JP5425292B2 - Gate drive device - Google Patents

Description

  The present invention relates to a gate drive circuit used in voltage-driven switching devices such as IGBTs and FETs.

  In a conventional switching device, the gate of the switching device is driven from a gate power supply through a drive IC or a drive circuit via a gate resistor (see, for example, Patent Document 1).

JP-A-8-33315 ([0008] to [0011] FIG. 6)

In such a conventional gate drive device, there is a problem that the time for the switching device to transition from OFF to ON varies greatly depending on the individual characteristics of the element.
Hereinafter, with reference to FIGS. 27 and 28, the variation in the ON transition time during the turn-on period will be described in detail along with the operation of the IGBT as an example. It is assumed that the load is an inductive load L and the current I (A) is flywheeled with the load and a diode. FIG. 27 is a circuit configuration diagram, and FIG. 28 is an operation explanatory diagram thereof.

When an ON command is issued from the control signal (gate control signal), the gate drive IC applies the voltage VDD of the control power supply to the gate (G) of the IGBT 1 through the gate resistance Rg to charge the gate input capacitance Cge. . At this time, the IGBT 1 remains OFF until the gate voltage reaches the gate threshold voltage (Vth) ([1] in FIG. 28).
When Vth passes and current begins to flow between CE of IGBT1, and the gate voltage becomes Vmirror, the collector current Ic of IGBT1 becomes I (A) (period [1] to [2] in FIG. 28).

  The time until this current is turned on from OFF corresponds to the time until the gate voltage exceeds Vth and becomes Vmirror (referred to as Vmirror = mirror voltage), and is expressed by the following equation.

t _I-ON = -CRln (1-Vmirror / VDD)-{-CRln (1-Vth / VDD)}

Here, the mirror voltage and Vth vary depending on individual characteristics. For example, in an IGBT having a high mirror voltage, the above time is exponentially increased, that is, switching is slow (FIG. 28 [2] ′). .
When the gate voltage becomes a mirror voltage and further charging is continued, the Vce of the IGBT 1 changes to the ON state (period [2] to [3] in FIG. 28).
The time during this time is expressed by the following equation using the mirror charge (Qgc) charged in the feedback capacitor (Cgc).

t _V-ON = Qgc × Rg / (VDD−Vmirror)

  The charging current Ig to the gate during this period is expressed by the following equation.

  Ig = ΔV / Rg = (VDD−Vmirror) / Rg

For this reason, the higher the mirror voltage, the longer the time until the ON transition of Vce (period [2] ′ to [3] ′ in FIG. 28).
Further, until the Vce completely transitions to the ON state, further charging with the mirror voltage is necessary, and the period depends on the Ig current (FIG. 28 [4] [4] ′).

  The mirror voltage is determined by the gate threshold voltage Vth, current amplification factor gm, and output current Ic of the IGBT 1 as shown in the following equation, and greatly depends on Vth.

  Vmirror = Vth + √ (Ic / gm)

Accordingly, the variation in Vth becomes the variation in the CR charging time, and the variation in the IcON transition time (t _I-ON ). Further, the variation in Vth and gm causes the variation in the mirror voltage, the variation in the charging current, and the variation in the charging time, resulting in the variation in the VceON transition time (t _V-ON ).

The relationship between the ON transition time (t _ON = t _I-ON + t _V-ON ) and the loss is expressed by the following equation.

Ploss (on) = 1/2 × Ic × Vce × t _I-ON × f
+ 1/2 × Ic × Vce × t _V-ON × f
= 1/2 × Ic × Vce × t _ON × f
Where Vce: Vce voltage at steady state, Ic: Collector current after ON, f: Switching frequency

As described above, the variation in IcON transition time and the variation in VceON transition time both cause variations in switching loss.
Although it is possible to reduce the influence of variation by making the gate resistance value Rg smaller, in the IGBT that is actually used, the connection of the gate resistance should not be excessively increased. It is generally shown that is essential. As a measure against EMI, it is a general measure to limit dV / dt and dI / dt during switching.
Therefore, conventionally, the minimum value of the ON transition time ton is designed under the condition of the minimum mirror voltage, and the gate resistance at the switching speed (max) is determined. Then, the switching speed when the mirror voltage is maximum is obtained under the condition that the gate resistance is determined, and the switching loss must be designed based on this time. Therefore, the variation in loss due to the variation in mirror voltage tends to increase. The OFF transition is the same and has the same problem.

  The present invention has been made to solve the above-described problems, and suppresses variations in switching speed due to variations in Vth and mirror voltage in a plurality of switching devices driven by a gate driving device, and loss. An object of the present invention is to obtain a gate driving device capable of minimizing the variation of.

A gate driving device according to the present invention is connected to the gate of a voltage-driven switching device, and outputs a gate signal to the gate for turning on / off the switching device based on an on / off gate control signal.
As a gate driving device for one or both of turn-on operation and turn-off operation,
Operation of constant current pulse gate drive circuit that creates gate signal with constant current output, constant voltage pulse gate drive circuit that creates gate signal with constant voltage output, and operation of constant current pulse gate drive circuit and constant voltage pulse gate drive circuit And a determination switching circuit for switching between
The determination switching circuit includes a gate voltage detection circuit that detects a gate voltage, a first determination circuit that determines a magnitude between the gate voltage and a predetermined first set value, and a gate voltage and a predetermined second set value. In the second determination circuit for determining the magnitude and the turn-on operation, first, the constant current pulse gate drive circuit is connected to the gate, and it is determined by the first determination circuit that the gate voltage has exceeded the first set value. When a constant voltage pulse gate drive circuit is connected to the gate instead of the constant current pulse gate drive circuit, the constant current pulse gate drive circuit is first connected to the gate in the turn-off operation. A switching circuit for connecting the constant voltage pulse gate drive circuit to the gate instead of the constant current pulse gate drive circuit when determined to be less than the set value of 2;
A first setting value for changing the first setting value of the first determination circuit to a setting value reduced by a predetermined amount when the first determination circuit determines that the gate voltage has exceeded the first setting value in the turn-on operation. A second circuit for changing the second set value of the second determination circuit to a set value increased by a predetermined amount when the gate voltage is determined to be less than the second set value by the second determination circuit in the change circuit and the turn-off operation. With a set value change circuit
The voltage of the control power source of the constant current pulse gate driving circuit is set higher than the voltage of the control power source of the constant voltage pulse gate driving power source.

