JP2718166B2 - Drive circuit for switching element for upper arm - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to the above-described upper-arm switching element and drive circuit in a bridge including at least upper-arm and lower-arm switching elements. In order to simplify the configuration of the reverse bias application circuit to prevent false firing of the above and to realize the miniaturization of the entire drive circuit, a capacitor connected between the control voltage application electrodes of the upper arm switching element is used. When the lower arm switching element is off, the capacitor is charged negatively, and when the lower arm switching element is turned on, the capacitor is discharged to apply a reverse bias to the upper arm switching element. It has a reverse bias application circuit.

[Industrial applications]

The present invention relates to a drive circuit for a switching element for an upper arm thereof in various bridge circuits such as an H bridge for driving a DC motor and a bridge for an inverter used in the field of power electronics and the like. The reverse bias application circuit required to prevent erroneous firing of the switching element.

[Conventional technology]

 FIG. 4 shows an example of a conventional DC motor drive circuit.

In the figure, four transistors 1, 2, 3, 4,.
And 4 connected between its collector and emitter
The diodes 5, 6, 7, 8 are bridge-connected to the DC motor M in an H-shape. A main power supply 9 is connected between the collectors of the upper-arm transistors 1 and 2 and the emitters of the lower-arm transistors 3 and 4 therein, and the emitters of the lower-arm transistors 3 and 4 are connected to the entire circuit. Ground (GND).

The upper arm transistor 1 is turned on by applying a forward bias to the upper arm transistor 1.
And a transistor 11 for applying a reverse bias to prevent erroneous ignition due to turning off of the lower arm transistor 3.
And a photocoupler 12 for switching these transistors 10 and 11. Furthermore, a power supply circuit 13 that is insulated from the main power supply 9 and supplies a positive power supply for applying the forward bias through the transistor 10.
And a negative power supply circuit 14 for supplying a negative power supply for applying the reverse bias through the transistor 11. Various systems such as a forward system and a flyback system can be used as the negative power supply circuit 14, but the flyback system is shown here. The other upper-arm transistor 2 is also provided with a drive circuit having the same configuration as the drive circuit 15 including the above-described bias application circuit and power supply circuit, but is omitted here.

On the other hand, for the lower-arm transistor 3, a lower-arm drive circuit 16 having substantially the same configuration as the above-described upper-arm drive circuit 15 except that the photocoupler 12 and the power supply circuits 13 and 14 are removed. Is provided. A driving circuit similar to this is provided for the other lower-arm transistor 4, but is omitted here.

In the above configuration, in order to rotate the motor M in both the forward and reverse directions, a predetermined drive signal is supplied from the controller 17 to each of the drive circuits 15 and 16 so that the four transistors 1, 2, 3, and 4 are connected to the motor M. On and off in a lotus shape. That is, when one of the upper-arm transistors 1 and 2 is turned on and the other is turned off, the on-state transistor is chopped by one of the lower-arm transistors 3 and 4 that are obliquely positioned across the motor M. By doing so, the motor M is rotated.

Further, for example, the upper arm transistor 2 is always turned on, and the lower arm transistor
When the motor M is rotated by chopping, a large voltage change dv / dt is applied to the upper arm transistor 1 when the lower arm transistor 3 is turned on.
The upper arm transistor 1, which should always be in the off state, is likely to be erroneously fired. Therefore, when the transistor 1 for the upper arm is always in the off state, the transistor 11 is turned on instead of the transistor 10 to apply a reverse bias between the base and the emitter of the transistor 1 for the upper arm. To prevent false firing.

[Problems to be solved by the invention]

In the bridge circuit as described above, it is necessary to apply a reverse bias to the upper arm transistor as described above as a countermeasure against erroneous firing of the upper arm transistor. Conventionally, a means for applying a reverse bias including the transistor 11 and a negative power supply circuit 14 insulated from the main power supply 9 as shown in FIG. However, since these circuits are extremely large, there has been a problem that the entire driving circuit is enlarged accordingly.

Such a problem has arisen not only in the above-described H-bridge for driving a DC motor, but also in various bridge circuits including a switching element for an upper arm which needs to apply a reverse bias to prevent false firing.

In view of the above-mentioned conventional problems, the present invention can simplify the configuration of a reverse bias application circuit for preventing erroneous firing of the switching element for the upper arm, and can realize a reduction in the size of the entire driving circuit. It is an object of the present invention to provide a drive circuit for an arm switching element.

