JP2009188746A - Gate drive circuit of voltage controlled type transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gate drive circuit of a voltage controlled type transistor which can charge with a stable voltage, can use the charged voltage at the time of turnoff, and can turn on a gate discharging transistor provided on the side of secondary winding wire of a pulse transformer at the time of turnoff at high speed. <P>SOLUTION: The gate drive circuit of the voltage controlled type transistor has the pulse transformer 10, an MOS transistor 20, a diode 21, a capacitor 30, a diode 31, a gate discharging pnp transistor 40, and a resistor 41, wherein a voltage generated at a secondary winding wire 12 by a voltage applied to a primary winding wire 11 is applied to a gate of a voltage controlled type transistor 50 through the transistor 20 and the diode 21, and charges the capacitor 30 through the diode 31, so that the voltage applied to the primary winding wire 11 is not applied to the secondary winding wire 12. By a reverse voltage generating at the secondary winding wire 12, current through the capacitor 30, the resistor 41, the diode 21, and the transistor 20 flows. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a voltage-controlled transistor gate drive circuit, and more particularly to an insulated gate drive circuit that electrically insulates a path for transmitting a drive signal.

  An insulated gate drive circuit is used as a gate drive circuit for a voltage controlled transistor. Some insulating gate drive circuits use a pulse transformer (Patent Documents 1, 2, etc.).

  In Patent Document 1, the reverse induced voltage induced in the third winding in the secondary winding of the pulse transformer when the switching element provided on the primary winding side of the pulse transformer is switched from energization to cutoff. Is stored in a capacitor and used as reverse bias energy between the gate and source of the field effect transistor at the time of turn-off.

In Patent Document 2, a capacitor is charged with the excitation energy of a pulse transformer when the voltage control transistor is driven off, and a reverse bias voltage is applied between the gate and source of the voltage control transistor when the voltage control transistor is turned off. Yes.
JP-A-63-67014 JP 2005-136842 A

  However, when the capacitor is charged with a counter electromotive force generated in the secondary winding of the pulse transformer at the time of turn-off, the voltage is not stabilized, and the voltage of the capacitor changes particularly when the duty ratio is changed.

  The present invention has been made under such a background, and an object of the present invention is to charge a stable voltage so that the charged voltage can be used at the time of turn-off, and the secondary winding of the pulse transformer at the time of turn-off. Another object of the present invention is to provide a voltage-controlled transistor gate drive circuit capable of turning on a gate discharge transistor provided on the side at high speed.

  In the first aspect of the present invention, a primary winding and a secondary winding are provided, and a first terminal that is one end of the secondary winding and a second terminal that is the other end of the secondary winding. A transformer having a tap connected to a source or an emitter of a voltage controlled transistor, a primary circuit for applying a voltage to the primary winding, and a voltage generated in the secondary winding to the voltage controlled transistor A secondary circuit that is applied to the gate of the transistor, wherein the secondary circuit has a transistor connected between the first terminal and the gate of the voltage controlled transistor, and an anode connected to the transistor. And a first diode whose cathode is connected to the gate of the voltage-controlled transistor, a capacitor connected between the tap and the second terminal, and an anode between the capacitor and the second terminal. A diode connected to the capacitor and a cathode connected to the second terminal, a drain or a collector connected to an anode of the second diode, and a source or emitter connected to the voltage A gate discharge transistor connected to the gate of the control transistor; one end connected to the drain or collector of the gate discharge transistor; the other end connected to the gate or base of the gate discharge transistor; and the first A resistor connected to the cathode of the diode, and a voltage generated in the secondary winding by the voltage applied to the primary winding by the primary side circuit via the transistor and the first diode. And applied to the gate of the voltage controlled transistor The capacitor is charged via the diode of 2 and the voltage applied to the primary winding by the primary circuit is no longer applied, so that the capacitor, the resistor, The gist is that a current flows through the first diode and the transistor.

  According to the first aspect of the present invention, the voltage generated in the secondary winding by the voltage applied to the primary winding by the primary side circuit is applied to the gate of the voltage controlled transistor via the transistor and the first diode. Apply and charge the capacitor via the second diode. Therefore, the capacitor can be charged with a stable voltage.