According to the present invention, by driving the transition period at the time of gate driving with a constant current output, the variation of the transition period due to the variation of the gate threshold voltage and the mirror voltage in the switching device can be minimized, the switching speed, Switching voltage variation can be greatly suppressed. In addition, voltage-driven switching devices having a MOS-type gate structure can be switched to constant voltage drive without compromising the reliability of the gate oxide film of the switching device. There is an unprecedented remarkable effect that it can be driven.
Further, it is possible to prevent constant current driving, constant voltage driving switching flutter, and the like due to the fluctuation of the gate voltage in the vicinity of each set value.
Furthermore, it is possible to suppress variations in the constant current set value due to solid variations in parts used in the constant current pulse gate drive circuit.

1 is an overall configuration diagram of a gate driving device according to a first embodiment of the present invention. FIG. 5 is a waveform diagram for explaining the operation of the gate drive device according to the first embodiment. 3 is a circuit diagram of an ON constant current pulse gate drive circuit 21. FIG. It is a circuit diagram of ON constant current pulse gate drive circuit 21-1. 3 is a circuit diagram of a determination / switching circuit 4. FIG. It is a circuit diagram of ON constant current pulse gate drive circuit 21-2. It is a circuit diagram of ON constant current pulse gate drive circuit 21-3. 3 is a circuit diagram of an OFF constant current pulse gate drive circuit 22. FIG. It is a circuit diagram of the OFF constant current pulse gate drive circuit 22-1. It is a circuit diagram of the OFF constant current pulse gate drive circuit 22-2. It is a circuit diagram of OFF constant current pulse gate drive circuit 22-3. It is a whole block diagram which shows the 2nd example of the gate drive device by Embodiment 1 of this invention. FIG. 10 is a circuit diagram of a determination / switching circuit 4 ′ used in the second example of the gate driving device. It is a whole block diagram which shows the 3rd example of the gate drive device by Embodiment 1 of this invention. FIG. 6 is a circuit diagram of a determination / switching circuit 4 ″ used in a third example of a gate driving device. It is a partial block diagram of the gate drive device by Embodiment 2 of this invention. 3 is a circuit diagram of a voltage limiting circuit 5. FIG. It is a whole block diagram of the gate drive device by Embodiment 2 of this invention. It is the example 1 of the improvement circuit example of the element variation by Embodiment 3 of this invention. It is the example 2 of an improvement circuit of the element variation by Embodiment 3 of this invention. It is a circuit diagram of the current switching part 211 by Embodiment 4 of this invention. It is a circuit diagram of the current switching part 221 by Embodiment 4 of this invention. It is a wave form diagram for operation | movement description by Embodiment 4 of this invention. It is a circuit diagram of the 1st determination circuit 41 by Embodiment 5 of this invention. It is a circuit diagram of the 2nd determination circuit 42 by Embodiment 5 of this invention. It is a circuit diagram of the determination circuit 43 by Embodiment 6 of this invention. It is a structural example of the conventional gate drive circuit. It is a wave form diagram which shows the operation state of the conventional gate drive circuit.

Embodiment 1 FIG.
FIG. 1 is an overall configuration diagram of a gate driving apparatus according to Embodiment 1 of the present invention. The output of the constant current pulse gate drive circuit 2 is connected to the gate of the switching device 1, and the output of the constant voltage pulse gate drive circuit 3 is further connected.
The determination / switching circuit 4 inputs the control signal (gate control signal) and the gate voltage of the switching device 1 (the gate voltage detection circuit is not shown), and the constant current pulse gate drive circuit 2 is turned ON / constant current / OFF constant. The current control signal is connected to the constant voltage pulse gate drive circuit 3 as an ON constant voltage / OFF constant voltage control signal.
Here, the voltage VDD2 of the control power supply used for the constant current pulse gate drive circuit 2 is set higher than the voltage VDD1 of the control power supply of the constant voltage pulse gate drive circuit 3. As described in detail later, this is to suppress variations in the constant current setting value due to solid variations in components (semiconductor devices) used in the constant current pulse gate drive circuit 2.

Next, the operation will be described by taking as an example the case where the inductive load L is driven in the circuit configuration using the gate driving device of FIG. FIG. 2 shows a chart of the control signal, the gate voltage waveform, the IGBT collector current Ic, and the collector-emitter voltage Vce in this configuration. It is assumed that the inductive load L is flywheeled with a current I (A) in a closed circuit of the load and the diode.
In FIG. 2, considering the variation in Vmirror (mirror voltage), the operation of a product with a mirror voltage of Vmirror1 is shown in black, and the operation of a product with a Vmirror2 is shown in gray.

Hereinafter, the ON operation (turn-on operation), and therefore, the operation until “H” is input to the control signal and the IGBT 1 is turned ON will be described in detail.
When “H” is input to the control signal, an ON constant current control signal is output according to the determination of the determination / switching circuit 4. As a result, the ON constant current pulse gate drive circuit 21 operates, the constant current Ig is supplied to the gate of the switching device 1, and the gate input capacitance Cge is charged with a constant current.
At this time, the IGBT 1 remains OFF until the gate voltage reaches the gate threshold voltage (Vth) (FIG. 2 [1], [1] ′). When Vth passes and current begins to flow between CE of IGBT1, and the gate voltage becomes mirror voltage, collector current Ic of IGBT1 becomes I (A) (FIGS. 2 [1] to [2], [1] ' ~ [2] 'period).
Here, Vth (gate threshold voltage) is a gate voltage when a current of 0.01% as a switching element rated current ratio flows through the switching element.

  In the case of constant voltage-resistance driving through a conventional resistor, the time until this current is turned from OFF to ON is expressed as follows by modifying the above-described equation and depends on VDD and Vth. It was.

t _{I-ON old} = −Cge · Rg · ln {1-1 / (VDD−Vth) · √ (Ic / gm)}

  On the other hand, as shown in FIG. 1, when driving with a constant current, the time until the current turns from OFF to ON is expressed by the following equation and does not depend on VDD or Vth.

t _I-ON = Cge · 1 / Ig · √ (Ic / gm)

Thereby, it is possible to eliminate variations in time t _I-ON .
When the gate voltage becomes a mirror voltage and further charging is continued, the Vce of the IGBT 1 transitions to ON (periods [2] to [4], [2] ′ to [4] ′ in FIG. 2).