[Means for solving the problem]

The drive circuit of the present invention includes a reverse bias application circuit including a capacitor connected between electrodes for applying a control voltage of the upper arm switching element (for example, between a base and an emitter in the case of a bipolar transistor). In this reverse bias application circuit, when both the upper-arm switching element and the lower-arm switching element are off, the voltage applied between the main electrodes of the lower-arm switching element (for example, between the collector and the emitter in a bipolar transistor). Thereby, the capacitor connected to the upper arm switching element is negatively charged, while the lower arm switching element is turned on while the upper arm switching element is turned off, The charged capacitor is discharged to apply a reverse bias between the control voltage application electrodes of the upper arm switching element.

[Action]

In the reverse bias application circuit according to the present invention, a reverse bias can be applied by using charging and discharging of the capacitor as described above. With this reverse bias application circuit,
When the lower-arm switching element is turned on, a reverse bias is reliably applied to the upper-arm switching element, so that there is no danger of erroneous firing.

According to the present invention, it is possible to apply a reverse bias only with the above-described capacitor and simple components for charging and discharging the capacitor, so that the driving circuit can be significantly reduced in size.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a DC motor drive circuit to which one embodiment of the present invention is applied.

In this figure, similarly to the conventional circuit shown in FIG. 4, four transistors 1, 2, 3, 4 and four diodes 5, 6, 7, connected between their collectors and emitters, respectively. 8 is bridge-connected to the DC motor M. And the upper arm transistor 1,
The main power supply 9 is connected between the collector of the lower arm transistor 2 and the emitters of the lower arm transistors 3 and 4, and the emitter side of the lower arm transistors 3 and 4 is the ground (GND) of the entire circuit.

Further, in order to drive the upper arm transistor 1,
An upper arm drive circuit 21 is provided. This drive circuit
Reference numeral 21 denotes a forward bias applying circuit 22 for applying a forward bias to the upper arm transistor 1 to turn it on, and a reverse bias applying circuit for preventing the upper arm transistor 1 from being erroneously fired.
23. The forward bias application circuit 22
Is selected from the drive circuit 15 for the upper arm shown in FIG.
Reverse bias application circuit such as transistor 11 and negative power supply circuit 14
It has the same configuration as that except for those (all are enclosed by broken lines in the figure).

The reverse bias application circuit 23 includes a diode 31,
It comprises a capacitor 32 and two resistors 33,34. Specifically, the anode of the diode 31 and one end of the resistor 33 are connected to the base of the upper-arm transistor 1,
One end of a capacitor 32 and a resistor 34 are connected to the cathode of a diode 31.
Are connected at one end. Further, the other end of the capacitor 32 and the other end of the resistor 33 are connected to the emitter of the transistor 1 for the upper arm, and the other end of the resistor 34 is connected to the emitter of the transistor 3 for the lower arm.

On the other hand, for the lower arm transistor 3, a driving circuit having the same configuration as the lower arm driving circuit 16 shown in FIG.
24 are provided.

A drive circuit similar to the drive circuit 21 for the upper arm is provided for the other upper-arm transistor 2, and the drive circuit for the lower arm is also provided for the other lower-arm transistor 4. A circuit similar to the circuit 24 is provided, but is omitted here. Further, a controller (see the controller 17 in FIG. 4) for controlling the drive circuits for the upper arm and the lower arm is also omitted here.

Next, the operation of the motor drive circuit having the above configuration will be described below.

In the above-described circuit, in order to rotate the motor M in both the forward and reverse directions as in the prior art, a predetermined drive signal is supplied from a controller (not shown) to each of the drive circuits 21 and 24, so that the four transistors 1, 2 3, 4 are turned on and off in a lotus shape with respect to the motor M. That is, when one of the upper-arm transistors 1 and 2 is turned on and the other is turned off, the on-state transistor is chopped by one of the lower-arm transistors 3 and 4 that are obliquely positioned across the motor M. By doing so, the motor M
To rotate.

At this time, for example, when the upper-arm transistor 2 is always turned on and the lower-arm transistor 3 is chopped, a reverse bias is applied to prevent erroneous firing of the upper-arm transistor 1 when the lower-arm transistor 3 is turned on. The application circuit 23 applies a reverse bias to the upper-arm transistor 1. The operation at that time will be specifically described below with reference to FIG.

