efficiency driving operation.
  • According to one aspect of the present invention, a drive circuit is provided for applying a drive voltage through an output terminal to a switching element. The drive circuit has a high-side drive unit and a low-side drive unit. In response to a high-side control signal, the high-side drive unit applies a high-side drive current to the output terminal for increasing the drive voltage. In response to a low-side control signal, the low-side drive unit applies a low-side drive current to the output terminal for decreasing the drive voltage.
  • The high-side drive unit has a high-side supplying circuit, a high-side amplifying circuit, a high-side detecting circuit, and a high-side adjusting circuit. The high-side supplying circuit generates a first high-side drive current in response to the high-side control signal. The high-side amplifying circuit generates a second high-side drive current based on the first high-side drive current and applies the second high-side drive current to the output terminal for increasing the drive voltage. The second high-side drive current is larger than the first high-side drive current. The high-side detecting circuit is coupled to the output terminal for generating a high-side detection signal representative of the high-side drive voltage. The high-side adjusting circuit is implemented by a high-side differential comparator for dynamically adjusting the first high-side drive current based on a comparison of the high-side detection signal and a predetermined high-side threshold voltage.
  • The low-side drive unit has a low-side supplying circuit, a low-side amplifying circuit, a low-side detecting circuit, and a low-side adjusting circuit. The low-side supplying circuit generates a first low-side drive current in response to the low-side control signal. The low-side amplifying circuit generates a second low-side drive current based on the first low-side drive current and applies the second low-side drive current to the output terminal for decreasing the drive voltage. The second low-side drive current is larger than the first low-side drive current. The low-side detecting circuit is coupled to the output terminal for generating a low-side detection signal representative of the low-side drive voltage. The low-side adjusting circuit is implemented by a low-side differential comparator for dynamically adjusting the first low-side drive current based on a comparison of the low-side detection signal and a predetermined low-side threshold voltage.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • The above-mentioned and other objects, features, and advantages of the present invention will become apparent with reference to the following descriptions and accompanying drawings, wherein:
  • FIG. 1 is a detailed circuit diagram showing a conventional drive circuit for a switching element;
  • FIG. 2 is a circuit block diagram showing a drive circuit for a switching element according to the present invention;
  • FIG. 3 is a waveform timing chart showing an operation of a drive circuit for a switching element according to the present invention;
  • FIG. 4 is a detailed circuit diagram showing one example of a high-side drive unit according to the present invention; and
  • FIG. 5 is a detailed circuit diagram showing one example of a low-side drive unit according to the present invention.
    • DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • The preferred embodiments according to the present invention will be described in detail with reference to the drawings.
  • FIG. 2 is a circuit block diagram showing a drive circuit 20 for a switching element SW according to the present invention. FIG. 3 is a waveform timing chart showing an operation of a drive circuit 20 for a switching element SW according to the present invention. As shown in FIG. 2, the drive circuit 20 according to the present invention is a combination of a high-side drive unit 20H and a low-side drive unit 20L. In response to a high-side control signal INH, the high-side drive unit 20H is activated to apply a high-level drive voltage VO through an output terminal OUT to the switching element SW. In a case where the switching element SW is implemented by an NMOS transistor, the high-level drive voltage VO is applied to turn on the switching element SW. In response to a low-side control signal INL, the low-side drive unit 20L is activated to apply a low-level drive voltage VO through the output terminal OUT to the switching element SW. In a case where the switching element SW is implemented by an NMOS transistor, the low-level drive voltage VO is applied to turn off the switching element SW. The activation of the high-side drive unit 20H by the high-side control signal INH should not be overlapped in time with the activation of the low-side drive unit 20L by the low-side control signal INL. Therefore, the control signals INH and INL effectively turn on/off the switching element SW through the drive circuit 20.
  • More specifically, the high-side drive unit 20H has a high-side supplying circuit 21H, a high-side amplifying circuit 22H, a high-side detecting circuit 23H, and a high-side adjusting circuit 24H. At first, the high-side control signal INH activates the high-side supplying circuit 21H to supply a high-side drive current IHa. Based on the high-side drive current IHa, the high-side amplifying circuit 22H generates a magnified high-side drive current IHb to be applied to the output terminal OUT. As a result, the magnified high-side drive current IHb causes the drive voltage VO to rise more rapidly and thus shortens the transient time of the switching element SW from off to on.
