JPH04123516A - Insulation type transistor driving circuit - Google Patents

Abstract

PURPOSE:To obtain a small-sized insulation type transistor (TR) driving circuit by driving a TR with the output of a transformer. CONSTITUTION:A high frequency signal fed from a high frequency supply means 1 is modulated by an input signal 3, a high frequency power supply voltage is generated according to a modulated wave and inputted to a transformer 6 and a TR 10 is driven in response to the output of the transformer 6. Also a high frequency power supply voltage is inputted to the transformer 6 at all times and the output of the transformer 6 is switched according to an input signal 3. Thus, it is not required to employ a large pulse transformer and a large auxiliary power supply and the small-sized insulation type TR driving circuit is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an isolated transistor drive circuit, and more particularly to an isolated transistor drive circuit that is smaller than conventional ones and can drive power transistors and the like.

[Prior Art] A plurality of power transistor switches are often used in power conversion circuits of electric motor servo systems and inverter systems. In that case, the drive circuits for these power transistor switches have different ground levels and therefore need to be insulated from each other.

FIG. 6 shows a transistor drive circuit using a conventional pulse transformer. In the figure, a low frequency pulse signal is input to the primary side of a pulse transformer 61. The transistor 65 is driven by the secondary output of the pulse transformer 61.

Further, a transistor drive circuit as shown in FIG. 7 is also used. The drive circuit shown in the figure has auxiliary power supplies 71 and 72, and receives a PWM signal (input signal) through a photocoupler 73. The input signal and the drive circuit are insulated by the photocoupler 73. The input PWM signal is amplified and drives power transistor 75. Auxiliary power supply 71.
72 usually consists of a DC-DC converter including an isolation transformer.

[Problems to be Solved by the Invention] Incidentally, in the drive circuit using the pulse transformer shown in FIG. 6, since the frequency of the input signal to the pulse transformer is low, the transformer itself becomes very large. If this is made small, the switching characteristics will deteriorate and sufficient drive power will not be obtained.

On the other hand, the device using the auxiliary power source shown in FIG. 7 can be downsized to some extent. However, while control circuits are becoming smaller, such as with digital servos using microprocessors, such transistor drive circuits with auxiliary power supplies occupy a relatively large volume, making it difficult to miniaturize the entire control device. The current situation is that it is becoming a hindrance.

SUMMARY OF THE INVENTION In view of the problems in the conventional example described above, it is an object of the present invention to provide an isolated transistor drive circuit that is smaller than the conventional one.

[Means for Solving the Problems] In order to achieve the above object, an isolated transistor drive circuit according to the present invention includes a high-frequency signal supply means for supplying a high-frequency signal, and a high-frequency signal supplying means for modulating the high-frequency signal as an input signal. The device includes modulation means for outputting a modulated wave, means for generating a high-frequency power supply voltage according to the modulated wave, and a transformer for inputting the high-frequency power supply voltage, and the transistor is driven by the output of the transformer. It is characterized by

Further, a high frequency signal supply means for supplying a high frequency signal, a means for generating a high frequency power supply voltage according to the high frequency signal,
It is characterized by comprising a transformer into which the high-frequency power supply voltage is input, and a switching means for switching the output of the transformer according to the input signal, and a transistor is driven by the output of the switching means.

[Function] According to the above-described isolated transistor drive circuit according to the present invention, the high frequency signal supplied by the high frequency signal supply means is modulated according to the input signal.

A high frequency power supply voltage is generated according to the modulated wave and input to the transformer. And depending on the output of this transformer,
The transistor is activated.

Alternatively, a high-frequency power supply voltage may be constantly input to the transformer, and the output of the transformer may be switched in accordance with the input signal.

Since the input to the transformer is a high frequency power supply voltage, the size of the transformer can be small.

[Example] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows a circuit diagram of a transistor drive circuit according to a first embodiment of the present invention. In the figure, 1 indicates an oscillation source (high frequency signal supply means) that outputs a high frequency signal, and 2 indicates an AND circuit (modulation means).

Oscillation source 1 outputs a 16 MHz high frequency signal.

