JP2014042394A - Device for driving switching element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive device that can prevent a switching element from malfunctioning even if the slew rate of a main power supply changes.SOLUTION: The drive device includes a first driving power circuit 33 for generating on the basis of a main power supply a constant voltage having a slower slew rate than the main power supply, and supplying it as a first driving power supply, and a second driving power circuit 35 for supplying a second driving power supply depending on the voltage of the main power supply, and supplies the first and/or second driving power supply to a pre-driver 6 for driving an N channel MOSFET 3. For a period where an output state of the pre-driver 6 is unstable, a pull-down resistive element 38 fixes an output potential at a low level. When the main power supply is input, a second driving power supply control circuit 49 disables the second driving power circuit 35 from supplying the second driving power supply until the voltage of the driving power supply exceeds a first threshold, and again when the voltage of the main power supply exceeds a second threshold.

Description

  The present invention relates to an apparatus for driving a switching element to supply an energization current from a power supply apparatus to a load apparatus.

  FIG. 12 shows an example of a configuration in which a series regulator and an LDO (Low Drop Out) circuit are used together as a driving power source in a control circuit that controls switching of an N-channel MOSFET as an output switching element. The gate of an N-channel MOSFET 3 is connected to the control terminal 2 of the drive control IC 1. The N-channel MOSFET 3 is connected in series with a coil 4 (load device) between a power source VB, which is a battery (power supply device), and the ground, for example, and a common connection point (drain) of both is connected to the anode of the diode 5. Has been. The N-channel MOSFET 3 is switching-controlled by a pre-driver 6 built in the drive control IC 1.

  The pre-driver 6 includes a P-channel MOSFET 6P and an N-channel MOSFET 6N that are connected in series, and a common connection point (drain) of both is connected to the control terminal 2. The source of the P-channel MOSFET 6P is connected to the pre-driver power supply terminal 7 of the drive control IC1. A bypass capacitor 8 is externally attached to the pre-driver power supply terminal 7.

  The predriver power is supplied by a drive power supply circuit 10 and an LDO circuit 11 connected between the power supply terminal 9 and the predriver power supply terminal 7 of the drive control IC 1. The drive power supply circuit 10 includes a series circuit of a resistance element 12 and a Zener diode 13 connected between the power supply terminal 9 and the ground, and a gate connected to a common connection point between them, a drain connected to the power supply terminal 9, and a source connected to the power supply terminal 9. The N-channel MOSFET 14 is connected to the pre-driver power supply terminal 7. For example, a power supply VB is supplied to the power supply terminal 9 as a main power supply.

  The LDO circuit 11 includes a P-channel MOSFET 15 having a source connected to the power supply terminal 9 and a drain connected to the pre-driver power supply terminal 7. The output terminal of the comparator 17 is connected to the gate of the P-channel MOSFET 15 through the buffer circuit 16 and the level shift circuit 25. A series circuit of resistance elements 18 and 19 is connected between the power supply terminal 9 and the ground, and their common connection point is connected to the non-inverting input terminal of the comparator 17. A bandgap reference circuit (BG) 20 is connected to the power supply terminal 9 and supplies the generated reference voltage to the inverting input terminal of the comparator 17.

  A PWM signal is given to the gates of the P-channel MOSFET 6P and the N-channel MOSFET 6N constituting the pre-driver 6 via the buffer circuit 21, and the gate potential of the N-channel MOSFET 3 is preliminarily turned on by either one being turned on. Switching control is performed at either the driver power supply level or ground level. Although not specifically illustrated, the PWM signal is generated by detecting the potential on the cathode side of the diode 5 and comparing it with a carrier wave level such as a triangular wave by a comparator. That is, feedback control is performed by switching the N-channel MOSFET 3 so that the cathode side potential becomes a predetermined potential. The drive control IC 1 configured as described above and each externally attached element constitute a switching power supply circuit 22.

  In the drive control IC 1, if the power supply voltage of the power supply terminal 9 is within the normal range, the pre-driver power supply voltage is changed from the gate potential (zener voltage) of the N-channel MOSFET 14 constituting the drive power supply circuit 10 to the gate-source voltage Vgs. Will be reduced. At this time, since the potential of the inverting input terminal in the comparator 17 is higher than the reference voltage, the gate of the P-channel MOSFET 15 is at a high level, and the LDO circuit 11 stops operating.

