JP2010193649A - Semiconductor switching element driving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor switching element driving circuit that can reduce the size of a transformer by making small a voltage time product to be applied to the transformer. <P>SOLUTION: In a transformer (7), a primary winding is connected to a pulse voltage source (1) via a capacitor (5), one end of a secondary winding is connected to a first on/off control terminal of a voltage-driven semiconductor switching element (13) via a diode (9) for preventing a backward current, and the other end of the secondary winding is connected to a second on/off control terminal of the voltage-driven semiconductor switching element (13). When a negative voltage of a predetermined value or above appears on the secondary winding of the transformer (7), a parasitic capacitance (13a) of the voltage-driven semiconductor switching element (13) is discharged by means of a shorting means (15 and 17). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor switching element driving circuit used for a switching power supply and the like, and more particularly to a semiconductor switching element driving circuit that controls on / off of a voltage driving type semiconductor switching element via a transformer.

In a switching power supply or the like, the control circuit and the main circuit may be placed at different potentials. In this case, a control signal for on / off control of the switching element in the main circuit may be transmitted in an insulated state. Necessary.
A semiconductor switching element driving circuit configured to transmit the on / off control signal in an isolated manner has been proposed by, for example, Patent Document 1. FIG. 4 shows a simplified conventional drive circuit.

In this drive circuit, the output Va of the pulse voltage source 10 is transmitted by being insulated by the transformer 20. FIG. 5A shows the simplest example of the output Va of the pulse voltage source 10. The output Va according to this example has a waveform that is symmetrical with respect to amplitude and time width.
The output Vb of the transformer 20 (having a waveform similar to the output Va of the pulse voltage source 10) is input to the gate of the semiconductor switching element 40 to be driven via the resistor 30. Here, an IGBT (insulated gate bipolar transistor) is used as the semiconductor switching element 40.

In general, the gate of an insulated gate element such as IGBT or MOSFET has a parasitic capacitance (indicated by reference numeral 40a in FIG. 4). On the other hand, the transformer 20 has a leakage inductance. Although these may generate LC resonance with each other, this resonance is not desirable for stably controlling the semiconductor switching element 40. Therefore, a braking resistor 30 for preventing the above-described resonance is provided between the transformer 20 and the gate of the semiconductor switching element 40.
The resistor 30 forms an RC filter (low-pass filter) together with the parasitic capacitance 40a. For this reason, the gate voltage of the semiconductor switching element 40, that is, the terminal voltage Vc of the parasitic capacitance 40a, shows a waveform slightly delayed from the output Va of the pulse voltage source 10, as shown in FIG. 5B. .

  The semiconductor switching element 40 is turned on when the terminal voltage Vc of the parasitic capacitance 40a becomes equal to or higher than the threshold voltage Vth of the semiconductor switching element 40, and when the terminal voltage Vc falls below the threshold voltage Vth. Turn off. Therefore, the terminal voltage Vc does not necessarily have a negative polarity. However, in order to avoid magnetic saturation of the transformer 20, the positive and negative voltage time products need to be equal, so the terminal voltage Vc is shown in FIG. Have a good waveform.

JP 2008-193854 A

Especially when the size of the entire device is limited by a small capacity circuit, it is necessary to make the transformer 20 as small as possible. For this reason, it is desirable that the transformer 20 be constructed using an iron core that is as small as possible. However, if the cross-sectional area of the iron core is reduced, the magnetic flux density is increased and magnetic saturation is likely to occur.
In the conventional semiconductor switching element driving circuit, when magnetic saturation occurs in the transformer 20, the primary side of the transformer 20 is short-circuited, so an overcurrent flows through the primary side. On the secondary side of the transformer 20, the semiconductor switching element 40 cannot be kept on due to the decrease in the voltage V3.
Since the magnetic flux density is inversely proportional to the number of turns of the coil of the transformer 20, it is conceivable to decrease the magnetic flux density by increasing the number of turns. However, in order to increase the number of turns of the coil in a limited volume, it is necessary to make the winding thin. Therefore, considering the availability of the winding material, the reliability of the winding, etc., the magnetic flux density by the above method As a result, there is a limit to the reduction in the size of the transformer 20, and thus miniaturization of the transformer 20 itself is limited.