  • The high-side detecting circuit 23H is coupled to the output terminal OUT for generating a high-side detection signal VH representative of the drive voltage VO. In response to the high-side detection signal VH, the high-side adjusting circuit 24H controls the high-side applying circuit 21H for dynamically adjusting the magnitude of the high-side drive current IHa. More specifically, it is necessary for a relatively large drive current to speed up the rising rate of the drive voltage VO at the beginning when the switching element SW starts approaching conductive from nonconductive. Under such circumstance, the high-side adjusting circuit 24H allows the high-side supplying circuit 21H to supply as much the high-side drive current IHa as possible. Once the drive voltage VO reaches or goes beyond a predetermined high-side threshold voltage VHth, the drive voltage VO is considered to become large enough for definitely making the switching element SW conductive. Under such circumstance, the high-side adjusting circuit 24H prevents the high-side supplying circuit 21H from supplying any of the high-side drive current IHa to the high-side amplifying circuit 22H, thereby stopping the generation of the high-side drive current IHb. Therefore, the high-side adjusting circuit 24H effectively saves the current consumption of the high-side drive unit 20H, achieving a high-efficiency driving operation.
  • More specifically, the low-side drive unit 20L has a low-side supplying circuit 21L, a low-side amplifying circuit 22L, a low-side detecting circuit 23L, and a low-side adjusting circuit 24L. At first, the low-side control signal INL activates the low-side supplying circuit 21L to supply a low-side drive current ILa. Based on the low-side drive current ILa, the low-side amplifying circuit 22L generates a magnified low-side drive current ILb to be applied to the output terminal OUT. As a result, the magnified low-side drive current ILb causes the drive voltage VO to fall more rapidly and thus shortens the transient time of the switching element SW from on to off.
  • The low-side detecting circuit 23L is coupled to the output terminal OUT for generating a low-side detection signal VL representative of the drive voltage VO. In response to the low-side detection signal VL, the low-side adjusting circuit 24L controls the low-side applying circuit 21L for dynamically adjusting the magnitude of the low-side drive current ILa. More specifically, it is necessary for a relatively large drive current to speed up the falling rate of the drive voltage VO at the beginning when the switching element SW starts approaching nonconductive from conductive. Under such circumstance, the low-side adjusting circuit 24L allows the low-side supplying circuit 21L to supply as much the low-side drive current ILa as possible. Once the drive voltage VO reaches or goes below a predetermined low-side threshold voltage VLth, the drive voltage VO is considered to become small enough for definitely making the switching element SW nonconductive. Under such circumstance, the low-side adjusting circuit 24L prevents the low-side supplying circuit 21L from supplying any of the low-side drive current ILa to the low-side amplifying circuit 22L, thereby stopping the generation of the low-side drive current ILb. Therefore, the low-side adjusting circuit 24L effectively saves the current consumption of the low-side drive unit 20L, achieving a high-efficiency driving operation.
  • FIG. 4 is a detailed circuit diagram showing one example of a high-side drive unit 20H according to the present invention. When the high-side control signal INH is at the low level state, a transistor H1 is turned off such that a current source I1 supplies a high-side drive current IHa through a transistor H2 to a base electrode of a transistor H3. The high-side drive current IHa is magnified with a factor of P through the transistor H3 and then supplied to a base electrode of a transistor H4 to be magnified once again with another factor of β. Consequently, a magnified high-side drive current IHb supplied from a collector electrode of the transistor H4 is approximately equal to β2 times the original high-side drive current IHa. The magnified high-side drive current IHb causes the drive voltage VO to rise more rapidly and thus shortens the transient time of the switching element SW from off to on.
  • In the high-side detecting circuit 23H, a transistor H5 and a current source 12 are coupled to form a level shifter. The transistor H5 has a base electrode connected to the output terminal OUT for detecting the drive voltage VO, and an emitter electrode for generating a high-side detection signal VH. Therefore, the high-side detection signal VH is equal to the drive voltage VO minus a base-emitter voltage VBE(H5) of the transistor H5.