A 15.5 kHz PWM (pulse width modulation) signal is input to one input terminal 3 of the AND circuit 2 .

The oscillation source 1 is connected to the other input terminal of the AND circuit 2 . The output terminal of the AND circuit 2 is connected to the base of the transistor 4. The emitter of the transistor 4 is connected to the oscillation source 1, and the collector is connected to one terminal of the primary winding of the transformer 6. The other primary winding input terminal of the transformer 6 is supplied with a DC voltage of +5V.

Transistor 4 and the +5V DC voltage form means for generating a high frequency power supply voltage.

Specifically, the transformer 6, which is a two-winding reactor, has a Ni-Zn ferrite core with a diameter of 6 mm and a primary winding of 12 turns and a secondary winding of 20 turns. .

A rectifying diode 7 is connected in series to the secondary winding of the transformer 6. Further, a load resistor 8 (lkΩ) is connected. 9 is a smoothing capacitor, and 10 is a power MOSFET to be driven.

The smoothing capacitor 9 uses the gate-source capacitance (approximately 1000 pF) of the MOSFET 10.

As described above, an isolated transistor drive circuit was constructed using a buck-boost type 16 MHz switching converter. This drive circuit is used in a servo system for an electric motor. Converter switching frequency (16
As the oscillation source 1 (MHz), a clock oscillator of a microprocessor used in the control circuit of the servo system was used.

Next, the operation of this drive circuit will be explained with reference to FIG.

A 16 MHz high frequency signal supplied from an oscillation source 1 is modulated by an AND circuit 2 according to an input PWM signal. The modulated wave that is the output of the AND circuit 2 is supplied to the base of the transistor 4.

Transistor 4 is switched according to this modulated wave, thereby supplying a high frequency power supply voltage to the primary winding of transformer 6.

The electromotive force on the secondary side of the transformer 6 is rectified by a rectifying diode 7 and supplied to a load resistor 8.

Further, the signal is smoothed by a smoothing capacitor 9 and drives the FET 10. In this way, the switching converter can be
It is operated intermittently according to the M signal (15.5 kHz), and a PWM waveform drive power is obtained at the gate of the power MO5FETIO.

FIG. 2 shows an example of the waveform of the primary winding voltage of the transformer 6.

The horizontal axis indicates time, and one segment is 20nseC.

The vertical axis indicates the primary winding voltage, which is 5V in one section. As can be seen from the figure, the primary winding of transformer 4 has a 16MH
A high frequency power supply voltage of z is applied.

FIG. 3 shows an example of the waveform of the gate-source voltage of the power MOSFET 10 (ie, the output voltage of this drive circuit). The horizontal axis indicates time, and one segment is 20 μsec. The vertical axis shows the gate-source voltage of FET 10, 1
The voltage is 5v.

As can be seen from the figure, the output voltage of this drive circuit is 1
It can be seen that the desired PWM waveform of 5.5 kHz is obtained.

In this example, when Ω was used as the load resistor 8, the input power of the drive circuit (converter) was about 85 mW, and the output power was about 50 mW. Note that most of the loss is due to the truss 6, which is a two-winding reactor.

According to the above embodiment, a large transformer such as a pulse transformer is not used, and the auxiliary power supply numbered 71°72 is not used, so that the overall structure can be made extremely compact. Furthermore, since a high frequency of 16 MHz is used, the transformer 6 may be small. Furthermore, since the gate-source capacitance of MOSFETIO is used as the smoothing capacitor 9, there is no need to connect a particular capacitor.

Since the clock oscillator of the microprocessor used in the control circuit is used as the oscillation source 1, there is no need to prepare a new oscillation source.

FIG. 4 shows a circuit diagram of a transistor drive circuit according to a second embodiment of the invention. In the figure, 41 is an oscillation source that outputs a high frequency signal, and 44 is a transistor. The oscillation source 41 outputs a 16 MHz high frequency signal. Oscillation source 4
1 is connected to the base of transistor 44. The collector of transistor 44 is connected to one end of the primary winding of transformer 46, and the emitter is grounded. transformer 4
The other end of the primary winding 6 is supplied with a DC voltage of +5.