  In view of such circumstances, an object of the present invention is to provide a semiconductor switching element driving circuit capable of reducing the voltage time product applied to the transformer and reducing the size of the transformer.

In order to achieve the above object, according to the present invention, a primary winding is connected to a pulse voltage source via a capacitor, and one end of the secondary winding is connected to the first of the voltage-driven semiconductor switching element via a reverse blocking diode. A transformer having the other end of the secondary winding connected to the second on / off control terminal of the voltage-driven semiconductor switching element and the secondary winding. Short-circuit means for short-circuiting between the first on / off control terminal and the second on / off control terminal when a negative voltage of a certain value or more occurs;
A semiconductor switching element driving circuit is provided.

  As the transformer, it is possible to use a transformer having a magnetic characteristic that saturates at a voltage / time product having a value smaller than the voltage / time product of the pulse voltage generated by the pulse voltage source.

  The short-circuit means may include a voltage detection element that detects a negative voltage equal to or greater than the predetermined value, and a short-circuit switch element that conducts based on a detection signal of the voltage detection element. In a preferred embodiment, a transistor is interposed between the first on / off control terminal and the second on / off control terminal as the shorting switch element, and the voltage detecting element A zener diode is interposed between one end of the secondary winding and the base of the transistor.

  It is desirable that a resistor for suppressing overcurrent and resonance is connected in series to the capacitor. Further, it is preferable that a resonance suppression resistor is interposed between the reverse blocking diode and the first on / off control terminal of the voltage-driven semiconductor switching element.

  In the embodiments, IGBTs or MOS-FETs are used as the voltage-driven semiconductor switching elements, but the present invention can also be applied to voltage-driven semiconductor switching elements different from these.

  According to the present invention, since the capacitor takes part of the voltage that the transformer has handled in the conventional circuit, the value of the voltage-time product related to the transformer becomes small. Therefore, even when a small transformer is used, the switching element can be stably switched, so that a low-cost and small semiconductor switching element driving circuit can be provided.

1 is a circuit diagram showing an embodiment of a semiconductor switching element drive circuit according to the present invention. It is a wave form diagram which shows operation | movement of the circuit shown in FIG. FIG. 2 is an operation waveform diagram of the circuit shown in FIG. 1 in the case where a transformer having a magnetic characteristic that is easily saturated is used. It is a circuit diagram which shows an example of the conventional semiconductor switching element drive circuit. It is a wave form diagram which shows the operation | movement of the conventional circuit shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows an embodiment of a semiconductor switching element driving circuit according to the present invention. In FIG. 1, the output of the pulse voltage source 1 is connected to the primary winding of a transformer 7 through a resistor 3 and a capacitor 5 connected in series. One end of the secondary winding of the transformer 7 is connected to the gate (first on / off control terminal) of the voltage-driven semiconductor switching element 13 to be driven via the diode 9 and the resistor 11, and the other end is connected. The semiconductor switching element 13 is connected to the emitter (second on / off control terminal).

  One end of the secondary winding of the transformer 7 is also connected to the base of the transistor 17 via the Zener diode 15. The transistor 17 has an emitter connected to a line connecting the diode 9 and the resistor 11, and a collector connected to a line connecting the other end of the secondary winding of the transformer 7 and the emitter of the semiconductor switching element 13.

As the voltage-driven semiconductor switching element 13, a switching element having a MOS gate structure such as an IGBT (insulated gate bipolar transistor) or a MOS-FET is used. In the present embodiment, an IGBT is used. The gate of the semiconductor switching element 13 which is an insulated gate element has a parasitic capacitance 13a.
The semiconductor switching element 13 functions as a switching element of a switching power supply, for example.

