JPH0141051B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for transmitting an on/off drive signal to a power switching element such as a power transistor while being isolated from a signal source.

Conventionally, signal transmission circuits using photocouplers have been widely used as insulated signal transmission means for driving the bases of power transistors and the like. However, such conventional circuits suffer from malfunctions due to noise such as signal transmission delays and potential fluctuations between insulations.

In order to overcome these problems, the applicant first connects an isolation transformer to a high frequency power source to obtain an isolated alternating current signal, and also obtains a synchronization signal and drive energy from this alternating signal.
The synchronization signal and the on/off command signal are outputted as a control signal through an exclusive OR circuit, and the synchronization signal and the control signal are outputted through an exclusive OR circuit held at a predetermined drive energy as a signal obtained through an isolation transformer. We have developed an isolated drive circuit for a power switching element configured to receive an element drive signal that is equal to the on/off command signal and has a predetermined drive energy by inputting the on/off command signal, and have filed a patent application.

That is, the basic configuration of the isolated drive circuit for the power switching element according to the above proposal is as shown in FIG. That is, in Figure 1,
Reference numeral 10 indicates a high frequency power supply, 12 indicates an exclusive OR circuit for control, 14 indicates an isolation transformer for power supply, 16 indicates an isolation transformer for signals, and 18 indicates an exclusive OR circuit. However, in the isolated drive circuit having the configuration shown in FIG. 1, the voltage output from the high frequency power supply 10 is input to the control exclusive OR circuit 12 and the power supply isolation transformer 14. At this time, high frequency power supply 1
The output voltage A of 0 and the output voltage A' induced in the isolation transformer 14 have voltage waveforms as shown in FIG. The exclusive OR circuit 12
, an on/off command signal B is input from a required signal source, and as a result, the exclusive OR circuit 12
Then, the exclusive OR operation of the power supply voltage A and the command signal B is performed, and the control signal C shown in FIG.
Output. That is, in the exclusive OR circuit 12, the calculation C=AV-B is performed, and when the command signal B is "0", the control signal C is in phase with the power supply voltage A, and when the command signal B is "1", the control signal C is in phase with the power supply voltage A. In this case, the control signal C has a phase opposite to that of the power supply voltage A.

In this way, the control signal C obtained in the control exclusive OR circuit 12 has a high frequency AC waveform, so the signal isolation transformer 16
Isolated without delay through the control signal
C' and is input to the exclusive OR circuit 18 of the element drive main circuit. Further, this exclusive OR circuit 18 is connected to the power supply isolation transformer 14.
The power supply voltage A' obtained through the control signal C' is inputted, and the exclusive OR operation of the control signal C' and the power supply voltage A' is performed, and as shown in FIG.
Outputs an element drive signal B' equal to .

However, in the isolated drive circuit having the above configuration, the element drive circuit that obtains the element drive signal has an exclusive connection with the signal isolation transformer 16.
Since it is equipped with an OR circuit 18, there is a drawback that the logic operation time in the exclusive OR circuit 18 and a time delay for appropriately amplifying the operation result occur.

Therefore, as a result of various studies in order to overcome the problems in the above-mentioned isolated drive circuit for the power switching element, the inventor of the present invention has developed an isolation transformer for obtaining an AC signal isolated from a high frequency power source.
An isolation transformer for obtaining a control signal isolated from the control signal forms an addition signal and a subtraction signal based on the signals respectively obtained from the control signal, and synthesizes the addition signal and subtraction signal by full-wave rectification, respectively. It has been found that by doing so, the original on/off control signal can be restored at high speed, and the above-mentioned problems can be solved.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an isolated type of power switching element that has a simple structure, can transmit signals quickly and reliably, and can speed up restoration of control signals particularly on an isolated secondary side. To provide a driving circuit.

In order to achieve the above object, the present invention includes a high frequency power source, an isolation transformer for obtaining an isolated AC signal from the high frequency power source, and a predetermined on/off control using the AC signal from the high frequency power source as a synchronous signal. a control circuit for obtaining a control signal from the signal; an isolation transformer for obtaining an isolated control signal from the control signal; and two of the respective isolation transformers.
A circuit that forms an addition signal and a subtraction signal from the AC signal and control signal obtained on the next side, and further rectifies and synthesizes the addition signal and subtraction signal, respectively, to restore the on/off control signal. It is characterized by configuring.