  When the power supply voltage at the power supply terminal 9 decreases and the potential at the inverting input terminal of the comparator 17 falls below the reference voltage, the P-channel MOSFET 15 is used to avoid the influence of the voltage drop due to the gate-source voltage Vgs. The power is turned on and pre-driver power is supplied via the LDO circuit 11. As a prior art related to the above configuration, there is, for example, Patent Document 1.

JP 2005-130622 A

  Here, there is no particular problem when the slew rate of the main power supplied to the power supply terminal 9 is slow as shown in FIG. Although a bypass capacitor 8 of about several μF is connected to the pre-driver power supply terminal 7, the current capability by the N-channel MOSFET 14 of the drive power supply circuit 10 and the P-channel MOSFET 15 of the drive power supply circuit 11 is high. Therefore, even when the slew rate of the main power supply is fast as shown in FIG. 13A, the pre-driver power supply voltage changes substantially following the slew rate of the main power supply. Then, a high-level signal may be output to the gate of the N-channel MOSFET 3 for a moment due to the coupling through the parasitic capacitance 23 between the pre-driver power supply terminal 7 and the output terminal of the pre-driver 6, and this phenomenon may malfunction. May lead to

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a driving device for a switching element that can prevent a malfunction of the switching element even when the slew rate of the main power supply changes. .

  According to the switching element drive device of the first aspect, the first drive power supply circuit that generates a constant voltage having a slew rate slower than the main power supply based on the main power supply and supplies the constant voltage as the first drive power supply, and the main power supply And a second drive power supply circuit for supplying a second drive power supply according to the voltage of the first and second drive power supplies to the drive circuit for driving the switching element. Further, the potential determining means determines the output potential during a period when the output state of the drive circuit becomes unstable because the main power supply voltage is low. Then, when the main power supply is turned on, the second drive power supply control means invalidates the supply of the second drive power supply by the second drive power supply circuit until the voltage of the drive power supply exceeds the first threshold, and the main power supply When the voltage exceeds the second threshold, it is invalidated again. In this case, the first threshold value is set to a voltage level at which the drive circuit can output stably.

  With this configuration, when the main power supply is turned on, the second drive power supply circuit operates between the time when the voltage exceeds the first threshold value and the time when the second power supply voltage exceeds the second threshold value. The second drive power is supplied. On the other hand, the first drive power supply circuit operates immediately after the main power supply is turned on, but since the slew rate of the first drive power supply is slower than that of the main power supply, the occurrence of malfunction immediately after the turn-on is suppressed.

The figure which is a 1st Example and shows the structure of a switching power supply circuit Timing chart showing changes in each voltage when the main power is turned on The figure which shows the change of the main power supply voltage, and the change of the operation state of the 1st, 2nd drive power supply circuit FIG. 1 equivalent view showing the second embodiment FIG. 1 equivalent view showing the third embodiment FIG. 1 equivalent view showing the fourth embodiment FIG. 1 equivalent view showing the fifth embodiment FIG. 1 equivalent view showing the sixth embodiment FIG. 1 equivalent view showing the seventh embodiment 2 equivalent diagram FIG. 1 equivalent view showing the eighth embodiment 1 equivalent diagram showing the prior art (A) is a timing chart showing changes in each voltage when the slew rate of the main power supply is fast, and (b) when the slew rate of the main power supply is slow.

(First embodiment)
Hereinafter, the same parts as those in FIG. 12 are denoted by the same reference numerals, description thereof will be omitted, and different parts will be described. In FIG. 1, a step-up switching power supply circuit 31 is obtained by replacing the drive control IC 1 shown in FIG. 11 with a drive control IC 32 (drive device). The first drive power supply circuit 33 is configured by inserting an operational amplifier 34 between the common connection point of the resistor element 12 and the Zener diode 13 and the gate of the N-channel MOSFET 14 in the drive power supply circuit 10. The common connection point is connected to the non-inverting input terminal of the operational amplifier 34, and the inverting input terminal of the operational amplifier 34 is connected to the pre-driver power supply terminal 7. The second drive power supply circuit 35 (LDO circuit) replaces the amplifier 16 with a buffer circuit 36 with an enable terminal (control terminal), and a signal input to the buffer circuit 36 is level-shifted via a level shift circuit 37. The

  The output terminal of the pre-driver 6 (drive circuit) is pulled down by a resistance element 38 (potential determining means). An output terminal of a buffer circuit 39 with an enable terminal instead of the buffer circuit 21 is connected to the gates of the P-channel MOSFET 6P and the N-channel MOSFET 6N.