  In addition, when the voltage applied to the primary winding is not applied by the primary side circuit, the reverse voltage generated in the secondary winding causes a current to flow through the capacitor, resistor, first diode, and transistor, thereby causing gate discharge. The transistor can be turned on faster. As the gate discharge transistor is turned on, a reverse bias is applied between the gate and source of the voltage controlled transistor or between the gate and emitter by the charged capacitor, and the voltage controlled transistor is turned off at high speed.

  Here, the voltage control type transistor refers to a MOS transistor or IGBT. The gate discharge transistor refers to a p-channel MOS transistor or a bipolar transistor. Furthermore, a transistor refers to an IGBT including a MOS transistor and a reversely connected diode.

  The voltage-controlled transistor gate drive circuit according to claim 1, wherein the gate of the transistor is between a pair of voltage dividing resistors connected in series between the first terminal and the tap. A connected configuration is preferable.

  According to the present invention, it is possible to charge at a stable voltage and use the charged voltage at the time of turn-off, and to turn on the gate discharge transistor provided on the secondary winding side of the pulse transformer at a high speed at the time of turn-off. it can.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
FIG. 1 shows an insulated gate drive circuit of a voltage controlled transistor in this embodiment.

  In FIG. 1, an n-channel type voltage control type transistor 50 has a resistor 51 connected to the gate. A resistor 52 is connected between the gate and source of the voltage control transistor 50.

  The gate drive circuit includes a pulse transformer 10. The pulse transformer 10 has a primary winding 11 and a secondary winding 12. Regarding the primary winding 11 of the pulse transformer 10, one end is a first terminal 11a, the other end is a second terminal 11b, and a tap 11c is provided between the first terminal 11a and the second terminal 11b. Regarding the secondary winding 12 of the pulse transformer 10, one end is a first terminal 12a, the other end is a second terminal 12b, and a tap 12c is provided between the first terminal 12a and the second terminal 12b.

  A primary circuit for applying a voltage to the primary winding 11 of the pulse transformer 10 and a secondary circuit for applying a voltage generated in the secondary winding 12 to the gate of the voltage control type transistor 50 are provided. The primary side circuit includes a diode 13, a MOS transistor 14, resistors 15, 16 and 18, and a capacitor 17. The secondary circuit includes transistors 20 and 40, a capacitor 30, diodes 21, 22, 25 and 31, and resistors 23, 24 and 41.

  Regarding the primary circuit, the first terminal 11 a of the primary winding 11 of the pulse transformer 10 is grounded via a diode 13. The second terminal 11 b of the primary winding 11 is grounded via the MOS transistor 14. A resistor 15 is connected to the gate of the MOS transistor 14. A resistor 16 is connected between the gate and source of the MOS transistor 14. A power supply (Vcc) terminal is connected to the tap 11 c of the primary winding 11. A capacitor 17 and a resistor 18 are connected in series between the tap 11 c of the primary winding 11 and the drain of the MOS transistor 14.

  Then, a pulse signal is sent as a drive signal for the voltage-controlled transistor 50 to the gate of the MOS transistor 14 via the resistor 15, and the MOS transistor 14 is turned on in response to the input of the pulse signal, and the primary winding 11 of the pulse transformer 10. The winding between the tap 11c and the second terminal 11b is energized.

On the other hand, for the secondary circuit, the source of the voltage control type transistor 50 is connected to the tap 12 c of the secondary winding 12 of the pulse transformer 10.
Between the first terminal 12a of the secondary winding 12 of the pulse transformer 10 and the gate of the voltage control type transistor 50, the p-channel type MOS transistor 20 and the diode 21 are sequentially arranged from the first terminal 12a of the secondary winding 12. The diode 22 and the resistor 51 are connected in series. The anode of the diode 21 is connected to the MOS transistor 20, the cathode of the diode 21 is connected to the anode of the diode 22, and the cathode of the diode 22 is connected to the resistor 51. As described above, the MOS transistor 20 is connected between the first terminal 12a of the secondary winding 12 of the pulse transformer 10 and the gate of the voltage control type transistor 50, and the diode 21 as the first diode is further connected to the MOS transistor. The anode is connected to the MOS transistor 20 and the cathode is connected to the gate of the voltage controlled transistor 50 between the gate 20 and the gate of the voltage controlled transistor 50.

In the MOS transistor 20, a parasitic diode 27 is formed, which is a built-in diode (body diode) between the source and the drain.
A pair of voltage dividing resistors 23 and 24 and a diode 25 are connected in series between the first terminal 12a of the secondary winding 12 of the pulse transformer 10 and the tap 12c. The gate of the MOS transistor 20 is connected between the pair of voltage dividing resistors 23 and 24. The diode 25 has an anode on the resistor 24 side and a cathode on the tap 12c side.