In the above-described isolated drive circuit, the circuit for restoring the on/off control signal includes a pair of full-wave rectifier bridges made up of rectifier diodes, and these bridge circuits are connected in series to obtain the control signal from the connection point. It can be configured as follows.

In this case, it is preferable to connect a voltage dividing resistor and a smoothing capacitor for setting forward bias and reverse bias to the power switching element to the series-connected full-wave rectifying bridge circuit, respectively.

In addition, the isolation transformer for AC signals and the isolation transformer for control signals are placed close to each other, and the secondary winding is wound around each core in an O-shape to extract the addition signal. It is preferable to configure the subtraction signal to be extracted by winding it in the shape of a letter.

Next, as an example of an insulated drive circuit for a power switching element according to the present invention, a gate control circuit for a power switching element will be described in detail as an example.

FIG. 3 shows an embodiment of the circuit of the present invention. For convenience of explanation, the same reference numerals are given to the same components as those of the circuit shown in FIG. 1, and detailed explanation thereof will be omitted.

That is, in the present invention, similarly to the conventional circuit, the high frequency output voltage A generated in the high frequency power supply 10 is inputted to the power supply isolation transformer 14 and the control exclusive OR circuit 12 that inputs the on/off control signal B, respectively. It is configured to input the control signal C obtained by the exclusive OR circuit 12 to the signal isolation transformer 16.

However, in the present invention, the signal A'+C' to be added and the signal A'-C' to be subtracted from the secondary side output signals A' and C' of the power isolation transformer 14 and the signal isolation transformer 16, respectively. Configure the circuit to obtain .

On the other hand, the control signal A′+ obtained in this way
A full-wave rectifying bridge circuit consisting of high-speed rectifying diodes 20-23 and 24-27 for full-wave rectifying C', A'-C' is provided, and these bridge circuits are connected in series. Note that resistors 28 and 29 are connected between both terminals of the bridge circuit connected in series in this way.
and capacitors 30 and 31 are connected. As a result, the same signal B' as the original control signal B is restored at the connection point E of the bridge circuit. Therefore, the control signal B' obtained in this manner can be used as a gate control voltage for the power switching element 32.

Further, in the circuit of the present invention, as a means for obtaining the addition signal A'+C' and the subtraction signal A'-C' from the respective secondary side output signals A' and C' of the power isolation transformer 14 and the signal isolation transformer 16. As shown in FIG. 3, this can be easily realized by a circuit configuration in which each of the transformers 14 and 16 has a plurality of secondary windings, and these secondary windings are externally connected in series. As an alternative, as shown in FIG. The addition signal A'+C' is taken out, and the subtraction signal A'- is obtained from the secondary winding by winding the secondary winding in a figure 8 shape around both cores.
It can also be configured to extract C′. In this case, the former type of external connection can be omitted, which is advantageous in manufacturing.

Next, the operation of the circuit of the present invention configured as described above will be explained with reference to the operation waveform diagrams shown in FIGS. 1 to 8.

First, the output voltage A obtained from the high frequency power supply 10
[See FIG. 4 1] is input to the power isolation transformer 14 and the exclusive OR circuit 12. This exclusive OR circuit 12 receives an on/off control signal B from a required signal source [Fig.
Reference] is input, and the exclusive OR operation of this command signal B and the power supply voltage A is performed to obtain the control signal C.
[See FIG. 4, 3] is output, and this control signal C is input to the signal isolation transformer 16. The above operation is exactly the same as that of the circuit shown in FIG. 1 above.

Next, on the secondary sides of the power isolation transformer 14 and the signal isolation transformer 16, the power supply voltage A' (see FIG. 4 1) and the control signal C' [see FIG. 4 3] induced in the secondary windings, respectively. Reference] addition signal
A'+C' (see Figure 4) and subtraction signal A'-
We obtain C' [see Fig. 4, 5]. Further, these signals are each subjected to full-wave rectification by a full-wave rectifying bridge circuit (see FIGS. 6 and 7). Since the full-wave rectified signal is applied to the power switching element 32 via the resistors 28 and 29 and the capacitors 30 and 31, the same signal as the original control signal B is sent to the connection point E of the bridge circuit. The signal B' (see FIG. 4, 8) is restored.