A rectifying diode 51 is connected to the secondary winding of the transformer 46.
and phototransistor of photocoupler 52 (light receiving side)
are connected in series. Similarly, this diode 5
Another set of rectifier diodes 5 in the opposite direction to 1 etc.
3 and a phototransistor (light receiving side) of a photocoupler 54 are connected. 56 is the input signal 15.5
This is a kHz PWM signal source. This PWM signal source 56 is connected to a light emitting diode (light emitting side) of the photocoupler 52. Further, this PWM signal is connected to a light emitting diode (light emitting side) of a photocoupler 54 via an inverter 55.

48 is the same load resistance (lkΩ) as the first number 8, and 49 is a smoothing capacitor using the same gate-source capacitance of the FET to be driven as the first number 9. MO to be driven
Since the SFET is the same as in FIG. 1, it is not shown.

Combining the buck-boost type and forward type as described above,
A drive circuit that switches using a PWM signal (15.5kHz) was constructed.

FIG. 5 shows an example of the waveforms of the PWM signal that is the input signal 56 and the gate-source voltage VGS (of an unillustrated FET) that is the output of the drive circuit.

The operation of this drive circuit will be explained with reference to FIGS. 4 and 5.

The 16MHz high frequency signal supplied from the oscillation source 41 is
Supplied to the base of transistor 44.

As a result, the transistor 4 is switched at 16 MHz, and the high frequency power supply voltage is supplied to the primary winding of the transformer 46.

The input PWM signal is input to the light emitting diode of the photocoupler 52. It is also input to the light emitting diode of the photocoupler 54 via the inverter 55. therefore,
As shown in FIG. 5, the output of the transformer 46 is rectified by the diode 51 while the PWM signal is at H level (section TI in the figure), and is rectified by the diode 51 while the PWM signal is at L level (section T2 in the figure).
) is rectified by the diode 53. As a result, the fifth
■ Output voltage as shown in the figure. S is obtained.

Note that in the first and second embodiments described above, the transformer may be an air core transformer or a thin film transformer.

Furthermore, the object to be driven is not limited to transistors, but also elements that require a certain amount of driving power.

[Effects of the Invention] As explained above, according to the present invention, since the drive circuit is configured using a switching converter that operates at a high frequency, there is no need to use a large pulse transformer or an auxiliary power supply, and insulation is possible. It is possible to realize a small transistor drive circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a transistor drive circuit according to a first embodiment of the present invention, FIG. 2 is an example of a waveform of the primary winding voltage of a transformer in the drive circuit of FIG. 1, and FIG. An example of the output voltage waveform of the drive circuit in FIG. 1, FIG. 4 is a circuit diagram of a transistor drive circuit according to the second embodiment of the present invention, and FIG. An example of the waveform of the gate-source voltage VGS, FIG. 6 shows a transistor drive circuit using a conventional pulse transformer, and FIG. 7 shows a transistor drive circuit using a conventional auxiliary power supply. 1.41... Oscillation source, 2... AND circuit, 3.56... PWM signal, 4.44... Transistor, 6.46... Transformer, 7.51.53... Diode , 8.48...Load resistance, 9.49...Smoothing capacitor, 10...MOSFET. 52.54...Photocoupler, 55...Inverter.

Claims (2)

[Claims] (1) a high-frequency signal supply means for supplying a high-frequency signal; a modulation means for modulating the high-frequency signal according to an input signal and outputting a modulated wave; and a means for generating a high-frequency power supply voltage according to the modulated wave; 1. An isolated transistor drive circuit comprising: a transformer into which the high-frequency power supply voltage is input; and a transistor is driven by the output of the transformer. (2) a high-frequency signal supply means for supplying a high-frequency signal; a means for generating a high-frequency power supply voltage according to the high-frequency signal;
An isolated transistor drive circuit comprising: a transformer into which the high-frequency power supply voltage is input; and switching means for switching the output of the transformer according to an input signal, and driving a transistor by the output of the switching means. .