In the conventional constant voltage-resistance drive, the charging current Ig to the gate after the mirror voltage is
Ig _old = ΔV / Rg = (VDD−Vmirror) / Rg
When the mirror charge (Qgc) charged in the feedback capacitor (Cgc) is used, the time for the Vce of the IGBT 1 to transition to the ON state is
t _{V-ON old} = Qgc × Rg / (VDD-Vmirror)
Therefore, the higher the mirror voltage, the longer this time.
However, as shown in FIG. 1, by driving with constant current, the time for the Vce of the IGBT 1 to transition to the ON state is
t _V-ON = Qgc / Ig
And is turned on in a certain time without being affected by the mirror voltage.

  Next, the OFF operation (turn-off operation), and therefore, the operation from when “L” is input to the control signal until the IGBT 1 is turned OFF will be described in detail. When “L” is input to the control signal, the determination / switching circuit 4 outputs an OFF constant current control signal. As a result, the OFF constant current pulse gate drive circuit 22 operates, charges are discharged from the gate of the switching device 1 with a constant current, and the gate capacitance Cge + Cgc is discharged with a constant current. At this time, the IGBT 1 remains ON until the gate voltage becomes the mirror voltage (period [5] to [6] in FIG. 2).

When the gate voltage drops to the mirror voltage, the Vce voltage starts to rise gradually and transitions to OFF. At this time, the charging time of the mirror charge (Qgc) to be charged in the feedback capacitor (Cgc) is the OFF time of Vce.
Regarding the charging time of the mirror charge (Qgc), in the conventional constant voltage-resistance driving,
t _{V-OFF old} = Qgc × Rg / Vmirror
Therefore, the higher the mirror voltage, the shorter the time to the Vce OFF transition.
On the other hand, as shown in FIG. 1, by driving with a constant current, the time to the Vce OFF transition is
t _V-OFF = Qgc / Ig
And is turned off in a certain time without being affected by the mirror voltage. (Period of FIG. 2 [6]-[8]).

When the gate voltage falls below the mirror voltage, Vce transitions to OFF, so that the capacity viewed from the gate driving device decreases from Cge + Cgc so far to Cge.
When the discharge is further continued, Ic of the IGBT 1 transitions to OFF. At the initial stage, since the gate voltage is a mirror voltage, the collector current Ic of the IGBT 1 is I (A), but when the gate voltage gradually decreases and transitions to Vth, Ic becomes almost 0 (A) and is turned OFF. Transition (period [8] to [9] in FIG. 2).

In the conventional constant voltage-resistance drive, the time until this current is turned from ON to OFF, and therefore the period until the gate voltage falls below the mirror voltage and becomes Vth,
t _{I-OFF old} = Cge · Rg · ln (1 + 1 / Vth · √ (Ic / gm))
And was dependent on Vth. On the other hand, as shown in FIG. 1, by driving with a constant current, this period is
t _I-OFF = Cge / Ig × √ (Ic / gm)
And does not depend on Vth, and transitions to OFF in a certain time.
As described in detail above, by driving with a constant current, it is possible to greatly suppress variations in switching speed.

  In the ON operation of the device used in FIG. 2, Vce suddenly changes to ON during the period from [2] to [3], and until [4], it completely changes to ON (Vcesat). Further, in the OFF operation, Vce gradually changes to OFF during the period [6] to [7], and suddenly changes to OFF during the period [7] to [8]. Depending on the case, there is a device that transitions at a constant dV / dt during the period of [2] to [4] and [6] to [8].

Next, a specific circuit example of each component in FIG. 1 will be described. As described above, the constant current driving can eliminate the variation in switching speed depending on VDD and Vth (and the mirror voltage). However, in order to realize this, it is possible to drive at a high speed and the variation in Ig. A small high-speed constant current drive circuit is required.
FIG. 3 shows a specific configuration example of the ON constant current pulse gate drive circuit 21. The ON constant current pulse gate drive circuit 21 capable of constant current drive at high speed receives the ON constant current operation command, Q1 'is turned OFF, Q2 is turned ON, and the V0 voltage is output at high speed. As a result, the base voltage of Q1 becomes the V0 voltage, and constant current driving is possible as can be seen from the following equation.

VDD2-R3 × (Ib + Ic) −V _EB = V0
Ib = Ic / h _FE
From the above two formulas,
_{Ic = (VDD2-V EB -V0} ) / R3 × {h FE / (h FE +1)}

  In order to stop the constant current, Q2 is turned off and Q1 'is turned on to output the VDD2 voltage or the VDD2 voltage or higher at a high speed. As a result, the base current of Q1 stops flowing and Q1 is turned off.

  At this time, in order to drive at a high speed constant current, it is necessary to “supply the V0 voltage at a high speed” and “the Q1 must respond at a high speed”, and these conditions depend on the performance of the device alone, but are discrete. Since the device is used, it can be easily configured by using a low-capacity high-speed switching device.

Next, the phenomenon of suppressing variation in Ig (indicated as Ic in FIG. 3) by increasing the power supply voltage of the constant current drive circuit will be described. In the ON constant current pulse gate drive circuit 21, Q2 is controlled by the ON constant current control signal. When is turned on, V0 becomes the base voltage of Q1 and is driven at a constant current. When the output voltage of Q1 becomes equal to or higher than V0, the circuit does not operate with a constant current. Therefore, V0 must be equal to or higher than the maximum mirror voltage considering the variation of the switching device 1 to be driven.
At this time, in the constant current operation region,
_{Ic = (VDD2-V EB -V0} ) / R3 × {h FE / (h FE +1)}
It becomes.

However, V _EB generally has an individual difference variation, which causes a constant current variation. Taking into account the variation of the V _EB, the _{V EB} of the two _devices, when _{V EB1} and _{V EB2,}
I _C1 / I _C2 = (VDD2−V0−V _EB1 ) / (VDD2−V0−V _EB2 )
From this, for example, when VDD2 = 15V, V0 = 13.5V, and V _EB = 0.8 to 1.0V,
I _C1 / I _C2 = (15V-13.5V-0.8V) / (15V-13.5V-1.0V) = 0.7V / 0.5V = 1.4
And an error of about 40%.

