JPS6053487B2 - Isolated drive circuit for power switching elements - 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. To avoid such problems, for example,
Isolated signal transmission circuits that utilize pulse transformers are also known.

However, this type of circuit also has the disadvantage of not being able to transmit low frequency or direct current signals, and the isolated transmission of drive energy is always a problem.
Therefore, as a result of various studies in order to overcome all the problems of the conventional isolated signal transmission circuit described above, the inventor of the present invention connected an isolation transformer to a high frequency power source to obtain an isolated AC signal. A synchronization signal and drive energy are obtained from this AC signal, and the synchronization signal and on-off command signal are outputted as a control signal via an exclusive OR circuit, and an exclusive OR circuit that is held at a predetermined drive energy is used. By inputting a synchronization signal and an alternating current signal obtained from the control signal through an isolation transformer into a circuit, the circuit is configured to obtain an element drive signal that is equal to the on-off command signal and has a predetermined drive energy, It has been found that the above problems can be solved all at once.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an isolated drive circuit for a power switching element that has a simple configuration, can transmit signals quickly and reliably, can be manufactured compactly and inexpensively, and is highly reliable. .

In order to achieve the above object, the present invention includes a high frequency power source, a power supply isolation transformer that obtains an isolated alternating current signal from the high frequency power source, and a power supply isolation transformer that obtains a synchronizing signal from the alternating current signal and performs on-off switching with the synchronizing signal. a control circuit that obtains a control signal from the command signal; and a control circuit that obtains drive energy and a synchronization signal from the AC signal, and converts the synchronization signal and the control signal from the control circuit into a signal obtained through an isolation transformer. - an element drive main circuit that obtains an element drive signal that is equal to the off command signal and has a predetermined drive energy; In the isolated drive circuit for the power switching element, the control circuit includes a signal source that outputs an on-off command signal and an exclusive OR circuit, and the exclusive OR circuit includes an insulated transformer for power supply. A synchronizing signal and an on-off command signal are input based on the AC signal obtained from the voltage dividing winding of the
It is preferable to configure the device to output an off control signal.

In addition, the main element drive circuit is a signal isolation transformer. and an exclusive OR circuit, the exclusive OR circuit is maintained with a DC voltage obtained by rectifying a synchronization signal based on an AC signal obtained from a voltage dividing winding of a power isolation transformer, and further includes a It is preferable to input an on-off control signal obtained through a signal isolation transformer and output an element drive signal maintained at a predetermined DC voltage.

Furthermore, the element drive main circuit can be configured to drive the element by connecting the obtained element drive signal to the base or gate of the power switching element via a resistor.

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

FIG. 1 shows an embodiment of the circuit of the present invention, in which reference numeral 10 is a high frequency power supply, 12 is a power transistor, 14 is an isolation transformer for power supply, 16 is a main circuit for driving the base of the power transistor 12, and 18 is a power supply. 3 shows a control circuit that generates a control signal for controlling the on-off of transistor 12. FIG.

The base drive main circuit 16 connects the output obtained from the voltage dividing winding W2l of the power isolation transformer 14 to diodes 20, 2.
2 and smoothing capacitors 24 and 26 to obtain a DC base drive power source. For this reason,
The base drive main circuit 16 is provided with an exclusive OR circuit 28, and a control signal sent from the control circuit 18, which will be described later, is sent to the exclusive OR circuit 28 via a pulse transformer, that is, a signal isolation transformer 30. A base drive signal based on the control signal is output, and this output signal is supplied to the base terminal of the power transistor 12 via the current limiting resistor 32. On the other hand, control circuit 1
Reference numeral 8 denotes an executor that generates a control signal for controlling the power transistor 12 on and off by inputting the output obtained from the voltage dividing winding Wl2 of the power isolation transformer 14 and an on-off command signal from a predetermined signal source 34. Crusive OR circuit 36
It is equipped with Therefore, this exclusive OR circuit 3
The control signal outputted from the base drive main circuit 16 is
The signal is input to the signal isolation transformer 30. Next, the operation of the circuit of the present invention configured as described above will be explained with reference to the operation waveform diagram shown in FIG.

First, the output voltages A and A'' induced by the high frequency power supply 10 through the power supply isolation transformer 14 in the voltage dividing windings Wl2 and W2l, respectively, have voltage waveforms as shown in FIG. 21.These outputs The voltages A and N become synchronization signals and are input as power supply voltages to the input terminals of the exclusive OR circuit 36 of the control circuit 18 and the exclusive OR circuit 28 of the base drive main circuit 16, respectively.Control circuit 1
At step 8, the signal source 34 outputs the on-off command signal 8 shown in FIG. As a result, the exclusive OR circuit 36 performs an exclusive OR operation on the power supply voltage A and the command signal B1, and outputs the control signal C1 shown in FIG. 2. That is, the exclusive OR circuit 36 performs the calculation C1 = A sa B1, and when the command signal 8 is "0", the control signal C1 matches the power supply voltage A, and when the command signal B1 is "1". In this case, the control signal C1 has a phase opposite to that of the power supply voltage A. In this way, the control circuit 1
Since the control signal C1 obtained in step 8 has a high-frequency AC waveform, it is first isolated without delay via the signal isolation transformer 30 in the base drive main circuit 16, and becomes the control signal q'', which becomes an exclusive signal. It is input to the other input terminal of the OR circuit 28.