  Between the power supply terminal 9 and the ground, a series circuit of resistance elements 40 and 41 and a series circuit of resistance elements 42 and 43 are connected. The common connection point of the resistance elements 40 and 41 is connected to the non-inverting input terminal of the comparator 44, and the common connection point of the resistance elements 42 and 43 is connected to the non-inverting input terminal of the comparator 45. The output terminal of the comparator 44 is connected to the enable terminal of the buffer circuit 39, and the output terminal of the comparator 45 is connected to the input terminal of the level shift circuit 37.

  Further, a series circuit of resistance elements 46 and 47 is connected between the pre-driver power supply terminal 7 and the ground, and the common connection point of both is connected to the non-inverting input terminal of the comparator 48 (signal output means). Has been. The output terminal of the comparator 48 is connected to the input terminal of the level shift circuit 37.

  Note that the reference voltage from the bandgap reference circuit 20 is applied to the inverting input terminals of the comparators 44, 45, and 48. These are substantially (relative) by changing the voltage dividing ratio by the resistors. ) Are different reference voltages. Here, the reference voltage given to the comparator 44 is a voltage UVLO for causing the pre-driver 6 to output a PWM signal via the buffer circuit 39 (the UVLO shown in FIG. 13 is not shown in FIG. 12). The buffer circuit 21 is controlled in the same manner as the buffer circuit 39 with respect to UVLO).

The reference voltage supplied to the comparator 48 is a first threshold voltage for stopping the operation of the second drive power supply circuit 35 immediately after the main power supply is turned on. The reference voltage supplied to the comparator 45 is a second threshold voltage for stopping the operation of the second drive power supply circuit 35 again when the main power supply voltage rises to some extent. The magnitude relationship between these voltages is as follows.
First threshold voltage <voltage UVLO <second threshold voltage The comparators 45 and 48 constitute a second drive power supply control circuit 49 (second drive power supply control means).

  Next, the operation of this embodiment will be described with reference to FIGS. As shown in these drawings, the first drive power supply circuit 33 continues to operate immediately after the main power supply is turned on. On the other hand, the operation of the second drive power supply circuit 35 is controlled by the second drive power supply control circuit 49 until the predriver power supply voltage exceeds the second threshold voltage after the main power supply voltage exceeds the first threshold voltage. It works only for a while.

  As shown in FIG. 2, when the main power supply is turned on, only the first drive power supply circuit 33 initially operates. In the first drive power supply circuit 33, the amplifier 34 controls the gate potential of the N-channel MOSFET 14 according to the potential difference between the main power supply voltage applied to the non-inverting input terminal and the pre-driver power supply voltage. The output form of the first drive power supply circuit 33 is a source follower. Therefore, when a response delay using the phase delay property of the amplifier 34 is generated, the slew rate of the first drive power supply voltage generated by the first drive power supply circuit 33 is slower than the slew rate of the main power supply. By the operation of the first drive power supply circuit 33, for example, even when the voltage of the main power supply is high and the rise of the voltage becomes relatively steep, the occurrence of malfunction due to the coupling by the parasitic capacitance 23 is suppressed. .

  Immediately after the main power supply is turned on, the first drive power supply voltage does not become a constant voltage but a voltage that fluctuates at a low level, so that the voltage that the pre-driver 6 tries to output is indefinite. However, since the output terminal is pulled down by the resistance element 38, the low level is determined during this period, and the N-channel MOSFET 3 is not turned on carelessly.

  When the main power supply voltage exceeds the first threshold voltage, the buffer circuit 36 sets the gate of the P-channel MOSFET 15 to the low level, so that the second drive power supply circuit 35 starts operation. During this period, the second drive power supply voltage having a smaller voltage drop than the first drive power supply is output via the P-channel MOSFET 15 (LDO output). When the main power supply voltage exceeds the voltage UVLO while the second drive power supply circuit 35 is operating, a PWM signal is output via the pre-driver 6 and the N-channel MOSFET 3 (switching element) starts a switching operation. .