Therefore, the signal B′ obtained in this way is
When used as a gate control voltage for the power switching element 32, the forward bias voltage _VH and reverse bias voltage _VL can be arbitrarily set by appropriately selecting the voltage division ratio of the resistors 28 and 29. In this case, the capacitors 30 and 31 act as smoothing capacitors to transiently stabilize the forward bias V _H and reverse bias V _L output voltages.

As is clear from the embodiments described above, according to the circuit of the present invention, elements having a delay such as a logic operation circuit and an amplifier circuit including active elements on the secondary side of the isolation transformer (actually several tens of nanoseconds) ) is removed, the delay time of the signal in the secondary circuit can be ignored, and the power switching element can be driven at high speed. Further, since the circuit of the present invention can use only inexpensive passive elements on the secondary side of the isolation transformer, manufacturing costs can be reduced. Further, in the circuit of the present invention, by using a structure as shown in FIG. 5 as an insulating transformer, there is an advantage that the structure can be made smaller and wiring reactance etc. can be minimized.

Therefore, since the circuit of the present invention is capable of transmitting everything from high frequency signals to direct current signals as an insulated signal transmission circuit with a small delay time, its application range is extremely wide. In other words, the power FET shown in Figure 3
Not only can it be used as a series or parallel drive circuit for transistors, but it can also be applied to applications such as grid modulation circuits for traveling wave tubes, such as rapidly changing the grid potential relative to the -10kV cathode potential. be.

Although the preferred embodiments of the present invention have been described above, it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of drawings]

Fig. 1 is an isolated drive circuit diagram of a conventional power switching element, Fig. 2 1 to 4 are operating waveform diagrams of the circuit shown in Fig. 1, and Fig. 3 is an insulated drive circuit diagram of a power switching element according to the present invention. A circuit diagram showing an embodiment of the drive circuit, FIGS. 4 1 to 8 are operational waveform diagrams of the circuit shown in FIG. 3, and FIGS. 5 a and b are a preferred configuration example of an isolation transformer used in the circuit of the present invention. FIG. 10...High frequency power supply, 12...Exclusive OR circuit, 14...Isolation transformer, 16...Isolation transformer, 18...Exclusive OR circuit, 20-27...Rectifier diode, 28, 29...
...Resistor, 30, 31... Capacitor, 32... Power switching element.

Claims (1)

[Claims] 1. A high frequency power source, an isolation transformer for obtaining an insulated AC signal from the high frequency power source, and a control signal obtained from a predetermined on/off control signal using the AC signal from the high frequency power source as a synchronization signal. a control circuit, an isolation transformer for obtaining a control signal isolated from the control signal, and two of each of the isolation transformers.
A circuit that forms an addition signal and a subtraction signal from the AC signal and control signal obtained on the next side, and further rectifies and synthesizes the addition signal and subtraction signal, respectively, to restore the on/off control signal. An isolated drive circuit for a power switching element characterized by comprising: 2. In the isolated drive circuit according to claim 1, the circuit for restoring the on/off control signal includes a pair of full-wave rectifying bridge circuits configured with rectifying diodes, and these bridge circuits are connected in series. An isolated drive circuit for a power switching element configured to obtain a control signal from its connection point. 3. In the isolated drive circuit according to claim 2, the series-connected full-wave rectifier bridge circuit is provided with a voltage dividing resistor and a smoothing capacitor for setting forward bias and reverse bias for the power switching element, respectively. An isolated drive circuit for connected power switching elements. 4. In the isolated drive circuit according to any one of claims 1 to 3, the isolation transformer for AC signals and the isolation transformer for control signals are:
They are placed close to each other, and the secondary winding is connected to each core.
An insulated drive circuit for a power switching element configured to take out an addition signal by winding it in a figure-8 shape, and take out a subtraction signal by winding a secondary winding around each iron core in a figure-8 shape.