  A capacitor 30 is connected via a diode 31 between the tap 12c of the secondary winding 12 of the pulse transformer 10 and the second terminal 12b. Specifically, the capacitor 30 has one end connected to the tap 12 c of the secondary winding 12 of the pulse transformer 10 and the other end connected to the anode of the diode 31, and the cathode of the diode 31 is connected to the secondary winding 12 of the pulse transformer 10. It is connected to the second terminal 12b. In this way, the capacitor 30 is connected between the tap 12c of the secondary winding 12 of the pulse transformer 10 and the second terminal 12b, and the diode 31 as the second diode is connected to the secondary of the capacitor 30 and the pulse transformer 10. Between the second terminal 12 b of the winding 12, the anode is connected to the capacitor 30 and the cathode is connected to be the second terminal 12 b of the secondary winding 12 of the pulse transformer 10.

  A gate discharge pnp transistor 40 is connected between the anode of the diode 31 and the gate of the voltage control type transistor 50. Specifically, the collector of the gate discharge pnp transistor 40 is connected to the anode of the diode 31, and the emitter of the gate discharge pnp transistor 40 is connected to the gate of the voltage control transistor 50 via the resistor 51 ( (The gate discharge pnp transistor 40 has a collector connected to the anode of the diode 31 and an emitter connected to the gate of the voltage-controlled transistor 50). A base of the pnp transistor 40 is connected to the anode of the diode 22, and a resistor 41 is connected between the base and collector of the pnp transistor 40. That is, one end of the resistor 41 is connected to the collector of the pnp transistor 40, and the other end is connected to the base of the pnp transistor 40 and the cathode of the diode 21.

Next, the operation of the gate drive circuit configured as described above will be described.
FIG. 2 shows when the MOS transistor 14 is on. FIG. 3 shows the time when the MOS transistor 14 is switched from on to off, that is, when the MOS transistor 14 is turned off. FIG. 4 shows the MOS transistor 14 when it is off.

First, the operation when the MOS transistor 14 of FIG. 2 is on will be described.
As shown in FIG. 2, when the MOS transistor 14 as a switching element is turned on, the winding between the tap 11c of the primary winding 11 of the pulse transformer 10 and the second terminal 11b is turned on as shown by reference numeral A1 in FIG. When energized, a voltage is generated in the secondary winding 12 of the pulse transformer 10. As a result, as indicated by reference numeral A2 in FIG.

  When the MOS transistor 20 is turned on, as indicated by symbol A3 in FIG. 2, a current flows through the resistor 51 via the first terminal 12a of the secondary winding 12 of the pulse transformer 10 → the MOS transistor 20 → the diode 21 → the diode 22; A voltage is applied to the gate of the voltage controlled transistor 50. As a result, the voltage control type transistor 50 is turned on.

  On the other hand, as indicated by reference numeral A4 in FIG. 2, the tap 12c of the secondary winding 12 of the pulse transformer 10 → the capacitor 30 → the diode 31 → the second terminal 12b of the secondary winding 12 of the pulse transformer 10 between both ends of the capacitor 30. A current flows along the path leading to, and the capacitor 30 is charged.

  In this way, the voltage generated in the secondary winding 12 by the voltage applied to the primary winding 11 by the primary side circuit is applied to the gate of the voltage control type transistor 50 through the MOS transistor 20 and the diode 21. The capacitor 30 is charged via the diode 31.

Next, the operation when the MOS transistor 14 is turned off will be described.
As shown in FIG. 3, when the MOS transistor 14 is switched from on to off, a counter electromotive force (reverse voltage) is generated in the secondary winding 12 of the pulse transformer 10. Then, as indicated by reference numeral A10 in FIG. 3, tap 12c of secondary winding 12 of pulse transformer 10 → capacitor 30 → resistance 41 → parasitic capacitance of diode 21 → parasitic diode 27 of MOS transistor 20 → secondary of pulse transformer 10 A current flows along a path to the first terminal 12a of the winding 12. Specifically, the parasitic capacitance of the diode 21 is charged by the counter electromotive force (reverse voltage) of the pulse transformer 10, and a current flows through the path A10. Here, a potential difference occurs between both ends of the resistor 41, and the voltage between the base and the emitter of the pnp transistor 40 increases. Then, as indicated by reference numeral A11 in FIG. 3, the resistance 51 → the emitter-base of the pnp transistor 40 → the parasitic capacitance of the diode 21 → the parasitic diode 27 of the MOS transistor 20 → the secondary of the pulse transformer 10 A current flows in a path to the first terminal 12a of the winding 12 (a base current of the pnp transistor 40 flows).