  Thereafter, when the main power supply voltage further rises and exceeds the second threshold voltage, the buffer circuit 36 becomes H output (off control) by the output signal of the comparator 45, and the second drive power supply circuit 35 stops its operation. Thereafter, the first drive power supply having a constant voltage is output from the first drive power supply circuit 33. Here, by setting the second threshold voltage to be lower than the rated value of the gate voltage of the N-channel MOSFET 3, the second drive power supply voltage that rises as the main power supply voltage rises is applied to the gate of the N-channel MOSFET 3. Application is prevented.

  As described above, according to the present embodiment, the first drive power supply circuit 33 that generates a constant voltage having a slew rate slower than that of the main power supply based on the main power supply and supplies it as the first drive power supply, and the voltage of the main power supply And a second drive power supply circuit 35 that supplies a second drive power supply corresponding to the first drive power supply, and supplies the first and / or second drive power supply to the pre-driver 6 that drives the N-channel MOSFET 3. Further, the pull-down resistor element 38 determines the output potential at a low level during a period in which the output state of the pre-driver 6 becomes unstable because the main power supply voltage is low. Then, when the main power is turned on, the second drive power supply control circuit 49 disables the supply of the second drive power by the second drive power supply circuit 35 until the voltage of the pre-driver power supply exceeds the first threshold, and When the voltage of the main power source exceeds the second threshold, it is invalidated again.

  With this configuration, the slew rate of the first drive power supply supplied by the first drive power supply circuit 33 is slower than that of the main power supply, so that the occurrence of malfunction immediately after being turned on is suppressed. The second drive power supply control circuit 49 compares the main power supply voltage with the second threshold value and stops the operation of the second drive power supply circuit 35. Therefore, when the main power supply voltage rises to some extent, It is possible to prevent an overvoltage from being applied to the gate.

  Further, the first drive power supply circuit 33 is connected to the N-channel MOSFET 14 connected between the main power supply and the pre-driver power supply terminal 7, and the N-channel MOSFET 14 so that the pre-driver power supply voltage is equal to the given reference voltage. An amplifier 34 for driving the gate is used. Therefore, the slew rate of the first drive power supply voltage can be made slower than that of the main power supply by the feedback control by the amplifier 34 and the source follower operation by the N-channel MOSFET 14.

  The second drive power supply circuit 35 includes a P-channel MOSFET 15 connected between the main power supply and the pre-driver power supply terminal 7 and a buffer circuit 36 whose output terminal is connected to the gate of the P-channel MOSFET 15. The buffer circuit 36 outputs a high level signal when a disable signal is input to the control terminal, and the second drive power supply control circuit 39 outputs a signal that becomes a low level when the voltage of the pre-driver power supply exceeds the first threshold value. The comparator 48 outputs to the buffer circuit, and the comparator 45 outputs a disable signal to the control terminal of the buffer circuit 36 when the main power supply voltage exceeds the second threshold.

  Therefore, when the main power supply voltage exceeds the first threshold value and the second drive power supply circuit 35 operates, the voltage drop of the second drive power supply with respect to the main power supply voltage is only the ON voltage of the P-channel MOSFET 15. When the main power supply voltage exceeds the second threshold, the comparator 45 outputs a high level signal via the buffer circuit 36, so that the operation of the second drive power supply circuit 35 can be stopped.

(Second embodiment)
A switching power supply circuit 51 shown in FIG. 4 includes a drive control IC 52 instead of the drive control IC 32 of the first embodiment. The second drive power supply circuit 53 is obtained by replacing the buffer circuit 36 of the second drive power supply circuit 35 with the buffer circuit 16, and replacing the level shift circuit 37 with the level shift circuit 37a. In this case, the output signal of the comparator 45 is given to the input terminal of the buffer circuit 16 via the level shift circuit 37 a, and the comparator 45 also constitutes a part of the second drive power supply circuit 53.

  Further, a constant current circuit 54 (potential determination means, second drive power supply control means) is connected between the output terminal of the pre-driver 6 and the ground instead of the resistance element 38. The constant current circuit 54 is controlled by the output signal of the comparator 48. In FIG. 4, the illustration of the comparator 44 for enabling the buffer circuit 39 is omitted (the same applies to the following embodiments).