Here, it is assumed that a drive signal as shown in FIG. 2A is input to the lower arm transistor 3 by the lower arm drive circuit 24. In this case, the voltage V _CE between the collector and the emitter of the lower arm transistor 3 is equal to the second voltage V _CE .
As shown in FIG. 2B, the voltage is 0 V when the lower arm transistor 3 is in the on state, and becomes substantially equal to the voltage of the main power supply 9 when the lower arm transistor 3 is in the off state. Then, when the lower arm transistor 3 is turned off, the voltage between the points a and b of the reverse bias application circuit 23 becomes equal to the collector-emitter voltage V _{CE of the} lower arm transistor 3 (that is, the power supply voltage). The capacitor 32 is negatively charged by the voltage obtained by dividing the power supply voltage by the resistor 33 and the resistor 34.
A negative charging voltage as shown by a curve A in FIG. 3C is applied between the base and the emitter of the upper arm transistor 1 as a reverse bias. On the other hand, when the lower arm transistor 3 is turned on, the points a and b of the reverse bias application circuit 23 become equipotential, so that the capacitor 32 discharges according to the time constant determined by the resistor 33 and the capacitor 32. As a result, the base-emitter voltage V _BE of the upper arm transistor 1 changes as shown by the curve B in FIG.
Become V

Therefore, when the lower arm transistor 3 is turned on, a reverse bias is reliably applied between the base and the emitter of the upper arm transistor 1, so that a large voltage change dv / dt occurs due to the turn-on. Also,
There is no danger of the upper arm transistor 1 being ignited incorrectly.

According to this embodiment, a reverse bias applying circuit including the transistor 11 and the like as shown in FIG.
With a diode 31, a capacitor 32 and two resistors 33, 34
Can be used in place of the reverse bias applying circuit 23 having a very simple configuration, which makes it possible to greatly reduce the number of components and significantly reduce the size of the entire driving circuit.

Next, a DC motor drive circuit to which another embodiment of the present invention is applied is shown in FIG.

In the circuit shown in the figure, the reverse bias applying circuit shown in FIG.
23 has a configuration in which a transistor 35 is added between a resistor 34 and a ground (GND). In the circuit of FIG. 1, when the upper-arm transistor 1 is turned on, the drive current is bypassed to the resistor 34 via the diode 31. In this embodiment, when the upper-arm transistor 1 is turned on. The transistor 35 is turned off to cut off the drive current bypass circuit. As a result, it is possible to save the drive current and, consequently, to save the energy of the entire drive circuit.

In addition, as an element for the upper arm and the lower arm constituting the bridge, as long as it can be driven by applying a reverse bias, for example, a field effect transistor (FET), an electrostatic induction transistor (SIT), or a thyristor is used. Various switching elements can be used.

Further, as the reverse bias application circuit, a circuit configuration other than the above embodiment may be used as long as a reverse bias can be applied to the upper arm switching element by using charging and discharging of the capacitor as described above.

[Effects of the Invention] According to the present invention, the reverse bias application circuit necessary for preventing erroneous firing of the switching element for the upper arm can be replaced with a very simple configuration including a capacitor, so that a conventional large-sized switching device is used. The necessity of a negative power supply circuit or the like is eliminated, and therefore, the entire drive circuit can be significantly reduced in size.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a DC motor driving circuit to which one embodiment of the present invention is applied, and FIGS. 2 (a) to 2 (c) are for explaining the operation of the reverse bias applying circuit 23 shown in FIG. FIG. 3 is a circuit diagram showing a DC motor drive circuit to which another embodiment of the present invention is applied, and FIG. 4 is a circuit diagram showing a conventional DC motor drive circuit. 1, 2,... Upper-arm transistor 3, 4,... Lower-arm transistor 9, 9 main power supply, 21 upper-arm drive circuit, 22 forward bias application circuit, 23 reverse bias application circuit , 24: Lower arm drive circuit, 31: Diode, 32: Capacitor, 33, 34: Resistor, 35: Transistor.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-47-23826 (JP, A) JP-A-48-21971 (JP, A) JP-A-48-37124 (JP, A)

Claims (1)

(57) [Claims] An upper-arm switching element of a bridge circuit comprising at least an upper-arm switching element (1) and a lower-arm switching element (3) directly connected to the upper-arm switching element. A drive circuit for the upper-arm switching element for driving ON and OFF, comprising a capacitor (32) connected between electrodes for applying a control voltage of the upper-arm switching element; When the lower-arm switching elements are both off, the capacitor is charged negatively by the voltage applied between the main electrodes of the lower-arm switching elements, while the upper-arm switching elements remain off. When the lower-arm switching element is turned on, discharge the charged capacitor. Driving circuit of arm switching element on, characterized in that it comprises a reverse biasing circuit (23) which is adapted to apply a reverse bias between the control voltage application electrode of the serial upper arm switching element.