However, if VDD2 is 19V, which is 4V higher,
I _C1 / I _C2 = (19V-13.5V-0.8V) / (19V-13.5V-1.0V) = 4.7V / 4.5V = 1.04 ...
Error of about 4.4%, and the variation of the constant current Ig can be greatly improved.
As described above, it is possible to realize a high-speed constant current drive circuit with less Ig variation including high-speed constant current operation and device variation.

  FIG. 4 shows an ON constant current pulse gate drive circuit 21-1, which is a modification of FIG. In the circuit of FIG. 4, when Q2 is turned on, the value V0 divided by R1 and R2 becomes the base voltage of Q1, and when Q2 is turned off, VDD2 can be applied to the base of Q1.

As described above, by making VDD2> VDD1, high accuracy can be achieved and switching speed variation can be greatly reduced. However, if driving is continued with only the ON constant current pulse gate drive circuit 21, IGBT1 As a result, a high voltage of VDD2 is applied to the gate of the transistor, and the reliability of the gate oxide film is lowered.
Therefore, the determination / switching circuit 4 that observes the gate voltage and switches between constant current driving and constant voltage driving controls the gate driving circuit from the constant current pulse gate driving circuit 2 to the constant voltage pulse after the ON or OFF transition period ends. Switching to the gate drive circuit 3 prevents application of overvoltage. The power source of the constant voltage pulse gate drive circuit 3 is set to VDD1, and a voltage that does not deteriorate the reliability of the gate oxide film is set.

FIG. 5 shows an example of the determination / switching circuit 4. When receiving the control signal (gate control signal) “H”, the determination / switching circuit 4 deactivates the OFF signal and outputs the ON signal. At this time, the gate voltage of the IGBT 1 is observed, and the first determination circuit 41 determines that the gate voltage is equal to or lower than the first set value VH (VH is set to a value equal to or greater than the maximum mirror voltage variation). If the gate voltage exceeds VH, the signal is switched to the ON constant voltage signal.
When the control signal “L” is received, the ON signal is deactivated and an OFF signal is output. At this time, the gate voltage of the IGBT 1 is observed, and if the gate voltage is equal to or higher than VL which is the second set value (VL is set to a value equal to or lower than the Vth minimum voltage) by the second determination circuit 42, the gate voltage is set to OFF. A current signal is output, and when the gate voltage becomes less than VL, the signal is switched to an OFF constant voltage signal.
Thereby, switching drive control between the constant current pulse gate drive circuit 2 and the constant voltage pulse gate drive circuit 3 is performed, and an overvoltage is prevented from being applied to the gate.

  As a result of considering the Ig variation of the constant current pulse gate drive circuit 21, when the mirror voltage is low and the VDD2 voltage becomes VDD2 <recommended gate voltage (VDD1) of IGBT1, VDD2 is set to the same voltage as VDD1. Also good. Further, as shown in a specific example in a later stage, a method of switching between constant current driving and constant voltage driving only in the ON transition or only in the OFF transition can be adopted.

In pursuing the above constant current drive circuit, the contents of Patent Document (Japanese Patent No. 3680722 (mainly [0025] to [0027] see FIG. 8)) examined by the inventors for reference are introduced below. .
FIG. 8 of this patent document uses a constant current circuit by an OP amplifier for driving with a constant current, and operates to suppress the gate current only during a period in which the current and voltage change.
However, even in a constant current circuit using a relatively high-speed OP amplifier, the response characteristic of the constant current with respect to the command value is not so fast, and in particular, when the constant current is turned off, the characteristics expected by the inventors are obtained. Was difficult. This is presumably due to the response speed and output slew rate inside the OP amplifier, the gate characteristics of the MOS-FET to be driven, the power supply voltage vs. the maximum output voltage characteristic of the OP amplifier, and the like. For this reason, a response delay to the constant current increase command and a response delay to the constant current decrease command (0 A) occur. In particular, the response delay at the time of the constant current decrease command is due to a shortage of the slew rate. It takes time to turn off. Then, when the device is turned off and Q13 is turned on, there is a possibility that an excessive through current flows through E1, R12, Q12, Q13, and R13, and until the partial pressure of R12 and R13, until Q12 is turned off. There is a possibility that the IGBT will continue to be ON for the period of time.
In addition, since the gate capacitance and the feedback capacitance of Q12 are considerably large capacitive loads for the OP amplifier, there is a possibility of oscillation and abnormal heat generation due to an increase in output effective current.
Therefore, the high-speed drive circuit shown in FIG. 3 of the present embodiment is necessary. Note that Q1 of the ON constant current pulse gate drive circuit 21 is a transistor, but it may be a circuit using a current controllable element such as an FET.

As a further use state, in an abnormal situation such as an arm short circuit in which the switching device 1 is to be shifted to a shut-off sequence at high speed, a delay in the time until the gate current supply is stopped may be a fatal problem.
In the following, a circuit example in the case where it is necessary to increase the speed of the constant current drive OFF in the ON constant current pulse gate drive circuit 21 will be described with reference to FIGS.

  The ON constant current pulse gate drive circuit 21-2 in FIG. 6 uses a level convertible IC drive type, outputs “L” in constant current operation, and performs constant current operation in R1 to R3 and Q1. . At the timing when the constant current is stopped, the transistor Q1 can be instantaneously turned off by supplying VDD2 from the IC1. Therefore, the Q1 OFF speed can be further improved.

In the constant current operation, the ON constant current pulse gate drive circuit 21-3 sets the control signal to “H”, turns off Q1 ′, turns on Q2, and performs constant current operation on R1 to R3 and Q1. . At the timing of stopping the constant current, the control signal is set to “L”, Q2 is turned OFF, and Q1 ′ is turned ON. With the current from Q1 ′, a voltage of VDD2 or VDD2 or higher is directly supplied to the base of Q1, and the transistor Q1 is instantaneously turned off, and at the same time, the output capacitor and the feedback capacitor of Q2 can be charged. Therefore, the aforementioned Q1 OFF speed is further improved.
Examples of switches used for Q2 and Q1 ′ include semiconductor switching devices such as MOS-FETs and transistors.

