JP2016005295A - Insulated gate signal transmission circuit - Google Patents

Abstract

An object of the present invention is to reduce a transmission delay while maintaining an overcurrent detection protection function of a photocoupler of an insulated gate signal transmission circuit of a switching element.
A gate voltage of a switching element is obtained by connecting a pulse transformer circuit and a photocoupler connected in parallel with capacitors and 4 connected in series to the input and output of the pulse transformer 2 and resistors 11 and 12 connected in parallel. Is generated.
[Selection] Figure 1

Description

  The present invention relates to a circuit for insulating and transmitting a gate signal of a switching element.

  FIG. 2 shows a conventional circuit that insulates the switching signal, amplifies it to a predetermined voltage, and applies it to the gate terminal of the switching element. In FIG. 2, the photocoupler 1 insulates the input switching signal S, amplifies it to a predetermined voltage, and outputs it. The voltage buffer 8 applies a voltage according to the output of the photocoupler 1 to the gate terminal of the switching element 10 via the gate resistor 9. As described above, the switching element 10 is turned on / off according to the insulated switching signal S.

JP 2006-074372 A

"Avago Technology's ACPL-36JV-000E Data Sheet", Avago Technologies, 2010, June 15

  Since the photocoupler has a signal transmission delay between input and output of several hundreds nsec, it is a problem of the prior art that the operation of the switching element does not follow the switching signal. For example, when two switching elements connected in parallel with the same switching signal as shown in FIG. 3 are used in an insulated gate signal transmission circuit using different photocouplers, if the signal delay times of the photocoupler 1 and the photocoupler 21 are different, the switching is performed. Since the elements 10 and 30 cannot be turned on and off at the same time, the current flowing through the switching element is unbalanced according to the time difference, and the current is concentrated on one switching element, which may damage the switching element. is there.

  In order to solve this problem, Patent Document 1 uses a pulse transformer instead of a photocoupler. The photocoupler disclosed in Non-Patent Document 1 has a function of detecting an overcurrent of a current flowing through a switching element in addition to means for insulatingly transmitting a switching signal. Therefore, when the photocoupler is not used as in Patent Document 1, it is necessary to prepare a separate overcurrent detection circuit, which makes the circuit complicated and expensive.

In order to solve the above problems, the present invention provides:
A photocoupler that provides isolated output of the voltage corresponding to the switching signal;
A pulse transformer circuit comprising a pulse transformer in which a capacitor is connected in series with a resistor in input and output, and the switching signal is input;
A voltage buffer for applying a voltage corresponding to a voltage inputted through a resistor to the output of the photocoupler and the output of the pulse transformer circuit to the gate terminal of the switching element through a gate resistor; And

  In the present invention, when the switching signal changes, the output voltage of the pulse transformer circuit changes without delay, and the gate terminal voltage of the switching element can be changed via the voltage buffer. Therefore, by applying the present invention to a circuit in which a plurality of switching elements are connected in parallel as shown in FIG. 3, the deviation of the gate terminal voltage of these switching elements can be eliminated, and the current balance of each switching element is maintained. be able to.

  When the switching signal does not change, the gate terminal voltage of the switching element depends on the photocoupler output voltage. Therefore, if the photocoupler has an overcurrent detection function of the switching element, if the overcurrent is detected, the output voltage of the photocoupler can be changed in the off direction without changing the switching signal, so the switching element is turned off. be able to.

It is explanatory drawing of the insulated gate signal transmission circuit of this invention. (Example 1) It is explanatory drawing of the conventional insulated gate signal transmission circuit. It is a switching element parallel circuit diagram using two conventional insulated gate signal transmission circuits. It is a figure showing the example of each part voltage waveform of this invention.

  FIG. 1 is an example of an insulated gate signal transmission circuit according to the present invention, and FIG. 4 is a diagram showing an example of voltage waveforms at various parts in FIG. This will be described below with reference to FIGS.

  The photocoupler 1 insulates the input switching signal S, amplifies it to a predetermined voltage V5, and outputs it. An example of the switching signal S and the output voltage V5 of the photocoupler 1 at this time is shown by the waveforms of S and V5 in FIG. 4. At the rising edge of the switching signal S, V5 has a delay of tdr and the falling edge. There is a delay of tdf.