Next, the operation of the semiconductor switching element driving circuit according to the present embodiment will be described with reference to the waveform diagram of FIG.
When the pulse voltage V1 output from the pulse voltage source 1 rises as shown in FIG. 2A, the path of the pulse voltage source 1 → resistor 3 → capacitor 5 → transformer 7 → pulse voltage source 1 on the primary side of the transformer 7 Then, current flows along the path of the transformer 7 → diode 9 → resistor 11 → parasitic capacitance 13 a → transformer 7 on the secondary side of the transformer 7.
The current flowing to the secondary side of the transformer 7 charges the parasitic capacitance 13a, and as a result, the semiconductor switching element 13 is turned on. FIG. 2C shows the terminal voltage V3 of the parasitic capacitance 13a (gate voltage of the semiconductor switching element 13).

  Thereafter, as the capacitor 5 is charged, the terminal voltage of the capacitor 5 gradually increases. The voltage applied to the primary winding of the transformer 7 is obtained by subtracting the terminal voltage of the capacitor 5 from the output voltage V 1 of the pulse voltage source 1. Therefore, as the terminal voltage of the capacitor 5 increases, the voltage applied to the primary winding of the transformer 7 decreases, and the output voltage V2 of the transformer 7 also decreases.

As shown in FIG. 2B, the output voltage V2 of the transformer 7 once decreases to 0V, then exhibits negative polarity due to resonance between the capacitor 5 and the leakage inductance of the transformer 7, and then becomes 0V again. At this time, the voltage V3 across the parasitic capacitance 13a is maintained at a constant value as shown in FIG. The reason is as follows.
The transistor 17 is in an off state.
The diode 9 prevents the discharge of the parasitic capacitance 13a;
The semiconductor switching element 13 does not absorb current more than that charged by the parasitic capacitance 13a.

When the output voltage V1 of the pulse voltage source 1 becomes 0 V, the voltage applied to the capacitor 5 (approximately equal to the peak value of the voltage V1) is applied to the primary winding of the transformer 7 with the reverse polarity, so that FIG. As shown in b), the output voltage V2 of the transformer 7 is also negative. The Zener voltage Vz of the Zener diode 15 is set lower than the voltage obtained by adding the negative voltage V2 and the terminal voltage V3 of the parasitic capacitance 13a. Therefore, the Zener diode 15 is turned on when the transformer 7 outputs a negative voltage of a certain value or more, so that a current flows through the path of the parasitic capacitance 13a → the resistor 11 → the transistor 17 → the Zener diode 15 → the transformer 7 → the parasitic capacitance 13a. Flows and the transistor 17 is turned on.
The parasitic capacitance 13a is short-circuited through the transistor 17 and the resistor 11 that are turned on. Therefore, as shown in FIG. 2C, the terminal voltage V3 of the parasitic capacitance 13a becomes 0V, and the semiconductor switching element 13 is turned off.

As is clear from the above description, in the semiconductor switching element driving circuit according to this embodiment, the output voltage V2 of the transformer 7 maintains the positive polarity only during the charging of the parasitic capacitance 13a by the charging operation of the capacitor 5, and Even when the output voltage V2 is not positive, the voltage V3 of the charged parasitic capacitance 13a is maintained at a predetermined level until the output voltage V1 of the pulse voltage source 1 becomes 0V. Therefore, the semiconductor switching element 13 can be stably turned on / off despite the small voltage-time product applied to the transformer 7. The transformer 7 can be miniaturized by reducing the voltage time product.
The resistor 11 corresponds to the resistor 30 shown in FIG. 4 and is provided to prevent LC resonance due to the parasitic capacitance 13a and the leakage inductance of the transformer 7.