Similarly to the ON constant current pulse gate drive circuit 21, the OFF constant current pulse gate drive circuit 22 used for the constant current pulse gate drive circuit 2 can be driven at a high speed and requires a high speed constant current drive circuit with small variations in Ig.
FIG. 8 shows an OFF constant current pulse gate drive circuit 22 capable of high-speed constant current drive. In the figure, when an OFF constant current operation command is received, Q3 ′ is turned OFF, Q4 is turned ON, and the V1 voltage is output at high speed. As a result, the base voltage of Q3 becomes V1, and constant current driving is possible as shown below.

R6 × (Ib + Ic) + V _BE = V1
Ib = Ic / h _FE
From the above two formulas, Ic = (V1−V _BE ) / R6 × {h _FE / (h _FE +1)}
Further, in order to stop the constant current, Q4 is turned off and Q3 ′ is turned on to output a common potential (Vcom) voltage or Vcom or less at high speed. As a result, the base current of Q3 stops flowing and Q3 is turned off. In the above equation, the common potential (Vcom) = 0V.

  At this time, in order to drive at a high speed constant current, “V1 voltage is supplied at high speed” and “Q3 responds at high speed”. Since it is used, it can be easily configured using a low-capacity high-speed switching device.

Further, it is possible to suppress variations in Ig (indicated by Ic in FIG. 8) by lowering Vcom of the constant current drive circuit to 0 V or less. The reason why the variation can be suppressed will be described below. In the OFF constant current pulse gate drive circuit 22, when Q4 is turned ON by the OFF constant current control signal, V1 becomes the base voltage of Q3 and is driven with constant current. When the output voltage of Q3 becomes V1 or less, the circuit does not operate with a constant current. Therefore, V1 must be set to be equal to or less than the minimum Vth voltage considering the variation of the switching device 1 to be driven.

At this time, in the constant current operation region,
Ic = (V1-Vcom- _VBE ) / R6 * { _hFE / ( _hFE + 1)}
Here, V _BE generally has an individual difference variation, and this causes a variation in a constant current. Taking into account the variation of the V _EB, the _{V EB} of the two _devices, when _{V EB1} and _{V EB2,}
I _C1 / I _C2 = (V1−Vcom−V _BE1 ) / (V1−V _BE2 )
From this, for example, when Vcom = 0 V, V1 = 4.5 V, and V _BE = 0.8 to 1.0 V,
I _C1 / I _C2 = (4.5V-0V-0.8V) / (4.5V-0V-1.0V)
= 3.7V / 3.5V = 1.057 ...
Thus, an error of about 5.7% is obtained.

However, if Vcom = 4V, which is 4V lower, I _C1 / I _C2 = {4.5V − (− 4V) −0.8V} / {(4.5V − (− 4V) −1.0V)
= 7.7V / 7.5V = 1.0266 ...
And an error of about 2.7%, and variation in the constant current Ig can be improved.
As described above, it is possible to realize a high-speed constant current drive circuit with less Ig variation including high-speed constant current operation and device variation.
Note that Q3 of the OFF constant current pulse gate drive circuit 22 is a transistor, but a circuit using a current controllable element such as an FET may be used.

FIG. 9 shows an OFF constant current pulse gate drive circuit 22-1 which is a modification of FIG. In the circuit of FIG. 9, when Q4 is turned on, the OFF constant current signal is amplified by the voltage follower, and the value V1 divided by R4 and R5 becomes the base voltage of Q3, and when Q4 is turned off, it becomes the base of Q3. Vcom can be applied.
In this circuit example as well, in consideration of variations in V _BE , Vcom may be set to a negative voltage instead of the emitter voltage of switching device 1 in order to reduce variations in constant current.

Next, in the OFF constant current pulse gate drive circuit 22, an example of a circuit when speeding up when stopping constant current drive is necessary will be described with reference to FIGS.
The OFF constant current pulse gate drive circuit 22-2 in FIG. 10 employs a configuration in which an OFF constant current control signal is buffered by the IC 1 to obtain output voltage accuracy and drive current. As the driving current, a circuit current for dividing R4 and R5 and a base current Ib of the transistor Q3 are required.

In the constant current operation, the OFF constant current pulse gate drive circuit 22-3 in FIG. 11 sets the control signal to “H”, turns off Q3 ′, turns on Q4, and performs constant current operation on R4 to R6 and Q3. . At the timing of stopping the constant current, the control signal is set to “L”, Q4 is turned OFF, and Q3 ′ is turned ON. With the current to Q3 ′, a voltage of Vcom or Vcom or less is directly supplied to the base of Q3, and the transistor Q3 is instantaneously turned off, and at the same time, the output capacitor and the feedback capacitor of Q4 can be charged. Therefore, the Q3 OFF speed can be further improved.
Examples of switches used for Q4 and Q3 ′ include semiconductor switching devices such as MOS-FETs and transistors.
_Further, in consideration of variations of _{V BE, which} may _V BE + R6 × Ie becomes higher than the least Vth value. At this time, the common potential of ▽ is a negative voltage instead of the emitter voltage of the switching device 1 in order to reduce the variation of the constant current.

  As described above, in the transition period such as turn-on and turn-off, the variation of the transition period due to the variation of the gate threshold voltage Vth and the mirror voltage can be minimized by driving the gate with a constant current. Variations in switching speed and switching loss can be greatly reduced. Furthermore, by switching to the constant voltage drive, there is an unprecedented remarkable effect that the device can be driven without impairing the reliability of the gate oxide film of the device.

In the above description, the constant current pulse gate drive circuit is used for both turn-on and turn-off. However, it can be used only for turn-on or only for turn-off as required. Hereinafter, a configuration example in which switching between constant current driving and constant voltage driving only in the ON transition will be described.
That is, there may be a problem when the ON state varies depending on use conditions, or the OFF state. For example, when the boost converter is operated in the discontinuous mode, since hard switching is performed at the time of OFF, variation at the time of OFF is suppressed and variation of switching loss is suppressed. At the time of ON, although the voltage is suddenly changed, the current is very slow compared with the switching speed because of charging the boosting inductance, so there is no problem even if there is no constant current drive circuit at the time of ON.