  Next, the operation of the second embodiment will be described. From immediately after the main power supply is turned on until the main power supply voltage exceeds the first threshold voltage, the output signal of the comparator 48 (potential determining means) shows a low level. During this period, the constant current circuit 54 is operated to set the output terminal of the pre-driver 6 to the low level. Therefore, even if the second drive power supply circuit 53 starts steeply during the above period and malfunctions via the parasitic capacitance 23, the output terminal of the pre-driver 6 is low level if the constant current circuit 54 is operating. As a result, the malfunction caused by the second drive power supply circuit 53 is invalidated. When the main power supply voltage exceeds the first threshold voltage, the output signal of the comparator 45 turns to high level, and the constant current circuit 54 stops its operation. The subsequent operation is the same as in the first embodiment.

  As described above, according to the second embodiment, until the main power supply voltage exceeds the first threshold voltage, the constant current circuit 54 is operated to determine the output terminal of the pre-driver 6 at a low level. Therefore, the operation of the constant current circuit 54 can slow down the slew rate of the pre-driver power supply voltage and prevent malfunctions. When the main power supply voltage exceeds the second threshold voltage, the comparator 45 sets the gate of the P-channel MOSFET 15 to the high level, so that the subsequent operation of the second drive power supply circuit 53 can be stopped.

(Third embodiment)
The drive control IC 62 of the switching power supply circuit 61 shown in FIG. 5 deletes the amplifier 34 of the first drive power supply circuit 33 and connects the gate of the N-channel MOSFET 14 to the cathode terminal of the Zener diode 13 (constant voltage generating means). Yes. A capacitor 63 is connected to the Zener diode 13 in parallel. Thus, the first drive power supply circuit 64 is configured. In the second embodiment, a component for controlling the operation of the constant current circuit 54 by the output signal of the comparator 48 is added.

  Next, the operation of the third embodiment will be described. The operation of fixing the output terminal of the pre-driver 6 to the low level by the constant current circuit 54 from immediately after the main power is turned on until the first threshold voltage is exceeded is performed as in the second embodiment. As for the first drive power supply circuit 64, the capacitor 63 is charged through the resistance element 12 when the main power supply is turned on. Therefore, the speed at which the gate potential of the N-channel MOSFET 14 increases is higher than the main power supply voltage. Become slow. The first driving power supply voltage at the time when charging of the capacitor 63 is completed is obtained by subtracting the gate-source voltage Vgs of the N-channel MOSFET 14 from the Zener voltage Vz of the Zener diode 13. Accordingly, malfunctions can be prevented as in the first and second embodiments.

(Fourth embodiment)
The drive control IC 66 of the switching power supply circuit 65 shown in FIG. 6 replaces the component that controls the operation of the constant current circuit 54 with the output signal of the comparator 45 in the third embodiment into a series circuit of the pull-down resistor element 38 and the PNP transistor 67. It is a replacement. Then, on / off control of the PNP transistor 67 is performed by the output signal of the comparator 48. Even when configured in this manner, the same effect as in the third embodiment can be obtained.

(5th Example)
The drive control IC 72 of the switching power supply circuit 71 shown in FIG. 7 includes a series circuit (signal output means) of a Zener diode 73 and a resistance element 74 as signal output means in place of the comparator 48 of the first embodiment. The common connection point between them is connected to the enable control terminal of the buffer circuit 36 via the level shift circuit 37. These constitute the second drive power supply control circuit 75.

  Next, the operation of the fifth embodiment will be described. The first drive power supply circuit 35 is controlled by the comparator 45 in the same manner as in the first embodiment until immediately after the main power supply is turned on until the predriver power supply voltage exceeds the first threshold voltage. When the pre-driver power supply voltage exceeds the forward voltage (first threshold voltage) of the diode 73, the diode 73 becomes conductive and the cathode potential becomes high level. As a result, the buffer circuit 36 is disabled and the P-channel MOSFET 15 is turned off. In the case of the fifth embodiment configured as described above, the same effect as that of the first embodiment can be obtained.