  • The high-side adjusting circuit 24H is implemented by a differential comparator for comparing the high-side detection signal VH and a predetermined high-side threshold voltage VHth. Based on such a comparison, the high-side adjusting circuit 24H dynamically adjusts the magnitude of the high-side drive current IHa. More specifically, the high-side detection signal VH controls a base electrode of a transistor H6 while the high-side threshold voltage VHth controls a base electrode of a transistor H7. The transistors H6 and H7 have their emitter electrodes connected together to a current source I3. Following that the high-side detection signal VH becomes larger, the current source I3 distributes more current components through the current path formed by the transistor H6. Once the high-side detection signal VH goes beyond the high-side threshold voltage VHth, the current supplied from the current source 13 completely flows through the current path formed by the transistor H6. Since a collector electrode of the transistor H6 is connected to the current source I1 of the high-side supplying circuit 21H, such the current sinking through the transistor H6 causes a drop in the high-side drive current IHa, thereby achieving the dynamical adjustment of the high-side drive current IHa in accordance with the drive voltage VO.
  • In one embodiment, the current source I3 is designed to be larger than or equal to the current source I1 such that the current supplied from the current source I1 is completely sunk through the transistor H6 and no more transferred as the high-side drive current IHa when the high-side detection signal VH goes beyond the high-side threshold voltage VHth. Therefore, the high-side adjusting circuit 24H effectively saves the supply of the high-side drive current IHa, achieving a high-efficiency driving operation. In another embodiment, the high-side threshold voltage VHth is designed to make a collector-emitter voltage VCE(H4) of the transistor H4 large enough for preventing the transistor H4 from operating into a deep saturation region, thereby keeping a fast response of the drive voltage VO upon transition.
  • After the high-side drive current IHa is stopped, a resistor R3 provides the transistor H3 with a discharge path while a resistor R4 provides the transistor H4 with another discharge path, thereby ensuring that the high-side amplifying circuit 22H is shut down. In addition, the transistor H2 is coupled to the transistor H6 such that a collector-emitter voltage VCE(H6) of the transistor H6 is set equal to an emitter-base voltage VEB(H2) of the transistor H2, thereby ensuring that the transistor H6 is normally operated before the high-side detection signal VH goes beyond the high-side threshold voltage VHth.
  • FIG. 5 is a detailed circuit diagram showing one example of a low-side drive unit 20L according to the present invention. When the low-side control signal INL is at the low level state, a transistor L1 is turned off such that a current source 14 supplies a low-side drive current ILa to a base electrode of a transistor L2. The low-side drive current ILa is magnified with a factor of β through the transistor L2 and then supplied to a base electrode of a transistor L3 to be magnified once again with another factor of β. Consequently, a magnified low-side drive current ILb supplied from a collector electrode of the transistor L3 is approximately equal to β2 times the original low-side drive current ILa. The magnified low-side drive current ILb causes the drive voltage VO to fall more rapidly and thus shortens the transient time of the switching element SW from on to off.
  • In the low-side detecting circuit 23L, a transistor L4 and a current source I5 are coupled to form a level shifter. The transistor L4 has a base electrode connected to the output terminal OUT for detecting the drive voltage VO, and an emitter electrode for generating a low-side detection signal VL. Therefore, the low-side detection signal VL is equal to the drive voltage VO plus an emitter-base voltage VEB(L4) of the transistor L4.
  • The low-side adjusting circuit 24L is implemented by a differential comparator for comparing the low-side detection signal VL and a predetermined low-side threshold voltage VLth. Based on such a comparison, the low-side adjusting circuit 24L dynamically adjusts the magnitude of the low-side drive current ILa. More specifically, the low-side detection signal VL controls a base electrode of a transistor L5 while the low-side threshold voltage VLth controls a base electrode of a transistor L6. Each of transistors L7 and L8 is diode-connected and provided as a load at respective collector electrodes of the transistors L5 and L6. The transistors L5 and L6 have their emitter electrodes connected together to a current source I6. Following that the low-side detection signal VL becomes smaller, the current source I6 distributes more current components through the current path formed by the transistor L5. Once the low-side detection signal VL goes below the low-side threshold voltage VLth, the current supplied from the current source 16 completely flows through the current path formed by the transistor L5. Since a transistor L9 forms a current mirror with the transistor L7 and has a collector electrode connected to the current source 14 of the low-side supplying circuit 21L, such the current sinking through the transistor L9 causes a drop in the low-side drive current ILa, thereby achieving the dynamical adjustment of the low-side drive current ILa in accordance with the drive voltage VO.