  On the other hand, in the pulse transformer circuit 13, a capacitor 3 is connected in series to the input side of the pulse transformer 2 and a resistor 11 is connected in parallel, and a resistor 12 is connected in parallel to the output side of the pulse transformer 2 and a capacitor 4 is connected in series. It has a configuration. When the switching signal S is connected to the input side of the pulse transformer circuit 13, the input voltage waveform V1 and output voltage waveform V2 of the pulse transformer and the output waveform V3 of the pulse transformer circuit are as shown in FIG.

  The output of the photocoupler 1 is connected to the input of the voltage buffer 8 via the resistor 5 and the output of the pulse transformer circuit is connected to the input of the voltage buffer 8 via the resistor 6, and the resistance value of the resistor 6 is sufficiently larger than the resistance value of the resistor 5. If it is small, the input voltage of the voltage buffer 8 substantially depends on the output voltage of the pulse transformer circuit 13. However, the output voltage V3 of the pulse transformer circuit 13 coincides with the output voltage V5 of the photocoupler 1 as the capacitor 4 is gradually charged and discharged with time.

  The voltage buffer 8 applies a voltage corresponding to the input voltage to the gate terminal of the switching element 10 via the gate resistor 9. As described above, the switching element 10 is turned on and off without delay according to the insulated switching signal S.

  For example, when the switching element 10 is on, the switching signal S is 5V and V5 = 15V, and when the switching element 10 is off, the switching signal S is 0V and V5 = −15V. Then, since the voltage Vc2 of the capacitor 4 is -15V when S = 0V, the turn ratio of the pulse transformer is preferably about 1: 8 in order to make the voltage of V3 larger than 15V when changing to S = 5V. Then, when changing to S = 5V, V2 = 40V and V3 = 25V. If the resistance value ratio between the resistors 5 and 6 is 5: 1, V4 becomes about 18 V at this time, and a positive gate voltage can be applied to the switching element via the voltage buffer 8 without delay. The Zener diode 7 has a role of restricting the voltage buffer 8 from being supplied with a voltage higher than PV or NV, which is the power source of the voltage buffer 8.

  The photocoupler 1 has an overcurrent detection function. When the overcurrent of the switching element 10 is detected, the photocoupler 1 sets the output voltage V5 to a negative voltage regardless of the switching signal S. Then, the input voltage of the voltage buffer 8, the output voltage V3 of the pulse transformer circuit 13, and the potential Vc2 of the capacitor 4 are gradually changed to V5, and the switching element 10 can be turned off.

  Since the present invention only adds a circuit using a pulse transformer in parallel to an insulated gate signal transmission circuit using a conventional photocoupler, the transmission delay of the gate signal can be easily reduced, and the switching element can be controlled with high accuracy. This eliminates the need to take into account variations in the transmission time of the photocoupler when setting the dead time for preventing the short-circuit between the positive and negative potentials of the voltage type PWM inverter, and the dead time can be set short. Can be controlled with high accuracy, and the performance of the apparatus using the voltage type PWM inverter can be improved.

DESCRIPTION OF SYMBOLS 1,21 Photocoupler 2 Pulse transformer 3, 4 Capacitor 5, 6, 11, 12 Resistance 7 Zener diode 8, 28 Voltage buffer 9, 29 Gate resistance 10, 30 Switching element 13 Pulse transformer circuit

Claims (1)

In an insulated gate signal transmission circuit that insulates and transmits a switching signal and applies a predetermined voltage to the gate terminal of the switching element.
A photocoupler that insulates and outputs a voltage corresponding to the switching signal;
A pulse transformer circuit comprising a pulse transformer in which a capacitor is connected in series with a resistor in input and output, and the switching signal is input;
And a voltage buffer for applying a voltage corresponding to a voltage inputted to the output of the photocoupler and the output of the pulse transformer circuit via a resistor to the gate terminal of the switching element via a gate resistor. Insulated gate signal transmission circuit.

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