  As a result, the pnp transistor 40 is turned on, and the resistor 51 → the emitter-collector of the pnp transistor 40 → the capacitor 30 → the source of the voltage control transistor 50 from the gate of the voltage control transistor 50 as indicated by reference numeral A12 in FIG. A current path leading to is formed. Therefore, a negative bias voltage by the capacitor 30 is applied to the gate of the voltage controlled transistor 50, and the voltage controlled transistor 50 is turned off at high speed.

  In this way, the reverse voltage generated in the secondary winding 12 of the pulse transformer 10 when the MOS transistor 14 is turned off, that is, the voltage applied to the primary winding 11 by the primary side circuit is no longer applied. Due to the reverse voltage generated in the secondary winding 12, the tap 12c of the secondary winding 12 of the pulse transformer 10 → the capacitor 30 → the resistor 41 → the parasitic capacitance of the diode 21 → the parasitic diode 27 of the MOS transistor 20 → the secondary of the pulse transformer 10 The pnp transistor 40 is turned on at high speed when a current flows through a path to the first terminal 12a of the winding 12. When the pnp transistor 40 is turned on, a reverse bias is applied between the gate and the source of the voltage control type transistor 50 by the charged capacitor 30, and the voltage control type transistor 50 can be turned off at high speed.

Next, the operation when the MOS transistor 14 of FIG. 4 is off will be described.
In FIG. 4, as indicated by reference numeral A <b> 20, a current flows from the source side terminal of the voltage control type transistor 50 in the capacitor 30 to the resistor 52 → the resistor 51 → the emitter-base of the pnp transistor 40 → the resistor 41 → the capacitor 30. Flows. As a result, the pnp transistor 40 is kept on. Therefore, the current flows along the current path indicated by A12 in FIG. 4, that is, the path from the gate of the voltage control transistor 50 to the resistor 51 → the emitter-collector of the pnp transistor 40 → the capacitor 30 → the source of the voltage control transistor 50. As a result, the negative bias voltage is applied to the gate of the voltage controlled transistor 50.

  Thus, in the prior art (Patent Documents 1 and 2), when the capacitor is charged with the counter electromotive force generated in the secondary winding of the pulse transformer at the time of turn-off, the voltage is not stabilized, and particularly when the duty ratio changes, the capacitor Will change the voltage. On the other hand, in this embodiment, the capacitor 30 is charged when the MOS transistor 14 is turned on, so the capacitor voltage is a ratio of the number of turns between the tap 12c and the first terminal 12a and the number of turns between the tap 12c and the second terminal 12b. It is determined by (turn ratio) and can be charged with a stable voltage and used at turn-off. That is, the pulse transformer 10 having the tap 12c provided in the secondary winding 12 is used to charge the capacitor 30 when the MOS transistor 14 is turned on, and the voltage control type when the negative power source (capacitor 30) is switched from on to off. By pulling out the gate voltage of the transistor 50, the voltage controlled transistor 50 can be operated at high speed. Further, the tap 12c of the secondary winding 12 of the pulse transformer 10 → the capacitor 30 → the resistor 41 → the parasitic capacitance of the diode 21 → the parasitic diode 27 of the MOS transistor 20 → the secondary winding of the pulse transformer 10 due to the counter electromotive force of the pulse transformer 10. The pnp transistor 40 can be turned on at high speed when a current flows through the path of the line 12 to the first terminal 12a. As a result, a high speed off operation (high speed switching operation) of the voltage control type transistor 50 can be realized. Specifically, a fall operation time of 100 ns or less can be realized as a turn-off operation. Further, by providing the MOS transistor 20, when the MOS transistor 14 shown in FIG. 4 is turned off, the MOS transistor 20 is turned off to cut off the current path, thereby preventing the voltage controlled transistor 50 from being turned on accidentally. (It is possible to prevent erroneous firing when the voltage-controlled transistor 50 is turned off.)