  • In one embodiment, the current source I6 is designed to be larger than or equal to the current source I4 such that the current supplied from the current source I4 is completely sunk through the transistor L9 and no more transferred as the low-side drive current ILa when the low-side detection signal VL goes below the low-side threshold voltage VLth. Therefore, the low-side adjusting circuit 24L effectively saves the supply of the low-side drive current ILa, achieving a high-efficiency driving operation. In another embodiment, the low-side threshold voltage VLth is designed to make a collector-emitter voltage VCE(L3) of the transistor L3 large enough for preventing the transistor L3 from operating into a deep saturation region, thereby keeping a fast response of the drive voltage VO upon transition. After the low-side drive current ILa is stopped, a resistor R5 provides the transistor L3 with a discharge path, thereby ensuring that the low-side amplifying circuit 22L is shut down.
  • While the invention has been described by way of examples and in terms of preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications.

Claims (20)

1. A drive circuit for applying a drive voltage through an output terminal to a switching element, comprising:
a supplying circuit for generating a first drive current in response to a control signal;
an amplifying circuit for generating a second drive current based on the first drive current and applying the second drive current to the output terminal for changing the drive voltage, wherein the second drive current is larger than the first drive current;
a detecting circuit coupled to the output terminal for generating a detection signal representative of the drive voltage; and
an adjusting circuit implemented by a differential comparator for dynamically adjusting the first drive current based on a comparison of the detection signal and a predetermined threshold voltage,
wherein the differential comparator comprises:
a first control terminal receiving the detection signal;
a second control terminal for receiving the threshold voltage;
a first current path controlled by the first control terminal;
a second current path controlled by the second control terminal; and
a current source for distributing a predetermined adjustment current between the first current path and the second current path based on the comparison of the detection signal and the threshold voltage, wherein:
the first current path is coupled to the supplying circuit for dynamically adjusting the first drive current.
2. (canceled)
3. The drive circuit according to claim 1, wherein:
the adjustment current is designed to be larger than or equal to the first drive current.
4. The drive circuit according to claim 1, wherein:
the adjusting circuit reduces the first drive current when the detection signal increases to approach the threshold voltage.
5. The drive circuit according to claim 4, wherein:
the adjusting circuit completely prevents the first drive current from being applied to the amplifying circuit when the detection signal goes beyond the threshold voltage.
6. The drive circuit according to claim 1, wherein:
the adjusting circuit reduces the first drive current when the detection signal decreases to approach the threshold voltage.
7. The drive circuit according to claim 6, wherein:
the adjusting circuit completely prevents the first drive current from being applied to the amplifying circuit when the detection signal goes below the threshold voltage.
8. The drive circuit according to claim 1, wherein:
the amplifying circuit applies the second drive current to the output terminal for increasing the drive voltage, and
the amplifying circuit comprises:
a first transistor having a base electrode for receiving the first drive current, an emitter electrode coupled to a ground potential, and a collector electrode, and
a second transistor having a base electrode coupled to the collector electrode of the first transistor, an emitter electrode coupled to a supply voltage source, and a collector electrode for applying the second drive current to the output terminal.
9. The drive circuit according to claim 1, wherein:
the amplifying circuit applies the second drive current to the output terminal for decreasing the drive voltage, and
the amplifying circuit comprises:
a first transistor having a base electrode for receiving the first drive current, an emitter electrode, and a collector electrode coupled to a supply voltage source, and
a second transistor having a base electrode coupled to the emitter electrode of the first transistor, an emitter electrode coupled to a ground potential, and a collector electrode for applying the second drive current to the output terminal.