3 shows that the capacitance of the capacitor 5 is set larger than that of the example shown in FIG. 1, and the transformer 7 has a voltage / time product smaller than the voltage / time product of the voltage pulse V 1 generated by the pulse voltage source 1. FIG. 6 illustrates an operation waveform diagram in the case of using a material that causes magnetic saturation.
Also in this example, the parasitic capacitance 13a is charged when the output voltage V1 of the pulse voltage source 1 rises, and the semiconductor switching element 13 is turned on. Thereafter, the capacitor 5 is gradually charged by the exciting current flowing on the primary side of the transformer 7. For example, the transformer 7 reaches a saturation point at time t1 shown in FIG. 3 and its excitation inductance rapidly decreases, so that the primary side is almost short-circuited. The resistor 3 is provided for the purpose of preventing an overcurrent from flowing to the pulse voltage source 1 at this time and preventing resonance between the capacitor 5 and the leakage inductance of the transformer 7.

  The capacitor 5 is charged to the peak of the output voltage V1 of the pulse voltage source 1 in a short time, and accordingly, the output voltage V2 of the transformer 7 becomes approximately 0V. However, at this time, the voltage V3 of the parasitic capacitance 13a is based on the same principle as described above (the transistor 17 is in the OFF state. The diode 9 prevents the parasitic capacitance 13a from being discharged. The above current is not absorbed.).

When the output voltage V1 of the pulse voltage source 1 becomes 0V, the voltage of the capacitor 5 is applied to the transformer 7 with the reverse polarity, and as a result, it is parasitic on the same principle (formation of a discharge path by turning on the transistor 17). Capacitance 13a is discharged. Also at this time, the transformer 7 is saturated after a certain time and is short-circuited. For this reason, the capacitor 5 is discharged until its terminal voltage becomes approximately 0V.
Thus, according to the semiconductor switching element drive circuit according to the present embodiment, a small-sized transformer that saturates when the output voltage V1 of the pulse voltage source 1 is applied can be used as the transformer 7.

DESCRIPTION OF SYMBOLS 1 Pulse voltage source 3 Resistance 5 Capacitor 7 Transformer 9 Diode 11 Resistance 13 Voltage drive type semiconductor switching element 13a Parasitic capacitance

Claims (7)

The primary winding is connected to a pulse voltage source through a capacitor, and one end of the secondary winding is connected to a first on / off control terminal of the voltage-driven semiconductor switching element through a reverse blocking diode, A transformer in which the other end of the secondary winding is connected to a second on / off control terminal of the voltage-driven semiconductor switching element;
Short-circuit means for short-circuiting between the first on / off control terminal and the second on / off control terminal when a negative voltage of a certain value or more is generated in the secondary winding;
A semiconductor switching element driving circuit comprising:   2. The semiconductor switching element drive circuit according to claim 1, wherein the transformer has a magnetic characteristic that saturates at a voltage / time product having a value smaller than a voltage / time product of a pulse voltage generated by the pulse voltage source. .   The said short-circuit means is provided with the voltage detection element which detects the negative voltage more than the said fixed value, and the switch element for short circuit which conduct | electrically_connects based on the detection signal of this voltage detection element. Semiconductor switching element drive circuit.   The short-circuit switch element is a transistor interposed between the first on / off control terminal and the second on / off control terminal, and the voltage detection element is a secondary winding of the transformer. 4. The semiconductor switching element driving circuit according to claim 3, wherein the semiconductor switching element driving circuit is a Zener diode interposed between one end of the semiconductor device and the other base.   2. The semiconductor switching element driving circuit according to claim 1, wherein a resistor for suppressing overcurrent / resonance is connected in series to the capacitor.   2. The semiconductor switching element drive according to claim 1, wherein a resistance for suppressing resonance is interposed between the reverse blocking diode and the first on / off control terminal of the voltage driven semiconductor switching element. circuit.   2. The semiconductor switching element drive circuit according to claim 1, wherein the voltage driven semiconductor switching element is an IGBT or a MOS-FET.

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