According to the above embodiment, the following effects can be obtained.
(1) a capacitor 30 for applying a reverse bias between the gate and the source of the voltage control type transistor 50, a MOS transistor 20 for preventing malfunction when turned off, a gate discharge pnp transistor 40, diodes 21 and 31, And the resistor 41 are used to charge the capacitor 30 when the MOS transistor 14 is turned on and use the back electromotive force to tap the secondary coil 12 tap 12c of the pulse transformer 10 → the capacitor 30 → the resistor 41 → the diode 21. The pnp transistor 40 is turned on at high speed by passing a current through a path from the parasitic capacitance → the parasitic diode 27 of the MOS transistor 20 → the first terminal 12 a of the secondary winding 12 of the pulse transformer 10. Therefore, it is possible to charge with a stable voltage and use the charged voltage at the time of turn-off, and at the time of turn-off, the gate discharge pnp transistor 40 provided on the secondary winding side of the pulse transformer can be turned on at high speed.

  (2) Since the gate of the MOS transistor 20 is connected between the pair of voltage dividing resistors 23 and 24 connected in series between the first terminal 12a of the secondary winding 12 of the pulse transformer 10 and the tap 12c. The MOS transistor 20 can be turned on and off with a simple configuration.

The embodiment is not limited to the above, and may be embodied as follows, for example.
As an alternative to FIG. 1, a capacitor 80 may be connected in parallel to the diode 21 as shown in FIG. As a result, not only the parasitic capacitance of the diode 21 but also the capacitor 80 can be used.

Although the n-channel MOS transistor 50 is used as the voltage control type transistor, an IGBT may be used instead of the MOS transistor.
Although the bipolar transistor 40 is used as the gate discharge transistor, a p-channel MOS transistor may be used instead.

  In place of the p-channel MOS transistor 20, an n-channel MOS transistor or IGBT can be used. However, when replacing with IGBT, since there is no body diode, a diode is connected separately.

  The primary circuit may have any configuration as long as a voltage can be applied to the primary winding of the transformer.

The circuit block diagram of the insulated gate drive circuit of the voltage control type transistor in this embodiment. The operation | movement explanatory drawing of the gate drive circuit at the time of ON for demonstrating an effect | action. The operation | movement explanatory drawing of the gate drive circuit at the time of turn-off for demonstrating an effect | action. The operation | movement explanatory drawing of the gate drive circuit at the time of OFF for demonstrating an effect | action. The circuit block diagram of the gate drive circuit of the voltage control type transistor in another example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Pulse transformer, 11 ... Primary winding, 12 ... Secondary winding, 12a ... 1st terminal, 12b ... 2nd terminal, 12c ... Tap, 14 ... MOS transistor, 20 ... MOS transistor, 21 ... Diode, 30 ... Capacitors, 31 ... diodes, 40 ... pnp transistors, 41 ... resistors, 50 ... voltage controlled transistors.

Claims (2)

A voltage control type transistor having a primary winding and a secondary winding, and a tap provided between a first terminal which is one end of the secondary winding and a second terminal which is the other end of the secondary winding. A transformer connected to the source or emitter of
A primary circuit for applying a voltage to the primary winding;
A secondary side circuit for applying a voltage generated in the secondary winding to the gate of the voltage controlled transistor;
The secondary circuit includes a transistor connected between the first terminal and a gate of the voltage controlled transistor;
A first diode having an anode connected to the transistor and a cathode connected to the gate of the voltage controlled transistor;
A capacitor connected between the tap and the second terminal;
A second diode having an anode connected to the capacitor and a cathode connected to the second terminal between the capacitor and the second terminal;
A gate discharge transistor having a drain or collector connected to the anode of the second diode and a source or emitter connected to the gate of the voltage controlled transistor;
A resistor having one end connected to the drain or collector of the gate discharge transistor and the other end connected to the gate or base of the gate discharge transistor and the cathode of the first diode;
With
The voltage generated in the secondary winding by the voltage applied to the primary winding by the primary circuit is applied to the gate of the voltage controlled transistor via the transistor and the first diode, and The capacitor is charged via the diode of 2 and the voltage applied to the primary winding by the primary circuit is no longer applied, so that the capacitor, the resistor, A voltage-controlled transistor gate drive circuit, wherein a current flows through the first diode and the transistor. 2. The gate drive of a voltage controlled transistor according to claim 1, wherein the gate of the transistor is connected between a pair of voltage dividing resistors connected in series between the first terminal and the tap. circuit.

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