10. The drive circuit according to claim 1, wherein:
the detection circuit is implemented by a level shifter such that the detection signal is formed by shifting the drive voltage with a predetermined potential difference.
11. The drive circuit according to claim 10, wherein:
the predetermined potential difference is implemented by a base-emitter voltage of a transistor.
12. A drive circuit for applying a drive voltage through an output terminal to a switching element, comprising:
a high-side supplying circuit for generating a first high-side drive current in response to a high-side control signal;
a high-side amplifying circuit for generating a second high-side drive current based on the first high-side drive current and applying the second high-side drive current to the output terminal for increasing the drive voltage, wherein the second high-side drive current is larger than the first high-side drive current;
a high-side detecting circuit coupled to the output terminal for generating a high-side detection signal representative of the high-side drive voltage;
a high-side adjusting circuit implemented by a high-side differential comparator for dynamically adjusting the first high-side drive current based on a comparison of the high-side detection signal and a predetermined high-side threshold voltage;
a low-side supplying circuit for generating a first low-side drive current in response to a low-side control signal;
a low-side amplifying circuit for generating a second low-side drive current based on the first low-side drive current and applying the second low-side drive current to the output terminal for decreasing the drive voltage, wherein the second low-side drive current is larger than the first low-side drive current;
a low-side detecting circuit coupled to the output terminal for generating a low-side detection signal representative of the low-side drive voltage; and
a low-side adjusting circuit implemented by a low-side differential comparator for dynamically adjusting the first low-side drive current based on a comparison of the low-side detection signal and a predetermined low-side threshold voltage.
13. The drive circuit according to claim 12, wherein:
the high-side differential comparator comprises:
a first high-side control terminal for receiving the high-side detection signal;
a second high-side control terminal for receiving the high-side threshold voltage;
a first high-side current path controlled by the first high-side control terminal;
a second high-side current path controlled by the second high-side control terminal; and
a high-side current source for distributing a predetermined high-side adjustment current between the first high-side current path and the second high-side current path based on the comparison of the high-side detection signal and the high-side threshold voltage, wherein:
the first high-side current path is coupled to the high-side supplying circuit for dynamically adjusting the first high-side drive current.
14. The drive circuit according to claim 13, wherein:
the high-side adjustment current is designed to be larger than or equal to the first high-side drive current.
15. The drive circuit according to claim 12, wherein:
the low-side differential comparator comprises:
a first low-side control terminal for receiving the low-side detection signal;
a second low-side control terminal for receiving the low-side threshold voltage;
a first low-side current path controlled by the first low-side control terminal;
a second low-side current path controlled by the second low-side control terminal; and
a low-side current source for distributing a predetermined low-side adjustment current between the first low-side current path and the second low-side current path based on the comparison of the low-side detection signal and the low-side threshold voltage, wherein:
the first low-side current path is coupled to the low-side supplying circuit for dynamically adjusting the first low-side drive current.
16. The drive circuit according to claim 15, wherein:
the low-side adjustment current is designed to be larger than or equal to the first low-side drive current.
17. The drive circuit according to claim 12, wherein:
the high-side adjusting circuit reduces the first high-side drive current when the high-side detection signal increases to approach the high-side threshold voltage.
18. The drive circuit according to claim 17, wherein:
the high-side adjusting circuit completely prevents the first high-side drive current from being applied to the high-side amplifying circuit when the high-side detection signal goes beyond the high-side threshold voltage.
19. The drive circuit according to claim 12, wherein:
the low-side adjusting circuit reduces the first low-side drive current when the low-side detection signal decreases to approach the low-side threshold voltage.
20. The drive circuit according to claim 19, wherein,
the low-side adjusting circuit completely prevents the first low-side drive current from being applied to the low-side amplifying circuit when the low-side detection signal goes below the low-side threshold voltage.
US10/907,397 2005-03-31 2005-03-31 Drive circuit for a switching element Expired - Fee Related US7123060B1 (en)

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KR101675562B1 (en) 2010-05-04 2016-11-11 삼성전자주식회사 Power device

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