In addition, in the pulse generator by PFN, the variation at the ON time becomes a problem, and when it is OFF, even if the variation occurs, the loss / performance is not affected. Become.
As for the inverter drive, when the IGBT is subjected to lifetime control and Vcesat is reduced, the tail current flows even when the OFF constant current drive is performed, and the effect of the constant current drive may not be obtained. In such a case as well, an OFF constant current drive circuit is not necessary, and the loss varies due to variations in OFF, and therefore the ON constant current drive circuit can suppress variations and suppress variations in loss.
In particular, when devices are connected in series or in parallel, this variation is useful because variation is often important depending on whether it is ON or OFF.

FIG. 12 shows a gate drive device that switches between constant current drive and constant voltage drive when the turn is ON. The constant current pulse gate drive circuit 2 ′ uses an ON constant current pulse gate drive circuit 21 that is driven with a constant current only when ON. At the same time, the determination / switching circuit 4 ′ receives a control signal (gate control signal) and the gate voltage of the switching device 1, and controls an ON constant current control signal, an ON constant voltage control signal, and an OFF constant voltage control signal. Is output.
Here, as in the above description, the voltage VDD2 is set higher than VDD1, and the variation of the constant current set value due to the solid variation of components used in the constant current drive circuit is suppressed.

A specific example of the determination / switching circuit 4 ′ is shown in FIG. When receiving the control signal “H”, the determination / switching circuit 4 ′ deactivates the OFF signal and outputs the ON signal. At this time, the gate voltage of the IGBT 1 is observed. If the gate voltage is lower than VH (set a value equal to or higher than the mirror voltage maximum value), an ON constant current control signal is output, and if the gate voltage exceeds VH, the ON constant voltage is output. Switch to the control signal. When the control signal “L” is received, the ON signal is made inactive and a control signal with an OFF constant voltage is output.
Thereby, drive control of the constant current pulse gate drive circuit 2 ′ and the constant voltage pulse gate drive circuit 3 is performed.

  This configuration can be used when it is important to stabilize the switching speed at turn-on and to reduce the variation in switching loss at turn-on. With this configuration, by driving the gate with a constant current during the turn-on transition period, variations in the transition period due to variations in Vth and mirror voltage can be minimized, greatly increasing the variation in switching speed and switching loss. Can be reduced. Further, by switching to constant voltage driving, there is an unprecedented remarkable effect that the device can be driven without impairing the reliability of the gate oxide film of the device.

FIG. 14 shows a gate driving device that switches between constant current driving and constant voltage driving at the time of turn-off. The constant current pulse gate drive circuit 2 ″ uses an OFF constant current pulse gate drive circuit 22 that is driven with a constant current only when OFF. At the same time, the determination / switching circuit 4 ″ uses a control signal (gate control signal) and a switching device. 1 is input, and an OFF constant current control signal, an ON constant voltage control signal, and an OFF constant voltage control signal are output.
Here, as described above, the common potential indicated by the symbol ▽ used in the constant current pulse gate drive circuit 2 ″ may be a negative voltage in order to reduce variations in the constant current.

A specific example of the determination / switching circuit 4 ″ in this case is shown in FIG. 15. When the determination / switching circuit 4 ″ receives the control signal (gate control signal) “H”, the OFF signal is deactivated, and the ON constant voltage is set. Output a control signal. When the control signal “L” is received, the ON signal is made inactive and an OFF signal is output. At this time, the gate voltage of the IGBT 1 is observed, and if the gate voltage is equal to or higher than VL (a value equal to or lower than the Vth minimum voltage), an OFF constant current control signal is output, and if the gate voltage becomes lower than VL, the OFF constant voltage Switch to control signal.
Thereby, drive control of the constant current pulse gate drive circuit 2 ″ and the constant voltage pulse gate drive circuit 3 is performed.

  This configuration can be used when it is important to stabilize the switching speed at turn-off and to reduce the variation in switching loss at turn-off. With this configuration, by driving the gate with a constant current during the turn-off transition period, variation in the transition period due to variations in Vth and mirror voltage can be minimized, greatly increasing the variation in switching speed and switching loss. It is possible to achieve a remarkable effect that has not been achieved so far.

Embodiment 2. FIG.
In the first embodiment, when switching from constant current driving to constant voltage driving needs to be performed at high speed, the gate of VDD2> IGBT is caused by a delay in response of the determination / switching circuit 4 and the constant current pulse gate driving circuit 2. When the recommended voltage is used, an overvoltage is applied to the gate of the IGBT 1 and the reliability of the gate oxide film is lowered, and there is a possibility that the gate breakdown is caused in the worst case. Therefore, the voltage limiting circuit 5 shown in FIG. 16 is attached between the ON constant current pulse gate drive circuit 21 and the gate terminal of the IGBT 1.
The voltage limiting circuit 5 observes the gate signal at the output terminal, and turns off the high-speed shut-off element when the voltage exceeds a specified voltage. Note that the voltage limiting circuit 5 may be controlled so as to continue the cut-off state during the OFF operation period in conjunction with the control signal. FIG. 17 shows a circuit example.

In FIG. 17, Q5 used in the voltage limiting circuit 5 is configured using a high-speed and low Vth FET. By connecting the source terminal of Q5 to the gate terminal of IGBT1, the source voltage of Q5 does not become higher than the voltage applied to the gate of Q5. Accordingly, by setting the voltage V2 connected to the gate of Q5 to a voltage to be output-divided by R7 and R8 and to be output-protected, the Q1 is delayed due to the OFF delay of Q1 or the response delay of the determination / switching circuit 4. Even when the collector-side output voltage of the transistor rises more than expected, the gate of the IGBT 1 can be protected.
For example, when constant current driving is performed up to 13V (VH of the first determination circuit 41 is set to 13V), 1.5 (Vth of Q5) + 0.5V (equivalent to Id / gm) is added as the gate voltage of Q5. There is a design example such as 15V.
Note that the gate voltage of Q5 is strongly influenced by the gate voltage of IGBT1, which is the source terminal of Q5, so it is necessary to stabilize the gate voltage with C1 or the like. Further, when output protection is performed with VDD1, it is not necessary to divide the voltage with R7 and R8, but it is necessary to stabilize the gate voltage with C1 or the like.