(Sixth embodiment)
The drive control IC 82 of the switching power supply circuit 81 shown in FIG. 8 is obtained by replacing the resistance element 12 in the first drive power supply circuit 33 of the first embodiment with a constant current circuit 83. Thereby, the first drive power supply circuit 85 is configured. Even in such a configuration, the Zener voltage of the Zener diode 13 can be applied to the non-inverting input terminal of the comparator 34 as a reference voltage.

(Seventh embodiment)
The switching power supply circuit 91 shown in FIG. 9 is configured as a step-down type. That is, a series circuit of a P-channel MOSFET 92 (switching element) and a diode 5 is connected between the power supply VB and the ground, and one end of the coil 4 is connected to a common connection point between them (the cathode of the diode 5). ing. The drive control IC 93 also has a configuration corresponding to the P-channel MOSFET 92. In the following description, the same reference numerals are used for the components corresponding to the configuration shown in FIG.

  In the drive control IC 93, the pre-driver 6 and the second drive power control circuit 49 arranged between the pre-driver power terminal 7 and the ground in FIG. 1 are connected to the main power terminal 9 (supplied with the power supply VB). It is arranged between the pre-driver power supply terminal 7. The resistance element 38 is also connected between the main power supply terminal 9 and the pre-driver power supply terminal 7 and functions as a pull-up resistor. The bypass capacitor 8 is also connected between the power supply VB and the pre-driver power supply terminal 7.

  The first drive power supply circuit 94 and the second drive power supply circuit 95 are disposed between the pre-driver power supply terminal 7 and the ground. The first drive power supply circuit 94 is configured using a P-channel MOSFET 96 instead of the N-channel MOSFET 14, and the second drive power supply circuit 95 is configured using an N-channel MOSFET 97 instead of the P-channel MOSFET 15. The first drive power supply circuit 94 uses a series circuit in which the upper and lower sides of the resistance element 12 and the Zener diode 13 are switched.

  Next, the operation of the seventh embodiment will be described with reference to FIG. The operation patterns of the first drive power supply circuit 94 and the second drive power supply circuit 95 according to changes in the main power supply voltage are the same as those in FIG. 3 of the first embodiment. Accordingly, the potential of the pre-driver power supply terminal 7 (source potential of the N-channel MOSFET 6N) rises at a slower slew rate than the main power supply by the first drive power supply circuit 94 until the main power supply voltage reaches the first threshold voltage. When the main power supply voltage exceeds the first threshold voltage, the second drive power supply circuit 95 operates and the potential of the pre-driver power supply terminal 7 becomes the ground level. Thereby, the drive voltage applied to the pre-driver circuit 6 changes so as to increase as the main power supply voltage increases.

  When the main power supply voltage further rises and exceeds the second threshold voltage, the second drive power supply circuit 95 stops operating, and constant voltage control by the first drive power supply circuit 94 is performed. That is, since the potential of the non-inverting input terminal of the amplifier 34 is a potential obtained by subtracting the Zener voltage from the main power supply voltage, the potential increases as the main power supply voltage increases. The amplifier 34 controls the gate potential of the P-channel MOSFET 96 according to the potential difference between the potential of the inverting input terminal and the non-inverting input terminal. As a result, the drive voltage applied to the pre-driver circuit 6 is controlled so that the difference voltage from the voltage becomes constant even when the main power supply voltage rises.

As described above, according to the seventh embodiment, the present invention can also be applied to the step-down switching power supply circuit 91.
(Eighth embodiment)
The switching power supply circuit 81A of the eighth embodiment shown in FIG. 11 is obtained by replacing the Zener diode 13 of the drive control IC 82 of the sixth embodiment with the resistance element 12 to provide a drive control IC 82A. Other configurations are the same as those of the sixth embodiment. Even in this configuration, the reference voltage to be applied to the non-inverting input terminal of the comparator 34 can be determined by the constant current value of the constant current circuit 83 and the resistance value of the resistance element 12.

The present invention is not limited to the above-described embodiments, and the following modifications or expansions are possible.
The switching element is not limited to a MOSFET but may be a bipolar transistor or an IGBT.
As for the potential determination means, for example, the embodiment using the resistance element 38 may be replaced with the constant current circuit 54 or the like, or may be replaced with a reverse pattern.
As a configuration for applying a constant voltage in the first drive power supply circuit, a band gap reference circuit may be used.
The configuration of the second to sixth embodiments may be applied to the seventh embodiment.
The main power source may be of any type as long as the slew rate when it is turned on may vary depending on the state.