The exclusive OR circuit 28 holds the power supply voltage A'' as a DC voltage that is rectified by diodes 20 and 22 and smoothed by capacitors 24 and 26, and is configured to maintain exclusive OR between the power supply voltage A'' and the control signal C1''. Performing a logical sum operation, Figure 2 4
As shown in FIG. 2, a base drive signal D1 equal to the command signal B1 (see FIG. 2) is output. In this case, the voltage of the base drive signal D1 becomes a DC voltage that maintains the exclusive OR circuit 28. The base drive signal D1 obtained in this way is transmitted to the power transistor 1 via the current limiting resistor 32.
Drives the base of 2. As is clear from the embodiments described above, the isolated base drive circuit for a power switching element according to the present invention includes a system that isolates and transmits drive energy from a high-frequency power source and a synchronization signal, and a system that transmits an on-off control signal. Since the exclusive OR circuit and the transmission system via the signal isolation transformer are organically coupled, the following excellent effects can be expected.

(1) The transmission delay of on-off signals is minimized.

(2) Malfunctions due to noise such as potential fluctuations between insulations are reduced, and reliability is improved. (3) Low frequency signals or direct current (continuously on or off) signals can also be accurately transmitted.

(4) It is possible to provide a large number of voltage dividing windings (secondary windings) of a power supply isolation transformer and also provide a large number of signal sources, so that a large number of power switching elements can be individually controlled on and off.

In this case, the entire device can be manufactured with a simple configuration, small size, and low cost. That is, according to the present invention, the drive energy transmission system can be simplified. Although the preferred embodiments of the present invention have been described above, the present invention is applicable not only to ordinary power transistors but also to base or gate drive circuits of various power switching elements such as thyristors, triacs, GTO thyristors, and FET power transistors. Not only that, but the delay time of on-off control is minimized, so it is suitable for driving power switching elements connected in series, and various other design changes can be made without departing from the spirit of the present invention. Of course.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of an insulated base drive circuit for a power switching element according to the present invention, and FIGS. 2 1 to 4 are operational waveform diagrams of the circuit shown in FIG. 1. 10... High frequency power supply, 12... Power transistor star, 14... Power isolation transformer, 16... Base drive main circuit, 18...・・・
Control circuit, 20, 22...diode, 24, 26
... Smoothing capacitor, 28 ... Exclusive OR circuit, 30 ... Signal isolation transformer, 32 ...
...Current limiting resistor, 34...Signal source, 36.
...Exclusive OR circuit.

Claims (1)

[Claims] 1. A high-frequency power source, a power supply isolation transformer that obtains an isolated AC signal from the high-frequency power source, and a power supply isolation transformer that obtains a synchronization signal from the AC signal and a control signal from this synchronization signal and an on-off command signal. a control circuit that obtains a drive energy and a synchronization signal from the alternating current signal, and transmits this synchronization signal and a control signal from the control circuit to a signal obtained through an isolation transformer, which is equal to the on-off command signal. What is claimed is: 1. An isolated drive circuit for a power switching element, comprising: an element drive main circuit for obtaining an element drive signal having a predetermined drive energy; 2. In the isolated drive circuit according to claim 1, the control circuit includes a signal source that outputs an on-off command signal and an exclusive OR circuit, and the exclusive OR circuit includes an isolation transformer for power supply. An isolated drive circuit for a power switching element configured to input a synchronization signal based on an alternating current signal obtained from a voltage-divided winding and an on-off command signal and output a predetermined on-off control signal. 3. In the isolated drive circuit according to claim 1 or 2, the element drive main circuit includes a signal isolation transformer and an exclusive OR circuit, and the exclusive OR circuit is connected to the power isolation transformer. A synchronization signal based on an AC signal obtained from a voltage dividing winding is held at a DC voltage obtained by rectifying it, and the synchronization signal and an on-off command signal obtained via a signal isolation transformer are inputted to obtain a predetermined signal. An isolated drive circuit for a power switching element configured to output an element drive signal held at a DC voltage. 4. In the isolated drive circuit according to any one of claims 1 to 3, an element drive signal obtained from the element drive main circuit is supplied to the base or gate of the power switching element via a resistor. An isolated drive circuit for power switching elements.