As described above, by attaching the voltage limiting circuit 5, the OFF characteristic of Q1 can be relaxed, the response speed of the determination / switching circuit 4 can be relaxed, and further, the voltage of VDD2 of the ON constant current pulse gate drive circuit 21 can be reduced. The voltage can be set to suppress the variation in the _VEB voltage of Q1 and the variation in the constant current setting value due to the temperature characteristics, improving the stability of the constant current circuit and improving the gate of the device. There is an outstanding effect that the oxide film can be driven without impairing the reliability of the oxide film.

In FIG. 17, the ON constant current pulse gate drive circuit 21-1 is used as an example of the ON constant current pulse gate drive circuit, but other constant current pulse gate drive circuits may be used. Even if it is used for the constant voltage pulse gate driving circuit 3, the same effect can be obtained, and the gate of the IGBT 1 can be protected. Further, the present invention is not limited to the configuration shown in the circuit block of FIG.
For reference, FIG. 18 shows an example of the entire circuit configuration of the gate driving device that realizes the second embodiment.

Embodiment 3 FIG.
As described above, in the constant current pulse gate drive circuit 21 used in the first embodiment, for example, the variation in the V _EB of Q1 and the temperature characteristic can cause the constant current variation in the constant current pulse gate drive circuit 2.
In the third embodiment, the characteristic fluctuation of the semiconductor device itself such as Q1 constituting the constant current pulse gate drive circuit 21 is suppressed. Therefore, as shown in FIG. 19 and FIG. 20, a circuit in which Q1 and D1 (or Q1 ″) as a compensation semiconductor device are configured in the same IC chip under the same conditions.

Q1 and that manufactured under the same conditions on the same IC or on a chip D1 or Q1 ", becomes consistent with the variation characteristics of (V _F increases if V _EB increases) the variation direction of the V _EB, relative to individual difference variation In addition, correction can be made and temperature compensation can be achieved by matching the temperature conditions, and constant current characteristics can be improved with respect to temperature changes.

Embodiment 4 FIG.
In the fourth embodiment, by making it possible to switch the constant current output by the constant current pulse gate drive circuit 2 of the first embodiment, it is possible to obtain more excellent driving characteristics according to the driving conditions. Is.
When a motor or the like is driven in a switching device such as an IGBT, the amount of radiation noise and loss change due to switching depending on operating conditions. That is, increasing the switching speed increases the noise level, but decreases the turn-on loss and the turn-off loss. If the switching speed is slowed down to prevent electromagnetic noise, turn-on loss and turn-off loss increase. In other words, it can be said that noise and switching speed are in a trade-off relationship.

  However, it has been necessary to determine the switching speed under the driving conditions where noise is most likely to occur at a fixed switching speed as in the prior art. That is, under the most noisy operating conditions, the switching speed must be reduced (slowed) to a level where EMI (electromagnetic interference) does not become a problem, and as a result, the switching speed is limited more than necessary. Tended to increase losses more than necessary.

FIGS. 21 and 22 show the fourth embodiment. FIG. 21 shows a set of switches SW1 and R3 ′ in parallel with R3 for setting a constant current in the ON constant current pulse gate drive circuit 21-1. Are provided with a current switching unit 211 as a current switching circuit for switching and driving a constant current output value. For example, an FET or a transistor is used as SW1.
The same applies to the OFF side. FIG. 22 shows that the constant current output value is obtained by attaching at least one set of switches SW2 and R6 ′ in parallel with R6 for setting the constant current in the OFF constant current pulse gate drive circuit 22-1. The current switching unit 221 is provided as a current switching circuit for performing the switching drive.
FIG. 23 shows a drive timing chart when the current switching unit 211 and the current switching unit 221 are attached.

In the fourth embodiment, it is possible to dynamically control the trade-off relationship between noise and switching loss by varying the switching speed with a gate driving device that stabilizes the switching speed by constant current driving. As a result, the switching speed can be controlled in accordance with the operating conditions, and the switching speed is lowered and the generation of noise is suppressed in the operating region / condition where the amount of radiation noise due to the switching noise is large. Further, in an operation region / condition in which the amount of radiation noise due to switching noise is small, it is possible to perform control such as increasing the switching speed and reducing loss.
When the resistance is switched by applying the conventional constant voltage-resistance driving method, there is a possibility that the effect cannot be sufficiently exhibited due to the individual difference in switching speed. In the method, since the individual difference variation is eliminated, the effect of switching the switching speed based on the constant current switching can be sufficiently exhibited.

In addition, although the case of the motor load has been described above, it can be applied not only to the motor load but also to an inductance load, a capacitive load, and a resistance load by switching between an operation condition where the noise of the load is likely to occur and an operation condition where the noise is difficult to occur. Is possible.
In the fourth embodiment, the example in which both the current switching unit 211 and the current switching unit 221 are provided has been described. However, either of them can be provided.

Further, the configuration of FIG. 21 can also be used as a configuration that completely cuts off an unexpected current supply due to a delay in the current OFF operation by Q1. Hereinafter, this usage procedure will be described.
In this case, the constant current pulse gate drive circuit 2 sets the constant current at the time of gate drive by R3 ′, turns off SW1 at the timing of stopping the constant current output, and instantaneously switches R3 ′ that determines the constant current to R3. Then, the constant current driving circuit is operated so that the current due to the OFF delay does not affect the gate circuit.

Specifically, the “switch” signal is turned off simultaneously with the stop timing of the constant current to turn off SW1, and after the time considering the OFF delay of Q1, the original drive current is obtained from the state where the current is suppressed Therefore, after considering the OFF delay time, the “switch” signal is turned on to turn on SW1. Thereby, the OFF delay of Q1 can be improved.
At this time R3 >> R3 ′
R3 is much larger than the gate OFF resistance.
Although it is possible not to use R3, by giving a value to R3, the OFF state of Q1 is ensured, and a stable initial state is given to C _EB which is the feedback capacity of Q1. Thus, in the next timing to ON of the gate at a constant current prevents the C _EB of Q1 transient current characteristics are deteriorated by an unstable charge state, the high-speed constant current characteristic of the constant-current-pulse gate drive circuit 2 It becomes possible to stabilize.