  In the drawing, 3 is an N-channel MOSFET (switching element), 6 is a pre-driver (drive circuit), 31 is a switching power supply circuit, 32 is a drive control IC (drive device), 33 is a first drive power supply circuit, and 35 is a second drive power supply circuit. A drive power supply circuit, 38 is a resistance element (potential determination means), 48 is a comparator (signal output means), and 49 is a second drive power supply control circuit (second drive power supply control means).

Claims (6)

A device for driving the switching element (3, 92) to supply an energization current from the power supply device (VB) to the load device (4),
A first drive power supply circuit (33, 64, 85, 85A, 94) that generates a constant voltage having a slower slew rate than the main power supply and supplies the first drive power supply based on the main power supply;
A second drive power supply circuit (35, 53, 95) for supplying a second drive power supply according to the voltage of the main power supply;
A drive circuit (6) that is supplied with the drive power and drives the switching element;
A potential determination means (38, 45, 54) that operates to determine the output potential during a period when the output state of the drive circuit is unstable;
When the main power is turned on, the supply of the second drive power by the second drive power supply circuit is disabled until the voltage of the drive power exceeds a first threshold, and the voltage of the main power is A second drive power supply control means (49, 54, 75) for disabling again when a second threshold set higher than one threshold is exceeded,
The switching element driving device, wherein the first threshold is set to a voltage level at which the driving circuit can stably output. The first drive power supply circuit includes an N-channel MOSFET (14) connected between the main power supply and a drive power supply line;
An amplifier (34) for driving the gate of the N-channel MOSFET so that the voltage of the drive power supply is equal to a given reference voltage;
The second drive power supply circuit includes a P-channel MOSFET (15) connected between the main power supply and the drive power supply line;
A buffer circuit (36) having an output terminal connected to the gate of the P-channel MOSFET,
The buffer circuit is configured to output a high level signal when a disable signal is input to the control terminal,
The second drive power control means includes a comparator (48) that outputs an enable signal to the buffer circuit when the voltage of the drive power exceeds the first threshold value;
2. The signal output means (45, 75) for outputting a high level signal to a control terminal of the buffer circuit when the voltage of the main power source exceeds the second threshold value. Switching device drive device.   3. The switching element driving device according to claim 2, wherein the signal output means includes a comparator (45) having an output terminal connected to a control terminal of the buffer circuit. The signal output means (75) includes a series circuit of a diode (73) and a resistance element (74) connected between the drive power supply line and the ground.
The forward voltage of the diode is set equal to the first threshold;
3. The switching element driving device according to claim 2, wherein a common connection point of the series circuit is connected to a control terminal of the buffer circuit. The first drive power supply circuit includes an N-channel MOSFET (14) connected between the main power supply and a drive power supply line;
An amplifier (34) for driving the gate of the N-channel MOSFET so that the voltage of the drive power supply is equal to a given reference voltage;
The second drive power supply circuit includes a P-channel MOSFET (15) connected between the main power supply and the drive power supply line;
When the voltage of the main power supply exceeds the second threshold, the comparator (45) is configured to output a high level signal to the gate of the P-channel MOSFET,
The second drive power control means includes a current source (54) connected between the output terminal of the drive circuit and the ground;
The switching element drive according to claim 1, further comprising a comparator (48) that outputs a control signal to operate the current source until a voltage of the drive power source exceeds the first threshold value. apparatus. The first drive power supply circuit includes an N-channel MOSFET (14) connected between the main power supply and a drive power supply line;
The resistor is connected between the main power source and the ground, and a common connection point between them is connected to the gate of the N-channel MOSFET and a series circuit of constant voltage generating means (13).
The second drive power supply circuit includes a P-channel MOSFET (15) connected between the main power supply and the drive power supply line;
When the voltage of the main power source exceeds the second threshold, the comparator (45) outputs a high level signal to the gate of the P-channel MOSFET.
2. The switching according to claim 1, wherein the second drive power supply control means is constituted by a capacitor (63) connected in parallel to a constant voltage generation means (13) constituting the first drive power supply circuit. Device drive device.

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