Embodiment 5 FIG.
By the way, when an overcurrent flows through the switching device 1 in the turn-on operation, a configuration is adopted in which the gate is forcibly turned off by a high-speed protection circuit configured outside before the control circuit instructs an emergency stop. Sometimes. At this time, in the determination / switching circuit 4 or the like in each of the previous embodiments, the gate voltage is lowered due to the high-speed protection circuit or the like, but the constant current driving may be performed again. Depending on the circuit constants of the high-speed protection circuit and the circuit constants of the constant current pulse gate drive circuit, the gate voltage may rise again, which may hinder the function of the high-speed protection circuit.
In the fifth embodiment, the above problems are solved, and the first determination circuit 41 and the second determination circuit 42 used in the previous determination / switching circuit 4 or the like have so-called hysteresis characteristics. .

That is, in FIG. 24, the first setting value changing circuit 51 is provided in the first determination circuit 41. When the gate voltage exceeds the first set value (VH: set a value equal to or greater than the maximum mirror voltage variation) and the output of the comparator rises from “L” to “H”, Q51 is turned on and the first The set value is reduced by a predetermined amount.
In FIG. 25, the second determination circuit 42 is provided with a second set value change circuit 52. When the gate voltage becomes less than the second set value (VL: set value less than Vth minimum voltage) and the output of the comparator rises from “L” to “H”, Q52 is turned OFF and the second set value is set. Increases by a predetermined amount.

  As a result, in the gate voltage that can be switched from a constant current to a constant voltage, the above-mentioned problems at the time of switching the gate drive condition, abnormal constant current drive due to fluctuation of the gate voltage near the VH determination voltage, low voltage drive switching flutter, etc. Can be prevented.

Embodiment 6 FIG.
FIG. 26 shows a determination circuit 43 according to the sixth embodiment, and a set value change circuit 53 is provided. By setting the upper limit value of the hysteresis characteristic in the previous embodiment 5 to VH (a value equal to or greater than the maximum mirror voltage variation) and the lower limit value to VL (a value equal to or less than the Vth minimum voltage), one determination circuit In 43, VH determination and VL determination are output.
That is, in the turn-on operation, when the gate voltage exceeds VH, the output of the comparator rises from “L” to “H” and outputs a VH determination, and the constant current drive is switched to the constant voltage drive. At the same time, Q53 is turned ON and the set value is changed to VL. In the turn-off operation, when the gate voltage becomes less than VL, the output of the comparator falls from “H” to “L” and outputs a VL determination, and the constant current drive is switched to the constant voltage drive. At the same time, Q53 is turned OFF and the set value is changed to VH.

As a result, it is possible to limit the driving to one constant current per one pulse of the gate driving, and when the gate voltage drops due to the operation of the external gate limiting circuit in the arm short circuit or the overload protection operation, the constant current pulse is performed again. It is possible to prevent malfunction that current is supplied from the gate drive circuit.
Further, the comparison circuit (see FIG. 5), which required two circuits in the first embodiment, can be made into one circuit.

In the above example, the operation of the comparator is described as active H in the description of the circuit. However, as a matter of course, the same effect can be obtained by setting the output of the comparator as active L and correcting the logic circuit on the left. be able to.
As an example of designing with active L, for example, when a general-purpose analog comparator IC is used, most of the analog comparator ICs have an open collector type output terminal. Therefore, there is an example in which the transition of the output signal is faster in the active L than in the active H. In such a case, the operation delay is prevented by selecting and designing the active L operation.

  It should be noted that the present invention can be freely combined with each other within the scope of the invention, and each embodiment can be appropriately modified or omitted.

1 switching device, 2, 2 ', 2 "constant current pulse gate drive circuit,
3 constant voltage pulse gate drive circuit, 4, 4 ', 4 "judgment / switching circuit,
5 voltage limiting circuit, 21, 21-3 to 1 ON constant current pulse gate drive circuit,
22, 22-1 to 3 OFF constant current pulse gate drive circuit, 41 first determination circuit,
42 second determination circuit, 43 determination circuit, 51 first set value change circuit,
52 Second set value change circuit, 53 Set value change circuit, 211, 221 Current switching unit.

Claims (4)

A gate driving device connected to a gate of a voltage-driven switching device and outputting a gate signal to the gate for turning on / off the switching device based on an on / off gate control signal;
As the gate driving device for one or both of the turn-on operation and the turn-off operation,
Constant current pulse gate drive circuit for generating the gate signal with constant current output, constant voltage pulse gate drive circuit for generating the gate signal with constant voltage output, and operation of the constant current pulse gate drive circuit and the constant voltage pulse gate It has a judgment switching circuit that switches between the operation of the drive circuit,
The determination switching circuit includes a gate voltage detection circuit that detects the voltage of the gate, a first determination circuit that determines the magnitude of the gate voltage and a predetermined first set value, and the gate voltage and a predetermined second In the second determination circuit for determining the magnitude of the set value and the turn-on operation, first, the constant current pulse gate drive circuit is connected to the gate, and the gate voltage is changed by the first determination circuit. When it is determined that the set value of 1 is exceeded, the constant voltage pulse gate drive circuit is connected to the gate instead of the constant current pulse gate drive circuit. In the turn-off operation, first, the constant current pulse gate drive circuit is When the gate voltage is determined to be less than the second set value by the second determination circuit, the constant current pulse gate drive circuit is replaced. The constant-voltage-pulse gate drive circuit comprises a switching circuit connected to the gate,
In the turn-on operation, when the first determination circuit determines that the gate voltage exceeds the first set value, the first set value of the first determination circuit is changed to a set value reduced by a predetermined amount. And the second setting value of the second determination circuit when the gate voltage is determined to be less than the second setting value by the second determination circuit in the turn-off operation. A second set value changing circuit for changing the set value to a set value increased by a predetermined amount,
A gate driving device characterized in that the voltage of the control power source of the constant current pulse gate driving circuit is set higher than the voltage of the control power source of the constant voltage pulse gate driving power source. 2. The gate drive according to claim 1, further comprising a voltage limiting circuit that is inserted between the constant current pulse gate driving circuit and the gate of the switching device and limits the gate voltage to a predetermined voltage value or less. apparatus. A compensation semiconductor device connected to the semiconductor device is provided on the same chip as the semiconductor device constituting the constant current pulse gate drive circuit, and fluctuations caused by temperature changes in the constant current output of the constant current pulse gate drive circuit. The gate driving device according to claim 1, wherein the gate driving device is suppressed. 4. The gate drive device according to claim 1, wherein the constant current pulse gate drive circuit includes a current switching circuit that switches a value of the constant current output. 5.

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